SCR (Selective Catalytic Reduction) denitration control system and control method for aluminum melting furnace

Abstract

The invention belongs to the technical field of SCR denitration, and particularly relates to an aluminum melting furnace SCR denitration control system and method. The urea solution or the ammonia water is accurately controlled by adopting the micro-flow metering pump, the precision problem of a conventional regulating valve and a flow meter on micro-flow control is solved, the stroke frequency and the impact weighing of the micro-flow metering pump are controlled through the main control system, PID control is interlocked with NOX at the outlet of the low-temperature SCR reactor, and the low-temperature SCR reactor outlet is controlled. The emission of NOX can be accurately controlled within a standard range, and the denitration effect and the environmental protection performance are effectively improved. The main control system controls the flame length and the flame size of the first combustor according to the flue gas temperature and the flue gas flow speed, so that the flue gas leading to the low-temperature SCR reactor reaches the first target temperature, the problem that the catalytic reaction effect is affected due to the fact that the temperature of the flue gas entering the low-temperature SCR reactor is too low is solved, and it is guaranteed that the denitration reaction is conducted smoothly.

Description

Technical Field

[0001] The present invention belongs to the technical field of SCR denitration, and particularly relates to a SCR denitration control system and a control method for an aluminum melting furnace. Background Art

[0002] In the SCR denitration control system, the conventional control method for the transportation of urea solution or ammonia water is to adopt a control mode combining a delivery pump, a regulating valve, a flowmeter, etc., to send the urea solution or ammonia water into the urea pyrolysis device or the evaporation device. The urea solution or ammonia water generates ammonia gas through the urea pyrolysis device or the evaporation device, and the ammonia gas then enters the ammonia injection grid for ammonia injection. The regulating valve and the flowmeter adopt PID control, and then according to the NO X concentration value at the outlet of the SCR reactor, the opening of the regulating valve is controlled to achieve the accurate supply of the urea solution or ammonia water. This method is applicable to conventional flow control. Due to the accuracy problems of the regulating valve and the flowmeter, it is very difficult for micro-flow control.

[0003] Meanwhile, ammonia gas preparation usually adopts urea hydrolysis or urea pyrolysis to produce ammonia gas. Urea hydrolysis requires water sources such as steam and demineralized water, and urea pyrolysis requires electric heating or high-temperature gas heating. These two methods consume a large amount of electricity and gas. In some occasions, without high-temperature gas, sufficient electric energy, demineralized water and other resources, urea hydrolysis and urea pyrolysis cannot realize the normal operation of the low-temperature SCR denitration system.

[0004] In addition, in the low-temperature SCR denitration system, the flue gas temperature entering the denitration reactor is usually very low, only about 100 degrees Celsius, while the normal low-temperature denitration temperature requires about 230 degrees Celsius, which cannot meet the temperature required for low-temperature SCR denitration, thereby affecting the denitration effect.

[0005] Therefore, there is an urgent need for a brand-new SCR denitration control system and a control method for an aluminum melting furnace to effectively solve the problems of inaccurate control of urea solution or ammonia water in the existing SCR denitration system and poor denitration effect caused by factors such as temperature and resources, so as to improve the overall performance and applicability of the low-temperature SCR denitration system.

[0006] In view of this, the present invention is specifically proposed. Summary of the Invention

[0007] The purpose of the present invention is to overcome the above-mentioned disadvantages of the prior art and provide a SCR denitration control system and a control method for an aluminum melting furnace.

[0008] To achieve the above purpose, the present invention provides the following technical solutions:

[0009] On the one hand, the present invention provides an SCR denitration control system for an aluminum melting furnace, including a main control system, and a flue gas heating device, a urea solution or ammonia water conveying device, a urea solution or ammonia water pyrolysis device, an interlock control system, and a first safety protection control system controlled by the main control system;

[0010] The main control system controls the flue gas heating device, and according to the flue gas temperature (80 - 110 °C) and the flue gas flow rate (9 - 14 m / s), controls the flame length and flame size of the first burner of the flue gas heating device, so as to control the flue gas leading to the low-temperature SCR reactor to reach the first target temperature (210 - 280 °C);

[0011] The main control system controls the urea solution or ammonia water conveying device to adjust the flow rate of the pyrolyzed urea solution or ammonia water in real time. The control of the urea solution or ammonia water conveying device uses a micro flow metering pump to accurately convey the urea solution or ammonia water. By controlling the stroke number and stroke weight of the micro flow metering pump through the main control system, accurate control is achieved. The main control system collects the NO X concentration at the outlet of the low-temperature SCR reactor in real time, and realizes the interlock PID control (interlock PID control: calculates the control signal according to the error between the set value and the actual value) of the stroke number of the micro flow metering pump and the NO X at the outlet of the low-temperature SCR reactor, and controls the NO X emission within the standard range;

[0012] The main control system controls the urea solution or ammonia water pyrolysis device, and uses the second burner of the urea solution or ammonia water pyrolysis device to pyrolyze the urea solution or ammonia water, and controls the temperature of the ammonia gas generated by pyrolysis to the second target temperature (280 - 450 °C) required for the reaction of the low-temperature SCR reactor; that is, the urea solution or ammonia water is conveyed to the gun inlet through a metering pump, atomized by the gun and enters above the flame of the second burner of the urea solution or ammonia water pyrolysis device, and the urea solution or ammonia water is heated and decomposed into ammonia gas by the flame, and then the ammonia gas reaching the second target temperature is sent into the low-temperature SCR reactor for denitration reaction. At the same time, the ratio of natural gas to combustion-supporting air is controlled to control the flame size and flame length; the urea solution or ammonia water conveying device is connected to the urea solution or ammonia water pyrolysis device;

[0013] The main control system controls the interlock control system, which is used for the interlock PID control of the flue gas heating device with the urea solution or ammonia water pyrolysis device and the urea solution or ammonia water conveying device. According to the flue gas temperature, the urea solution or ammonia water pyrolysis device and the urea solution or ammonia water conveying device are started, and the flow rate of the urea solution or ammonia water conveyed during pyrolysis is controlled according to the NO X concentration at the outlet of the low-temperature SCR reactor;

[0014] The main control system controls the first safety protection control system, which is used to feed back various safety operation parameters obtained by real-time monitoring of the low-temperature SCR denitrification system of the aluminum melting furnace to the main control system. The main control system decides whether to stop the operation of the low-temperature SCR denitrification system of the aluminum melting furnace based on the obtained safety operation parameters.

[0015] Specifically, the flue gas heated by the flue gas heating device and the ammonia generated by the urea solution or the ammonia water pyrolysis device are both directed to the low-temperature SCR reactor for denitration reaction.

[0016] Specifically, the main control system collects the flue gas temperature before heating in real time, and controls the flame length and flame size of the first burner according to the flue gas temperature and flue gas flow rate; after the flue gas temperature after heating reaches the first target temperature, the main control system controls the urea solution or ammonia water pyrolysis device and the urea solution or ammonia water delivery device to start, and controls the ammonia obtained after pyrolysis to the second target temperature required for the reaction of the low-temperature SCR reactor.

[0017] Specifically, the urea solution or ammonia water delivery device uses a micro-flow metering pump to accurately deliver the urea solution or ammonia water.

[0018] Specifically, the low-temperature SCR denitrification control system of the aluminum melting furnace also includes a second safety protection control system controlled by the main control system. The second safety protection control system monitors the ammonia concentration of the urea solution or ammonia water pyrolysis device and the carbon monoxide concentration of the flue gas heating device respectively. If the ammonia concentration or the carbon monoxide concentration exceeds the safety value, the main control system will alarm, or the main control system will control the shutdown of the second burner or the first burner.

[0019] Furthermore, when the ammonia concentration or carbon monoxide concentration exceeds the safety value, the main control system controls the combustion-supporting air in the urea solution or ammonia pyrolysis device to purge to reduce the ammonia concentration; or controls the combustion-supporting air in the flue gas heating device to purge to reduce the carbon monoxide concentration.

[0020] On the other hand, the present invention provides a control method for an aluminum melting furnace SCR denitration control system, and the specific steps are as follows:

[0021] Step 1: First, according to the flue gas temperature and flue gas flow rate before heating, the main control system starts the first burner in the flue gas heating device in advance, and the advance time t1 is 20-50s, and then the low-temperature flue gas is introduced into the flue gas heating device. When the flue gas reaches the first target temperature, it is led to the low-temperature SCR reactor to prevent the low-temperature flue gas from entering the low-temperature SCR reactor in advance and affecting the catalytic reaction effect;

[0022] Step 2: After the flue gas is heated to the first target temperature, the interlock control system turns on the urea solution or ammonia water conveying device and the urea solution or ammonia water pyrolysis device, and starts the second burner to pyrolyze the urea solution or ammonia water. At the same time, after controlling the generated ammonia gas to reach the second target temperature, it is sent to the low-temperature SCR reactor to react with the flue gas;

[0023] Step 3: The main control system controls the flow rate of the urea solution or ammonia water conveyed by the urea solution or ammonia water conveying device according to the NO X concentration at the outlet of the low-temperature SCR reactor;

[0024] Step 4: The main control system monitors the safe operation parameters of the low-temperature SCR denitration system of the aluminum melting furnace in real time according to the first safety protection control system, and decides whether the low-temperature SCR denitration system of the aluminum melting furnace continues to operate according to the safe operation parameters;

[0025] When all the safe operation parameters are less than or equal to the set safety values, the low-temperature SCR denitration system of the aluminum melting furnace continues to operate and proceeds to Step 5;

[0026] When some of the safe operation parameters are higher than the set safety values, the main control system alarms to prompt the staff or controls the low-temperature SCR denitration system of the aluminum melting furnace to stop operating gradually;

[0027] Step 5: When the low-temperature SCR denitration system of the aluminum melting furnace needs to end the operation normally, the main control system first controls the urea solution or ammonia water conveying device to stop conveying, then controls the urea solution or ammonia water pyrolysis device to stop operating, and finally controls the flue gas heating device to stop operating, then the low-temperature SCR denitration system of the aluminum melting furnace ends the operation.

[0028] Specifically, in Step 4, when the first safety protection control system monitors that the safe operation parameter of the regenerator differential pressure is higher than the set safety value, according to the difference between the safe operation parameter and the safety value, the main control system alarms, or:

[0029] Delay for t2, and the interlock control system controls the urea solution or ammonia water conveying device to stop conveying the urea solution or ammonia water, where t2 is 40 - 90 s;

[0030] Delay for t3 again, and the main control system shuts down the second burner, where t3 is 20 - 50 s;

[0031] Delay for t4 again, and the main control system stops the operation of the flue gas heating device, where t4 is 40 - 90 s;

[0032] Delay for t5 again, and the main control system controls the combustion-supporting fans in the urea solution or ammonia water pyrolysis device and the flue gas heating device to stop operating respectively, where t5 is 20 - 50 s.

[0033] Specifically, in step 4, when the first safety protection control system monitors that the pressure safety operation parameter of the urea solution or ammonia water conveying device is higher than the set safety value, the main control system alarms according to the difference between the safety operation parameter and the safety value, or:

[0034] Delay for 40 - 90 s, and the interlock control system controls the urea solution or ammonia water conveying device to stop conveying the urea solution or ammonia water;

[0035] Delay for another 20 - 50 s, and the main control system shuts down the second burner;

[0036] Delay for another 40 - 90 s, and the main control system stops the operation of the flue gas heating device;

[0037] Delay for another 20 - 50 s, and the main control system controls the combustion-supporting fans in the urea solution or ammonia water pyrolysis device and the flue gas heating device to stop running respectively.

[0038] Specifically, in step 4, when the first safety protection control system monitors that the liquid level of the urea solution or ammonia water is lower than the set safety value, the main control system alarms according to the difference between the safety operation parameter and the safety value, or:

[0039] Delay for t6, and the interlock control system controls the urea solution or ammonia water conveying device to stop conveying the urea solution or ammonia water, where t6 is 40 - 90 s;

[0040] Delay for another t7, and the main control system shuts down the second burner, where t7 is 20 - 50 s;

[0041] Delay for another t8, and the main control system stops the operation of the flue gas heating device, where t8 is 40 - 90 s;

[0042] Delay for another t9, and the main control system controls the combustion-supporting fans in the urea solution or ammonia water pyrolysis device and the flue gas heating device to stop running respectively, where t9 is 20 - 50 s.

[0043] Specifically, in step 4, when the first safety protection control system monitors the low-pressure pressure signal of the natural gas pipeline pressure switch of the second burner, or when the combustion-supporting air pipeline pressure switch detects the low-pressure pressure signal, the natural gas solenoid valve is interlocked and closed, and at the same time, the urea solution or ammonia water conveying system is interlocked and stopped. After the conveying system stops, delay for 40 - 90 s and then stop the operation of the flue gas heating device;

[0044] Delay for another 40 - 90 s, and the main control system controls the induced draft fan and the combustion-supporting fan to stop running.

[0045] Specifically, in step 4, when the first safety protection control system detects a high pressure signal from the natural gas pipeline pressure switch of the second burner, or when the combustion air pipeline pressure switch detects a high pressure signal, the natural gas solenoid valve is interlocked to close, and the urea solution or ammonia water delivery system is interlocked to stop. After the delivery system stops, the flue gas heating device is stopped after a delay of 40-90 seconds;

[0046] After another delay of 40-90s, the main control system controls the induced draft fan and combustion-supporting fan to stop running.

[0047] Specifically, in step 4, when the first safety protection control system detects that a fault occurs in the first burner or the second burner:

[0048] If the outlet temperature of the flue gas heating device, urea solution or ammonia pyrolysis device is greater than or equal to the set value of 280°C, the low-temperature SCR denitrification system of the aluminum melting furnace will continue to work;

[0049] If the outlet temperature of the flue gas heating device, urea solution or ammonia pyrolysis device is lower than the set value:

[0050] Delay t10, the interlocking control system controls the urea solution or ammonia water delivery device to stop delivering the urea solution or ammonia water, and the t10 is 3-8s;

[0051] After a further delay of t11, the main control system turns off the second burner of the urea solution or ammonia water pyrolysis device, wherein t11 is 5-15s;

[0052] After a further delay of t12, the main control system controls the combustion-supporting fans in the urea solution or ammonia water pyrolysis device and the flue gas heating device to stop running, wherein t12 is 20-50s.

[0053] Specifically, in step 4, when the first safety protection control system monitors that the temperature of the flue gas inlet of the flue gas heating device is greater than the first target temperature required for denitrification, the first burner stops running and the remaining systems maintain normal operation.

[0054] Specifically, during operation, when an emergency occurs, the low-temperature SCR denitrification system is equipped with an "emergency stop" button; all equipment can be stopped with one button to ensure equipment safety.

[0055] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0056] The invention uses a micro-flow metering pump to accurately control the urea solution or ammonia water, thus overcoming the accuracy problem of conventional regulating valves and flow meters in micro-flow control. The stroke number and stroke weight of the micro-flow metering pump are controlled by the main control system, and are connected with the NO at the outlet of the low-temperature SCR reactor. X Interlocking PID control can turn NOX The precise control of emissions within the standard range effectively improves the denitrification effect and environmental protection performance; the main control system controls the flame length and flame size of the first burner according to the flue gas temperature and flue gas flow rate, so that the flue gas leading to the low-temperature SCR reactor reaches the first target temperature, avoiding the problem that the catalytic reaction effect is affected by the too low temperature of the flue gas entering the low-temperature SCR reactor, and ensuring the smooth progress of the denitrification reaction.

[0057] Furthermore, the urea solution or ammonia water pyrolysis device uses the second burner to pyrolyze the urea solution or ammonia water, and controls the temperature of the ammonia gas generated by pyrolysis to the second target temperature required for the reaction in the low-temperature SCR reactor, ensuring the efficient pyrolysis of ammonia gas and the appropriate denitrification reaction temperature, which is beneficial to improving the denitrification efficiency.

[0058] Furthermore, the interlock control system interlocks the PID control of the flue gas heating device with the urea solution or ammonia water pyrolysis device and the urea solution or ammonia water conveying device, turns on the relevant devices according to the flue gas temperature, and controls the conveying flow rate of the urea solution or ammonia water according to the NO X concentration at the outlet of the low-temperature SCR reactor, realizing the coordinated operation and precise control among various systems, and further optimizing the denitrification process.

[0059] Furthermore, the first safety protection control system and the second safety protection control system real-time monitor various safety operation parameters of the system. When the parameters are abnormal, the main control system can give an alarm in time or take measures such as stopping the operation of relevant devices. For example, when the ammonia gas concentration or carbon monoxide concentration exceeds the safety value, it can give an alarm, cut off the fire source or perform auxiliary combustion air blowing and sweeping, etc., ensuring the safe and stable operation of the low-temperature SCR denitrification system for the aluminum melting furnace.

[0060] The low-temperature SCR denitrification control system and control method for the aluminum melting furnace of the present invention solve the problem of precise control of urea solution or ammonia water, and the problem that the conventional low-temperature SCR denitrification system cannot operate normally in the absence of high-temperature gas, sufficient electric energy, demineralized water and other resources, realizing denitrification control under these special working conditions and broadening the application range of the low-temperature SCR denitrification system. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The accompanying drawings here are incorporated into the specification and form a part of this specification, and are used together with the specification to explain the principles of the present invention.

[0062] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0063] Figure 1Schematic diagram of the low-temperature SCR denitration control system for the aluminum melting furnace of the present invention;

[0064] Figure 2 Flow chart of the control method of the low-temperature SCR denitration control system for the aluminum melting furnace of the present invention. Detailed implementation mode

[0065] Here, the exemplary embodiments will be described in detail, and the examples are shown in the drawings. The implementation modes described in the following exemplary embodiments do not represent all implementation modes consistent with the present invention. On the contrary, they are only examples consistent with some aspects of the present invention detailed in the appended claims.

[0066] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the drawings and embodiments.

[0067] Embodiment 1

[0068] See Figure 1 As shown, this embodiment provides an SCR denitration control system for an aluminum melting furnace, including a main control system, and a flue gas heating device, a urea solution or ammonia water conveying device, a urea solution or ammonia water pyrolysis device, an interlock control system, and a first safety protection control system controlled by the main control system;

[0069] The main control system controls the flue gas heating device, and according to the flue gas temperature (80 °C) and flue gas flow rate (10 m / s), controls the flame length and flame size of the first burner of the flue gas heating device to control the flue gas leading to the low-temperature SCR reactor to reach the first target temperature of 230 °C;

[0070] The main control system controls the urea solution or ammonia water conveying device to adjust the flow rate of the pyrolyzed urea solution or ammonia water in real time. The control of the urea solution or ammonia water conveying device uses a micro flow metering pump to accurately convey the urea solution or ammonia water. By controlling the stroke number and stroke weight of the micro flow metering pump through the control system, accurate control is achieved. The main control system collects the NO X concentration at the outlet of the low-temperature SCR reactor in real time, and realizes the interlock PID control (interlock PID control: calculates the control signal according to the error between the set value and the actual value) of the stroke number of the micro flow metering pump and the NO X at the outlet of the low-temperature SCR reactor, and controls the NO X emission within the standard range;

[0071] The main control system controls the urea solution or ammonia water pyrolysis device, uses the second burner of the urea solution or ammonia water pyrolysis device to pyrolyze the urea solution or ammonia water, and controls the temperature of the ammonia gas generated by pyrolysis to the second target temperature of 280°C required for the reaction in the low-temperature SCR reactor; that is, the urea solution or ammonia water is transported to the spray gun inlet through a metering pump, atomized through the spray gun and enters above the flame of the second burner of the urea solution or ammonia water pyrolysis device, and the urea solution or ammonia water is heated and decomposed into ammonia gas by the flame, and then the ammonia gas reaching the second target temperature is sent into the low-temperature SCR reactor for denitrification reaction. At the same time, the ratio of natural gas to combustion-supporting air is controlled at 1:(8-12) to control the flame size and flame length; the urea solution or ammonia water transportation device is connected to the urea solution or ammonia water pyrolysis device;

[0072] The main control system controls the interlock control system, which is used to interlock the PID control of the flue gas heating device with the urea solution or ammonia water pyrolysis device and the urea solution or ammonia water transportation device, start the urea solution or ammonia water pyrolysis device and the urea solution or ammonia water transportation device according to the flue gas temperature, and control the flow rate of the urea solution or ammonia water transported during pyrolysis according to the NO concentration at the outlet of the low-temperature SCR reactor; X concentration;

[0073] The main control system controls the first safety protection control system, which is used to feedback the safety operation parameters obtained by real-time monitoring of the low-temperature SCR denitrification system of the aluminum melting furnace to the main control system, and the main control system decides whether to stop the operation of the low-temperature SCR denitrification system of the aluminum melting furnace according to the obtained safety operation parameters.

[0074] Specifically, the main control system real-time collects the flue gas temperature before heating, and controls the flame length and flame size of the first burner according to the flue gas temperature and flue gas flow rate; after the flue gas temperature after heating reaches the first target temperature, the main control system controls the start of the urea solution or ammonia water pyrolysis device and the urea solution or ammonia water transportation device, and controls the ammonia gas obtained by pyrolysis to the second target temperature required for the reaction in the low-temperature SCR reactor.

[0075] Specifically, the main control system controls the micro-flow metering pump of the urea solution or ammonia water transportation device to achieve precise control of the urea solution or ammonia water, 3 L / h.

[0076] Specifically, the low-temperature SCR denitrification control system of the aluminum melting furnace further includes a second safety protection control system that accepts the control of the main control system. The second safety protection control system respectively monitors the ammonia gas concentration of the urea solution or ammonia water pyrolysis device and the carbon monoxide concentration of the flue gas heating device. If the ammonia gas concentration or carbon monoxide concentration exceeds the safety value, the main control system gives an alarm, or the main control system controls to close the second burner or the first burner.

[0077] Further, when the ammonia concentration or carbon monoxide concentration exceeds the safety value, the main control system controls the combustion-supporting air in the urea solution or ammonia water pyrolysis device to purge, so as to reduce the ammonia concentration; or controls the combustion-supporting air in the flue gas heating device to purge, so as to reduce the carbon monoxide concentration.

[0078] See Figure 2 As shown, this embodiment also provides a control method for the SCR denitration control system of an aluminum melting furnace, and the specific steps are as follows:

[0079] Step 1: First, according to the flue gas temperature and flue gas flow rate before heating, the main control system turns on the first burner in the flue gas heating device 30 s in advance, and then introduces the low-temperature flue gas into the flue gas heating device. When the flue gas reaches the first target temperature, it is sent to the low-temperature SCR reactor to avoid the low-temperature flue gas entering the low-temperature SCR reactor in advance and affecting the catalytic reaction effect;

[0080] Step 2: When the flue gas is heated to the first target temperature, the interlock control system turns on the urea solution or ammonia water conveying device and the urea solution or ammonia water pyrolysis device, and uses the second burner to pyrolyze the urea solution or ammonia water. At the same time, when the generated ammonia reaches the second target temperature, it is sent to the low-temperature SCR reactor to react with the flue gas;

[0081] Step 3: The main control system controls the flow rate of the urea solution or ammonia water conveyed by the urea solution or ammonia water conveying device according to the NO X concentration at the outlet of the low-temperature SCR reactor;

[0082] Step 4: The main control system monitors the safe operation parameters of the low-temperature SCR denitration system of the aluminum melting furnace in real time according to the first safety protection control system, and decides whether the low-temperature SCR denitration system of the aluminum melting furnace continues to operate according to the safe operation parameters;

[0083] When all the safe operation parameters are less than or equal to the set safety value, the low-temperature SCR denitration system of the aluminum melting furnace continues to operate and proceeds to step 5;

[0084] When some of the safe operation parameters are higher than the set safety value, the main control system alarms to prompt the staff or controls the low-temperature SCR denitration system of the aluminum melting furnace to stop operating gradually;

[0085] Step 5: When the low-temperature SCR denitration system of the aluminum melting furnace needs to end the operation normally, the main control system first controls the urea solution or ammonia water conveying device to stop conveying, then controls the urea solution or ammonia water pyrolysis device to stop operating, and finally controls the flue gas heating device to stop operating, then the low-temperature SCR denitration system of the aluminum melting furnace ends the operation.

[0086] Specifically, in step 4, when the first safety protection control system monitors that the safe operating parameter of the pressure difference of the heat storage body is higher than the set safety value (1000 Pa), the main control system alarms according to the difference between the safe operating parameter and the safety value, or:

[0087] Delay for 60 s, and the interlock control system controls the urea solution or ammonia water conveying device to stop conveying the urea solution or ammonia water;

[0088] Delay for another 30 s, and the main control system shuts down the second burner;

[0089] Delay for another 60 s, and the main control system stops the operation of the flue gas heating device;

[0090] Delay for another 30 s, and the main control system controls the combustion-supporting fans in the urea solution or ammonia water pyrolysis device and the flue gas heating device to stop operating respectively.

[0091] Specifically, in step 4, when the first safety protection control system monitors that the pressure safe operating parameter of the urea solution or ammonia water conveying device is higher than the set safety value, the main control system alarms according to the difference between the safe operating parameter and the safety value, or:

[0092] Delay for 60 s, and the interlock control system controls the urea solution or ammonia water conveying device to stop conveying the urea solution or ammonia water;

[0093] Delay for another 30 s, and the second burner shut down by the main control system;

[0094] Delay for another 60 s, and the main control system stops the operation of the flue gas heating device;

[0095] Delay for another 30 s, and the main control system controls the combustion-supporting fans in the urea solution or ammonia water pyrolysis device and the flue gas heating device to stop operating respectively.

[0096] Specifically, in step 4, when the first safety protection control system monitors that the liquid level of the urea solution or ammonia water is lower than the set safety value, the main control system alarms according to the difference between the safe operating parameter and the safety value, or:

[0097] Delay for 60 s, and the interlock control system controls the urea solution or ammonia water conveying device to stop conveying the urea solution or ammonia water;

[0098] Delay for another 30 s, and the main control system shuts down the second burner;

[0099] Delay for another 60 s, and the main control system stops the operation of the flue gas heating device;

[0100] Delay for another 30 s, and the main control system controls the combustion-supporting fans in the urea solution or ammonia water pyrolysis device and the flue gas heating device to stop operating respectively.

[0101] Specifically, in step 4, when the first safety protection control system monitors a low-pressure signal of the natural gas pipeline pressure switch of the second burner, or when the combustion air pipeline pressure switch detects a low-pressure signal, the natural gas solenoid valve is interlocked and closed, and at the same time, the urea solution or ammonia water delivery system is interlocked and stopped. After the delivery system stops, it delays for 60 s, and then stops the operation of the flue gas heating device;

[0102] After delaying for another 60 s, the main control system controls the induced draft fan and the combustion air fan to stop running.

[0103] Specifically, in step 4, when the first safety protection control system monitors a high-pressure signal of the natural gas pipeline pressure switch of the second burner, or when the combustion air pipeline pressure switch detects a high-pressure signal, the natural gas solenoid valve is interlocked and closed, and at the same time, the urea solution or ammonia water delivery system is interlocked and stopped. After the delivery system stops, it delays for 60 s, and then stops the operation of the flue gas heating device;

[0104] After delaying for another 60 s, the main control system controls the induced draft fan and the combustion air fan to stop running.

[0105] Specifically, in step 4, when the first safety protection control system monitors a fault prompt of the first burner or the second burner:

[0106] If the outlet temperature of the flue gas heating device, the urea solution or ammonia water pyrolysis device is greater than or equal to the set value, the low-temperature SCR denitration system of the melting furnace continues to operate;

[0107] If the outlet temperature of the flue gas heating device, the urea solution or ammonia water pyrolysis device is less than the set value of 280 °C:

[0108] It delays for 5 s, and the interlock control system controls the urea solution or ammonia water delivery device to stop delivering urea solution or ammonia water;

[0109] After delaying for another 10 s, the main control system closes the second burner of the urea solution or ammonia water pyrolysis device;

[0110] After delaying for another 30 s, the main control system controls the combustion air fans in the urea solution or ammonia water pyrolysis device and the flue gas heating device to stop running.

[0111] Specifically, in step 4, when the first safety protection control system monitors that the temperature at the flue gas inlet of the flue gas heating device is greater than the first target temperature of 230 °C required for denitration, the first burner stops running, and the rest of the systems operate normally.

[0112] Specifically, during the operation, in case of an emergency, the low-temperature SCR denitration system is provided with an "emergency stop" button to stop all equipment with one key to ensure the safety of the equipment.

[0113] Example 2

[0114] See Figure 1 As shown, this embodiment provides an SCR denitration control system for an aluminum melting furnace, including a main control system, and a flue gas heating device, a urea solution or ammonia water conveying device, a urea solution or ammonia water pyrolysis device, an interlock control system, and a first safety protection control system controlled by the main control system;

[0115] The main control system controls the flue gas heating device. According to the flue gas temperature of 100°C and the flue gas flow rate of 12 m / s, it controls the flame length and flame size of the first burner of the flue gas heating device to control the flue gas leading to the low-temperature SCR reactor to reach the first target temperature of 250°C;

[0116] The main control system controls the urea solution or ammonia water conveying device to adjust the flow rate of the pyrolyzed urea solution or ammonia water in real time. The control of the urea solution or ammonia water conveying device uses a micro-flow metering pump to accurately convey the urea solution or ammonia water. By controlling the stroke number and stroke weight of the micro-flow metering pump through the control system, accurate control is achieved. The main control system collects the NO X concentration at the outlet of the low-temperature SCR reactor in real time, and realizes the interlock PID control (interlock PID control: calculates the control signal according to the error between the set value and the actual value) of the stroke number of the micro-flow metering pump and the NO X at the outlet of the low-temperature SCR reactor, and controls the NO X emission within the standard range;

[0117] The main control system controls the urea solution or ammonia water pyrolysis device to pyrolyze the urea solution or ammonia water using the second burner of the urea solution or ammonia water pyrolysis device, and controls the temperature of the ammonia gas generated by pyrolysis to the second target temperature of 380°C required for the reaction of the low-temperature SCR reactor; that is, the urea solution or ammonia water is conveyed to the inlet of the spray gun through a metering pump, atomized through the spray gun and enters above the flame of the second burner of the urea solution or ammonia water pyrolysis device, and the urea solution or ammonia water is heated and decomposed into ammonia gas by the flame, and then the ammonia gas reaching the second target temperature is sent into the low-temperature SCR reactor for denitration reaction. At the same time, the ratio of natural gas to combustion-supporting air is controlled at 1:(8 - 12) to control the flame size and flame length; the urea solution or ammonia water conveying device is connected to the urea solution or ammonia water pyrolysis device;

[0118] The main control system controls the interlock control system, which is used for interlock PID control of the flue gas heating device, the urea solution or ammonia water pyrolysis device, and the urea solution or ammonia water conveying device. According to the flue gas temperature, the urea solution or ammonia water pyrolysis device and the urea solution or ammonia water conveying device are started, and the flow rate of the urea solution or ammonia water conveyed during pyrolysis is controlled according to the NO X concentration at the outlet of the low-temperature SCR reactor;

[0119] The main control system controls the first safety protection control system, which is used to feed back various safety operation parameters obtained by real-time monitoring of the low-temperature SCR denitration system of the aluminum melting furnace to the main control system. The main control system decides whether to stop the operation of the low-temperature SCR denitration system of the aluminum melting furnace according to the obtained safety operation parameters.

[0120] Specifically, the main control system collects the flue gas temperature before heating in real time, and controls the flame length and flame size of the first burner according to the flue gas temperature and flue gas flow rate. After the flue gas temperature after heating reaches the first target temperature, the main control system controls the start of the urea solution or ammonia water pyrolysis device and the urea solution or ammonia water conveying device, and controls the ammonia gas obtained after pyrolysis to the second target temperature required for the reaction in the low-temperature SCR reactor.

[0121] Specifically, the main control system controls the micro-flow metering pump of the urea solution or ammonia water conveying device to achieve precise control of the urea solution or ammonia water, 3 L / h.

[0122] Specifically, the low-temperature SCR denitration control system of the aluminum melting furnace further includes a second safety protection control system that accepts the control of the main control system. The second safety protection control system monitors the ammonia gas concentration of the urea solution or ammonia water pyrolysis device and the carbon monoxide concentration of the flue gas heating device respectively. If the ammonia gas concentration or the carbon monoxide concentration exceeds the safety value, the main control system gives an alarm, or the main control system controls to turn off the second burner or the first burner.

[0123] Furthermore, when the ammonia gas concentration or the carbon monoxide concentration exceeds the safety value, the main control system controls the combustion-supporting air in the urea solution or ammonia water pyrolysis device to be purged to reduce the ammonia gas concentration; or controls the combustion-supporting air in the flue gas heating device to be purged to reduce the carbon monoxide concentration.

[0124] See Figure 2 As shown, this embodiment also provides a control method for the SCR denitration control system of the aluminum melting furnace. The specific steps are as follows:

[0125] Step 1: First, according to the flue gas temperature and flue gas flow rate before heating, the main control system turns on the first burner in the flue gas heating device 40 s in advance, and then introduces the low-temperature flue gas into the flue gas heating device. When the flue gas reaches the first target temperature, it leads to the low-temperature SCR reactor, avoiding the premature entry of the low-temperature flue gas into the low-temperature SCR reactor and affecting the catalytic reaction effect;

[0126] Step 2: After the flue gas is heated to the first target temperature, the interlock control system starts the urea solution or ammonia water conveying device and the urea solution or ammonia water pyrolysis device, and uses the second burner to pyrolyze the urea solution or ammonia water. At the same time, after controlling the generated ammonia gas to reach the second target temperature, it is sent to the low-temperature SCR reactor to react with the flue gas;

[0127] Step 3: The main control system controls the flow rate of the urea solution or ammonia water conveyed by the urea solution or ammonia water conveying device according to the NO X concentration at the outlet of the low-temperature SCR reactor;

[0128] Step 4: The main control system monitors the safe operation parameters of the low-temperature SCR denitration system of the aluminum melting furnace in real time according to the first safety protection control system, and decides whether the low-temperature SCR denitration system of the aluminum melting furnace continues to operate according to the safe operation parameters;

[0129] When all the safe operation parameters are less than or equal to the set safety values, the low-temperature SCR denitration system of the aluminum melting furnace continues to operate and proceeds to Step 5;

[0130] When some of the safe operation parameters are higher than the set safety values, the main control system alarms to prompt the staff or controls the low-temperature SCR denitration system of the aluminum melting furnace to stop operating gradually;

[0131] Step 5: When the low-temperature SCR denitration system of the aluminum melting furnace needs to end the operation normally, the main control system first controls the urea solution or ammonia water conveying device to stop conveying, then controls the urea solution or ammonia water pyrolysis device to stop operating, and finally controls the flue gas heating device to stop operating, then the low-temperature SCR denitration system of the aluminum melting furnace ends the operation.

[0132] Specifically, in Step 4, when the first safety protection control system monitors that the safe operation parameter of the regenerator differential pressure is higher than the set safety value (1000 pa), according to the difference between the safe operation parameter and the safety value, the main control system alarms, or:

[0133] Delay for 80 s, and the interlock control system controls the urea solution or ammonia water conveying device to stop conveying the urea solution or ammonia water;

[0134] Delay for another 40 s, and the main control system shuts down the second burner;

[0135] Delay for another 80 s, and the main control system stops the operation of the flue gas heating device;

[0136] Delay for another 40 s, and the main control system controls the combustion-supporting fans in the urea solution or ammonia water pyrolysis device and the flue gas heating device to stop operating respectively.

[0137] Specifically, in step 4, when the first safety protection control system monitors that the pressure safety operation parameter of the urea solution or ammonia water conveying device is higher than the set safety value, the main control system alarms according to the difference between the safety operation parameter and the safety value, or:

[0138] Delay for 80 s, and the interlock control system controls the urea solution or ammonia water conveying device to stop conveying the urea solution or ammonia water;

[0139] Delay for another 40 s, and the main control system shuts down the second burner;

[0140] Delay for another 80 s, and the main control system stops the operation of the flue gas heating device;

[0141] Delay for another 40 s, and the main control system respectively controls the combustion-supporting fans in the urea solution or ammonia water pyrolysis device and the flue gas heating device to stop operating.

[0142] Specifically, in step 4, when the first safety protection control system monitors that the liquid level of the urea solution or ammonia water is lower than the set safety value, the main control system alarms according to the difference between the safety operation parameter and the safety value, or:

[0143] Delay for 80 s, and the interlock control system controls the urea solution or ammonia water conveying device to stop conveying the urea solution or ammonia water;

[0144] Delay for another 40 s, and the main control system shuts down the second burner;

[0145] Delay for another 80 s, and the main control system stops the operation of the flue gas heating device;

[0146] Delay for another 40 s, and the main control system respectively controls the combustion-supporting fans in the urea solution or ammonia water pyrolysis device and the flue gas heating device to stop operating.

[0147] Specifically, in step 4, when the first safety protection control system monitors the low-pressure pressure signal of the natural gas pipeline pressure switch of the second burner, or when the combustion-supporting air pipeline pressure switch detects the low-pressure pressure signal, the natural gas solenoid valve is interlocked and closed, and at the same time, the urea solution or ammonia water conveying system is interlocked and stopped. After the conveying system stops, delay for 80 s and stop the operation of the flue gas heating device;

[0148] Delay for another 80 s, and the main control system controls the induced draft fan and the combustion-supporting fan to stop operating.

[0149] Specifically, in step 4, when the first safety protection control system monitors the high-pressure pressure signal of the natural gas pipeline pressure switch of the second burner, or when the combustion-supporting air pipeline pressure switch detects the high-pressure pressure signal, the natural gas solenoid valve is interlocked and closed, and at the same time, the urea solution or ammonia water conveying system is interlocked and stopped. After the conveying system stops, delay for 80 s and stop the operation of the flue gas heating device;

[0150] After a further delay of 80 s, the main control system controls the induced draft fan and the combustion-supporting fan to stop running.

[0151] Specifically, in step 4, when the first safety protection control system detects a fault prompt in the first burner or the second burner:

[0152] If the outlet temperature of the flue gas heating device, the urea solution or the ammonia pyrolysis device is greater than or equal to the set value, the low-temperature SCR denitration system of the aluminum melting furnace continues to operate;

[0153] If the outlet temperature of the flue gas heating device, the urea solution or the ammonia pyrolysis device is less than the set value of 280 °C:

[0154] After a delay of 7 s, the interlock control system controls the urea solution or ammonia delivery device to stop delivering the urea solution or ammonia;

[0155] After a further delay of 15 s, the main control system closes the second burner of the urea solution or ammonia pyrolysis device;

[0156] After a further delay of 40 s, the main control system controls the combustion-supporting fan in the urea solution or ammonia pyrolysis device and the flue gas heating device to stop running.

[0157] Specifically, in step 4, when the first safety protection control system detects that the temperature at the flue gas inlet of the flue gas heating device is greater than the first target temperature of 250 °C required for denitration, the first burner stops running, and the rest of the systems operate normally.

[0158] Specifically, during operation, in case of an emergency, the low-temperature SCR denitration system is provided with an "emergency stop" button to stop all equipment with one key to ensure the safety of the equipment.

[0159] From Example 1 and Example 2, it can be concluded that the control system and control method of the present invention can perform denitration treatment on flue gas with different temperatures and different flows by precisely controlling the flow rate of the urea solution or ammonia, and also meet the use requirements in occasions without high-temperature gas, sufficient electric energy, demineralized water and other resources.

[0160] When there is a conflict between the main control system and the interlock control system, the main control system shall prevail.

[0161] The above are only specific embodiments of the present invention, which enable those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention.

[0162] It should be understood that the present invention is not limited to the above-described content and various modifications and changes can be made without departing from its scope. The scope of the present invention is only limited by the appended claims.

Claims

1. An SCR denitration control system for an aluminum melting furnace, characterized in that: It includes a main control system, and a flue gas heating device, a urea solution or ammonia water conveying device, a urea solution or ammonia water pyrolysis device, an interlocking control system, and a first safety protection control system controlled by the main control system; The main control system controls the flue gas heating device, and utilizes the first burner of the flue gas heating device to heat the flue gas leading to the low-temperature SCR reactor to a first target temperature; Controlling the urea solution or ammonia water delivery device to adjust the flow rate of the pyrolyzed urea solution or ammonia water in real time; Controlling the urea solution or ammonia water pyrolysis device, utilizing the second burner of the urea solution or ammonia water pyrolysis device to pyrolyze the urea solution or ammonia water, and controlling the temperature of ammonia gas generated by pyrolysis to a second target temperature required for the reaction of the low-temperature SCR reactor; the urea solution or ammonia water delivery device is in communication with the urea solution or ammonia water pyrolysis device; The interlock control system is used to interlock the flue gas heating device with the urea solution or ammonia water pyrolysis device and the urea solution or ammonia water delivery device with PID control, and to start the urea solution or ammonia water pyrolysis device and the urea solution or ammonia water delivery device according to the flue gas temperature, and to control the NO X Concentration controls the flow rate of urea solution or ammonia during pyrolysis; Control the first safety protection control system to feed back various safety operation parameters obtained by real-time monitoring of the low-temperature SCR denitrification system of the aluminum melting furnace to the main control system, and the main control system decides whether to stop the operation of the low-temperature SCR denitrification system of the aluminum melting furnace based on the obtained safety operation parameters.

2. The SCR denitration control system for an aluminum melting furnace according to claim 1 is characterized in that: The main control system collects the flue gas temperature before heating in real time, and controls the flame length and flame size of the first burner according to the flue gas temperature and flue gas flow rate; after the flue gas temperature after heating reaches the first target temperature, the main control system controls the urea solution or ammonia water pyrolysis device and the urea solution or ammonia water delivery device to start, and controls the ammonia obtained after pyrolysis to the second target temperature required for the reaction of the low-temperature SCR reactor.

3. The SCR denitration control system for an aluminum melting furnace according to claim 1 is characterized in that: The urea solution or ammonia water delivery device uses a micro-flow metering pump to accurately deliver the urea solution or ammonia water.

4. The SCR denitration control system for an aluminum melting furnace according to claim 1, characterized in that: The low-temperature SCR denitrification control system of the aluminum melting furnace also includes a second safety protection control system controlled by the main control system. The second safety protection control system monitors the ammonia concentration of the urea solution or ammonia water pyrolysis device and the carbon monoxide concentration of the flue gas heating device respectively. If the ammonia concentration or the carbon monoxide concentration exceeds the safety value, the main control system will alarm, or the main control system will control the shutdown of the second burner or the first burner.

5. The SCR denitration control system for an aluminum melting furnace according to claim 4, characterized in that: When the ammonia concentration or carbon monoxide concentration exceeds the safety value, the main control system controls the combustion-supporting air in the urea solution or ammonia pyrolysis device to purge, and at the same time turns off the second burner to reduce the ammonia concentration; or controls the combustion-supporting air in the flue gas heating device to purge, and at the same time turns off the first burner to reduce the carbon monoxide concentration.

6. The control method of the aluminum melting furnace SCR denitration control system according to any one of claims 1 to 5 is characterized in that: The specific steps are as follows: Step 1: First, the main control system starts the first burner in the flue gas heating device in advance by a time t1, and then introduces the low-temperature flue gas into the flue gas heating device. When the flue gas reaches the first target temperature, it is led to the low-temperature SCR reactor; Step 2: When the flue gas is heated to the first target temperature, the interlocking control system starts the urea solution or ammonia water delivery device and the urea solution or ammonia water pyrolysis device, and starts the second burner to pyrolyze the urea solution or ammonia water, and controls the generated ammonia gas to reach the second target temperature before being passed to the low-temperature SCR reactor to react with the flue gas; Step 3: The main control system generates NO X The concentration controls the flow rate of the urea solution or ammonia solution conveying device conveying the urea solution or ammonia solution; Step 4: The main control system monitors the safe operation parameters of the low-temperature SCR denitration system of the aluminum melting furnace in real time according to the first safety protection control system, and determines whether the low-temperature SCR denitration system of the aluminum melting furnace continues to operate according to the safe operation parameters; When the safety operation parameters are all less than or equal to the set safety values, the low-temperature SCR denitrification system of the aluminum melting furnace continues to operate and proceeds to step 5; When some safety operation parameters are higher than the set safety values, the main control system will alarm the staff, or control the aluminum melting furnace low-temperature SCR denitrification system to gradually stop operation; Step 5, when the low-temperature SCR denitrification system of the aluminum melting furnace needs to end operation normally, the main control system first controls the urea solution or ammonia water conveying device to stop conveying, then controls the urea solution or ammonia water pyrolysis device to stop operating, and finally controls the flue gas heating device to stop operating, and then the low-temperature SCR denitrification system of the aluminum melting furnace ends operation.

7. The control method according to claim 6, characterized in that: In step 4, when the first safety protection control system detects that the pressure safety operation parameter of the urea solution or ammonia water delivery device is higher than the set safety value, the main control system alarms, or: Delay t2, the interlocking control system controls the urea solution or ammonia water delivery device to stop delivering the urea solution or ammonia water; After another delay of t3, the main control system turns off the second burner; After another delay of t4, the main control system stops the operation of the flue gas heating device; After a further delay of t5, the main control system controls the combustion-supporting fans in the urea solution or ammonia water pyrolysis device and the flue gas heating device to stop running.

8. The control method according to claim 6, characterized in that: In step 4, when the first safety protection control system detects that the liquid level of the urea solution or ammonia water is lower than the set safety value, the main control system alarms, or: Delay t6, the interlocking control system controls the urea solution or ammonia water delivery device to stop delivering the urea solution or ammonia water; After another delay of t7, the main control system turns off the second burner; After another delay of t8, the main control system stops the operation of the flue gas heating device; After a further delay of t9, the main control system controls the combustion-supporting fans in the urea solution or ammonia water pyrolysis device and the flue gas heating device to stop running.

9. The control method according to claim 6, characterized in that: In step 4, when the first safety protection control system detects that a fault occurs in the first burner or the second burner: If the outlet temperature of the flue gas heating device, urea solution or ammonia pyrolysis device is greater than or equal to the set value, the low-temperature SCR denitrification system of the aluminum melting furnace will continue to work; If the outlet temperature of the flue gas heating device, urea solution or ammonia pyrolysis device is lower than the set value: Delay t10, the interlocking control system controls the urea solution or ammonia water delivery device to stop delivering the urea solution or ammonia water; After another delay of t11, the main control system turns off the second burner; After a further delay of t12, the main control system controls the combustion-supporting fans in the urea solution or ammonia water pyrolysis device and the flue gas heating device to stop running.

10. The control method according to claim 6, characterized in that: In step 4, when the first safety protection control system detects that the temperature of the flue gas inlet of the flue gas heating device is greater than the first target temperature required for denitrification, the first burner stops running and the remaining systems maintain normal operation.

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