Device and method for realizing full-load denitration of thermal power generating unit

Abstract

The invention discloses a device for realizing full-load denitration of a thermal power generating unit. A full-load period includes the stages of a unit grid connection stage, a unit grid connection to low-load stage, a daily dispatching range stage, a low-load stage to the unit stop disconnection process. The device comprises a boiler, a high-pressure heater bank, adjacent steam turbine generator units, a flue gas bypass and a newly-increased final-stage high-pressure heater, the boiler is connected with an SCR (selective catalytic reduction) reaction area through an SCR inlet flue duct, the flue gas bypass is parallelly connected onto the SCR inlet flue duct from a coal economizer entrance of the boiler or a previous heating surface, and an air door baffle is arranged on the flue gas bypass. The device is adapted to SCR denitration systems and can completely operate at various load stages, and NOx (nitrogen oxide) emission of the thermal power generating unit is reduced and meets relevant national emission standards.

Description

technical field [0001] The invention relates to the field of power plants, in particular to a device and method for realizing full-load denitrification of a thermal power unit. Background technique [0002] At present, domestic thermal power plants widely use Selective Catalytic Reduction (SCR) denitrification technology to control the emission of nitrogen oxides (NOx). The flue gas temperature in the SCR reactor is generally designed to be between 320°C and 420°C, because when the flue gas temperature is between 340°C and 380°C, the activity of the catalyst active material is the highest, and the catalytic reduction reaction efficiency is the highest. When the temperature of the flue gas is lower than 320°C, the ammonia gas used for the reaction will react with the SO3 in the flue gas to form ammonium sulfate and ammonium bisulfate. wear and tear, reducing the activity of the catalyst; when the temperature of the flue gas entering the SCR reactor is lower than 320°C, the S...

AI Technical Summary

Problems solved by technology

[0008] (1) Since the flue gas flows away from the economizer bypass, the feed water cannot be fully heated, which will inevitably reduce the thermal efficiency of the boiler and increase the coal consumption

[0009] (2) The performance requirements for the bypass flue baffle are relatively high. If the bypass baffle cannot be closed after being opened, the temperature of the flue gas entering the SCR reactor will be overheated under high load, which will easily cause catalyst sintering. In addition, Furnace efficiency drops due to flue gas leakage

[0010] (3) Increasing the flue gas bypass cannot meet the requirement that the flue gas temperature reach the minimum denitrification temperature limit from the unit grid connection to the low load area. Therefore, the grid connection to the low load denitrification device needs to be out of operation

[0014] (1) Since the heat transfer coefficient of the feed water is much lower than that of the flue gas, the temperature of the flue gas entering the SCR reactor can be increased through the feed water bypass, but the effect is not obvious, far worse than that of the economizer flue gas bypass

Therefore, the low-load denitration device cannot be put into operation

[0015] (2) Due to the reduction of the feed water entering the economizer, the temperature of the feed water at the outlet of the economizer will increase. In extreme cases, the feed water at the outlet of the economizer will be gasified and the economizer will be burned

[0016] (3) Due to the existence of the feedwater bypass of the economizer, the heat exchange effect of the feedwater is reduced, and the exhaust gas loss is increased

[0022] (1) The limitations are large. At present, there are few units designed and equipped with air supply valves in China. Only Siemens’ million units and 660MW supercritical units have this equipment. There is no supplementary air valve for millions of units, so this technology can only be used on about 10% of my country's installed capacity

[0023] (2) Cancellation of the original function of the air supply valve reduces the frequency regulation capability of the unit

[0025] (4) The cost of transformation is high. Due to the high parameters of the steam extracted by the air supply valve, the pipes and valves used in the system are expensive, and the design and manufacture of the zero-level high-pressure device are difficult. If the system has a heat exchange device, it uses high-alloy steel materials, and the cost is relatively high high

[0026] (5) The operation of the system is complicated. Because the system adopts the zero-level high addition, the original design distribution principle of the water supply system is broken, the heater end difference is large, and the pressure drop of the system at low load is particularly large, which cannot reach the design capacity. Moreover, the noise in the pipeline is particularly high, and the safety risk is great

Based on the above-mentioned method of increasing the flue gas temperature, it is actually impossible to achieve the denitrification of the unit at each load stage. Those skilled in the art are all committed to the development of full-load denitrification technology.

Images