Limestone wet scrubbing

The main purpose of magnesia addition to a limestone wet scrubbing system is to facilitate high S02 removal. For a wet scrubber that cleans flue gas from a utility coal-fired boiler, the scrubber inlet gas S02 concentration is typically about 700 ppm by volume per one weight percent sulfur in the fired coal. For sub-bituminous coal having only 0.7 weight percent sulfur content, the inlet S02 concentration is about 500 ppm, and, for example, the outlet S02 has to be less than 50 ppm to achieve 90 percent removal. In order to avoid serious inhibition of mass transfer because of S02 back-pressure, the equilibrium S02 partial pressure should be about four or more times lower than the actual S02 partial pressure in the gas. Thus, Figure 3 indicates that for this low-sulfur coal system, the scrubber inlet pH should be at least 5.5, and the outlet pH at least... 

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... 

Limestone Wet Scrubbing of Sulfur Dioxide from Power Generation Flue Gas for High and Low Sulfur Fuels... 

Lime and Limestone Wet Scrubbing. The problem of atmospheric pollution by sulfur oxides has been given extensive attention by research and development firms in recent years and several process types are being proposed for full scale application. Lime and limestone wet scrubbing appears to be the most promising approach for immediate application. The major diflSculty with the limestone or lime systems is solid deposition in the absorption device which could create unreliability and unscheduled shutdowns for the power plant. 

The problem with sulfur dioxide containment is that many smelter processing units produce sulfur dioxide concentrations of 1-2% whereas the minimum economic concentration for sulfur dioxide conversion processes (e.g., for sulfuric acid or sulfur production) is 3.5-4%. Thus, the economic solution to containment requires either modification of the smelter process to obtain higher sulfur dioxide concentrations, or capture of sulfur dioxide at relatively low concentrations followed by some means of regeneration of a high concentration of sulfur dioxide (Chap. 3). Throw-away approaches to sulfur dioxide containment, lime or limestone wet scrubbing, are worthy of consideration by small-scale smelters (e.g., Eqs. 13.35-13.37). 

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

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. 

This report describes the results of the Shawnee Lime and Limestone Wet Scrubbing Test Program conducted by EPA s Industrial Environmental Research Laboratory, Research Triangle Park, North Carolina (IERL-RTP). In this program, flue gas desulfurization (FGD) tests were conducted at the EPA 10 MW prototype Shawnee Test Facility located at the Tennessee Valley Authority (TVA) coal-fired Shawnee Power Station near Paducah, Kentucky. Bechtel Group, Inc. of San Francisco was the major contractor and test director, and TVA was the constructor and facility operator. Results of the program before July 1978 have been reported elsewhere (1.2) ... 

A primary objective of the EPA alkali wet scrubbing test program during the last several years has been to enhance SO2 removal and improve the reliability and economics of lime and limestone wet scrubbing systems by use of adipic acid as a chemical additive. 

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. 

Last October Research-Cottrell started up its first gas cleaning system, a 115 MW limestone wet scrubbing system at Arizona Public Service s Cholla plant. In this unit particulate and sulfur dioxide are... 

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

Gleason, R. J., Heacock, F., Limestone Wet Scrubbing of Sulfur Dioxide... 

Removal of SO., by the Limestone Wet-Scrubbing Process, EPA Contract EHS-D-71-24, October 1971. 

Saarberg-HoUer (S-H-V) Process. The S-H-U process is a limestone wet scrubbing process with formic acid enhancement The S-H-U absorber has both cocunent and counter-current sections. The flue gas enters the absorber at the top of the cocurrent flow section and flows downward past several levels of spray nozzles where the pH drops rapidly. The scrubber slurry collects in the sump. The flue gas then turns upward into the second scrubbing stage, the countercurrent flow section, where the final increment of SO2 removal occurs. The flue gas exits either through a combination of a vertical flow and a horizontal flow mist eliminator or vertical flow mist eliminators. 

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