CN206631437U - Suppress the control system that purging influences on thermal power plant's discharged nitrous oxides - Google Patents

Abstract

The utility model belongs to the technical field of nitrogen oxide emission control and relates to a control system for suppressing the influence of purging on the emission of nitrogen oxides in thermal power plants. The control system includes sequentially connected SCR reactors, DCS flue gas volume dynamic detectors, NO _x concentration variation calculation modules, differential integration modules, ammonia injection volume calculation modules and ammonia injection controllers, SCR reactors and NO _x A purge state signal monitor is arranged between the concentration variation calculation modules, and a first delay module is arranged between the DCS flue gas volume dynamic detector and the differential integration module. The system integrates the NO _x concentrations at the inlets of the A and B sides of the SCR reactor through the differential integration module, and when the inlet of the A side is purged, the change of the NO _x concentration of the inlet of the B side is added to the A side; When purging at the B-side inlet, the _NOx concentration change at the A-side inlet is added to the B-side, which can effectively prevent the rise of nitrogen oxides and ammonia escape caused by inaccurate _NOx measurement during the purge operation.

Description

A Control System for Suppressing the Impact of Purging on Nitrogen Oxide Emissions in Thermal Power Plants

technical field

The utility model belongs to the technical field of nitrogen oxide emission control, in particular to a control system for suppressing the influence of purging on the emission of nitrogen oxides in thermal power plants.

Background technique

Thermal power plants are one of the main sources of nitrogen oxide emissions. Nitrogen oxides are the basis for the formation of nitric acid rain, which is highly toxic and destructive to human health and the ecological environment. At present, flue gas denitrification is the most important method of nitrogen oxide treatment. The general denitrification control system first measures the actual flue gas volume, the _NOx content at the inlet and outlet of the flue gas, etc., and then calculates the required ammonia injection amount based on the preset denitrification efficiency. The calculated ammonia injection amount is consistent with the actual The ammonia flow rate is compared and used as the control command of the ammonia injection regulating valve to maintain the appropriate ammonia flow rate with a reasonable valve opening. Most of the existing SCR (Selective Catalytic Reduction, Selective Catalytic Reduction) denitrification technologies use _NOx (nitrogen oxide) analyzers as instruments for measuring _NOx , but the _NOx analyzers perform a purging action about every four hours. During the purging action, the _NOx analyzer can be regarded as no action, that is, it enters the "blind zone", and the _NOx content cannot be measured at this time, resulting in the inability of the entire denitrification system to accurately control the amount of ammonia injection, resulting in too little ammonia injection resulting in nitrogen oxides The content rises, and excessive ammonia injection leads to problems such as ammonia escape.

Utility model content

The purpose of this utility model is to aim at the deficiencies of the prior art, to provide a method that can effectively prevent the rise of nitrogen oxides and the escape of ammonia caused by inaccurate _NOx measurement during the purging action. Control system for the impact of pollutant emissions.

The technical scheme for solving the problem of the utility model is to provide a control system for suppressing the impact of purging on the discharge of nitrogen oxides in thermal power plants, including sequentially connected SCR (Selective Catalytic Reduction, selective catalytic reduction) reactors, DCS ( Distributed Control System (distributed control system) flue gas volume dynamic detector, NO _x concentration change calculation module, differential integration module, ammonia injection calculation module and ammonia injection controller, the SCR reactor and NO _x concentration change A purging state signal monitor is provided between the computing modules, a first delay module is provided between the DCS flue gas volume dynamic detector and the differential integration module, and the SCR reactor has an A-side inlet and a B-side inlet.

Further, a sub-delay module is provided between the first delay module and the differential integration module.

Further, the _NOx concentration variation calculation module includes a first selection module and a subtraction module connected to each other, and the first selection module is respectively connected to a purging state signal monitor and a DCS flue gas volume dynamic detector, and the The subtraction module is connected with the differential integration module.

Further, a second delay module is provided between the first selection module and the DCS smoke volume dynamic detector.

Further, the differential integration module includes an interconnected addition module and a second selection module, the addition module is connected to the _NOx concentration variation calculation module, and the second selection module is connected to the first delay module and the ammonia injection module respectively. Quantity calculation module is connected.

A control method for suppressing the impact of purging on nitrogen oxide emissions from thermal power plants, including the following steps:

Step 1: When there is no purge action at the A-side inlet and B-side inlet of the SCR reactor, the second delay module detects the NO of the A-side inlet and B-side inlet of the SCR reactor detected by the DCS flue gas volume dynamic detector The measured values of the _x concentration are filtered respectively, and the first selection module takes the filtered measured values of the NO _x concentration of the A-side inlet and the B-side inlet of the SCR reactor as input quantities respectively, and respectively obtains the NO _x of the A-side inlet before purging Concentration maintenance value and NO _x concentration maintenance value at B-side inlet before purging;

Step 2: Start the purge operation to purge the A-side inlet or B-side inlet of the SCR reactor. At this time, the first selection module will measure the filtered NO _x concentration of the side inlet of the SCR reactor that has the purge action. value as the input, and then the subtraction module subtracts the NO _x concentration maintenance value of the corresponding side inlet before purging from the filtered NO _x concentration measured value to obtain the NO _x concentration change of the corresponding side inlet;

Step 3: The differential integration module integrates the NO _x concentration of the A-side inlet and the B-side inlet of the SCR reactor respectively, and adds the change in the NO _x concentration of the B-side inlet to the A side when the A-side inlet is purging; When purging at the B-side inlet, the change in _NOx concentration at the A-side inlet is added to the B-side;

Step 4: Add the NO _x concentration of the A-side inlet of the integrated SCR reactor obtained in Step 3 as a feed-forward to the calculation of the ammonia injection amount of the A-side inlet, and use the B of the integrated SCR reactor obtained in Step 3 The NO _x concentration at the side inlet is added to the calculation of the ammonia injection amount at the B side inlet as feedforward, and the ammonia injection amount is corrected according to the load of the unit, and the ammonia injection controller adjusts the opening of the ammonia injection valve according to the corrected ammonia injection amount .

Further, in the step 3:

The method for integrating the NO _x concentration at the A-side inlet of the SCR reactor is: when the A-side inlet of the SCR reactor has no purge action, the second selection module selects the filtered NO _x measured at the A-side inlet of the SCR reactor value as the input quantity; when the A-side inlet of the SCR reactor has a purging action, the second selection module selects the sum of the A-side inlet _NOx concentration maintenance value of the SCR reactor and the B-side inlet _NOx concentration variation as the input quantity , to obtain the integrated value of NO _x concentration at the A-side inlet of the SCR reactor;

The method for integrating the NO _x concentration at the B-side inlet of the SCR reactor is: when there is no purge action at the B-side inlet of the SCR reactor, the second selection module selects the filtered NO _x measured at the B-side inlet of the SCR reactor value as the input quantity; when the B-side inlet of the SCR reactor has a purging action, the second selection module selects the sum of the B-side inlet _NOx concentration maintenance value of the SCR reactor and the A-side inlet _NOx concentration change as the input quantity , to obtain the integrated value of NO _x concentration at the B-side inlet of the SCR reactor.

Further, the calculation of the ammonia injection amount of the A side inlet in the step 4 includes the following steps:

4.1. Calculate the flue gas flow rate V at the A-side inlet of the SCR reactor, and the calculation formula is:

Among them, W is the total air volume of flue gas passed into the SCR reactor, the unit of W is t/h, and t/h means ton/hour;

4.2, Calculation of the _NOx mass flow in the flue gas flow V of the A-side inlet of the SCR reactor The calculation formula is:

Wherein, _C1 represents the integrated _NOx concentration at the A-side inlet of the SCR reactor, and _C2 represents the set value of the _NOx concentration at the outlet of the SCR reactor;

4.3, Calculate the mass flow rate of ammonia gas The calculation formula is:

4.4. Correct the amount of ammonia injection, the correction formula is:

in, Indicates the amended ammonia injection amount, F(x) is a broken line function, x represents unit load, and the output value of F(x) is obtained according to the data analysis of on-site unit load,

The calculation method of the ammonia injection amount to the B-side inlet of the SCR reactor is the same as the calculation method for the A-side inlet.

Further, in the step 4.3, the mass flow rate of ammonia Can also be converted to volume flow The conversion formula is:

The beneficial effects of the utility model are:

1. The control system described in this utility model overcomes the problem that the _NOx analyzer in the prior art denitrification control strategy is inaccurate during the purging process, which is likely to cause misoperation, resulting in increased nitrogen oxide emissions and ammonia escape. The control system described in the utility model can effectively suppress the impact of purging on nitrogen oxide emissions from thermal power plants;

2. The control system for suppressing the influence of purging on the emission of nitrogen oxides in thermal power plants described in the utility model can be implemented in various distributed control systems (DCS) of thermal power plants through configuration methods. The control system has been installed in a power plant Successfully used on #1 and #2 units (660MW);

3. After adopting the technology of the utility model, there is no obvious sudden change in the escape rate of nitrogen oxides and ammonia at the flue gas outlet during the purging operation, which effectively suppresses a series of effects caused by the purging operation and reduces the emission of pollutants.

Description of drawings

Fig. 1 is the schematic block diagram of the structure of the control system that suppresses purging to the influence of thermal power plant nitrogen oxide discharge described in the utility model;

Fig. 2 is a schematic flow chart of a method for integrating the NO _x concentration of the A-side inlet of the SCR reactor using the control system described in the present invention;

Fig. 3 is a schematic flowchart of a method for integrating the NO _x concentration at the B-side inlet of the SCR reactor using the control system of the present invention.

detailed description

Below in conjunction with accompanying drawing and specific embodiment, the utility model is described further.

As shown in Figure 1, a control system for suppressing the impact of purging on nitrogen oxide emissions in thermal power plants includes sequentially connected SCR reactors, DCS flue gas dynamic detectors, _NOx concentration change calculation modules, differential integration Module, ammonia injection amount calculation module and ammonia injection controller, a purging state signal monitor is arranged between the SCR reactor and the _NOx concentration change calculation module, the DCS flue gas amount dynamic detector and differential integration module There is a first delay module between them, and the SCR reactor has an A-side inlet and a B-side inlet.

A sub-delay module is arranged between the first delay module and the differential integration module.

The _NOx concentration variation calculation module includes a first selection module and a subtraction module connected to each other, and the first selection module is respectively connected to a purging state signal monitor and a DCS flue gas dynamic detector, and the subtraction module and The differential integration module is connected.

A second delay module is provided between the first selection module and the DCS smoke volume dynamic detector.

The differential integration module includes an addition module connected to each other and a second selection module, the addition module is connected to the _NOx concentration variation calculation module, and the second selection module is connected to the first delay module and the ammonia injection amount calculation module respectively connected.

As shown in Figure 2 and Figure 3, a control method for suppressing the impact of purging on nitrogen oxide emissions from thermal power plants includes the following steps:

Step 1: When there is no purge action at the A-side inlet and B-side inlet of the SCR reactor, the selection signal of the first selection module is 0. Since the measured values of NO _x at the inlets on both sides often have disturbances, the second delay of the inertial link As a filtering operation, the module filters the measured values of _NOx at the inlets on both sides, and the second delay module separately performs the measured values of the _NOx concentration at the A-side inlet and B-side inlet of the SCR reactor detected by the DCS flue gas volume dynamic detector. Filtering processing, the first selection module respectively takes the filtered _NOx concentration measured values of the A-side inlet and B-side inlet of the SCR reactor as input quantities, and respectively obtains the _NOx concentration maintenance value and the purging value of the A-side inlet before purging. NO _x concentration maintenance value at the front B-side inlet;

Step 2: Start the purge operation to purge the A-side inlet or B-side inlet of the SCR reactor, that is, after the purge signal of the A-side inlet and the B-side inlet of the SCR reactor pass through an OR operation module Then be connected with the first selection module, and now the selection signal of the first selection module is 1, and Fig. 2 shows that the A side inlet of the SCR reactor is purged, and Fig. 3 shows that the B side inlet of the SCR reactor is purged, At this time, the first selection module takes the filtered measured value of NO _x concentration at the inlet of the side of the SCR reactor with purging action as input, and then the subtraction module subtracts the measured value of the filtered NO _x concentration from the corresponding side before purging. The NO _x concentration maintenance value at the inlet can be used to obtain the NO _x concentration change at the corresponding side inlet;

Step 3: The differential integration module integrates the NO _x concentration of the A-side inlet and the B-side inlet of the SCR reactor respectively, and adds the change in the NO _x concentration of the B-side inlet to the A side when the A-side inlet is purging; When purging at the B-side inlet, the change in _NOx concentration at the A-side inlet is added to the B-side;

As shown in Figure 2, the method for integrating the NO _x concentration at the A-side inlet of the SCR reactor is: when there is no purge action at the A-side inlet of the SCR reactor, the selection signal of the second selection module is 0, and the second The selection module selects the filtered NO _x measured value of the A-side inlet of the SCR reactor as the input quantity; when the A-side inlet of the SCR reactor has a purge action, the selection signal of the second selection module is 1, and the second selection module selects The sum of the _NOx concentration maintenance value at the A side inlet of the SCR reactor and the _NOx concentration change at the B side inlet is used as the input amount to obtain the integrated _NOx concentration value at the A side inlet of the SCR reactor;

As shown in Figure 3, the method for integrating the NO _x concentration at the B-side inlet of the SCR reactor is: when there is no purge action at the B-side inlet of the SCR reactor, the selection signal of the second selection module is 1, and the second The selection module selects the filtered NO _x measured value of the B-side inlet of the SCR reactor as the input quantity; when the B-side inlet of the SCR reactor has a purge action, the selection signal of the second selection module is 1, and the second selection module selects The sum of the maintained value of _NOx concentration at the B-side inlet of the SCR reactor and the variation of the _NOx concentration at the A-side inlet is used as the input quantity to obtain the integrated value of the _NOx concentration at the B-side inlet of the SCR reactor.

Step 4: Add the NO _x concentration of the A-side inlet of the integrated SCR reactor obtained in Step 3 as a feed-forward to the calculation of the ammonia injection amount of the A-side inlet, and use the B of the integrated SCR reactor obtained in Step 3 The NO _x concentration at the side inlet is added to the calculation of the ammonia injection amount at the B side inlet as feedforward, and the ammonia injection amount is corrected according to the load of the unit, and the ammonia injection controller adjusts the opening of the ammonia injection valve according to the corrected ammonia injection amount .

In said step 4, the calculation of the injection amount of ammonia at the A side inlet comprises the following steps:

4.1. Calculate the flue gas flow rate V at the A-side inlet of the SCR reactor, and the calculation formula is:

Among them, W is the total air volume of flue gas passed into the SCR reactor, the unit of W is t/h, and t/h means ton/hour;

4.2, Calculation of the _NOx mass flow in the flue gas flow V of the A-side inlet of the SCR reactor The calculation formula is:

Wherein, _C1 represents the integrated _NOx concentration at the A-side inlet of the SCR reactor, and _C2 represents the set value of the _NOx concentration at the outlet of the SCR reactor;

4.3, Calculate the mass flow rate of ammonia gas The calculation formula is:

4.4. Correct the amount of ammonia injection, the correction formula is:

in, Indicates the amended ammonia injection amount, F(x) is a broken line function, x represents unit load, and the output value of F(x) is obtained according to the data analysis of on-site unit load,

The calculation method of the ammonia injection amount to the B-side inlet of the SCR reactor is the same as the calculation method for the A-side inlet.

In the step 4.3, the mass flow rate of ammonia

Can also be converted to volume flow The conversion formula is:

The utility model is not limited to the above-mentioned embodiments. Without departing from the essential content of the utility model, any deformation, improvement and replacement conceivable by those skilled in the art all fall within the protection scope of the utility model.

Claims (5)

1. The control system for suppressing the impact of purging on nitrogen oxide emissions in thermal power plants is characterized in that it includes sequentially connected SCR reactors, DCS flue gas volume dynamic detectors, _NOx concentration change calculation modules, differential integration modules, Ammonia injection amount calculation module and ammonia injection controller, a purge state signal monitor is installed between the SCR reactor and the _NOx concentration variation calculation module, and a dynamic detector of DCS flue gas amount and a differential integration module are arranged A first delay module is provided, and the SCR reactor has an A-side inlet and a B-side inlet. 2. The control system for suppressing the impact of purging on nitrogen oxide emissions in thermal power plants according to claim 1, characterized in that a sub-limiting module is arranged between the first delay module and the differential integration module. 3. the control system for suppressing purging according to claim 1 on the impact of thermal power plant nitrogen oxide emissions, characterized in that, the NO _x concentration variation calculation module includes a first selection module and a subtraction module connected to each other, so The first selection module is respectively connected with the purging state signal monitor and the DCS flue gas volume dynamic detector, and the subtraction module is connected with the differential integration module. 4. The control system for suppressing the impact of purging on nitrogen oxide emissions in thermal power plants according to claim 3, wherein a second time delay is provided between the first selection module and the DCS flue gas volume dynamic detector module. 5. the control system for suppressing purging according to claim 1 on the impact of nitrogen oxide emissions in thermal power plants, characterized in that, the differential integration module includes an interconnected addition module and a second selection module, and the addition module and the second selection module The _NOx concentration variation calculation module is connected, and the second selection module is connected with the first delay module and the ammonia injection quantity calculation module respectively.