I would like to ask about the recovery of waste heat from flue gas
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Hello everyone, I’m a beginner. I am currently working on a project related to the utilization of waste heat from alumina production flue gas. There is one question: the flue gas exits at 160 degrees Celsius, and heat exchange takes place with water using a heat exchanger; as a result, the temperature of the flue gas at the exit is 125 degrees Celsius. I would like to know why the exit temperature is set at 125 degrees. Wouldn’t it be better if the temperature were lower, thereby allowing for more effective heat exchange? Additionally, the main components of this flue gas are as follows: CO2 at 9.2%, CnHm at 0.2%, O2 at 0.6%, CO at 19.7%, CH4 at 1.9%, H2 at 22.8%, and N2 at 45.6%. What should be the required exit temperature for such flue gas? Also, what is the dew point temperature at which corrosion occurs? Thank you!
Since your fuel contains no sulfur, acid dew point corrosion should not occur. The dew point temperature at which corrosion occurs due to sulfur is not a fixed value; it depends on the sulfur content in the fuel. Theoretically, the lower the flue gas outlet temperature, the better – there might be other considerations at play!
Okay! Thank you so much! I’ll study it further!
Theoretically, flue gas cannot be free of sulfur; therefore, SO2 must be present. Where sulfur is present, the issue of acid dew point arises. Generally, flue gas should not be discharged at too low a temperature; otherwise, if the temperature falls below the acid dew point, acid will form and condense on the inner walls of the flues or chimneys, causing corrosion in those areas. So it must be higher than the acid dew point temperature. Not only must the temperature entering the chimney be above the acid dew point, but it is also necessary to ensure that the temperature upon leaving the chimney remains above the acid dew point. So under normal conditions, the flue gas temperature is around 120–140°C.
Oh, I see. Thank you for helping me understand this. But I still have one question: smoke generally contains sulfur, right? So where does this sulfur come from? I am currently in charge of the recovery of smoke from alumina production, and it’s logical to assume that sulfur is present there. There must be a certain range for the dew point corrosion temperature related to this sulfur, right? Do you know what that range is? Does it mean that if the sulfur can be removed, the temperature required for heat exchange can be made as low as possible, thereby increasing efficiency?
The dew point temperature needs to be calculated based on the sulfur content in order to achieve control