Scrubbing lime-limestone

Chemical scrubbing systems for SO/ absorption fall into two broad categories (a) Disposable systems and (b) regenerative systems. Typical of systems in use for a number of years are those that use an aqueous slurry of an insoluble caldum compound, which can be discarded after use. Disposable 02-removal systems use aqueous slurries of finely ground materials, such as lime, limestone or dolomite, to produce a mixture of insoluble sulfites and sulfates. On passing through the scrubber, S02 from the waste gas dissolves to form sulfurous acid S02 ... 

There are several ways to classify processes for the removal of SO2 from stack gases wet or dry, recovery or non-recovery, and absorption, adsorption, or catalytic oxidation. Except for catalytic oxidation, each of these has been described by others in this volume. In reviewing these processes and many others. Combustion Engineering (C-E) decided that wet lime/limestone scrubbing without recovery of sulfur was worth developing because of its simplicity and low cost. 

The controlling chemical reactions for the lime/limestone wet scrubbing SO2 removal systems have been established. In both the lime and limestone systems, the principal absorption reaction is calcium sulfite plus sulfur dioxide to form calcium bisulfite. Methods of preventing both calcium sulfite and calcium sulfate scaling are presented. 

The Air Quality Control Systems (AQCS) using lime/limestone wet scrubbing have three basic types of chemical process equipment (1) scrubbers, (2) reaction tanks, and (3) solid-liquid separators, in addition to several auxiliary pieces of equipment such as pumps, demisters, and reheaters. The SO2 in the flue gas is transferred into the liquid in the scrubber, the sulfur in the liquid is converted to solid calcium sulfite, and calcium sulfate in the reaction tanks and solid calcium sulfite and sulfate are separated from the liquid and disposed from the solid-liquid separators such as clarifiers, vacuum filters, and ponds. 

System. Intern, Lime/Limestone Wet Scrubbing Symp, 2nd, New... 

Buffer Additives for Lime/Limestone Slurry Scrubbing... 

Buffer additives are attractive for enhancing SO2 removal and/or CaC03 utilization in lime/limestone slurry scrubbing processes for flue gas desulfurization. This work was sponsored by EPA to provide experimental data on commercial synthesis, gas/liquid mass transfer enhancement, and oxidative degradation of useful buffer additives. 

Lime/limestone slurry scrubbing is the dominant commercial technology for flue gas desulfurization 0.). SO2 is absorbed at 50-55°C and pH 5.5-6.0 in an aqueous slurry of excess CaC03 and product solids. The CaS03/CaS04 product is disposed of as solid waste. With greater than 500-1000 ppm SO2 in the flue gas, SO2 absorption is controlled by liquid-film mass transfer resistance because of the limited solubility of SO2 gas and alkaline solids. Additives that buffer between pH 3 and pH 5.5 enhance S02 absorption by providing dissolved alkaline species for reaction with SO2 (8). 

Borgwardt, R.H., Proceedings Industry Briefing on EPA Lime/ Limestone Wet Scrubbing Test Programs, 1979, EPA-600/7-79-092 p.1-9. 

Adipic Acid-Enhanced Lime/Limestone Test Results at the EPA Alkali Scrubbing Test Facility... 

This paper summarizes the results of tests conducted from July 1978 through March 1981 at the EPA, 10-MW equivalent, lime/limestone wet-scrubbing FGD test facility, during which adipic acid as an additive was tested and shown to be a powerful scrubber additive for improving SO2 removal. The optimum concentration of adipic acid is only 700 to 1500 ppm at a scrubber inlet pH of 5.2 or higher. SO2 removal efficiencies in excess of 90 percent and reliable operation were demonstrated in four long term, limestone/adipic acid runs. Factorial tests were also conducted to characterize SO2 removal as a function of gas and slurry flow rates, pH, and adipic acid concentration. Intermediate duration optimization runs and favorable economics are also reported. 

Burbank, D. A. Wang, S. C. Proceedings The Fifth Industry Briefing on IERL-RTP Lime/Limestone Wet Scrubbing Test Programs (December 1979), EPA-600/9-80-032, NTIS PB 80-199813, July 1980, pp. 27-113. 

Lime/Limestone Scrubbing Model Users Manual," EPA-600/8-... 

Commercialization of Lime-Limestone Flue Gas Scrubbing Technology... 

Comparison of Lime—Limestone Wet Scrubbing with Other Systems... 

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