CN100422639C - Catalytic combustion control system - Google Patents

Abstract

A catalytic combustion control system, which is composed of a fluid premix control system and a PLC control device. The fluid premix control system includes a fan with a Venturi mixer connected in series, and the throat suction port of the Venturi mixer is proportional to the The regulating valve is connected, the inlet of the proportional regulating valve is connected with the outlet of the zero pressure valve, the zero pressure valve is connected in parallel with the needle valve, and the PLC control device includes a PLC controller CPU. Using the combination of fluid control and PLC automatic control technology, in a fluid premixing system, only need to control the input frequency of the fan through the PLC control device to control the output air volume of the fan, so as to realize the control of different gas required for the catalytic combustion process -Air mixed concentration; automatic control ignition, preheating flame combustion and catalytic combustion can be realized directly on the catalyst carrier of the catalytic burner; the structure of the catalytic burner is simplified, the volume is reduced, the cost is reduced, and the degree of automation is improved and control accuracy.

Description

Catalytic combustion control system

(1) Technical field

The invention relates to a catalytic combustion control system and method of a gas catalytic burner.

(2) Background technology

The survival and development of human beings depend on the development and utilization of energy, but the negative effects such as environmental pollution brought about by the development and utilization of energy are increasingly threatening the survival of human beings and the sustainable development of society. For example, the emissions of SO ₂ , NOx, CO ₂ , CO and incompletely burned hydrocarbons UHC produced by common combustion of fossil fuels cause acid rain, photochemical smog and greenhouse effect, causing serious damage to the ecology and threatening human health. To solve the problem of environmental pollution caused by combustion, it is necessary to change the traditional and backward combustion methods, improve combustion efficiency, develop new burners and combustion control technologies, and carry out comprehensive prevention and control of combustion pollution.

Catalytic combustion is a new technology that can fundamentally solve the low combustion efficiency and high pollution emissions caused by ordinary combustion. It uses catalysts to control the combustion chemical reaction process and release heat under certain conditions. Catalytic combustion can reduce activation energy, accelerate necessary chemical reactions, and minimize harmful or unnecessary reactions. At present, the catalytic combustion of natural gas has achieved a combustion efficiency higher than 99.99%, and the harmful substances NOx, CO, and UHC emitted by the flue gas are all less than 10×10 ^-6 , so it can be seen that catalytic combustion can completely burn the fuel and effectively eliminate pollutants. Control is a very ideal and environmentally friendly combustion method.

The mechanism of catalytic combustion is complex, the conditions are harsh, and the reaction must occur under certain conditions. The core technology is catalyst components, preparation technology and catalytic combustion control technology. For the catalytic combustion of natural gas with methane as the main component, honeycomb ceramics are often used as the carrier, and a porous active water washing layer is coated on the wall of the porous honeycomb carrier to form a rough and porous surface to increase the surface area of the catalytic reaction. Rare earth materials and noble metal catalysts suitable for high-temperature catalytic combustion of natural gas usually use Pd, Pt and coating preparation processes. The catalyst is loaded on the surface of the honeycomb ceramic body, and then the ceramic body is installed on the catalytic burner, and then according to the activity of the catalyst and catalytic combustion Mechanism, application of fluid and PLC control technology to control the whole process of catalytic combustion. Catalytic combustion control technology is one of the necessary conditions to control and complete the catalytic combustion reaction. It mainly includes uniform mixing of air and gas according to the required ratio, ignition, preheating, catalytic combustion temperature and safety control.

The catalytic combustion of natural gas is fuel-lean, fully premixed flameless combustion, the mixed concentration of air and natural gas is about 5%, and the temperature of the mixed gas passing through the catalyst-loaded honeycomb ceramic body is greater than the light-off temperature T1 of the catalyst, so that the catalytic combustion reaction can occur. When the gas mixture concentration is constant, the combustion power or temperature T of catalytic combustion is proportional to the standard volume flow rate of the mixed gas, and the upper limit of the catalytic combustion temperature must be controlled below the maximum limit temperature T2 of the catalyst, so the requirements for industrial catalytic combustion are relatively high. degree of automation control. The methane honeycomb ceramic catalytic burner reported in the literature (V.Dopont, F.Moallemi, A.Williamas and S.-H.Zhang, Int.J.Energy Res.2000; 24:1181-1201), and the Chinese Patent Office The disclosed invention patent application specification "catalytic combustion device" CN1173919A and "catalytic combustion system" CN1695002A need a preheating burner before loading the catalyst carrier or catalytic burner, or set up another set of gas mixing system to provide start-up fuel, Before the catalytic combustion, the preheating burner is ignited first, and the catalyst is heated by the preheating burner. When the temperature of the catalyst reaches the light-off temperature, the preheating burner is turned off, and then the lean fuel is passed to the catalytic burner for catalytic combustion, because Lean fuel cannot be ignited and burned at room temperature. Therefore, the existing catalytic combustion technology not only makes the structure of the catalytic burner complex and bulky, but also increases the cost and technical difficulty of the catalytic combustion control system.

(3) Contents of the invention

The purpose of the present invention is to provide a catalytic combustion control system, which adopts the technology of combining fluid control and PLC automatic control to solve the problem that in a set of fluid premixing system, only the input frequency f of the fan needs to be controlled by the PLC control device to control the fan The output air volume Qa can achieve the problem of controlling the different gas-air mixing concentrations required in the catalytic combustion process; solve the problems of ignition, preheating, flaming combustion and catalytic combustion directly on the catalyst carrier of the catalytic burner; solve the problem of catalytic combustion at the same time Process purging, preheating flaming combustion, catalytic combustion and safety automatic control issues simplify the structure of the catalytic burner, reduce the volume, reduce the cost, and improve the degree of automation and control accuracy of the control system.

In order to achieve the above object, the present invention proposes the following technical solutions:

A catalytic combustion control system, used to control the combustion reaction of the catalytic burner 1, is characterized in that it is composed of two parts connected by a fluid premixing control system and a PLC control device;

The fluid premixing control system includes: a blower 3 connected in series with a Venturi mixer 4, which is used to purge the catalytic burner 1 and use the Venturi mixer 4 to introduce gas and perform uniform premixing. The output of the Venturi mixer 4 The tuyere is connected to the air inlet of the catalytic burner 1, the throat suction port of the Venturi mixer 4 is connected to a proportional regulating valve 5, which is used to set the premixed concentration of catalytic combustion gas and air, and the inlet of the proportional regulating valve 5 It is connected to the outlet of a zero pressure valve 6 to ensure that the gas is close to normal pressure. The two ends of the inlet and outlet of the zero pressure valve 6 are connected in parallel with a needle valve 7 to set the optimum gas and air ratio from ignition to preheating for ordinary combustion. Premix concentration;

PLC control devices include:

A PLC controller CPU14;

A frequency converter 15 connected to the control signal output end of the PLC controller CPU14 and used to control the input frequency f of the blower fan 3;

A digital/analog conversion module 18 connected to the output terminal of the control signal of the PLC controller CPU and the input terminal of the frequency converter 15;

A temperature sensor 13 for detecting the temperature of the catalyst carrier and for controlling the constant temperature catalytic combustion;

An analog/digital conversion module 17 connected with the signal of the temperature sensor and connected with the signal input end of the PLC controller CPU;

A main fire solenoid valve 8 connected to the gas main pipe 20 for controlling the gas premix switch and connected to the zero pressure valve 6;

A gas switch for controlling the igniter 11, the ignition solenoid valve 9 connected in the gas branch pipe 21:

An ignition transformer 10 for discharging and igniting the igniter 11;

An ultraviolet probe 12 placed near the igniter for judging whether the igniter 11 and the catalyst carrier 2 are ignited;

A visible light detector 16 placed in front of the catalyst carrier 2 and connected with the PLC controller CPU14 signal;

A text display with a signal connection to the PLC controller CPU14.

The above-mentioned catalyst carrier 2 is a honeycomb ceramic carrier or a metal carrier, and the catalyst is loaded on the carrier.

A catalytic combustion control method using the above catalytic combustion control system: the input frequency of the fan 3 is controlled by the PLC controller CPU14 through the frequency converter 15, the input frequency of the fan 3 is proportional to the output air flow Qa, when the air passes through the Venturi mixing When using the nozzle of the device 4, a negative pressure is formed around the nozzle to inject gas, and the injected gas passes through the zero pressure valve 6, and the standard flow rate of the gas passing through the zero pressure valve 6 is proportional to the air standard flow rate of the injected gas. Another gas passes through the needle valve 7 connected in parallel with the zero pressure valve 6, and the standard gas flow rate through the needle valve 7 is basically constant. Uniform premixing, the premixing concentration Qg/Qg+Qa of gas and air is related to the Reynolds number or flow rate of air passing through the Venturi nozzle. When the Reynolds number is small, the mixing concentration of gas and air is high. increases, the mixed concentration of gas and air will gradually decrease, and when the Reynolds number is greater than a value, the mixed concentration of gas and air will no longer change with the increase of Reynolds number, see Figure 3 and Figure 5, according to the fluid mixing control of the present invention The relationship between the Reynolds number and the gas mixture concentration and the relationship between the output frequency of the frequency converter and the gas mixture concentration Qg/Qg+Qa, by controlling the input frequency of the fan 3, the different gas and gas required for ignition, preheating, and catalytic combustion are respectively controlled. Air mixture concentration, and control of catalytic combustion power or temperature in the catalytic combustion stage.

This catalytic combustion control method using the above-mentioned catalytic combustion control system is characterized in that the steps are as follows:

Step 1: Start the operation, and the PLC controller CPU14 starts the fan 3 through the frequency converter 15 .

Step 2: Pre-purging, the frequency of the fan is controlled by the frequency converter 15 to increase continuously, the input frequency f of the frequency converter 15 is proportional to the output flow Qa of the fan 3, and the air enters the catalytic burner 1 through the Venturi mixer 4 to complete the pre-purging ; In step 2, the increment of frequency converter frequency is 0.1~1Hz/S.

Step 3: The igniter is ignited. After the pre-purge is completed, the PLC controller CPU14 reduces the input frequency of the fan 3 through the frequency converter 15, and conducts the ignition transformer 10 to discharge and ignite. At the same time, the ignition solenoid valve 9 is opened, and the gas passes through the gas branch pipe 21 enters the igniter 11, the igniter 11 is ignited, if the igniter 11 is not ignited, then close the ignition solenoid valve 9.

In step 3, within 8 seconds of turning on the ignition transformer 10, it is judged by the ultraviolet probe 12 whether the igniter 11 is on fire. After the zero pressure valve 6 converges, it passes through the proportional regulating valve 5 and is mixed by the air injection of the Venturi mixer 4. The uniform premixed gas enters the catalytic burner 1 and is ignited by the igniter 11 through the catalyst carrier 2; the catalytic burner 1 is ignited by After being ignited, the PLC controller CPU14 converts the fan's

When the input frequency increases, the ignition solenoid valve 9 is closed at this time, and the catalyst carrier 2 is in the normal combustion preheating stage.

Step 4: The catalytic burner is ignited. After the igniter 11 is ignited, the main fire solenoid valve 8 is opened. After the gas is merged from the gas main pipe 20 through the zero pressure valve 6 and the needle valve 7, it enters the Venturi mixer 4 through the proportional control valve 5 and The air is evenly mixed, the mixed concentration of gas and air is slightly greater than the explosion limit of the gas, the gas mixture enters the catalytic burner 1, and is ignited by the igniter 11 when passing through the catalyst carrier 2; if the catalyst carrier 2 is not ignited, the main Fire solenoid valve 8, blower fan 3 carry out back-purging, re-ignition.

Step 5: Preheating, after successful ignition, increase the frequency of fan 3, when the frequency reaches the frequency of the preheating control point, the mixed concentration of gas and air is slightly less than the theoretical complete combustion concentration of gas, keep the preheating frequency unchanged, turn off the ignition solenoid Valve 9, catalyst carrier 2 is in the normal combustion preheating stage.

Step 6: Detection of the light-off temperature. If the temperature detected by the temperature sensor 13 is lower than the light-off temperature of the catalyst, keep the frequency of the preheating control point unchanged, continue the normal combustion preheating, and gradually increase the preheating temperature to reach the light-off temperature. When the temperature is high, increase the frequency of fan 3 until the frequency reaches the stable initial frequency of catalytic combustion or the frequency corresponding to the set catalytic combustion temperature.

Step 7: Set the temperature to judge, through the catalytic combustion control system, make the fan maintain the stable starting frequency of catalytic combustion or the frequency corresponding to the set temperature. If the combustion temperature is lower than the set temperature, increase the control frequency of the fan. If the combustion temperature If the temperature is higher than the set temperature, reduce the control frequency of the fan, and the increment of the increase or decrease frequency of the fan control is 0.01 to 1 Hz/s; in step 7, the temperature sensor 13 detects the set temperature of the catalyst carrier 2 to judge the set temperature .

Step 8: Catalytic combustion control. After the combustion enters the catalytic combustion section, repeat step 7 to increase or decrease the frequency of the fan. The catalytic combustion control system automatically controls the constant temperature catalytic combustion between the light-off temperature of the catalyst and the maximum limit temperature.

Step 9: Stop or flameout detection. In the stable stage of catalytic combustion, if the flameout is manually ordered or the catalyst carrier 2 is faulty, etc., it will enter step 10. If not, return to step 7; in step 9, the visible light detector 16 Stop or flameout detection during the catalytic combustion phase.

Step 10: Turn off the main fire solenoid valve 8, and proceed to step 11 after blowing the catalytic burner 1 by the blower.

Step 11: End, the fan stops.

Beneficial effects of the present invention: please refer to Fig. 3, the existing Venturi zero-pressure valve mixing technology can only provide equal proportion premixed gas, and the present invention can provide continuous premixed gas with different proportions as required to meet the requirements of ignition, premixed gas Special requirements for different mixing concentrations of hot ordinary combustion, catalytic combustion gas and air. In the present invention, a needle valve is connected in parallel next to the zero-pressure valve to set the flow of gas flowing through it. When the air flow Qa or Reynolds number Re is small, one gas flow in proportion to the air flow passes through the zero-pressure valve, and the other The gas with the same flow rate passes through the needle valve. After the two gas streams meet, they enter the Venturi and mix with the air through the proportional control valve. At this time, the mixing concentration of the air and the gas is relatively high. The mixed concentration of gas will gradually and smoothly decrease. When the Reynolds number is greater than a certain value, the mixed concentration of air and gas will be a constant and will no longer change with the increase of Reynolds number. Therefore, by controlling the flow Qa or Reynolds number of the fan, the required mixing ratio of air and gas for ignition, preheating, common combustion and catalytic combustion can be achieved, and at the same time, the combustion power or combustion temperature can be controlled in the catalytic combustion section.

In order to simplify the structure of the catalytic burner, reduce the volume, and improve the degree of automation and control precision of the control system, the present invention adopts the technology of combining fluid control and PLC automatic control to provide a fluid premix control system, which Including: a blower for blowing and providing the air required for gas premixing; a Venturi mixer connected in series with the blower; a proportional regulating valve connected with the Venturi mixer, a zero pressure valve and a zero pressure valve The needle valves connected in parallel with the pressure valve are used to control the mixing ratio of air and gas. When the air (Qa) passes through the nozzle of the Venturi mixer, a negative pressure is formed around the nozzle to inject gas (Qg). One of the gas passes through the zero-pressure valve, and the other passes through the needle valve connected in parallel with the zero-pressure valve. After the two gases are combined, they enter the Venturi mixer through the proportional regulating valve and mix with the air in the mixing chamber and the gradual expansion section. The uniformly mixed gas enters the After the catalytic burner is rectified, it can burn through the honeycomb ceramic carrier loaded with catalyst. The mixing ratio of air and gas or the gas mixing concentration (Qg/(Qa+Qg) of the present invention is related to the air Reynolds number Re of the Venturi nozzle, and the Reynolds number Re is a function Re∝f(Qa) of the air flow rate Qa, In other words, as long as the air flow Qa is controlled, the gas mixture concentration and the total flow of the gas-air mixture can be controlled.

The present invention adopts the technology combining fluid control and PLC automatic control, and its PLC control system is composed of a group of programmable controllers and a frequency converter, which can complete the following five functions: ① used to control the input frequency f of the fan to control The output flow Qa of the fan, so as to achieve the control of purge, gas mixing concentration and combustion power or temperature; ② used to control the opening or closing of the gas solenoid valve; ③ used to control the opening or closing of the igniter transformer; ④ through the temperature sensor Distinguish temperature and control catalytic combustion process; ⑤Use ultraviolet probe and visible light detector to judge ignition, flameout and safety control.

The present invention only needs to set up a set of gas premixing system, and by controlling the input frequency f of the fan to control the output air volume Qa of the fan, different mixing ratios required for catalytic combustion can be realized, which can be realized only in a set of gas premixing system The ignition, flaming combustion preheating and catalytic combustion are realized directly on the catalyst carrier of the catalytic burner. It solves the technical problems of complex structure and bulky catalytic burner, high cost and technical difficulty of the catalytic combustion control system, and there is no need to set up a preheating burner and two sets of gas premixing systems like the existing catalytic burner. Therefore, the present invention simplifies the structure of the catalytic burner, reduces the volume, improves the degree of automation and control precision of the control system, and greatly reduces the cost, and is especially suitable for the control of industrial high-power gas catalytic burners.

(4) Description of drawings

Fig. 1 is a structural schematic diagram of the catalytic combustion control system of the present invention.

Figure 2 is a schematic diagram of the relationship between the catalytic combustion programmable controller and the controlled device.

Fig. 3 is a schematic diagram showing the comparison of the technical effects of the prior art and the present invention.

Fig. 4 is a graph showing the linear relationship between the output frequency f of the inverter and the output flow Qa of the fan.

Fig. 5 is a graph showing the control relationship between the output frequency f of the inverter of the present invention and the gas mixture concentration.

Fig. 6 is a flowchart of catalytic combustion control execution in the present invention.

1-catalytic burner; 2-loaded catalyst carrier; 3-fan; 4-venturi mixer; 5-proportional control valve; 6-zero pressure valve; 7-needle valve; 8-main fire solenoid valve; 9-ignition Solenoid valve; 10-ignition transformer; 11-igniter; 12-ultraviolet probe; 13-temperature sensor. 14-PLC controller CPU; 15-inverter; 16-visible light detector; 17-analog/digital conversion module; 18-digital/analog conversion module; 19-text display; 20-gas main pipe; 21-gas branch pipe.

f-fan input frequency, f1-ignition control frequency, f2-preheat combustion control frequency, f3-catalytic combustion stable initial frequency, f4-maximum temperature control frequency, fb-purge control frequency. L1-ignition gas premix concentration, L2-preheating common combustion gas premix concentration, L3-catalytic combustion gas premix concentration. Qa- standard air flow output by fan, Qg- standard flow of premixed gas. T1 is the ignition temperature, T2 is the maximum limit temperature, and Tc is the set combustion temperature.

(5) Specific implementation methods

Referring to Fig. 1 and Fig. 2, the catalytic combustion control system of the present invention is composed of a fluid premix control system and a PLC control device.

The fluid premixing control system includes; a blower 3 connected in series with a Venturi mixer 4, which is used to purge the catalytic burner 1 and use the Venturi mixer 4 to inject gas and perform uniform premixing. The outlet of the Venturi mixer 4 The tuyere is connected to the air inlet of the catalytic burner 1, and the throat suction port of the Venturi mixer 4 is connected to a proportional regulating valve 5, which is used to set the optimal gas premix concentration in the catalytic combustion stage. The inlet of the proportional regulating valve 5 is connected to the The outlet connection of a zero-pressure valve 6 is used to ensure that the gas entering the proportional regulating valve 5 is close to normal pressure. The inlet and outlet ends of the zero-pressure valve 6 are connected in parallel with a needle valve 7, which is used to set the ignition to preheating and flaming combustion. Optimum gas premix concentration.

PLC control devices include:

A PLC controller CPU14, with memory characteristics, I/O characteristics, integrated communication functions, power supply characteristics, digital input and output characteristics, such as model S7-200, CPU244.

A frequency converter 15 connected to the control signal output end of the PLC controller CPU14 and used to control the input frequency f of the blower fan 3 .

A digital/analog conversion module 18 connected to the control signal output end of the PLC controller CPU14 and the input end of the frequency converter 15 respectively, the model of the module is EM232, for example.

A temperature sensor 13 for detecting the temperature of the catalyst-loaded carrier.

An analog/digital conversion module 17 connected with the signal of the temperature sensor 13 and connected with the signal input end of the PLC controller CPU14, the model of the module is, for example, EM235.

A main fire solenoid valve 8 connected to the gas main pipe 20 for controlling the gas premix switch and connected to the zero pressure valve 6 .

A gas switch for controlling the igniter 11, and an ignition solenoid valve 9 connected in the gas branch pipe 21.

An ignition transformer 10 for discharging and igniting the igniter 11.

An ultraviolet probe 12 placed near the igniter for judging whether the igniter 11 and the catalyst carrier 2 are ignited.

A visible light detector 16 placed in front of the catalyst carrier 2 and connected with the PLC controller CPU14 for signal.

A text display 19 connected with the PLC controller CPU14 signal, used for parameter setting, working status and data display, such as model TD-200.

A catalytic combustion control method using the above catalytic combustion control system: the input frequency f of the fan 3 is controlled by the PLC controller CPU14 through the frequency converter 15, the input frequency f of the fan 3 is proportional to the output air flow Qa, when the air passes through the Venturi When using the nozzle of the mixer 4, a negative pressure is formed around the nozzle to inject gas, and the injected gas passes through the zero pressure valve 6, and the standard flow rate of the gas passing through the zero pressure valve 6 is equal to the air standard flow rate of the injected gas. The other gas passes through the needle valve 7 connected in parallel with the zero pressure valve 6, and the standard gas flow rate through the needle valve 7 is basically constant. After the two gas streams are combined, they enter the mixing chamber and the gradual expansion section of the Venturi through the proportional regulating valve 5 Evenly premixed with air, the premixed concentration Qg/Qg+Qa of gas and air is related to the Reynolds number or flow rate of air passing through the Venturi nozzle. When the Reynolds number is small, the mixed concentration of gas and air is higher. gradually increases, the mixing concentration of gas and air will gradually decrease. When the Reynolds number is greater than a value, the mixing concentration of gas and air will no longer change with the increase of Reynolds number. See Figure 3 and Figure 5. The relationship between the controlled Reynolds number and the gas mixture concentration and the relationship between the output frequency f of the frequency converter and the gas mixture concentration Qg/Qg+Qa, by controlling the input frequency of the fan 3, the differences required for ignition, preheating, and catalytic combustion are respectively controlled. The mixed concentration of gas and air, and the control of catalytic combustion power or temperature in the catalytic combustion stage.

Referring to Fig. 1, Fig. 2, Fig. 5 and Fig. 6, the catalytic combustion control method of the present invention adopts the technology combining fluid control and PLC automatic control, and its specific control steps are as follows:

Step 1: Before running, set parameters such as temperature through text 19, issue a running command, and the PLC controller CPU 14 starts the fan 3 through the frequency converter 15.

Step 2: Pre-purge, adjust the output frequency of the frequency converter 15 through the digital/analog conversion module 18 to control the input frequency of the fan, increase the frequency from 0 to fb, keep the frequency fb unchanged, and enter the catalytic combustion through the Venturi mixer 4 Unit 1, purge before completion.

Step 3: The igniter is ignited, and after the pre-purge is completed, the PLC controller CPU14 reduces the input frequency of the fan 3 from fb to f1 through the frequency converter 15, and the increment of frequency decrease is 0.1-1Hz/s, maintains the frequency f1, and Conduction ignition transformer 10 discharges ignition, opens ignition solenoid valve 9 simultaneously, gas enters igniter 11 by gas branch pipe 21, and igniter 11 is ignited, if igniter 11 does not ignite, then closes ignition solenoid valve 9.

In the present invention, within 8 seconds after the ignition transformer 10 is turned on, after the ultraviolet probe 12 judges whether the igniter 11 is on fire, when the ignition is on, the PLC controller CPU14 commands the main fire solenoid valve 8 to open, and the gas passes through the needle valve 7 and zero pressure After the valves 6 converge, they pass through the proportional regulating valve 5 and are mixed by the air injection of the Venturi mixer 4. The uniform premixed gas enters the catalytic burner 1 and is ignited by the igniter 11 through the catalyst carrier 2; after the catalytic burner 1 is ignited , the PLC controller CPU14 increases the input frequency of the fan from f1 to f2 through the frequency converter 15, and the increment of the frequency increase is 0.01～1Hz/s, and the frequency f2 is maintained. The catalyst carrier 2 is in the normal combustion preheating stage, and the ignition electromagnetic is turned off at this time Valve 9.

Step 4: The catalytic burner is ignited. After the igniter 11 is ignited, the main fire solenoid valve 8 is opened. After the gas is merged from the gas main pipe 20 through the zero pressure valve 6 and the needle valve 7, it enters the Venturi mixer 4 through the proportional control valve 5 and The air is uniformly mixed, and the mixed concentration L1 of the gas and air is slightly greater than the upper limit of the explosion concentration of the gas. The gas mixture enters the catalytic burner 1 and is ignited by the igniter 11 when passing through the catalyst carrier 2; if the catalyst carrier 2 is not ignited, it will Close the main fire electromagnetic valve 8, blower blower 3 carries out post-purging, and re-ignites.

Step 5: Preheating, after the ignition is successful, increase the frequency of fan 3, when the frequency reaches the frequency f2 of the preheating control point, the mixed concentration of gas and air is slightly less than the theoretical complete combustion concentration L2 of the gas, keep the frequency unchanged, and turn off the ignition solenoid The valve 9 and the catalyst carrier 2 are in the preheating stage of ordinary flaming combustion.

Step 6: Detection of the light-off temperature. If the detection temperature of the temperature sensor 13 is lower than the light-off temperature t1 of the catalyst, keep the frequency f2 of the preheating control point unchanged, and continue the preheating combustion. When the combustion temperature is t1, increase the frequency of the fan 3 until the frequency reaches the catalytic combustion stable initial frequency f3 or the frequency fd corresponding to the set catalytic combustion temperature Td (T2>Td≥T1).

Step 7: Set the temperature to judge, through the PLC control system, make the fan maintain the catalytic combustion stable initial frequency f3 or the frequency fd corresponding to the set temperature tc, if the temperature sensor 13 detects that the combustion temperature of the catalyst carrier 2 is lower than the set temperature , then increase the fan control frequency, if the combustion temperature is higher than the set temperature, then reduce the fan control frequency, the increment of the fan control increase or decrease frequency is 0.01~1Hz/s.

Step 8: Catalytic combustion control. After the combustion enters the stable stage of catalytic combustion, repeat step 7. Through temperature judgment, increase or decrease the frequency of the fan, so that the catalytic burner 1 can automatically control the constant temperature catalysis between the light-off temperature t1 and the maximum limit temperature t2. combustion.

Step 9: Stop or flameout detection. In the stable stage of catalytic combustion, if the flameout is commanded or the visible light detector 16 detects that the catalyst carrier 2 is flamed out, it will enter step 10, and if not, return to step 7.

Step 10: Turn off the main fire solenoid valve 8, and proceed to step 11 after blowing the catalytic burner 1 by the blower.

Step 11: End, the fan stops.

The selection of control parameters is related to the combustion power of the burner. Examples are as follows:

Ignition control frequency range f1=5～10Hz;

Preheating combustion frequency range f2=11～19Hz;

The control frequency range f3-f4 of the catalytic combustion section is 20-50Hz;

Purge frequency f4>fb≥f3;

Catalyst light-off temperature is related to catalyst components, t1=360～600℃;

Catalyst maximum control temperature t2 = 1160°C;

Normal temperature t0=40～50℃.

Operation control process of catalytic burner 1:

The PLC controller CPU14 issues instructions to start the fan 3 through the frequency converter 15, adjust the output frequency of the frequency converter 15 through the EM232 module 18 to control the air volume Qa of the fan 3, and the starting frequency gradually increases from 0 to the blowing frequency fb (f4>fb≥f3 ), the increment of the inverter frequency is 0.1-1Hz/S, the fan maintains the frequency fb, the air enters the catalytic burner 1 through the Venturi mixer 4, and the pre-purging is completed.

After the pre-purge is completed, the PLC controller CPU14 adjusts the output frequency f of the frequency converter 15 through the EM232 module 18, reduces the input frequency of the fan from fb to f1, reduces the flow rate of the fan, and the increment of frequency converter frequency reduction is 0.1~ 1Hz/S, then the PLC controller CPU14 sends out an ignition signal command, conducts the ignition transformer 10 to discharge and ignite, and at the same time, the PLC controller CPU14 sends out a signal to open the ignition solenoid valve 9, so that a stream of gas flows through the igniter 11, and the gas meets the ignition The transformer 10 is ignited and ignited; when the ignition transformer 10 starts to ignite, the ultraviolet probe 12 starts to detect the igniter 11 at the same time, if the ultraviolet probe 12 detects that the igniter 11 is not ignited within 8 seconds, the PLC controller CPU14 will stop the ignition transformer 10 is discharged, and the ignition solenoid valve 9 is turned off at the same time.

After the ultraviolet probe 12 judges that the igniter 11 is ignited, the igniter 11 continues to burn. At the same time, the PLC controller CPU14 controls the main fire solenoid valve 8 to open. Venturi mixer 4 mixes with air. Referring to Fig. 5, the gas and air mixed concentration corresponding to the blower fan frequency f1 of ignition is L1 (for natural gas, L1=about 17%), and evenly mixed gas enters catalytic burner 1, is passed through the honeycomb ceramic carrier 2 of loading catalyst The igniter 11 is lighted; if the honeycomb ceramic carrier 2 of the loaded catalyst is not ignited by the ultraviolet probe 12, the PLC controller 15 will shut off the main fire solenoid valve 8, and carry out post-purging, and turn off the fan after a few minutes, waiting for inspection or restarting ignition.

After the ultraviolet probe 12 judges that the ignition is successful, the PLC controller CPU14 adjusts the frequency converter 15 through the EM232 module 18 to increase the input frequency f of the fan and the air flow Qa of the fan. When the input frequency of the inverter reaches f2, the corresponding gas mixture concentration is L2 (for natural gas, L2=about 10%), keep the frequency f2 of the frequency converter unchanged, and close the ignition solenoid valve 9 at the same time, and the catalyst carrier 2 is in normal combustion preheating stage, the temperature gradually increases, and when the temperature sensor 13 detects that the preheating temperature of the catalyst carrier 2 reaches the light-off temperature _t1 of the catalyst, the PLC controller CPU14 adjusts the frequency converter 15 through the EM232 module 18 to control the input frequency f of the fan, The frequency increases from f2 to f3 or fd (f4>fd≥f3), the corresponding gas and air mixture concentration is L3 (for natural gas, L3=about 5%), and the increment of frequency converter frequency is 0.01～1Hz/S , the catalytic burner enters the catalytic combustion stage. In the catalytic combustion stage, the input frequency of the fan is increased, and the gas mixture concentration remains basically unchanged, but the combustion power or combustion temperature increases.

In the catalytic combustion stage, the PLC controller CPU14 judges whether the catalyst carrier 2 reaches the set combustion temperature tc through the temperature sensor 13 and the analog/digital conversion module 17. If it is higher or lower than the set temperature, the PLC controller CPU14 passes the digital/analog The conversion module 18 and the frequency converter 15 control the fan to reduce or increase the fan frequency to control the catalytic combustion temperature to achieve constant temperature combustion.

In the catalytic combustion stage, if the flameout is artificially ordered or after the visible light detector 16 detects that the catalytic carrier 2 is flameout, the PLC controller CPU14 will close the main fire electromagnetic valve 8, and carry out purging after flameout. When the temperature reaches the normal temperature T0, the PLC controller CPU14 will issue an instruction to stop the fan 3 from running.

The above embodiments are described for the catalytic combustion of natural gas as the fuel gas, but the present invention is not limited to the above embodiments. The invention is suitable for all types of gas catalytic combustion control, such as coal bed methane, marsh gas, coal gas, petroleum liquefied gas, thermal cracking oil to gas, catalytic cracking oil to gas and the like. It is only necessary to select a catalyst suitable for the gas composition and the corresponding ignition gas mixing concentration L1 (slightly greater than the upper limit of the gas explosion concentration), preheating ordinary combustion gas mixing concentration L2 (slightly lower than the theoretical complete combustion concentration) and catalytic Combustion gas mixed concentration L3 (optimum catalytic combustion concentration), resetting the opening of the proportional control valve 5 and the needle valve 7, through the catalytic combustion control system of the present invention can achieve the purpose of catalytic combustion control.

Claims (7)

1. a control system for catalytic combustion is used to control the combustion reaction of catalytic burner (1), it is characterized in that: it is connected to form by fluid premix control system and PLC control device two large divisions;

Fluid premix control system comprises: a typhoon machine (a 3) series connection venturi mixer (4), be used for purging catalytic burner (1) and utilize venturi mixer (4) injection gas and carry out even premix, the air outlet of venturi mixer (4) is connected with the air inlet of catalytic burner (1), the trunnion inlet scoop of venturi mixer (4) is connected with a ratio adjusting valve (5), be used for setting best combustion gas of catalytic combustion stage-air pre-mixing concentration, the import of ratio adjusting valve (5) is connected with the outlet of a zero-pressure valve (6), be used for guaranteeing that combustion gas is near normal pressure, the import and export two ends of zero-pressure valve (a 6) needle-valve (7) in parallel is used for setting the best combustion gas-air pre-mixing concentration of preheating flaming phase of lighting a fire;

The PLC control device comprises:

A PLC controller CPU (14);

One is connected and is used to control the frequency converter (15) of blower fan (3) incoming frequency f with PLC controller CPU (14) control signal output;

A D/A switch module (18) that connects the input of PLC controller CPU (14) control signal output and frequency converter (15) respectively;

Temperature that is used to detect catalyst carrier, be used to control the temperature sensor (13) of constant temperature catalytic combustion;

A mould/number conversion module (17) that is connected and is connected with temperature sensor (13) signal with PLC controller CPU (14) signal input part;

One is connected in combustion gas and is responsible in (20), is used to the main thermoelectricity magnet valve (8) controlling combustion gas premix switch and be connected with zero-pressure valve (6);

Switch that is used for control point firearm (11), be connected the igniter solenoid valve (9) of combustion gas arm (21);

An ignition transformer (10) that is used for igniter (11) discharge igniting;

One places near the igniter, is used for ultraviolet ray that whether judging point firearm (11) and catalyst carrier (2) lighted pop one's head in (12);

A visible-light detector (16) that places catalyst carrier (2) the place ahead and be connected with PLC controller CPU (14) signal;

A text display that is connected with PLC controller CPU (14) signal.

2. control system for catalytic combustion according to claim 1 is characterized in that: said catalyst carrier (2) is honeycomb ceramic carrier or metallic carrier, and catalyst in load on the carrier.

3. an application rights requires the catalytic combustion control method of 1 described control system for catalytic combustion, it is characterized in that: by the incoming frequency of PLC controller CPU (14) by frequency converter (15) control blower fan (3), the incoming frequency of blower fan (3) is directly proportional with the air mass flow of output, when air passes through the nozzle of venturi mixer (4), around nozzle, form the negative pressure injection gas, by the combustion gas of injection one by zero-pressure valve (6), the combustion gas normal flow by zero-pressure valve (6) becomes geometric ratio to concern with the standard air flow of injection gas; Another burst combustion gas is by the needle-valve (7) in parallel with zero-pressure valve (6), standard gas flow substantially constant by needle-valve (7), after merging, two bursts of combustion gas enter hybrid chamber and the divergent segment and the even premix of air of venturi through ratio adjusting valve (5), combustion gas is relevant by the Reynolds number or the flow of Venturi nozzle with the premix concentration and the air of air, when Reynolds number hour, combustion gas and Air mixing concentration are bigger, increase gradually along with Reynolds number, combustion gas and Air mixing concentration reduce gradually, after Reynolds number is greater than a value, combustion gas and Air mixing concentration no longer change with the increase of Reynolds number, mix the Reynolds number of control and the relation of combustion gas mixing concentration according to fluid, incoming frequency by control blower fan (3), control igniting respectively, preheating, different combustion gas that catalytic combustion is required and air melting concn, and in catalytic combustion stage control catalytic combustion power or temperature.

4. an application rights requires the catalytic combustion control method of 1 described control system for catalytic combustion, it is characterized in that step is as follows:

Step 1: the operation beginning, PLC controller CPU (14) starts blower fan (3) by frequency converter (15);

Step 2: preceding purging, be increased to the purging frequency by frequency converter (15) control blower fan frequency, the incoming frequency of frequency converter (15) is directly proportional with the output flow of blower fan (3), and air enters catalytic burner (1) by venturi mixer (4), finishes preceding purging;

Step 3: igniter igniting, after preceding purging is finished, PLC controller CPU (14) is reduced to spark rate by frequency converter (15) with the incoming frequency of blower fan (3), and conducting ignition transformer (10) discharge sparking, open igniter solenoid valve (9) simultaneously, combustion gas is by combustion gas arm (21) inlet point firearm (11), and igniter (11) is lighted, if igniter (11) is not lighted, then close igniter solenoid valve (9);

Step 4: catalytic burner igniting, after igniter (11) is lighted, open main thermoelectricity magnet valve (8), after combustion gas converges by zero-pressure valve (6) and needle-valve (7) from the combustion gas person in charge (20), passing ratio control valve (5) enters venturi mixer (4) evenly to be mixed with air, combustion gas and Air mixing concentration are slightly larger than the explosion ratio upper limit of combustion gas, and combustion gas mixing gas enters catalytic burner (1), are lighted by igniter (11) during by catalyst carrier (2); If catalyst carrier (2) is not lighted, then can close main thermoelectricity magnet valve (8), blower fan (3) carries out post-purge, again igniting;

Step 5: preheating, after lighting a fire successfully, increase the frequency of blower fan (3), after frequency reaches preheating control point frequency, combustion gas and Air mixing concentration are slightly less than combustion gas theoretically complete combustion concentration, it is constant to keep pre-heat frequency, closes igniter solenoid valve (9), and catalyst carrier (2) is in the ordinary combustion warm-up phase;

Step 6: initiation temperature detects, if the detected temperatures of temperature sensor (13) is lower than the initiation temperature of catalyst, it is constant to keep preheating control point frequency, continue the ordinary combustion preheating, along with preheat temperature raises gradually, when reaching initiation temperature, increase blower fan (3) frequency, arrive catalytic combustion until frequency and stablize initial frequency or set the pairing frequency of catalytic combustion temperature;

Step 7: design temperature is judged, make blower fan keep the pairing frequency of temperature that catalytic combustion is stablized initial frequency or setting by the PLC control system, if detecting ignition temperature, temperature sensor (13) is lower than design temperature, then increase the blower fan controlled frequency, if ignition temperature is higher than design temperature, then reduce the blower fan controlled frequency, the increment of blower fan control increase and decrease frequency is 0.01～1Hz/s;

Step 8: catalytic combustion control, burning enters catalytic combustion after the stage, and repeating step 7 is judged by temperature, and the frequency of increase and decrease blower fan makes catalytic burner (1) automatic control constant temperature catalytic combustion between initiation temperature and maximum limit temperature;

Step 9: stop or misfire detection, in the catalytic combustion stabilization sub stage, if order is flame-out or visible-light detector (16) to detect catalyst carrier (2) flame-out, then can enter step 10, if not, then return step 7;

Step 10: close main thermoelectricity magnet valve (8), blower fan enters step 11 after purging catalytic burner (1);

Step 11: finish, blower fan stops.

5. catalytic combustion control method according to claim 4 is characterized in that: in step 2, the frequency increment that frequency converter increases is 0.1～1Hz/s.

6. whether catalytic combustion control method according to claim 4 is characterized in that: in step 3, connect in 8 seconds at ignition transformer (10), put by ultraviolet ray probe (12) judging point firearm (11) and catch fire.

7. catalytic combustion control method according to claim 4 is characterized in that: in step 7, by the preheat temperature or the catalytic combustion temperature of temperature sensor (13) detection catalyst carrier (2), carry out temperature and judge.

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