Efficient combustion control method for coke oven waste gas denitration hot blast stove

Abstract

The invention relates to an efficient combustion control method for a coke oven waste gas denitration hot blast stove. The method comprises the steps of ignition, air-fuel ratio measurement, air-fuel ratio maintenance and the like. According to the efficient combustion control method for the coke oven waste gas denitration hot-blast stove, the actual air-fuel ratio of air to fuel gas can be measured before combustion of the hot-blast stove, and the combustion efficiency of the hot-blast stove is improved; the gas content in the pipeline can be monitored, and the gas explosion hidden danger is eliminated; by quantifying the circulating gas flow, large changes of parameters such as system temperature are avoided, and stable operation of the system is achieved; finally, the heated waste gas flow is used as a variable for automatic temperature adjustment, and the efficiency of the denitration system is improved.

Description

Technical Field

[0001] The present invention relates to a high-efficiency combustion control method for a denitrification hot blast stove of coke oven waste gas, belonging to the technical field of automatic control. Background Art

[0002] The waste gas generated by the combustion heating of the coke oven gas (coke oven gas or blast furnace gas) exchanger is the main source of nitride and sulfide pollution in the pre-ironmaking process. To meet the emission standards, the waste gas that was originally directly discharged through the flue and chimney will be subjected to desulfurization and denitrification treatment. To improve the purification efficiency of pollutants in the coke oven waste gas, a part of the waste gas to be purified (circulating gas) will be subjected to circulating combustion heating treatment through a denitrification hot blast stove to improve the purification chemical reaction efficiency of the waste gas and the catalyst.

[0003] In the current heating technology of the coke oven waste gas denitrification hot blast stove, the combustion of a given flow rate of gas (blast furnace gas or coke oven gas, the main fuel component is CO) is used to achieve the purpose of heating the circulating gas. Generally, a temperature sensor is set at the outlet of the hot blast stove to judge whether the circulating gas is heated to the set temperature. If the temperature does not reach the set value, the gas and combustion-supporting air flow rates will be increased continuously. In this process, it is difficult to confirm the proportional relationship between the gas and the combustion-supporting air, and it is also difficult to confirm the proportional relationship between the gas combustion amount and the waste gas flow rate to be heated. The resulting consequence is that it is necessary to frequently and significantly adjust the gas and air flow rates. At the same time, in order to avoid CO generated by incomplete combustion of the gas, the actual flow rate of the combustion-supporting air will be much higher than the required flow rate. The resulting consequence is that the excess combustion-supporting air reduces the flue gas outlet temperature and lowers the operating efficiency of the entire hot blast stove. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: to overcome the above-mentioned technical drawbacks, and provide a combustion control method that automatically calculates the actual air-fuel ratio of the hot blast stove, adjusts the temperature with the waste gas flow rate produced by the coke oven as a variable, and automatically adjusts the required gas flow rate and combustion-supporting air flow rate according to the set temperature to improve the combustion efficiency of the hot blast stove.

[0005] To solve the above-mentioned technical problem, the technical solution proposed by the present invention is: a high-efficiency combustion control method for a denitrification hot blast stove of coke oven waste gas, comprising the following steps: (1) Ignition; there is a set of ignition systems on the hot blast stove, including an ignition gas regulating valve, an igniter, a flame detector switch, an air regulating valve, and a combustion hot gas regulating valve; The ignition gas regulating valve is connected to the gas pipeline and is used to provide gas for the hot blast stove through a small fire burner; the air regulating valve is connected to the air pipeline and is used to provide air for the hot blast stove; the combustion hot gas regulating valve is connected to the discharge pipeline of the hot blast stove; The igniter and the flame detector switch are both located beside the small fire burner; When the hot blast stove ignition process is ready, the combustion hot gas regulating valve is in the fully open state. Start the igniter, and then sequentially open the air regulating valve and the ignition gas regulating valve. If the flame detector switch detects a flame signal, it is determined that the small fire ignition is successful. If no flame signal is detected, it is determined that the small fire ignition process fails, and the hot blast stove control system will terminate the ignition process; After the small fire ignition is successful, the gas is injected into the hot blast stove through the main gas pipeline by the large fire burner nozzle. Then stop the igniter and close the ignition gas regulating valve. If the flame detector switch continuously detects a flame signal, it is determined that the large fire ignition of the hot blast stove is successful. Otherwise, it is determined that the large fire ignition of the hot blast stove fails, and the gas supply will be shut down and the ignition process will be stopped; (2)Measure the air-fuel ratio; use a flue gas detection device and a gas monitoring device; the flue gas detection device is installed behind the hot blast stove. First, use a flue gas sampling device to sample the flue gas discharged from the hot blast stove. After the temperature sensor measures the temperature of the flue gas, use a cooler to cool the flue gas. The cooled flue gas is measured by a carbon monoxide detector to obtain the content of CO in the flue gas; The gas monitoring device calculates the flow rates between various media by installing flow regulating valves and flow detection devices in the gas pipeline, combustion-supporting gas pipeline, and circulating gas pipeline of the hot blast stove, and measures the proportional relationship between various media; In the small fire ignition stage, the gas supply is denoted as Qr; gradually adjust the air supply Qk until the carbon monoxide detector detects the presence of CO. Calculate the air-fuel ratio of the air and gas introduced into the hot blast stove at this time as K = Qk / Qr; then increase the air supply to 1.1K; (3)Maintain the air-fuel ratio; in the large fire ignition stage, the combustion-supporting air supply Qk increases. Taking the gas supply Qr as the independent variable, adjust the air supply Qk so that Qk = 1.1 * K * Qr.

[0006] A further improvement of the above solution is that during the operation of the hot blast stove, the flue gas detection device continuously detects the CO content in the flue gas. If the detected CO content exceeds the standard, increase the air flow or shut down the gas supply.

[0007] A further improvement of the above solution is that when the small fire ignition is completed and the ignition gas regulating valve is completely closed, the air supply is uniformly reduced at a rate of 10% per minute to reduce the air volume injected into the hot blast stove until the air supply meets Qk = K * Qr. During this process, the flue gas detection device continuously detects the CO content in the flue gas. If the detected CO content exceeds the standard, stop reducing the air supply or shut down the gas supply.

[0008] A further improvement of the above solution is as follows: After the hot blast stove burns stably, circulating gas to be heated is injected into the furnace. Let the exhaust gas flow rate discharged from the coke oven be Qf. To achieve a temperature rise of ΔTf, circulating gas with a flow rate of Qx needs to be heated by ΔTx. The calculation formula for Qx is Qx = α * Qf * ΔTf, where α is the injection ratio of exhaust gas and circulating gas. To heat the circulating gas to ΔTx, the required gas volume Qr is calculated by the formula Qr = β * Qx * ΔTx, where β is the injection ratio of circulating gas and gas. Then the required air volume Qk = K * Qr = K * β * Qx * ΔTx. The formula for the gas supply volume and the coke oven exhaust gas flow rate is obtained as: Qr = β * Qx * ΔTx = β * α * Qf * ΔTf * ΔTx. By measuring the exhaust gas flow rate Qf, the gas valve, air valve, and circulating gas valve are adjusted to achieve stable control of the target exhaust gas temperature and flow rate.

[0009] A further improvement of the above solution is as follows: Continuously monitor the exhaust gas temperature to verify whether the value of β * α * ΔTf * ΔTx is accurate; the carbon monoxide detector in the flue gas detection device will continuously monitor whether there is CO in the combustion gas. If the detected CO content is found, increase the air flow rate or shut down the gas.

[0010] The high-efficiency combustion control method for the coke oven exhaust gas denitrification hot blast stove provided by the present invention can measure the actual air-fuel ratio of air and gas, improve the combustion efficiency of the hot blast stove; can monitor the gas content in the pipeline, eliminate the potential hazard of gas explosion; by quantifying the circulating gas flow rate, avoid large changes in system parameters such as temperature, and achieve stable operation of the system; finally, automatic temperature adjustment is carried out with the exhaust gas flow rate to be heated as a variable to improve the efficiency of the denitrification system. Description of the Drawings

[0011] Figure 1 It is a schematic structural diagram of the ignition and flame detection system of a preferred embodiment of the present invention.

[0012] Figure 2 Hot blast stove ignition logic judgment diagram.

[0013] Figure 3 It is a structural diagram of the flue gas detection device of a preferred embodiment of the present invention.

[0014] Figure 4 It is a layout diagram of the hot blast stove gas monitoring device equipment of a preferred embodiment of the present invention.

[0015] Figure 5 Schematic diagram of signals connected to the hot blast stove combustion control system. Embodiment

[0016] Example: For the efficient combustion control method of the coke oven waste gas denitration hot blast stove in this example, two sets of equipment, namely the small fire flame detector and the large fire flame detector, are installed in the traditional hot blast stove, which are respectively used to judge whether the small fire ignition process and the large fire ignition process are successful. If the installation positions of the two sets of equipment are not appropriate, it is easy to cause signal interference and then lead to safety accidents. However, in this example, only one flame detector switch is installed inside the hot blast stove to realize the detection of small fires and large fires. The specific method is as follows: An ignition system is installed in the hot blast stove furnace, including an ignition gas regulating valve Q1, an igniter IG, a flame detector switch MO, an air regulating valve M2, and a combustion hot gas regulating valve M4, as Figure 1 shown. Among them, the ignition gas regulating valve Q1 is connected to the gas pipeline, and the gas is injected into the hot blast stove through the small fire burner. The metering igniter G1 is installed beside the small fire burner and is used to ignite the gas injected into the hot blast stove. The flame detector switch MO faces the small fire and large fire burners and is used to detect whether there is a flame at their outlets. The air regulating valve M2 is installed on the air pipeline and is used to quantitatively inject the air injected by the fan into the hot blast stove for combustion support. The combustion hot gas regulating valve M4 is installed on the discharge pipeline after combustion and discharges the combustion gas. When the ignition process of the hot blast stove is ready, the combustion hot gas regulating valve M4 is in the fully open state, the igniter IG is turned on, and then the air regulating valve M2 and the ignition gas regulating valve Q1 are opened in sequence. At this time, due to the mixing of gas and air, an open flame appears at the outlet of the ignition gas pipeline. The flame detector switch MO should detect the flame signal, and it can be judged that the small fire ignition is successful. If the flame signal is not detected within the set time, it is judged that the small fire ignition process fails, and the hot blast stove control system will terminate the ignition process. After confirming the successful ignition of the small fire, the hot blast stove control system will close the relief valve Q4 on the gas pipeline, open the gas cut-off valves Q2 and Q3, and then open the main gas valve M1 to inject the gas into the hot blast stove furnace for combustion. A large amount of gas injected into the hot blast stove from the gas pipeline will be ignited by the small fire system to generate a large fire. The flame detector switch MO will continuously detect the flame signal, and the control system will stop the igniter IG and close the ignition valve Q1. If the flame detection signal still exists at this time, it can be judged that the large fire ignition process of the hot blast stove is successfully completed. Otherwise, after delaying to the set time, it is judged that the large fire ignition process of the hot blast stove fails, the gas valve M1 will be shut down and the ignition process will be stopped. The main logic judgment process is as Figure 2 shown. Through this method, it is possible to reliably judge whether the two ignition processes are successful.

[0017] This example provides a method for automatically calculating the air-fuel ratio. This method includes a set of flue gas detection device and a gas monitoring device. Among them, the flue gas detection device is installed behind the hot blast stove and is used to detect the temperature and CO content of the combustion gas. The main structure is as Figure 3As shown in the figure. The flue gas detection device includes a flue gas collection device installed after the exhaust pipe of the hot blast stove, which can collect the flue gas after combustion from four directions to ensure the effectiveness of sampling. The sampled flue gas is aggregated and transmitted to the next stage. A flue gas temperature detection device T1 is installed on the next-stage pipe to measure the real-time temperature of the flue gas. A cooler CT is installed behind the pipe to quickly cool the high-temperature flue gas to avoid damaging the subsequent instruments and exhaust equipment due to high temperature. The cooled flue gas passes through the pipe installed with a CO detector B1 to measure the CO content in the flue gas. An axial flow fan AX and a check valve V are also installed on the pipe of the flue gas detection device. During the process of collecting flue gas, the axial flow fan AX is started to suck the sampled flue gas into the sampling pipe, and the check valve V can prevent the flue gas from flowing back. The flue gas after sampling finally flows back into the flue gas exhaust pipe.

[0018] The gas monitoring device calculates the flow rates of various media by installing flow regulating valves and flow detection devices in the gas pipeline, combustion-supporting gas pipeline, and circulating gas pipeline, and measures the proportional relationship between them by the control system to judge the high-efficiency and safety characteristics of combustion. The installation layout diagrams of these devices are as Figure 4 shown. A temperature, pressure, and gas flowmeter A1 is installed on the gas pipeline to convert the pilot gas and main gas for starting the fire entering the hot blast stove into standard gas volumes; a temperature, pressure, and gas flowmeter A2 is arranged on the air pipeline to convert the combustion-supporting air entering the hot blast stove into standard air volumes. A temperature, pressure, and gas flowmeter A3 is installed on the circulating gas pipeline to convert the circulating gas to be heated entering the hot blast stove into the standard flow rate of the gas to be heated.

[0019] During the pilot-fire stage, the combustion hot gas regulating valve M4 is opened, and the axial flow fan in the flue gas detection device starts to operate, sucking the flue gas generated during the pilot-fire stage through the sampling pipe at the outlet of the hot blast stove for sampling. After passing through the cooler CT, the flue gas reaches the CO detector B1 to detect the CO content therein. At the initial stage of ignition, by controlling the ignition gas regulating valve Q1, the supply quantity Qr of the pilot gas is ensured to be stable, and by controlling the air flow regulating valve Q2, the injected air is ensured to fully ignite the pilot gas. Then the control system reduces the air supply quantity Qk at a fixed speed until the CO detector B1 detects the presence of CO indicating incomplete combustion. At this time, the control system can calculate the air-fuel ratio of the gas medium in this gas pipeline as K = Qk / Qr. After calculating the air-fuel ratio, the control system controls the air flow regulating valve Q2 to increase the supply quantity of the combustion-supporting air, and gives the air flow to 1.1 times the air-fuel ratio to ensure the full combustion of the gas. At this time, the CO detector will detect that the CO content in the flue gas is zero or below the set value.

[0020] After the process of igniting the small fire in the hot blast stove ends and enters the stage of igniting the large fire, continue to control the air flow regulating valve Q2 to increase the supply of combustion-supporting air Qk. The gas flow regulating valve M1 will open to inject gas into the hot blast stove. Since the gas flow meter A1 measures the total gas volume injected into the hot blast stove, during the stage of closing the ignition gas regulating valve Q1 and opening the gas flow regulating valve M1, with the gas volume Qr as the variable, adjust the air flow regulating valve M2 to ensure that the required injected air flow is Qk = 1.1 * K * Qr, so that the gas can burn fully. At this time, the flue gas detection device continuously detects the CO content in the flue gas after combustion. Once the CO content is detected or the content exceeds the standard, the air flow will be increased continuously or the gas will be shut down to avoid accidents such as incomplete combustion or explosion. When the ignition gas regulating valve Q1 is completely closed, the gas can only be injected into the hot blast stove through the gas flow regulating valve M1 on the main gas pipeline. At this time, the control system controls the air flow regulating valve M2 to continuously and uniformly reduce the air flow injected into the hot blast stove at a flow rate reduction of 10% per minute until the air flow meets Qk = K * Qr. During this process, the flue gas detection device continuously detects the CO content in the flue gas after combustion. This process is also a process of re-verifying the air-fuel ratio. Once the CO content is detected or the content exceeds the standard, the reduction of the air flow will be stopped or the gas will be shut down to avoid accidents such as incomplete combustion or explosion.

[0021] After the hot blast stove burns stably, it will be possible to inject the circulating gas to be heated into the furnace. The heated circulating gas is mixed with the waste gas from the coke oven combustion and heated up to react better with the denitration catalyst. Since the waste gas generated by the coke oven combustion has the characteristics of cyclic fluctuation, to ensure the stability of the waste gas denitration and purification process, the flow rate of the circulating gas to be heated will also change according to the flow rate of the waste gas to be purified to achieve uniform heating. At the same time, to ensure the combustion effect of the denitration hot blast stove and reduce the fluctuations of the system flow rate and temperature caused by the fluctuations of the heating gas, the combustion control system will continuously adjust the gas regulating valve M1, the air regulating valve M2 and the circulating gas flow regulating valve M3 under the condition of collecting various medium variables to achieve the stability of the gas at the outlet of the hot blast stove. The schematic diagram of the process parameter signals and valve control transmitter control signals connected to the control system is as Figure 5As shown in the figure. Let the flow rate of the waste gas discharged from the coke oven detected by the control system be Qf. To achieve a temperature rise of ΔTf, it is necessary to heat the circulating gas with a flow rate of Qx by ΔTx. The calculation formula for Qx is Qx = α * Qf * ΔTf, where α is the injection ratio of the waste gas and the circulating gas. According to the principle of conservation of heat and heat transfer, α is a fixed value. To heat the circulating gas to ΔTx, it is necessary to burn gas to heat it. The calculation formula for the gas volume Qr is Qr = β * Qx * ΔTx, where β is the injection ratio of the circulating gas and the gas. Similarly, according to the principle of conservation of heat and heat transfer, β is a fixed value. Since the air-fuel ratio of the gas and air is fixed, the required combustion-supporting air volume Qk = K * Qr = K * β * Qx * ΔTx. Therefore, when the temperature rises ΔTf and ΔTx are stable, a formula between the gas flow rate and the waste gas flow rate of the coke oven to be heated can be finally obtained with the flow rate of the waste gas to be heated as a variable: Qr = β * Qx * ΔTx = β * α * Qf * ΔTf * ΔTx. The control system dynamically adjusts the gas control valve M1, the air control valve M2, and the circulating gas flow control valve M3 through the measured waste gas flow rate Qf to achieve stable control of the target waste gas temperature and flow rate. After heating the circulating gas, T1 in the flue gas detection device will continuously monitor whether the gas temperature meets the standard to verify whether the value of β * α * ΔTf * ΔTx is accurate; the CO detector B1 in the flue gas detection device will continuously monitor whether there is CO in the combustion gas. In the case of detecting that the CO content exceeds the standard, the air flow rate will be increased or the gas will be shut down emergently to avoid gas explosion accidents.

[0022] The present invention is not limited to the above embodiments. Any technical solution formed by equivalent replacement falls within the protection scope required by the present invention.

Claims

1. An efficient combustion control method for a hot blast stove for denitrifying coke oven waste gas, characterized in that, it comprises the following steps: (1) Ignition: There is an ignition system on the hot blast stove, which includes an ignition gas regulating valve, an igniter, a flame detector switch, an air regulating valve, and a combustion hot gas regulating valve; The ignition gas regulating valve is connected to the gas pipeline and is used to provide gas for the hot blast stove through a small fire burner; the air regulating valve is connected to the air pipeline and is used to provide air for the hot blast stove; the combustion hot gas regulating valve is connected to the discharge pipeline of the hot blast stove; Both the igniter and the flame detector switch are located beside the small fire burner; When the ignition process of the hot blast stove is ready, the combustion hot gas regulating valve is in the fully open state, the igniter is turned on, and then the air regulating valve and the ignition gas regulating valve are opened in sequence. When the flame detector switch detects a flame signal, it is determined that the small fire ignition is successful. If no flame signal is detected, it is determined that the small fire ignition process fails, and the hot blast stove control system will terminate the ignition process; After the small fire ignition is successful, gas is injected into the hot blast stove through the main gas pipeline by the large fire burner, then the igniter is stopped, and the ignition gas regulating valve is closed. If the flame detector switch continuously detects a flame signal, it is determined that the large fire ignition of the hot blast stove is successful, otherwise it is determined that the large fire ignition of the hot blast stove fails, and the gas supply will be shut down and the ignition process will be stopped; (2) Measuring the air-fuel ratio: Use a flue gas detection device and a gas monitoring device; the flue gas detection device is installed behind the hot blast stove. First, use a flue gas collection device to collect the flue gas discharged from the hot blast stove, then measure the temperature of the flue gas by a temperature sensor, and then use a cooler to cool the flue gas. The cooled flue gas is measured for the content of CO in the flue gas by a carbon monoxide detector; The gas monitoring device calculates the flow rates between various media and measures the proportional relationship between various media by installing flow regulating valves and flow detection devices on the gas pipeline, combustion-supporting gas pipeline, and circulating gas pipeline of the hot blast stove; In the small fire ignition stage, the gas supply amount is denoted as Qr; gradually adjust the air supply amount Qk until the carbon monoxide detector detects the presence of CO, and calculate the air-fuel ratio of the air and gas introduced into the hot blast stove at this time as K = Qk / Qr; then increase the air supply amount to 1.1K; (3) Maintaining the air-fuel ratio; in the large fire ignition stage, the combustion-supporting air supply amount Qk increases. Taking the gas supply amount Qr as the independent variable, adjust the air supply amount Qk so that Qk = 1.1 * K * Qr.

2. The efficient combustion control method for a hot blast stove for denitrifying coke oven waste gas according to claim 1, characterized in that: During the operation of the hot blast stove, the flue gas detection device continuously detects the CO content in the flue gas. If the detected CO content exceeds the standard, increase the air flow rate or shut down the gas supply.

3. The efficient combustion control method for a hot blast stove for denitrifying coke oven waste gas according to claim 1, characterized in that: After the ignition of the small fire is completed and the ignition gas regulating valve is completely closed, the air supply amount is uniformly reduced at a rate of 10% per minute to reduce the air amount injected into the hot blast stove until the air supply amount satisfies Qk = K * Qr. During this process, the flue gas detection device continuously detects the CO content in the flue gas. If the detected CO content exceeds the standard, the reduction of the air supply amount is stopped or the gas is shut down.

4. The high-efficiency combustion control method for the coke oven waste gas denitration hot blast stove according to claim 1, characterized in that: After the hot blast stove burns stably, circulating gas to be heated is injected into the furnace; assuming the waste gas flow rate discharged from the coke oven is Qf, to achieve a temperature rise of ΔTf, it is necessary to heat the circulating gas with a flow rate of Qx by ΔTx. The calculation formula for Qx is Qx = α * Qf * ΔTf, where α is the injection ratio of the waste gas and the circulating gas; to heat the circulating gas to ΔTx, the required gas amount Qr is calculated by the formula Qr = β * Qx * ΔTx, where β is the injection ratio of the circulating gas and the gas; then the required air amount Qk = K * Qr == K * β * Qx * ΔTx; the formula between the gas supply amount and the coke oven waste gas flow rate is obtained as: Qr = β * Qx * ΔTx = β * α * Qf * ΔTf * ΔTx; the gas valve, air valve, and circulating gas valve are adjusted through the measured waste gas flow rate Qf, so as to achieve stable control of the target waste gas temperature and flow rate.

5. The high-efficiency combustion control method for the coke oven waste gas denitration hot blast stove according to claim 4, characterized in that: Continuously monitor the waste gas temperature to verify whether the value of β * α * ΔTf * ΔTx is accurate; the carbon monoxide detector in the flue gas detection device will continuously monitor whether there is CO in the combustion gas. If the CO content is detected, the air flow rate is increased or the gas is shut down.

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