Economic limestone scrubbing

The economics seem to be better for systems where dry powdered fresh lime plus ground recycled lime is injected along with a relatively coarse spray which impinges on and dries out from the reagent, as described by Stouffer et al. [lirEC Res., 28(1) 20 (1989)]. Withum et al. [9th Ann. Pitt. Coal Prep. Util. Env. Control Contractors Conf. (1993)] describes an advanced version of that system that has been further optimized to the point that it is competitive with wet limestone scrubbing for >90 percent flue gas desulfurization. 

The economics of limestone scrubbing, with or without additive, have been projected for forced oxidation systems designed to... 

Conditions for Economic Analysis of Limestone Scrubbing with Forced Oxidation and with or without Additive... 

Since the conventional MgO process has not gained widespread acceptance, efforts are underway to make the process more energy efficient, less dependent on fuel oil and, most importantly, more competitive economically with a limestone scrubbing system. This paper is the result of TVA s initial investigation into an improved MgO process. The purpose is to describe the new MgO process, to detail some of the technical uncertainties requiring further development work, and to present preliminary conceptual design economics for this improved MgO FGD system. 

The first-year annual revenue requirements for the spray dryer MgO process are about 11 lower than those for the comparable limestone scrubbing process. This economic advantage for the spray dryer MgO process increases to nearly... 

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). 

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. 

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. 

Four chapters address alternatives to throwaway slurry scrubbing. The development of the limestone dual alkali process is reviewed. Two chapters present results related to dry scrubbing with nahcolite or lime. A conceptual design and economics are given for MgO scrubbing using a spray dryer. 

For economic reasons, the use of RME as scrubbing liquid requires initial tar concentrations in the product gas to be relatively low. At the Giissing plant, tar concentrations downstream the fabric filter are reduced to approximately 2.5 g/Nm by the preliminary dry de-tarring treatment referred to earlier injection of fine limestone particles into the gasifier freeboard. Benzene and remaining tar compounds are then almost completely removed in the RME scrubber, operating at 5 C [33]. 

The catalytic reduction of NO, is usually placed between the economizer of the boiler and the air preheater (Figure 6.18.9). The SCR catalyst used in this way is in the so-called high dust mode and the resistance of the catalyst against attrition by ash particles should be high. Downstream of the air preheater fly ash is collected by an electrostatic precipitator. By way of a heat exchanger and flue gas desulfurization (e.g., SO2 separation by scrubbing using a slurry of a sorbent, usually limestone or lime) the flue gas is passed to the stack. 

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