Illinois coal: can we scrub it clean?

By JAMES KROHE JR.

"WHICH are we exhausting more rapidly? Our supplies of energy or fresh air?" asked a February editorial in the Alton Telegraph. At issue was clean air standards as applied to the use of Illinois coal. The Telegraph plainly thought the cost of cleaning the air was too high merely for the benefit of pleasing "a few who are offended by a bit of coal smoke."

But coal smoke does more to the environment than make the air smell bad, obscure the sun and coat cities with soot as it did in the 19th and early 20th centuries. In ways that scientists don't fully understand yet, coal smoke is a killer. That is why Congress started in 1970 to pass laws limiting the amount that may be allowed into the air, and that is why industry has been engaged for nearly a decade in the continuous and not always friendly struggle with state and federal environmental protection agencies over how best to limit coal smoke.

Coal is a chemically miscellaneous substance, and when it is burned, its smoke contains an equally miscellaneous assortment of elements. One of the constituents of Illinois coal is sulfur, and when coal is burned in a power plant boiler (as about 85 percent of all Illinois coal is), that sulfur is converted into sulfur dioxide (SO2) which wafts out of the smokestack along with other gases and clouds of dust and ash.

Sulfur dioxide is a corrosive, toxic gas with a smell so acrid that its presence can be detected in concentrations as low as 0.3 parts per million. The amounts of SO2 pumped into the atmosphere around large power plants can be considerable. According to the Illinois Environmental Protection Agency (IEPA), for example, the SO2 spewed out by the Commonwealth Edison's Powerton generating plant near Pekin during 1978 amounted to 317,687 tons. That plant does not yet comply with state SO2 emission limits.

Once in the atmosphere, this SO2 undergoes a variety of complex chemical reactions with other matter in the air. Some of it is adsorbed by microscopic bits of matter (adhering in layers to the particulates). Some of it is oxidized into sulfur trioxide (SO2), which in turn is easily transformed, in the presence of water vapor, into a dilute sulfuric acid mist (H2SO4). Sulfur trioxide also reacts with other basic oxides to form sulfate aerosols -- ultramicroscopic particles less than one ten-thousandth of a centimeter in diameter that are suspended in the air and can enter the lungs and lodge there.

It has been estimated that from 5 to 20 percent of the particulate matter in urban air is made up of sulfuric acid droplets and particulate sulfates. In certain high concentrations these sulfur oxides can damage plant leaves, corrode exposed metal, even degrade paints on buildings. Based on a 1970 study of damage to paint and zinc in Illinois' five largest metropolitan areas, an IEPA report puts the damage at nearly $7 billion in 1977 dollars.

The effects of sulfur oxides on human health are similarly destructive. The precise agent at fault in sulfur-polluted air has not been identified; SO2's adsorption by particulate matter makes it impossible to separate the effects of the two when both are breathed together. It is widely thought that SO2 by

itself is a relatively harmless irritant, but when breathed with associated particulate matter, the combined effect is a serious irritant. More recent research has indicated that sulfates, including sulfuric acid, are far more irritating to human bronchial tissue than SO2.

Whether the specific agent is SO2 or the various sulfates of which it is a precursor, high concentrations of SO2 maintained over several days are known to raise death rates well above normal. Even fairly low constant concentrations of the gas lead to higher-than-normal incidences of respiratory diseases, especially among the very young and the old. Concentrations well below the current clean air rules for SO2 (365 micrograms -- one millionth of a gram -- per cubic meter allowed throughout any 24-hour period) aggravate the symptoms of persons suffering from disabling respiratory conditions.

Presently there are no limits on sulfate concentrations set by the clean air laws. But, increased attacks of asthma and signs of distress among those suffering heart and lung ailments follow when sulfate concentrations reach even 8-10 micrograms per cubic meter over a 24-hour period. Sulfate sampling done statewide by the IEP A in 1978 revealed that average annual sulfate levels exceeded this unofficial threshhold level in virtually all the state's metropolitan areas.

Limiting SO2

In the face of such evidence, those burning coal have had to meet increasingly strict limits on how much SO2 they may discharge into the atmosphere. Under the federal Clean Air Act of 1970, states were required to develop air cleanup plans including specific programs to control SO2 emissions from existing coal-fired plants. Under other provisions of the same act, new plants built after 1972 became subject to even more stringent federal SO2 limits. Amendments to the Clean Air Act passed in 1977 require the U.S. EPA to review and revise its standards for such new plants every four years with compliance to be judged on the use of what the agency deems the-best available technologies for the removal of SO2 from coal smoke. In effect, this will mean a gradual but continual tightening of the lid on SO2 emissions. The U.S. EPA's current "best available control technology" is a scrubber, technically known as a flue gas desulfur-ization unit. Though complex in construction and operation, scrubbers are simple in principle. As the dirty gases and dust produced by coal combustion emerge from boilers, they are given a chemical bath. The SO2 present in such flue gases is absorbed by an alkaline solution, and the final precipitant is a harmless sludge. The fly ash is captured by electrostatic precipitators in a separate step. The scrubbed flue gas conies out of the smokestacks with about 10 percent of the sulfur present in the original fuel and as little as 2 percent of the dust and ash that would be produced without any controls. About 50 scrubbing processes have been developed, but all but one of the scrubbers presently in use or being built in Illinois are variants on the so-called wet limestone process, which uses limestone as the SO2 absorber. The end product is a calcium sulfate/sulfite sludge which must be disposed of.

The first wet limestone scrubber in the country began operation at Commonwealth Edison's Will County plant in 1972. ComEd's first experience with scrubbers was not a happy one, and it vividly illustrates the complaints that utilities have been making about scrubbers ever since.

For one thing, scrubbers cost a great deal of money to build. The Central Illinois Public Service Co. (CIPS) expects to pay $121 million for a scrubber for its Newton plant in Jasper County, and to pay for it, CIPS asked the Illinois Commerce Commission for a 12 percent rate increase. The CIPS scrubber is the most expensive one being built in the state, partly because of the large size of the plant and partly because of a more sophisticated double-alkali system for SO2 removal. Even the smallest wet limestone scrubber now under construction in Illinois will cost $20 million, and the rule of thumb is that a scrubber will account for one-fourth the cost of a new coal-fired power plant.

Scrubbing trouble

and a switch to a lower sulfur coal blend, improved performance measurably. But when Com Ed engineers used the system to scrub high sulfur Illinois coal, the unit produced so much extra sludge that the plant's disposal facilities were overloaded. Since 1977 the company has not used the scrubber to remove SO2; instead, the company is complying with clean air rules by burning low sulfur coal imported from the West. Today the only part of the Will County scrubber unit still working is a precipitator, used to help reduce the emissions of fly ash from the smokestacks.

ComEd's experience was not unique. The Central Illinois Light Co. (CILCO) has had somewhat better luck with the wet limestone system it installed at its Duck Creek plant in Fulton County in 1976. That scrubber at least is still running, if fitfully; though it cost $32.5 million to build and an estimated $3 million a year to run, the unit has only functioned sporadically and not continuously as required. And another wet scrubbing system -- the once vaunted catalytic oxidation process -- was tried on a demonstration basis at Illinois Power Co.'s Wood River plant beginning in 1972, but it was abandoned two years later.

Largely because scrubber designers have learned from the failures of their first attempts, second generation scrubbers now being installed around the state are expected to be more reliable. Scrubbers' poor reputation among coal consumers already has had unfortunate economic consequences for Illinois; ComEd's reluctance to install scrubbers at its Powerton plant, for instance, was one of the reasons why the firm decided to switch to low sulfur coal from western states in order to meet the SO2 emission limits set by the state. Plants built after 1972 that fall under federal authority, however, may not use low sulfur coal alone as a compliance stratagem, and the most recent of the U.S. EPA's "new source performance standards," issued as a result of the 1977 Clean Air Act amendments, further requires that all plants built after 1979 remove a minimum of 70 percent of the sulfur from low sulfur coals and 90 percent from high sulfur coals. This means that utilities building new plants must install scrubbers. They are likely to do so reluctantly.

Monitoring sulfates Scrubbers are not the only means by which noxious coal emissions may be controlled. Under certain circumstances, for example, state environmental protection authorities have granted temporary compliance to power plants which build taller smokestacks. The taller stacks disperse flue gases over a wider area and so avert the buildup of sulfur pollutants near plant sites. But SO2 is not simply a local problem, although most clean air regulations continue to treat it as such. By putting SO2 higher into the air with tall stacks, it will linger longer in the atmosphere where it can be oxidized into sulfuric acid and particulate sulfates which drift downwind for hundreds of miles and can fall as acid rain as far away as eastern Canada. The transportability of SO2 may explain an apparent anomaly, namely that while concentrations of SO2 have been dropping in Illinois cities since 1970, concentrations of sulfates appear to have remained more or less constant. But it was only recently that the IEPA routinely began monitoring Illinois air for sulfates.

Last May, during a public hearing in Chicago into the IEPA's latest state implementation plan for air pollution control, staff of Chicago's Department of Energy and Environmental Protection (DEEP) recommended that SO2 limits be kept low in Illinois. There has been considerable pressure from the coal industry and others to raise state limits as high as possible without violating federal standards, their argument being that some state rules are stricter than necessary. But Chicago's DEEP was worried about the buildup of sulfates in the city, and DEEP guessed the sulfates were coming into Chicago from SO2 sources hundreds of miles upwind. "It is therefore our hope," DEEP concluded, "that efforts to use high sulfur coal in Illinois and neighboring states do not increase the sulfate levels in Chicago."

Creating sludge

The sludge from CIPS' Newton scrubber, for instance, emerges from the system between 50 to 70 percent solid. The company expects to spend approximately $13 million annually to stabilize this soupy mess by mixing it with fly ash from the plant's boilers and with lime, after which it will be moved by conveyor to an adjacent 320-acre field. It has been predicted that this one scrubber will produce enough sludge over the plant's expected 30-year life to build a sidewalk four feet wide and four inches thick around the earth at the equator 13.5 times.

Sludge disposal is clearly a drawback to all throwaway scrubber systems, and not just because of its cost. ComEd is installing a $60 million wet limestone scrubber on one of four boilers at its Powerton plant near Pekin. The plant is built atop porous soils; because of potential ground water contamination, the state has not yet given the company the requisite permits to dump sludge nearby. And although scrubber sludge is not now classed among hazardous wastes, some utilities worry that that may change. The potential hazard of scrubber sludge is that it can contain traces of dangerous heavy metals found in coal, as does the fly ash which many companies bury in common sites with sludge. If sludge is redefined as a hazardous waste, of course, the costs of properly disposing of it will go higher. Because of these problems, some inventors have explored ways of converting scrubber sludge into usable products instead of throwing it away. Referred to as recovery or regeneration processes, such systems transform sludges into sulfur or gypsum. But the cost of constructing and running recovery systems has been discouragingly high.

This complex arrangement of ductwork, tanks and piping represents a major part of the double alkali flue gas desulfurization system (scrubber) now undergoing initial tests at Central Illinois Public Service Co.'s Newton Power Station. When in operation, the scrubber will cleanse flue gas from the boiler of the station's 590-megawatt Unit 1, before sending emissions to the chimney for discharge 530 feet above ground.

Making fertilizer

Sen. Gene Johns (D., Marion) is working closely with U.S. Rep. Paul Simon (D., Carbondale) to find federal funding for such a plant. A likely candidate is the Southern Illinois Power Co-op's plant in Marion.

Using FBC

The system that is attracting the most attention is called fluidized bed combustion (FBC). FBC is a method by which both particulates and SO are removed during combustion rather than after, as is the case with scrubbers. Pulverized coal is injected into a heated combustion chamber and is suspended by jets of gas over a bed of limestone or some other mineral sorbent. The coal particles burn at about 1500 degrees Fahrenheit, or half the temperature of a traditional boiler. Because of the reduced combustion temperature, fewer of the noxious chemical byproducts like SO2 are produced, and the SO2 that is generated is captured by the sorbent and can be removed with ash. Water pipes inside the combustion chamber carry off heat for steam. Tests indicate that up to 90 percent of the sulfur in even the dirtiest coal is captured, an efficiency matched by the best scrubber.

The FBC has attracted an attentive audience in Illinois. In November 1978, Gov. James R. Thompson signed an agreement setting aside $750,000 in state Coal and Energy Development Bond funds which, when added to some $7.5 million in federal money, will build an FBC demonstration plant at the Great Lakes Naval Training Station in Lake County. The unit, which will burn some 15,000 tons of coal a year, is expected to run for a minimum of 30 months beginning in 1981.

In the slightly more distant future, the conversion of coal into other fuels offers some hope for burning Illinois coal cleanly. One conversion process is the gasification of coal into low-Btu gas (a likely fuel for power plant boilers) or high-Btu gas (a substitute for natural gas). Another conversion process is the liquefaction of coal into fuel oils and diesel fuel. Both processes remove sulfur from coal and so produce a cleaner burning fuel than the original coal. However, the manufacture of cleaner fuels from coal is itself a dirty process. The noxious gallery of waste products includes tars, gaseous hydrogen sulfide and assorted chemicals. The U.S. EPA has warned that it is impossible to determine the extent of pollution that might attend full-scale coal conversion, and more ominously, "the exact extent of the health and ecological effects of these potential pollutants remains essentially unknown."

Upsetting ecology

The reason is the so-called "greenhouse effect." Sunlight penetrates the atmospheric blanket of CO2 to be trapped by it near the earth's surface, gradually warming the planet. A shift in the earth's mean temperature of only a few degrees Fahrenheit is expected to be enough to cause melting of polar ice and the consequent flooding of coastal cities. More worrisome is the possibility that wind and rainfall patterns will be altered, turning now-fertile fields into deserts.

All fossil fuels give off CO2 when burned, but coal gives off more of it --24 percent more than oil and 76 percent more than natural gas according to one estimate. Already the amount of CO2 being pumped into the earth's atmosphere from the combustion of fossil fuels exceeds the ability of the planet's natural CO2 disposal systems -- chiefly the oceans and forests -- to absorb it. Last year the National Academy of Sciences called together experts to examine the problem, and they calculated that the atmospheric load of the gas may double within 75 years. Scientists working for the federal Department of Energy, using more recent data that took into account increased fossil fuel consumption among developing countries, more recently predicted a doubling of atmospheric CO2 by the year 2035, with effects becoming apparent as early as 1990. And, in July, four more scientists reporting to the Council on Environmental Quality carried the same message to the White House: Increased reliance on fossil fuels like coal could lead to global disaster.

Carbon dioxide buildup contributing to the greenhouse effect may be stopped only by ceasing to burn fossil fuels like coal. Fortunately, sulfur oxides have proven to be more manageable. At present, every county in Illinois except three -- Peoria, Tazewell and Massac -- are regarded by the IEPA as "attainment areas," meaning they meet both the 24-hour and annual limits for SO2. The primary annual standard has not been violated anywhere in the state since 1975, and of those continuing violations of the primary 24-hour standard, the sources are known, the violations sporadic and control steps are being taken to end them. Clearly, Illinois' air is cleaner than it was.

But air that meets SO2 standards is not necessarily healthful air. Epidemiologists generally agree that there are no known safe threshhold levels for SO2 below which there are no adverse health effects. In the absence of known threshhold levels, current standards are the product of pressures that had as much to do with politics as they do with public health. Environmental protection must be traded off against often contradictory social and economic needs, and this is a point of special relevance to coal states like Illinois.

The U.S. needs energy, and Illinois needs jobs, and as scrubbers have proven, there is no easy or inexpensive way to have energy and jobs and clean air.

Jeopardizing health

James Krohe Jr. is associate editor of the Illinois Times in Springfield; he specializes in planning, land use and energy issues.