SCR (selective catalytic reduction) denitration system control method for preventing urea from being excessively sprayed

Abstract

The invention discloses an SCR (selective catalytic reduction) denitration system control method for preventing urea from being excessively sprayed. The method comprises the following steps: step 1, detecting nitrogen oxide concentration at a gas outlet, entering a PID (photoionization detector) mode if the value of the concentration is less than a set value, or else entering step 2; step 2, controlling a spraying speed of the urea, enabling the spraying speed to increase along with the increase of time, detecting the nitrogen oxide concentration at the gas outlet, entering the PID mode if thenitrogen oxide concentration is reduced along with the increase of time, or else entering step 3; step 3, reducing urea spraying speed, detecting the nitrogen oxide concentration at the gas outlet until the nitrogen oxide concentration is less than the set value of the concentration, and then entering the PID mode. By open-loop control and closed-loop PID mode combination control, the excessive spraying state of the urea can be corrected, so that the control mode can always be controlled towards a set minimum nitrogen oxide concentration direction, and the nitrogen oxide concentration is prevented from continuously abnormally rising.

Description

technical field [0001] The invention belongs to the technical field of chemical industry, relates to SCR denitrification technology, in particular to a control method of an SCR denitrification system for preventing excessive injection of urea. Background technique [0002] SCR denitrification is currently the most mature flue gas denitrification technology. It is a post-furnace denitrification method that uses the reducing agent NH3 or urea to selectively react with NOx to generate N2 and H2O under the action of a metal catalyst. The world's popular SCR processes are mainly divided into two types: ammonia-based SCR and urea-based SCR. These two methods both use the reducing function of ammonia to NOx, and under the action of catalyst, NOx (mainly NO) is reduced to N2 and water which have little impact on the atmosphere, and the reducing agent is NH3. The SCR method has high denitration efficiency and relatively low price. It is widely used in domestic and foreign projects a...

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Problems solved by technology

However, due to the particularity of the urea solution, that is, too much sprayed and atomized urea will lead to oversaturation of the reaction substances, and the nitrogen oxides will not react completely, making the nitrogen and oxygen concentration measured by the sensor higher and the input deviation greater. like figure 1 As shown, there is a turning point in the curve of urea injection speed and nitrogen oxide concentration. In the case of excessive injection of urea, the PID feedback control technology is difficult to achieve the control purpose

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