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What are the design requirements for the flue of a gas boiler

Update:20-05-2022
Summary:

The flue is the main way for gas-fired boilers to emit […]

The flue is the main way for gas-fired boilers to emit flue gas. If the design is unreasonable, it is easy for the flue gas generated by the boiler during operation to be unable to be discharged outside the boiler normally, causing damage to the gas-fired boiler. So, what are the design requirements for the flue of a gas boiler?

1. The flue should be designed as straight as possible, which will make the flue have good air tightness, less accessories and less resistance. The horizontal flue should be laid with a head-up arrangement of more than 1%, and try to avoid downhill layout.

2. The flue and chimney of the oil and gas boiler room shall be constructed of steel or reinforced concrete, and the lowest point of the flue and chimney shall be provided with a water-sealed air-conditioning water drainage pipe.

3. The thickness of the steel plate of the metal flue is generally 4~6mm. When designing the flue, sufficient reinforcing ribs should be configured to ensure the strength and rigidity requirements.

4. The thermal expansion of the flue should be compensated, and the compensation should be calculated and selected correctly.

5. The steel flue should have thermal insulation measures and reliable fixation.

6. One boiler should correspond to one chimney in the oil-fired gas boiler room. When several boilers need to share a flue or chimney due to conditions, the ventilation and drafting force of each boiler should be balanced.

7. Necessary thermal measurement points and environmental protection measurement points should be set in appropriate positions when the flue is arranged. For a single oil-fired boiler with a rated evaporation greater than or equal to 20t/h or a single rated thermal power greater than or equal to 14MW, a fixed and continuous monitoring instrument for the emission concentration of soot and SO2 in the flue gas must be installed.

8. In places where flue gas is easy to gather and when multiple boilers share a chimney or a general flue, an explosion-proof door should be installed on the flue behind each oil-fired gas boiler. The position of the explosion-proof door should be conducive to pressure relief. It should be set in an appropriate position that does not endanger the safety of personnel and before turning. When the explosive gas may endanger the safety of the operator, a pressure relief guide pipe should be installed on the explosion-proof device.

9. For some boiler rooms with long flue, the resistance should be calculated, and the corresponding blower and induced draft fan (when there is an induced draft fan) should be selected to ensure smooth exhaust.

10. Corresponding anti-corrosion measures should be considered for the chimney. The temperature of the flue gas at the chimney outlet should be 15°C higher than the dew point temperature of the flue gas; when the exhaust gas temperature is lower than the dew point temperature of the flue gas, effective measures should be taken to prevent the backflow of the flue gas.

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