Determination of chimney dimensions
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The height of chimneys is generally specified in environmental impact assessments, but apart from the volume and flow rate of the flue gas, what other factors influence the diameter of steel chimneys?
There are many factors to consider; for details, please refer to GB 50051-2002 Code for Design of Chimneys
What is the specific impact on the wind speed at the exhaust outlet?
It is related to both the height of the chimney and the direct and detection openings
It’s actually a matter of the emission velocity; the wind speed of the exhaust gas at the chimney outlet must be no less than 1.5 times the calculated wind speed at that outlet. Otherwise, backdrafts will occur in the chimney, preventing the exhaust gas from being expelled
If you need to design it yourself, version 50051 has 13 versions, with several calculation points having been modified. Also, sir upstairs, where did the statement that \"the wind speed at the chimney outlet must be no less than 1.5 times the calculated wind speed at that outlet\" come from? Is the diameter related to the inlet pressure? Previously, I was only exposed to positive pressure at the inlet, so the flow velocity in the chimneys was relatively high; my understanding is that this approach helps reduce investment costs and wind resistance
The inner diameter of the chimney outlet should be such that, under the highest load conditions in the boiler room, the flow velocity of the flue gas does not become too high, thereby avoiding excessive resistance； At the lowest load of the boiler room, the flow velocity at the chimney outlet should be no less than 2.5~3 m/s to prevent backflow of air.
For boilers with natural ventilation, in addition to meeting the specified requirements regarding chimney height, it is also necessary to ensure that the suction force generated by the chimney is sufficient to overcome the total resistance of the boiler and flue system. For a furnace with negative pressure combustion, it is also necessary to ensure a negative pressure of 20~40 Pa at the furnace outlet.