Water Treatment Handbook UNITOR

UNITOR

ASA

Mail: P.O. Box 300 Skøyen, N-0212 Oslo, Norway Office: Drammensvn. 211, N-0277 Oslo, Norway Tel: +47 22 13 14 15. Fax: +47 22 13 45 00 Tlx: 76004 UNTOR N

ID. NO. 08 173 REV. NO. 00 LOBO 09.97 5K COUNTRY OF ORIIGIN: NORWAY

Water Treatment Handbook

C H E M I C A L S

Marine Chemicals

Water Treatment Handbook A PRACTICAL APPLICATION MANUAL

1st Edition

Unitor ASA, P.O. Box 300 Skøyen, N-0212 Oslo, Norway Office: Drammensveien 211, N-0277 Oslo, Norway Tel: +47 22 13 14 15. Fax: +47 22 13 45 00 Tlx: 76004 UNTOR N

ID. NO. 08 173

REV. NO. 00

LOBO

09.97

5K

COUNTRY OF ORIGIN: NORWAY

FOREWORD This manual has been edited to specifically apply to Unitor’s Marine Chemical Market. It has been prepared to give the marine engineer basic insight into the chemical water treatment of marine propulsion boilers, low pressure auxiliary and exhaust boilers, diesel engines, evaporators and other associated equipment. The purpose and design of Unitor marine chemical products is to provide the marine engineer with the most environmentally-friendly products and with the most practical and simple applications of their use. Unitor has designed the Spectrapak test kits to accurately determine chemical concentrations of the various products and systems they are being used to check. The Spectrapak tablet system is the most practical and economical testing system available to the marine engineer. Our water treatment programmes are designed to utilize the simplest water testing procedures along with the assistance of our worldwide service personnel and Unitor’s Laboratories which provide the technical expertise required to answer all questions in regard to marine chemical applications. Unitor’s products have been designed to provide the ship operator with a variety of products and systems to cover all requirements for the many different types of boiler systems and crew requirements, which will be detailed in this manual. Unitor has introduced the most up-to-date log review system to utilize today’s technology in communications and computers to provide the operator and marine engineer with a “Rapid Response” to our log review system. Unitor is dedicated to providing the marine operator with the most reliable products available in the marine chemical industry along with the many other areas of expertise and standardisation worldwide. Our products and services are available 7 days a week and we are committed to maintaining this for the marine industry.

INDEX

Page

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV 1 Water Treatment Philosophy and Overview . . . . . . . . . . . . . . . . . . . . . . .

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2 Basic Chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6

3 Problems of Boiler Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4 Types of Boiler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 5 Boiler Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 6 Unitor Boiler Water Treatment Products . . . . . . . . . . . . . . . . . . . . . . . . . 28 7 Combined Treatment for Low Pressure Boiler Water . . . . . . . . . . . . . . . 29 8 Tests for Boiler Water, Low Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 9 Unitor Coordinated Treatment Products . . . . . . . . . . . . . . . . . . . . . . . . . . 34 10 Tests for Boiler Water, Medium Pressure . . . . . . . . . . . . . . . . . . . . . . . . 38 11 High Pressure Boiler Water Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 12 Boiler Wet Layup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 13 Boiler Blowdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 14 Chemical Cleaning of Boilers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 15 Diesel Engine Cooling Water Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . 60 16 Reporting Analysis Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 17 Water Tests, Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 18 Evaporator Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 19 Marine Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 20 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

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WATER TREATMENT HANDBOOK


III

INTRODUCTION This Product Applications Handbook has been designed to provide specific information on the variety of chemical and related products and systems available from Unitor. This handbook will give all the information required to maintain these various products, including the application of individual chemical products to properly maintain Low Pressure, Medium Pressure and High Pressure Boilers, Diesel Engine Cooling Systems and Evaporators. Single Function Treatment Products: 1. Hardness Control 2. Alkalinity Control 3. Oxygen Control (Hydrazine) 4. Catalysed Sodium Sulphite (Powdered & Liquid) 5. Condensate Control 6. Boiler Coagulant Low Pressure Boilers, Water Treatments: 1. Combitreat (powdered) 2. Liquitreat 3. Condensate Control

1 Water Treatment Philosophy and Overview 1.1

TYPES OF WATER

General Water could generally be described as the most important of all chemical substances. Its chemical designation is H2O; the water molecule is composed of 2 Hydrogen atoms and 1 Oxygen atom. Natural water Raw water is the description of the water to which we have daily access. We can obtain our water from: 1. The ocean 2. Surface sources (e.g. from lakes) 3. Underground sources The water will vary in composition. The natural water cycle may be as below:

Cooling Water Treatments: 1. Dieselguard NB (powder) 2. Rocor NB Liquid Sea Water Cooling Treatment: 1. Bioguard Evaporator Treatment: 1. Vaptreat

While it is evaporating from the surface of a lake or the ocean into the atmosphere, we can designate the water vapour H2O. In the atmosphere, clouds will form, and during suitable humidity and temperature, the clouds will deposit water (rain). While the rain is falling towards the earth, it absorbs gases which are in the air, e.g. CO2 (Carbon Dioxide), SO2 (Sulphur Dioxide) and O2 (Oxygen). When the water hits the earth, it absorbs additional Carbon Dioxide (from biological degradation). The rainwater which is now slightly acid will dissolve various minerals from the soil.

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2 Basic Chemistry The chemistry of water It is necessary to examine some of the basic theories in order to understand the various problems associated with water treatment. While rain is falling through the air, it absorbs gaseous contaminants, e.g. O2 (Oxygen), which solubility in pure water depends on temperature. At 20 °C, 9 mg/l O2 may dissolve, and at 50 °C approx. 5.5 mg O2/l,

TEMPORARY HARDNESS (Alkaline Hardness) is due to bicarbonates of Calcium and Magnesium which are Alkaline in nature. They are “temporary” because when heated they rapidly break down to form Carbon Dioxide and the corresponding carbonates which deposit as scale. PERMANENT HARDNESS (Non-Alkaline Hardness) is due mainly to Sulphates and Chlorides of Calcium and Magnesium which are acid in nature. They are “permanent” and do not break down, but under certain conditions deposit to form scale of varying hardnesses.

and at 90 °C approx. 1.5 mg O2/l, and

2.1

at 100 °C approx. 0.0. mg O2/l, so, the higher the temperature, the less O2 can dissolve in water. CO2 (Carbon Dioxide) dissolves in water as follows: CO2 + H2O > H2CO3 H2CO3 is a very weak acid. In contact with CaCO3 (ordinary lime), it is reactive and the lime dissolves as follows: CaCO + H CO > Ca++ + 2HCO – 3

2

3

3

Ca(HCO3)2 is called Calcium Bicarbonate. SO2 (Sulphur Dioxide) is an air pollutant which stems from flue gases, so there is usually a high atmospheric content of this gas around industrial areas. 2SO2 + O2 + 2H2O > 2H2SO4 H2SO4 is called Sulphuric Acid, and this acid also dissolves lime (CaCO3) as follows: CaCO3 + H2SO4 > CaSO4 + H2O + CO2. CaSO4 is called Calcium Sulphate (gypsum). In other words, the gases dissolved in the water will increase the leaching of the subsoil’s minerals, so that we may have solutions in water due to: TOTAL HARDNESS

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2 / BASIC CHEMISTRY

Temporary hardness

Permanent hardness

Calcium Bicarbonate Ca (HCO3)2 Magnesium Bicarbonate Mg (HCO3)2

Calcium Sulphate CaSO4 Magnesium Chloride MgCl2

BOILER WATER TREATMENT FUNDAMENTALS

The concept of employing water, fresh or distilled, as a power generating source and heat exchange medium originated and was realised with the inception of the steam generator or boiler, and has been applied most successfully and beneficially in this manner ever since. Water has the ability to transfer heat from one surface to another, thereby maintaining the system within the correct operational temperature range while generating steam to carry out work. However, water can adversely affect metal components under the operational conditions normally found in steam boilers and other heat exchange devices. The extent of deterioration depends on the specific characteristics of the water and the system in which it is being used. In order to counteract the detrimental properties normally attributed to water and its contaminants (dissolved and suspended solids and dissolved gases), special chemical treatment programmes have been devised. Accepted water treatment processes and procedures are constantly being upgraded and modernised, and new methods are being developed to complement and/or replace older ones. Unitor utilizes the most modern, practical programmes for the marine operator. Although water from marine evaporators and boiler condensate return systems is essentially “pure”, minute quantities of potentially harmful salts and minerals can be carried by this composition and feedwater into the boiler, where they will accrue, ultimately resulting in serious problems in the steam generating unit. In addition, the water can also contain dissolved gases, i.e. CO2 and Oxygen, which can result in corrosion of the system. Using unprocessed fresh water (e.g. shore water) as a makeup source can present some of the same problems experienced with distilled water, but in addition, certain contaminants which are naturally present in fresh water can be extremely destructive in boiler systems if not dealt with promptly and effectively. Soluble salts such as Chloride, Sulphate and Carbonate are present


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as electrolytes in the untreated water, leading to galvanic and other types of corrosion, depending on the conditions in the system. In addition, Sulphates and Carbonates have the potential to form insoluble, adherent, insulating “hard water” scale deposits on heat exchanger surfaces.

2.2

CONTRIBUTING ELEMENTS WHICH AFFECT BOILER WATER TREATMENT

Most dissolved mineral impurities in water are present in the form of ions. These ions contain an electrical charge which is either positive (cation) or negative (anion). These ions can join together to form chemical compounds. To know which ions will combine, we need to know their electrical charge. Ions of concern to us include the following: Positive ions

Chemical symbol

Negative ions

Chemical symbol

Sodium Calcium Magnesium Hydrogen

Na+ Ca++ Mg++ H+

Chloride Bicarbonate Carbonate Hydroxide

Cl – HCO3 CO3– – OH –

Cations will combine only with anions. An example of this combining of ions is the action between Calcium and Carbonate. The chemical compound which forms is Calcium Carbonate. Other impurities which will affect the boiler water treatment control include Copper, Iron Oxides, oil and dissolved gases. 2.2.1 Copper Copper is introduced into a system by corrosion of Copper piping and Copper alloys. In boilers, the source of this corrosion could be dissolved gases in the boiler water or the excessive use of Hydrazine which will corrode Copper and Copper alloys, allowing Copper to be carried back to the boiler. Copper in the boiler displaces metal from the tube surfaces and plates out on the tubes. This condition often occurs under existing scale and sludge deposits, which is known as under deposit Copper corrosion. Copper deposits are a serious problem in high pressure boilers. Waterside deposits may be submitted to Unitor for complete analysis and determination of the correct procedures to follow for cleaning. 2.2.2 Oil To prevent oil from entering condensate and feedwater systems, certain safety equipment is generally incorporated to detect, remove, and arrest such contamination.

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2 / BASIC CHEMISTRY

Oil contamination may occur through mechanical failure, for example, faulty oil deflectors at turbine glands passing lubrication oil to gland seal condensers and main condensers, etc., or undetected leaks at tank heating coils. Any oil film on internal heating surfaces is dangerous, drastically impairing heat transfer. Oil films therefore cause overheating of tube metal, resulting in possible tube blistering and failure. If oil contamination is suspected, immediate action must be undertaken for its removal. The first corrective measure in cleaning up oil leakage is to find and stop the point of oil ingress into the system. Then, by using a Unitor degreaser, a cleaning solution can be circulated throughout the boiler system to remove the existing oil contamination. Complete details on this cleaning operation are covered later in the handbook. Boiler Coagulant can assist in removing trace amounts of oil contamination. Consult your Unitor representative for more specific recommendations. 2.2.3 Iron Oxides Iron may enter the boiler as a result of corrosion in the pre-boiler section or may be redeposited as a result of corrosion in the boiler or condensate system. Often, Iron Oxide will be deposited and retard heat transfer within a boiler tube, at times resulting in tube failure. This usually occurs in high heat transfer areas, i.e. screening tubes nearest to the flame. When iron is not present in the raw feedwater, its presence in the boiler indicates active corrosion within the boiler system itself. Rust, the reddish form, is fully oxidized. More often, in a boiler with limited Oxygen, it is in the reduced or black form as Magnetite (Fe3O4). Fe3O4 is magnetic and can be readily detected with a magnet. It is a passivated form of corrosion and its presence shows that proper control of the system is being maintained. 2.2.4 Magnesium Carbonate (MgCO3) Magnesium hardness in fresh water usually accounts for about onethird of the total hardness. The remaining two thirds can normally be attributed to calcium. Since Magnesium Carbonate is appreciably more soluble in water than Calcium Carbonate, it is seldom a major component in scale deposits. This is due to the preferential precipitation of the Carbonate ion by Calcium as opposed to Magnesium which remains in solution until all soluble Calcium is exhausted. Once this point is reached, any free Carbonate remaining in solution will combine with the Magnesium and begin precipitating out as


9

Magnesium Carbonate when the solubility of this salt is exceeded. Because of this latter phenomenon, where “soft” water is used for boiler structure, any Magnesium present must be removed along with the Calcium. 2.2.5 Magnesium Sulphate (MgSO4) Magnesium Sulphate is an extremely soluble salt, having a solubility of 20 % in cold water and 42 % in boiling water. It exists as the Sulphate only in water with a low pH. Because of its high solubility, it will not normally precipitate. The Sulphate ion, however, will be precipitated by the Calcium hardness present if no free Carbonate exists. 2.2.6 Magnesium Chloride (MgCl2) Magnesium Chloride, like Magnesium Sulphate, is soluble in fresh water. In the high temperature and alkaline conditions normally maintained in a boiler, any soluble Magnesium ions in the boiler water become extremely reactive with Hydroxyl ions, which may be present in high concentrations in this type of environment. This can result in the formation of Magnesium Hydroxide precipitates which form insulating scale on the boiler tube surfaces. If Chloride ions are also available, they react with the Hydrogen ions previously associated with the precipitated Hydroxyl ions, to form Hydrochloric acid, thereby lowering the alkalinity of the water. If this situation is allowed to continue, the pH of the boiler water will decrease until acid conditions result in corrosion of the metal surfaces. Unlike Carbonate and Sulphate ions, the Chloride ion does not precipitate in the presence of soluble Calcium. 2.2.7 Silica (SiO2) Silica scale is not normally found in boiler systems except in minute quantities. It can be admitted to the system when severe carryover occurs in evaporators processing water with a high Silica content. Other sources of such feedwater may be high Silica river or raw fresh water as well as distilled/deionized or unprocessed fresh water which has been stored and taken from cement-washed or silicatecoated tanks. Once formed, pure Silica scale is extremely difficult to remove. It forms a tight adherent glass-like film on metal surfaces, thereby preventing proper heat transfer. In addition, in steam-generating devices it can carry over with the steam coating the after-boiler sections, particularly the superheater. If a turbine forms part of the system, the Silica can deposit on the blades as well as cause erosion of the finned surfaces of the blading, resulting in imbalance of the turbine, which in turn may result in turbine failure.

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2 / BASIC CHEMISTRY

Besides the pure form of Silica (i.e. Silicon Dioxide), possible Silicate deposits can form in combination with Calcium and Magnesium, which are extremely insoluble in water and very difficult to dissolve and remove. Besides being an extremely difficult process, the chemical removal of Silica and silicate deposits can also be very hazardous, since it involves the use of Hydrofluoric Acid or Ammonium Bifluoride, both of which are severely destructive to human tissue by inhalation, ingestion and physical contact. In some instances, alternate acid and alkaline washings have been used to successfully combat this problem. The only alternative to chemical cleaning is mechanical removal. 2.2.8 Calcium Carbonate (CaCO3) Calcium Bicarbonate alkalinity exists in almost all unprocessed fresh water under normal conditions. Its solubility is about 300–400 ppm at 25 °C. If heat is applied or a sharp increase in pH occurs, the Calcium Bicarbonate breaks down to form Carbon Dioxide and Calcium Carbonate. While the bicarbonate salt has been shown to be moderately soluble in water, the solubility of Calcium Carbonate at 25 °C is only about 14 ppm. This value continues to decrease as the temperature increases, becoming the least where the temperature is greatest. In a boiler, this would be on the surface of the furnace tubes where contact is made with the water. The resulting insoluble Calcium Carbonate precipitate forms “building block-like” crystals which adhere not only to one another, but also to the hot metal surfaces, resulting in a continuous, insulating scale deposit over the entire heat exchange area.This deposit will continue to grow, building upon itself to form a thick coating until all the Calcium Carbonate produced is exhausted. If suspended matter is also present in the water, it can become entrained within the crystal structure, creating a larger volume of deposit than that formed by the Carbonate precipitation alone. If this condition is allowed to continue, heat exchange efficiency at the water/tube interface falls rapidly, resulting in an increase in fuel consumption necessary to compensate for the decline in thermal transfer and to regain design temperature as well as steam production requirements. This increase in the furnace-side temperature needed to run the system at optimum conditions exposes the metal surfaces to overheating which, in turn, can cause blistering fatigue, fracture, and failure of boiler tubes. In addition, if pockets of water become trapped beneath the scale deposits and are in contact with the hot metal surfaces, concentration of acid or alkaline materials may occur and lead to the formation of local electrolytic cells (underdeposit corrosion).


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2.2.9 Calcium Sulphate (CaSO4) Although Calcium Sulphate is more soluble in water than Calcium Carbonate, it can be just as troublesome when present in boiler and cooling water systems. Calcium Sulphate, like Calcium Carbonate, but unlike most salts, has an inverse temperature/solubility relationship in water. As gypsum, the hydrated form in which Calcium Sulphate is normally present in fresh water, its solubility increases until a temperature of about 40 °C is achieved. At 40 °C, its solubility is 1,551 ppm; at 100 °C, which is the normal boiling point of water, its solubility decreases to 1,246 ppm, and at 220 °C it falls to 40 ppm. Calcium Sulphate reacts at high-temperature surfaces essentially in the same manner as Calcium Carbonate and with the same effects and consequences. However, whereas Calcium Carbonate deposits are relatively easy to remove using a comprehensive acid cleaning procedure, Calcium Sulphate is essentially impervious to the effects of normal acid descaling methods and usually must be removed by mechanical means.

D. ALKALINITY RELATIONSHIP TABLE

2.2.10 Dissolved Gases Gases such as Oxygen and Carbon Dioxide that are dissolved in distilled or fresh water, will further contribute to the deterioration of the boiler system. Dependent upon conditions in the system (e.g. temperature, pressure and materials of construction), dissolved Oxygen can cause pitting corrosion of steel surfaces, while Carbon Dioxide lowers the pH, leading to acid and galvanic corrosion. Carbon Dioxide has the added disadvantage of forming insoluble carbonate scale deposits in an alkaline environment when Calcium and Magnesium are present.

*This is the correct alkalinity relationship for boiler water

2.2.11 Acidity, Neutrality and Alkalinity All water can be classified into one of these categories. Acidity, Neutrality and Alkalinity are only very general terms. We require more accurate methods of testing to know the degree of each condition. When testing boiler water, it is important to understand what you are testing for.

Hydroxide Alkalinity

Carbonate Alkalinity

Bicarbonate Alkalinity

P Alkalinity =0

0

0

Equal to total

P Alkalinity less than 1/2 M Alkalinity

0

2 times P Alkalinity

M Alkalinity minus 2 times P Alkalinity

P Alkalinity equal to 1/2 M Alkalinity

0

2 times P Alkalinity

0

*P Alkalinity greater than 1/2 M Alkalinity

2 times P Alkalinity minus M Alkalinity

2 times the difference between M and P Alkalinity

0

P Alkalinity equal to M Alkalinity

Equal to M Alkalinity

0

0

pH The pH of a solution is a measurement of the concentration of active acid or base (alkaline constituent) in a solution. To give a precise definition, pH is the negative logarithm of the Hydrogen ion concentration. A simpler explanation of pH is that it is a measure of relative acidity or alkalinity of water. In other words, it reflects how acidic or alkaline the water is. pH is the number between 0 and 14 which denotes the degree of acidity or alkalinity. A pH value of 7 indicates neutral. Below 7 indicates increasing acidity. Above 7 up to 14 indicates increasing alkalinity.

Acidic

Neutral

Alkaline

A. ALKALINITY. The presence of Alkalinity in a water sample may be due to many different substances. For the sake of simplicity, the presence of Bicarbonate, Carbonate and Hydroxide contributes to the alkalinity of water.

1

B. P ALKALINITY. Phenolphtalein (P) Alkalinity (pH values greater than 8.3) measures all the Hydroxide and one half of the Carbonate Alkalinity which is sufficient for our purpose of control. Bicarbonates do not show in this test as they have a pH of less than 8.4.

pH is a very important factor for determining whether a water has a corrosive or scale-forming tendency. Water with a low pH will give rise to corrosion of equipment.

2

3

4

5

6

7

8

9

10

11

12

13

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C. M ALKALINITY. Total Alkalinity or M Alkalinity (pH values greater than 4.3) measures the sum of Bicarbonate, Carbonate and Hydroxide Alkalinity.

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2 / BASIC CHEMISTRY


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3 Problems of Boiler Water Feedwater produced by distillation for use in a boiler is not “pure”, even with a good distillation method. Worse still is ordinary water taken from ashore to be used as feedwater. The water will contain some of the elements (impurities) mentioned in Chapter 5. Problems will then arise when the water is used in the boiler. The types of problem will depend on the type of impurities and in which quantities they are present.

3.1.1 Pitting Corrosion “Pitting” is the most serious form of waterside corrosion and is the result of the formation of irregular pits in the metal surface as shown in the figure below. Evidence of pitting is usually found in the boiler shell around the water level and is most likely caused by poor storage procedures when the boiler is shut down for lengthy periods, and by inadequate Oxygen scavenging.

The most common problems are: – CORROSION – SCALING – CARRYOVER

3.1

CORROSION

The corrosion processes can affect boilers in the following ways: ”General wastage” is the overall reduction of metal thickness and is common in heating surface areas, such as boiler tube walls. This “thinning” of boiler tubes is often found in boilers having open feed systems (mostly auxiliary boilers) without any protective treatment. An example of wastage is given in the figure below.

General wastage of a boiler tube.

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3 / PROBLEMS OF BOILER WATER

Pitting corrosion.

3.1.2 Stress Corrosion “Stress corrosion” cracking is the process caused by the combined action of heavy stress and a corrosive environment. The stages of failure of the metal due to stress corrosion are shown below. Corrosion is initiated by breakdown of the surface film followed by the formation of a corrosion pit which becomes the site for stress corrosion cracking, eventually leading to mechanical failure due to overloading of the mechanical strength of the metal. This form of attack is often found around the ogee ring in vertical auxiliary boilers, when undue stressing is set up by poor steam-raising procedures.

Stress corrosion


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3.1.3 Other Related Problems “Corrosion fatigue” occurs when a sufficiently high alternative stress level causes failure of the subjected material. It is the joint action of a corrosive environment and cyclic stressing and results in a series of fine cracks in the metal. This is found in water tube boilers where irregular circulation through tubes in high temperature zones induce these cycling stresses. ”Caustic cracking” results from the contact of water of concentrated caustic alkalinity and steel which has not been stress relieved, e.g. in riveted seams. This form of cracking follows the grain boundaries. This is rarely observed nowadays, as both high and low pressure boilers are usually of all welded construction and are stress relieved. Caustic corrosion takes place only in high pressure boilers (above 60 bar) when excessively high concentrations of Sodium Hydroxide (Caustic Soda) cause breakdown of the magnetite layer and localised corrosion. This form of attack is often controlled by the coordinated PO4 Treatment Programme. ”Hydrogen attack” is another form of corrosion damage that can take place in ultra high pressure boilers. Whichever form of corrosive attack occurs, the risk of tube failure or serious structural damage is very apparent, both often leading to considerable expense in the shape of repair costs.

3.2

SCALING

Causes and Effects If the inside of a boiler is scaled, there is a great risk that the boiler material will overheat, leading to tube failure. The efficiency of operation will also be adversely affected. Hardness in the feedwater will usually present problems in relation to the operation of boilers. Hardness of more than 5dH° (90 ppm as CaCO3) in the feedwater will, as the temperature rises, cause an increase in the formation of sludge in the feedwater tank. If scale-preventing chemicals are put into the feedwater tank, this problem will be aggravated, as nearly all precipitation of sludge will take place in the feedwater tank. The suction pipe stub of the feed water line will usually be placed 5–10 cm above the bottom. However, if the feed water is not very clean, sludge will after a time be sucked into the piping and choking may occur. In a modern centrifugal pump, the very narrow vanes may be blocked, which will cause the pump to stop. Finally, there is a risk of the valves sticking and becoming blocked. In spite of the fact that a boiler plant may be equipped with a water treatment system of some sort, there will always be a risk of hardness or other type of pollution in the feedwater, because: 1. The capacity of the water treatment system is insufficient. 2. There are defects in the water treatment system.

3.1.4 Factors Affecting Corrosion

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1) pH

Metal oxides are more soluble as pH decreases. Corrosion is increased.

2) Dissolved solids

Chloride and Sulphate can penetrate passive metal oxide film which protects the base metal from corrosion.

3) Dissolved gases

Carbon Dioxide and H2S reduces pH and promotes acid attack. Oxygen promotes pitting corrosion.

4) Suspended solids

Mud, sand, clay, etc. settle to form deposits, promoting different corrosion cells.

5) Micro organisms

Promote different corrosion cells.

6) Temperature

High temperature increases corrosion.

7) Velocity

High velocity promotes erosion/cavitation.

8) Copper

Copper ions plate out on steel surfaces and promote pitting corrosion.


3. The condensate is polluted: a. By heat exchanger leaks b. By lubrication oil Daily analysis of the quality of the feedwater will ensure that action can be taken in time to prevent irregularities. Hardness in the boiler water will inevitably lead to the formation of scale and the rate of this formation will depend on the composition and quantity of the hardness, on the temperature conditions in the boiler and on the circulation in the boiler. Increased surface heating effect means increased production of steam bubbles, which again will make more boiler water “pass” the spot on the heating surface (where the steam bubbles are formed) and this spot will thus also be “passed” by the hardness-producing and corroding salts in the boiler water. In addition, the most common hardness salts are less soluble at increasing temperatures. This explains why the largest amount of encrustation will always be found where the temperature of the heating surface is the highest. Scale formed just at this point means that the critical temperature of the boiler material will be reached quickly and that damage to the boiler will be inevitable.


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3.3 Illustration of Typical Conditions With a Clean Boiler Tube

Change in Conditions When a Layer of Scale of just 3 mm Thickness Exists

CARRYOVER

Carryover is any contaminant that leaves the boiler with the steam. Carryover can be: • Solid

• Liquid

• Vapour

Effects of carryover: • Deposits in non-return valve • Deposits in control valves

• Deposits in superheaters • Deposits on turbine

Carryover in superheaters can promote failure due to overheating. Turbines are prone to damage by carryover, as solid particles in steam can erode turbine parts. When large slugs of water carry over with steam, the thermal and mechanical shock can cause severe damage.

The scale causes the fuel consumption to increase by approx. 18 percent. Stress will arise in the steel as a result of the insulating effect of the scale.

Excess Fuel Consumption in %, depending on Thickness of Scale

Causes of carryover: Mechanical: • Priming • Soot blowing

• Sudden load changes • High water level

Chemical: Foaming due to: • High Chlorides • Suspended solids

• High TDS • Oil

• Boiler design

• High alkalinity • Silica

Curve of middle values. The differences in the test results can be explained by differences in the composition of scale (porous–hard).

The most common form of encrustation in a steam system stems from carryover. The boiler manufacturers stipulate a maximum allowed salinity of the boiler water (as a rule at 0.4° Be = 4000 mg salts dissolved per litre). If this value is exceeded, there is a risk of normal bubble size being prevented; larger bubbles will be produced and the turbulence in the water surface will increase and cause foaming. The foam may be carried over with the steam, particularly when the generation of steam is at maximum, which causes boiler water (containing Sodium Hydroxide and salt) to pass out into the steam pipes. The content of Silicic Acid is important for boilers with high pressures. Silicic Acid in its volatile form may be carried away with the steam and be deposited on turbine blades, for instance, on which it will form a very hard, porcelaine-like scale. However, not only the chemical composition may cause carryover. Circumstances such as periodic overloads, periods of a too high a water level (or more correctly: too small a steam volume) are two of the most common causes. Finally, impurities from the condensate, such as oil from the preheater’s coils if they are leaking are very common causes of priming.

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4 Types of Boiler What is a boiler? A boiler is a steel pressure vessel in which water under pressure is converted into steam by the application of combustion. In other words, it is simply a heat exchanger which uses radiant heat and hot flue gases, liberated from burning fuel, to generate steam and hot water for heating and processing loads. There are two types: Fire tube boilers and water tube boilers.

4.1

FIRE TUBE BOILER

Hot flue gases flow inside tubes that are submerged in water within a shell. • Pressures up to about 10 bar • Produce up to 14 tonnes of steam/hr • Can meet wide and sudden load fluctuations because of large water volumes • Usually rated in HP

4.2

WATER TUBE BOILER

Typical packaged boiler. Packaged boilers include a pressure vessel, burner, all the controls, air fans, and insulation. The boiler is tested at the manufacturer’s plant and shipped to the customer, ready for use, when the fuel lines and piping and electrical connections have been installed.

Water flows through tubes that are surrounded by hot combustion gases in a shell. • Usually rated in tons of steam/hr • Used for H.P. steam • High capacity BOILERS HAVE SIX BASIC PARTS 1) 2) 3) 4) 5) 6)

Burner Combustion space Convection section Stack Air fans Controls and accessories

Typical Scotch Marine firetube boiler (courtesy of Orr & Sembower, Inc.).

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4 / TYPES OF BOILER


21

4.3

FIRETUBE BOILERS

Wet back designs Have a water wall at the back of the boiler in the area where combustion gases reverse direction to enter tubes. Dry back designs Refractory is used at the back, instead of a water wall. Internal maintenance is simplified, but refractory replacement is expensive and overheating, gauging and cracking of tube ends at the entrance to return gas passages often cause problems.

4.5

HIGH TEMPERATURE WATER (HTW) HEATING SYSTEMS

In recent years, interest has been revived in high temperature hot water heating systems for institutional, industrial and commercial plants. By increasing the temperature and pressure of the hot water and increasing the size of the generators, some advantages are gained over the low pressure steam heating systems previously used. In other cases, special forced circulation boilers have been designed, which consist of many rows of tubes without a steam drum. In another type, heat is supplied by steam from a standard type of boiler which heats the water in a direct contact heater. This is referred to as a cascade system.

WATERSYSTEM AND STEAMSYSTEM

4.4

CLAYTON STEAM GENERATOR

The coil type generator is a vertical coil with fuel combustion taking place inside the coil. High quality feedwater and a closely monitored chemical treatment programme are mandatory. The most common problem is Oxygen pitting on the inside portion of the coil near the fire. The two most common name brands are Vapor-Clarkson and Clayton.

22

4 / TYPES OF BOILER

Medium-sized watertube boilers may be classified according to three basic tube arrangements.


23

5 Boiler Systems 4.6

FIRETUBE BOILERS Advantages: • Lower initial cost • Few controls • Simple operation Disadvantages: • Drums exposed to heat, increasing the risk of explosion • Large water volume, resulting in poor circulation • Limited steam pressure and evaporation

WATERTUBE BOILERS Advantages: • Rapid heat transmission • Fast reaction to steam demand • High efficiency • Safer than firetube boilers

5.1

TYPICAL BOILER SETUP ON A MOTOR SHIP 5.1.1 The Boiler System This does not just consist of a boiler. As indicated by the figure above, it is a complete plant. Most motor ship boilers operate at low pressure, that is, not more than 20 bar pressure. This makes it suitable for the single treatment: the combined boiler water treatment. The steam plant consists of the following:

Disadvantages: • More control than firetube boilers • Higher initial cost • More complicated to operate

Storage tank This tank will hold the make-up water to be supplied to the various systems as they lose water through leaks and through evaporation. Normally, this water is made by a “low pressure” evaporator (this will be described later on). The water produced in this way is normally of good quality if the evaporator is set up correctly. When it is introduced to the boiler, it will require the minimum amount of treatment. However, at some stage the vessel will very likely take water from ashore, and the quality can vary considerably. This water would probably require more treatment to correctly condition it for use. Hot well, observation tank or cascade tank This has a very important function for the dosing of chemical treatments. This is where all the water collects on returning from the various areas where steam has been used. It is also where water enters the system from the storage tank(s) to make up the quantity required in the system. If the steam has been used for heating fuel, the returns from that tank may contain oil, or if cargo heating has been used, some of

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4 / TYPES OF BOILER


25

the cargo product may be returned with the steam. That is why this tank is sometimes called the observation tank – steam returns can be inspected for contamination here. There is a series of plates and filters in the hot well which allows the contaminating oil, etc., to be removed. Any sort of contamination is definitely not wanted in the water entering the boiler, as it would cause damage. Dosage of the combined product boiler water treatment is normally carried out into the hot well.

The system described provides the more common, modern system. There are many systems where the exhaust gas boiler and the oil-fired boiler are combined (composite boiler). A diagram of one is shown below. One section of the tube is used for the oil-fired boiler and the other section for the exhaust gases to pass through. This unit must be situated in the funnel area because the exhaust trunking passes that way and it is placed at a convenient point.

The boiler: The water is drawn from the hot well by the feed pump and pumped into the upper drum of the boiler (this is normally called the steam drum). From here it circulates in the boiler, is heated and turns into steam. There are normally two different ways in which it is heated.

5.1.2 The Steam Lines The steam comes from the steam drum of the boiler and is distributed to the areas where it is required. That is for heating tanks, fuel, hot water, etc. No testing is required in this area under normal circumstances. Once the useful heat has been taken out of the steam, it enters the steam return lines and comes back to the drains cooler.

1. When the main diesel engine is running, the water is pumped from the lower drum (called the water drum) and circulated through a heat exchanger in the exhaust trunking which takes the exhaust gases away from the engine to the atmosphere. The remaining heat in these exhaust gases is used to generate the steam. 2. The auxiliary boiler has a burner (one or more) which uses either heavy oil or diesel oil to provide the heat to produce steam. If the heat available from the exhaust gases is insufficient, the oil fired burner(s) can be used to make the steam required by the vessel.

5.1.3 Drains Cooler This unit is another heat exchanger and it is there to ensure that all the returning steam is turned to water. The returns would be a mixture of hot water and steam before this cooler, and the cooler ensures that any return steam is condensed to water. The drains cooler normally uses sea water to cool the steam returns, and this can be a source of contamination if there is a leak. This will show up as a high chloride level in the feedwater if it occurs. Sunrod Exhaust Gas Economiser.

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5 / BOILER SYSTEMS


27

6 Unitor Boiler Water Treatment Products

7 Combined Treatment for Low Pressure Boiler Water

6.1

THE MAIN PURPOSE OF BOILER WATER TREATMENT IS

7.1

A. To eliminate the total hardness of the boiler water.

Liquitreat is a combined chemical treatment product suitable for use in small, low pressure boilers. It precipitates hardness, provides the boiler water with the necessary alkalinity, and scavenges dissolved Oxygen. Liquitreat should be added when deemed necessary as shown by water analysis results. If the boiler is open and not being fired, Liquitreat can be poured through a manhole, but when the boiler is in operation, the treatment must be applied through a special dosing line. When a dosing arrangement is utilized, the chemical must be flushed to remove any residual left in the dosage lines and equipment. If dosing lines are not fitted, the chemical can be added directly to a feed tank as required. Ensure proper circulation through the feed tank to allow the chemical to enter the boiler being treated. Under low load conditions, complete changeover in the feed tank can take some time. It is necessary to know the details of the flow pattern in the boiler for proper testing and dosing of the chemical treatment to take place. When several boilers have a common feed tank, dosing should be carried out through independent dosing lines to ensure the proper treatment of each boiler. Re-test within 2 hours of when the boiler water chemical treatment was dosed to the boiler water. For further recommendations on product dosage and control limits, refer to the product data sheet in the Marine Chemical’s Manual.

B. To maintain the correct pH and alkalinity values in feedwater and boiler water. C. To prevent corrosion, especially corrosion caused by Oxygen. D. To prevent the formation of scale, among other things by conditioning the sludge. E. To avoid foaming.

6.2

UNITOR PRODUCTS

Combined Treatment 1. Liquitreat 2. Combitreat Single Function Treatment 1. Alkalinity Control

LIQUITREAT

2. Hardness Control

7.2

3. Oxygen Control

Combitreat is a combined product chemical treatment similar to Liquitreat but in powder form without Oxygen scavenger, which precipitates hardness and provides the boiler water with the necessary alkalinity. Combitreat should be applied as a solution and added when deemed necessary as shown by water analysis results. The recommended dosage must be dissolved in warm water, 30–60 °C in a suitable steel or plastic container, not exceeding the solubility limit of 180 grams per litre. Combitreat must be added slowly to the water (not vice versa) and the solution being prepared must be constantly stirred. Combitreat is best dosed by means of a bypass potfeeder directly in the boiler water feed line. It can also be dosed into the hot well after premixing with hot water at a ratio of 1 kg per 9 litres of water.

4. Catalysed Sodium Sulphite 5. Cat. Sulphite L 6. Boiler Coagulant 7. Condensate Control

COMBITREAT

NOTE: In addition to our combined product chemicals, Condensate Control should be used in all boiler systems to keep the Condensate pH level between 8.3–9.0. Also, the hot well temperature is of great importance when it comes to Oxygen scavenging (ref. basic chemistry at the beginning of the book). We recommend that you maintain a hot well temperature of between 70 °C and 90 °C. For further recommendations on product dosage and control limits, refer to the product data sheet in the Marine Chemicals Manual.

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6 / UNITOR BOILER WATER TREATMENT PRODUCTS


29

8 Tests for Boiler Water, Low Pressure 8.1

UNITOR’S LOW PRESSURE COMBINED BOILER WATER TREATMENT PROGRAMME

The tests recommended in order to maintain boiler water within the desired level of quality when treating with Unitor Liquitreat/Combitreat are as follows: A. P-Alkalinity – Recommended Limits: 100–300 ppm as CaCO3. B. Chlorides – 200 ppm maximum as Cl. C. Condensate pH – 8.3–9.0. Dosage level of Liquitreat/Combitreat is based on the P-Alkalinity value of the boiler water. However, Chlorides and condensate pH must also be controlled and maintained as recommended. Knowledge of all relevant parameters is desirable to enable better interpretation and correct application of treatment. To increase the condensate pH, use Unitor’s Condensate Control in conjunction with your combined product boiler water treatment. It is recommended that you dose Condensate Control on a continuous basis, to maintain the condensate pH within the recommended range of 8.3–9.0 at all times.

8.2

CONTROLLING ALKALINITY

The alkalinity is a more accurate indicator of the boiler water condition than is the pH. The Phenolphtalein (P) alkalinity is measured to determine whether the correct conditions of alkalinity exist in the boiler to:

8.4

pH

Recommended limits of 9.5–11.0. An additional test to determine the pH of the boiler water can be carried out to give a better overall understanding of the boiler water quality. This test is optional. The pH of the boiler water should be maintained within the range of 9.5–11.0 to prevent any corrosion attack on the boiler metal. pH values below 9.5 indicate, a greater possibility of corrosion and in such a situation, treatment levels should be increased accordingly to restore boiler water to optimum quality.

8.5

CONDENSATE pH

To control corrosion in after boiler, condensate and feedwater sections, the condensate pH should be kept between 8.3 and 9.0. Monitoring the pH of this water is very important in being able to maintain a complete Boiler Water Treatment Management Programme.

8.6

TESTING REQUIREMENTS 8.6.1 Low Pressure Boiler Water Treatments: A. Unitor Combined Treatment Products a. Combitreat – For systems up to 17.5 bar. b. Liquitreat – For systems up to 30 bar. B. Test Equipment – Unitor Spectrapak 310 Test Kit.

A. Provide a suitable environment for the precipitation of hardness salts as desirable sludge materials. B. To help the formation of Magnetite (Fe3O4) in the presence of Oxygen scavengers (i.e. Hydrazine/Sulphite). C. Maintain Silica in solution to prevent Silica scale formation.

8.3

CONTROLLING CHLORIDES

The Chloride value will reveal any presence of dissolved salts in the boiler. An increase, gradual or sudden, in the level of Chlorides is an indication of contamination by sea water, and Chlorides are often used as a reference point when controlling rate of blowdown. Too high a Chloride level indicates that undesirable amounts of salts are present, leading to possible foaming and/or scale and deposit formation.

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8 / TESTS FOR BOILER WATER/LOW PRESSURE

C. Specification Control Limits. a. P-Alkalinity: 100–300 ppm (as CaCO3). b. Chloride: 200 ppm maximum. c. Boiler Water pH: 9.5–11.0 (optional). d. Condensate pH: 8.3–9.0. D. Testing preparations and equipment. a. Boiler Water Sample preparation: – Cool sample to 20–25 °C. – Filter as required. b. Sample Analysis: – Spectrapak 310 Test Kit Reagents: – P-Alkalinity tablets – Chloride tablets. – pH strips with ranges 6.5–10.0 and 7.5–14.0. – Equipment – 200 ml sample bottles. – Test procedures.


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8.6.2 P-Alkalinity test A. Take a 200 ml water sample in the stoppered bottle provided. B. Add one P-Alkalinity tablet and shake to disintegrate. If P-Alkalinity is present, the sample will turn blue.

It is essential that the condensate pH is maintained within 8.3–9.0. Test this with Unitor’s pH paper and use Condensate Control to adjust pH upwards if necessary. 8.6.5 Instructions Sulphite Test Kit (optional test for low pressure single product treatment)

C. Repeat tablet addition until the blue colour changes to permanent yellow. Calculation: P-Alkalinity ppm (CaCO3) = (No. of tablets used x 20) –10 For example: If 8 tablets are used, then P-Alkalinity = (8 x 20) –10 = 150 ppm.

8.6.6 Testing procedure: A. Take a 20 ml sample in the shaker tube supplied. B. Add one Sulphite No. 1 tablet; shake to dissolve. C. Add Sulphite No. 2 L.R. tablets one at a time until the sample turns blue. Note the number of tablets used.

D. Mark the result obtained on the log sheets provided, against the date at which the test was taken.

D. Calculate as follows: Sulphite content = Number of Sulphite No. 2 L.R. tablets x 10.

8.6.3 Chloride test A. For boilers under 30 bar, take a 50 ml sample in the stoppered bottle provided.

E. After use, thoroughly rinse out the shaker tube before storage. PLEASE NOTE! The Sulphite No. 1 tablet is used only to condition the sample. Do not count this tablet when calculating the Sulphite level.

B. Add one Chloride tablet and shake to disintegrate; sample will turn yellow if chlorides are present. C. Repeat tablet addition until the yellow colour changes to orange/brown. Calculation: Chloride ppm = (No. of tablets used x 20) –20 For example: If 4 tablets are used then Chloride ppm = (4 x 20) –20 = 60 ppm. D. Mark this result on the Spectrapak 310 log sheet, against the date at which the test was taken. 8.6.4 pH test: For boiler water pH test, 7.5–14.0. For Condensate water, 6.5–10.0. A. Take a 50 ml sample of water to be tested in the plastic sample container provided. B. Using the white 0.6 grm scoop provided, add one measure of the pH reagent to the water sample, allow to dissolve – stir if required. C. Select the correct range of pH test strip and dip it into the water sample for approximately 10 seconds. D. Withdraw strip from sample and compare the colour obtained with the colour scale on the pH indicator strips container. E. Record the pH value obtained on the log sheet provided, against the date at which the test was taken.

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8 / TESTS FOR BOILER WATER/LOW PRESSURE

8.7

TEST RESULTS – COMBINED TREATMENT A. Recording – Always use Unitor’s Rapid Response log forms to record all readings and to keep track of all results. 1. Log form – Combined Boiler Water Treatment Log, no. 310. 2. Frequency – Samples should be drawn, tested and results logged at least every three days. B. Reporting – The completed log sheet for the month should be distributed as shown at the bottom of the form, at the end of each month: 1. White copy – to Unitor’s Rapid Response Centre in Norway (address labels at back of log pad) 2. Pink copy – Vessel owner 3. Yellow copy – to be kept onboard C. Evaluation 1. Logs will be reviewed at the Unitor Rapid Response Centre for adherence to recommended specifications, with the aid of Unitor’s Rapid Response staff. 2. A report letter indicating the status of the ship’s system, any problems and relevant recommendations will be issued to the ship’s operator.


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9 Unitor Coordinated Treatment Products The use of combined product treatment for medium and high pressure boilers, is not recommended. Because higher pressures and temperatures increase the tendency of scaling and corrosion, which makes it necessary to have the possibility of changing the chemical conditions and test parametres individually. The Unitor Coordinated Treatment Programme includes single function chemicals which are dosed and monitored separately. This programme may of course also be applied to low pressure boilers as an alternative to combined product treatment.

9.3

OXYGEN CONTROL (HYDRAZINE, N2H4)

Hardness Control is a Phosphate powder product used in boiler water treatment to precipitate dissolved calcium hardness salts and to convert these salts to non-adherent Calcium Phosphate sludge, which can be easily removed by blowdown. Hardness Control is highly effective in achieving this function; minimum dosages are required. Reduced dosage of chemicals minimises dissolved and suspended solids in the boiler water. Hardness Control provides neutral reaction products in the boiler. A high level of dissolved and suspended solids are the principal causes of carryover and priming. Note here the term “phosphate hide-out”; as the temperature of the boiler increases, less Phosphate can be held in solution in the boiler water. Therefore, testing and dosage of Phosphate to control hardness salts deposits should be done when the boiler is under full load conditions. If the Phosphate residual increases under low load conditions, this is an indication of a dirty boiler, and increased bottom blows should be carried out to remove the sludge. The sludge holds excess Phosphate and re-dissolves when the boiler water temperature is reduced. For further recommendations on product dosage and control limits, refer to the Marine Chemicals Manual.

Hydrazine is a colourless liquid at ambient temperatures, being completely miscible with water. Its solution has an odour resembling Ammonia, but is less pungent. It is used to efficiently scavenge and remove Oxygen from condensate, feedwater and boiler water. Hydrazine reacts with Oxygen, acting as a scavenger. The reaction results in Nitrogen and water, no solids being added to the boiler system. Some of the Hydrazine will carry over with the steam, helping to maintain the condensate pH in an alkaline range, which thereby helps combat acid formation. Hydrazine will also form Magnetite which will act as a protective layer against further corrosion. Hydrazine should be added to the system using a separate dosing tank. The tank should be filled daily with Hydrazine diluted with condensate or distilled water. This solution should be dosed continuously to the storage section of the de-aerator. Alternatively, Hydrazine can be fed continuously to the feed pump suction or atmospheric drain tank over a 24-hour period. It is important that Hydrazine should not be overdosed. At temperatures above 270 °C, Hydrazine starts to break down, creating free Ammonia. Excessive free Ammonia and Oxygen, when combined, form a corrosive condition on non-ferrous metals. This corrosive action can cause Copper to deposit in the watersides of boilers, causing additional boiler problems, as discussed earlier.

9.2

The reaction of Hydrazine in boilers is therefore threefold:

9.1

HARDNESS CONTROL

ALKALINITY CONTROL

Alkalinity Control is used to obtain the correct pH level necessary for the Phosphate treatment to react with Calcium salts. In addition, Alkalinity Control is used to maintain the required alkalinity in the boiler water to prevent acid corrosion. By adopting simple testing procedures to determine the Phenolphthalein alkalinity (P-Alkalinity) and the total alkalinity (M-Alkalinity), we can determine the amount of free caustic present in the boiler water by using the formula 2(P) – M = OH. If a positive number is obtained, free caustic (OH-Alkalinity) is present in the boiler water.

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The term “excess chemicals” or “reserve of chemicals” ensures that chemicals are always readily available to perform their necessary functions. For further recommendations on product dosage and control limits, refer to the Marine Chemicals Manual.

9 / UNITOR COORDINATED TREATMENT PRODUCTS

1. It scavenges any free or dissolved Oxygen. 2. It reduces red Iron Oxide to a metal-protective black oxide coating (Magnetite). 3. It raises the pH of the condensate reducing acid corrosion of the condensate and re-boiler sections of the system. For further recommendations on product dosage and control limits, refer to the Marine Chemicals Manual.


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9.4

CATALYSED SODIUM SULPHITE (POWDER) AND CAT. SULPHITE L (LIQUID)

Unitor’s Catalysed Sulphite products are used as scavengers in place of Hydrazine where economy is of importance, or used in low pressure boilers with open feed systems where feed inlet temperatures are low. Sulphite combined with Oxygen forms Sulphate, which adds solids to the boiler water. It should subsequently not be used in boilers at pressures above 30 bars where the TDS level is critical. Sulphite is also used as a substitute for Hydrazine when rust and scale deposits are present in boiler systems on ships being returned to service. Hydrazine tends to remove Iron Oxide deposits present throughout the boiler system. An amine (Condensate Control) should be used in conjunction with Oxygen scavengers to maintain the condensate pH within the desirable ranges throughout the entire condensate and feedwater system. For further recommendations on product dosage and control limits, refer to the Marine Chemicals Manual.

9.5

CONDENSATE CONTROL

Condensate Control is a neutralising volatile amine recommended for use in all boiler systems to raise the pH of condensate and steam to a non-corrosive level (pH 8.3–9.0). The dosage is determined by the results of a daily condensate pH test. Condensate Control should be dosed using a continuous feed system. It can be introduced, using a flowmeter or metering pump, to the condensate pump discharge, the hot well, the condensate return tank, or to the de-aerator storage tank. Condensate Control can be dosed together with Oxygen scavengers. However, optimum control of condensate pH is achieved by dosing separately from the Hydrazine dosage system. For further recommendations on product dosage and control limits, refer to the Marine Chemicals Manual.

9.6

9.7

CHEMICAL INJECTION POINTS FOR LOW PRESSURE Boiler systems

The following diagram depicts a typical Low Pressure Boiler System. Note injection point for chemicals; when dosing chemicals, the recommendation to achieve the best possible results is to always dose all chemicals in the diluted form on a continuous basis. 1 Dosage to hot well or feed tank. All chemicals can be dosed at these points. However, the recommended dosage of Alkalinity Control and Hardness Control is either no. 2 feed line or no. 3 chemical feed injection directly to the boiler. Oxygen Control and Sulphite should preferably be dosed to the feed tank on a continuous basis. All combined products can be dosed into the hot well. 2 Dose to injection no. 2 is required to the feed line by means of a pressure injector or dosage pump. Dosage should be continuous, however water can be shock treated. 3 Dosage direct to boiler no. 3. All chemicals can be dosed to this point by means of pressure pot injector or dosage pump. Alkalinity Control or Hardness Control is best controlled at this location and and the use of Hydrazine, Sulphite or Condensate Control is recommended on a continuous basis in the condensate system.

BOILER COAGULANT

Boiler Coagulant is a polymeric compound used in boilers contaminated with small quantities of oil, or as a sludge conditioner in conjunction with the use of Hardness Control when high levels of solids are experienced. Boiler Coagulant should be dosed at 250cc per day. No testing is necessary if used regularly. Daily flash blowdown is recommended to remove precipitated solids or coagulated oil. For further recommendations on product dosage and control limits, refer to the Marine Chemicals Manual.

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9 / UNITOR COORDINATED TREATMENT PRODUCTS


37

10 Tests for Boiler Water, Medium Pressure (31–60 BAR) In dosing medium pressure boilers, utilise Unitor’s Coordinated Boiler Water Treatment Management Programme. This includes Alkalinity Control, Hardness Control, Oxygen Control, Condensate Control and Boiler Coagulant. The following tests are recommended to maintain medium pressure boiler water within the desired level of quality when utilising Unitor’s Coordinated BWT Programme are as follows:

10.3.1 Phosphate (ppm) PO4 A. Take the comparator with the 10 ml cells provided. B. Slide the Phosphate disc into the comparator. C. Filter the water sample into both cells up to the 10 ml mark.

10.1 UNITOR TESTS REQUIRED CONTROL LIMITS

D. Place one cell in the left-hand compartment.

1. 2. 3. 4. 5. 6. 7.

E. To the other cell add one Phosphate tablet, crush and mix until completely dissolved.

P-Alkalinity: . . . 100–130 ppm CaCO3 M-Alkalinity: . . Below 2 x P-Alkalinity Phosphate: . . . . 20–40 ppm as PO4 Hydrazine: . . . . 0.03–0.15 ppm as N2H4 Chlorides: . . . . . <30 ppm pH (boil. water): 9.5–11.0 pH (condens.): . 8.3– 9.0

10.2 UTILISE UNITOR’S SPECTRAPAK 311/312*/SULPHITE TEST KIT Reagents A. Phosphate tablets B. Chloride tablets C. P-Alkalinity tablets D. M-Alkalinity tablets E. pH papers (6.5–10.0 & 7.5–14.0) F. pH reagent G. Filter paper H. Hydrazine reagent* I. Sulphite tablets*

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10.3 TEST PROCEDURES

F.

After 10 minutes, place this cell into the right-hand compartment of the comparator.

G. Hold the comparator towards a light. H. Rotate the disc until a colour match is obtained. I.

Record the result obtained on the Spectrapak 311/312 log sheet against the date on which the test was taken.

10.3.2 Chloride (ppm) Cl The range of Chlorides to be tested determines the size of water sample used. To save tablets, the use of a small water sample is recommended when the Chloride level is expected to be high, i.e. for low Chloride levels use 100 ml water sample, for higher Chloride levels use 50 ml water sample. However, it should be noted that the accuracy of the test results increases with the size of the water sample.

Equipment A. 200 ml sample bottles B. Lovibond 2000 comparator C. Phosphate disc 3/70 D. 10 ml molded cells E. Hydrazine disc 3/126* F. Sulphite test tube*

A. Take the water sample in the stopper bottle provided.

* Optional. Either the Hydrazine Test Kit (Spectrapak 312) or the Sulphite Test Kit must be utilised. The one to be used depends on the Oxygen scavenger in use. Please note that Sulphite is not adviceable to use in boilers above 30 bar.

D. Count the number of tablets used and perform the following calculation:

10 / TESTS FOR BOILER WATER MEDIUM PRESSURE

B. Add one Chloride tablet and shake to disintegrate. Sample will turn yellow if Chlorides are present. C. Repeat tablet addition, one at a time (giving time for the tablet to dissolve), until the yellow colour changes to permanent red/brown.


39

For 100 ml water sample: Chloride ppm = (Number of tablets x 10) –10 e.g. 4 tablets = (4 x 10) –10 = 30 ppm Chloride.

A. Take a 50 ml sample of water to be tested in the plastic sample container provided.

For 50 ml water sample: Chloride ppm = (Number of tablets x 20) –20 e.g. 4 tablets = (4 x 20) –20 = 60 ppm.

B. Using the white 0.6 grm scoop provided, add one measure of the pH reagent to the water sample, allow to dissolve – stir if required.

E. Record the result obtained on the log sheet provided, against the date on which the test was taken.

C. Select the correct range of pH test strip and dip it into the water sample for approximately 10 seconds.

10.3.3 P-Alkalinity (ppm) CaCo3

D. Withdraw the strip from the sample and compare the colour obtained with the colour scale on the pH indicator strips container.

A. Take a 200 ml water sample in the stopper bottle. B. Add one P-Alkalinity tablet and shake or crush to disintegrate. C. If alkalinity is present the sample will turn blue. D. Repeat the tablet addition, one at a time (giving time for the tablet to dissolve), until the blue colour turns to permanent yellow. E. Count the number of tablets used and carry out the following calculation: P-Alkalinity, ppm CaCO3 = (Number of tablets x 20) –10 e.g. 12 tablets = (12 x 20) –10 = 230 ppm CaCO3 F.

Record the result on the log sheet provided, against the date on which the test was taken.

10.3.6 Hydrazine PPM* (Spectrapak 312) A. Take the comparator with the 10 ml cells provided. B. Slide the Hydrazine disc into the comparator. C. Add the water sample to both cells up to the 10 ml mark. D. Place one cell in the left-hand compartment of the comparator. E. To the other cell add one measure of Hydrazine powder (using the black 1 grm scoop provided) and mix until completely dissolved. F.

Wait 2 minutes and place the cell in the right hand compartment of the comparator.

G. Retain the sample for the M-Alkalinity test.

G. Hold up to the light and rotate the disc until a colour match is obtained.

10.3.4 M-Alkalinity (PPM CaCO3)

H. Record the reading shown as ppm Hydrazine.

A. To the P-Alkalinity sample add one M-Alkalinity tablet and shake or crush to disintegrate. B. Repeat tablet addition, one at a time (giving time for the tablet to dissolve), until the sample turns to permanent red/pink. C. Count the number of tablets used and carry out the following calculation: M-Alkalinity, ppm CaCO3 = (Number of P & M tablets x 20) –10 e.g. If 12 P and 5 M-Alkalinity tablets are used, M-Alkalinity = [(12 + 5) x 20] –10 = 330 ppm CaCO3

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E. Record the pH value result on the log sheet provided, against the date at which the test was taken.

10.3.7 Sulphite PPM* (Spectrapak 312) A. Take a 20 ml sample in the shaker tube supplied. B. Add one Sulphite No. 1 tablet; shake to dissolve. C. Add Sulphite No. 2 L.R. tablets one at a time until the sample turns blue. Note the number of tablets used. Calculate as follows: Sulphite content = Number of Sulphite No. 2 L.R. tablets x 10

D. Record the result on the log sheet provided, against the date on which the test was taken.

D. After use, thoroughly rinse out the shaker tube before storing. Please note: The Sulphite No. 1 tablet is used only to condition the sample. Do not count this tablet when calculating the sulphite level.

10.3.5 pH Test 7.5–14.0 For boiler water 6.5–10.0 For condensate water

10.3.8 Test results – Coordinated treatment A. Recording – Always use Unitor’s Rapid Response log forms to record all readings and to keep track of all results.



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11 High Pressure Boiler Water Control 1. Log form – Coordinated Boiler Water Treatment Log, no.311/312, or ask for special form above 30 bar pressure. 2. Frequency – Samples should be drawn, tested and results logged minimum every third day. * This is an optional extra (to the Spectrapak 311). This test must be performed below 21 °C. A cooling coil should be fitted at the sampling point or the sample should be cooled immediately under cold running water. Cloudy samples should be filtered before testing.

B. Reporting – The completed log sheet for the month should be distributed as shown at the bottom of the form, at the end of each month: 1. White copy – to Unitor’s Rapid Response Centre in Norway (address labels at back of log pad).

11.1 TYPES OF WATER Proper control using all aspects of your chemical treatment programme for boilers operating above 60 bar is extremely important. The high temperatures and pressures involved require your direct and constant attention to the conditions in the boiler and associated equipment in regulating the pre-treatment of the boiler water. Unitor recommends that you test your boiler, condensate and feedwater at least once and preferably twice a day. The crucial aspect of controlling a high pressure boiler system is knowing the performance of your pre-treatment equipment. The evaporator should be producing enough high-quality distilled water to provide sufficient composition and to handle leaks throughout the system and blowdown requirements.

2. Pink copy – vessel owner. 3. Yellow copy – to be kept onboard. C. Evaluation 1. Logs will be rewied at the Unitor Rapid Response Centre for adherence to recommended specifications, with the aid of Unitor’s computerized Rapid Response programme and staff. 2. A report letter indicating the status of the ship’s system, any problems and relevant recommendations will be issued to the ship’s operator.

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The efficient operation of the de-areator is critical. The function of the de-areator is to: A. Remove dissolved gases from the condensate. B. Pre-heat feedwater. C. Act as a storage tank for the boiler and suction head for the feed pump. In many cases, improper operation of the de-areator heater will affect the entire control and results of your chemical treatment programme. Ensure that the Ammonia level is being kept below a maximum level in the condensate of 0.3 ppm at all times and the feedwater indicates less than 10 ppb dissolved Oxygen. Be certain to maintain proper operating temperatures and pressures in the de-areator. Temperature variations between the upper and lower sections of the de-areator indicate faulty operation of the unit. To help resolve a condition where Ammonia levels exceed the allowed limit of 0.3 ppm, the de-areator should be vented to the atmosphere. Controlled venting is critical to ensure that excess water and heat are not lost to the atmosphere to reduce your Ammonia level below the maximum allowable level. At times, the efficiency of the gland exhaust condenser re-dissolves the gases which are intended to be vented off to the atmosphere and which continually attributes to the build-up of the Ammonia


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levels in the condensate. Of course, precise control and dosage of Hydrazine is critical in controlling this factor. Overdosage of Hydrazine will greatly affect the build-up of Ammonia in your system. Always dose enough Hydrazine to react with the trace amounts of Oxygen left in your feedwater after deaeration. Unitor recommends a 0.05 ppm residual of Hydrazine in your boiler water. However, theoretically, any test results above 0.03 ppm will indicate the presence of Hydrazine and this is an adequate residual to assure Oxygenfree boiler water. Controlling the pH and Phosphate coordination of the boiler water is also very critical. The coordination of the dosage of these products will prove to maintain your internal boiler surfaces free from caustic embrittlement corrosion and deposition. Unitor’s high pressure coordinated pH-Phosphate boiler water treatment programme is designed to maintain your boilers in optimum condition. If you experience any difficulties in controlling the programme prescribed herein, contact your local Unitor representative. Lastly, a routine for set periodic blowdown will enhance the results of this boiler water treatment programme. Even if test results are within good range of the recommendations, sludge is forming in the boiler at all times. This is a normal reaction of the chemicals you are treating. Plan a schedule that will fit into the vessel’s normal operating procedures to allow a complete blowdown procedure, including a bottom blow and a blow of each header and to remove the sludge build-up. Unitor recommends that this routine be performed twice a day. Of course, if conditions warrant it, additional blows should be performed.

SPECTRAPAK TEST

UNITOR TREATMENT

Water to be analysed

Spectrapak water analysis

Control limits

Unitor treatment products

Feedwater

Hardness Oxygen (optional) Chlorides

0 < 10 ppb < 5 ppm

Oxygen Control –

Boiler water

P-Alkalinity M-Alkalinity pH (coordinate) Phosphate (coordinate) Hydrazine Chlorides Silica Cond.

Reference Reference 9.6–10.2 10–25 ppm 0.05–0.10 ppm < 20 ppm < 3 ppm < 300 µS/cm

Alkalinity Control Alkalinity Control Alkalinity Control Hardness Control Oxygen Control – – –

Condensate

pH

8.3–9.0

Chlorides Ammonia

< 5 ppm < 0.3 ppm

Condensate Control – –

11.3 TESTING HP – BOILER WATER TEST KIT PC 22 PHOTOMETER 11.2 TREATMENT PROGRAMME FOR BOILERS OPERATING IN THE RANGE OF 60–83 BAR Unitor recommeds the use of coordinated Phosphate/pH water treatment control. The following high pressure boiler programme is based on the pressures, temperatures and operating conditions of boilers operating in the range of 60–83 bar. Maintaining the chemical concentrations and parameters prescribed will protect your boiler system. The following are specific control parameters and products required.

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11 / HIGH PRESSURE BOILER WATER CONTROL

PC 22 LED filter photometers are micro-processor controlled and have been specially designed for this purpose. Production using the most modern SMD technology, ergonomically-styled housing and the robust character of the instruments guarantees high precision in analysing in laboratories as well as using the instruments in the field. The four-line display enables the clear indication of the complete date setting and an exemplary user’s direction. System Specifications The PC 22 Photometer combines the sum of experience, determined by the daily experience which establishes precise measurement results within a short period. The aspects of compact measurement, ergonomical operation, modern design and a high measure of spraywater protection were taken into account in designing the housing. The foil keyboard, which incorporates an acoustic feedback via a beeper, is scratch-resistant and acid/solvent-resistant. The electronic components are sealed to provide maximum protection against corrosion.


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Delivery Contents of SPEKTRAPACK PC 22 1 1 1 1 4 1 4 1 1 1 1 1 1

Ph-meter PC 22 Photometer in a case 9 V-Battery 12 V-Mains adapter Cells Conductivity meter Stoppers Measuring cylinder 100 ml Test tube brush Stirring rod Cleaning kit Manual Guarantee-Certificate

Reagents Ammonia Silica P-Alk M-Alk Hardness Phosphate Hydrazine Chloride

Optional dissolved Oxygen test. The set is very easy to use and gives a quick accurate answer. The test results given can easily be compared with similar equipment in a lab. (Unitor recommends using the Chemetrics dissolved Oxygen test. Consult the Unitor office to arrange availability.) 11.3.1 Spares Standard spares are available from your local Unitor Marine Chemical representative. Order all spares from the on-going supply list provided with these test instructions. A Replacement Tablet Reagent Pack. Estimate 3-monthly requirements. 11.3.2 Safety Reagents are for chemical testing only; not to be taken internally. Keep away from children. Wash hands after use.

condensate water. High pressure boiler water using the co-ordinated Phosphate-pH control method should always be tested using the pH meter for accuracy and the best results. Note: Never touch the pH electrode sensor. Always rinse the sensor in untreated distilled water after use and keep the sensor damp. Store in distilled water. To use, follow the manufacturer’s instructions provided with the instrument. Calibration and slope adjustment can be checked using pH 7 and pH 10 buffers. G. Conductivity Meter. Note: Existing pH and conductivity meters can be used if onboard. Also verify test reults by standard solutions, pH buffer solutions or laboratory verification. H. Ammonia. I.

Hardness.

J. Dissolved Oxygen (optional). Testing feed water for dissolved Oxygen entering the boiler may be conveniently analyzed by inserting Oxygen ampoule into a flowing stream of the sample. Feedwater should be allowed to flush from sample line for a minimum of 10 minutes before taking sample. When the ampoule tip is snapped, vacuum inside the ampoule pulls the sample in where it mixes with the pre-measured reagent inside. A deep reddish/violet colour forms proportional in intensity to the dissolved Oxygen content of the sample. After inverting the ampoule several times to mix the contents, compare that colour with the liquid colour standards in the kit to determine the concentration of Oxygen. K. Silica. L. Boiler pH. M. Condensate pH.

11.3.3 High Pressure Procedures A. Phosphate. B. P-Alkalinity. C. M-Alkalinity. D. Chloride (Boiler and Condensate Water). E. Hydrazine. This test should not be performed at a temperature above 21 °C. A cooling coil should be fitted at the sampling point or the sample should be cooled immediately under running water. Cloudy samples should be filtered before testing. F. pH (Boiler and Condensate Water). The electronic pH meter is the most accurate and reliable method of testing high purity boiler and

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11.4 TEST RESULTS – HIGH PRESSURE BOILER WATER TREATMENT 11.4.1 Recording Always use Unitor’s Rapid Response log forms to record all readings and to keep track of all results. A. Log form – Ultra High Pressure Boiler Water Treatment Log, no. 314. B. Frequency – Samples should be drawn, tested and results logged at least once per day. 11.4.2 Reporting The completed log sheet for the month should be distributed as shown at the bottom of the form, at the end of each month:


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A. White copy – to Unitor’s Rapid Response Center in Norway (address labels at back of log pad)

11.5.2

Coordinated phosphate/pH treatment system

B. Pink copy – Vessel owner C. Yellow copy – to be kept onboard 11.4.3 Evaluation A. Logs will be reviewed at the Unitor Rapid Response Centre for adherence to recommended specifications. B. A report letter indicating the status of the ship’s system; any problems and relevant recommendations will be issued to the ship’s operator.

11.5 INTERPRETING TEST RESULTS 11.5.1 Hydrazine testing and control For reasons of economy, try to minimise the quantity of Hydrazine employed to scavenge Oxygen as well as reducing the amount of Ammonia that will be formed by the breakdown of Hydrazine. Ammonia in the presence of Oxygen is corrosive to Copper and Copper alloys (non-ferrous alloys). It will be necessary to test the Hydrazine residuals in the boiler daily in order to obtain complete protection with minimum doses of Hydrazine. If the Hydrazine residual in the boiler is over 0.1 ppm, reduce the dosage of Hydrazine until the boiler Hydrazine residual falls below the recommended maximum of 0.1 ppm. If the Hydrazine residual does not immediately drop below the 0.1 ppm level, the boiler should be blown down to reduce the Hydrazine level. New boilers, or those recently open for inspection and repair, may take several weeks to achieve a normal boiler Hydrazine residual due to oxides. This is normal, and until a Hydrazine residual is obtained in the boiler water, test the feedwater for the Hydrazine content. Maintain the Hydrazine reading in the feedwater between 0.02 and 0.03 ppm. No Oxygen is entering the boiler with the feedwater when Hydrazine is present in the water. However, be certain not to exceed the max. level of 0.1 ppm in boiler water. Hydrazine may be dosed into the feed pump suction, or preferably, to the storage section of the de-aerator, which will maximize the residence and reaction time of Oxygen control. A separate dosing tank and pump set should be used for dosing Hydrazine to the system. (Condensate Control may be fed with the Hydrazine.) The estimated daily dose should be mixed with condensate and the pump should be set to deliver the daily dosage over an entire 24-hour period.

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If a pump and tank set is not available, Hydrazine (and Condensate Control) can be added to the system through a tank and flowmeter into the atmospheric drain tank, with injection point well below the water level of the tank. Most boiler treatments use Sodium Hydroxide to produce the required alkalinity in the boiler water. This procedure is often called “The Free Caustic Regime”, which means that if a sample of the boiler water were evaporated to dryness in an inert atmosphere, the remaining solids would contain Sodium Hydroxide. High concentrations of Sodium Hydroxide can cause inter-crystalline cracking and, in high pressure boilers operating with a high heat flux, caustic gouging can occur. Caustic gouging is a reaction between Sodium Hydroxide and iron to form Sodium Ferrate. Nascent Hydrogen is liberated by this reaction and can cause Hydrogen embrittlement of the steel; often the embrittlement occurs simultaneously with the loss of boiler metal due to gouging. To prevent this from occurring, a coordi-


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nated phosphate to pH ratio method is used to produce the alkalinity required to protect the boiler steel from corrosion. The method of control, in practice, is to determine the pH of the boiler water and the Phosphate ppm level. These figures are then checked against the graph. If the intersection of Phosphate/pH values falls within the parallelogram zone or below the curve, no free Sodium Hydroxide will be present, which is the desired situation. If the pH is high according to Phosphate/pH chart, blow down to reduce it to the appropriate range, which also reduces the Phosphate level. If the pH is low and the Phosphate reading is in the proper range, add Alkalinity Control. If the Phosphate reading is below the recommended limits, add Hardness Control only. This procedure will also reduce the pH. If the Phosphate reading is high, blow down to the correct level. The correct balance of Phosphate to pH, to eliminate free Caustic, is easily achieved with the use of quality distilled feedwater. When both Alkalinity Control and Hardness Control are required, raise the Hardness Control before the Alkalinity Control. NOTE: Balance of Phosphate/pH to eliminate free caustic is easily achieved with the use of distilled (evaporated) feedwater. If raw or contaminated water is employed, it may be difficult or impossible to achieve a proper balance.

11.6 UNITOR TREATMENT CHEMICALS – DOSAGE GUIDES 11.6.1 Hardness Control – Dosage Guide Phosphate test Hardness control Result ppm gr/ton 0– 5 20.77 5–10 16 10–15 11 15–20 No Dose 20–25 No Dose 25 and above Blow down 11.6.2 Alkalinity Control – Dosage Guide pH test Alkalinity control result ppm ml/tonne 8.4 18 8.6 17 8.8 17 9.0 16 9.2 16 9.4 15 9.6 13 9.8–10.2 Satisfactory 10.3 and above Blow down

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11.6.3 Oxygen control – Dosage guide Hydrazine test results Oxygen control Less than 0.05 ppm Increase dosage 25 % 0.05–0.10 ppm Maintain dosage more than 0.10 ppm Decrease dosage 25 % Note:

Adjustment

Bear in mind that variations in plant loads and the efficiency of the de-areateor will affect the actual dosage of Hydrazine.

11.6.4 Condensate control – Dosage chart Litres per 10 tonnes Boiler Water Capacity Condens. pH Less than 8.3 8.3–9.0 over 9.0 Dosage Increase by 25 % Maintain daily Reduce by 25 % every ltr/day every 72 hours dose 0.75 ltr 72 hours 11.6.5 Initial dosage for each ton capacity boiler water HARDNESS CONTROL 23 gr/tonne ALKALINITY CONTROL 180 ml/tonne OXYGEN CONTROL 120 ml/tonne CONDENSATE CONTROL 0.75 ltr/day Note:

All dosage recommendations given above are estimations only, will vary depending on local conditions as makeup water quality, type of boiler and boiler load.

Water treatment on-going supply list – 6 months estimate

11.7 RECOMMENDED DOSAGE POINTS FOR MEDIUM PRESSURE AND HIGH PRESSURE CONDENSATE AND FEEDWATER SYSTEMS 11.7.1 Hydrazine Continuous to the storage section of the de-aerator. 11.7.2 Condensate Control Should be dosed to the condensate system on a continuous basis. Note:

The testing point for Condensate pH should be up-stream (before) from the dosage point of Condensate Control.

For steam vessels, separate dosages of Oxygen Control and Condensate Control are recommended for better individual control of each chemical. However, if only one dosing unit is available, both Oxygen Control and Condensate Control can be dosed together. Hydrazine and Condensate Control are compatible with each other.


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12 Boiler Wet Layup 11.7.3 Recommended Sampling Points Point (A) Condensate pH, Ammonia, Chlorides. Point (B) Feed Water Dissolved Oxygen, pH, TDS, Chlorides. Note:

Testing can be done at the discharge from the feed pump. However, if high dissolved Oxygen residuals are found, water in the storage area of the de-aerator should be checked to ensure no air is leaking into the feed pump.

Boilers are likely to suffer more from corrosion during periods when not in use or laid up. They must be protected. Proper layup procedures are essential. Corrosion will occur if : A. Low pH conditions occur. B. Oxygen is present in the boiler water. The procedure starts 2–3 days before the layup date 1 Test the boiler treatment levels and blow down the boiler at regular intervals to reduce potential sludge. The boiler should not be laid up dirty. 2 Raise the treatment levels for alkalinity to the maximum allowable level for that boiler pressure. 3 The boiler should then be treated with a high level of Oxygen Control after it has been isolated from the main steam line. Gentle firing of the boiler should be used to fully circulate the treatment with the boiler vented. 150–200 ppm Hydrazine is dosed into the boiler. (This works out at 1.25 litres/tonne of water.) NB! Full water capacity must be used to calculate this – not working capacity. 4 The vent cock on top of the boiler should be opened and the boiler filled with feedwater that is as hot as possible (90 °C). 5 The boiler should be given a “head”of water to ensure that the boiler is kept full of water. This is achieved by connecting a hose of a drum of treated water to the boiler vent cock to make up for any losses due to leaks. 6 Where super heaters are in place, the manufacturer’s instructions must be followed. 7 This principle of wet layup can be used for exhaust gas economisers, etc. 8 “Wet” layup of boilers is for the short term. A different procedure should be used for a long term layup . Returning to Service Drain the boiler of excess Hydrazine, refill with water and warm through in the normal way.

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13 Boiler Blowdown Blowdown is the mechanical process employed to remove and lower excessive concentrations of dissolved and suspended solids in boiler water. This procedure must be exercised on a regular basis to prevent solids from building up which in turn can result in steam carryover leading to contamination of the after-boiler system. In addition, the consequential concentration and accumulation of sludge and scale in the boiler can cause heavy deposits to collect on heat exchange surfaces. Once formed, these deposits reduce heat transfer and restrict water circulation, causing the boiler to operate at less than its optimum design efficiency. In order to compensate for the loss in thermal transfer, the fuel consumption must be increased to raise the temperature on the furnace-side of the boiler. This in turn can cause overheating and tube failure. In general, most feedwater and makeup water is processed and monitored prior to entering the boiler to ensure that the concentrations of naturallyoccuring solids are at a minimum. If done properly, only small amounts of these contaminants are allowed to get through. These, however, will concentrate in the system and therefore must be dealt with by the addition of water treatment chemicals. Solids concentrations in boiler water are usually determined by a conductivity meter which displays a visual readout of the ability of the boiler water to transmit an electrical current. This characteristic, called the specific conductance, is directly related to the solids content of the solution being measured. The greater the solids concentration, the higher the reading. The scale on the meter usually measures the results in units of electrical conductance as either siemens or microohms per centimeter at 25 °C. This value can be multiplied by a specific factor to determine the dissolved solids concentration. Some meters have scales that read directly in parts per million of total dissolved solids. Thus, these devices are called both conductivity and TDS meters. In some systems, these meters are permanently installed to continuously monitor boiler, condensate and feedwater. Understand and know the conductivity meter you are using. An upper limit for the maximum allowable concentration of dissolved solids is usually specified for a system based on the characteristics of that system. Operational temperature and pressure are normally given primary consideration. The higher the value of these parameters, the lower the tolerance of the system for dissolved and suspended solids and therefore the lower the specification limit. Once this value has been reached or exceeded, the system must be blown down to reduce the solids content as much as possible without sacrificing other aspects of the system operation.

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13 / BOILER BLOWDOWN

The Chloride residue is used as a reference value for the TDS level, and is used to determine blowdown requirements. An upper Chloride concentration limit is prescribed for the system being monitored. Blowdown as percent is expressed as: Cl in feedwater x 100 Cl in boiler.

= % Blowdown

A bottom blowdown may be done to rapidly remove high solids content in the boiler water. Continuous or intermittent surface blowdown may be used to achieve controlled reduction of TDS. The method used is usually dictated by the severity of the contamination and the conditions of the specific system involved. Observe all manufacturers’ recommendations for blowdown procedures as improper procedures can be detrimental to the boiler. Therefore, the process used must be implemented and performed judiciously, bearing in mind all parameters of the system (i.e. available makeup water, available chemicals, boiler load requirements, etc.). EXCESSIVE BLOWDOWN WASTES WATER, HEAT & CHEMICALS. Dumping the Boiler Occasionally it may be necessary to remove the entire contents of the waterside of the boiler system, or to prepare the unit for dry layup when it is to be decommisioned for an extended period of time. The boiler must never be emptied while the system is still hot, as this can cause solids to bake onto the hot surfaces, forming deposits which are extremely difficult to remove. Since the boiler internals retain heat for a considerable period of time after the system is taken off line, a wait of at least twenty-four hours is recommended from when the unit is shut down before commencing the dumping process.


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14 Chemical Cleaning of Boilers Many different types of contaminants can be found in the waterside of a boiler system. These can originate from impurities naturally found in or added to the water or from extraneous materials which have gained entrance due to faulty, worn or defective equipment associated with the system. This contamination can be in the form of hardness scale, oil, metallic oxides, sludge and various combinations of these as well as other miscellaneous materials. The procedure(s) required to clean the system will therefore depend on the nature and condition of the substances to be removed. The best initial approach to chemical cleaning is to inspect the fouled system as thoroughly as possible to determine the nature and extent of contamination. If possible, samples of the offending materials should be taken for examination and if necessary sent in for laboratory analyses. Once the results of this preliminary investigation and/or lab analysis are known, the appropriate cleaning procedure or procedures can be determined and implemented as follows.

J. During this period, make short blowdowns from drums and headers, adding water as necessary to maintain the initial level. K. After twenty-four hours, shut down the boiler and allow to cool until the pressure drops to zero. L. Open all vents and drains and allow boiler to drain. M. While draining, or as soon as possible after draining, flush the boiler with high-pressure, hot, fresh water. N. Inspect the system, removing any sludge or scum which may have accumulated during the cleaning process. O. If results of the cleaning are unsatisfactory, repeat the procedure. P. Secure boiler and return to service. Q. If system is to be laid up, do so in accordance with recommended wet or dry procedure.

14.1 BOILING OUT PROCEDURE 14.1.1 Parameters A. Pre-commission cleaning of new systems to remove preservatives, mill scale and other contaminants of construction. B. Subsequent to major system repairs, prior to returning to service. C. Removal of trace amounts of oil contamination. 14.1.2 Procedure A. Mechanically remove as much oily matter and as many other loose contaminants as possible. B. Fill the boiler to about one half its capacity with hot fresh water. C. Add Unitor Alkleen Safety Liquid at the rate of 15 litres/tonne of boiler capacity. D. Secure manhole openings and fill boiler to normal steaming level. E. Open drum vents and drains on superheater outlets. F. Carefully and slowly commence firing while maintaining below operating conditions. G. When steam begins to appear at vents, close vents and superheater inlet drain. Leave outlet drain or outlet vent slightly open. H. Allow pressure in the system to increase at a rate no greater than 7 kg/cm2 per hour until one half of normal operating pressure or maximum 21 kg/cm2, whichever value is lower, is reached. I. Maintain this condition for at least twenty-four hours, if necessary by intermittent firing of the boiler. Do not exceed originallydetemined cleaning pressure.

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14 / CHEMICAL CLEANING OF BOILERS

14.2 DEGREASING PROCEDURE For removal of light to heavy contamination resulting from ingress of oil due to defective machinery, equipment seals, or bunker or cargo tank heating coils. A. Determine the source of oil contamination and take appropriate steps to eliminate the problem prior to initiating the cleaning operation. B. Inspect boiler interior as thoroughly as possible to determine the approximate degree of contamination (i.e. light, moderate, heavy). While boiler is open, muck out as much oil and oily sludge found in boiler as possible before closing the boiler up. You are also recommended to plug down comers, if present, to allow circulation through main tubes of boiler. Install external circulation pump to circulate cleaning solution from water drum back to steam drum. Make all necessary connections. C. Secure inspection access openings and introduce the appropriate amount of Tankleen Plus and fresh water based on the estimated degree of contamination as follows. Ensure all boiler internals needed to be cleaned. Degree of Contamination Light Moderate Heavy*

% by Volume of Tankleen Plus in Water 1–2 % 2–3 % 3–5 %

* If contamination is particularly heavy, Tankleen Plus can be substituted by Carbon Remover at the rate of about 10 % by volume.


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D. If circulation pump is being used, start circulating solution. Fire the boiler for about 5 minutes, then secure for 15–20 minutes. Continue this process until the water temperature reaches 50–60 °C. Do not allow the temperature to go above 60 °C. Continue this operation for about 12 hours. E. Drain the boiler. F. Rinse thoroughly with high-pressure water (with heat if available). G. Drain and inspect as thoroughly as possible. H. If necessary, repeat steps 3 through 7. I. Secure all access openings and fill with feedwater. Remove plugs from down comer if this method was employed. J. Startup initial dosage of treatment chemicals and initiate boiler operation. K. Monitor treatment residuals and adjust as necessary to bring boiler water treatment programme employed into proper specification. L. Add 250 ml Unitor Boiler Coagulant every 12 hours and increase blowdown to remove any excess oil that remains for at least one week after the unit is returned to service.

G. Continually check temperature and pH of the solution at regular intervals. Maintain temperature as previously indicated. If pH goes above 4, add additional Descaling Liquid or Descalex. When using Descalex, take sample of original solution to compare with later samples. If solution changes to a yellowish colour, additional Descalex is required. H. When the circulation period is complete, drain the system and rinse thoroughly with fresh water to remove any excess debris. I. Neutralise any remaining traces of acid by circulating a 0.5 % solution of Alkalinity Control through the circuit for 2–4 hours. J. Drain the neutralizing solution, checking the effluent to ensure it has a pH of 7 or greater. If not, repeat steps 9 and 10. K. Re-inspect system interior and if necessary repeat steps 2 or 3 through 11 as indicated. L. Remove by-pass connections, secure all access openings and fill with feedwater. M. Add start-up dosage of treatment chemicals and initiate boiler operation. N. Check for proper treatment residual levels, adding additional chemicals if necessary to bring within proper specification limits.

14.3 DESCALING AND DERUSTING PROCEDURE

Refer to Descalex and Descaling Liquid Product Data Sheet for additional information.

A. Inspect boiler interior as thoroughly as possible to determine degree of contamination (i e. light, moderate, heavy). B. If deposits are covered with an oily or greasy film, degrease as outlined in steps 1 through 8 of Unitor’s degreasing procedure (previous, this section). C. Subsequent to degreasing or, if not required, construct a circuit for recirculating the acid cleaning solution through the boiler, being certain to by-pass all sections of the system containing non-ferrous metals. Ensure this circuit is vented at its highest point to allow the release of gases produced during the cleaning process. D. Introduce a solution containing the appropriate amount of Descalex or Descaling Liquid mixed with fresh water, based on the estimated degree of contamination as follows:

Degree of Contamination

Descaling Liquid in Water

Descalex in Water

Light Moderate Heavy

5–10% 10–15% 15–20%

3–5% 5–10% 10–15%

E. The descaling process can be accelerated by controlled heating of the cleaning solution. This must be done with great care, never allowing the solution temperature to exceed 60 °C. F. Circulate for 4–12 hours depending upon the degree of contamination.

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14 / CHEMICAL CLEANING OF BOILERS


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15 Diesel Engine Cooling Water Treatment 15.1 PROBLEM AREAS There are four key areas which must be considered when treating diesel engine cooling water systems. 15.1.1 Scale Scale results when a compound precipitates from the water phase because its solubility has been exceeded. Scale is a dense, adherent deposit of minerals and is tightly bonded to itself and to metal surfaces. Scale forming on metal surfaces requires four simultaneous factors: A. B. C. D.

Exceeding the solubility of the compound in water. Formation of small nuclear particles. Adequate contact time for crystal growth. Scale re-deposition exceeds the rate of dissolution.

One primary factor influencing scale adherence is surface roughness. The rougher the surface, the greater the probability of adherent scale forming. Also, scale forms more readily on corroding surfaces than on non-corroding surfaces. Easily corroded metals (mild steel) result in significantly more scale than metals that do not corrode (stainless steel). In addition to the four primary factors influencing scale deposition, there are other factors that offset the formation of scale. Wildly fluctuating pH is a significant cause of scale deposition in closed loop systems. Unitor uses Borates to buffer and control this fluctuating pH. As the pH of the system increases, so does the scaling potential for almost all common scale. This would include Calcium Carbonate, Calcium Sulphate, and Iron Oxide. Low pH extrusions can accelerate corrosion, provide nucleating sites and increase the potential for some forms of Silica scale. Scale formation in diesel engine cooling water systems can be controlled by various methods. Removing scale-forming Ions from the water before that water enters the cooling system is the most effective method. Almost all engine manufacturers recommend the use of distilled water. Distilled water is free of minerals. However, it is aggressive water and, if untreated, can lead to corrosion. 15.1.2 Corrosion Corrosion is the phenomenon that returns metals to their native states as chemical compounds or minerals.

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15 / DIESEL ENGINE COOLING WATER TREATMENT

In diesel engines containing dissimilar metals, our concern is galvanic corrosion. When exposed to water, one metal becomes anodic and the other cathodic, setting up a galvanic cell. For example, when Copper and Mild Steel are connected in water, the Mild Steel becomes the Anode, because it will give up electrons more readily than the Copper. The metal loss occurs at the anode, so the Mild Steel corrodes. Unitor recommends the use of a corrosion inhibitor containing Nitrite, Borate and Azole. Nitrite protects Mild Steel and Iron, while Azole protect Copper from corrosion. Nitrite acts by forming a protective metal oxide (passivating film) on the metal to be protected. 15.1.3 Fouling Fouling is different from scaling in that fouling deposits are formed from material suspended in the water, while scale deposits are formed from minerals in solution. Materials that cause fouling in cooling water systems are suspended solids and oil leaking into the system. We must control fouling in a diesel engine cooling water system, as it interferes with the effectiveness of corrosion inhibitors. 15.1.4 Microbiological activity Nitrites act as a food source for some types of bacteria. While the presence of bacteria is not as widespread in diesel engine cooling water systems as in other cooling water systems, it is a potential problem. The problem becomes apparent when conducting chemical tests of the cooling water. If the personnel on the vessel are dosing Nitrites and do not get a reading and the pH begins to fall, there is a possibility of microbiological activity. This can be verified by simple test methods (“dip slides”), or by sending a sample of the water to Unitor.

15.2 UNITOR COOLING WATER TREATMENT PRODUCTS Diesel engines have almost completely replaced turbines as the main propulsion unit in ships. These engines need to be cooled and water is used for this purpose. This water must be conditioned to ensure that scale does not deposit on the heat transfer surfaces in the cooling system. 15.2.1 The System The water is circulated around the engine and any loss due to leaks, etc. is made up from the expansion tank. As it circulates through the engine cooling spaces, the water picks up the engine heat, and this hot water goes to a heat exchanger where it is cooled.


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The steam heater is used to warm the engine up from cold. An air separator is normally installed to get rid of entrained air in the system. The water added to the expansion tank is termed “make-up” water. Distilled water shall preferably be used for these cooling systems. This is normally made onboard by a fresh water evaporator (or generator). A useful way of increasing the plant efficiency is to utilise the heat taken from the engine to provide a heat source to the evaporator. If evaporated water cannot be used for make-up, then fresh shore water will have to be used. This is normally much higher in impurities. The engine water temperature is in the region of 65 °C to 75 °C at the inlet to the engine. It is maintained at this temperature by controlling the cooling. The cooler is bypassed if the temperature drops. 15.2.2 Corrosion As mentioned above, this is the main problem in diesel engine cooling systems. The water contains some Oxygen, and if it is untreated, an ideal environment will exist for all types of corrosion.

15.3 DIESELGUARD NB AND ROCOR NB LIQUID 15.3.1 How do they work? All the information is contained in the relevant product data sheets but can be summarised as follows: They provide a very thin coating to all metal surfaces to prevent the corrosion from starting. The water is also made alkaline by the treatment to ensure that there is no acid corrosion. It is important that there is an excess of treatment in the system to replace any breakdown in the coating and to treat the makeup water as it enters the system. The testing for this is quickly carried out by the Spectrapak 309 Cooling Water Test Kit.

– The chart below can be used to determine the dosage requirement necessary to achieve a nitrite residual level between the minimum and maximum specification range limits. Nitrite (as ppm NO2)

0

180

360

540

720

900 1080 1260 1440 1620–2400

Dieselguard NB Kg/1000 L 2.88 2.52 2.16 1.80 1.44 1.08 0.72 0.36

0

0

15.3.3 Rocor NB liquid dosage chart Unitor Rocor NB Liquid A. Initial dosage for an untreated system is 9 litres/1,000 litres of distilled water. This will bring the treatment level up to a minimum level of 1000 ppm. B.

The chart below can be used to determine the dosage requirement necessary to achieve a Nitrite residual level between the minimum and maximum specification range limits.

Nitrite (as ppm NO2)

0

Rocor NB Liquid L/1000 L 13.0 Note:

180

360

540

720

900

11.3

9.7

8.1

6.5

4.9

1080 1260 3.3

1.7

1440–2400 0

When initially dosing a cooling water system, it is typical that the initial dosage may vary from vessel to vessel, or system to system.Total passivation of the cooling water system will consume more product than when making Nitrite up as maintenance dosages. The quality of make-up water will also affect initial dosage rates.

Some points to note: – All cooling water treatments must be approved by accepted Government bodies for use where the water is used as a heat source for an evaporator making drinking water. – The treatments must also be accepted by the engine manufacturer. The Unitor products are covered in these areas. 15.3.2 Dieselguard NB dosage chart Unitor Dieselguard NB – Initial dosage for an untreated system is 2 kg/1,000 liters of makeup water. This will bring the treatment level up to a minimum level of 1000 ppm.

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15.4 TESTS FOR DIESEL ENGINE COOLING WATER TREATED WITH DIESELGUARD NB/ROCOR NB LIQUID The following tests are recommended to maintain cooling water within the prescribed limits when using Dieselguard NB/Rocor NB Liquid: 1. Nitrite 2. pH 3. Chlorides

1000–2400 ppm as NO2 8.3–10.0 50 ppm maximum

15.4.1 Nitrite – Recommended Limits 1000–2400 ppm as NO2 The Nitrite concentration should be maintained within the above recommended limits to effectively inhibit any corrosive or scaling action within a closed cooling system. Over-concentration should be avoided to minimise the cost of maintaining the system. Under-dosage can set up a condition where accelerated corrosion can occur in areas which become unprotected. Dieselguard NB/Rocor NB Liquid is dosed according to the recommended nitrite level.

15.5 SAMPLING OF DIESEL ENGINES: Accessible sampling cocks should exist on all cooling systems for each diesel engine. This including, but not limited to, main jacket water, piston cooling, fuel oil valve, auxiliary engines, low temperature systems, etc. A representative sample must be taken from each cooling water system to be tested. To minimise the effort in obtaining cooling water samples, a sample cock located in a position to draw a sample/having access to draw the sample quickly and easily will make the task of drawing samples a simple one. In each case of drawing a sample, the container should be filled with the water to be tested, then sealed and labelled. It is advisable to conduct the appropriate tests within 30 minutes of drawing the sample, although this time limit can be extended when sample container is completely filled and sealed. 15.5.1 Sampling Procedure: The suggestion is for one sample bottle for each system to be tested. Mark each bottle clearly for each system. A. Provide a clean bottle for each sample drawn:

15.4.2 pH – Recommended Limits 8.3–10 The effectiveness of a corrosion inhibitor is restricted to within a certain pH range. Treatment with Dieselguard NB/Rocor NB Liquid ensures that this pH range is observed when the Nitrite level is sufficiently maintained to prevent corrosion. Under certain conditions because of external contamination, the pH may not fall into the range usually found with the correct Nitrite dosage. In such cases, Unitor recommends dosing 50 ml of Unitor’s Alkalinity Control per tonne of cooling water to raise the pH value when the pH is below 8.3. Re-test pH after dosage to prove that the pH value is being maintained between 8.3 and 10.0.

The bottle should contain 0.5 litre, should be made of glass or plastic, have a screw cap that seals air-tight and a label indicating pertinent data: a. Nature of water sample: 1. High temperature system 2. F.O. valve 3. Piston 4. Auxiliary 5. Low temperature system b. Sampling point/location

15.4.3 Chlorides – Recommended limit max. 50 ppm The Chlorides value of the cooling water should be kept as low as possible. Any increase in value whether sudden or gradual, will be an indication of sea water contamination. Check with the engine manufacturer for other specified limits. If the Chloride level exceeds 50 ppm, the possibility of corrosion in the system increases because Chlorides have a negative effect on the passivation film created by nitrites. Therefore, until corrective action has succeeded in bringing the Chloride level back down below 50 ppm, the nitrite level should be kept close to the upper limit (2400 ppm). 15.4.4 Sampling and testing of cooling water Samples should be drawn, tested and results logged for each system at least of once per week and if possible six times per month.

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B. Allow effluent to flush through sampling line a minimum of three to five minutes. C. Cool effluent to less than 25 °C before commencing to draw sample. D. Rinse bottle at least three times with sample water. E. Secure cap on bottle air tight. F. Be sure sample is representative of total coolant in system. G. Draw sample from same point in the system each time. H. Sample should be analysed as soon as possible after securing.


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15.6 TEST EQUIPMENT – UNITOR SPECTRAPAK 309 TEST KIT TEST PROCEDURES 15.6.1 Sample preparation: A. Cool sample to 21–25 °C B. Filter if necessary to clarify. 15.6.2 Spectrapak 309 content: A. Reagents: a. Nitrite No. 1 tablets b. Nitrite No. 2 tablets c. Chloride tablets d. pH test strips (6.5–10.0) B. Equipment: a. Syringe b. Plastic sample container 15.6.3 Test methods: A. Nitrite test a. Take a 5 ml water sample with the syringe and put into the container provided. b. Make the sample up to 50 ml using distilled water. c. Add two Nitrite No. 1 tablets and shake to disintegrate (or crush with the rod provided). Sample will be white. d. Add one Nitrite No. 2 tablet and shake to disintegrate. e. Continue adding the Nitrite No. 2 tablets one at a time until a pink color persists for at least one minute. Calculation: Nitrite(ppm) = number of No. 2 tablets x 180 For example: If 9 tablets are used Nitrite = 9 x 180 = 1620 ppm. f. Mark the result obtained on the log sheets provided against the date on which the test was taken. B. Chloride test a. Take a 50 ml water sample in the container provided. b. Add one Chloride tablet and shake to disintegrate; sample should turn yellow if Chlorides are present. c. Repeat tablet addition one at a time until the yellow colour changes to orange/brown. Calculation: Chloride ppm = (number of tablets used x 20) –20 For example: If 3 tablets are used, Chloride ppm = (3 x 20) –20 = 40 ppm d. Mark the result obtained on the log sheets provided, against the date on whichthe test was taken.

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C. pH test a. Dip one of the test strips into the water sample so that the colour zone is completely immersed. b. Compare the colour obtained with the reference, and read off the printed pH value. c. Mark the result obtained on the log sheet provided, against the date on which the test was taken.

15.7 TEST RESULTS 15.7.1 Recording The test results should be recorded on the Spectrapak 309 Rapid Response log forms. 15.7.2 Reporting Completed monthly log should be distributed as shown: A. White copy – Send to Unitor Rapid Response Centre. B. Pink copy – Vessel’s head office. C. Yellow copy – Retain for ship’s records. 15.7.3 Evaluation A. Logs will be reviewed for adherence to specification requirements by Unitor’s computerised RAPID RESPONSE system and staff. B. A log review indicating the status of the system, problems and recommendations will be issued to the ship’s operator.

15.8 DESCALING LOW SPEED MARINE DIESEL ENGINE COOLING WATER SYSTEMS Note: Be careful – use protective glasses and gloves Connect a thin (1/3”–1/2”) transparent hose to some low point of the system and run it up to the level of the top of the expansion tank. You now have a level indicator for the system. Drain the system and fill up with clean tap water to the lowest level in the expansion tank sight glass. Connect the pressure side of the chemical cleaning module to the cooling water inlet manifold. Make return connection from the bottom of the expansion tank to the mixing tank of the module. The ship’s fresh cooling water pump should be isolated from the system and not used for circulation, i.e. suction and pressure valves closed. The same applies to auxiliary machinery such as evaporators, generators, etc. These should be boiled out separately if necessary.


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Sufficient Descalex to mix up a 5–10 % solution is gradually filled into the mixing tank, well dissolved and fed into the inlet manifold. Take a sample of the solution for later colour comparison. The solution should be heated to 60 °C using the engine’s cooling water pre-heater. Circulate the system for 1/2 hour, then close the shut-off valves on all cylinders except one, and circulate for 15 minutes. Continue to circulate one cylinder at a time for 15 minutes each, over a period of 4 to 6 hours, checking the solution colour and temperature regularly. If the solution colour changes from red to orange or yellow, indicating acid neutralisation, add sufficient Descalex to the solution to return it to its original colour (usually 25 g per liter of solution). This reinforcement of the solution should not be done more than twice. If after two reinforcements the acid is still neutralised, the solution should be drained off and the process started again with a fresh solution. This will usually only be necessary when dealing with very thick deposits. When the cleaning solution retains its red colour for one hour, the cleaning operation may be considered complete and the solution can be drained off. Fill up the engine with clean fresh water and circulate each cylinder for ten minutes. Then drain each cylinder separately in order to get the highest possible dumping speed. Open all inspection covers and check that all debris that has formed during descaling is flushed out. Close covers. Fill up the engine again and add 0.5 % Alkalinity Control. Circulate the solution to remove any remaining acidity and passivate steel surfaces. Circulation must be maintained until sufficient level of pH value is obtained. This should be tested through the whole engine. Drain the engine. Adding the inhibitor – DIESELGUARD NB – ROCOR NB LIQUID. Refill the engine with fresh water produced by the evaporator to the lowest level in the expansion tank sight glass. Add sufficient cooling water treatment for the initial dosage through the cleaning module. Disconnect the cleaning module. Put all valves in normal operating position and circulate the system with the main cooling water pump for 15 minutes. Vent the system thoroughly during this time. Check the treatment concentration and adjust to 1500 ppm nitrite content. Fill the expansion tank to the normal operating level using water from the evaporator production. Check the acid content of the system lubricating oil directly after the descaling operation and repeat after 24 hours. Virtually the same procedure as above can be followed when descaling 4 or 2 stroke trunk engines. However, this kind of engine seldom has shut-off valves on the individual cylinders and therefore all cylinders must be circulated simultaneously. Medium-speed engines of this kind often have a drain bore “Tell Tale Bore”

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from the space between the upper (water) and the lower (oil) cylinder liner O-ring. This is to check for leakages. The bores should be inspected when the engine is running. If leaks are indicated, NO descaling should be performed unless the engine can be dismantled and the cylinder liners pulled out immediately after the descaling operation. Otherwise, you cannot be sure that all acid is flushed out/ neutralised, and corrosion of the sealing surface may occur.

15.9 DEGREASING MARINE DIESEL ENGINE COOLING WATER SYSTEMS When diesel engine cooling water systems become contaminated with oil and and grease, the system should be cleaned to remove oily deposits, as they can interfere with the cooling water corrosion treatment. In Service Cleaning This method may be undertaken with engine running at normal speed. 1) Take a 0.25 litre cooling water sample for future comparison and let it stand in a clear glass container. 2) Calculate the amount of Tankleen Plus required for solution of 0.5 % i.e. 5 litres per 1000 litres cooling water. Drain off similar amount of cooling water from engine if necessary. Slowly and intermittently add the cleaner to the cooling system via either the expansion or return tank. 3) After 5 hours, take a 0.25 litre cooling water sample. This should be allowed to stand in a clear glass container until any oil has risen to the top. The progress of the cleaning operation can be gauged by comparing thickness of this oil level with that of the first sample. A sample should be taken after 5–6 hours to monitor cleaning progress. 4) The cleaner can be left in the engine for a few days until a convenient port is reached where the engine can be drained. 5) Drain off the complete engine cooling system and flush thoroughly with clean water prior to re-filling with water of the required quality, to which an appropriate anti-corrosion treatment such as Dieselguard NB or Rocor NB Liquid should be added. Out of service Cleaning This method may be used when engine is stopped. 1) Take a 0.25 litre sample of cooling water for future comparison and allow it to stand in a clear glass container. 2) Drain the cooling system and flush out with water – then refill the system.


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16 Reporting Analysis Results 3) Calculate the amount of cleaner required for a solution strength of 2 % i.e. 20 litres per 1000 litres cooling water. Drain of similar amount of cooling water from engine if necessary. Add Tankleen Plus to the expansion tank or return tank. 4) Circulate the solution through the system and heat until the water reaches a temperature of about 60 °C. 5) Continue circulation of the solution through the system for a minimum of 5 hours. 6) Take a sample of cleaning solution from the system after a minimum of 5 hours. 7) When cleaning is completed, drain off the cooling water system, and thoroughly flush with clean water prior to refilling and adding an anticorrosion treatment such as Dieselguard NB or Rocor NB Liquid.

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One important aspect of a good water treatment management system is to ensure that analysis results and any action taken are recorded as the events take place and the reports are properly maintained for future reference. As mentioned earlier, special log forms are supplied separately for both boiler water treatment and diesel engine cooling water treatment. These should be completed by the water treatment officer responsible. Attention should be paid not only to recording the results of various water analyses, but to reporting any changes in circumstances that may have a direct or an indirect influence on the results, including any major cleaning or repairs to the system. In order that Unitor may keep a watchful eye on water treatment programmes onboard individual vessels, it is essential that the instructions for our Rapid Response programme are followed and logs sent promptly to our Rapid Response Centre for review and comment. Unitor will monitor the progress and performance of the onboard water treatment programme and liaise with the vessel’s head office and ship accordingly. Examples of how to complete the report logs are given overleaf. Make sure you use the correct log form in conjunction with your treatment programme. Picture page 72, 73, 74, 75, and 76, shows log examples.


71

CHEMICALS

Unitor ASA

Chemical Business Unit P.O. Box 300 Skøyen N-0212 Oslo Norway

72

16 / REPORTING ANALYSIS RESULTS


73

CHEMICALS

CHEMICALS

Unitor ASA

Unitor ASA


74




75

CHEMICALS

Unitor ASA


17 Water Tests, Summary 17.1 SPECTRAPAK TEST KITS 309 Test Kit:

– Nitrite – pH – Cl

310 Test Kit:

– P-Alkalinity – Cl – pH

311 Test Kit:

– P-Alkalinity – M-Alkalinity – PO4 – Cl – pH

312 Test Kit:

– Hydrazine/Sulphite

PC 22 Test Kit:

– P-Alkalinity – M-Alkalinity – PO4 – Cl – pH – Conductivity – Hardness – Ammonia – Hydrazine – Silica Samples to be tested: – Boiler water – Feed water – Condensate return – Make up water – Engine cooling water

17.2 TESTING Boiler water:

76


– P-Alkalinity – M-Alkalinity – Cl – PO4 – pH – Hydrazine/Sulphite – Conductivity – Silica – Appearance


77

Feed water:

– Cl – Conductivity

Make up water:

– Cl – Hardness – Silica

Condensate return:

– Cl – pH – Ammonia

Other actions in conjunction with previously mentioned: Alkalinity If P-Alkalinity test results are above limits even after not dosing chemicals, check the P-Alkalinity of the make-up water. Chlorides If high Chloride readings exist after blowdown, check for sources of salt water leaks: A) Drain cooler

Engine cooling water: – Nitrites – Chlorides – pH – Appearance

– – – – –

TEST DAILY AS REQUIRED TEST WEEKLY EVERY FOUR DAYS AS REQUIRED

Record all chemical tests on the Rapid Response logs.

17.3 TROUBLESHOOTING

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Fault

Action

P-Alkalinity

Too high Too low

Blowdown Dose Alkalinity Control to the boiler

M-Alkalinity

Too high

Blowdown

Chlorides

Too high

Blowdown

pH

Too low Too high

Dose Alkalinity Control to boiler Blowdown

Phosphate

Too high Too low

Blowdown Dose Hardness Control

Hydrazine/Sulphite Too high Too low

Blowdown Check for source of Oxygen leakage Increase chemical dosage

Conductivity

Blowdown

17 / WATER TESTS, SUMMARY

pH Check pH of condensate. If too low, increase dosage of Condensate Control. If too high, decrease dosage of Condensate Control. Phosphate If unable to maintain a Phosphate reading after dosing Hardness Control, check the make-up water for Chlorides. Hydrazine/Sulphite Check temperature of feedwater. In most cases, the higher the temperature of the feedwater, the lower the dosage of Oxygen Control or Sulphite. Conductivity If conductivity readings remain high after blowdown, check for:

17.3.1 Boiler water tests

Too high

C) Heat exchangers

Always check the Chlorides of the feedwater, condensate return and make-up water when Chloride readings in the boiler continue to be above maximum limits. If you have steam on deck, check the return lines.

Testing is mandatory to make sure the water treatment programmes are effective. BOILER WATER FEED WATER CONDENSATE ENGINE COOLING WATER MAKE-UP WATER

B) Condenser

A) Chloride levels/leaks

B) Condensate return

C) Phosphate level

17.3.2 Cooling water tests Nitrites

Fault

Action

Too low

Dose Dieselguard NB or Rocor NB Liquid. Stop dosing of chemical until the Nitrite level is back down below the max. limit.

Too high

pH

Too low

Check for salt water leaks and combustion gas leakage.

Chlorides

Too high

Check for leaks. Increase the chemical dosage to bring the Nitrite level close to the upper limit (2400 ppm).


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Nitrite If Nitrite readings remain low after dosing Dieselguard NB or Rocor NB Liquid, you may have a bacteriological problem. The cooling water should then be analysed with appropriate test “dip slides” which can be ordered from Unitor. Unitor also has available an effective biocide called MAR-71, which is specially developed for bacteriological problems. pH Increase chemical dosage. If Nitrite level is within recommended limits, dose Alkalinity Control to increase the pH. 17.3.3 Sea water cooling treatment To avoid fouling in sea water systems, Unitor has developed a very effective Amine-based dispersant of marine growth such as Shellfish Algae and micro-organisms in order to prevent the a.m. problem. Because of its filming properties, the product also acts as a corrosion inhibitor. Bioguard can be used in both static and flowing systems such as ballast tanks and looped cooling systems.

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17 / WATER TESTS, SUMMARY

The diagram on the previous page shows the typical dosage layout. This can be modified to suit a particular situation. Although the product will gradually clean fouled systems, treatment should preferably be started on a clean system. Dosage for sea water cooling systems: Dose 0.6 ltr Bioguard for every 100 m3 of seawater flowing through the system per hour. The system throughput is to be determined either from the rating of the pump(s) or from the system specifications. Treatment is necessary in coastal waters and should commence three days before entering these waters and continue for three days after leaving coastal waters. The calculated dose should be given over a one-hour period and repeated every 48 hours. Dosage for static ballast tanks: Dose one litre of Bioguard per 100 m3 of water prior to ballasting, followed by a monthly dose of 2 litre per 100 m3. NB! Bioguard should only be diluted with fresh water prior to dosing if necessary.


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18 Evaporator Treatment THE FRESH WATER EVAPORATOR (OR GENERATOR) There are two main types: THE VACUUM or FLASH EVAPORATOR and THE STEAM HEATED EVAPORATOR

18.1 THE VACUUM EVAPORATOR Vacuum is maintained in the evaporator, considerably reducing the boiling point of the water. The heat source used is the engine jacket water. The jacket water is circulated through the lower section of the evaporator where the heating section is. This heating section is a series of vertical tubes surrounded by the heating water. Sea water is pumped into the vertical tubes from below to be heated by the jacket water. The water vapour produced rises to the top of the evaporator where it comes into contact with cooling tubes and condenses. The condensate is then taken off for storage. The system is very efficient when correctly set up, but there are several points to consider: A. 3 percent of seawater is dissolved minerals. B. Evaporators of this type have a tendency to allow the seawater to foam and so salt is carried over with the distilled water. The treatment is to be fed continuously. The evaporator vacuum will pull the treatment in and it will enter the evaporator with the seawater. Sufficient treatment should be mixed for 24 hours operation. Treatment is essential to keep the evaporator operating efficiently for longer periods of time. It works in the following ways: a. Some of the dissolved solids may form scale and the treatment will help prevent the solids from adhering to the heating surfaces and keep these scale formers in solution. b. The sludge will be conditioned to make extraction of the concentrated sea water (brine) easier. c. The foaming tendency of the brine will be suppressed by anti-foaming agents. Unitor treatment is: Vaptreat. Average dosage: 0.3 l/10 tonnes of distillate produced. This is calculated on a standard brine density of 1.038 kg/l.

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18 / EVAPORATOR TREATMENT


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FRESH WATER GENERATOR Type AFGU 1-E-10/1-E-15

19 Marine Equipment 19.1 SOME COMMON MARINE EQUIPMENT 19.1.1 High Pressure Boilers > 30 bar • Babcox & Wilcox • Combustion Engineering • Foster Wheeler • IHI 19.1.2 Low Pressure Boilers < 30 bar • Sunrod • Aalborg • Cochran • Osaka • Kawasaki • MHI 19.1.3 Slow Speed Diesel Enginees < 120 rpm • Mitsubishi • Sulzer • MAN B & W • Gøtaværken • Fiat GMT 19.1.4 Medium Speed Diesel Engines 120–900 rpm • Wartsila • Sulzer • Pielstick • Enterprise • MAN B & W • MaK • Deutz • Bergen Diesel • Daihatsu 19.1.5 High Speed Diesel Engines > 900 rpm • Hitachi • Yanmar • EMD • Cummins • Caterpillar 19.1.6 Evaporators • Alfa-Laval Desalt • Atlas (bought by Alfa-Laval) • Nirex • Maxim • Weir

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18 / EVAPORATOR TREATMENT


85

Notes:

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20 / NOTES

Notes:


87

Notes:

88

20 / NOTES

Water Treatment Handbook UNITOR

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