(Submitted on completion of summer vocational training at NTPC, NTP C, Sipat)
National tional T herm herma al Pow Power Corpora Corporation, tion, SIP SI PAT (Chha (Chhatti ttisgarh )
Under the guidance of:-
Submitted By:-
Shri G.B.P. Srivastava
Saket Swagat Sahoo Sahoo
Senior Manager,
Chemical Engg.(4th sem)
Chemistry Department
IT-GGU, Bilaspur(C.G) Page | 1
I hereby declare this work entitled “ Summer training project report on Power Plant Chemistry”, submitted towards completion of vocational training comprises of my original work work pursued under the supervision of Guides at NTPC Si pat . The results embodied in this report have not been submitted to any other Institute or University for the fulfillment of any an y other curriculum.
SUBM ITTE TTED BY:-
Saket Swagat Sahoo Chem hemical cal E ngg ngg. (4th sem), I ns nsti titute tute of Te T echnol chnolog ogy, y, G uru G has hasidas das U nivers niversiity,B ty,Biilaspur(C pur(C.G .G.). .).
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I hereby declare this work entitled “ Summer training project report on Power Plant Chemistry”, submitted towards completion of vocational training comprises of my original work work pursued under the supervision of Guides at NTPC Si pat . The results embodied in this report have not been submitted to any other Institute or University for the fulfillment of any an y other curriculum.
SUBM ITTE TTED BY:-
Saket Swagat Sahoo Chem hemical cal E ngg ngg. (4th sem), I ns nsti titute tute of Te T echnol chnolog ogy, y, G uru G has hasidas das U nivers niversiity,B ty,Biilaspur(C pur(C.G .G.). .).
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This is to certify that Mr. Saket Swagat Sahoo of Institute of Institute of Technology, Guru Ghasidas University, Bilaspur has undergone Vocational training training from 04/06/2012 to 30/06/2012 30/06/2012 at National Thermal Power Corporation, Sipat in the Chemistry Department and has made the project under my guidance.
Project Guide:-
Shri hr i GBP GBP Sriva Sri vast stav ava a Senior Manager, Chemist Chemistrr y Depar Depar tment tment
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First of all I would like to thank Shri GBP Srivastava for guiding me throughout the training period. I am grateful to Shri Abhishek Das who took out time from his busy schedule to explain the working of DM plant to me. I would also like to express my sincere gratitude to Shri K. Satyanarayana, Shri D.Mishra and Shri B.Ganguly for their sustained encouragement. I am also thankful to all the laboratory instructors who imparted lectures on various topics. Lastly, I would like to thank Employee Development Centre for providing me with this beautiful opportunity. Thanking you Saket Swagat Sahoo
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National thermal Power Corporation Limited(NTPC) is the largest Indian state-owned electric utilities company based in New Delhi, India. It is listed in Forbes Global 2000 for 2011 ranked it 348th in the world. It is an Indian public sector company listed on the Bombay Stock Exchange and National Stock Exchange in which at present the Government of India holds 84.5% (after divestment the stake by Indian government on 19th October, 2009) of its equity. With a current generating capacity of 39,174 MW, NTPC has embarked on plans to become a 75,000 MW company by 2017. It was founded on November 7, 1975 with 100% ownership of the Central government. In 1997, Government of India granted NTPC status of “Navratna being one of the nine jewels of India, enhancing the powers to the ‟
Board of Directors. NTPC became a Maharatna company in May, 2010, one of the only four companies to be awarded this status. NTPC s core business is engineering, construction and operation of power ‟
generating plants and providing consultancy to power utilities in India and abroad. The total installed capacity of NTPC in India is as follows at present:
By 2017, the power generation portfolio is expected to have a diversified fuel mix with coal based capacity of around 27,535 MW, 3,955 MW through gas, 1,328 MW through Hydro generation, about 1400 MW from nuclear sources and around 1000 MW from Renewable Energy Sources (RES). NTPC has adopted a multi-pronged growth strategy which includes capacity addition through green field projects, expansion of existing stations, joint ventures, subsidiaries and takeover of stations . NTPC has been operating its plants at high efficiency levels. Although the company has 18.10% of the total national capacity, it contributes 28.60% of total power generation due to its focus on high efficiency. Page | 5
Location : 20 Km from Bilaspur, CG Capacity : 3 X 660 MW Stage-I and 2 X 500 MW Stage-II Water Source : From Hasdeo right bank canal Coal Mines : Dipika Mines of SECL Korba. Coal Transport : By dedicated MGR (42 Kms)
Highlights:- * Super Critical Technology first time in India *765 KV Transmission System first time in India *100 Mtr. wide peripheral green belt around the project *Submerged ash dyke *State-of-the-art Technology for Environmental Management
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Power plant chemistry is the involvement of chemistry to increase the efficiency of power p lants by minimizing the loss due to corrosion and deposition, by providing solutions to reuse effluents and other discharges and helping maintain the stringent environmental norms laid out by the government. So in essence the key areas where chemistry is used are: Water Treatment Maintaining quality of Coal Checking Quality of Oil Utilization of Ash
Water Treatment Since water is the basic requirement for the production of the working substance, it is necessary to have an arrangement to provide water which is not contaminated by unwanted materials. For this a water treatment unit is provided which receives water from a source, then de-mineralizes it and finally after further treatment, is fed into a boiler feed pu mp. Some of the systems involved in the treatment of water are de-mineralization plant, raw water pump house, clarification plant and many others. The type of water used is different for different purposes. The process of coo ling requires raw water, whereas steam formation, and many other major processes require d e-mineralized water. De-mineralization plants consist of cation, anion and mixed bed exchangers. The final water from this stage consists of hydrogen ions and hydroxyl ions which is the chemical composition of pure water. Poor water treatment lets water interact with the surfaces of pipes and vessels which contain it. Steam boilers can scale up or corrode, and these deposits will mean more fuel is needed to heat the same amount of water. Cooling towers can also scale up and corrode, but left untreated, the warm, dirty water they can contain will encourage bacteria to grow. This reduces efficiency, shortens plant life and makes operations unreliable and unsafe. Industrial water treatment seeks to manage four main problem areas:
Scaling
Corrosion
Microbiological activity
Disposal of residual wastewater.
Boilers do not have many problems with microbes as the high temperatures prevent their growth.
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Scaling occurs when the chemistry and temperature conditions are such that the dissolved mineral salts in the water are caused to precipitate and form solid deposits. These can be mobile, like fine silt, or can build up in layers on the metal surfaces of the systems. Scale is a problem because it insulates and heat exchange becomes less efficient as the scale thickens, which wastes energy. Scale also narrows pipe widths and therefore increases the energy used in pumping the water through the pipes. Corrosion occurs when the parent metal oxidizes (as iron rusts, for example) and gradually the integrity of the plant equipment is compromised. The corrosion products can cause similar problems to scale, but corrosion can also lead to leaks, which in a pressurized system can lead to catastrophic failures. Water treatment therefore should remove the dissolved ox ygen and maintain the boiler water with the appropriate pH and alkalinity levels.
Microbes can thrive in untreated cooling water, which is warm and sometimes full of organic nutrients, as wet cooling towers are very efficient air scrubbers. Dusts, flies, grass, fungal spores and so on collect in the water and create a sort of "microbial soup" if not treated with biocides. With the proper treatment, a significant proportion of industrial on-site wastewater might be reusable. This can save money in three ways: Lower charges for lower water consumption Lower charges for the smaller volume of effluent water discharged Lower energy costs due to the recovery of heat in recycled wastewater.
The steps followed in treatment of water can be categorized as:1) Pre-Treatment- Pre-treatment removes materials that can be easily collected from the raw water before they damage or clog the pumps and sewage lines of primary treatment clarifiers (trash, tree limbs, leaves, branches etc.). The importance of Pre-Treatment lies in the fact that that quality of water deteriorates day by day, so to maintain a certain level of quality before the raw water is sent for treatment pre-treatment is done. The importance of pre-treatment increases during monsoons.
2) Demineralization- It primarily involves removal of impurities by ion-exchange metho d. It is the second stage of water purification. 3) Condensate Purification- The corrosion product accumulated in water steam cycle need to be removed to avoid their deposition on heat exchange surfaces. Also any cooling water ingress to water steam cycle is to be treated. For this Condensate Polishing Units are provided. The different steps undertaken in treatment of water have been articulated in the flow sheet given below:Page | 8
F igur e 1- W ater tr eatment plant flow sheet
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Description Raw water is obtained from Right bank canal of Hasdeo barrage by a canal upto Harshdivishal where a raw water makeup pump house is present. Water from pump house is received into reservoir no. 1. Max. Water level = 280.5m (Sea level) Top of embankment = 282.0m (Sea level) Bed level = 272.0m. (Sea level) Total Height = 10m Water level = 8.5m 2 Total area covered = 17500 m
Then after raw water has been acquired it is sent to aerator for aeration.
Aerator Aeration is a process to bring water into close contact with air to hasten the transfer of a gas between two phases. Basically it is an arrangement by which air is circulated through, mixed with or dissolved in a liquid or substance. It is also known as aerification.
[Air] O2 (free) -> O2 (Dissolved) [Water] There are two main aeration methods water-into-air and air-into-water and sometimes a combination of both. The water-into-air aerator is designed to produce small droplets or thin sheets of water exposed to Page | 10
the atmosphere. The air-into-water aerator creates small bubbles of a ir that rises through the water being aerated. Some aerators operate by a combination of both methods. Cascade aerators are the most common type of aerator used in water treatment due to its simplicity and reliability. Examples of water-into-air aerator are:
cascade aerators (single or multiple drop)
multiple platform aerators, commonly known as circular cascade aerators
spray aerator
Examples of air-into-water aerators are:
venturi aerators
draft tube aerators
Example of combination aerators are:
mechanical aerators pressure aerators
F igur e 2- Cascade Aer ator
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What happens in aeration? The content of each gas in the atmosphere and in water is in equilibrium. Gases will be liberated when their concentration in water is higher than at equilibrium. Conversely, gases will be absorbed by water when their concentration in water is below than at equilibrium. There processes of absorption or liberation called aeration in water treatment, are v ery slow unless large water surface are exposed or unless the water is agitated.
Factors affecting aeration: The efficiency of aeration depends on the amount of surface contact between air and water, pH and temperature of water, time of contact and type of aerator, and is generally measured by the increase in concentration of oxygen or by the decrease in the concentration of carbon dioxide in the water.
Purpose of aeration: Volatile organic contaminants like methane, ethane, ethylene etc, & dissolved gases (CO2, H2S,
and NH3 etc.) are reduced, which are thought to be contributing to odor & taste. Aeration removes soluble Fe (II) & Mn (II) compounds to a great extent through oxidation that produces insoluble oxides or hydrated oxides.
4 Fe( II) + O2 + 10 H2O 4 Fe (OH) 3↓ + 8 H+ 2 Mn (II) + O 2 + 2 H2O → 2 MnO2 ↓ + 4 H+ Oxygen dissolved in this process also removes H2S through oxidation.
2 H2S + O2 → 2 H2O + 2 S↓ Carbon dioxide – Calcium bicarbonate equilibrium is also distributed due to stripping out of
Carbon dioxide.
Ca(HCO3)2 → CaCO3↓ + H2O + CO2↑
Chlorine Dosing When the water has been passed through the aerator, it is brought into stilling chamber. Here, chlorine is injected into raw water generally at the rate of 2.5 mg/l. Since, chlorine is known for its bactericidal properties, so this process helps in reducing bacteria count. It also has several other advantages. They are:
It kills algae and reduces color.
It is responsible for oxidation and precipitation of Iron and Manganese.
It reduces color and assists the settlement process. Page | 12
How is chlorine used? Chlorine cannot be used directly in its gaseous state. It is first dissolved in water. It reacts in water according to the reactions given below.
Cl2 + H2O <=====> HOCl + HCl HOCl <=====> OCl- + H+ The equilibrium is dependent on pH.
At pH below 2, all chlorine is in molecular form At pH below 5, all chlorine is in the form of Hypochlorous acid (HOCl). At pH below 10, all chlorine is in the form of hypochlorite ion OCl -. The bactericidal effect of chlorine is maximum when chlorine is in the form of hypochlorous acid. The oxidizing action is best in the form of hypochlorite ion.
Some important terms Turbidity is the cloudiness or haziness of a fluid caused by individual particles (suspended solids) that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality. Units of turbidity are FTU (Formazin T urbidity Unit) and Nephelometric Turbidity Units (NTU). Fluids can contain suspended solid matter consisting of particles of many different sizes. While some suspended material will be large enough and heavy enough to settle rapidly to the bottom of the container if a liquid sample is left to stand (the settable solids), very small particles will settle only very slowly or not at all if the sample is regularly agitated or the particles are colloidal. These small solid particles cause the liquid to appear turbid.
Flocculation according to the IUPAC definition is "a process of contact and adhesion whereby the particles of dispersion form larger-size clusters." Flocculation is synonymous with agglomeration, aggregation, and coagulation / coalescence. It is a process wherein colloids come out of suspension in the form of floc or flakes by the addition of a clarifying agent. The action differs from precipitation in that, prior to flocculation, colloids are merely suspended in a liquid and not actually dissolved in a solution. In the flocculated system, there is no formation of a cake, since all the flocs are in the suspension.
Reactor Clarifier The next step in water purification is clarification. The process basically involves addition of chemicals to assist the removal of particles suspended in water. Particles can be inorganic such as clay and silt or
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organic such as algae, bacteria, viruses, protozoa and natural organic matter. Inorganic and organic particles contribute to the turbidity and color of water. The addition of inorganic coagulants such as aluminum sulfate (or alum) or iron (III) salts such as iron (III) chloride cause several simultaneous chemical and physical interactions on and among the particles. Within seconds, negative charges on the particles are neutralized by inorganic coagulants. Also within seconds, metal hydroxide precipitates of the a luminum and iron (III) ions begin to form. These precipitates combine into larger particles under natural processes such as Brownian motion and through induced mixing which is sometimes referred to as flocculation. The term most often used for the amorphous metal hydroxides is “floc.” Large, a morphous aluminum and iron (III) hydroxides adsorb and enmesh particles in suspension and facilitate the removal of particles by subsequent proce sses of sedimentation and filtration.
Actually the clarifier is a circular RCC structure. It consists of a ce ntral zone, which contains motor driven impeller and helps to mix the chemical. The Alum and Lime are added directly to this zone. It also contains the sludge scrapper at the bottom of the clarifier, which helps to collect the sludge to dispose from the centre of clarifier by gravity to the sludge pit. After mixing, it goes to the flocculation zon e. Where the colloidal particles gets neutralize with the alum and coagulate to form the larger particle. Then water after being entrapped in the sludge blanket comes out through outlet channel.
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T able 1- R aw W ater Analysis
1
calcium
26
2
Magnesium
14
3
Sodium
25
4
Potassium
0
5
T otal Cations
65
6
Bicarbonates
40
7
Carbonates
0
8
Nitrates
0
9
Chlorides
8
10
Sulphates
17
11
T otal Anions
65
12
Silica
11
13
Iron
1
14
pH(no unit)
7.6-8.2
15
T urbidity
700NT U (max.)
16
Organic Matter
2 Page | 15
T able 2- Cl arifi ed W ater Analysis
1
Calcium
51.2
2
Magnesium
14
3
Sodium
25
4
Potassium
0
5
T otal Cations
90.2
6
Bicarbonates
35.7
7
Carbonates
0
8
Nitrates
0
9
Chlorides
15
10
Sulphates
39.5
11
T otal Anions
90.2
12
Silica
11
13
Iron
0.3
14
pH(No value)
6.8-8.0
15
T urbidity
20 NT U (max.)
16
Organic Matter
0.05 Page | 16
F i g u r e 3 - Cl a r i f i e r a t N T P C, S i p a t
Filter water analysis It is same as that of clarified water except for the turbidity which should be around 2.0 NTU (Nephelometric turbidity units)
GSF and Sump The gravity sand filter use relatively coarse sand and other granular media to remove particles and impurities that have been trapped in a floc through the use of flocculation chemicals--typically salts
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of aluminum or iron. Water and flocs flows through the filter medium under gravity or under pumped pressure and the flocculated material are trapped in the sand matrix. Mixing, flocculation and sedimentation processes are typical treatment stages that precede filtration. Chemical additives, such as coagulants, are often used in conjunction with the filtration system. Rapid sand filtration has very little effect on taste and smell and dissolved impurities of drinking water, unless activated carbon is included in the filter medium.
Filtration Process The clear water from the clarifier enters into the inlet channel. From the inlet channel it overflow into the filter bed which is made up of six layers of sand/ gravels size ranging from 0 .68mm to 60mm.While going down the bed it get cleaned by entrapping the suspended particle in the voids in the bed and clear water having turbidity 2 NTU comes out into the clarified storage tank from where it goes to clarified water sump
Filter Backwashing The water used for backwashing is the filtered water supplied from the overhead tank over chemical 3 house. The capacity of the overhead tank is 300m minimum/ or 1.5 times of water required for complete backwash of one filter (both sections). The water rushes into the gravity filter from the bo ttom of the filter through the gravels and sand bed. It makes the bed loose and fluidized and removes the mud and silt accumulated in the gravity filter making it ready for the service.
Entering the sump Filtered water from the two section of the filtered water reservoir shall enter the sump through two numbers of isolation valves. Filtered water from the sump shall be pumped by Filtered water pumps to DM plant.
De-mineralization Plant Equipment and systems in DM Plant (3x660 MW) DM Stream Section Filter Water Pumps : 3 Nos. Activated carbon Filters with all necessary equipments: 2 Nos. Strong Acid Cation Exchange units with all necessary equipments: 2 Nos. Weak Base Anion exchange units with all necessary equipments: 2 Nos. Strong Base Anion exchange units with all necessary equipments: 2 Nos. Page | 18
Mixed Bed exchange units with all necessary equipments: 2 Nos. Degasser units : 2 Nos. Blowers for each degasser units : 2 Nos. DM water storage tanks: 2 Nos. (With capacity of 2476 m3 each)
DM plant pump house section DM make-up pumps: 4 Nos. Boiler fill pumps: 2 Nos. DM water regeneration pumps : 2 Nos.
DM Stream Regeneration section Acid storage tanks (common for Stage-I & Stage-II) : 4 Nos. Alkali storage tanks (common for Stage-I & Stage-II) : 2 Nos. Acid unloading pumps (common for Stage-I & Stage-II) : 2 Nos. Alkali unloading pumps (common for Stage-I & Stage-II) : 2 Nos. Alkali Preparation Tanks : 2 Nos. Alkali transfer pumps : 2 Nos. Alkali filter: 1 No. Alkali measuring tanks : 2 Nos. Hot water Tank: 1 No. Acid measuring tanks: 2 Nos. Safety Shower: 1 No.
Effluent treatment section (Neutralization Pit) Common for St-I, St-II & CPU St-I Neutralization pit: 2 Nos. Priming Tanks: 2 Nos. Lime Tank: 1No. Effluent transfer pump: 3 Nos
Activated Carbon Filter :( ACF) It is a filter with anthracite fills to remove chlorine, odor a nd organic substances by adsorption phenomenon from the water. There are two ACFs in Stage-I DM Plant.
Parameter at the outlet of ACF
Residual (Free) chlorine: Nil Organic matter: Below detectable limit Turbidity: <0.5 NTU
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Demineralization: Demineralization (also known as deionization) of water results in removal of all minerals in water. The process uses cation resin In H+ form for the removal of cations and anion resin in OH- form to remove anions. There are two basic types of demineralization . a. Two bed b. Mixed bed Also there are several extensions depending on the chemistry of raw water. Here in Stage-I combination is:
SAC-Degasser-WBA-SBA-MB Strong Acid Cation exchanger: (SAC) Resins provide sulphonic acid(SO3H) group which gives H+ ion for exchange with water.
Reactions:
Ca (HCO3)2 (l) + 2ZH(s) MgCl2 (l) + 2ZH (s)
CaZ2(s) + 2H2CO3 (l) Mg Z2 (s) + 2HCl (l) Page | 20
Na2SO4 (l) + 2ZH (s) H2CO3 (l)
2NaZ(s) + H2SO4 (l)
H2O (l) + CO2 (g)
Degasser Degasser system comprises of degasser tower, degassed water storage tank, degasser blowers and degassed water pumps. The purpose of degasser system is to reduce the load on strong Base anion exchange unit(SBA). In this system, water and air counter flow with each other through blowers. This removes the carbon dioxide
F i g u r e 4 - D e g a sse r sy st e m
Weak Base Anion exchanger: (WBA ) WBA are used in conjugation with SBA in demineralization system to reduce regen eration cost as they can be regenerated with small amount. They contain tertiary amine groups which exchange with mineral acids like HCl and H2SO4, but they cannot remove weakly ionized acids like H2CO3.
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Reactions:
H2SO4 (l) + ROH (s) HCl (l) + 2ROH (s)
R 2SO4 (s) + H2O (l) R 2SO4 (s) + 2 H2O (l)
Strong Base Anion Exchanger: (SBA) -
SBA are capable of exchanging anions like Cl , silica etc. They exchange through active quaternary ammonium exchange sites.
Reactions:
H2SO4 (l) + ROH (s)
R 2SO4 (s) + H2O (l)
HCl (l) + 2ROH (s)
R 2SO4 (s) + 2 H2O (l)
CO2 (l) + ROH (s)
RHCO3 (s)
SiO2 (l) + ROH (s)
RHSiO3 (s)
Mixed Bed Unit Mixed bed unit consist of SAC and SBA resins intimately mixed in the same unit to bring about demineralization. In effect it is multiple two bed dec entralizing pairs resulting in very high qualit y of DM water. The SAC resin is in hydrogen form and the SBA resin is in the hydroxide form. The reactions of the SAC & SBA resins in service are the same as for two- bed demineralization process.
DM Water Tank DM water tank is used for DM water storage. There are Two DM tanks (1& 2) for Stage-I, having interconnection with each other and also with tanks 3 & 4 of Stage-II.
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Coal Analysis Coal is a fossil fuel consisting of carbonized veg etable matter deposited in the Carboniferous period. It has been subjected to a series of complex natural transformation due to geological heat and pressure over millions of years. It can be considered as non-renewable resource of energy because it cannot be replenished on a human time scale. Coal has a highly heterogeneous organic matrix, which is invariably associated with mineral matter and moisture. So, to have an efficient industrial utilization of coal, in-depth understanding of its physical as well as chemical character is is required. For selecting a coal for power generation some essential analysis and tests are necessary, some of them are: Proximate Analysis Ultimate Analysis, CV, HGI different forms of moisture ash analysis Ash Fusion tests
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Proximate Analysis Amongst all these test and analyses, Proximate Analysis is perhaps the simplest and important as it throws light on the nature of coal as well as its industrial utilization aspects. The analysis is done on airdry sample of coal size 212μ and it involves determination of moisture, ash, volatile ma tter and fixed carbon percentages. Moisture-
1) Total moisture = Inherent Moisture + Free Moisture 2) Total Moisture = X + Y (1− X/100) X= Percentage loss in mass of original sample Y= Percentage loss of mass in air-dried sample
Ash-
Coal contains inorganic substances that are converted into ash on combustion of coal. Weigh 1 gm of sample of 212μ size in a silica dish, spread uniformly. Keep it in a muffle furnace at room temperature. Raise the temperature to 815 ± 100 C. Maintain the temperature for 1 hour. Take out cool and weigh.
[Wt. of (Dish + Ash) - Empty dish] x 100 Ash = Wt. of sample taken
Volatile matter-
It contains mainly carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), tar vapours etc. These are the pyrolysed product of coal. Heat an empty, clean V.M. crucible with lid at 900 ± 100 C for 7 min. remove and cool on a metal plate for 1 min and further cool it for 10 min in a desiccator, then take empty weight. Take 1 gm of coal in it. Keep on a silica stand in an electrically heated furnace maintained at 900 ± 100 C for 7 min. After 7 min. take out, cool for 1 min on a metal plate then in the desiccator for 10 min. and weigh.
Wt. of crucible with coal - Wt. after heating = a (say) Wt. of coal taken
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V. M. (%) = (a - Moisture) x 100 Fixed Carbon
Fixed Carbon (%) = 100 − (Ash % + VM % + Moisture %) Calorific Value Calorific value gives us the amount of heat evolved by the complete combustion of one gram of fuel. In the laboratory we determine the gross calorific value of coal by Bomb-Calorimeter. Gross calorific value is employed to find out: a) Thermal efficiency of a combustor b) Coal equivalent of any fuel c) Coal consumption per KWH d) Useful heat value of coal (UHV)
UHV = 8900 − 138 (CA + CM)
CA = Conditioned ash CM = Conditioned moisture
F igur e 5- Automatic B omb calor imeter
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Oil Analysis Fuel OilsIn India fuel oil fired boilers are not being used because of acute storage of oil and for being very expensive. Here oil is being used in boilers only at the time of starting or for stabilizing flame if the combustion of coal used is not proper Following characteristic of fuel oils are considered while selecting for boiler : Specific
gravity
Viscosity Calorific value Flash point Pour point Sulphur content Heavy metals Water content Acidity etc.
Lubricating Oil-
In power plant various lubricating oils are used to minimize the friction between two surfaces and also as a heat carrier. The friction is minimized by introduction of oil film between surfaces moving relative to each other. The following tests are to be carried out for monitoring of the oil Viscosity Viscosity Index Contamination by dirt and metallic particles Total acidity Oxidation Stability Demulsibility Anti-rust properties
Foaming Characteristics
Some of the tests are explained belowViscosity Index:
Relationship of viscosity with temperature is determined by viscosity index. Page | 26
V.I = (L-U/L-H) * 100 U = Kinematic viscosity at 37.8 0C of the oil whose viscosity index is to be calculated L = Kinematic viscosity at 37.8 0C of the oil having V.I. = 0 H = Kinematic viscosity at 37.8 0C of the oil having V.I. = 100 L, H, & U have same viscosity at 8.90C.
Contamination by dirt and metallic properties:
For this 100gm of the oil to be tested is diluted with 300 cm3 of reptane solvent and left for two hours. The mixture is filtered through a fine glass mesh, which is weighed before and after the filtration. The test carried out measures the total amount of insoluble organic or inorganic material in oil. The organic material is generally caused by degradation of the oil and the inorganic material comes from wearing or corrosion of the metal parts of the lubrication system Total Acidity
The total acidity of the oil is determined by extracting both organic and inorganic acid by alcohol and titrating with standard solution. It is expressed as mg of KOH consumed per gram of oil. Increase in total acidity indicates degrading of the oil by oxidation, contamination etc. during its long use. This oil can corrode the metal surface over which it is flowing.
Insulating OilIn power plant bulk quantity of insulating oils are used in transformers, circuit breakers, switchgears etc. These oils perform a dual function acting as a coolant and insulator. For monitoring the quality of transformer insulating oils the following tests should be performed periodically: Total acidity Oxidation stability Viscosity Flash point Moisture content Dielectric strength Breakdown voltage Mechanical impurities etc
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Important TermsFlash point- It is the temperature at which oil on heating ignites on the introduction of test flame. It indicates comparatively degree of safety of storage, transportation and its use. Pour Point - Pour point is the temperature at which a cloud or haze of wax crystals appear at the bottom of the test jar when the oil is cooled under prescribed condition. It gives a rough idea of the temperature above which the oil can be safely handled without any fear of congealing of filter clogging. Dielectric Strength- Maximum voltage at which oil can stand. Higher the value betters the oil.
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Pollution Control Installed generation capacity is day by day increasing. Projected rate of growth and level of power generation and increasing concern about the consequent environmental impact, have compelled the government to think a fresh and find ways to protect the environment. A number of new regulations have come in to force to check the degradation of environment and more will come in future. The major control measure adopted in recent times is installation of electrostatic precipitators (ESP) to reduce particulate concentration in the flue gas. Major air pollutants from fossil fuel fired power p lants include
particulate matter (SPM & RSPM)
SOx
NOx
CO.
Particulate Matter 3
Particulates are emitted in the stack at a rate of about 78g/M for the representative 210MW plant. The use of 99.9% efficient ESP reduces the particulate emission rate into the atmosphere to about 158 mg/ 3 3 M which nearly satisfies the mandate limit of 150 mg/ M . Techniques for controlling particulate emission, from a thermal power station, are utilizing control equipments, which remove the particulate emissions, released in to the atmosphere. The basic techniques of particulate collection equipments are: a. Mechanical collector b. Wet collector c. Fabric filter (bag house) d. ESP Sulphur Dioxides
The second most important air pollutant emitted by the coal fired power plant is SOx. The S content on an average in Indian coal is less compared to the coal found elsewhere in the world. Besides using fuels low in S content, the possible methods for reducing SOx emissions from coal/ fossil fuel combustion are: Use of tall stacks to increase atmosphere dispersion and dilution. Flue gas desulphurization/ flue gas treatment Desulphurization of fuel itself wealth.
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. Oxides of Nitrogen
Nitrogen oxides are formed from fuel nitrogen or from the molecular nitrogen of combustion air. Gas power stations are more prone to NOx formation because of high temperature. Several techniques are used to reduce NOx emissions from coal combustion. The primary techniques can be classified into one of two fundamentally different methods: combustion control and post combustion control. Combustion controls are the most widely used method s of controlling NOx formation in all types of boilers and include: Low excess air (LEA) Burners out of service (BOOS) Biased burning firing Over fire air (OFA) Low NOx burners
Post combustion control methods are: Selective non-catalytic reduction (SCNR) Selective catalytic reduction (SCR)
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All the minor & major sections in the chemistry department of power plant had been visited & also understood to the best of my knowledge. I believe that this training has made me well versed with the various processes going on in the chemistry section of the plant. I hope that the practical knowledge gained through this training would be beneficial to me in future
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