Cause Analysis And Its Cleaning Method Of Gas-Gas Heater Scaling In Flue Gas Desulfurization System

The wet FGD technology with limestone-gypsum has been main choice in China's thermal power plant with all FGD technologies throughout the world. Gas-gas heater (GGH) has been installed in FGD system In order to improve gas lift height and prevent subsequent equipment corrosion.The engineering practice indicated that scaling always take place in the operation of GGH,and most of GGH scale badly, affecting the security of plant operation and economic efficiency. Through the investigation on the GGH scaling situation of some large-scale power plants in Hebei Southern Power Grid, the hazard and cause analysis were maked. The reasons ingenerating scale deposit and blockage in the operation of GGH in FGD system and its cleaning methods were studied deeply in this experiment and some measures and suggestions to decrease the trend of GGH scale depositing and blockage were also presented.The scale of GGH in defferent power plants were analyzed in chemical gauging and instrumental method respectively and 15 defferent types of cleaning agents were selected for cleaning of the scale sample and the effect of cleaning and corrosion on the surface enamel layer by them in defferent temperature and concentration were investigated in order to find and optimize the best cleaning conditions. The cleaning mechanism were analyzed at the same time.The results showed that such factors can cause the scaling of GGH: GGH design defects, high concentration of dust in un-treated gas, the poor performence of mist eliminator and so on; GGH scale can be divided into hard scale and debris, the former is mostly constituted by calcium compound,SiO2 and Fe2O3,while the basic composition of the later are Sulfate and Fe2O3; At room temperature, Concentration of 5% of the UNGGH-acid 01 and UNGGH-complex 03, and 5% of the UNGGH-base 02 are better choices for cleaning the hard scale.This paper had certain direction and reference value for establishing the project about the wet flue gas desulfurization and alleviating the problems of GGH scaling in coal fired power plants.