What are the safety control requirements for gas burners

According to the combustion characteristics of gas in the furnace, the safety control requirements mainly include pre-blowing, automatic ignition, combustion state monitoring, protection against ignition failure, flameout protection, gas pressure high and low limit protection, air pressure shortage protection, power failure protection, and measures to prevent gas leakage accidents.

1. Pre-blowing

Before ignition, the burner must be pre-blown for a period of time to blow away or dilute the residual gas in the furnace and flue. Because there is inevitably residual gas in the working furnace of the burner, if ignition is carried out 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 the blowing volume, and is generally set to 15-60 seconds.

2. Automatic ignition

The gas burner should adopt 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, and the ignition time is generally: 2 to 5 seconds.

3. Combustion state monitoring

The combustion state must be dynamically monitored. Once the flame detector senses the flameout signal, it must be fed back to the burner in a very short time, and the burner will immediately enter the protection state and cut off the gas supply.

The flame detector should be able to sense the flame signal normally, neither sensitive nor slow. Because it is sensitive, if the combustion state fluctuates, it is easy to cause false operation and slowness, and the feedback flame signal is delayed, which is not conducive to safe operation.

It is generally required that the response time from flameout to the flame detector sending a flameout signal does not exceed 0.2 seconds.

4. Protection against ignition failure

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 the ignition temperature field is formed first to facilitate ignition and combustion. If the ignition fails, the flame detector cannot sense the flame signal, and the burner enters the protection state.

The time from ignition to entering the protection 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 it is too long, a large amount of gas will enter the furnace when the fire cannot be ignited. Generally, it is required that the burner judges the flame signal sensed by the flame detector 2-3 seconds after the gas is introduced. If it does not ignite, it will enter the protection state, and if it ignites, it will maintain combustion.

5. Flameout protection

During the combustion process, if the burner is accidentally extinguished, the burner will enter the protection state. Because the furnace is hot, it is easy to explode when the 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 of stable combustion, and the gas pressure is only allowed 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, and no backfire, and at the same time limit the output thermal power of the burner to ensure the safe and economical operation of the equipment. When the gas pressure exceeds this range, the burner should be locked.

The burner design generally uses a gas pressure switch to sense the pressure signal and output a switch 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 blast. If the fan fails and causes air interruption or insufficient air, the gas will be cut off immediately, otherwise the furnace will explode or backfire to the fan. 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.

Generally, a gas pressure switch is used to sense the air pressure signal and output a switch signal to control the corresponding work of the gas solenoid valve.

8. Power-off 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 a normally closed type. Once the power is 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 is the gas leakage to the environment through the pipeline, and the other is the gas leakage to the furnace through the end of the solenoid valve core.

Environmental leakage may cause explosion accidents at the work site, and must be taken seriously. First, ensure that the pipeline is sealed and regularly check for leaks. If the pipeline leaks, it must be eliminated before it can continue to be used. Secondly, avoid gas concentrations that cause poisoning and explosions. Good ventilation is required at the work site: configured ventilation holes and forced ventilation devices. In addition, fireworks and electrical components are prohibited at the work site to prevent open flames from causing explosions.