SO2 control

Sulfur Dioxide Processing, Repriuts of 1972—1974 Chem. Eng. Prog, articles, AIChE, New York (1975). Contaius thirteen papers on flue gas desulfurization, two on SO2 control iu pulp and paper, one on sulfuric acid tail gas, one on SO2 from ore roasting, and two on NO from nitric acid. 

Emissions control systems play an important role at most coal-fired power plants. For example, PC-fired plants sited in the United States require some type of sulfur dioxide control system to meet the regulations set forth in the Clean Air Act Amendments of 1990, unless the boiler bums low sulfur coal or benefits from offsets from other highly controlled boilers within a given utiUty system. Flue-gas desulfurization (FGD) is most commonly accomphshed by the appHcation of either dry- or wet-limestone systems. Wet FGD systems, also referred to as wet scmbbers, are the most effective solution for large faciUties. Modem scmbbers can typically produce a saleable waUboard-quaUty gypsum as a by-product of the SO2 control process (see SULFURREMOVAL AND RECOVERY). 

By the late 1980s six principal commercial CEBC technologies were available (42). In 1993 the largest CEBC ia operation is expected to be the Pyropower Corporation s 165 MWe reheat coal-fired unit, under constmction siace 1991 at the Poiat Aconi Station of Nova Scotia Power Corp. (43). Combustion and SO2 control ia this unit is to be carried out ia the water-cooled riser. The unit is expected to operate at 870°C to optimize sulfur capture. The cyclone separators are refractory-lined and are supported approximately 30 m above grade. 

Sulfur dioxide reduction to achieve required emission levels may be accomplished by switching to lower-sulfur fuels. Use of low-sulfur coal or oil, or even biomass such as wood residue as a fuel, may be less expensive than installing an SO2 control system after the process. This is particularly true in the wood products industry, where wood residue is often available at a relatively low cost. 

Figure 30-lC is distinctly different from the first two in the type of SO2 control processes used and the sequence of the particulate matter and SOj controls. It is a promising approach for up to 90% SO2 control of western United States coal, and there is a single waste product. Other features include the collection of particulate matter at temperatures below 90°C and the possibility for spray dryer cooling tower water integration. This. system may or may not include a catalytic NO unit. 

Figure 30-2 illustrates a wet SO2 desulfurization system using a spray tower absorber. Figure 30-3 illustrates a rotary atomizer injecting an alk ine slurry into a spray dryer for SO2 control. 

Tall stacks for SO2 dispersion have been used in the past but are no longer acceptable as the sole means of SO2 control. Acid plants have been installed at many smelters to convert the SO2 to sulfuric acid, even though it may not be desirable from an economic standpoint. 

Benson, L.B., Ray D Alesandro, J. Wilhelm and A.D. Randolph, "Improving Sludge Dewatering in Wet Lime FGD," Paper presented at First Combined FGD and Diy SO2 Control Symposium, October 25-28, St. Louis, Missouri (1988). 

Without platinum, alumina becomes more effective for removing SO2 as the temperature is increased. In this unpromoted case, the rate of oxidative adsorption of SO2 controls the amount of SO2 removed. Increasing the temperature increases that rate. 

Pollution control devices for particulates do not depend upon new technology whereas SO2 control does. Since the first decade of this century, as a result of Cottrell s original work (9j, the electrostatic precipitator had been used to collect fly ash particulates. These devices were used on many of the older coal burning plants which had converted to oil. On the reconversion to coal, they were put back in operation or else new ESP units were put in the place occupied by the older ones. The performance of these systems, when designed for a specific coal, was... 

The full potential for removing pyritic sulfur from various coals by physical coal cleaning is significant but difficult to achieve. However, SO2 control by precombustion removal of pyrite could be an important S02-emissions reduction strategy. The cleaned coal produced could be used in coal-fired utilities, constructed both pre-and post-NSPS, as well as in industrial boilers. To realize the potential for coal cleaning in actual practice, however, new techniques must be demonstrated in the laboratory and then at the "proof-of-concept" scale (approximately one ton of coal per hour). These new coal beneficiation techniques could be advanced physical-coal-cleaning (PCC) processes, or they could employ microbial desulfurization or chemical desulfurization to remove organic sulfur. These latter processes could be used by themselves or in concert with PCC processes. 

Effects of SO2 Addition during Fermentation. Separate 4.5 gallon carboys containing Chardonnay juice were inoculated with Saccharomyces bayanus, followed one hour later by treatment with 0 ppm SO2 (control), 50 ppm SO2, or 200 ppm SO2. Each treatment was done in duplicate for a total of six separate carboys. The wines... 

Table 4 Cost comparison of various SO2 control options...

Van der Brugghen, F.W. Koppins-Odink, J.M. Flue Gas cleaning in power stations in the Netherlands. In Proceedings First Combined Flue Gas Desulfurization and Dry SO2 Control Symposium Electric Power Research Institute, Paper 1-5, 1989, 1/69-1/94. 

The SO2 removal performance at Scholz reconfirms the high SO2 control capability of this technology observed in the previous pilot plant tests where SO2 removals of 95% were easily achieved by similar manipulation of the scrubber bleed pH. 

Both the pilot plant and the prototype tests have demonstrated the excellent SO2 control capability of the technology. SO2 removal efficiencies in excess of 95% have been consistently achieved. The use of finely ground limestone is necessary, but at the same time the limestone utilization is quite good—well in excess of 95%. Reasonable soda ash makeup rates were established in the pilot plant tests but could not be verified at Scholz due primarily to the poor mechanical condition of the equipment. 

Definitive SO2 Control Process Evaluation Limestone Double Alkali and Citrate FGD Process, EPA Pub. EPA-600/7-79-177, Aug. 1979. 

Carlson, C.P., Burtraw, D., Cropper, M. and Palmer, K. (2000). SO2 control by electric utilities What are the gains from trade Journal of Political Economy, 108, 1292-326. 

Oxygen enrichment of the roaster fluidizing air, the planned elimination/reduction of air ingress and targeted control of off-gas oxygen partial pressure has resulted in an increased SO2 partial pressure at the converter. On occasions dilution air is allowed into the gas stream under controlled conditions. Prior to 1996, Zincor did not require the use of dilution air for SO2 control at the converter. 

Jozewicz W, Kiichgessner DA (1989) Activation and reactivity of novel calcium-based sorbents for dry SO2 control in boilers. Powder Technol 58 221-229... 

It would need to embrace oil as well as coal consumers. However, its cost would be considerably less than introduction of SO2 controls. However, emission controls could have the adverse... 

Koch, G. H., Pednekar, S. P., Patterson, E. H., and Syrett, B. C., "Corrosion Control by Impressed Cunent Cathodic Protection in the Outlet Duct of a Pilot Wet Scrubber, Proceedings of the 1990 SO2 Control Symposium, Paper No. 4B-5, Electric Power Research Institute, Palo Alto, CA, 1990. 

The CAAA mandates the reduction of SO2 emissions from utility power plants in the United States to a maximum or "cap" of 8.9 million tons per year by January 1, 2000 and thereafter. Any expansion in capacity of coal-based power generation will be allowed to emit SO2 only if SO2 emissions are reduced elsewhere in the utility system. Since coal gasification combined cycle power plants can be designed for over 99% sulfur recovery, they can be built with minimum offsetting impact for SO2 control on other utility power plants. 

CO2 emissions can be reduced by the use of branded cement. There were no examples of SO2 control provided. 

Dry injection of limestone and hydrated lime particles in desulfurization processes is currently under active development (Stouffer et al, 1986 Weinstein, 1989 Yoon et al, 1986). Furnace dry sorbent injection for SO2 control consists of injecting a dry pulverized calcium based material directly into furnace cavity of a coal fired boiler. The product CaS04 and unreacted sorbent particles are removed from the furnace together with fly ash. Fan and Satija (1984), Milne et al (1990b) Krammer and Staudinger (1991) reported kinetic data and model expressions which are applicable to dry injection systems. 

Felsvang, K. et al (1988) " Update on Spray drier FGD experience in Europe and in the people s Republic of China", 1st Combined FGD and Dry SO2 Control Symp.St. LOUIS, Missouri. 

The Clean Air Act Amendments of 1990 built upon the SO2 control requirements of 1977 by expanding the clean air provisions in the revised Title L adding acid rain provisions, and capping SO2 emissions at 8.9 million tons of SO2 in the new Title IV. 

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