or about 2360 kW for the power plant. This power requirement amounts to 0.31% of the total electric power produced by t h e plant, which compares to 1.3-4.0% consumption of total output by a well-designed FGD scrubber (the precise amount depends mainly on t h e type and degree of flue gas reheat used). It is current practice to apply VC directly to cooling tower blowdown streams as a means of accomplishing water reuse in power plants. A comparison of that approach with t h e method discussed here shows that the integration of VC into the FGD system while using blowdown to replace FGD makeup water is a more efficient procedure: direct VC treatment of the blowdown stream shown in Figure 3 would require evaporation of 3.1 m3 instead of the 1.5 m3 required by t h e combined FGD/water-treatment system. This improvement results primarily from the fact t h a t t h e FGD scrubber serves as an evaporator to preconcentrate the blowdown prior t o VC treatment. Considering the power plant as a whole, water recovery is also increased nearly 50% (1.5 md of VC condensate plus 3.1 m3 of fresh water replaced by blowdown), while producing sufficient high-quality condensate to meet the needs for boiler makeup water. In conclusion, this analysis shows t h a t the application of water treatment to a FGD system can be expected to improve the efficiency of water reuse in power plants of t h e western U.S. and, in eastern applications, can facilitate the combustion of high-sulfur, high-chloride coals in a n environmentally acceptable manner. In either case, such systems should enhance the prospects for controlling t h e discharge of potentially harmful soluble salts, trace elements, and heavy metals from coal combustion by isolating them in a manner that will permit more effective and permanent disposal methods to be a p plied.
Literature Cited (1) Head, H. N., Wang, S.C., Keen, R. T.,“Proceedings: Symposium
on Flue Gas Desulfurization-Hollywood. Fla.”, 1977, Vol. I, EPA-600/7-78-058a ( N T I S P B 282 090), March 1978, pp 170204. (2) Head, H. N., in “Proceedings: Industry Briefing on EPA Lime/ Limestone Wet Scrubbing T e s t Programs (August 1978)”, E P A 600/7-79-092, March 1979. (3) Gleason, R. J., in “Proceedings: Second Pacific Chemical Engineering Congress”, Vol. I, Aug 1977, p 374. (4) Borgwardt, R. H., in “Proceedings: Symposium on Flue Gas Desulfurization-Hollywood! Fla.”, 1977, Vol. I, E€’A-600/7-78058a ( N T I S P B 282 090), March 1978, p p 205-28. (5) Weimer. L. D., EPA-600/7-77-106 (NTIS P B 278 373), Sept 1977. (6) Ando, J., in “Proceedings: Symposium on Flue Gas Desulfurization-Hollywood, Fla.”, 1977, Vol. I, EPA-600/7-78-058a ( N T I S P B 282 090), March 1978, p 62. ( 7 ) Head, H. N., Wang, S. C., Rabb, D. T., Borgwardt, R. H., Williams, J. E., Maxwell, M. A,, paper presented at the E P A Symposium on Flue Gas Desulfurization, Las Vegas, Nev., March 1979. (8) Epstein, M., EPA-650/2-75-047 ( N T I S P B 244 901), Appendix G, J u n e 1975. (9) Chang, C. S., Rochelle, G. T., paper presented at the 35th Southwest Regional Meeting, American Chemical Society, Austin, Tex., Dec 1979. (10) Lowell, P. S.,paper presented a t the EPA Lime/Limestone Wet Scrubbing Symposium, Nov 1971. (11) Anderson, J. H., Herrigel, H. R., Johansen, D. J.,paper presented a t the 36th Annual Meeting of the International Water Conference. Pittsburgh, Pa., Nov 1975. (12) Dascher, R. E., Lepper, R., Power, 121,23-8 (August 1977). (13) Epstein, M., Head, H . N., Wang, S. C., Burbank, D. A,, in “Proceedings: Symposium on Flue Gas Desulfurization-New Orleans, La.”, 1976; Vol. I. EPA-600/2-76-136a, May 1976, p p 145-204. (14) Richman, M., Kent, R., paper presented at the American Power Conference. Chicago, Ill.. April 1979. Received f o r review J u l y 19, 1979. Accepted December 3, 1979.
Polycyclic Organic Matter (POM) and Trace Element Contents of Carbon Black Vent Gas Robert W. Serth” Department of Chemical & Natural Gas Engineering, Texas A&l University, Kingsville, Tex. 78363
Thomas W. Hughes Monsanto Research Corporation, Dayton, Ohio 45407
Polycyclic organic material (POM) and trace element emissions were measured a t an oil-furnace carbon black plant as part of a program sponsored by the U.S. Environmental Protection Agency to characterize atmospheric emissions from industrial sources. Emission factors are presented in this paper for 20 POMs and 14 trace elements found in the main process vent gas from the plant. On a mass basis, approximately 8% of the POM content consisted of compounds classified as carcinogenic. Cadmium and mercury were among the trace elements detected in the vent gas. Carbon black (finely divided carbon produced by the thermal decomposition of hydrocarbons) is a major industrial chemical used primarily as a reinforcing agent in rubber compounds, especially tires. I t is currently manufactured in the United States at 30 plants having a combined capacity of approximately 1.9 X lo6 metric tondyear. T h e principal method of production is the oil-furnace process, which accounts for approximately 90% of the carbon black produced domestically. 298
Environmental Science & Technology
Air pollution problems associated with the oil-furnace process are due primarily t o t h e large amounts of particulate matter, carbon monoxide, hydrocarbons, and sulfur-containing compounds generated in the process (1-4). However, since the.process involves the combustion of natural gas and the high-temperature pyrolysis of aromatic liquid hydrocarbons, it is also a potential source of polycyclic organic material (POM) and trace element emissions. This paper presents results of field measurements of POM and trace elements in the main process vent gas at a typical oil-furnace carbon black plant. The work was performed under the auspices of the Industrial Environmental Research Laboratory (IERL) of the U.S. Environmental Protection Agency as part of IERL’s effort to characterize emissions from industrial sources. Process Description In the oil-furnace process, carbon black is produced by the pyrolysis of a n aerosolized liquid hydrocarbon feedstock in a refractory-lined steel furnace a t 1320 to 1540 “C. The heat required to carry out the decomposition reaction is supplied 0013-936X/80/09 14-0298$0 1.OO/O @ 1980 American Chemical
Society
by burning natural gas. The hot reaction gases and suspended carbon black particles are cooled to 230 "C by direct water sprays and then sent to a baghouse for recovery of the carbon black. The exhaust gas from the baghouse is either vented to the atmosphere through the main process vent or sent to a combustion device (thermal incinerator, CO boiler, or flare) to reduce the contaminant loading. About two-thirds of the carbon black plants in the United States now employ combustion devices to control carbon monoxide and hydrocarbon emissions. The raw carbon black recovered in the baghouse is further processed to produce a marketable product. This processing gives rise to a number of sources of air pollution in addition to the main process vent ( 1 ) .However, the main process vent gas constitutes the major source of air pollution from the oilfurnace process. A typical oil-furnace carbon black plant was selected for sampling in this program. All oil-furnace plants are similar in structure and operation, differing primarily in the details of furnace design and raw product processing operations. Therefore, the results obtained in this study can be considered representative of the oil-furnace process in general. (See, however, the qualifications regarding trace element emissions in the Discussion section.) Sampling and Analytical Procedures The main process vent gas was sampled a t a location downstream of the baghouse but upstream of the combustion device. Three runs each were made for POM and trace elements over a 4-day period. Two blank runs, one for POM and one for trace elements, were also made as a check on the sampling and analytical procedures. Modified versions of the EPA Method 5 sampling system were used for the two sets of measurements. In both cases, the sampling system was operated as specified in the Federal Register by traversing and maintaining isokinetic conditions a t each traverse point. The sampling period for each run was 2 h. For trace element sampling, the EPA Method 5 sampling train was modified in order to collect both particulate and inorganic materials as specified in the Level I environmental assessment sampling procedure ( 5 ) .The Method 5 probe assembly was connected to a heated Millipore Fluoropore type FA filter, 60 mm in diameter with a nominal pore size of 1000 nm. The exit side of the filter was connected to a series of four impingers. The first impinger contained 6 M Hz02, the second and third contained a mixture of 0.2 M (NH4)&08 and 0.02 M AgN03, and the fourth contained silica gel. The material collected in the probe, filter, and impingers was ashed in an L T E Model 505 low-temperature asher, digested in aqua regia, and diluted with distilled water. The samples were then analyzed for 23 elements by inductively coupled argon plasma (ICAP) atomic emission spectroscopy. Analyses were performed for three additional elements (arsenic, mercury, and selenium) by atomic absorption (AA) spectroscopy. For POM sampling, the standard Method 5 fiberglass filter was replaced by a Millipore Fluoropore type FA filter followed by an organic trap containing XAD-2 resin. In addition, a gas cooler was employed between the filter and resin trap in order to cool the gas and condense some of the water vapor in the gas stream. T h e resin trap was followed by a system of four impingers. The first impinger contained 10%KOH, the second and third contained toluene, and the fourth contained silica gel. The material collected in the probe, filter, resin trap, and impingers was subjected to solvent extraction and combined as described in ref 1 . The samples were then separated into eight fractions by liquid chromatography using a silica gel column as specified in ref 5 . The three fractions containing
Table 1. Emission Factors for Polycyclic Organic Compounds in Main Process Vent Gas carcinogenicity indicator a
compound
acenaphthylene anthracene/phenanthrene benzo [ c] phenanthrene benzofluoranthenes benzo [ghi]fluoranthene benzo [ ghi] perylene/anthanthrene benzopyrenes and perylene chrysenelbenz [ alanthracene dibenzanthracenes dibenzo[ c,g]carbazole dibenzopyrenes dibenzothiophene
dimethylanthracenes/phenanthrenes 7,12-dimethylbenz[a]anthracene fluoranthene pyrene indeno[ 1,2,3-cd] methy lanthracenes/phenanthrenes methylcholanthrene
methylfluoranthene/pyrene pyrene total
-
+++ ++
-
-
+++ + +++ +++
f
-
++++ + ++++ -
mean emission factor, pglkg
800 70
