Natural gas burner control system and safety issues

Natural gas burner control system and safety issues
In terms of the current situation in China, natural gas and coal are relatively abundant as raw materials, which are clean energy and have good social and economic benefits. The proportion of natural gas burners is more in line with my current industrial policy, so the market prospects are very good.
However, in the development process of natural gas burners, the three major hazards of natural gas characteristics, namely "flammable, explosive, and toxic", are the primary issues of safety control. Today, Guangzhou Kuitai Automatic Control Equipment mainly focuses on the control system of natural gas burners. The most important thing.
Safety control requirements of natural gas burner: according to the combustion characteristics of gas in the furnace, safety control requirements mainly include pre blowing, automatic ignition, combustion state monitoring, non ignition protection, flameout protection, high and low pressure limit protection, insufficient pressure protection, power failure protection, and measures to prevent gas leakage accidents.
Pre blowing
Ignite on natural gas burner
Previously, there must be a period of pre blowing to blow away or dilute the remaining gas in the furnace and flue. Due to the inevitable presence of residual gas in the working chamber of a natural gas burner, there is a risk of explosion if ignited without pre blowing. The remaining gas must be blown off 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, usually set at 15-60 seconds
2. Automatic ignition
The natural gas burner shall be ignited by electric Spark-ignition engine to facilitate automatic control. High voltage ignition transformers can be used to generate arc ignition, with output energy requirements of voltage ≥ 3.5KV, current ≥ 15mA, and ignition time generally 2-5 seconds.
3. Combustion status monitoring
The combustion status must be dynamically monitored. Once the flame detector detects a flameout signal, it must be fed back to the natural gas burner in a short period of time, and then enter a protective state and cut off the gas supply.
The flame detector must be able to sense the flame signal normally, neither sensitive nor dull. Due to its sensitivity, if the combustion state fluctuates, it is easy to cause faults and slowness. The delayed feedback flame signal is not conducive to safe operation. It is generally required that the response time of the flame detector from flameout to flameout signal shall not exceed 0.2 seconds.
4. Fire prevention
When the natural gas burner is ignited, gas is introduced, ignited, and burned. The ignition action requires the formation of an ignition temperature field before the introduction of gas, in order to facilitate ignition and combustion. If the ignition fails, the flame detector cannot sense the flame signal and the burner enters a protective state.
The time from ignition to entering the protective state should be appropriate, neither too short nor too long. If it is too short, there will be no time to form a stable flame; If the time is too long, a large amount of gas will enter the furnace when it cannot be ignited. Usually, it is required that the burner judge the flame signal detected by the flame detector within 2-3 seconds after gas supply. If it does not catch fire, it will enter a protected state, and if it catches fire, it will remain burning.
5. Flame out protection
During the combustion process of the burner, if it is accidentally extinguished, the burner will enter a protective state. Because the stove is very hot. Gas is prone to detonation, so it must enter a protective state and cut off the gas supply in a short period of time. The response time from the occurrence of flameout to the burner entering the protection state should not exceed 1 second.
6. Gas pressure high and low limit protection
The gas burner has a certain range of stable combustion and only allows gas pressure to fluctuate within a certain range. The purpose of limiting the high and low pressure of gas is to ensure the stability of the flame: no flameout, no flameout, or backfire, while limiting the output thermal power of the burner to ensure safe and economical operation of the equipment. When the gas pressure exceeds this range, the burner should be locked.
Burner design generally uses a gas pressure switch to sense the pressure signal, and outputs the switch signal to control the corresponding operation of the burner.
7. Air pressure
Insufficient protection of the gas burner design with high thermal intensity, and the combustion method adopts forced air explosion. If the fan malfunctions, the air is interrupted or insufficient, immediately cut off the gas, otherwise the furnace will explode or flash back to the fan. Therefore, while improving the quality of the fan, gas control must be interlocked with air pressure. When the air pressure is insufficient, the gas supply should be immediately cut off.
Usually, gas pressure switches are used to sense gas pressure signals and output switch signals to control the corresponding operation of gas solenoid valves.
8. Power outage protection
When the burner suddenly cuts off during operation, the gas supply must be immediately cut off to protect the safety of the equipment. The gas control solenoid valve must always be closed. Once the power is cut off, it will automatically shut down and cut off the gas supply. The response time for closing the solenoid valve is less than 5 seconds
Measures to prevent gas leakage accidents
Gas leakage includes two aspects: one refers to the leakage of gas into the environment through pipelines, and the other refers to the leakage of gas into the furnace through the electromagnetic valve core end.
Environmental leaks may lead to poisoning and explosion accidents among construction personnel, and must be taken seriously. Firstly, ensure that the pipeline is sealed and regularly check for leaks. If pipeline leakage must be eliminated, it can be used. Secondly, in order to avoid potential poisoning and explosion caused by gas concentration, it is required to have good ventilation at the work site: permanent ventilation holes and forced ventilation installation; In addition, it is required to prohibit the use of fireworks and explosion-proof electrical components at the workplace.
Leaks in the furnace may cause the furnace to explode. There are three methods to solve the problem of gas leakage in the furnace: firstly, strengthen the pre blowing time and blowing volume, and blow or dilute the gas in the furnace; The second is to use two solenoid valves in series to improve the safety of the system; 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 will be locked in operation. The measures to prevent gas leakage belong to external control and are generally not included in burner control.