Abstract: Fly ash deposition and wall up in the flue gas heater of the FGD is an old and difficult problem, and there is no better measure to resolve the problem. It is one of the innovations that the secondary hot air was used to heat the outlet flue gas of the FGD instead of the flue gas heater. The economical efficiency of the technology was theoretically discussed and analyzed in detail, and was compared with the economical efficiency using the steam heater. The results show that when using the technology of adding secondary hot air into the outlet flue gas of the FGD and the temperature of the clean flue gas increasing to 30 ℃, the net coal consumption rate was increased to more than 4.3 g /（kW·h）, which was at least 0.3 g /（kW·h） more than the net coal consumption rate when using technology of steam heater. It will largely limit the engineering application of the technology of adding secondary hot air into the outlet flue gas of the FGD.

Key words: secondary hot air, gas heater, steam heater, heat balance principle, coal consumption of power supply, desulfurization equipment, clean flue gas