According to the combustion characteristics of gas in the furnace, the safety control requirements mainly include pre-blowing, automatic ignition, combustion status monitoring, ignition misfire protection, flameout protection, gas pressure high and low limit protection, insufficient air pressure protection, and power outage. Measures to protect and prevent gas leakage accidents, etc.
1.Pre-blowing
Before the burner is ignited, there must be a period of pre-blowing to blow away or dilute the remaining gas in the furnace and flue. Because there is inevitably residual gas in the working furnace of the burner, if it is ignited without pre-blowing, there is a risk of explosion. The residual gas must be blown away or diluted to ensure that the gas concentration is not within the explosion limit.
The pre-blowing time is related to the furnace structure and air blowing volume and is generally set to 15-60 seconds.
2.Automatic ignition
Gas burners should use electric spark ignition to facilitate automatic control. A high-voltage ignition transformer can be used to generate arc ignition, and its output energy is required to be: voltage ≥ 3. 5K V, current ≥ 15 mA, and the ignition time is generally: 2 to 5 seconds.
3. Combustion status monitoring
The combustion state must be dynamically monitored. Once the flame detector senses a flameout signal, it must be fed back to the burner in a very short time. The burner will then enter the protection state and cut off the gas supply.
The flame detector must be able to sense the flame signal normally and should not be sensitive or slow. Because of its sensitivity, if the combustion state fluctuates, it is easy to cause malfunction and become slow, and the feedback flame signal lags behind, which is not conducive to safe operation.
It is generally required that the response time from the flameout to the flame detector sending out the flameout signal does not exceed 0.2 seconds.
4. Protection against fire
When the burner is ignited, gas is introduced and the gas ignites and burns. The ignition action is required to occur before the gas is introduced, and an ignition temperature field is formed first to facilitate ignition and combustion. If the ignition fails, the flame detector cannot detect the flame signal, and the burner enters the protection state.
The time from ignition to entering the protection state must be appropriate, neither too short nor too long. If it is too short, there will be no time to form a stable flame; if it is too long, a large amount of gas will enter the furnace when the fire cannot be ignited. It is generally required that the burner will judge the flame signal sensed by the flame detector after 2-3 seconds of passing the gas. If it is not on fire, it will enter the protection state, and if it is on fire, it will maintain combustion.
5. Flameout protection
During the combustion process of the burner, if it accidentally flames out, the burner will enter the protection state. Because the furnace is hot. Deflagration is likely to occur when gas enters, so it must enter the protection state in a very short time and cut off the gas supply.
From the occurrence of flameout to the burner entering the protection state, the response time of this process is required to be no more than 1 second.
6. Gas pressure high and low limit protection
The gas burner has a certain range for stable combustion, and only allows the gas pressure to fluctuate within a certain range. The purpose of limiting the high and low pressure of the gas is to ensure flame stability: no flameout, no flameout, and no backfire. At the same time, the output thermal power of the burner is limited to ensure safe and economical operation of the equipment. When the gas pressure exceeds this range, the burner operation should be locked.
Burner design generally uses a gas pressure switch to sense the pressure signal and output a switching signal to control the corresponding work of the burner.
7.Insufficient air pressure protection
The gas burner is designed with high thermal intensity, and its combustion method adopts forced air blast type. If the fan fails and causes air interruption or insufficient air, immediately cut off the gas, otherwise the furnace will explode or backfire to the fan. Therefore, while improving the quality of the fan, gas control must be interlocked with the air pressure. When the air pressure is insufficient, the gas supply should be cut off immediately.
Generally, a gas pressure switch is used to sense the air pressure signal and output a switching signal to control the corresponding work of the gas solenoid valve.
8.Power failure protection
If the burner suddenly loses power during operation, the gas supply must be cut off immediately to protect the safety of the equipment. The gas control solenoid valve must be normally closed. Once the power is cut off, it will automatically close and cut off the gas supply. Solenoid valve closing response time ≤5s.
9. Measures to prevent gas leakage accidents
Gas leakage includes two aspects. One refers to the gas leaking to the environment through the pipeline, and the other refers to the gas leaking into the furnace through the solenoid valve core end.
Environmental leaks may cause poisoning of personnel and explosion accidents at work sites, so we must attach great importance to them. First, ensure that the pipelines are sealed and check for leaks regularly. If there are leaks in the pipelines, they must be eliminated before continued use. Secondly, to avoid gas concentrations that cause poisoning and explosion, the work site is required to be well ventilated: permanent ventilation holes and forced ventilation are required. device; in addition, it is required that fireworks and explosion-proof electrical parts are prohibited at the work site.
Leakage in the furnace may cause an explosion in the furnace. There are three ways to solve the leakage problem in the furnace: first, strengthen the pre-blowing time and blowing volume to blow out or dilute the gas in the furnace; second, use two solenoid valves in series structure in the gas pipeline to improve system safety; third, use pipelines The leakage detection device detects the gas pipeline before ignition. If the gas leakage reaches a certain amount, the burner will be locked.
Measures to prevent gas leakage are peripheral controls and are generally not included in the burner body control.
According to the combustion characteristics of gas in the furnace, the safety control requirements mainly include pre-blowing, automatic ignition, combustion status monitoring, ignition misfire protection, flameout protection, gas pressure high and low limit protection, insufficient air pressure protection, and power outage. Measures to protect and prevent gas leakage accidents, etc.
1.Pre-blowing
Before the burner is ignited, there must be a period of pre-blowing to blow away or dilute the remaining gas in the furnace and flue. Because there is inevitably residual gas in the working furnace of the burner, if it is ignited without pre-blowing, there is a risk of explosion. The residual gas must be blown away or diluted to ensure that the gas concentration is not within the explosion limit.
The pre-blowing time is related to the furnace structure and air blowing volume and is generally set to 15-60 seconds.
2.Automatic ignition
Gas burners should use electric spark ignition to facilitate automatic control. A high-voltage ignition transformer can be used to generate arc ignition, and its output energy is required to be: voltage ≥ 3. 5K V, current ≥ 15 mA, and the ignition time is generally: 2 to 5 seconds.
3. Combustion status monitoring
The combustion state must be dynamically monitored. Once the flame detector senses a flameout signal, it must be fed back to the burner in a very short time. The burner will then enter the protection state and cut off the gas supply.
The flame detector must be able to sense the flame signal normally and should not be sensitive or slow. Because of its sensitivity, if the combustion state fluctuates, it is easy to cause malfunction and become slow, and the feedback flame signal lags behind, which is not conducive to safe operation.
It is generally required that the response time from the flameout to the flame detector sending out the flameout signal does not exceed 0.2 seconds.
4. Protection against fire
When the burner is ignited, gas is introduced and the gas ignites and burns. The ignition action is required to occur before the gas is introduced, and an ignition temperature field is formed first to facilitate ignition and combustion. If the ignition fails, the flame detector cannot detect the flame signal, and the burner enters the protection state.
The time from ignition to entering the protection state must be appropriate, neither too short nor too long. If it is too short, there will be no time to form a stable flame; if it is too long, a large amount of gas will enter the furnace when the fire cannot be ignited. It is generally required that the burner will judge the flame signal sensed by the flame detector after 2-3 seconds of passing the gas. If it is not on fire, it will enter the protection state, and if it is on fire, it will maintain combustion.
5. Flameout protection
During the combustion process of the burner, if it accidentally flames out, the burner will enter the protection state. Because the furnace is hot. Deflagration is likely to occur when gas enters, so it must enter the protection state in a very short time and cut off the gas supply.
From the occurrence of flameout to the burner entering the protection state, the response time of this process is required to be no more than 1 second.
6. Gas pressure high and low limit protection
The gas burner has a certain range for stable combustion, and only allows the gas pressure to fluctuate within a certain range. The purpose of limiting the high and low pressure of the gas is to ensure flame stability: no flameout, no flameout, and no backfire. At the same time, the output thermal power of the burner is limited to ensure safe and economical operation of the equipment. When the gas pressure exceeds this range, the burner operation should be locked.
Burner design generally uses a gas pressure switch to sense the pressure signal and output a switching signal to control the corresponding work of the burner.
7.Insufficient air pressure protection
The gas burner is designed with high thermal intensity, and its combustion method adopts forced air blast type. If the fan fails and causes air interruption or insufficient air, immediately cut off the gas, otherwise the furnace will explode or backfire to the fan. Therefore, while improving the quality of the fan, gas control must be interlocked with the air pressure. When the air pressure is insufficient, the gas supply should be cut off immediately.
Generally, a gas pressure switch is used to sense the air pressure signal and output a switching signal to control the corresponding work of the gas solenoid valve.
8.Power failure protection
If the burner suddenly loses power during operation, the gas supply must be cut off immediately to protect the safety of the equipment. The gas control solenoid valve must be normally closed. Once the power is cut off, it will automatically close and cut off the gas supply. Solenoid valve closing response time ≤5s.
9. Measures to prevent gas leakage accidents
Gas leakage includes two aspects. One refers to the gas leaking to the environment through the pipeline, and the other refers to the gas leaking into the furnace through the solenoid valve core end.
Environmental leaks may cause poisoning of personnel and explosion accidents at work sites, so we must attach great importance to them. First, ensure that the pipelines are sealed and check for leaks regularly. If there are leaks in the pipelines, they must be eliminated before continued use. Secondly, to avoid gas concentrations that cause poisoning and explosion, the work site is required to be well ventilated: permanent ventilation holes and forced ventilation are required. device; in addition, it is required that fireworks and explosion-proof electrical parts are prohibited at the work site.
Leakage in the furnace may cause an explosion in the furnace. There are three ways to solve the leakage problem in the furnace: first, strengthen the pre-blowing time and blowing volume to blow out or dilute the gas in the furnace; second, use two solenoid valves in series structure in the gas pipeline to improve system safety; third, use pipelines The leakage detection device detects the gas pipeline before ignition. If the gas leakage reaches a certain amount, the burner will be locked.
Measures to prevent gas leakage are peripheral controls and are generally not included in the burner body control.