Brapukuria power plant
Barapukuria Power Plant is one the largest coal based power plant which is owned and operated by BPDB in Dinajpur, Rajshahi. The installed capacity of the power plant is 250 MW. The land utilization by Barapukuria Power Plant is 290 acres in total which includes residential area, ash pond, recreational park etc. This power plant consumes approximately 0.72 million metric tons of coal per year which comes from nearby Barapukuria Coal Mine. This is a major power plant which has improved the under voltage problem in the northern zone and played a vital role in the development of power sector in Bangladesh.
Working Principle of a Steam Turbine Power Plant
Barapukuria Coal Based Thermal Power Plant is a steam turbine power plant. Electrical energy generation using steam turbine involves three energy conversions. First, extracting thermal energy from the fuel, in this case this is coal. Then use that thermal energy of the steam to convert it into kinetic energy to rotate the turbine. Finally, convert the mechanical energy of the turbine into electrical energy using a generator. In Barapukuria the steam is produced by burning coal in a combustion chamber. The chemical process of burning fuel releases heat. That heat is being used to create steam from a boiler. The steam has high kinetic energy. By directing that high temperature steam, rotation of the turbine is done. The turbine is coupled with the rotor of a generator which converts mechanical energy into electrical energy. This is the basic principle of a steam turbine power plant.
Currently, Barapukuria Coal Based Thermal Power Plant has two running units each with the capacity of 125 MW. So, the gross current capacity is 250 MW. Another unit with the capacity of 275 MW is under construction which is projected to be in service in 2018. But, due to lack of maintenance, the actual capacity of a single unit is around 80 MW. So, actual gross capacity of the plant is currently 2×80 MW = 160 MW.
Installed capacity Current capacity
Unit 1 125 MW 80 MW
Unit 2 125 MW 80 MW
Total 250 MW 160 MW
With regular maintenance and overhauling, the power plant can produce electricity of its
The fuel used in Barapukuria Coal Based Thermal Power Plant is bituminous coal. Theannual coal consumption of this power plant is 0.72 million metric tons at 70% plant factor. The coal consumption of each unit per day is 1200 metric tons and total 2400 metric tons for two units per day. The coal consumption per kilowatt hour (Kwh) is 0.4 Kg.
Annual consumption 0.72 million metric tons
1 unit per day 1200 metric tons
2 units per day 2400 metric tons
Per Kwh 0.4 Kg
The coal treatment of the power plant goes through different stages. The stages are shown below-
Unaltered coal comes directly from Barapukuria Coal Mine through conveyer belts to the reserve coal yard. From the coal yard, coal goes through a magnetic separator. The magnetic separator separates metals from the unaltered coal. Then, it goes to the coal crusher. The coal crusher crushes the coal into 20mm pieces. Then, the coal goes into the coal pulverizer which turns the coal into coal powders. Hot air is mixed with the coal powder. Mixture of the coal powder and hot air goes to the boiler for burning. The quality of the coal used in the power plant is very high. The gross calorific value of this coal is 6100 kcal/kg. Fig 4.1 shows Conveyer belts for coal transport at Barapukuria Power Plant.
Steam boiler is an essential part of thermal power plant. Steam boiler is a close vessel into which the water is heated until it converts into steam at required pressure. Water is stored inside the boiler. Fuel is burnt in a furnace and hot gasses are produced. The hot gasses come in contact with the water vessel where heat of the hot gasses transfer to the water and steam is produced. Then this high pressure steam is piped to the turbine of the power plant. Weather tubes carry water or flue gas, depending on that, boilers is of two types-
1. Fire tube boiler
2. Water tube boiler
Fire tube boiler:
The fire tube boiler consists of numbers of tubes through which hot gasses are passed. These hot gas tubes are immersed into water, in a closed area. These fire tubes or hot gas tubes heated up the water and convert the water into steam.Water tube boiler: In water tube boiler, the water is heated inside the tubes and hot gasses surround them. This is the opposite of fire tube boiler. In water tube boiler, the pressure of the steam is higher than the fire tube boiler. According to condition of furnace, boilers are of two types-
1. Internal combustion boiler
2. External combustion boiler
Internal combustion boiler:
The combustion of fuel and hot air occurs inside the boiler. Hot gas is produced from inside the boiler in this kind of boiler. External combustion boiler: In this kind of boiler the combustion occurs outside the boiler. Then, hot gas passes into the boiler to create steam. According to steam pressure, boilers are of two types-
1. Low pressure boiler
2. High pressure boiler
Low pressure boiler: In a modern low pressure boiler the pressure of the steam is less than 1.6Mpa and temperature is below 250oC. High pressure boiler: In a high pressure boiler the pressure of the steam is high and temperature is more than 250o C. According to supply water, boilers are of two types-
1. Natural circulation
2. Forced circulation
Natural circulation: Natural circulation of water set up by convention currents or gravity.
Forced circulation: Water pump is used to force the circulation of water.
According to drum, boilers are of two types-
1. Single drum boiler
2. Double drum boiler
Single drum boiler: Single drum is used to store demi water.
Multiple drums are positioned.
In Barapukuria, the boiler is of
1. water tube type
2. internal combustion type
3. high pressure type
4. natural circulation type and
5. single drum type
Type Single furnace type
Maximum Continuous Rating 400t/h
Main Steam Outlet Pressure 14.42 Mpa
Main Steam Outlet Temperature 538oC
Reheated Steam Flow 325t/h
Reheated Steam Pressure (In/Out) 2.31/2.21 Mpa
Reheated Steam Temperature (In/Out) 290oC/538oC
Fuel Bituminous Coal
Combustion 4 corner firing
Feed Water Temperature 248oC
Rated Power 125 MW
Manufacturer Shanghai Boiler Works Limited
This boiler has 6 furnace beds. Each furnace bed has 4 corner firing system. Mixture of hot air and coal powder is being supplied in the furnace bed. Then the combustion of the mixture creates hot gasses. Hot gas passes around the water tubes and heat is transferred from hot gasto water. The feedwater is preheated at 248oC. The steam produced in the tubes has temperature of 538oC. This high-temperature steam is piped to the turbine. The output stream has temperature of around 290oC which is passes through economizer and reheated to use again. This increases the efficiency of the boiler. Fig 4.2 shows under construction boiler for
the 3rd unit at Barapukuria.
A Steam Turbine is a mechanical device that extracts thermal energy from pressurized steam and transforms it into mechanical work. The basic parts of stream turbines are blades and rotors. A set of blades is known as a stage. They also have steam inlets and outlets. Two independent mechanisms, known as governors, are used to ensure safe operation of the turbine. There are two basic types of turbines-
1. Impulse turbine
2. Reaction Turbine
In an impulse turbine, high-pressure steam is fired through a narrow nozzle at the turbine blades to make them spin. The blades of an impulse turbine are usually bucket-shaped. In an impulse turbine, the steam is forced to hit the turbine at high speed. High-velocity steam from the nozzles kick into the blades and pushing them around with a series of impulses
In a reaction turbine, there is a second set of stationary blades attached to the inside of the turbine case. As the steam hits the rotor blades, it creates a reactive force on the blades which in turn creates the turning moment on the turbine rotor. The rotor becomes basically a set of rotating nozzles. The turbine used in Barapukuria is a reaction condensing and super high pressure turbine. It has re-heater combined with HP and IP cylinders. It has double casing with single shaft. Rated capacity of the turbine is 125 MW. The rotation of the turbine is clock wise as seem from turbine to the generator. The speed of the turbine is 3000 RPM. Table 4.4 shows technical specification of a turbine used in Barapukuria (for a single unit). Figure 4.3 shows Turbine compartment for unit-2 at Barapukuria Power Plant.
Alternator at Barapukuria power plant
An alternator is an electrical generator that converts mechanical energy into electrical energy. For simplicity most of the alternators use magnetic field as rotor and armature as stator. Alternators in power stations are driven by turbine or engines.The alternator used in Barapukuria power plant is Type QFS-125-2. It is a 2 pole generator. Rated capacity in KVA is 156250. Active power of the generator is 125 MW. Stator voltage is 13.8 KV. Stator current is 6537 A. The rotor current at no load is 627 A and at load is 1750 A. Rotor voltage at no load is 88 V and at load is 275 V. The speed of the alternator is 3000 RPM which generates 50 Hz current. The manufacturer is Shanghai Turbine Generator Company Limited.
Electrical power transformer is a device which transforms electrical energy from one circuit to another. It transforms electrical voltage in different level without changing the frequency. The transformer used in Barapukuria power plant is a step up transformer. The rating of the transformer used in Barapukuria is 13.8 KV/230 KV. The manufacturer of the transformer is Baoding Tianwei Baodian Electric Company Limited. The cooling system of the transformer is oil filled cooling system. MVA rating is 156.25 MVA. This is a three phase transformer with ONAF system. ONAF is oil forced air forced cooling of transformer.
The generated voltage of Barapukuria power plant is 13.8 KV and the supply voltage of the power station to the grid is 230 KV.
In Barapukuria power plant the cooling system is water cooling type. For this cooling system there are cooling towers and 14 deep tube wells. The cooling water consumption per day is 800-1000 metric tons. Cooling tower is a heat rejection device which extracts heat from equipment to the atmosphere through water steam. Cooling towers remove heat by circulating waters through water jackets. For this there is a capacity full of water, to purify this water lots of chemical is used in it. This water is sent to the de-mineralized tank through the pipe continuously. Water is circulated inside the system in water jackets around the boiler, turbine etc. To keep the temperature at the reasonable level, hot water leaving the jacket is sent to heat exchanger. Raw water is made to flow through the heat exchanger, where it takes up the heat of jacket water. It is then cooled in the cooling tower and recirculates again.
Waste management is very important for a coal based thermal power plant. Irresponsible management of waste can pollute the environment badly. So, waste management is very important for this power plant. Annual ashes generation of the power plant is 0.08 million metric tons per year when the plant is running at 70% plant factor. There are 2 ash ponds Barapukuria power plant covering 90 acres in this power station for ash collection. Other equipment is also used for waste management.
External fans are provided to give a sufficient amount of air for combustion. There are draft fans for drawing out combustible gasses from the furnace. Induced draft fan ID fans are used to remove the products of combustion from the boiler using negative pressure.
Electrostatic precipitator (ESP)
An ESP is a highly efficient device that removes particles like dust and smoke from the flowing gas using the force of an induced electrostatic charge. ESP is used to clean the air, improving operating environment and thus prevents pollution of the air. Fly ash and Bottom ash collector There are devices placed in the power station to collect the fly ash and bottom ash. These ashes can be used to manufacture cements.
Dust collector is a system used to enhance the quality of air released from the power plant. It collects dust and other impurities and designed to handle high-level dust loads. There are systems to remove the dust at a utine schedule.