Method and system for reducing disturbance of start and stop of double-inlet and double-outlet coal mill to denitration system

Abstract

The invention provides a method and system for reducing disturbance of start and stop of a double-inlet and double-outlet coal mill to a denitration system, and belongs to the technical field of automatic control of coal-fired power plants. The influence of coal level change of the coal mill on the capacity air volume is corrected, so that the measurement precision of the capacity air volume is improved, the capacity air volume can better represent the real fuel quantity during start and stop of the coal mill, stable operation of a unit combustion system is facilitated, and fluctuation of theconcentration of nitrogen oxides in flue gas is reduced; the change range and the change rate of the capacity air volume and the secondary air volume during start and stop of the double-inlet and double-outlet coal mill are reasonably controlled, so that the disturbance intensity of fluctuation of the combustion-supporting air volume and the fuel quantity to the combustion working condition is reduced; and the ratio of the capacity air volume to the secondary air volume is reasonably controlled, so that good matching of the combustion-supporting air and the fuel quantity is realized, large fluctuation of the oxygen content in the flue gas is reduced, the concentration fluctuation range of the nitrogen oxides generated in the flue gas is small, the change is gentle, and stable operation ofthe denitration system is facilitated.

Description

technical field [0001] The disclosure relates to the technical field of automatic control of coal-fired power plants, and in particular to a method and system for reducing the disturbance to the denitrification system caused by the start and stop of double-inlet and double-outlet coal mills. Background technique [0002] The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art. [0003] The units using the double-inlet and double-outlet pulverizer direct blowing pulverization system need to start and stop the coal mill frequently to change the amount of fuel entering the furnace when operating in a wide range of variable loads. During the start and stop of the coal mill, due to the large fluctuations and fast fluctuations of the volumetric air volume (or called the primary air volume carrying pulverized coal) and the combustion air volume (or called the secondary air volume) entering t...

AI Technical Summary

Problems solved by technology

However, when the double-inlet and double-outlet coal mill starts and stops, it also produces a very large disturbance to the concentration of nitrogen oxides in the flue gas, and no specific solution is given; at the same time, for starting the coal feeder and coal mill The process of establishing the capacity air volume during the transition period of the normal coal level is estimated by the simulation method without considering the actual change process of the coal level. This method will cause a large deviation between the estimated capacity air volume and the actual fuel volume entering the furnace, resulting in Parameters such as the main steam pressure of the unit and the concentration of nitrogen oxides in the flue gas produce large disturbances

There are also researchers who have proposed a medium-speed coal mill start-stop control method based on coal online compensation. The amount of coal in the boiler remains unchanged, and in view of the different characteristics of the influence of the start and stop of coal mills in different layers on boiler combustion, the coal amount compensated online during the start and stop of coal mills in different layers is corrected to reduce the impact of coal mill start and stop on boilers. Combustion disturbance, but it only compensates the amount of coal that enters the boiler during the start and stop of the coal mill, improves the calculation accuracy of the coal involved in combustion, and reduces the fluctuation of coal amount during the start and stop of the coal mill. Take corresponding measures for the large fluctuation of nitrogen oxides in the flue gas caused by the start and stop of the coal mill

[0005] The inventors of the present disclosure have found that most of the existing technologies only make reasonable corrections and compensations for the capacity air volume or fuel volume. The amount of coal does not match, resulting in oxygen-enriched combustion or oxygen-deficient combustion of pulverized coal, which in turn causes a sharp fluctuation of nitrogen oxides in the flue gas, forming a very large disturbance to the denitrification system; There is a sudden change in the manual adjustment, especially when the initial coal amount and the increase rate are too large when the coal feeder is started, resulting in a sudden change in the concentration of nitrogen oxides in the flue gas. Due to the common problem of measurement data lag in nitrogen oxide measuring instruments, The ammonia injection automatic adjustment system has no time to increase or decrease the amount of ammonia, resulting in large fluctuations in the concentration of nitrogen oxides in the flue gas after denitrification, which further leads to large fluctuations in the amount of ammonia injection. The strong disturbance of the denitrification system caused by the start and stop of the machine

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