The SOs concern in nations Delegates of a Working Group on Air Pollution Problems of the ECE discussed the status of advanced technologies for controlling man-made emissions of this global pollutant
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The Economic Commission for Europe (ECE), a specialized agency of the United Nations, contains 34 member nations. Its Working Group on Air Pollution Problems sent seventeen delegates to a second seminar, held in Washington D.C. in mid-November, which focused on the problems of SO2 emissions. This Working Group and its seminar is the principal forum for technical discussions and exchange of ideas in the field of air pollution between the Eastern and Western bloc countries. A first seminar was held in 1970 at ECE headquarters (Geneva, Switzerland): most likely a third will be held there in 1979. In no way is ECE involved with UNEP, the United Nations Environment Program, which is another specialized agency of the U.N. Nor is ECE to be confused with the European Economic Community, which represents Common Market Countries. ECE governments acknowledge that SO2 is a problem. Efforts to reduce the amount of SO2 in flue gases are being made in all industrialized countries. Therefore, member governments are faced with a wide range of control problems to be solved. About 75% of the world’s man-made air pollution is emitted from ECE countries. Collectively, in 1973 nearly 100 million tons of SO2 were emitted into the atmosphere by ECE countries. Of this total more than one half comes from two superpowers. The US. is first with 30.1 million tons: U.S.S.R. second
with 23.5 million tons: Canada third with 7 million tons; the U.K. fourth with 2.5 million tons, and Czechoslovakia, Germany, and France accounted for about 3-4 million tons each. These delegates were faced with the technological options for lowering SO2 levels in their respective areas. Although the options are many, none appeared to be the long-sought panacea to man’s modern technology problems: nor does any option appear applicable for instantaneous solutions. It is important to note that ECE consumes more than 70% of the world’s energy. It was also mentioned that this consumption of energy increased 20 YO between the 1970 and 1975 seminars. But the data on SO2 emissions were available only for the year 1973 so that no trend in such emissions could be established. The options Sulfur can be removed from the fuel before it is burned. Technologies here include coal washing and oil desulfurization. Or the product of sulfur combustion, SO2, can be removed from the stack gases. The principal technology is flue gas desulfurization (FGD) and its byproduct removal and utilization considerations. Alternatively, a sulfur-containing fuel can be converted to one that is nonpolluting by chemical coal cleaning, coal gasification, and coal liquefaction. There are also the techniques for burning sulfur-containing fuels without emissions, including fluidized bed combustion and integrated power cycles. After serious week-long deliberations the seminar, as part of its conclusions and recommendations, which will now be passed along to the senior advisers to ECE for their approval, concluded that technologies such as coal cleaning and FGD are making useful contributions to reducing sulfur emissions. Other advanced processes should be put into perspective. The seminar noted that coal gasification, chemical coal cleaning, fluidized bed combustion, and integrated power cycles are not fully developed and are unlikely to make a significant contributions to overall sulfur emissions reduction in the near future. Development of these technologies should be closely watched and evalu-
ated, also with respect to nitrogen oxide and solids (particulate matter) emission reduction. Among the recommendations, including one for another seminar, was one on SO2 monitoring. Each year, the member nations submit an annual report by April I to the senior ECE advisers. Beginning this year, the following information on SO2 emissions should be included: emissions per area and per capita annual progress of SO2 control and whether the controls are by emissions, fuel desulfurization, specification of sulfur content in fuel, or dispersion. In this way, it can be determined if there is an upward trend in SO2 emissions worldwide. It was also noted by the delegates that most of the largest single sources of SO2 emissions are in the range of 130-500 thousand tons per year. The largest, presumably a nickel smelter in Canada, emits 1 million tons per year. Although a year ago it was 2 million tonslyr, now it is about 3500 tonslday. More than haif of the total ECE emissions come from power plants. The other most significant portion comes from metallurgical operations. What about regulations? Both regulations and technological controls are being pursued in an effort to reduce SO2 levels. Generally speaking, most of the ECE countries have established national ambient standards for
so2. Arthur C. Stern, professor at the University of North Carolina at Chapel Hill and chairman of the Air Quality Criteria Advisory Committee (US.) that advises the U.S. EPA administrator Russell E. Train, summarized the standards issue. He mentioned that 35 countries, 12 Of their provinces, and all states of the U.S. had promulgated standards for SUIfur and sulfur-containing compounds. He distinguished between three types of standards for sulfur compounds: air quality standards emission standards for sources fuel standards. He noted that there was no standard for elemental sulfur or, for that matter, total sulfur in any of the 35 standards. In a conclusion, he noted a great disparity among the standards and regulations that affect desulfurization processes. For example, regulations on emission limits in Czechoslovakia and Germany are connected with stack height as well as production rates and capabilities. All the details of the myriad individual standards and regulations will be published early this year by Academic Press in A i r Pollution, Third Edition, Volume V; Stern is editor. Stern also acknowledged that there was still a problem in identifying the
U.S. delegate Harrington chaired the seminar
Radian president Carlton
an ootimistic note for FGD causative agent@) in air pollution health and early warning problems. He observed that U.S. air pollution alerts, such as that in Birmingham, Alabama, in February 1971,are not predicated on SO2 levels only but in combination with levels of other pollutants with US. national ambient air quality standardsCO, NO., hydrocarbons, particulate matter, and oxidants. Furthest along Of the many technologies mentioned, flue gas desulfurization (FGD) is the most widely applied today for reducing SOz. Conservatively, it was estimated that 1 % of U.S. power plants have experience with this technology. Although the major part of the FGD systems so far installed treat gases from utility boilers of power plants, FGD systems have also been installed in the metallurgical industry. For example, the large U.S.S.R. FGD installation at Magnitogorsk treats 2.5 million m3/h exhaust gases from the metal works. It has been in operation since 1963. Technologically, there are in fact 19 choices. according to the report by the U.S.S.R. delegate Y. Brodsky. who also Served as one of the vice chairman of
the seminar. Fourteen are wet processes; five are dry. All of the dry processes lead to sulfur with the exception of the Cat-Ox process, which yields SUIfuric acid. These options include throwaway and regenerable processes. Of course, removal is only the first part of the problem. Then, a decision must be made concerning what to do with the sludge from the throwaway process or the chemical from the recovery process. In his report on throwaway prccesses, the Swedish delegate P. 0. AIfredsson remarked that earlier it was believed that recovery processes would develop rapidly and supersede throwaway processes; this has not been the case. He also reported that in the US. cost studies showed that life-time operating costs are markedly higher for recovery systems than for throwaway systems, even if credits for recovery products are applied. But FGD systems are not entirely trouble free today. Some of the earlier throwaway commercial systems had such severe scaling and maintenance problems that continuous operation was not possible. More recent systems require significantly reduced maintenance, but the maintenance cost to some utilities even today is higher than desired. Nevertheless, research and development continue to improve the cakiumbased scrubbing technology. It is well recognized today that the addition of magnesium ion results in substantial improvement in scrubbing efficiency. In addfiion, the Norwegians have a process for scrubbing with seawater. The delegate from the Federal Republic of Germany mentioned that the Halter process, in which hydrochloric acid is added to the lime-based scrubbing operation, has eliminated the scaling problem that has plagued such systems for a long time. Japan, although not an ECE member, came up for discussion since one often hears of their reliability with scrubbers. Both operating conditions and by-product removal potentials favor their limescrubbing processes. Favorable experience with FGD in Japan is.attributed in some situations to the fact that the scrubbers are installed after oil-fired boilers. The installations, as a general rule, include precipitators. This no doubt makes the operation easier. Japan is also able to use the sludge material from FGD operations. About 60% of it is used in the manufacture of wall board the other 40% is used as an additive in cement manufacture. Japan is perhaps the only country in which there is a market for gypsum today. But in another two years that market may become saturated, and already the Japanese are looking for alternative uses for the gypsum material, mainly calcium sulfate. Volume 10. Number 2. February 1976 125
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Environmental Science & Technology
The sludge imbroglio In a by-product disposal and utilization report, Radian president Donald M. Carlton observed that electric utilities have shown reluctance in pursuing regenerable processes in part because of the requirement to enter the chemical marketplace. Electric utility engineering and operations staffs are geared to the generation and transmission of electric power not the operation of chemical plants, which is another reason for utility reticence in accepting FGD technology. While throwaway systems represent chemical plants, regenerable processes represent an even more radical departure from typical utility operations. Nevertheless, the problems of land disposal of calcium-based sludges are causing a more aggressive assessment of regenerable FGD process options, according to Carlton. He also mentioned that transportation is a big issue in handling the sludge or chemical. What is the material? Where will it be regenerated? Where will it be used? The problem with so-called abatement sulfur (by-product sulfur from pollution control systems) is shown by a Canadian example. It seems that every time the worldwide price of sulfur goes up, another source of sulfur is found. In 1952, the Canadian delegate related, Canada started by-product sulfur production from the removal of H2S from natural gas at 20 tonslyr. Today, production is at 7 million tonslyr. The price could vary from $2-50/ton. Since sulfur is inert in the environment, a football field has been constructed of block SUIfur at Alberta. Carlton reviewed a TVA report that examined the possibility of recovering pollution abatement by-product sulfuric acid from FGD processing and that it would be used in fertilizer production. He also noted that in this case no transportation was involved since it would be used at the same site where it is produced and regenerated. In summary, Carlton stated that for the immediate future, if increased coal utilization is to be the solution to the nation's energy requirements, coal combustion with FGD systems where required virtually is the only option. While several processes are candidates, calcium-based wet scrubbing appears to be the process of preference to date. Early failures and sludge disposal with its land-use questions, the uncertainty of the need for fixation, and its costs clearly have been stumbling blocks to the acceptance of calciumbased processes by the electric utility industry. Nevertheless, substantial technical progress has been made recently in the design and operation of FGD systems and the sludge disposal problem seems to be attaining manageable proportions, Carlton said.
Yet another option Residual oil desulfurization (ROD) is another way to get to lower SO2 levels. The seminar concluded that the range of cost for FGD and ROD to a certain extent overlap as do their field of application. FGD is probably more suitable for large-scale application with a medium to high load factor (such as a power plant), as well as for fossil fuels that may be difficult to desulfurize (coal). In the report on fuel oil desulfurization, Mr. A. J. J. van Ginneken, a representative from Stichting CONCAWE, a cooperative of oil-producing interests in Europe, noted that eight processes are available for the desulfurization of atmospheric and vacuum residues that have metal contents not exceeding 150-250 ppm. He noted that a total of more than 10 large units are in operation or under construction that apply seven processes. Reports from the operating units indicate that many major problems have been overcome (€S&T, June 1973, p 494). He also noted that all Middle East residual feeds could be desulfurized 8590%. Beyond a certain degree of desulfurization the marginal cost of further sulfur removal tends to increase sharply. In ROD, the catalyst is a crucial factor, largely determining the cost of the process. Looking ahead Energy is the new factor that has been introduced in SO2 reduction. The consumption of energy in the ECE region increased by approximately 20% between the 1970 and 1975 seminars. According to the van Ginneken report, the net energy consumption for ROD can be about 6-7 % . That of FGD can be as low as 3% in an ideal solution for a dry process or higher than 10% in actual practice for a wet regenerative process. It was also noted that tall chimneys do not consume energy, an aspect that merits careful consideration and further study. Soon comes that realization that there does not appear to be a unique global solution to the SO2 problem. Nor is there, for that matter, likely to be regional solutions. Apparently, each case is unique and site specific. What must happen now is further stimulation and development of these advanced technologies to meet the conditions in particular countries to reduce SO2. In order to burn high sulfur coal from the East Coast of the U.S. and at the same time meet the air quality standards, FGD systems would have to be installed. Considering that the only nearterm option appears to be calciumbased scrubbing with its attendant disposal problem, many questions arise on land disposal sites, transportation charges, if that route is elected, and SSM fixation, if that is the choice.
