Safety control requirements for gas burners
China is rich in natural gas and coal based gas (raw material is coal) resources; They are clean energy and have good social and economic benefits. The gas burner is in line with China's industrial policies, with good market prospects and broad development prospects. However, in the development and design of gas burners, gas characteristics such as flammability, explosiveness, and toxicity are the primary issues for safety control. Here are the safety control requirements for gas burners:
According to the combustion characteristics of the gas in the furnace, its safety control requirements mainly include pre blowing, automatic ignition, combustion status monitoring, non ignition protection, flameout protection, gas pressure high and low limit protection, insufficient air pressure protection, power outage protection, and prevention of gas leakage accidents.
1. Pre blowing: Before the burner is ignited, there must be a period of pre blowing to blow or dilute the remaining air in the furnace and flue. Due to the inevitable presence of residual gas in the working chamber of the burner, there is a risk of explosion if it is 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, and is generally set at 15-60 seconds.
2. Self ignition: Gas burners should be ignited by electric sparks for easy automatic control. High voltage ignition transformers can be used to generate arc ignition, with output energy requirements of voltage ≥ 3 5KV, current of "15 milliamperes", and ignition time generally of 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 burner in a short period of time, and the burner will enter a protective state and cut off the gas supply.
The flame detector should be able to sense the flame signal normally, neither sensitive nor slow. Due to its high sensitivity, if the combustion state fluctuates, it is easy to cause faults and dullness, and the feedback flame signal lags, which is not conducive to safe operation. It is generally required that the response time from the flameout signal to the flameout signal emitted by the flame detector should not exceed 0.2 seconds.
4. Anti ignition protection: When the burner is ignited, gas is introduced and ignited for combustion. 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 flame detector does not ignite, there is no 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 the gas is turned on. 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: If the burner unexpectedly extinguishes during combustion, the burner will enter a protective state. Due to the heat of the furnace, gas is prone to detonation, so it is necessary to enter a protective state and cut off the gas supply in a short period of time. The response time from shutdown to the protection state of the burner should not exceed 1 second.
6. Gas excitation height and 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: not extinguishing, not extinguishing or backfiring, limiting the output thermal power of the burner, and ensuring the safe and economic operation of the equipment. When the gas pressure exceeds this range, the burner should be locked in operation.
The design of a burner generally uses a gas pressure switch to sense the pressure signal and output the switch signal to control the corresponding operation of the burner.
7. Insufficient air pressure protection: The gas burner adopts a high heat intensity design, and its combustion method adopts a shot blasting system. If the fan malfunctions, the air is interrupted or insufficient, please cut off the air immediately, 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. Electricity 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 from the grounding electromagnetic valve core towards the furnace.
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 the pipeline leaks out, it can be used. The second is to avoid poisoning and explosion caused by gas concentration, requiring good ventilation at the work site: providing stable ventilation holes and forced ventilation. In addition, it is required to prohibit the use of explosion-proof pyrotechnic electrical components at the work site. Leaks in the furnace may cause the furnace to explode. There are three methods to solve the problem of gas leakage in the furnace: strengthening the pre blowing time and blowing volume, and blowing or diluting the gas in the furnace; The second is to use a series connected electromagnetic valve in the gas pipeline to improve system safety; The detection device detects the gas pipeline before ignition, and if the gas leakage reaches a certain amount, the burner is locked in operation.