Selective catalytic reduction (SCR) denitration system and method based on constraint predictive control

Abstract

The invention discloses a selective catalytic reduction (SCR) denitration system and method based on constraint predictive control. The flow of injected ammonia of the SCR denitration system is controlled by utilizing a predicting-proportioning cascade control policy; the flow of the injected ammonia is regulated by predicting the future change tendency of the concentration of NOx at an outlet of an SCR reactor and regulating the opening degree of an ammonia injection valve in advance; therefore, the defects of large inertia and delay of the SCR denitration system can be greatly overcome, the response speed of ammonia injection amount control to unit load change is increased, and the dynamic regulation quality of the SCR denitration system is improved; under the constraint predictive control, practical constrains, such as upper and lower constrains of valve opening degree, valve operation speed constrain and outlet NOx concentration constrain, are simultaneously considered and are used in parallel, so that the fact that the system performance is influenced due to saturation of execution mechanisms is avoided; based on ensuring the fact that the concentration of the NOx at the outlet reaches a target value, the ammonia injection amount is reduced as much as possible, and the operation cost and the ammonia escape rate are effectively reduced.

Description

technical field [0001] The invention belongs to the field of thermal automatic control, in particular to a selective catalytic reduction (SCR) denitrification system and method. Background technique [0002] The emission treatment of nitrogen oxides is of great significance to environmental pollution control and economic operation of coal-fired power plants. Among many flue gas denitrification schemes, the SCR method has the highest denitrification efficiency and is reliable in operation without secondary pollution. It is currently one of the most widely used and mature flue gas denitrification technologies at home and abroad. [0003] There are usually two ways to control the flow of ammonia gas in the SCR reactor: fixed molar ratio control mode (standard control mode) and outlet NO X Fixed value control mode. Among them export NO X The fixed value control method is to keep the export NO X Constant, according to ambient air quality standards, control reactor NO X It is...

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Problems solved by technology

Therefore, the SCR denitrification system is also one of the more difficult systems to control. There are two main reasons: one is that the SCR denitrification system has relatively large inertia and delay. differential) cascade control scheme, it is often difficult to achieve satisfactory control effects; in addition, in order to ensure that the NOx concentration at the outlet of the SCR reactor will not exceed the standard when the load of the unit changes frequently, the target value of the outlet NOx concentration is usually set low, and the amount of ammonia injection is relatively low. Large, high ammonia escape rate, easy to cause corrosion and blockage of downstream equipment, difficult to ensure the economy and safety of power plant operation

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