When gas fuel is mixed with air to a certain concentration, it will form explosive gas, which will explode once it meets high temperature and open flame. All kinds of gaseous fuels have their explosive concentration ranges, such as the lower explosive limit of natural gas is 5% and the upper explosive limit is 85%. The explosion usually occurs when the boiler stops during startup and operation, and sometimes it also occurs in the pipeline or boiler room. These accidents often lead to the destruction of combustion facilities or buildings and structures, and even cause casualties and huge losses. At the same time, combustible gas is extremely harmful to human body. For example, natural gas can suffocate, and the concentration of 10% can cause death; Almost all combustible gases contain carbon monoxide and heavy hydrocarbons, which is very toxic. Because combustible gas is explosive, toxic and corrosive, whether the design of gas supply system in gas-fired boiler room is reasonable has great influence not only on ensuring the safe and reliable operation of boiler, but also on the investment and operation economy of boiler room system. Therefore, in the design, we must pay enough attention. This paper discusses several problems often encountered in design.

The gas supply system of boiler room is generally composed of pressure regulating device, boiler room pipeline distribution system, purging and radiation pipeline, gas alarm ventilation system, etc.

1. According to the national boiler room design code, the boiler room can be set in a single building, or in the podium, basement, semi-basement, first floor, middle floor and top floor of a high-rise building. At the same time, the types of gas supplied by cities are also different, including artificial gas, liquefied petroleum gas and natural gas. Therefore, the suitable gas should be determined according to the location of the boiler room and the local gas supply type. If the boiler room is located in a semi-basement, it is forbidden to use liquefied petroleum gas and other gases with density greater than air as fuel.

2. The gas pressure required by the boiler burner is relatively high, generally reaching 0.005 MPa-0.03 MPa, and the hourly flow rate is relatively large. Ensuring the stability of gas pressure in front of boiler burner has a great relationship with combustion conditions and safe operation. If the pressure in front of the burner increases or decreases, the gas flow will also increase or decrease. Because of the unstable pressure, the combustion will be unstable, and even backfire and fire will occur. Therefore, a special pressure regulating device should be set up, which is separated from the civil gas, so as to reduce the pressure fluctuation in front of the boiler burner caused by the load change of other users and cause accidents. The pressure regulating device should be installed in a separate building or structure, or in a closed open space (pressure regulating cabinet), and can be installed in a special gas pressure regulating room in the boiler room if conditions permit. The gas surge chamber shall be a single-story building close to the external wall, separated from the adjacent rooms by a firewall without doors, windows and holes, with a fire resistance rating of not less than Grade II, a light roof with doors and windows opening outwards, and the ground shall be made of materials that do not generate sparks. The explosion venting area shall conform to the Code for Fire Protection Design of Buildings, and the ventilation frequency shall not be less than 6 times /h, and an emergency exhaust device shall be provided, and explosion-proof equipment shall be used for electrical facilities.

3. The gas regulator should be a direct regulator, because the gas flow required when the boiler starts can reach the rated flow instantly. Although the outlet pressure of indirect pressure regulator is relatively stable, it can't meet the large flow requirement of instantaneous start-up of boiler.

4. The gas pipeline in the boiler room generally adopts single mother pipe. In order to ensure the continuous and reliable gas supply, the boiler room that runs continuously all the year round should adopt double main pipes. When double main pipes are used, each main pipe can be considered as 75% of the maximum calculated gas consumption of the boiler room.

5. In order to quickly cut off the gas source in case of an accident in the boiler room and avoid the accident from expanding; Or when the gas pipeline in the boiler room needs maintenance, it is used to turn off the gas source. The main cut-off valve should be installed at the entrance of the boiler room gas pipeline, and the radiation pipe should be installed before the cut-off valve according to the gas flow direction. This valve should be installed in a safe and easy-to-operate place.

6. The gas pipeline in the boiler room should be laid overhead, which is conducive to the diffusion of leaked gas and avoids gathering indoors or in indoor dead corners to form explosive gas. Gases with higher density than air, such as blast furnace gas and liquefied gas, should be laid along the outer wall of the boiler room and easy to detect.

7. Shut-off valves and quick shut-off valves should be set on the gas main of each boiler. A manual cut-off valve should be installed on the gas supply branch pipe in front of each burner, and two solenoid valves should be installed in series behind the valve. The purpose of installing quick shut-off valve on the main pipeline leading to each boiler is to prevent the boiler from flameout during operation, and it is too late to quickly cut off the gas source and cause the boiler to explode. The cut-off valve is installed to cut off the gas source and adjust the flow.

8. The gas pipeline in the boiler room (such as the end of the main pipeline, between two valves in front of the furnace, etc.). ), installed radiation tube and purge port. When the pipeline is put into operation before overhaul or after long-term shutdown, the residual gas in the pipeline can be purged with inert gas or gas to ensure the safety of pipeline overhaul or boiler ignition. The installation position of the radiation pipe should be determined according to the layout of the gas pipeline in the boiler room, and the principle is to purge the gas or air in the pipeline.

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