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The comprehensive utilization technology of thermal power plant exhaust heat

1. The utilization technology of boiler steam-water circuit exhaust heat
The recycling utilization technology of boiler steam-water circuit exhaust heat contains two aspects: firstly, directly introduce boiler drainage into heater used for heating boiler feed water. This way is the conventional way of heat recycling with low use efficiency. Secondly, take use of the rest of the high grade heat energy in thermal power plant boiler drainage to work, then to drive the generator to produce electricity, and the output of the water vapor mixture is sent to the hot water station to produce heating or hot water for residents. This can make full use of recycling exhaust heat. The power generator here is a heat energy utilization system, which uses the exhaust heat of boiler drainage to heat screw expanding power generator, then through the coupling to drive the generator to generate electricity.
Water vapor mixture in high temperature after work, firstly goes into the machine’s female and male screw tooth groove A to make the screw to rotate, as the screw tooth rotates, tooth groove A gradually turns to position B, C and D, during this process the volume closed by the screw gradually increases, the hot water is depressed, cooled and expands to work, finally discharged from the back end of tooth E, and the rotating power generated by the work is outputted by male screw through the couplings to generators to drive the generator to produce electricity. Screw expansion generators has good adaptability ,which shows a better performance under the conditions of superheated steam, the mixture of saturated steam and high salt and low quality fluid, thus it can run well under the imbalanced conditions between the boiler drainage pressure fluctuation, temperature and flow rate, and can realize the unattended requirements.
2. The utilization technology of boiler exhausts system exhaust heat
The heat energy loss of exhaust fume accounts for 5%~12% of total thermal coal energy and 80% or higher of the total heat loss of boiler, so the flue gas exhaust heat loss of the tail of the boiler is the key point of the power plant exhaust heat utilization. Generally speaking, when the exhaust temperature rises every 10 ℃,the heat loss will increase 0.6% ~ 1.0%, which means coal consumption is increased 2 grams per kilowatt-hour.
In the thermal power plant operating in our country, the boiler exhaust smoke temperature is generally between 125 ℃ ~ 150 ℃, the heat loss of exhaust smoke with the high temperature turns to be one of the dilemmas countered by thermal power plants. At present, the main way to recycle this part of exhaust heat is to install flue gas cooler in exhaust system , through heat conduction medium such as air or water to transmit exhaust heat to the boiler feed water system or air intake system, to achieve the goal of energy saving by heating the combustion air and condensed water. However, when the flue gas is cooled, parts of acid corrosive gas in it such as SO2 will be condensate and will cause corrosive damages on pipes and other elements, so there are still many issues to be solved in practice.
In recent years, Europe and the United States begin to implement the flue gas deep cooler to sharply reduce the flue gas temperature, which reduced exhaust temperature from 190 ℃ to 90 ℃applied in Denmark showing a significant energy saving effect. The flue gas with high temperature going through cooler does heat exchange with the cold water in the internal finned tube bundle, to heat the water.
Separately arrange the cooler in accordance with the high and low temperature stage, and put high temperature stage before the dust precipitator and low-temperature stage after the dust precipitator, the cooler in high temperature stage before the dust precipitator can cool temperature down to about 120 ℃ to promote the efficiency of the dust precipitator behind, and make the dust removal effect better and energy consumption lower. As for the fiber bag precipitator, the flue gas with lower temperature can extend its service life. And cooler located behind the precipitator can deeply cool flue gas, and make the best of exhaust heat.
(1)boiler;(2)warm air blower;(3)air pre-heater(4)flue cooler(5) electrostatic precipitator (6) flue cooler(7) thionizer(8)anti-acid pump(9) wet stack
The exhaust heat recycle unit using cooler arrangement strategy is mainly used in the following three conditions: firstly, the new construction, which is sensitive to flue gas temperature, using the fiber bag precipitator ; secondly, the reconstruction project using booster fan of about 400 Pa margin and dust precipitator inlet air temperature is between 130 ℃ ~ 150 ℃ or higher; Thirdly, the reconstruction project using booster fan of about 400 Pa margin and space behind the dust precipitator is not enough to install the high and low temperature integral cooler, and flue gas temperature is about 130 ℃.
In addition to the above arrangement ways, the high and low temperature stage of the cooling device can be arranged after the dust precipitator in a whole or separately be arranged after the dust precipitator which depends on the actual situation and specific requirements to gain the optimum effect in the comprehensive utilization of exhaust heat, to achieve the purpose of saving energy and reducing consumption and controlling cost.