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author： 2020-05-31
Safety control requirements for gas burners (gas burners)
China has abundant natural gas and coal-to-gas (coal as the raw material) resources, and belongs to clean energy, with good social and economic benefits.The gas burner accords with the industrial policy of our country, the market prospect is very good, have the development prospect greatly.However, in the development and design of gas burner, the characteristics of gas - inflammable, explosive and toxic, the primary problem of safety control.The following safety control requirements of gas burner are introduced:
According to the combustion characteristics of gas in the furnace, the safety control requirements mainly include pre-blast, automatic ignition, combustion monitoring, protection against ignition, protection against flameout, protection against high and low limit of gas pressure, protection against insufficient air pressure, protection against power failure, and measures to prevent gas leakage accidents.
1. Preliminary blowing
Before ignition, the burner must have a period of time of pre-blowing to blow away or dilute the residual gas in the furnace and flue.Because there is inevitably residual gas in the working chamber of the burner, there is a risk of explosion if it is ignited without a pre-blast.The residual gas must be blown out or diluted to ensure that the gas concentration is not within the explosion limit.
The preblow time is generally set to 15-60 seconds, which is related to the furnace structure and blowing volume
2. Automatic ignition
The combustion engine should adopt electric spark ignition to realize automatic control.Arc ignition can be produced by high-voltage ignition transformer, whose output energy is required to be: voltage ≥ 3.5k V, current ≥15mA, ignition time is generally: 2 ~ 5 seconds.
3. Monitoring of combustion status
The combustion state must be dynamically monitored. Once the flame detector detects the flameout signal, it must be fed back to the burner in a very short time. The burner then enters the protective state and cuts off the gas supply.
The flame detector should be able to detect the flame signal normally, neither sensitive nor insensitive.Because of its sensitivity, if there is any fluctuation in the combustion state, it is easy to produce false action and slow, and the feedback flame signal lags, which is not conducive to safe operation.
The response time from flameout to flameout from the flame detector is generally not more than 0.2 seconds.
Protection against ignition
When the burner ignites, the gas enters, and the gas ignites.The ignition action is required to take place before the gas passes through, and the ignition temperature field is formed to facilitate ignition and combustion.If the ignition fails, the flame detector will not detect the flame signal, and the burner will enter the protective state.
The time from ignition to entry into protection should be adequate, neither too short nor too long.If too short, too late to form a stable flame;Too long, point not to cause a lot of gas into the furnace.Generally, it is required that the burner judge the flame signal detected by the flame detector within 2-3 seconds after the gas is injected.
5. Flameout protection
In the process of combustion, if the burner accidentally shut off, the burner into the protection state.Because the furnace is hot.Gas entering is prone to deflagration, so it is necessary to enter the protection state in a very short time to cut off the gas supply.
The response time of the process from the occurrence of flameout to the entering of the burner into the protective state shall not exceed 1 second.
6. Gas pressure limit protection
The steady combustion of gas burner has a certain range, and only the gas pressure is allowed to fluctuate within a certain range.The purpose of defining the high and low pressure of gas is to ensure the flame stability: no disconnection, no flameout and no tempering. Meanwhile, the thermal power output of the burner is limited to ensure the safe and economical operation of the equipment.When the gas pressure is beyond this range, the burner should be locked.
Gas pressure switch is generally used to detect the pressure signal and output the switch signal to control the corresponding work of the burner.
7. Insufficient air pressure protection
The design of gas burner has high thermal intensity, and its combustion mode adopts blast forced system.If the failure of the fan causes air interruption or air shortage, cut off the gas immediately, or furnace deflagration or tempering to the fan will occur.Therefore, while improving the quality of the fan, the gas control must be linked with the air pressure. When the air pressure is insufficient, the gas supply should be cut off immediately.
Generally, the gas pressure switch is used to detect the air pressure signal and output the switch signal to control the corresponding work of the gas solenoid valve.
8. Power-off protection
The combustion machine in the process of work suddenly power, must immediately cut off the gas supply, to protect the safety of the equipment.Gas control solenoid valve must be normally closed, once the power, automatically shut off to cut off the gas supply.Solenoid valve closing response time ≤5s.
9. Measures to prevent gas leakage
Gas leakage includes two aspects, one refers to the gas leakage to the environment through the pipeline, the other refers to the gas leakage through the solenoid valve core toward the furnace.
Environmental leakage may cause poisoning and explosion accident at work site.First of all, make sure the pipeline is sealed, check the pipeline leakage regularly, if the pipeline leakage must be eliminated before continuing to use;Secondly, to avoid the concentration of gas causing poisoning and explosion, it is required that the work site is well ventilated: permanent ventilation holes and forced ventilation devices are equipped;In addition, the requirements of the work site prohibit fireworks, electrical explosion-proof.
A leak in the furnace may cause an explosion in the furnace.There are three ways to solve the problem of leakage in the furnace: first, strengthen the pre-blowing time and blowing volume, blow off or dilute the gas in the furnace;Second, the gas pipeline adopts two solenoid valve series structure to improve the safety of the system;Third, the pipeline leak detection device is used to detect the gas pipeline before ignition. If the gas leak reaches a certain amount, the burner will be locked.
The measures to prevent gas leakage belong to the peripheral control, which is generally not included in the control of the burner itself.