STEAM GENERATION SYSTEM For HP and LP Boiler Boi ler System Syst em
OVERVIEW Steam The vaporized state of water which contains heat energy intended for transfer into a variety of processes from air heating to vaporizing liquids in the refining process. Steam is created from the boiling of water.
Sensib Sens ible le Heat Heat
Heat required to change the water temperature from 32°F to 212°F. Latent He Heat at
Heat required to change the state of water at its boiling temperature, into steam. It involves no change in the temperature of the steam/water mixture, and all the energy is used to change the state sta te from from liquid liquid (wat (water) er) to vapo vapour ur (sat (satura urated ted steam).
OVERVIEW Steam The vaporized state of water which contains heat energy intended for transfer into a variety of processes from air heating to vaporizing liquids in the refining process. Steam is created from the boiling of water.
Sensib Sens ible le Heat Heat
Heat required to change the water temperature from 32°F to 212°F. Latent He Heat at
Heat required to change the state of water at its boiling temperature, into steam. It involves no change in the temperature of the steam/water mixture, and all the energy is used to change the state sta te from from liquid liquid (wat (water) er) to vapo vapour ur (sat (satura urated ted steam).
OVERVIEW Boiler
LP Boilers
HP Boi ler
A closed vessel in which water under pressure is transformed into steam by the application of heat. In the boiler furnace, the chemical energy in the fuel is converted into heat, and it is the function of the boiler to transfer this heat to the contained water in the most efficient manner. It is designed to absorb the maximum amount of heat released in the process of combustion. This heat is transferred to the boiler water through radiation, conduction conduction and convection. The relative percentage of each is dependent upon the type of boiler, the designed heat transfer surface and the fuels.
OVERVIEW
Fire And Smoke-Tube Boiler
Firetube boilers are often characterized by their number of passes, referring to the number of times the combustion (or flue) gases flow the length of the pressure vessel as they transfer heat to the water. Each pass sends the flue gases through the tubes in the opposite direction. The number of passes the boiler contains affects the boiler efficiency, and its first cost to manufacturer. The more heat transfer surfaces the boiler has, the more efficient it can be.
PROCESS
Condensate from Process
Process Flow of Steam Generation System
PROCESS
Steam Generation System Plant
OPERATION Description Steam Generating Capacity Design Pressure
8,000 kg/hr (Saturated Steam) 6 bars
Operating Pressure
3.5 bars
Design Temperature
165°C
Operating Temperature
148°C
Efficiency
91%
Boiler Heating Surface
161 m2
Boiler Water Capacity
11.9 m3 (approximate)
Boiler Steam Capacity
3.9 m3 (approximate)
Type
Low Pressure Boiler Evaporator Description
Low pressure steam is used for the heatingup of the jacketed vessels and pipelines in the process area. Also, it is used for heating up the boiler feed water in the feed water deaerator up to 105OC.
Parameter
3-pass combined fire & smoke-tube evaporator w/ external & cooled irradiation chamber Large water space, double fire tube in 3-pass construction cooled over a length of 5,040 mm.
1st Pass
1 fire tube; ∅1,150 mm
2nd Pass
80 smoke tubes; ∅70 mm x 3.2 m
3rd Pass
51 pipes; ∅70 mm x 3.2 m
OPERATION Description Steam Generating Capacity
900 kg/hr (Saturated Steam)
Design Pressure
60 bars
Operating Pressure
55 bars
Design Temperature
276°C
Operating Temperature
271°C
Efficiency
90%
Boiler Heating Surface
12.5 m2
Boiler Water Capacity
2.0 m3 (approx)
Boiler Steam Capacity
0.8 m3 (approx)
Type
3-pass combined fire & smoke-tube evaporator w/ external & cooled irradiation chamber
Evaporator Description
Large water space, one fire tube in 3-pass construction cooled over a length of 3,000 mm
High Pressure Boiler
High pressure steam is used for heating-up the barrels of the extruder and the purification columns in the purification section.
Parameter
1st Pass
1 external & cooled irradiation chamber
2nd Pass
16 smoke tubes; ∅57 mm x 3.2 m
3rd Pass
10 pipes; ∅57 mm x 3.2 m
OPERATION
HP/LP Distr Dist ribut ion ibu tio n Steam System Syst em
OPERATION Economizer Description
Parameter Water Side
Flue Gas Side
Max. Allowable Pressure
60 bars
-
Operating Pressure
55 bars
-
Design Temperature (In/Out)
105 / 159 °C
394 / 200 °C
Exchange Surface Area
25 m2
Heat Output
58 kW
Capacity
13 Li
-
Feed Water Deaerator Tank Description
Feed Water Deaerator Tank •
Removes oxygen, carbon dioxide and other noncondensable gases from feed water
•
Heat-up the incoming makeup water and return condensate to an optimum temperature for Minimizing solubility of the undesirable gases -
Providing the highest temperature water for injection to the boiler
Parameter
Capacity
10 m3
Operating Temperature
105°C
Design Temperature
150°C
Operating Pressure
0.2 – 0.3 bar
Design Pressure
-1/+2 bar
Pipeline Throughput
14 tons/hr
Fresh Water Percentage
50% (approximate)
Condensate Percentage
50% (approximate)
Steam Consumption
1,250 kg/hr (approximate)
OPERATION Condensate Tank Description Capacity
Parameter 7 m3
Operating Temperature
100°C
Design Temperature
150°C
Operating Pressure
0.2 – 0.3 bar
Design Pressure
0.5 bar
Condensate Tank
Collects condensate resulting from the process area. Steam supplied to the process area condenses after heat is given off. The steam pressure drives the condensate back to the condensate tank. An exhaust to the atmosphere maintains the tank pressure. Recycling the condensate will reduce the cost of heating feed water to the boiler and the boiler water chemicals.
OPERATION
Condensate Loop
OPERATION
Float Trap
OPERATION HP/LP Boiler Instrument Instrum ent and Controls A dedicated PLC panel cabinets for each boiler controls the operation of these steam generators.
LP Boiler Controls Safety Featur e
Setting
HP Boiler Boiler Controls Controls Safety Featur e
Setting
PZAH 11 (safety manostat)
Causes a malfunction shutdown of LP1 at 5 barg. Auto restart is not possible.
PZAH 2 (safety manostat)
Causes a malfunction shutdown of LP2 at 58 barg. Auto restart is not possible.
PZAL 33 (manostat)
Shuts down burner at fuel oil pressure of 2.3 barg
PZAH 43 (manostat)
Shuts down burner at fuel oil pressure > 1 barg.
PZAH 33 (manostat)
Shuts down burner at fuel oil pressure of 2.7 barg
PZAL 31 (safety manostat)
Shuts down burner if fuel gas pressure ≤ 225 mbar or ≥ 275 mbar
OPERATION Deaerator Feed Water Instr ument and Contr ols Instrument Controls
The following solenoid switches and level indicators control the deaerator level: -
optical level display by means of the individual magnetic flaps
-
holding the preset water level constant a) When switch contact for LSL 25 is actuated fresh demin supply pump cuts in b) When switch contact for LSH 24 is actuated fresh demin supply pump cuts out c) When switch contact for LSL 26 is actuated fresh condensate supply pump cuts in d) When switch contact for LSH 27 is actuated fresh condensate supply pump cuts out
-
Shuts off the boiler feed water pumps when the water level in the deaerator falls below low level
Level Indicator
OPERATION HP/LP Boiler Instrument Instrum ent and Controls
OPERATION Fuel System
Propylene
LPG
Diesel
LP Burner
Diesel HP Burner
OPERATION
Boiler Boil er Burner
OPERATION
OPERATION Fuel System
Diesel Tank Section
LPG
OPERATION LP Boiler Operation
HP Boiler Operation
OPERATION Blowdown Systems It is the purge from a system of a small portion of the concentrated boiler water in order to maintain the acceptable level of dissolved and suspended solids in the system.
Continuous Surface Blowdown Aims to maintain control of dissolved solids (TDS) and prevents large variations in critical boiler water chemical balances.
Bottom Blowdown Removes the suspended solids from the drum, where sludge accumulates.
Manual (Bottom) Blowdown Usually remains necessary to control the sludge concentration in the boiler.
B/D valve
OPERATION
OPERATION Flash Drum Separates flash vapor from condensate in the boiler lye. This vessel has a holding capacity of 0.024 m3 at a designed parameters of 1 bar at 280OC.
Blowdown Cooler Collects the boiler lye periodically from the LP-steam boiler and HP-steam boiler. Condensate will separate from the lye. Exhaust vapor will be vented to the atmosphere and the collected lye should be drained periodically to the sewage.
OPERATION Standby Protection / Preservation
Wet Preservation This technique is implemented during S/Ds lasting for a month or less. The boiler is flooded with deaerated water due to the following: 1. To eliminate the liquid-vapor interface that can cause a water line corrosion 2. To prevent the condensation of acidic dropletes caused by CO2 absorption 3. To eliminate any dissolved oxygen that can cause corrosion The chemical dosing for both oxygen scavenger and corrosion inhibitor uses twice the treatment volume than the normal usage to eliminate the dissolved oxygen and maintain the pH quality of 9.5–11.0. Nitrogen blanketing can also be employed to displace air from the boiler.
Dry Preservation This technique is implemented for a prolonged S/Ds for more than a month. The boiler water is drained completely. Dessicants is then added to absorb any water vapor and thus control the relative humidity in the boiler.
WATER TREATMENT Boiler Problems Caused By Water
Scale
Scale forms mainly with hardness components or silica on the heating surface and the drum. Sometimes leads it leads to embrittlement and explosion of evaporation tube Cause of Problem • • • •
Poor water quality and fouled ion exchange resin Incomplete control of boiler water (blow down shortage, etc) Corrosion product brought into boiler from feed and condensate lines Insufficient chemical injection
WATER TREATMENT Boiler Problems Caused By Water
Corrosion
Corrosion at heating surface and feed and condensate lines is due to dissolved gasses (O2, CO2) and to accumulation of metal oxides and hydrates on heating surfaces. Cause of Problem • • • •
Corrosion product brought into boiler from feed and condensate lines Insufficient pH control and oxygen scavenging Insufficient boiler water control on pH and P-alkalinity Corrosion occurrence at shutdown or idling period
WATER TREATMENT External Bo iler Water Treatment External treatment, as the term is applied to water prepared for use as boiler feed water , usually refers to the chemical and mechanical treatment of the water source. The goal is to improve the quality of this source prior to its use as boiler feed water , external to the operating boiler itself. Such external treatment normally includes: 1. 2. 3. 4. 5. 6. 7.
Clarification Filtration Softening Dealkalization Demineralization Deaeration Heating
Feed Water Deaerator Tank
WATER TREATMENT Utilizes the fundamental principle: “The solubility of a gas in a liquid decreases with increasing liquid temperature”. Incoming water is sprayed into a steam atmosphere, where it is heated to within a few degrees of the saturation temperature of the steam . Most of the noncondensable gases (principally oxygen and free carbon dioxide) are released to the steam as the water is sprayed into the unit.
Deaerating Heater
Water cascades from tray to tray, breaking into fine droplets or films which intimately contact the incoming steam which removes all but the very last traces of oxygen.
Deaerated water falls to the storage space below, where a steam blanket protects it from recontamination.
WATER TREATMENT Internal Bo iler Water Treatment
Oxygen Scavenger Tank
This a chemical compound that removes dissolved oxygen in water by reduction reaction and thereby inhibits the corrosion caused by the oxygen. Its chemical potentiality is high enough to reduce oxygen The reaction product of the scavenger and oxygen does not have an aggressive effects on the boiler or on the steams and condensate lines
An ti sc alant Solution Tank
This type of boiler compounds prevents the scale formation and adjusts the pH of boiler water to inhibit corrosion. The phosphate-base type of antiscalant, Reacts with hardness components 2+ 2+ (Ca , Mg ) in water and converting them into suspendible substance. -
Keeps silica substances water soluble.
WATER TREATMENT Typical Water Quality Contr ol Parameters Control
WATER TREATMENT Raw Water (Typi cal Values)
Demin Water Qualit y Quality
Description
Parameter
Description
Parameter
pH @ 25OC
7.0 (estimated)
pH
Conductivity
max. 265 µs/cm
Conductivity
Silica
≤
150 ppm SiO2
Silica
< 0.05 ppm
Phosphate (Unfiltered)
≤
14 ppm PO4-3
Total Iron
0 ppm Fe
3.8 ppm PO4-3
Total Hardness
Phosphate (Filtered)
≤
Chloride
≤
10 ppm Cl-
Total Iron
≤
0.1 ppm Fe
Total Alkalinity
≤
P Alkalinity Total Hardness
125 ppm CaCO3 0 ppm CaCO3
≤
105 ppm CaCO3
• The raw water is considered as a ground water type of water.
< 7.0 < 3.0 µS/cm
0 ppm CaCO3
WATER TREATMENT Boiler Feed water quality Description CO2 Combined
LP water quality
Parameter
Description
Parameter
< 25 ppm
pH at 25°C
10.4 – 11.4
O2
< 0.02 ppm
Conductivity
< 500 μS/cm
Oil
< 0.5 ppm
Phosphate (PO 4-3)
20 - 30 ppm
pH at 25 °C (LP/HP)
8.5 – 9.5 *
Silica (SiO2)
Iron
< 0.02 ppm
Hydrate Alkalinity
Copper
< 0.003 ppm
Dissolved O 2
Silica (SiO2) Hardness Conductivity
< 40 ppm 100 – 300 ppm 0 ppm
< 0.2 ppm 0 < 2000 μS/cm
* Depends on the water treatment program.
HP water quality Description
Parameter
Conductivity
< 300 μS/cm
Phosphate (PO 4-3)
10 - 20 ppm
Silica (SiO2)
< 20 ppm
Dissolved O 2
0 ppm
Hydrate Alkalinity
0 ppm
Lessons Learned
1. Installation of platform at the boil er stacks. A platform was installed for sampling accessibility of flue gas. This was requested by DENR representatives in lieu of stack emission testing and permit to operate (Boilers).
2. Installation of sampling area for condensate tank and boi ler feed w ater (direct to Deaerating tank). The need to set up a new sampling points for both condensate and boiler feed water tank was for the adjustment of chemical dosing treatment and monitoring of dissolved oxygen at the boiler water lines. For the feed water, sampling is done at the bleed port of the feed water pump.
