SCR flue gas denitration optimization control system and method based on ammonia spraying amount compensator

Abstract

The invention discloses an SCR flue gas denitration optimization control method based on an ammonia spraying amount compensator. The method comprises the following steps of 1, determining variables related to the flue gas NOx generation and the outlet NOx concentration of an SCR reactor in a coal-fired unit and an SCR system; 2, acquiring related variable data in the step 1 from a DCS system; 3, performing input variable time delay estimation of a model by utilizing a fuzzy curve method, so that a sample after phase space reconstitution is obtained; 4, building an outlet NOx concentration dynamic prediction model according to the sample after the phase space reconstitution in the step 3, obtaining an outlet NOx concentration prediction value of the SCR reactor, and correcting the outlet NOx concentration dynamic prediction model according to an actual value of the field outlet NOx concentration; and 5, according to the outlet NOx concentration prediction value of the SCR reactor, obtained in the step 4, converting a deviation between the outlet NOx concentration prediction value of the SCR reactor and a set value into an ammonia spraying amount, timely compensating the ammonia spraying amount, and controlling the opening degree of an ammonia spraying valve to ensure that the outlet NOx concentration is stabilized to be the set value.

Description

technical field [0001] The invention relates to the technical field of flue gas denitrification of coal-fired units, in particular to an SCR (Selective Catalytic Reduction, Selective Catalytic Reduction) flue gas denitrification optimization control system and method based on an ammonia injection compensator. Background technique [0002] With the increasingly prominent problem of air pollution, the emission of air pollutants from thermal power units in my country has been strictly regulated. At present, the nitrogen oxides (nitrogen oxides, NO x ) emissions from the current 200mg / m 3 (100mg / m in key areas and new units 3 ) to 50mg / m 3 Below, reach ultra-low emission targets. traditional low NO x Combustion control is difficult to meet the emission standards, and it needs to cooperate with the tail flue gas denitrification device. SCR (selective catalytic reduction, selective catalytic reduction) flue gas denitrification technology has been widely used at home and abroa...

AI Technical Summary

Problems solved by technology

traditional low NO x Combustion control is difficult to meet the emission standards, and it needs to cooperate with the tail flue gas denitrification device. SCR (selective catalytic reduction, selective catalytic reduction) flue gas denitrification technology has been widely used at home and abroad, the most important of which is the control of the ammonia injection system.

When the working conditions are stable, ammonia injection control can usually achieve better results; but when the unit operating conditions change, such as coal type replacement, unit AGC load command frequent fluctuations, combustion conditions (such as air distribution mode, excess air coefficient, etc.) The change will make the flue gas NO x There are large disturbances, so there are many influencing factors in the SCR system, and the SCR reaction is easily affected by the activity of the catalyst, and the system shows the characteristics of nonlinearity and strong disturbances

Moreover, the SCR reaction itself needs a certain reaction time, and the NO x The measurement device usually has a sampling distance of more than 20 meters, which leads to the hysteresis of the measurement, which makes the SCR system show the characteristics of large inertia and large delay

The amount of ammonia injection is difficult to ensure the best NH 3 / NO x Compare

When too little ammonia is injected, it is easy to cause NO x Emissions increase or even exceed the standard; and excessive ammonia injection will not only affect the denitrification efficiency, but also cause excessive ammonia and SO in the flue gas 3 The reaction produces ammonium bisulfate and ammonium sulfate, which reduces the activity of the catalyst, causes dust accumulation and corrosion in the air preheater, and affects the safe operation of the boiler. At the same time, the increase in ammonia escape also causes waste of operating costs and secondary environmental pollution.

Due to the complex reaction process of the SCR system, the existing PID control is difficult to achieve a good control effect

[0003] It can be seen from the above that due to the complex reaction process of the current SCR flue gas denitrification system, especially when the working conditions change, it has nonlinearity, large inertia, large delay, strong disturbance and time-varying

At present, the conventional ammonia injection control system adopts a single-loop PID controller or a cascade PID controller with a feed-forward signal, but the PID control is not suitable for a large delay and large inertia system; and the inaccurate measurement of the flue gas flow rate causes NO x The total amount is inaccurate, which leads to poor control effect of the ammonia injection amount of the system, which affects the safe operation of the unit and the denitrification efficiency

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