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, power outage protection, and measures to prevent gas leakage accidents, etc.
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, there is a risk of explosion if ignited without pre-blowing. The remaining 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 blowing volume, and is generally set to 15-60 seconds.
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 >15mA. The ignition time is generally: 2~5 seconds.
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 be neither sensitive nor 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.
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 protective state should be appropriate, neither too short nor too long. If it is too short, it will not have time to form a stable flame; if it is too long, it will cause a large amount of gas to enter the furnace. It is generally required that the burner will judge the flame signal sensed by the flame detector within 2-3 seconds after gas is introduced. If it is not on fire, it will enter the protection state, and if it is on fire, it will maintain combustion.
During the combustion process of the burner, if the flameout occurs unexpectedly, the burner will enter the protection state. Since the furnace is hot, deflagration is likely to occur when gas enters, so it must enter the protection state in a very short time. Cut off the gas supply from flameout to the burner entering the protection state. The response time of this process is required to be no more than 1 second.
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 the stability of the flame: no flameout, no flameout or 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
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, cut off the gas immediately. Otherwise, furnace deflagration or backfire to the fan will occur. Therefore, while improving the quality of the fan, the gas control must be interlocked with the air pressure.
When the air pressure is insufficient, the gas supply should be cut off immediately.
A gas pressure switch is generally used to sense the air pressure signal and output a switching signal to control the corresponding work of the gas solenoid valve.
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 a normally closed type. Once the power is cut off, it will automatically close and cut off the gas supply. Solenoid valve closing response time ≤5s.
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 leakage may cause poisoning of personnel and explosion accidents at the work site, which must be taken seriously.
First, ensure that the pipeline is sealed, and check the pipeline for leaks regularly. If the pipeline leaks, it must be eliminated before continued use;
Secondly, to avoid gas concentrations that may cause poisoning and explosion, the work site is required to be well ventilated: permanent vents and forced ventilation devices must be installed;
In addition, it is required that fireworks and electrical parts are prohibited at the work site. Leakage in the explosion-proof furnace may cause an explosion in the furnace.
First, increase the pre-blowing time and air volume to blow out or dilute the gas in the furnace;
Second, the gas pipeline adopts a series structure of two solenoid valves to improve system safety;
The third is to use a pipeline leakage detection device to detect the gas pipeline before ignition. If the gas leakage reaches a certain amount, the burner operation will be locked;
Measures to prevent gas leakage are peripheral controls and are generally not incorporated into the burner body control.