High moisture carbon sources, such as lignite, often have moisture contents in excess of 40%, and thus, require drying to less than 20% moisture before being fed to Integrated Gasification Combined Cycle (IGCC) plants for power generation. To preserve plant efficiency, the Kemper County IGCC power plant featured a fluidized bed dryer system to dry high moisture lignite (&gt;45%) to a moisture content suitable for feeding to the gasifiers, resulting in a large amount of water evaporated (60-70 KPPH). For environmental and efficiency purposes, plans were to re-use this water at Kemper in other plant processes. The large amounts of ultrafine particles (&lt;5 µm) in the evaporated water, however, made reusing the water undesirable. Although other industrial plants often use filtration for similar applications, the high solids loading in the evaporated water at Kemper resulted in low throughput during continuous operation, making simple filtration ineffective.<br/>To improve the efficiency of the system, a prefiltration flocculation-sedimentation process was developed to allow the ultrafine particles to agglomerate and separate via sedimentation. Bench and pilot scale studies were conducted to optimize design, before scaling up the process at Kemper.<br/>A four-step sedimentation process was installed upstream of the water microfiltration process to produce high clarity water devoid of any suspended solids. The process consisted of six setting tanks to allow processing flow rates greater than 1000 gpm. Each settling tank operated according to its individual cycle, while processing water sequentially and in parallel with the other tanks. Inline static mixers allowed the complete mixing of the feed water stream with dilute polymer flocculants before the water entered the tank. The influent wastewater was treated using a primary polyamine based flocculant followed by a high molecular weight polyacrylamide based flocculant. Both polymers were diluted to 0.1% by weight.<br/>On an average, the Kemper unit processed 1.3 million gpd of process water with a maximum flow of 460 gpm across a single filtration vessel. The average total suspended solids (TSS) present in the influent wastewater was 30,000 mg/l. The unit could process up to 3 million gpd with an outlet TSS of less than 10 mg/l. Approximately 42 tons/day of ultrafine material was captured during the continuous operation of the present system.

Efficient removal of ultrafine coal particles from power plant effluent streams using flocculation-sedimentation-filtration process

255th National Meeting (2018)

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