Muhammad Faisal Sultan
Chemical Engineer
Comsats Institute of Information and Technology Lahore
Thermal Power Station:
A thermal power station is a power plant in which the prime mover is steam driven. Water is heated, turns into steam and spins a steam turbine which either drives an electrical generator or does some other work, like ship propulsion. After it passes through the turbine, the steam is condensed in a condenser and recycled to where it was heated; this is known as a Rankine cycle. The greatest variation in the design of thermal power stations is due to the different fuel sources. Some prefer to use the term energy center because such facilities convert forms of heat energy into electrical energy.
Thermal power station Muzaffargarh:
Installed Capacity:
This Power Station is a vital and major thermal power generating installation connected with National grid system in Pakistan. This Power Station was constructed in different Phases having total capacity of 1370 MW. It consists of:
Ø Three Russian units of 210 MW each
Ø Two Chinese units of 200 MW each
Ø One Chinese unit of 320 MW
Fuel:
Dual fuel combustion provision (Gas & Furnace Oil) has been made for all the machines. Furnace oil is transported through Railway Wagons and tank Lorries.
Amid sand dunes of area known as Rakh Khanpur, at a distance of 6 km. from Muzaffargarh City, is located Thermal Power Complex. A few years back nobody perceived that such a desert would yield green trees, more than 1,500 families would be residing here and a Power Station will turn into a huge Power Complex. Now, with the day and night efforts of foreign as well as Pakistani engineers, technicians and workers, the complex has grown to the realities with three sky-high chimneys, being highest concrete structure in Pakistan and visible from the bridge of River Chenab, which is flowing to the east of the site at distance of 8 km. In September, 1987 contract of supply and erection of a 3x210 MW capacity Thermal Power Station was signed with M/s. TECHNOPROMEXPORT of ex-USSR, Moscow, and 1,134 acres of government land was acquired. Initially, about 230 acres land for the Power Station and 164 acres for residential colony was leveled and subsequently construction was started. Later on contracts with Chinese firm M/s. CMEC, were signed for three units in two stages - Two Units each of 210 MW and one unit of 320 MW. In this way a power complex emerged which is going to be the biggest of all Thermal Stations in Pakistan with the possibility of construction of two more units. Presently, the total generation capability of three phases is envisaged as 1,370 MW.
Phase - 1 (Units 1, 2 & 3):
This phase consists of three steam units each capable of generating 210 MW electricity. The supplier started delivery of equipment to site in January, 1989, and after pre-assembly of equipment at Site, erection started in July, 1990. Unit No. 1 was commissioned in September, 1993 and Unit No. 2 in March, 1994.
Main Building:
It contains the turbine hall having a span of 45 meters and de-aerator bay, 12 meters wide.The steam turbines which drive generators are of three stages condensing type arrangedtransversely to the axis of turbine hall. The operational platform is at elevation 12.6 meters and a maintenance bay at ground floor near Unit No. 1. The power plant is designed on the block principle: boiler-turbine-generator-unit transformer. The fuel gas exhaust section of two units is connected with a 200 meter high stack, outer section of which is a 195-meter high concrete shell.
Combined Auxiliary Building:
The building is connected with the main building and it houses water treatment plant to produce 100 t/h demineralized water for the replenishment of station losses, hydrogen plant to provide hydrogen for cooling of generators rotors, maintenance shops, laboratories and central control room.
Fuel & Oil Facilities:
Fuel oil facilities are constructed for decanting, oil storage, preparation and supply of fuel to boiler nozzles. It also includes HSD storage as well as oil facilities for reception, storage, purification and centralized delivery of turbine oil and insulating oil to power plant.
Hydraulic Structures:
The cooling water used in condensers is re-circulated in closed cycle with inducted draft cooling towers. The water is being cooled for each unit in two cooling towers each consisting of eight fans. Two cooling towers carry 27,500 Cu m/h circulating water for condensers of one unit.
Startup Boiler:
One startup boiler using diesel oil as fuel with steam output of 50 t/h is provided to meet steam requirement for initial start of unit as well as a backup of power plant auxiliaries. A separate stack of 30-meter high has been constructed for it.
Electrical Part:
The electricity generated at 15.75 KV is brought out from Unit transformer at 220 KV and fed to the National Grid via a switchyard. Power Plant auxiliaries are fed at 6.6 KV.
Phase-II (Units 5 & 6):
It consists of two units of 210 MW each having equipment similar to Phase-I. Turbines are placed longitudinally in main building. Outdoor boilers exhaust of two units is connected to one stack
Overview:
There are many different types of power plants including thermal power plants and Hydel power plants. Thermal power plants use fuel such as Gas, HSD, Furnace Oil or nuclear fuel to produce heat energy that is converted to electrical energy through a series of intermediate processes. Hydel power plants convert the potential energy of water to electrical power as it flows from higher to lower elevations. The "traditional" thermal power plant is the Rankine cycle plant, named after the man who invented the cycle. A power plant cycle is a series of processes in which a fluid, generally water/steam, is used to convert heat energy to mechanical energy. The Rankine cycle in its simplest form consists of a boiler, a turbine, a condenser, and a boiler feed pump. Early plants had thermal efficiencies of approximately 25% to 30%. Only 25% to 30% of the heat energy in the fuel burned in these plants was converted to electrical energy. The rest was lost in various ways. The Rankine cycle has been refined considerably over the years and made more efficient by the addition of components like Economizer, Feed water heaters, Super heaters and Re-heaters. The efficiency of the Rankine cycle has also been improved by increasing the pressure and temperature of the cycle. The laws of thermodynamics and considerations such as material limitations have prevented any significant improvement since then. Power plants commonly use heat rate to measure efficiency.
Generator
Electrical Energy
Mechanical Energy
Turbine
Heat Energy
Boiler
Fuel Energy
Boiler:
The boiler is the main part of any thermal power plant. It converts the fuel energy in to steam energy. The fuel may be furnace oil, diesel oil, natural gas or coal. The boilers may be fired from the multiple fuels.
The type of boiler used in the TPS is “water tube type”.
Water Tube Boilers:
In water tube boilers, boiler water passes through the tubes while the exhaust gases remain in the shell side, passing over the tube surfaces. Since tubes can typically withstand higher internal pressure than the large chamber shell in a fire tube, water tube boilers are used where high steam pressures (as high as 3,000 psi) are required. Water tube boilers are also capable of high efficiencies and can generate saturated or superheated steam. The ability of water tube boilers to generate superheated steam makes these boilers particularly attractive in applications that require dry, high-pressure, high-energy steam, including steam turbine power generation.
Parameter of Boiler
Rated evaporating amount 680 t/h
Reheat steam amount 57508 t/h
Main steam pressure 140 kg/cm2g
Temperature 541 C°
Outlet pressure of Reheat System 23.8 kg/cm2g
Outlet Temperature of Reheat System 541 C°
Inlet pressure of Reheat System 25.8 kg/cm2g
Inlet Temperature of Reheat System 310 C°
Feed water temperature 251 C°
Boiler Efficiency (burn oil) 90.26%
Boiler Efficiency (burn gas) 85%
Exit gas temperature (burn oil) 153 C°
Exit gas temperature (burn gas) 136 C°
Consumption of crude oil 48.2 t/h
Consumption of natural gas 59650 Nm2/h
Main Parts of Unit:
The unit consist of the following main parts:
Ø Forced Draft Fan (FDF)
Ø Air Preheater (RAH)
Ø Burners
Ø Furnace
Ø Up Rise Tubes
Ø Down Comer Tubes
Ø Water Tubes
Ø Super Heaters
Ø Gas Recirculation Fan (GRCF)
Ø Re-Heater
Ø Induced Draft Fan (IDF)
Ø Chimney
Ø Boiler Drum
Ø Economizer
Forced Draft Fan (FDF):
The forced draft fan (FDF) sucks the air from the atmosphere which is used in the furnace for burning. The air from the atmosphere is passed through the filter to remove the dust and other particles from the air. The air from the FDF is then feeded to the regenerative air heaters.
Forced Draft (FD) fans purpose is to provide a positive pressure to a system. This basic concept is used in a wide variety of industries but the term FD Fans is most often found in the boiler industry. Fans for boilers force ambient air into the boiler, typically through a preheater to increase overall boiler efficiency. Inlet or outlet dampers are used to control and maintain the system pressure.
Induced Draft Fan:
ID fan sucks the flue gases from boiler and exhaust through chimney. Induced Draft (ID) fans are used to create a vacuum or negative air pressure in a system or stack. In an induced draft system, the fan is at the exit end of the path of flow, and the system is under negative pressure that is, the pressure in the flow area is below atmospheric, because the flue gas is being drawn through the fan.
Flue Gas Recirculation Fan (FGRF):
Flue gas recirculation (FGR) is a highly effective technique used for lowering Nitrogen Oxide (NOx) emissions from burners. This is particularly crucial, as NOx is a significant pervasive pollutant that produces a negative array of health and environmental by-products. NOx emission levels can be greatly reduced in industrial boilers by recirculating used flue gases back into the system. This process lowers the peak combustion temperature and drops the percentage of oxygen in the combustion air/flue gas mixture, delaying the formation of NOx caused by high flame temperatures.
Flue gas recirculation, or FGR, is the most effective method of reducing NOx emission from industrial boilers with inputs below 100 MMBtu/hr. FGR entails recirculating a portion of relatively cool exhaust gases back into the combustion process in order to lower the flame temperature and reduce NOx formation. It is currently the most effective and popular low NOx technology for fire tube and water tube boilers. Flue gas recirculation technology can be classified into two types; external or induced:
External flue gas recirculation utilizes an external fan to recirculate the flue gases back into the flame. External piping routes the exhaust gases from the stack to the burner. A valve controls the recirculation rate, based on boiler input.
Induced flue gas recirculation utilizes the combustion air fan to recirculate the flue gases back into the flame. A portion of the flue gases are routed by duct work or internally to the combustion air fan, where they are premixed with the combustion air and introduced into the flame through the burner.
Condensers:
Condensers make use of a condensing medium, such as air or water that absorbs heat from a vapor. As the vapor loses its heat to the condensing medium, its temperature falls to the saturation point, and it condenses to a liquid.
Cooling Towers:
A cooling tower is a heat rejection device, which extracts waste heat to the atmosphere though the cooling of a water stream to a lower temperature. The type of heat rejection in a cooling tower is termed "evaporative" in that it allows a small portion of the water being cooled to evaporate into a moving air stream to provide significant cooling to the rest of that water stream. The heat from the water stream transferred to the air stream raises the air's temperature and its relative humidity to 100%, and this air is discharged to the atmosphere. Evaporative heat rejection devices such as cooling towers are commonly used to provide significantly lower water temperatures than achievable with "air cooled" or "dry" heat rejection devices, like the radiator in a car.
Common applications for cooling towers are providing cooled water for air-conditioning, manufacturing and electric power generation. The smallest cooling towers are designed to handle water streams of only a few gallons of water per minute supplied in small pipes like those might see in a residence, while the largest cool hundreds of thousands of gallons per minute supplied in pipes as much as 15 feet (about 5 meters) in diameter on a large power plant.
Cooling Water Pump:
Cooling water pump is used to pump the hot water coming from the condenser to the top of the cooling tower where is it sprinkled downward. The used for this purpose is centrifugal pump. And it has following specifications.
CW Pump Specifications:
Type is single stage double suction centrifugal pump
Capacity 16000m3/H
Speed 370 rmp
Power 1600 Kw
Head 25m
Air Preheater:
An air preheater or air heater is a general term to describe any device designed to heat air before another process (for example, combustion in a boiler) with the primary objective of increasing the thermal efficiency of the process. They may be used alone or to replace a recuperative heat system or to replace a steam coil. The purpose of the air preheater is to recover the heat from the boiler flue gas which increases the thermal efficiency of the boiler by reducing the useful heat lost in the flue gas. As a consequence, the flue gases are also sent to the flue gas stack (or chimney) at a lower temperature, allowing simplified design of the ducting and the flue gas stack. It also allows control over the temperature of gases leaving the stack.
Chimney:
Chimneys are built using either precast or cast-in-place concrete blocks. The blocks typically contain vertical and horizontal steel reinforcements. These steel reinforcements protect the concrete from heat damage, such as cracking, that the hot gases can cause. Chimneys contain one or more flues, as the three flue chimney in the schematic below to the left shows, through which the stack gas travels. Each flue is insulated and lined to protect the concrete stack.
Linings can be made of brick, steel and occasionally glass-reinforced plastic. The lining must be resistant to abrasions and chemicals, primarily sulfuric and hydrochloric acid that can condense.
The air gap between the lining and the stack, or windshield, typically serves as the insulation for single flue chimneys. Multi-flue chimneys commonly use mineral wool, insulating brickwork, foam glass, or glass fiber as insulation. The insulation helps protect the stack from heat damage.
Chimneys are topped with a capping unit that caps the lining and the windshield. The capping unit is made of durable cement containing high amounts of alumina because it is located at the point where the flue gases are most likely to condense to form corrosive acids. Most chimneys include many pollution control systems, including electrostatic precipitators, mist eliminators, and wet scrubbers. These reduce the amounts and types of by-products that are vented into the atmosphere.
Economizers:
Flue gases from large boilers are typically 450 - 650°F. Stack Economizers recover some of this heat for pre-heating water. The water is most often used for boiler make-up water or some other need that coincides with boiler operation. Stack Economizers should be considered as an efficiency measure when large amounts of make-up water are used (i.e. not all condensate is returned to the boiler or large amounts of live steam are used in the process so there is no condensate to return) or there is a simultaneous need for large quantities of hot water for some other use. The savings potential is based on the existing stack temperature, the volume of make-up water needed, and the hours of operation. Economizers are available in a wide range of sizes, from small coil-like units to very large waste heat recovery boilers. The savings potential is a function of how much heat can be recovered, which is a function of how much cold water needs to be heated. A generally accepted "rule of thumb" is that about 5% of boiler input capacity can be recovered with a properly sized economizer. A higher percentage can be recovered with a Flue Gas Condenser, assuming there is enough cold water to condense all of the flue gas that is available. Therefore, for 'ball parking' purposes, start by comparing boiler input capacity with the need to heat water. An economizer that recovers 5% of boiler input should easily have a 2 year payback in a year-round application.
Boiler Protection:
ü Fuel protection
ü Gas pressure protection
ü Diesel oil protection
ü Furnace oil protection
ü FD fan trip
ü ID fan trip
ü Regenerative air pre heater trip
ü Drum level high
ü Drum low level
ü Reheat steam pressure drop
ü Furnace pressure low
ü Furnace flame out
ü Natural gas pressure high
Steam Cycle
Steam Turbine:
Turbine is used to convert the heat energy into mechanical energy. Turbine used in T.P.S Muzaffargarh is impulse-reaction steam turbine.
The load requirement is controlled by the steam flow through a governing valve. Maximum steam flow at full load is 670 tons/hour. When the load at the generator is suddenly decreased then the rpm (frequency) of the generator is increased and to decrease the frequency we lower down the steam flow which decreases the speed and maintains the frequency. If load is suddenly increased rotor speed becomes slower, to increase the speed, steam flow is increased.
Steam turbine has three parts.
1. High Pressure Turbine
2. Intermediate Pressure Turbine
3. Low Pressure Turbine.
1. HP (High Pressure) Turbine:
First of all steam from boiler comes into the HP turbine. Steam in the HP turbine is called live steam or main steam. Rotor blades diameter of this part of turbine is smallest of the other parts of the turbine.
Inlet steam temperature of the HP turbine is 540 Co and pressure is 130 kg/cm2.
Outlet steam temperature of the HP turbine is 290 Co and pressure is 16 kg/cm2.
2. IP (Intermediate Pressure) Turbine:
Steam comes into the IP turbine from HP turbine via reheaters. The steam pressure in this section of the turbine is 14 kg/cm2 and temperature is 540 Co.
3. LP (Low Pressure) Turbine:
The outgoing steam of the IP turbine entered into the LP turbine. Steam from the LP turbine goes into the condenser.
Specification of the steam turbine:
Maximum Load 210 MW
Live Steam Pressure 132 kg/cm2
Live Steam temperature 538 Co
Rated Speed 3000 rpm
HP Cycle Exhaust Steam temperature 300 Co
HP Cycle Exhaust Steam Pressure 20 kg/cm2
Reheat Steam Temperature 538 Co
Reheat Steam Pressure 14 kg/cm2
Turbine Protection:
ü Lube oil pressure (low and high)
ü Vacuum drop
ü Live steam temperature drop
ü Axial shift displacement
ü Gas cooling pump tripping
ü HP heater level high
ü All FW pump trip high vibration tipping
ü Trip unit by switch/emergency
Furnace Safeguard Supervisory System (FSSS)
The FSSS station consists of the following parts:
Ø Decanting area
Ø Fuel oil tanks
Ø First Lift pump
Ø Main Heaters
Ø Second Lift pump
Ø Diesel pumps
Ø Recirculation pumps
Ø Recirculation heaters
Ø Filters
Ø Control Room
Decant Area:
The furnace oil that is used as a fuel in the burners of the boiler furnace to produce the steam is transported to the TPS through two ways;
Ø Oil Tankers
Ø Train
For unloading of the fuel from oil tankers and train there is separate unloading or decanting station for each. The unloaded fuel oil is initially stored in the underground reservoir; from there it is filled in the main storage tanks.
2 pumps are used to fill the main storage tanks from the oil tankers decanting area. One of them is active (on load) and other is standby.
Fuel Oil Tanks:
From the decanting area the furnace oil is filled in the storage tanks. From there it is supplied to the burners of the boiler furnace after proper heating. Usually one storage tank is called service tank, from there furnace oil is supplied to the units. The furnace oil is filled in the other tanks first and then filled in the service tanks through recirculation pumps (RCP). The oil in the tanks is kept heated at the temperature 75 Co to 80 Co.
There are total 6 storage tanks for furnace oil each having a volume of 20,000 m3 hence each can store 2, 00, 00,000 liters. There are 2 diesel oil storage tanks each having capacity of 1000 ton.
First Lift Pump:
First lift pump takes the furnace oil from the service tank and supplied to the main heaters. There are total 04 first lift pumps which are operated according to the unit load conditions.
Main Heaters:
There are 04 main heaters each is connected to the respective first lift pump. The main heaters heat the furnace oil through the steam which comes from the boiler. Steam is use to heat the oil in the recirculation heaters.
The seam flows through the pipes which heats the oil outside the tube. The temperature and pressure of the steam in the main heaters is
Temp 270 Co
Pressure 11 – 13 kg/cm2
Second Lift Pump:
Second lift pumps take the furnace oil from the main heaters and supplied to boilers of the units. There are total 04 second lift pumps which are operated according to the unit load conditions. The temperature of the oil that is supplied to the boiler is 105 Co to 120Co.
Fuel Oil cycle:
The Generator
The generator is a device which converts the mechanical energy into electrical energy.
Cooling System of Turbo Generator:
The first question arises here is that why we need cooling of the generator? As the current flow in the stator and rotor of the generator is very high so it increases the temperature of the stator and rotor winding. As a result the resistance of the stator and rotor windings increases which increase the power losses and may cause the insulation break down.
Two types of cooling is used in the turbo generator of TPS.
1. Stator cooling
2. Rotor cooling
The stator of the turbo generator is cooled by the distillated or demineralized (demi) water. For this purpose a special plant is installed which prepares the demi water for the stator cooling. This demi water is also used for the cooling system of the thyrister converters. The water is passed though the hollow conductors of the stator winding for its cooling. The demi water is necessary for the cooling of the stator winding because raw water is not a pure insulator which may cause the flow of leakage current when passed through stator winding. The demineralized water plant removes the impurities and minerals of the raw water and make it good insulator whose Resistivity is taken at a minimum level of 200 kΩ.cm. The demi water that passes through the stator winding absorbs the heat of the stator winding making it cool and becomes hot itself. The demi water then passes through heat exchangers (coolers) where its temperature is decreased by the circulating water coming from the cooling towers. This demi water is also passed through the mechanical and magnetic filters before passing through stator winding and thyrister converters.
Water parameters in Heat Exchangers:
Rated temp.of cold water at inlet 32 Co
Min: temp of cold water 15 Co
No. of gas heat exchangers 02
Rated water flow in on heat exchangers 150 m3/h
Rotor Cooling:
The rotor cooling is done by the Hydrogen gas. Hydrogen gas is used for the following purposes:
1. Its heat exchange capability is much better than other gases
2. It is very lighter than other gases so do not overload the rotor.
3. Its preparation is very easy and cheap.
Hydrogen gas is filled in the generator and maintained at a pressure of 4kg/cm2
It takes all the heat of the rotor and cools the rotor winding and gets warmed itself. For the cooling of the gas there are four gas coolers inside the generator on each corner. Circulating water of the cooling tower is used in the gas cooler for the hydrogen cooling. Hydrogen gas is explosive if it is combined with oxygen under pressure so to avoid any leakage of gas and entrance of air inside the generator the rotor assembly is sealed by the seal oil whose pressure is at least 0.7kg/cm2 more than hydrogen gas inside the generator.
When the generator is turned off for a long time for maintenance purpose hydrogen is released from the generator in the air using special method. Method involves that firstly fill the generator with CO2 which release the hydrogen in the air and then in the end air is filled in the generator and CO2 is released in the air. This method is adopted because if hydrogen is released using air instead of CO2 then it can cause explosion due to oxygen in the air which will meet hydrogen under pressure in the generator.
After maintenance hydrogen gas is refilled in the generator using the reverse process as described above.
Water parameters in gas cooler:
Rated temp.of cold water at inlet 32 Co
Min: temp. Of cold water 15 Co
Max: water pressure 3 kg/cm2
No. of gas coolers 04
Rated water flow in gas cooler 76.5 m3/h
Chemical section
The chemical section consists of the following sections;
ü Hydrogen plant
ü Demineralization plant
ü Oil testing lab
ü Water testing lab
Hydrogen Plant:
Hydrogen plant prepares the hydrogen gas which is used for the cooling of the rotor of the turbo generator. The hydrogen gas is used for the cooling of the rotor of the turbo generator because it has better heat transfer characteristics, cheap and easy preparation and also it is very light and hence do not over load the rotor. The hydrogen is prepared by electrolysis of the water. For this DC supply is given to the electrolyzer. This Dc supply is produced after step down of the 6.6 kV supply to 400 V and then by 3-pahe rectifier. Raw water is used for the preparation of the hydrogen as it supports fast electrolysis action then de-mineralized water. Potassium Hydro oxide (KOH) is used as a catalyst. The oxygen and hydrogen are prepared in the ratio of 1:2.
A generalized layout of the hydrogen plant is shown in the figure below;
Electrolyzer
Alkaline Solution
Air compressor
Separating Columns
Rotor
Generator
Gas Scrubber
Purifier
Storage Tank
Dryer
DC Power Supply (330A)
v
v
v
v
v
v
Generation of Hydrogen Gas
Electrolyzer:
The process of electrolysis of the water takes place in the electrolysis. The process in which DC current is passed through the water resulting the separation of the cation and anion is known as electrolysis. The electrolyzer has 25 cells each takes 2.2 V, a total of 55 V DC and a maximum current of 1000 A. The separated hydrogen and oxygen then leaves the electrolyzer on its own ways.
Separating Column:
The hydrogen leaving the perforated flash box (PFB) enters the separating column which removes the small parts of alkali from it.
Gas Scrubber:
Gas scrubber is also called gas washer. It removes the impurities from the hydrogen such as dust particles etc.
Dryer:
The dryer dry the hydrogen coming out from the gas scrubber. As gas scrubber do the washing of the hydrogen gas so it has to be dried.
Receiver Tanks:
The receiver tanks store the prepared hydrogen gas. For this purpose 6 receiver tanks are used. The pressure inside the tanks is kept 10kg/cm2. 3 tanks are for oxygen and 3 are for Hydrogen storage.
Demineralization plant:
“The water which is free of all the impurities, minerals, gases like Oxygen Nitrogen and consists of only pure water (H2O) is called demineralized water”.
Demineralized plant is used for the preparation of demineralized water. Demineralized water is used for the preparation of steam, for the cooling of stator of generator and for the cooling of thyristors in the excitation system.
The plant has total generation capacity of 90 tons/hour. Raw water is used for the preparation of the demi water. Raw water is pumped out by the tube wells and stored in the raw water storage tanks.
Demi water is passed through the hollow conductors of stator winding for the stator cooling. It is used for this purpose because demi water acts as an insulator & has a resistivity of 200kOhms.it does not short circuit the windings. Demi water is used for the steam preparation in the boiler for the following reasons:
Raw water contains mineral like Calcium, Magnesium and sulphur. These minerals cause the stacks and corrosion in the boiler tubes which causes the heat loses and may damage the boiler tubes. The designed loss of the demi water in the steam cycle is 2%. Make up demi water is done in the hot well and feed water tank. A generalized layout of the demi water plant is shown in the figure below;
Preparation of Demineralized Water
Mechanical Filter
Raw Water
Cation Filter
Decarbonizer
Cation 2nd Filter
Anion Filter
Storage Tank
Mixed Bed
v
v
v
v
v
Mech. Clarifier filters:
In mechanical clarifier filter coal and gravels are is used to remove the unresolved particles from the water.
Cation filter:
In the cation filter resins is used which replaces the Na+ & Ca2+ ions in the water from the H+ ions. In the end water becomes acidic.
Decarbonizer exhaust:
It removes the carbonates from the water.CO2 is removed by showering of the water against air. It is also known as degasifier.
Anion filter:
In Anion filter castic soda (NaOH) is used which replaces the Cl- or SO4 ions with the OH- ions forming partial demi water.
Cation 2nd Filter:
It also removes the positive ions from the water.
Mixed filter:
In the mixed filter both the remaining anions and cations are removed. The water leaving the mixed bed is the pure distilled water.
Storage tanks:
This prepared demineralized water is then stored in the storage tanks.
Water treatment:
Ammonium hydroxide, Hydrazine and Trisodium phosphate are dozed at different points in the boiler such as boiler drum, for water treatment. The nature of this water is acidic, to minimize the acidity of this water ammonium hydroxide (NH4OH) is used. Hydrazine (N2H4) removes the Oxygen from water and protects the boiler tubes against corrosion. Trisodium phosphate (Na3PO4) is used in the boiler drum which removes the Ca, Mg and adds Na.
Oil Testing Lab:
Different tests of the furnace oil and the lubrication oil are performed in the oil testing laboratory to check their characteristics. The test on the transformer oil is also performed in this lab.
The following tests are performed on the furnace and lube oil:
ü Moisture test
ü Flash point test.
ü Viscosity test.
ü Specific gravity test.
ü Acidity test.
ü Chlorification test.
1. Moisture test:
Water 0.05% or more is determined by this method. High moisture decreases the calorific value of the oil. Water vapors evaporate easily with toluene on heating. Water droplets sink in the bottom of graduated tube on condensation early then toluene due to lower density.
Apparatus:
Dean and Stark Apparatus, Spirit lamp and Measuring Cylinder. OR Karl Fisher Moisture Test Apparatus.
2. Flash Point:
It is the temperature at which a fuel under given set of conditions has given off sufficient vapors to form an explosive mixture with air.
Apparatus:
Pesky marten’s apparatus, thermometer, spirit lamp, safety match.
3. Chlorification test:
The amount of heat liberated by the complete combustion of unit quantity of fuel is called calorific value. It is expressed in Cal/gm or Kilo. Cal/kg.
Apparatus:
Modern Bomb Calorimeter, water quantity and temperature moderator
4. Acidity:
In this test, we check the acidity of the oil. High acidity can be dangerous and causes corrosion in the equipment. Little acidity is tolerated.
Chemicals:
0.05 N KOH, distilled water, alkaline blue indicator, oil sample.
Apparatus:
Measuring flask, conical funnel, pipette, spirit lamp
Procedure:
Take 50 ml distilled spirit in a conical funnel. Neutralize it with 0.05N KOH and use alkaline blue indicator. After Boiling, take 10gm sample in separate flask and add it in the neutralized spirit. After cooling, add blue indicator and titrate it against 0.05 KOH. Note the wt. of KOH Used. Then calculate the acidity by the formula,
Muhammad Faisal Sultan
Chemical Engineer
Comsats Institute of Information and Technology Lahore
Thermal Power Station:
A thermal power station is a power plant in which the prime mover is steam driven. Water is heated, turns into steam and spins a steam turbine which either drives an electrical generator or does some other work, like ship propulsion. After it passes through the turbine, the steam is condensed in a condenser and recycled to where it was heated; this is known as a Rankine cycle. The greatest variation in the design of thermal power stations is due to the different fuel sources. Some prefer to use the term energy center because such facilities convert forms of heat energy into electrical energy.
Thermal power station Muzaffargarh:
Installed Capacity:
This Power Station is a vital and major thermal power generating installation connected with National grid system in Pakistan. This Power Station was constructed in different Phases having total capacity of 1370 MW. It consists of:
Ø Three Russian units of 210 MW each
Ø Two Chinese units of 200 MW each
Ø One Chinese unit of 320 MW
Fuel:
Dual fuel combustion provision (Gas & Furnace Oil) has been made for all the machines. Furnace oil is transported through Railway Wagons and tank Lorries.
Amid sand dunes of area known as Rakh Khanpur, at a distance of 6 km. from Muzaffargarh City, is located Thermal Power Complex. A few years back nobody perceived that such a desert would yield green trees, more than 1,500 families would be residing here and a Power Station will turn into a huge Power Complex. Now, with the day and night efforts of foreign as well as Pakistani engineers, technicians and workers, the complex has grown to the realities with three sky-high chimneys, being highest concrete structure in Pakistan and visible from the bridge of River Chenab, which is flowing to the east of the site at distance of 8 km. In September, 1987 contract of supply and erection of a 3x210 MW capacity Thermal Power Station was signed with M/s. TECHNOPROMEXPORT of ex-USSR, Moscow, and 1,134 acres of government land was acquired. Initially, about 230 acres land for the Power Station and 164 acres for residential colony was leveled and subsequently construction was started. Later on contracts with Chinese firm M/s. CMEC, were signed for three units in two stages - Two Units each of 210 MW and one unit of 320 MW. In this way a power complex emerged which is going to be the biggest of all Thermal Stations in Pakistan with the possibility of construction of two more units. Presently, the total generation capability of three phases is envisaged as 1,370 MW.
Phase - 1 (Units 1, 2 & 3):
This phase consists of three steam units each capable of generating 210 MW electricity. The supplier started delivery of equipment to site in January, 1989, and after pre-assembly of equipment at Site, erection started in July, 1990. Unit No. 1 was commissioned in September, 1993 and Unit No. 2 in March, 1994.
Main Building:
It contains the turbine hall having a span of 45 meters and de-aerator bay, 12 meters wide.The steam turbines which drive generators are of three stages condensing type arrangedtransversely to the axis of turbine hall. The operational platform is at elevation 12.6 meters and a maintenance bay at ground floor near Unit No. 1. The power plant is designed on the block principle: boiler-turbine-generator-unit transformer. The fuel gas exhaust section of two units is connected with a 200 meter high stack, outer section of which is a 195-meter high concrete shell.
Combined Auxiliary Building:
The building is connected with the main building and it houses water treatment plant to produce 100 t/h demineralized water for the replenishment of station losses, hydrogen plant to provide hydrogen for cooling of generators rotors, maintenance shops, laboratories and central control room.
Fuel & Oil Facilities:
Fuel oil facilities are constructed for decanting, oil storage, preparation and supply of fuel to boiler nozzles. It also includes HSD storage as well as oil facilities for reception, storage, purification and centralized delivery of turbine oil and insulating oil to power plant.
Hydraulic Structures:
The cooling water used in condensers is re-circulated in closed cycle with inducted draft cooling towers. The water is being cooled for each unit in two cooling towers each consisting of eight fans. Two cooling towers carry 27,500 Cu m/h circulating water for condensers of one unit.
Startup Boiler:
One startup boiler using diesel oil as fuel with steam output of 50 t/h is provided to meet steam requirement for initial start of unit as well as a backup of power plant auxiliaries. A separate stack of 30-meter high has been constructed for it.
Electrical Part:
The electricity generated at 15.75 KV is brought out from Unit transformer at 220 KV and fed to the National Grid via a switchyard. Power Plant auxiliaries are fed at 6.6 KV.
Phase-II (Units 5 & 6):
It consists of two units of 210 MW each having equipment similar to Phase-I. Turbines are placed longitudinally in main building. Outdoor boilers exhaust of two units is connected to one stack
Overview:
There are many different types of power plants including thermal power plants and Hydel power plants. Thermal power plants use fuel such as Gas, HSD, Furnace Oil or nuclear fuel to produce heat energy that is converted to electrical energy through a series of intermediate processes. Hydel power plants convert the potential energy of water to electrical power as it flows from higher to lower elevations. The "traditional" thermal power plant is the Rankine cycle plant, named after the man who invented the cycle. A power plant cycle is a series of processes in which a fluid, generally water/steam, is used to convert heat energy to mechanical energy. The Rankine cycle in its simplest form consists of a boiler, a turbine, a condenser, and a boiler feed pump. Early plants had thermal efficiencies of approximately 25% to 30%. Only 25% to 30% of the heat energy in the fuel burned in these plants was converted to electrical energy. The rest was lost in various ways. The Rankine cycle has been refined considerably over the years and made more efficient by the addition of components like Economizer, Feed water heaters, Super heaters and Re-heaters. The efficiency of the Rankine cycle has also been improved by increasing the pressure and temperature of the cycle. The laws of thermodynamics and considerations such as material limitations have prevented any significant improvement since then. Power plants commonly use heat rate to measure efficiency.
Generator
Electrical Energy
Mechanical Energy
Turbine
Heat Energy
Boiler
Fuel Energy
Boiler:
The boiler is the main part of any thermal power plant. It converts the fuel energy in to steam energy. The fuel may be furnace oil, diesel oil, natural gas or coal. The boilers may be fired from the multiple fuels.
The type of boiler used in the TPS is “water tube type”.
Water Tube Boilers:
In water tube boilers, boiler water passes through the tubes while the exhaust gases remain in the shell side, passing over the tube surfaces. Since tubes can typically withstand higher internal pressure than the large chamber shell in a fire tube, water tube boilers are used where high steam pressures (as high as 3,000 psi) are required. Water tube boilers are also capable of high efficiencies and can generate saturated or superheated steam. The ability of water tube boilers to generate superheated steam makes these boilers particularly attractive in applications that require dry, high-pressure, high-energy steam, including steam turbine power generation.
Parameter of Boiler
Rated evaporating amount 680 t/h
Reheat steam amount 57508 t/h
Main steam pressure 140 kg/cm2g
Temperature 541 C°
Outlet pressure of Reheat System 23.8 kg/cm2g
Outlet Temperature of Reheat System 541 C°
Inlet pressure of Reheat System 25.8 kg/cm2g
Inlet Temperature of Reheat System 310 C°
Feed water temperature 251 C°
Boiler Efficiency (burn oil) 90.26%
Boiler Efficiency (burn gas) 85%
Exit gas temperature (burn oil) 153 C°
Exit gas temperature (burn gas) 136 C°
Consumption of crude oil 48.2 t/h
Consumption of natural gas 59650 Nm2/h
Main Parts of Unit:
The unit consist of the following main parts:
Ø Forced Draft Fan (FDF)
Ø Air Preheater (RAH)
Ø Burners
Ø Furnace
Ø Up Rise Tubes
Ø Down Comer Tubes
Ø Water Tubes
Ø Super Heaters
Ø Gas Recirculation Fan (GRCF)
Ø Re-Heater
Ø Induced Draft Fan (IDF)
Ø Chimney
Ø Boiler Drum
Ø Economizer
Forced Draft Fan (FDF):
The forced draft fan (FDF) sucks the air from the atmosphere which is used in the furnace for burning. The air from the atmosphere is passed through the filter to remove the dust and other particles from the air. The air from the FDF is then feeded to the regenerative air heaters.
Forced Draft (FD) fans purpose is to provide a positive pressure to a system. This basic concept is used in a wide variety of industries but the term FD Fans is most often found in the boiler industry. Fans for boilers force ambient air into the boiler, typically through a preheater to increase overall boiler efficiency. Inlet or outlet dampers are used to control and maintain the system pressure.
Induced Draft Fan:
ID fan sucks the flue gases from boiler and exhaust through chimney. Induced Draft (ID) fans are used to create a vacuum or negative air pressure in a system or stack. In an induced draft system, the fan is at the exit end of the path of flow, and the system is under negative pressure that is, the pressure in the flow area is below atmospheric, because the flue gas is being drawn through the fan.
Flue Gas Recirculation Fan (FGRF):
Flue gas recirculation (FGR) is a highly effective technique used for lowering Nitrogen Oxide (NOx) emissions from burners. This is particularly crucial, as NOx is a significant pervasive pollutant that produces a negative array of health and environmental by-products. NOx emission levels can be greatly reduced in industrial boilers by recirculating used flue gases back into the system. This process lowers the peak combustion temperature and drops the percentage of oxygen in the combustion air/flue gas mixture, delaying the formation of NOx caused by high flame temperatures.
Flue gas recirculation, or FGR, is the most effective method of reducing NOx emission from industrial boilers with inputs below 100 MMBtu/hr. FGR entails recirculating a portion of relatively cool exhaust gases back into the combustion process in order to lower the flame temperature and reduce NOx formation. It is currently the most effective and popular low NOx technology for fire tube and water tube boilers. Flue gas recirculation technology can be classified into two types; external or induced:
External flue gas recirculation utilizes an external fan to recirculate the flue gases back into the flame. External piping routes the exhaust gases from the stack to the burner. A valve controls the recirculation rate, based on boiler input.
Induced flue gas recirculation utilizes the combustion air fan to recirculate the flue gases back into the flame. A portion of the flue gases are routed by duct work or internally to the combustion air fan, where they are premixed with the combustion air and introduced into the flame through the burner.
Condensers:
Condensers make use of a condensing medium, such as air or water that absorbs heat from a vapor. As the vapor loses its heat to the condensing medium, its temperature falls to the saturation point, and it condenses to a liquid.
Cooling Towers:
A cooling tower is a heat rejection device, which extracts waste heat to the atmosphere though the cooling of a water stream to a lower temperature. The type of heat rejection in a cooling tower is termed "evaporative" in that it allows a small portion of the water being cooled to evaporate into a moving air stream to provide significant cooling to the rest of that water stream. The heat from the water stream transferred to the air stream raises the air's temperature and its relative humidity to 100%, and this air is discharged to the atmosphere. Evaporative heat rejection devices such as cooling towers are commonly used to provide significantly lower water temperatures than achievable with "air cooled" or "dry" heat rejection devices, like the radiator in a car.
Common applications for cooling towers are providing cooled water for air-conditioning, manufacturing and electric power generation. The smallest cooling towers are designed to handle water streams of only a few gallons of water per minute supplied in small pipes like those might see in a residence, while the largest cool hundreds of thousands of gallons per minute supplied in pipes as much as 15 feet (about 5 meters) in diameter on a large power plant.
Cooling Water Pump:
Cooling water pump is used to pump the hot water coming from the condenser to the top of the cooling tower where is it sprinkled downward. The used for this purpose is centrifugal pump. And it has following specifications.
CW Pump Specifications:
Type is single stage double suction centrifugal pump
Capacity 16000m3/H
Speed 370 rmp
Power 1600 Kw
Head 25m
Air Preheater:
An air preheater or air heater is a general term to describe any device designed to heat air before another process (for example, combustion in a boiler) with the primary objective of increasing the thermal efficiency of the process. They may be used alone or to replace a recuperative heat system or to replace a steam coil. The purpose of the air preheater is to recover the heat from the boiler flue gas which increases the thermal efficiency of the boiler by reducing the useful heat lost in the flue gas. As a consequence, the flue gases are also sent to the flue gas stack (or chimney) at a lower temperature, allowing simplified design of the ducting and the flue gas stack. It also allows control over the temperature of gases leaving the stack.
Chimney:
Chimneys are built using either precast or cast-in-place concrete blocks. The blocks typically contain vertical and horizontal steel reinforcements. These steel reinforcements protect the concrete from heat damage, such as cracking, that the hot gases can cause. Chimneys contain one or more flues, as the three flue chimney in the schematic below to the left shows, through which the stack gas travels. Each flue is insulated and lined to protect the concrete stack.
Linings can be made of brick, steel and occasionally glass-reinforced plastic. The lining must be resistant to abrasions and chemicals, primarily sulfuric and hydrochloric acid that can condense.
The air gap between the lining and the stack, or windshield, typically serves as the insulation for single flue chimneys. Multi-flue chimneys commonly use mineral wool, insulating brickwork, foam glass, or glass fiber as insulation. The insulation helps protect the stack from heat damage.
Chimneys are topped with a capping unit that caps the lining and the windshield. The capping unit is made of durable cement containing high amounts of alumina because it is located at the point where the flue gases are most likely to condense to form corrosive acids. Most chimneys include many pollution control systems, including electrostatic precipitators, mist eliminators, and wet scrubbers. These reduce the amounts and types of by-products that are vented into the atmosphere.
Economizers:
Flue gases from large boilers are typically 450 - 650°F. Stack Economizers recover some of this heat for pre-heating water. The water is most often used for boiler make-up water or some other need that coincides with boiler operation. Stack Economizers should be considered as an efficiency measure when large amounts of make-up water are used (i.e. not all condensate is returned to the boiler or large amounts of live steam are used in the process so there is no condensate to return) or there is a simultaneous need for large quantities of hot water for some other use. The savings potential is based on the existing stack temperature, the volume of make-up water needed, and the hours of operation. Economizers are available in a wide range of sizes, from small coil-like units to very large waste heat recovery boilers. The savings potential is a function of how much heat can be recovered, which is a function of how much cold water needs to be heated. A generally accepted "rule of thumb" is that about 5% of boiler input capacity can be recovered with a properly sized economizer. A higher percentage can be recovered with a Flue Gas Condenser, assuming there is enough cold water to condense all of the flue gas that is available. Therefore, for 'ball parking' purposes, start by comparing boiler input capacity with the need to heat water. An economizer that recovers 5% of boiler input should easily have a 2 year payback in a year-round application.
Boiler Protection:
ü Fuel protection
ü Gas pressure protection
ü Diesel oil protection
ü Furnace oil protection
ü FD fan trip
ü ID fan trip
ü Regenerative air pre heater trip
ü Drum level high
ü Drum low level
ü Reheat steam pressure drop
ü Furnace pressure low
ü Furnace flame out
ü Natural gas pressure high
Steam Cycle
Steam Turbine:
Turbine is used to convert the heat energy into mechanical energy. Turbine used in T.P.S Muzaffargarh is impulse-reaction steam turbine.
The load requirement is controlled by the steam flow through a governing valve. Maximum steam flow at full load is 670 tons/hour. When the load at the generator is suddenly decreased then the rpm (frequency) of the generator is increased and to decrease the frequency we lower down the steam flow which decreases the speed and maintains the frequency. If load is suddenly increased rotor speed becomes slower, to increase the speed, steam flow is increased.
Steam turbine has three parts.
1. High Pressure Turbine
2. Intermediate Pressure Turbine
3. Low Pressure Turbine.
1. HP (High Pressure) Turbine:
First of all steam from boiler comes into the HP turbine. Steam in the HP turbine is called live steam or main steam. Rotor blades diameter of this part of turbine is smallest of the other parts of the turbine.
Inlet steam temperature of the HP turbine is 540 Co and pressure is 130 kg/cm2.
Outlet steam temperature of the HP turbine is 290 Co and pressure is 16 kg/cm2.
2. IP (Intermediate Pressure) Turbine:
Steam comes into the IP turbine from HP turbine via reheaters. The steam pressure in this section of the turbine is 14 kg/cm2 and temperature is 540 Co.
3. LP (Low Pressure) Turbine:
The outgoing steam of the IP turbine entered into the LP turbine. Steam from the LP turbine goes into the condenser.
Specification of the steam turbine:
Maximum Load 210 MW
Live Steam Pressure 132 kg/cm2
Live Steam temperature 538 Co
Rated Speed 3000 rpm
HP Cycle Exhaust Steam temperature 300 Co
HP Cycle Exhaust Steam Pressure 20 kg/cm2
Reheat Steam Temperature 538 Co
Reheat Steam Pressure 14 kg/cm2
Turbine Protection:
ü Lube oil pressure (low and high)
ü Vacuum drop
ü Live steam temperature drop
ü Axial shift displacement
ü Gas cooling pump tripping
ü HP heater level high
ü All FW pump trip high vibration tipping
ü Trip unit by switch/emergency
Furnace Safeguard Supervisory System (FSSS)
The FSSS station consists of the following parts:
Ø Decanting area
Ø Fuel oil tanks
Ø First Lift pump
Ø Main Heaters
Ø Second Lift pump
Ø Diesel pumps
Ø Recirculation pumps
Ø Recirculation heaters
Ø Filters
Ø Control Room
Decant Area:
The furnace oil that is used as a fuel in the burners of the boiler furnace to produce the steam is transported to the TPS through two ways;
Ø Oil Tankers
Ø Train
For unloading of the fuel from oil tankers and train there is separate unloading or decanting station for each. The unloaded fuel oil is initially stored in the underground reservoir; from there it is filled in the main storage tanks.
2 pumps are used to fill the main storage tanks from the oil tankers decanting area. One of them is active (on load) and other is standby.
Fuel Oil Tanks:
From the decanting area the furnace oil is filled in the storage tanks. From there it is supplied to the burners of the boiler furnace after proper heating. Usually one storage tank is called service tank, from there furnace oil is supplied to the units. The furnace oil is filled in the other tanks first and then filled in the service tanks through recirculation pumps (RCP). The oil in the tanks is kept heated at the temperature 75 Co to 80 Co.
There are total 6 storage tanks for furnace oil each having a volume of 20,000 m3 hence each can store 2, 00, 00,000 liters. There are 2 diesel oil storage tanks each having capacity of 1000 ton.
First Lift Pump:
First lift pump takes the furnace oil from the service tank and supplied to the main heaters. There are total 04 first lift pumps which are operated according to the unit load conditions.
Main Heaters:
There are 04 main heaters each is connected to the respective first lift pump. The main heaters heat the furnace oil through the steam which comes from the boiler. Steam is use to heat the oil in the recirculation heaters.
The seam flows through the pipes which heats the oil outside the tube. The temperature and pressure of the steam in the main heaters is
Temp 270 Co
Pressure 11 – 13 kg/cm2
Second Lift Pump:
Second lift pumps take the furnace oil from the main heaters and supplied to boilers of the units. There are total 04 second lift pumps which are operated according to the unit load conditions. The temperature of the oil that is supplied to the boiler is 105 Co to 120Co.
Fuel Oil cycle:
Furnace Oil Tanks
Oil Heaters
Quick Closing Valves
Boiler Furnace
Flue Gases
Air
Pre-Heater
FD Fan
ID Fan
Exhaust
(Chimney)
Fuel Oil Cycle
The Generator
The generator is a device which converts the mechanical energy into electrical energy.
Cooling System of Turbo Generator:
The first question arises here is that why we need cooling of the generator? As the current flow in the stator and rotor of the generator is very high so it increases the temperature of the stator and rotor winding. As a result the resistance of the stator and rotor windings increases which increase the power losses and may cause the insulation break down.
Two types of cooling is used in the turbo generator of TPS.
1. Stator cooling
2. Rotor cooling
The stator of the turbo generator is cooled by the distillated or demineralized (demi) water. For this purpose a special plant is installed which prepares the demi water for the stator cooling. This demi water is also used for the cooling system of the thyrister converters. The water is passed though the hollow conductors of the stator winding for its cooling. The demi water is necessary for the cooling of the stator winding because raw water is not a pure insulator which may cause the flow of leakage current when passed through stator winding. The demineralized water plant removes the impurities and minerals of the raw water and make it good insulator whose Resistivity is taken at a minimum level of 200 kΩ.cm. The demi water that passes through the stator winding absorbs the heat of the stator winding making it cool and becomes hot itself. The demi water then passes through heat exchangers (coolers) where its temperature is decreased by the circulating water coming from the cooling towers. This demi water is also passed through the mechanical and magnetic filters before passing through stator winding and thyrister converters.
Water parameters in Heat Exchangers:
Rated temp.of cold water at inlet 32 Co
Min: temp of cold water 15 Co
No. of gas heat exchangers 02
Rated water flow in on heat exchangers 150 m3/h
Rotor Cooling:
The rotor cooling is done by the Hydrogen gas. Hydrogen gas is used for the following purposes:
1. Its heat exchange capability is much better than other gases
2. It is very lighter than other gases so do not overload the rotor.
3. Its preparation is very easy and cheap.
Hydrogen gas is filled in the generator and maintained at a pressure of 4kg/cm2
It takes all the heat of the rotor and cools the rotor winding and gets warmed itself. For the cooling of the gas there are four gas coolers inside the generator on each corner. Circulating water of the cooling tower is used in the gas cooler for the hydrogen cooling. Hydrogen gas is explosive if it is combined with oxygen under pressure so to avoid any leakage of gas and entrance of air inside the generator the rotor assembly is sealed by the seal oil whose pressure is at least 0.7kg/cm2 more than hydrogen gas inside the generator.
When the generator is turned off for a long time for maintenance purpose hydrogen is released from the generator in the air using special method. Method involves that firstly fill the generator with CO2 which release the hydrogen in the air and then in the end air is filled in the generator and CO2 is released in the air. This method is adopted because if hydrogen is released using air instead of CO2 then it can cause explosion due to oxygen in the air which will meet hydrogen under pressure in the generator.
After maintenance hydrogen gas is refilled in the generator using the reverse process as described above.
Water parameters in gas cooler:
Rated temp.of cold water at inlet 32 Co
Min: temp. Of cold water 15 Co
Max: water pressure 3 kg/cm2
No. of gas coolers 04
Rated water flow in gas cooler 76.5 m3/h
Chemical section
The chemical section consists of the following sections;
ü Hydrogen plant
ü Demineralization plant
ü Oil testing lab
ü Water testing lab
Hydrogen Plant:
Hydrogen plant prepares the hydrogen gas which is used for the cooling of the rotor of the turbo generator. The hydrogen gas is used for the cooling of the rotor of the turbo generator because it has better heat transfer characteristics, cheap and easy preparation and also it is very light and hence do not over load the rotor. The hydrogen is prepared by electrolysis of the water. For this DC supply is given to the electrolyzer. This Dc supply is produced after step down of the 6.6 kV supply to 400 V and then by 3-pahe rectifier. Raw water is used for the preparation of the hydrogen as it supports fast electrolysis action then de-mineralized water. Potassium Hydro oxide (KOH) is used as a catalyst. The oxygen and hydrogen are prepared in the ratio of 1:2.
A generalized layout of the hydrogen plant is shown in the figure below;
Electrolyzer
Alkaline Solution
Air compressor
Separating Columns
Rotor
Generator
Gas Scrubber
Purifier
Storage Tank
Dryer
DC Power Supply (330A)
v
v
v
v
v
v
Generation of Hydrogen Gas
Electrolyzer:
The process of electrolysis of the water takes place in the electrolysis. The process in which DC current is passed through the water resulting the separation of the cation and anion is known as electrolysis. The electrolyzer has 25 cells each takes 2.2 V, a total of 55 V DC and a maximum current of 1000 A. The separated hydrogen and oxygen then leaves the electrolyzer on its own ways.
Separating Column:
The hydrogen leaving the perforated flash box (PFB) enters the separating column which removes the small parts of alkali from it.
Gas Scrubber:
Gas scrubber is also called gas washer. It removes the impurities from the hydrogen such as dust particles etc.
Dryer:
The dryer dry the hydrogen coming out from the gas scrubber. As gas scrubber do the washing of the hydrogen gas so it has to be dried.
Receiver Tanks:
The receiver tanks store the prepared hydrogen gas. For this purpose 6 receiver tanks are used. The pressure inside the tanks is kept 10kg/cm2. 3 tanks are for oxygen and 3 are for Hydrogen storage.
Demineralization plant:
“The water which is free of all the impurities, minerals, gases like Oxygen Nitrogen and consists of only pure water (H2O) is called demineralized water”.
Demineralized plant is used for the preparation of demineralized water. Demineralized water is used for the preparation of steam, for the cooling of stator of generator and for the cooling of thyristors in the excitation system.
The plant has total generation capacity of 90 tons/hour. Raw water is used for the preparation of the demi water. Raw water is pumped out by the tube wells and stored in the raw water storage tanks.
Demi water is passed through the hollow conductors of stator winding for the stator cooling. It is used for this purpose because demi water acts as an insulator & has a resistivity of 200kOhms.it does not short circuit the windings. Demi water is used for the steam preparation in the boiler for the following reasons:
Raw water contains mineral like Calcium, Magnesium and sulphur. These minerals cause the stacks and corrosion in the boiler tubes which causes the heat loses and may damage the boiler tubes. The designed loss of the demi water in the steam cycle is 2%. Make up demi water is done in the hot well and feed water tank. A generalized layout of the demi water plant is shown in the figure below;
Preparation of Demineralized Water
Mechanical Filter
Raw Water
Cation Filter
Decarbonizer
Cation 2nd Filter
Anion Filter
Storage Tank
Mixed Bed
v
v
v
v
v
Mech. Clarifier filters:
In mechanical clarifier filter coal and gravels are is used to remove the unresolved particles from the water.
Cation filter:
In the cation filter resins is used which replaces the Na+ & Ca2+ ions in the water from the H+ ions. In the end water becomes acidic.
Decarbonizer exhaust:
It removes the carbonates from the water.CO2 is removed by showering of the water against air. It is also known as degasifier.
Anion filter:
In Anion filter castic soda (NaOH) is used which replaces the Cl- or SO4 ions with the OH- ions forming partial demi water.
Cation 2nd Filter:
It also removes the positive ions from the water.
Mixed filter:
In the mixed filter both the remaining anions and cations are removed. The water leaving the mixed bed is the pure distilled water.
Storage tanks:
This prepared demineralized water is then stored in the storage tanks.
Water treatment:
Ammonium hydroxide, Hydrazine and Trisodium phosphate are dozed at different points in the boiler such as boiler drum, for water treatment. The nature of this water is acidic, to minimize the acidity of this water ammonium hydroxide (NH4OH) is used. Hydrazine (N2H4) removes the Oxygen from water and protects the boiler tubes against corrosion. Trisodium phosphate (Na3PO4) is used in the boiler drum which removes the Ca, Mg and adds Na.
Oil Testing Lab:
Different tests of the furnace oil and the lubrication oil are performed in the oil testing laboratory to check their characteristics. The test on the transformer oil is also performed in this lab.
The following tests are performed on the furnace and lube oil:
ü Moisture test
ü Flash point test.
ü Viscosity test.
ü Specific gravity test.
ü Acidity test.
ü Chlorification test.
1. Moisture test:
Water 0.05% or more is determined by this method. High moisture decreases the calorific value of the oil. Water vapors evaporate easily with toluene on heating. Water droplets sink in the bottom of graduated tube on condensation early then toluene due to lower density.
Apparatus:
Dean and Stark Apparatus, Spirit lamp and Measuring Cylinder. OR Karl Fisher Moisture Test Apparatus.
2. Flash Point:
It is the temperature at which a fuel under given set of conditions has given off sufficient vapors to form an explosive mixture with air.
Apparatus:
Pesky marten’s apparatus, thermometer, spirit lamp, safety match.
3. Chlorification test:
The amount of heat liberated by the complete combustion of unit quantity of fuel is called calorific value. It is expressed in Cal/gm or Kilo. Cal/kg.
Apparatus:
Modern Bomb Calorimeter, water quantity and temperature moderator
4. Acidity:
In this test, we check the acidity of the oil. High acidity can be dangerous and causes corrosion in the equipment. Little acidity is tolerated.
Chemicals:
0.05 N KOH, distilled water, alkaline blue indicator, oil sample.
Apparatus:
Measuring flask, conical funnel, pipette, spirit lamp
Procedure:
Take 50 ml distilled spirit in a conical funnel. Neutralize it with 0.05N KOH and use alkaline blue indicator. After Boiling, take 10gm sample in separate flask and add it in the neutralized spirit. After cooling, add blue indicator and titrate it against 0.05 KOH. Note the wt. of KOH Used. Then calculate the acidity by the formula,
0 comments:
Post a Comment