The public has been subjected to a great barrage of information and misinformation in the last few years about the practicability of scrubbing the sulfur dioxide from the stack gases produced by electric power stations. Indeed, the issue is still debated among knowledgeable engineers, managers, and environmentalists. Nevertheless a number of utility companies seem to have concluded that, while there may be some merit in continuing the debate in public, there is also merit in quickly installing the scrubbers and making them work.
Stack gas scrubbing, also referred to as flue gas desulfurization, is a method that "washes" the gases emanating from the combustion chambers in power plants by bringing them into contact with a solution of one of a number of possible chemicals dissolved in water. The chemicals react with the sulfur dioxide in the gas and convert it to a nongaseous form. About 90 to 95 percent of the sulfur entering the scrubber is removed from the stack gas and as a side benefit some of the particulates are removed as well. The sulfur compounds must then be removed from the scrubbing water. Depending on the particular scrubbing process, they are either precipitated out or subjected to further chemical modification to form a salable material such as sulfur or sulfuric acid.
(Dry scrubbing has been tried but success has been limited at best, and it now appears that until such a time as fluidized bed combustion technology becomes perfected—perhaps within ten to fifteen years—wet scrubbing to remove the sulfur dioxide is the best technology available for meeting the standards of the 1971 Clean Air Act.)
Support for the view that utilities are switching to scrubbing comes from several sources, beginning with published confirmation in the business press. The business and financial weekly, Barron's (July 14, 1975), reported, for example, that pollution control for utilities is starting to be profitable and that, despite strong objections by some utility spokesmen. spending on wet scrubbers is apt to grow at an annual rate of as much as 35 percent. The New York market research firm of Frost and Sullivan has estimated that stack gas scrubbing will grow from a $19 million industry in 1974 to a $243 million industry in 1983.
In September 1975 EPA administrator Russell Train stated that commitments of the electric power industry to flue gas desulfurization systems have increased more than 250 percent in the previous two years. These commitments represent 118 scrubbers, which will reduce sulfur dioxide emissions associated with the production of 47,330 megawatts of power. This is more than half of the 90,000 megawatts that the EPA estimates will require scrubbing equipment to meet standards for sulfur oxides by late 1980.
One would think that this fundamental change in the operating policy of large utilities could not have happened unless one or more stack gas scrubbing systems had been proved successful beyond equivocation. While a number of systems have functioned remarkably well, the expectation that a single, all-purpose system can be devised belies the complexity of the problem. Coals vary enormously in their composition, and scrubbing systems which function according to specifications for one plant often fail to function for another plant burning a different coal. Moreover, the most thoroughly tested systems result in the production of large quantities of waste which have physical properties somewhat like quicksand. This sludge can be chemically solidified and disposed of, but the cost of doing so is significant. Thus it is an overstatement to say that stack gas scrubbing is a totally demonstrated and practicable technology—but it is less of an overstatement than to claim that the effectiveness of stack gas scrubbing has not been demonstrated. Scrubbers are working, even though much more needs to be known about scrubbing technology.
The explanation for the emerging acceptance of scrubbers is evolutionary in nature. The passage of the Clean Air Act in 1971 and numerous state laws shortly thereafter limited the amount of sulfur dioxide which could be discharged to the atmosphere from power plants. The intention of the Clean Air Act was to bring sulfur dioxide emissions to a reasonable level by 1975. Initially, compliance by utilities was carried out mainly by switching from high-sulfur crude oil to lower-sulfur oil. With the oil embargo of late 1973, followed by a combination of radically higher oil prices and diminished availability, utilities were caught in a squeeze. The remaining options consisted of switching to low-sulfur coal or to blends of low- and high-sulfur coal designed to pass the EPA standard, or installing of scrubbing equipment. As the price of low-sulfur coal in the eastern part of the United States rose to record levels in 1974-75, the economic case for scrubbing became increasingly persuasive.
Between the passage of the Clean Air Act and the present, four years of research effort on scrubbers has resulted in a great deal of knowledge about them. Not only have new types been invented, but the effectiveness of previously developed types has been studied using different coals. The reliability of scrubbers has been dramatically increased because of the research carried out, including experimentation on full-scale plants. Engineers and chemists whose research was sponsored by the EPA are rapidly determining why scrubbers sometimes do not work, and the results of their research is being made public by the EPA. With court orders as the stick and a well-executed R&D program as the carrot, a quiet revolution has been achieved in the policy of the utilities.
A version of this article appeared in print in the Winter 1976 issue of Resources magazine.
