1. Thermal power plants, in the narrow sense, refers to coal-fired power plants that use coal to produce electricity. In the broad sense, they also include gas (natural gas), oil (diesel, etc.) energy. power plants and waste power plants. Thermal power plant generally refers to a power plant that produces pure electricity.
2. Thermal power plant refers to a power plant that combines heating and electrical power. Technically, it is called combined heat and power production. Thermal power plants generally use coal to produce electricity.
3. The process of coal-fired power plant:
Coal is finely crushed by the coal crusher and coal crusher, and then injected into the boiler for combustion. Water is pumped into the water wall. The superheated steam is heated untilsqu to the saturation temperature and heated to high temperature and high pressure in the superheater. The superheated steam enters the steam turbine to rotate the steam turbine at a speed of 3000 rpm. The steam turbine drives the generator to rotate, and the generator cooperates with the exciter to generate electrical energy for supply. The exhausted steam after the steam turbine work is condensed in the condenser and then preheated by the heater and economizer before entering the boiler cycle.
4. Process of a thermal power plant:
The process of a thermal power plant is much the same as that of a coal-fired power plant, except that during the process of generating steam turbine being work, part of the heat is extracted from a certain stage of the steam turbine. The steam required to heat the load is supplied to each heat user directly orafter being reheated by the boiler (heat user refers to the user who uses the heat). power plant to provide steam). There are two heating methods: direct steam supply and hot water supply, which are determined based on the needs of heat users. Compared to pure coal-fired units, thermal units have larger water losses, so the volume of feed water is relatively large.
5. According to an economic analysis, for units of the same capacity, the overall economic efficiency of heating units is better than that of units powered by pure coal. However, the relative capacities of thermal power plants are relatively. small (the largest in China is currently 300 MW), compared to the current large capacity units (1000 MW), the economic situation is much worse.
What are the clasification of water used in thermal power plants?
125 ~ 200 MW unit water surcharge: 2.0% of boiler maximum continuous evaporation + drum boiler blowdown loss (provided by the boiler factory boiler, not less than 0.3%) + cooling water of closed auxiliary engine, take 0.3 of the volume of cooling water ~0.5% + loss of external gas supply (depending on the actual situation) + loss of other steam and water used in power plants (depending on the actual situation).
The algorithm for units with other capacities is the same as above, except that the value of the first element is different:
300~600 MW unit: take 1.5% of the maximum continuous evaporation capacity of the boiler;
Units above 900 MW: take 1.0% of the boiler's maximum continuous evaporation
The amount of water replenished has little to do with the load. look closer, youYou will find that the above loss is not directly related to the load.
Since high temperature and high pressure water vapor in thermal power plants can drive steam turbines to rotate, why is the remaining gas not reused?
Thermal power plants use coal, oil and natural gas as fuel. Factory that produces electrical energy from fuel. Its basic production process is as follows: the fuel is burned in the boiler and the heated water is transformed into steam, which converts the chemical energy of the fuel. fuel into steam.The steam pressure causes the steam turbine to rotate and the thermal energy is converted into mechanical energy. The steam turbine then turns the generator, converting mechanical energy into electrical energy. Thermal power plants are classified as follows: According to fuel: coal-fired power plants, oil-fired power plants, gas-fired power plants, waste heat power plants, power plants using garbage and industrial waste as fuel; temperature: the working fluids in the boiler are It is water. The critical parameters of water are: 22.064 MPa and 373.99 ℃ At this pressure and temperature, the density of water and steam is the same, which is called the critical point of water. The pressure of the working fluid in the furnace is less than this pressure and is called subcritical boilers, pressures higher than this are called supercritical boilers. The steam temperature in the oven is not lower than 593°C or the steam pressure is not lower. than 31MPa, which is called ultra-supercritical.
Medium and low pressure power plants (3.92 MPa, 450 degrees), high pressure power plants (9.9 MPa, 540 degreesgrates), ultra high pressure power plants (13.83 MPa, 540 degrees), subcritical pressure power plants (16.77 MPa, 540 degrees), supercritical pressure power plants (22.11 MPa, 550 degrees) ; from the selection of parameters of supercritical or ultra-supercritical units that have been built and under construction at international and national level, for supercritical and ultra-supercritical units There is no hard limit, it is simply to know what the value of the parameter is. At present, domestic and international people generally think that as long as the main steam temperature reaches or exceeds 600°C, it is considered an ultra-supercritical unit. According to the prime mover: condensing steam turbine power plant, gas turbine power plant, internal combustion engine power plant, steam-gas turbine power plant, etc. depending on the energy produced, condensing steam plant (does notproduced as electricity), thermal; power plant (produces electricity and heat); According to the installed capacity of power plants: small capacity power plants (less than 100 MW), medium capacity power plants (100-250 MW), large and medium capacity power plants (250-1,000 MW), power plants of large capacity (above 1,000 MW); thermal power plants. There are several types of wastewater produced: industrial wastewater, domestic wastewater, coal-containing wastewater, and acid-base wastewater. classification, and the processes are also different.
The process of thermal power plants is roughly as follows. The combustion of fossil fuels releases heat into the reactor and the water can be directly heated to obtain water vapor. This steam is usually high pressure steam and is superheated. Furthermore, as the temperaturee of combustion gases is very high, most of this heat is also used to heat water to obtain steam, which is usually medium and low pressure steam. This steam is used to drive steam turbines to produce electricity. Specific designs vary, but modern designs essentially use steam to carry as much heat as economics allows. The temperature and pressure of the water vapor decrease after passing through the steam turbine, but the working principle of the steam turbine determines that the water vapor must still leave the steam turbine system. If this water vapor still has a use value, it will continue to be used. So the power plant actually has high pressure steam turbines, medium pressure steam turbines and low pressure steam turbines. After several operating phasesion, the energy that could be used to operate the steam turbine was virtually eliminated. But what comes out of the steam turbine system is still water. The steam still carries some heat inside. This heat must be removed through a heat exchange system to transform the low-pressure steam into water for recycling. The water used in the steam system is salt-free, specially treated water, which is very expensive and cannot be wasted. In other words, there is no gas left. The water vapor that has passed through the steam turbine is condensed and then recycled. Cooling water is generally used to further cool low pressure steam into liquid water. This cooling water is different from steam water. The requirements are much lower. Although there are certain index requirements, not all water can be used, but it is much simpler to process and its price est several times cheaper, so it can be wasted. Lost. The cooling water removes heat from the steam in the heat exchanger and the temperature of the cooling water increases. Generally, this temperature increase will not be very high, and a temperature increase of 10 degrees Celsius is relatively common. The temperature difference with the environment being too small, the energy of the water at this temperature is difficult to use. Indeed, we must find a way to lower the temperature of the cooling water so that it can be recycled (if it is sea water). is used at the beach, it is not necessary to pass it around). The cooling water tower, the tallest building in the plant, is used to cool this cooling water. The most common method is to take advantage of the large latent heat of water evaporation to lose water in the cooled water towerand remove heat, thereby lowering the cooling water to a usable temperature. This is where the main water consumption of thermal power plants is located.
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