The system of automatic control of the cleaning process of combustion products oxides of nitrogen limitation in the concentration of ammonia in the treated gases

 

(57) Abstract:

The invention relates to the field of process automation chemical cleaning combustion gases from nitrogen oxides. The system contains a nonlinear element, which is made taking into account the functional relationship between the load and the gross emissions of NOx. It is located between the Executive controller reagent supply and the sensor signal on the load of the boiler. The main adjustment knob through the adder is connected to the sensor signal on the concentration of NOxin the treated gas and the nonlinear element. The source of additional corrective signal is made in the form of additional corrective controller connected to the sensor, the concentration of NH3in the treated gases. The switch is made off, one input connected to the output of the main adjustment knob, the other to the output of the additional adjustment of the regulator, the output of the switch is to the Executive controller, and the switching element of the switch is connected with relay element having trip setting for connecting to the Executive additional regulator adjustment knob when the limit value 3in the treated gases to an acceptable level. Using this system gives the possibility of increasing the efficiency of automatic control of the cleaning process of combustion products oxides of nitrogen effective to limit leakage of ammonia. 1 Il.

The invention relates to the field of chemical cleaning products of combustion and can be used to automate the process of purification from nitrogen oxides by non-catalytic recovery of the last reagent in the form of ammonia or compounds that form ammonia by thermal decomposition.

The closest to the essential features analogue (prototype) of the invention can serve as a well-known automatic cascade control of the cleaning process of combustion products oxides of nitrogen (NOxin the boiler furnace, carried out by non-catalytic recovery NOxthe reagent in the form of ammonia (NH3or compounds forming NH3during thermal decomposition, containing the Executive controller reagent supply connected to the sensor signal on the load of the boiler and the sensor signal according to the flow rate of the reagent, the main adjustment knob to the restriction of NOxtreated the switch for a step change of the correction signal and the nonlinear element [1]. In this system, a source of additional corrective signal for restricting leakage of NH3to produce this signal, on the basis of empirical depending on the load of the boiler under different temperature intervals gases in the reaction zone of interaction of NH3with NOxwhich are changed by dispensing the reagent in the respective levels of the flue. The switch is set on the line of impact on additional corrective signal averaged temperature at all levels of dispensing reagent for step control, the scale of the acting signal depending on the load, the flow rate of the reagent and reverse signal according to the sum of the magnitude of temperature effects. Additional corrective signal for restricting leakage of NH3is summed with the signal from the main adjustment knob to the restriction of NOxand goes with him to the input of the Executive controller.

The main drawback of this solution is weak effect adjustment signal overshoot of NH3since , for all conditions, the main corrective signal of the control signal remains at a concentration in the treated gas NOxwhich is Ustilago breakthrough NH3. However, ammonia, interacting with the audience in gases with sulfur trioxide SO3leads to the deposition of ammonium salts on the heater of the boiler, which significantly affects its performance. In addition, ammonia itself is quite toxic, and therefore the release into the environment should be limited. Additional corrective influence to restrict leakage of NH3in the known system is not in a direct way and indirect indicators, which complicates the circuit and does not provide sufficiently reliable results.

Achieved results of the present invention is to improve the efficiency of automatic control of the cleaning process of combustion products oxides of nitrogen effective to limit leakage of ammonia.

This is provided by the fact that the automatic cascade control of the cleaning process of combustion products oxides of nitrogen (NOx) in the boiler furnace, carried out by non-catalytic recovery NOxthe reagent in the form of ammonia (NH3or compounds forming NH3during thermal decomposition, containing Executive supply regulator reagent, SOEDINENIYa to the restriction of NOxin the treated gas, a source of additional corrective signal for restricting leakage of NH3in the cleaned gases, switch to a step change of the correction signal and a nonlinear element according to the invention the non-linear element is made taking into account the functional relationship between the load and the gross emissions of NOxand is located between the Executive controller reagent supply and the sensor signal on the load of the boiler, the main adjustment knob through the adder is connected to the sensor signal on the concentration of NOxin the treated gas and a nonlinear element, a source of additional corrective signal is made in the form of additional corrective controller connected to the sensor, the concentration of NH3in the treated gas, the switch is made off, one input connected to the output of the main adjustment knob, the other to the output of the additional adjustment of the regulator, the output of the switch is to the Executive controller, and the switching element of the switch is connected with relay element having trip setting for connecting to the Executive controller additional corrective controller gulator at lower concentrations of NH3in the treated gases to an acceptable level.

The drawing is a schematic diagram of the automatic control system.

It contains the Executive controller 1 reagent supply connected to the sensor 2 signal on the load of the boiler and sensor 3 signal flow of the reagent, the main adjustment knob 4 to the restriction of NOxin the treated gas, a source of additional corrective signal for restricting leakage of NH3in the cleaned gases and the switch 6 for a step change of the correction signal. The main adjustment knob 4 is connected to the sensor 5 signal on the concentration of NOxin the treated gas and the sensor 2 signal on the load of the boiler. The source of additional corrective signal overshoot NH3made in the form of additional corrective controller 7 connected to the sensor 8 concentrations of NH3in the treated gases. Sensor 2 signal on the load connected to the controllers 1 and 4 through the nonlinear element 9, taking into account the functional relationship between the load and the gross emissions of NOx. Switch 6 dip made, one of its input 10 is connected to the output of the main corrective regulated 12 switch - the Executive controller 1, and the switching element 13 of the switch is connected with relay element 14, with trip setting for connecting to the Executive controller 1 additional adjustment of the controller 7 when the limit is reached, the concentration of NH3in the treated gas and the main adjustment knob 4 by reducing the concentration of NH3in the treated gases to an acceptable level. The output of the nonlinear element 9 and the sensor 5 signal on the concentration of NOxin the treated gases are connected to the main adjustment to the controller 4 through the adder 15. The output of the Executive controller 1 is connected with the mechanism for changing the flow area of the valve 16 in line 17 of injection into the furnace (not shown). The Executive controller 1 and the adjustment knobs 4, 7 provided with a setting device, respectively, 18, 19, 20 of the controlled values of the adjustable parameters.

The automatic control system is as follows.

In native mode Executive knob 1 affects the mechanism changes the flow area of the valve 16 under the influence of three signals: the signal from the sensor 2 to the load of the boiler to be converted to the ligature from the sensor 3 and the flow rate of the reagent and the signal from the main adjustment knob 4, support within the specified limits total emissions of NOx. Additional adjustment knob 7 to limit leakage of NH3in this mode the Executive knob 1 is turned off, but the sensor 8 concentrations of NH3in the treated gases through relay element 14 is in parallel with the switching element 13 of the switch 6. Upon reaching the maximum allowable concentrations of NH3relay element 14 moves the switching element 13 input 10 input 11 with the transfer of the Executive controller 1 to the signal from the additional adjustment of the regulator 7. However, regardless of the gross emissions of NOxregulation of injection is made only from conditions against exceeding limit values of leakage into the environment NH3more toxic than NOx. After reducing the concentration of NH3in the treated gases to a predetermined permissible value, the automatic switching of the Executive knob 1 to work with the main corrective signal maintenance mode within the specified limits of the gross emissions of NOx.

Sources of information

1. Von N.-N. Voje, C. Fisher, G. Mittelbach. Inbetrriebnahne-und Betriebserfahrungen mit SNCR-Anla is the process of purification of the products of combustion from oxides of nitrogen (NOxin the boiler furnace, carried out by non-catalytic recovery NOxthe reagent in the form of ammonia (NH3or compounds forming NH3during thermal decomposition, containing the Executive controller reagent supply connected to the sensor signal on the load of the boiler and the sensor signal according to the flow rate of the reagent, the main adjustment knob to the restriction of NOxin the treated gas, a source of additional corrective signal for restricting leakage of NH3in the cleaned gases, switch to a step change of the correction signal and the nonlinear element, wherein the nonlinear element is made taking into account the functional relationship between the load and the gross emissions of NOxand is located between the Executive controller reagent supply and the sensor signal on the load of the boiler, the main adjustment knob through the adder is connected to the sensor signal on the concentration of NOxin the treated gas and a nonlinear element, a source of additional corrective signal is made in the form of additional corrective controller connected to the sensor, the concentration of NH3in the treated gas, the switch is made of duchosal the corrective controller, the output of the switch is to the Executive controller, and the switching element of the switch is connected with relay element having trip setting for connecting to the Executive additional regulator adjustment knob when the limit is reached, the concentration of NH3in the treated gas and the main adjustment knob at lower concentrations of NH3in the treated gases to an acceptable level.

 

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