Advertisement

Everything You Want to Know About Thermal Power Plant in Nepal

All About Thermal Power Plant in Nepal: – A thermal power plant is a power plant where thermal energy is converted into electricity. In most parts of the world, the turbine works with steam. The water heats up, turns into steam and turns into a steam turbine, which drives an electric generator.

Advertisement

After passing through the turbine, the steam condenses in a condenser and is returned to the place where it was heated. This is known as the Rankine cycle.

The greatest deviation in the design of thermal power plants is due to the different sources of heat. fossil fuels dominate here, although nuclear thermal energy; Solar heat, biofuels, and waste incineration are also used. Some people prefer the term energy center because such systems convert thermal energy forms into electrical energy.

Certain thermal power plants are designed in addition to the production of electricity for the production of thermal energy for industrial purposes or for the production of urban heating or water desalination.

Main thermal plant in Nepal

The multi-fuel power plant is the largest thermal power plant in Nepal. It is located in Bansbari Morang, Biratnagar, one of the largest industrial areas in Nepal.

Thermal Power Plant Nepal

Thermal Power Plant

In the first phase, 4 units of 6.5 MW each were installed with the financial support of the Finnish Government in fiscal year 1990/91. Later, in fiscal year 1997/98, two more units of the same capacity were installed to complement the energy deficit during winter and night peaks, which was also funded by the Finnish government and reached a total capacity of 39 MW.

The cumulative generation of the power plant of the multi-fuel power station has now reached 578.69 GWh in the first round. This station generated 23.49 GWh of energy in fiscal year 2010/11 and only 0.62 GWh in fiscal year 2011/12.

The revision of the engines of the six units of the Multifuel power plant began in fiscal year 2009/10 and the contract with Wartsila took place on April 10, 2010.

The review was successfully completed this year. The project was jointly funded by the World Bank as part of the Energy Development Project, GON, and NEA. Project costs were $ 7.7 million. The main work of this project consisted of the revision of the 6×6.5 MW sets of Wartsila DG.

Types of thermal energy

Almost all coal, petroleum, nuclear, geothermal, solar thermal, and waste incineration plants, as well as many natural gas power plants, are thermal. Natural gas is often burned in both gas turbines and boilers.

The waste heat of a gas turbine in the form of hot exhaust gas can be used to generate steam by passing this gas through a heat recovery steam generator (HRSG). Steam is used to drive a steam turbine in a combined cycle plant, which improves overall efficiency.

Power plants that burn coal, fuel oil, or natural gas are often called fossil power plants. Some biomass thermal plants have also appeared. Non-nuclear thermal power plants, especially fossil power plants that do not use combined heat and energy, are sometimes referred to as conventional power plants.

Commercial electric power plants are generally built on a large scale and are designed for continuous operation. Almost all utility companies use three-phase generators to produce alternating current at a frequency of 50 Hz or 60 Hz.

Large companies or institutions can have their own power plants to supply heat or electricity to their plants, especially if the steam is generating anyway for other purposes. Until recently, most ships operated with steam plants in the twentieth century.

Steam power plants are now used only in large nuclear ships. Ship power plants generally attach the turbine directly to ship propellers through gearboxes. The power plants on these ships also supply steam to smaller turbines that power electric generators for energy.

The propulsion of nuclear ships is only used on seagoing vessels with some exceptions. There have been many turboelectric vessels in which a steam turbine drives an electric generator that drives an electric motor to drive.

Cogeneration plants, often called combined heat and energy (CHP) systems, generate electricity and heat for the heat of the process or the heating of spaces such as steam and hot water.

History of Thermal Power Plant

The alternative steam engine originally developed has been used since the 18th century for the production of mechanical electricity. James Watt made notable improvements.

When the first commercially developed central electric power, plants were built in 1882 at the Pearl Street station in New York, and at the Holborn Viaduct power station in London, reciprocal steam machines were used.

The development of the steam turbine in 1884 allowed larger and more efficient machine concepts for central power plants. Until 1892, the turbine was considered a better alternative to alternative engines.

The turbines offered higher speeds, more compact machines, and stable speed control, which allowed parallel synchronous operation of generators on a common bus. After about 1905, the turbines completely replaced the alternative engines in the large central power plants.

The largest piston engine generator sets ever built was completed in 1901 for the Manhattan Elevated Railway. Each of the seventeen units weighed around 500 tons and had a nominal output of 6000 kilowatts; A set of contemporary turbines of similar nominal power would have weighed approximately 20%.

[expand title=”The efficiency of thermal energy generation” tag=”h3″]

The efficiency of thermal energy generation

The energy efficiency of a conventional thermal power plant is defined as the salable energy that is generated as a percentage of the calorific value of the fuel consumed. With a simple gas turbine, energy conversion rates of 20 to 35% are achieved.

Typical coal power plants with vapor pressures of 170 bar and 570 ° C operate with an efficiency of 35 to 38% and have state-of-the-art fossil fuel power plants with an efficiency of 46%. Combined circulatory systems can reach higher levels. As with all thermal engines, its efficiency is limited and is governed by the laws of thermodynamics.

Carnot’s efficiency dictates that greater efficiencies can be achieved by increasing the steam temperature. Subcritical fossil fuel power plants can reach an efficiency of 36-40%. Supercritical designs have efficiencies ranging from low to medium 40%, with new “ultra-critical” designs that reach an efficiency of 45-48% at pressures of 4400 psi (30.3 MPa) and multi-stage reheating.

Above the critical point for 374 ° C (705 ° F) and 22.06 MPa (3212 psi) water, there is no phase transition from water to steam, but only a gradual decrease in density.

This in turn limits its thermodynamic efficiency to 30-32%. Some advanced reactor designs that will be investigated, such as the high-temperature reactor, the advanced gas-cooled reactor, and the supercritical water reactor, would operate at temperatures and pressures similar to current coal-fired power plants, producing comparable thermodynamic efficiency.

The energy of a thermal power plant, which is not used to generate electricity, must be released to the environment in the form of heat. This residual heat can be removed by a condenser with cooling water or in cooling towers.

If waste heat is used instead of district heating, this is called heat and energy combined. An important class of thermal power plants is assigned to desalination plants; These are generally found in desert countries with large reserves of natural gas.

The production of freshwater and electricity are equally important by-products in these plants. Different efficiency restrictions apply to other types of power plants. Most of the US hydroelectric power plants. UU.

They convert 90% of the energy of the water that falls into electricity, while the efficiency of a wind turbine is limited to approximately 59.3% in accordance with the Betz Law.,

[/expand][expand title=”Boiler and steam cycle” tag=”h3″]

Boiler and steam cycle

In the field of nuclear power plants, the term steam generator refers to a particular type of large heat exchanger used in a pressurized water reactor (PWR) to thermally connect the primary system (reactor plant) and the secondary system (steam plant) to produce steam.

In a nuclear reactor called a boiling water reactor (SWR), water is boiled to produce steam directly in the reactor itself, and there are no units called steam generators.

In some industrial environments, there may also be steam generator heat exchangers, known as heat recovery steam generators (HRSG), that use heat from an industrial process, most often using hot exhaust gases from a gas turbine. The steam generator boiler must generate steam at the purity, pressure, and temperature required for the steam turbine that drives the electric generator.

Geothermal plants do not need boilers because they use natural steam sources. Heat exchangers can be used when geothermal steam is very corrosive or contains solids in excessive suspension. The necessary safety valves are installed in suitable places to relieve excessive boiler pressure.

[/expand][expand title=”Feedwater heating and Deaeration” tag=”h3″]

Feedwater heating and Deaeration

The boiler feedwater used in the steam boiler is a means to transfer thermal energy from the combustion fuel to the mechanical energy of the rotating steam turbine. All feedwater consists of circulated condensed water and purified replacement water.

Since the metallic materials with which it comes into contact are exposed to corrosion at high temperatures and pressures, the replacement water is thoroughly cleaned before use.

A system of water softeners and ion exchangers produces water that is so pure that it becomes an electrical insulator with conductivity in the range of 0.3 to 1.0 micro siemens per centimeter.

The replacement water in a 500 MWe facility can be 120 US gallons per minute (7.6 l / s) to replace the cleaning management water drained from the boiler drums and compensate for low losses due to steam leaks in the system.

The feedwater cycle begins with the pumping of condenser condensation water after passing through steam turbines. The flow of condensate at full load in a 500 MW system is approximately 400 l / s (6,000 US gallons per minute).

The water is pressurized in two stages and passes through a series of six or seven intermediate feedwater heaters that are heated in each location with steam extracted from a suitable duct in the turbines and at each stage gaining temperature.

Typically, condensed and replacement water in the middle of this series of feedwater heaters before the second pressurization stage flows through a respirator that removes dissolved air from the water and cleans and further reduces its corrosivity.

Water after this point can be dosed with hydrazine, a chemical that removes the oxygen left in the water below 5 parts per billion (ppb). It is also dosed with pH control agents such as ammonia or morpholine to keep the water low in residual acid and, therefore, not corrosive.

[/expand][expand title=”Boiler operation” tag=”h3″]

Boiler operation

The boiler is a rectangular stove with a side length of 15 m and a height of 40 m. Its walls consist of a mesh of high-pressure steel tubes with a diameter of 58 mm.

Fuel, like. As the coal dust is blown through burners in the four corners or along a wall or two opposite walls in the oven, and ignites to burn quickly, forming a large fireball in the middle. Heat radiation from the fireball heats the water that circulates through the boiler tubes near the circumference of the boiler.

The speed of the circulation of water in the boiler is three to four times the performance. As water circulates in the boiler, it absorbs heat and turns into steam. It is separated from the water in a drum at the top of the oven.

Saturated steam is introduced into the superheated suspension tubes, which are hung when leaving the oven in the hottest part of the flue gases.  Plants that use lignite are increasingly deployed in places as diverse as Germany, Victoria, Australia, and North Dakota.

A lignite is a form of coal much younger than hard coal. It has a lower energy density than hard coal and needs a much larger oven for equivalent heat production. Such coals can contain up to 70% water and ash, resulting in lower oven temperatures and require larger induced draft fans.

Cooking systems also differ from black coal and typically extract hot gas from the furnace outlet level and mix it with the incoming coal in blower mills that inject the mixture of coal dust and hot gas into the boiler.

Systems that use gas turbines to heat water to turn it into steam use boilers called heat recovery steam generators (HRSG). From the waste heat of the gas turbine, superheated steam is generated, which is then used in a conventional water vapor generation circuit, as described in the Gas turbine combined cycle power plants section.

[/expand][expand title=”Boiler oven and steam drum” tag=”h3″]

Boiler oven and steam drum

Water enters the boiler through a section in the convection step called economizer. From the economizer, it passes to the steam drum and from there through downspouts to the inlet heads at the bottom of the water walls.

From these collectors, the water rises through the furnace water walls, where part of it becomes steam and the mixture of water and steam re-enters the steam drum.

This process can only be assisted by natural circulation (because the water in the downspouts is denser than the water/steam mixture in the water walls) or by pumping.

In the steam drum, the water returns to the downspouts, and the steam passes through a series of steam separators and dryers, which remove water droplets from the steam. Dry steam then flows to the superheater coils.

The boiler oven equipment includes nozzles and carbon feed primers, soot blowers, water spouts, and observation ports (on the oven walls) to observe the inside of the oven. The explosions in the furnace due to the accumulation of combustible gases after initiation are avoided by removing said gases from the combustion zone before the ignition of the coal.

The steam drum (as well as the coils and superheater distributors) have vents and drains necessary for the initial start-up.

[/expand][expand title=”Superheater” tag=”h3″]

Superheater

Fossil fuel power plants often have a superheater section in the steam generator oven. The steam passes through the drying device in the steam drum to the superheater, a set of pipes in the oven.

Here, the steam absorbs more energy from the hot combustion gases outside the hose, and its temperature now overheats beyond the saturation temperature. The superheated steam is passed through the main steam lines to the valves in front of the high-pressure turbine.

Nuclear power plants do not have such sections, but they produce steam in substantially saturated conditions. The experimental nuclear power plants were equipped with fossil superheaters to improve the total cost of ownership of the plant.

[/expand][expand title=”Steam condenser” tag=”h3″]

Steam condenser

The condenser condenses the steam from the turbine’s exhaust gas into a liquid to be able to pump it. If the condenser can be cooled, the pressure of the exhaust gases is reduced and the efficiency of the circuit increases.

The surface condenser is a shell and tube heat exchanger in which cooling water circulates through the tubes. The steam leaving the low-pressure turbine enters the jacket, where it cools and becomes condensate (water) when the pipes overflow.

Such condensers use steam ejectors or exhaust gases are driven by a rotating motor to continuously remove air and gases from the steam side to maintain a vacuum.

For optimum efficiency, the temperature in the condenser must be kept as low as possible to achieve the lowest possible pressure in the condensation vapor.

Since the temperature of the condenser can almost always be kept well below 100 ° C, when the water vapor pressure is much lower than the atmospheric pressure, the condenser generally operates under vacuum. Therefore, non-condensable air should be prevented from entering the closed circuit.

Typically, the cooling water causes the vapor to condense at a temperature of approximately 25 ° C (77 ° F), and this produces an absolute pressure in the condenser of approximately 2-7 kPa (0.59-2.07 inHg), that is Vacuum of approximately -95 kPa (-28 inHg) in relation to atmospheric pressure. The large volume reduction that occurs when water vapor condenses in liquid creates a low vacuum that helps the steam pass and increases turbine efficiency.

The limiting factor is the temperature of the cooling water, which in turn is limited by the average climatic conditions prevailing at the power plant site (possibly the temperature can be lowered beyond the turbine limits in winter, resulting in excessive condensation in the water turbine).

Systems operating in hot climates may need to reduce energy if the condenser’s cooling water source heats up. Unfortunately, this generally coincides with periods of high energy consumption for the air conditioner.

The condenser generally uses circulating cooling water from a cooling tower to supply residual heat to the atmosphere, or continuous cooling water (OTC) from a river, lake or ocean.

In the United States, approximately two-thirds of power plants use OTC systems, which often have significant adverse environmental effects. The effects include thermal pollution and the death of a large number of fish and other aquatic species with cooling water.

[/expand][expand title=”A mechanical cooling tower with Marley vacuum” tag=”h3″]

A mechanical cooling tower with Marley vacuum

The heat absorbed by the circulating cooling water in the condenser tubes must also be dissipated to maintain the cooling capacity of the water during circulation.

This is done by pumping warm water from the condenser through cooling towers with the natural draft, forced draft or induced draft which reduce the temperature of water by evaporation by approximately 11 to 17 ° C at 30 ° F) – residual heat leaving the environment The flow rate of the cooling water in a 500 MW unit at full load is approximately 14.2 m³ / s (500 ft³ / s or 225,000 US gal/min.

The condenser tubes are made of brass or stainless steel to prevent corrosion on both sides. Many systems have an automatic cleaning system that scrubs sponge rubber balls through the tubes without having to disconnect the system.

The cooling water used to condense the steam in the condenser returns to its source without being changed, except for being heated. When water returns to local waters (instead of a cooling tower), it is often quenched with “raw” cold water to avoid thermal shock when it is introduced into that body of water.

Another form of condensation system is the air-cooled condenser. The process is similar to that of a radiator and a fan. The residual heat from the low-pressure part of a steam turbine flows through the liquefaction pipes, the pipes are generally grooved and the ambient air is forced through the ribs with the help of a large fan.

The steam condenses in water to be reused in the water-steam cycle. Air-cooled condensers generally operate at a higher temperature than water-cooled versions. Water-saving reduces circuit efficiency (resulting in more carbon dioxide per megawatt-hour of electricity).

The powerful condensate pumps return the condensed steam (water) from the bottom of the condenser to the water/steam circuit.

[/expand][expand title=”Reheater” tag=”h3″]

Reheater

Power plant stoves may have a reheater section that contains pipes heated by hot combustion gases outside the pipes. The exhaust of the high-pressure turbine is directed through these heated tubes to collect more energy before the intermediate and then the low-pressure turbine is driven.

[/expand][expand title=”Air Path” tag=”h3″]

Air Path

External fans provide enough air for combustion. The primary air fan draws air from the atmosphere and first heats the air in the air preheater for a better economy. The primary air then passes through the coal sprayers and transports the pulverized coal to the burners for injection into the oven.

The secondary air fan removes air from the atmosphere and first heats the air in the air preheater for a better economy. In burners, the secondary air is mixed with the carbon / primary air stream.

The induced draft fan helps the FD blower by removing flammable gases from the oven while maintaining a slight negative pressure in the oven to prevent the escape of combustion products from the boiler housing.

[/expand][expand title=”Steam turbine generator” tag=”h3″]

Steam turbine generator

The turbine generator consists of a series of interconnected steam turbines and a generator on a common axis. At one end there is usually a high-pressure turbine followed by a medium pressure turbine and finally one, two or three low-pressure turbines and the generator.

As steam flows through the system and loses pressure and thermal energy, its volume increases, and, at each subsequent stage, larger diameter and longer blades are required to recover the remaining energy. The total rotating mass can exceed 200 tons and 30 meters long.

It is so difficult that it must be turned slowly even at a stop (at 3 rpm), so that the shaft does not bend or break out of balance. This is so important that it is one of the six functions of the backup batteries on-site. (The other five are emergency lighting, communication, station alarms, generator hydrogen seal system, and gubernatorial lubricant).

In a typical power plant of the late twentieth century, superheated steam from the boiler is pumped through pipes from 360 to 410 mm in diameter at a temperature of 540 ° C (2,400 psi). to the high-pressure turbine, where the pressure across the stage drops to 600 psi (4.1 MPa, 41 atm) and 600 ° F (320 ° C). It is discharged through cold heat pipes from 610 to 660 mm (24 to 26 inches) in diameter and returned to the boiler, where steam is reheated to 540 ° C (1000 ° F) in special superheat pipes.

The hot post-heating steam is sent to the medium pressure turbine, where it falls both at temperature and pressure, and goes directly to the low-pressure turbines with long blades and finally to the condenser.

The generator is usually 9 m long and has a diameter of 3.7 m. It contains a stationary stator and a rotating rotor, each with heavy copper conductors one kilometer in length.

Usually, there is no permanent magnet, which prevents a black start. In operation, it generates up to 21,000 amps at 24,000 volts AC (504 MWe) while rotating synchronously with the network at 3,000 or 3,600 rpm. The rotor rotates in a sealed chamber cooled with hydrogen gas.

It is chosen because it has the highest known heat transfer coefficient of all gases and reduces air resistance losses due to its low viscosity. This system requires special handling during start-up, with the air in the chamber first displaced by carbon dioxide before hydrogen is introduced.

The network frequency is 60 Hz in North America and 50 Hz in Europe, Oceania, Asia (Korea and parts of Japan are exceptions), and parts of Africa. The desired frequency influences the design of large turbines since they are highly optimized for a certain speed. The current flows to a distribution point where the transformers increase the voltage for transmission to the destination.

Steam turbine generators have auxiliary systems with which they can work satisfactorily and safely. The steam turbine generator is a rotating plant and generally has a large diameter heavy shaft.

Therefore, the shaft not only requires supports but must also be held in position during execution. To minimize frictional resistance to rotation, the shaft is provided with multiple bearings.

The bearing housings on which the shaft rotates are coated with a low friction material, such as babbitt metal. Oil lubrication reduces friction between the shaft and the bearing surface and limits the heat generated.

[/expand][expand title=”Stack gas path and clean up” tag=”h3″]

Stack gas path and clean up

As the combustion exhaust gas leaves the boiler, it passes through a flat rotating metal mesh basket that absorbs heat and returns to the incoming fresh air as the basket rotates.

This is called an air preheater. The gas leaving the boiler is loaded with fly ash, small particles of globular ash. The combustion gas contains nitrogen and the combustion products are carbon dioxide, sulfur dioxide, and nitrogen oxides.

Fly ash is removed by cloth bag filters in baghouses or electrostatic precipitators. Once removed, the fly ash byproduct can sometimes be used in concrete production. However, this flue gas cleaning is only performed on systems equipped with the appropriate technology.

However, most coal power plants in the world do not have these facilities. Legislation in Europe has proven effective in reducing smoke pollution. Japan has been using combustion gas purification technologies for more than 30 years and in the USA. China is now beginning to combat the pollution of coal power plants.

If required by law, sulfur and nitrogen oxide pollutants are removed by exhaust scrubbers with powdered limestone or another wet alkaline suspension to remove these contaminants from the exhausted cell of the output cell. Other devices use catalysts to remove nitrous oxide compounds from the exhaust stream.

The gas that pumps the exhaust chimney may have dropped to approximately 50 ° C (120 ° F) at this time. A typical exhaust cell can have a height of 150 to 180 meters to disperse the remaining components of the flue gases in the atmosphere.

The highest exhaust gas stack in the world is 419.7 meters high at the Ekibastuz GRES-2 Kazakh power plant. In the United States and other countries, atmospheric dispersion modeling is required to determine the height of the exhaust chimney required to comply with local clean air regulations.

The United States also requires that the height of an exhausted battery correspond to the stack height called “Good Engineering Practices” (GEP). For existing exhaust batteries that exceed the height of the GEP battery, modeling batteries for the distribution of air pollution for those batteries should use the height of the GEP battery instead of the actual height of the battery.

[/expand][expand title=”Fly ash collection” tag=”h3″]

Fly ash collection

Fly ash is trapped by electrostatic filters or cloth bag filters (or sometimes both) located at the oven exit and in front of the induced draft fan and removed from the exhaust gas.

Fly ash is regularly removed from capture containers under bag separators or filters. In general, fly ash is pneumatically transported in storage silos, and then transported by trucks or railroad cars.

[/expand][expand title=”Collection and disposal of ashes at the bottom” tag=”h3″]

Collection and disposal of ashes at the bottom

At the bottom of the oven, there is a receiver for the bottom ashes. This funnel is kept full of water to extinguish the ashes and clinkers that fall from the oven.

Measures are taken to crush the clinker and transport the crushed clinker and bottom ashes to a storage location. Ash extractors are used to extract ashes from municipal waste containers.

[/expand][expand title=”Auxiliary systems” tag=”h3″]

Auxiliary systems

Since steam is continuously extracted and condensate is continuously returned to the boiler, losses due to discharges and leaks must be balanced to maintain the desired water level in the boiler’s steam drum.

For this purpose, continuous replacement water is added to the boiler water system. The impurities in the raw water introduced into the plant generally consist of calcium and magnesium salts that impart hardness to the water. Due to the hardness of the replacement water, boiler deposits are formed on the water surfaces of the pipe, which leads to overheating and failure of the pipes.

Therefore, the salts must be removed from the water, and this is done by a desalination plant (DM). A DM plant generally consists of mixed bed cations, anions, and exchangers.

All ions in the final water of this process consist essentially of hydrogen ions and hydroxide ions that recombine in pure water. Water with very pure DM becomes highly corrosive due to its high affinity for oxygen when it absorbs oxygen from the atmosphere.

The capacity of the DM plant is determined by the type and amount of salts in the raw water inlet. However, some storage is essential since the DM system may be out of service due to maintenance. For this purpose, a storage tank is installed, from which DM water is continuously extracted for the composition of the boiler.

The DM water tank is made of materials that are not attacked by corrosive water, such as. B. PVC. Pipes and valves are usually made of stainless steel. Sometimes, a steam blanket or a stainless-steel donut float is placed in the water of the tank to avoid contact with air.

In the steam space of the surface condenser (that is, on the vacuum side), DM water is usually replenished. This arrangement not only sprays water but also deaerates DM water, eliminating dissolved gases through ventilation through an ejector connected to the condenser.

[/expand][expand title=”Fuel preparation system” tag=”h3″]

Fuel preparation system

In coal-fired power plants, raw coal from coal storage is first divided into small pieces and then transported to coal transport tanks in boilers. The coal is then pulverized to a very fine powder. The sprayers can be ball mills, rotary drum mills, or other types of mills.

Some power plants burn fuel oil instead of coal. The oil must be kept warm in the fuel tanks (above the pour point), so that the oil does not freeze and can no longer be pumped. The oil is usually heated to approximately 100 ° C before being pumped through the oven oil spray nozzles.

Boilers in some power plants use recycled natural gas as the main fuel. Other power plants may use treated natural gas as an auxiliary fuel when their main fuel supply (coal or oil) is interrupted. In such cases, separate gas burners are provided in the boiler stoves.

[/expand][expand title=”Barring gear” tag=”h3″]

Barring gear

The barring gear (or “cogwheel”) is the mechanism provided to rotate the turbine-generator shaft at a very slow speed after the unit is stopped. Once the unit is “tripped” (that is, the steam inlet valve is closed), the turbine will stop. If it stops completely, the turbine shaft tends to bend or bend if left in position for too long.

This is because the heat inside the turbine housing tends to concentrate in the upper half of the housing, making the upper part of the shaft warmer than the lower half. Therefore, the shaft could deform or bend a millionth of an inch.

This small axis deviation, which can only be detected by eccentricity meters, would be sufficient to cause harmful vibrations when restarting the entire steam turbine generator unit.

Therefore, the shaft rotates automatically at low speed (approximately 1% of the nominal speed) using the ratchet wheel until it has cooled sufficiently to allow a complete stop.

[/expand][expand title=”Oil system” tag=”h3″]

Oil system

An additional pump of the oil system is used to supply oil during the start-up of the steam turbine generator. It provides the hydraulic oil system required for the steam blocking valve at the main inlet of the steam turbine, the control valves, the oil systems for bearings and seals, the corresponding hydraulic relays, and other mechanisms.

At a given speed, the turbine takes control when a pump driven by the main axis of the turbine starts, the functions of the auxiliary system.

[/expand][expand title=”Generator cooling” tag=”h3″]

Generator cooling

While small generators can be cooled with air drawn through filters in the inlet, larger units generally require special cooling arrangements. Hydrogen gas cooling in an oil-sealed housing is used because it has the highest known heat transfer coefficient of all gases and reduces air resistance losses due to its low viscosity.

This system requires special treatment during start-up, with the air in the generator housing first displaced by carbon dioxide before hydrogen is introduced. This ensures that highly flammable hydrogen does not mix with atmospheric oxygen.

The hydrogen pressure inside the housing is maintained slightly above atmospheric pressure to prevent outside air from entering. Hydrogen must be sealed against leaks at the point where the shaft leaves the housing.

Mechanical seals with a very small annular space around the shaft are installed to avoid friction between the shaft and the seals. Sealing oil is used to prevent the escape of hydrogen gas into the atmosphere.

[/expand][expand title=”The high voltage generator system” tag=”h3″]

The high voltage generator system

The generator voltage for modern generators connected to the network ranges between 11 kV in smaller units and 30 kV in larger units. The generator power lines are usually large aluminum channels because they have a high current compared to the cables used in smaller machines.

They are enclosed in aluminum bus channels that are well-grounded and supported by suitable insulators. The generator’s high voltage lines are connected to booster transformers for connection to a high voltage electrical substation (typically in the range of 115 kV to 765 kV) for greater transmission through the local network.

High voltage lines contain the required protection and measurement equipment. The generator and the steam turbine transformer form a single unit. Smaller units can share a common generator elevator transformer with individual circuit breakers to connect the generators to a common bus.

[/expand][expand title=”Monitoring and alarm system” tag=”h3″]

Monitoring and alarm system

Most plant inspections are automatic. Sometimes, however, manual intervention may be necessary. Therefore, the system is equipped with monitors and alarm systems that alert system operators when certain operating parameters deviate significantly from their normal range.

[/expand][expand title=”Emergency lighting and battery communication” tag=”h3″]

Emergency lighting and battery communication

A central battery system, consisting of lead and acid cell units, is provided to supply important elements such as power station control systems, communication systems, generator hydrogen sealing systems, oil lubricating oil pumps. turbine and emergency lighting with emergency power when necessary.

This is essential for the safe and damage-free disconnection of the devices in an emergency situation.

[/expand][expand title=”Emergency lighting and battery communication” tag=”h3″]

 Water circulation system

To dissipate the heat load of the main turbine exhaust steam, condense out of the steam condenser from the fill box and the low-pressure heater by continuously adding cooling water to the main condenser, causing condensation.

It is estimated that cooling water consumption of indoor power plants will reduce the availability of electricity for most thermal power plants by 2040-2069.

[/expand]

This is the information that I knew about the Thermal power plant in Nepal. Do you know more about Thermal plant in Nepal? If yes, then please let me know.

Author: Er. Shishir Acharya

Advertisement