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

Abstract

The disclosure provides a method and system for reducing the disturbance of the denitrification system caused by the start and stop of a double-inlet and double-outlet coal mill, which belongs to the technical field of automatic control of coal-fired power plants. The measurement accuracy of the capacity air volume makes the volume air volume more representative of the real fuel volume during the start-up and stop of the coal mill, which is conducive to the stable operation of the combustion system of the unit and reduces the fluctuation of the concentration of nitrogen oxides in the flue gas; through reasonable control of double inlet and double outlet The range and rate of change of capacity air volume and secondary air volume when the coal mill starts and stops reduces the disturbance intensity of combustion air volume and fuel volume fluctuations on combustion conditions; by reasonably controlling the ratio of capacity air volume and secondary air volume, it realizes The good match between the combustion air and the amount of fuel reduces the large fluctuations in the amount of oxygen in the flue gas, making the fluctuation range of the concentration of nitrogen oxides generated in the flue gas small and smooth, which is conducive to the stable operation of the denitrification system.

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...

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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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