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 Power
Among cooling water degritting, pump seal water and miscellaneous other power plant applications, Krebs Cyclones are used extensively to process limestone and gypsum slurries in wet flue gas desulfurization (WFGD) systems at coal fired electric utilities.
In wet flue gas desulfurization systems, limestone (calcium carbonate) is ground to a powder in a wet ball mill. Krebs Cyclones are used to classify the ball mill discharge, returning coarse particles to the ball mill for further grinding. Finely ground limestone (typically 90% passing 45 micron) reports to the cyclone overflow and is stored in a limestone slurry storage tank (at 25-30% solids by weight).
The stored limestone slurry is sprayed countercurrently against the power plant boiler flue gas, absorbing SO2 from the flue gas. The SO2 reacts with the limestone, forming gypsum (calcium sulfate). Krebs Cyclones are used to dewater and thicken the byproduct gypsum slurry from about 15% solids by weight to 45% solids by weight ahead of a vacuum belt filter. The vacuum belt filter produces a filter cake that can be disposed of in a landfill or in some cases processed to make wallboard. The cyclone overflow is returned to the absorber where fine unreacted limestone is converted to gypsum and fine gypsum crystals grow larger.
Frequently, small diameter hydrocyclones are used to process a portion of the overflow from the gypsum dewatering hydrocyclones. The purpose of this stage of hydrocyclones is to produce a relatively solids free (<1.5% solids by weight) stream that can be sent to a wastewater treatment plant as a chloride bleed from the system.
Hydrocyclones for the limestone grinding circuit and for gypsum dewatering are typically 4" to 6" diameter hydrocyclones but occasionally are as large as 10" diameter. Due to the presence of chlorides in the process, hydrocyclone housings are usually of FRP construction and fitted with replaceable gum rubber liners for abrasion resistance. Hydrocyclone apexes can be manually adjustable gum rubber liners or fixed silicon carbide ceramic inserts. Radial manifold assemblies for the hydrocyclones are fabricated from carbon steel and have spark tested, vulcanized gum rubber and/or chlorobutyl lining. Exposed carbon steel surfaces are epoxy painted for corrosion resistance.
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