Comparison of Gypsum Dewatering Technologies at Flue Gas Desulfurization Plants
Abstract: Recovering gypsum from flue gas desulfurization (FGD) plants is becoming more important as the technical feasibility of substituting FGD gypsum for natural gypsum in traditional applications such as wall board, cement and soil conditioners has been demonstrated. It is estimated that there are over 200 new coal-fired plants and over 1000 upgrades of existing coal-fired plants in various stages around the world. An important aspect of gypsum recovery is the solid-liquid separation technology that is used.
This paper discusses three technologies that are used by coal-fired power plants to dewater and dry gypsum. These are centrifuges, continuous vacuum belt filters (CBF) and continuous-indexing vacuum belt filters (CI-BF) and rotary vacuum filters. Each technology is examined for their ability to filter, wash and dry the gypsum to meet the moisture content for salable FGD gypsum as compared with natural gypsum. The paper continues with an analysis of the utilities required for each technology including electricity and water usage and the ability to reuse water in the process. Finally, maintenance, reliability, uptime and redundancy requirements are discussed as well as general overview of instrumentation and PLC controls and communication is covered.
The paper concludes by describing the important information that power plant engineers should review before deciding on a solid-liquid separation technology. These parameters include type of FGD process, type of coal, limestone purity, water analysis, operating data, composition of the gypsum slurry and other upstream or downstream equipment. Finally, to meet the plants overall environmental objectives, a unique approach is described that takes the wastewater treatment sludge and incorporates it with the gypsum for a cement product.
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