TECHNOLOGY
New pilot plants tackle S02 pollution Chemical, coal, and power industries push S02 cleanup as government action increases The worldwide campaign against sulfur dioxide air pollution is accelerating with completion this month of two new pilot plants—one by the Department of Interior's Bureau of Mines and the other by a four-company combination in Japan (C&EN, June 27, page 2 3 ) . The facilities will both work on extracting S 0 2 from stack gas. The two new test stations come on the heels of a wave of developments, including several antipollution milestones, this spring: • Monsanto will construct a postpilot prototype plant, to be completed by mid-1967, for treatment of flue gas sulfur oxides in an electric power plant (C&EN, May 2, page 6 1 ) . • The National Coal Association and Electric Research Council initiated an estimated $4.3 million research program to find the maximum safe concentration of sulfur dioxide in the air and to develop economical methods of controlling the pollutant. • A University of Florida pilot operation led Dr. C. I. Harding and Sergio F. Galeano to conclude late last month before the Air Pollution Control Association in San Francisco that sulfur dioxide effluent from paper mill power plants can be turned profitably into sulfite process liquor. • New York City got a tough antipollution law requiring stepped-up reduction of sulfur content in fuel oil and coal (C&EN, May 16, page 6 1 ) . • The Department of Health, Education, and Welfare intervened in three Federal Power Commission cases to advocate replacement of coal in selected locations by natural gas. • The U.S. Senate Subcommittee on Air and Water Pollution, headed by Sen. Edmund S. Muskie (D.-Me.), held hearings on Senate bill 3112, which would give the federal air pollution program added authority and funds. Toxicity. The welter of civic and private activity hinges mainly on sulfur dioxide's health hazard, a matter of considerable controversy. Testifying before the Senate subcommittee, H E W Division of Air Pollution chief Vernon G. MacKenzie left no doubt about the division's view. He repeated his often-stated position that "sulfur oxide pollution arising chiefly from the burning of coal and heavy 36 C&EN JULY 4, 1966
fuel oil is already a serious threat to public health and welfare in many urban communities." H E W adds that it has derived a statistical relationship between sulfur dioxide concentration in air and the incidence of respiratory diseases. H E W predicts an alarming rise in sulfur dioxide emission at least until 1975. Significantly, H E W notes that the burgeoning coal-fueled electric power industry already produces the greatest part of sulfur dioxide emission and will increase its share to about 6 5 % by 1980. The coal industry responds sharply to what it considers a misinterpretation of figures. Speaking in May before the American Mining Congress in Pittsburgh, Pa., president James R. Garvey of Bituminous Coal Research, Inc., Monroeville, Pa. (affiliated with
the National Coal Association), had emphatic words of his own. "There has been no substantiating evidence produced that minor amounts of sulfur oxides in the air we breathe are in any way harmful." The National Coal Association points out that no direct causal relationship has been proved to date on the toxic effect of sulfur dioxide concentrations in air. Nevertheless, Mr. Garvey adds, bituminous coal producers must "face up to the reality that there will be a gradual tightening of the allowable limits." Probably the most stringent of such limitations in existence is the antipollution law signed by Mayor Lindsay in New York on May 20. The ordinance directs that sulfur content of coal and residual heating oil burned in the city be decreased to 2.2% in eight months,
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2.0% in three years, and 1% in five years. Consolidated Edison Co. of New York has reacted to the ordinance by changing fuel purchase plans. Vice president W. Donham Crawford outlined Con Edison's course in a speech to coal men at the National Coal Association's convention in Washington, D.C., late last month (C&EN, June 27, page 2 1 ) . He foresaw that bringing sulfur content down to 1% would hurt coal prices and challenged the delegates to find a solution. Then he frankly stated that some of Con Edison's older stations had "only one avenue"—conversion to natural gas. The switch to natural gas has also gained backing from H E W in certain instances. The department has formally intervened in three undecided cases before FPC to argue for fuel conversion in Los Angeles, New York, and Miami. In these cases, H E W bases its briefs on the position that "the use of natural gas . . . to alleviate serious air pollution problems should be given the highest priority." H E W suggests specifically that the maximum safe sulfur dioxide concentration in the air should be 0.1 p.p.m. (24hour concentrations should not exceed this figure more than 1% of the time for a 150-day period).
In the face of HEW-supported competitive pressure, the coal and power industries are pushing various schemes to cut the amount of sulfur dioxide venting from steam plants. Ironically for Manhattan lawmakers, the most promising of these have nothing to do with decreasing the initial sulfur percentage in bituminous coal. Recovery. A solution from Japan embodied in a present pilot operation was presented by Dr. Raisaku Kiyoura of Tokyo Institute of Technology to the meeting of the Air Pollution Control Association in San Francisco last month. His dry catalytic oxidation process removes sulfur dioxide from stack gases (reducing its concentration from 0.2 to 0.02%) in oil-fired electric power plants. In the recovery procedure, sulfur dioxide in a flue gas is oxidized to sulfur trioxide over vanadium pentoxide at 380° to 450° C. Moisture present in the gas reacts with sulfur trioxide to form gaseous sulfuric acid. Ammonia gas is then injected into the system to form 99% pure ammonium sulfate crystals. These aggregate to sizes above 100 micron—suitable for bagging and shipping as fertilizer. A key point in the recovery cycle is holding temperatures above the dew
point of sulfuric acid (between 220° and 260° C ) . This prevents formation of liquid sulfuric acid with its attendant corrosion problems. After earlier bench scale and small pilot trials, Japanese engineers are now finishing construction of a medium-sized $170,000 plant (290 to 590 s.c.f.m.) at Omuta on the southern island of Kyushu. This plant will operate on bypass flue gas from the boiler of one of Toyo Koatsu's power plants. Pilot-plant studies of this unit will likely wind up at the end of this year. Dr. Kiyoura estimates cost for a 600-Mw. plant at 44 cents per metric ton of fuel oil or 0.09 mill per kilowatthour. Total capital investment would run about $6.67 million, he figures. In the U.S., Monsanto has already pilot-tested (in 1961) a dry process, gas-phase sulfur dioxide recovery system at Pennsylvania Electric Co/s Seward Station. (This test was conducted jointly by Penelec, Air Preheater Corp., Research-Cottrell, Inc., and Monsanto.) Monsanto is currently designing a prototype facility to remove sulfur dioxide from flue gases by catalytic oxidation at the Portland, Pa., generating station of Metropolitan Edison Co. (Both Penelec and Met Ed are subsidiaries of General Public Utilities Corp. of New York.) Capital
-Monsanto and Kiyoura-TJT. processes remove 90% S02 In fluaps
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SEMIPILOT. Graduate student adjusts valve on semipilot sulfur dioxide removal plant developed by Prof. Raisaku Kiyoura of Tokyo Institute of Technology. The process handles 21 to 41 s.c.f.m. flue gas, which it converts to by-product ammonium sulfate. A larger, full-pilot operation starts up this month
cost will be over 1 million and planned capacity 24,000 s.c.f.m.—the largest known to date. Monsanto expects its experimental program at Portland to last about one year after startup. Construction should be completed by mid-1967. After that, testing will proceed on such unexplored matters as economics, catalyst regeneration, and formation mechanisms of sulfuric acid mists and other possible end products. The Monsanto prototype process is based on the pilot-plant reaction sequence. The procedure is an adaptation of the contact catalytic procedure in sulfuric acid production. Gas from coal combustion in the boiler passes first at about 900° F. through an electrostatic precipitator for removal of solid fly ash particles. The near-perfect efficiency (over 99%) of this step is necessary to avoid clogging the catalyst bed in the next phase. The catalyst, vanadium pentoxide, converts 90% of the sulfur dioxide (which enters the converter at 2000 p.p.m. in the stack gas) to sulfur trioxide at about 880° F. The new gas constituents flow through a rotary preheater to raise the temperature of incoming air on its way to the boiler. This drops the temperature of the sulfur trioxide and remaining sulfur dioxide to about 200° F. and causes a sulfuric acid mist to form. Cool surrounding surfaces at this point precipitate much of the acid, and the rest condenses in an adjoining mist collector. In all, about 90% of the original sulfur in the coal can be recovered as 70% sulfuric acid. A third recovery operation is the Bureau of Mines pilot plant at the
Pittsburgh Coal Research Center. The facility will test the bureau's alkalized alumina process for absorbing sulfur dioxide from stack gas. The reaction sequence leads eventually to elemental sulfur, which can be marketed with resulting credit. The Pittsburgh plant has a rated capacity of 165 pounds of coal per hour or about 415 s.c.f.m. of stack gases. Desulfurization. The bureau is also working on various schemes for desulfurizing coal, including magnetic separation and conventional crushing or specific-gravity separation. Desulfurization has long been a gleam in the industry's eye. Among interested organizations, Bituminous Coal Research has made numerous tests to reduce sulfur content. In some instances, such as with one grade of Pennsylvania coal, crushing to 60 mesh and floating at 1.6 specific gravity reduced sulfur content to 1%. However, this order of reduction rarely happens. The trouble is that most coal contains an irreducible minimum of chemically bonded sulfur. Unfortunately, as HEW-sponsored studies point out, this level tends to increase in Midwest seams, which serve the largest segment (the fivestate region around the Great Lakes) of the coal-burning power industry. Pressing to come up with the right answer, the coal industry recognizes the huge stakes involved. Con Edison vice president Crawford summarizes the challenge in a sentence, "It is conceivable that coal could be legislated out of business in some areas due to inability to meet stringent air pollution code provisions at a competitive price."
