Safety control requirements for gas steam boiler burners

Safety control requirements for gas steam boiler burners
Due to the abundant resources of natural gas and coal to gas (using coal as raw material) in our country and being classified as clean energy, it has good social and economic benefits. Gas boilers comply with China's industrial policies and have broad market and development prospects. However, in the development and design of gas burners, combustion, explosion, and toxicity are the main issues. According to the combustion characteristics of the gas in the furnace, safety control requirements mainly include pre blowing, automatic ignition, combustion status monitoring, ignition protection, flameout protection, high and low pressure limit protection, insufficient pressure protection, power outage protection, gas leakage prevention, etc.
1. Pre blowing air
Before ignition, the pre blowing burner must have a period of pre blowing to remove or dilute residual gas in the furnace and flue. Due to the inevitable presence of residual gas from the burner in the working furnace, there is a risk of explosion without a pre blowing point. In order to ensure that the gas concentration is not within the explosion limit range, it must be blown out or diluted. The pre blowing time is generally set at 15-60 seconds, which is related to the furnace structure and the amount of soot blowing.
2. Automatic ignition
The burner should use electric spark ignition for easy automatic control. High voltage ignition transformers can generate arc ignition, requiring an output energy of voltage greater than 3.5 kV, current ≥ 15 mA, and ignition time generally between 2-5 seconds.
3. Monitoring of combustion status
The combustion status must be dynamically monitored. Once the flame detector detects a shutdown signal, it must provide feedback to the burner in a very short time, and the burner immediately enters a protective state while cutting off the gas supply. Fire alarms can sense flame signals normally and are neither sensitive nor sluggish. Due to high combustion sensitivity, if there are fluctuations, it is easy to cause misoperation and feedback flame signal lag, which is not conducive to safe operation. Generally speaking, the response time from turning off the engine to the flame detector should not exceed 0.2 seconds.
4. Ignition protection
When the burner catches fire, gas enters and ignites. The ignition process requires the formation of an ignition temperature field before the gas inlet for ignition and combustion. If there is no fire, the flame detector cannot sense the flame signal, and the burner will enter a protective state. The time from self ignition to entering the protective state should be appropriate and not too short or too long. If it is too short, there is no time to form a stable flame; If it is too long, ignition will not cause a large amount of gas, and it will enter the furnace. In general, the burner needs to check the flame signal of the detector within 2-3 seconds of the intake valve. If it does not catch fire, it will enter a protective state, and if it catches fire, it will continue to burn.
5. Flameout protection
The burner unexpectedly stalls during the combustion process and enters a protective state. Due to the heat in the furnace, gas is prone to explosion upon entry, so it is necessary to enter a protective state in a very short time and cut off the gas supply. This process requires a response time of no more than 1 second from stalling to entering the protective state.
6. Air pressure high and low limit protection
The gas burner burns stably within a certain range, only allowing pressure fluctuations within a certain range. The purpose of limiting the low pressure of gas flow is to ensure the stability of the flame: to limit the output heat of the burner and ensure the safe and economical operation of the equipment without extinguishing, extinguishing, or tempering. When the gas pressure exceeds this range, the burner should be locked in operation. Burner design generally uses a pressure switch to sense pressure signals and output switch signals to control the corresponding operation of the burner.
7. Insufficient air pressure protection
The gas burner is designed with high thermal intensity and the combustion method is forced blowing. If the fan malfunctions and causes air interruption or insufficient air, the gas should be immediately cut off, otherwise furnace explosion or tempering may occur. So while improving the quality of the fan, gas control must be linked to air pressure. When the air pressure is insufficient, the gas supply should be immediately cut off. Usually, a pressure switch is used to sense the pressure signal, output a switch quantity signal, and control the corresponding operation of the gas solenoid valve.
8. Power outage protection
If the burner suddenly loses power during operation, the gas supply must be immediately cut off to protect equipment safety. The air control solenoid valve must be frequently closed, and once there is a power outage, the air supply will automatically shut off. The response time for closing the solenoid valve is ≤ 5 seconds
9. Gas leakage prevention
Measures to prevent gas leakage accidents: Gas leakage includes two aspects: one is the leakage of gas into the environment through pipelines, and the other is the leakage of gas towards the furnace through the electromagnetic valve core end. Special attention should be paid to environments that may cause poisoning and explosions. Firstly, ensure that the pipeline is sealed and regularly check for leaks. If there is a leak in the pipeline, it must be eliminated before it can continue to be used; Secondly, to avoid gas concentrations that can cause poisoning and explosions, it is required that the work site has good ventilation: permanent ventilation holes and forced ventilation devices should be installed; In addition, it is required that fireworks and explosion-proof electrical components are prohibited at the work site.
Leakage inside the furnace may cause an explosion inside the furnace. There are three solutions to leakage in the furnace: first, strengthen the pre blowing time and the amount of blowing air, remove or dilute the gas in the furnace; The second is to adopt a dual solenoid valve series connection structure to improve the safety of the system; The third is to use a pipeline leakage detection device to detect gas pipelines before ignition. If the gas leakage reaches a certain amount, lock the burner in operation.