Study Of GGH Scaling Problem In The Wet Flue Gas Desulfurization System

In coal-fired power plants, limestone wet flue gas desulfurization (WFGD) is commonly used to control the emissions of SO2 in flue gas. Gas-Gas heat Exchanger(GGH) is an important equipment to transfer heat from origanal flue gas to net flue gas in the WFGD system. GGH scaling is a frequent problem in WFGD system running, which decreases heat exchange efficiency. The original flue gas of high temperature makes against the desulfurization reaction and the net flues gas of low temperature corrods flue. They both seriously affect the economic secure operation of desulfurization system.Some site samples have been analyzed comparatively in Ding zhou and Dai hai power plants whose GGHs scaling strength were different. The samples were analyzed for samples surface by SEM, for phase components by XRD and for chemical componsition by XRF. It is showed that GGH scaling was characterized with high Si/Al ratio and high Na content, and that the escaped fly ash in the original gas was absorbed selectively in the GGH scaling. The strength of GGH scaling depended on the nature of fly ash. High-Al fly ash could escape more from electrostatic precipitators and caused harder GGH scaling than other fly ashes. As a main ingredient in GGH scaling, CaSO4 kept as gypsum in the scaling origianally. It changed into anhydrite when being blown with high temperature steam, which enables the loose of the scaling to be cleaned easily. Based on the actual conditions of the two power plants, a series of improvement measures for the GGH scaling differences are proposed, such as increasing the intensity of steam purge, adding soot blowers, improving the defogging efficiency and so on. To decrease the probability of GGH scaling and stoppage.