Environ. Sci. Technol. 1991,2 5 , 347-348
COMMUNICATIONS N20 Emissions from Fossil Fuel Fired Power Plants Takahisa Yokoyama" and Shaw Nishinomiya Komae Research Laboratory, Central Research Institute of Electric Power Industry, 2-1 1-1 Iwato Kita, Komae shi, Tokyo 201, Japan
Hlromltsu Matsuda Yokosuka Research Laboratory, Central Research Institute of Electric Power Industry, 2-6-1 Nagasaka, Yokosuka shi, Kanagawa Ken 240-0 1, Japan
Introduction Fossil fuel combustion have been considered to be a major anthropogenic emissions source for NzO (1-3). More recently, data collected in the past on N 2 0 concentrations in boiler flue gas have come into question because of problems with sample collection methods. Formation of NzO in sample flasks due to reaction of collected gases has been observed ( 4 ) . Thus, previously reported values were probably elevated by this artifact formation and emissions factors for N 2 0 are probably too high (5, 6). This communication summarizes results of field measurements of N 2 0 concentrations in flue gas a t 43 fossil fuel fired power plants (oil, coal, and gas fired) in Japan. The units studied were selected on the basis of fuel type, output, boiler type, combustion conditions, environmental control system configurations, etc. (Table I). In particular, the effect of NO, control systems including selective catalytic reduction (SCR) and combustion modification was examined.
Table I. Plant Data"
boiler
600 175 250 500 700
(a) Coal Fired FF, LNB,FGR, 2SC FF, LNB,FGR, 2SC FF, LNB,FGR, 2SC FF, LNB,FGR, 2SC FF, LNB,FGR, 2SC FF, LNB,FGR, 2SC FF, LNB,2SC
700
265 250 500 450 250 350 600 600 1000 350 375 250 600 350 500
Measurement Methods The procedure used to collect gas samples during this study is based on JIS K 0095 (7). In order to prevent artifact formation, a series of traps were installed between the sampling port and the collection bag. A rock wool impinger was used to remove water, the remaining water vapor was removed by use of a calcium chloride packed column, carbon dioxide was removed by a soda lime packed column, and sulfur dioxide was removed by a sodium hydroxide packed column. Tests performed prior to initiating the field program showed that N 2 0 losses in the traps were negligible. The sampling bag was a 10-L Tedlar bag, which was shown to allow stable storage of samples for a t least 72 h. N 2 0 levels were measured by ECD or TCD gas chromatography (8)as soon as possible after sample collection.
500
250 156 220 350 175 600 220 600 600 350 350 265 350 600 1000
Results and Discussion Figure 1 plots flue gas concentration of NzO for the 43 plants studied. The average flue gas N 2 0 concentration for the 43 units was 0.3 ppm, which was equivalent to the average background atmospheric N,O levels a t the sites studied. Theaverage flue gas N 2 0 concentrations for coal, O i l , and LNG fired units were 0.5 (7 units, range 0.2-0.8 ppm), 0.3 (21 units, range 0.1-0.8 pprn), and 0.1 ppm (15 units, range (0.2 ppm), respectively. There was no par0013-936X/91/0925-0347$02.50/0
plant output, MW
175 175 1000 375 250 600
(b) Oil Fired FF, LNB,FGR, 2SC FF. LNB.FGR. 2SC CF; FGR; 2sc CF, FGR, 2SC FF, LNB,2SC FF, LNB,2SC CF, LNB,FGR FF, LNB,FGR FF, LNB,FGR FF, FGR, 2SC FF, LNB,FGR, 2SC CF, LNB,FGR, 2SC FF, LNB,FGR, 2SC FF, LNB,FGR, 2SC FF, FGR, 2SC CF. 2SC FF; LNB,FGR, 2sc CF, FGR, 2SC CF, LNB,FGR, 2SC FF, LNB,FGR, 2SC CF, LNB,FGR, 2SC (c) LNG Fired CF, LNB,FGR CF, LNB,FGR, 2SC FF, LNB,FGR, 2SC FF, LNB,FGR, 2SC FF, LNB,FGR, 2SC FF, LNB CF, LNB,FGR FF, LNB,FGR CF, LNB,FGR FF, LNB,FGR, RB FF, LNB,FGR, RB FF, LNB,FGR FF, LNB,FGR FF, LNB,FGR, 2SC CF, LNB,FGR, 2SC
"Abbreviations: FF, front firing; CF, corner firing; 2SC, twostage combustion; RB, reburning; LNB, low-NO, burner; FGR, flue gas recirculation; FGD, flue gas desulfurization; SCR, selective catalytic wduction.
0 1991 American Chemical Society
Environ. Sci. Technol., Vol. 25, No. 2 , 1991 347
1-2 orders of magnitude less than the emission factors used in current emission inventories (2, 3 ) . Acknowledgments
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We thank Chubu Electric Power Co., Chugoku Electric Power Co., Electric Power Development Co., Hokkaido Electric Power Co., Hokuriku Electric Power Co., Kansai Electric Power Co., Kyushu Electric Power Co., Shikoku Electric Power Co., Tohoku Electric Power Co., and Tokyo Electric Power Co. for their assistance in conducting this study. Registry No. NzO, 10024-97-2.
Literature Cited Table 11. Effect of Flue Gas Treatment on Dry N 2 0 Concentration for Coal Fired Units
output, MW 176 250 500
700
SCR inlet,
SCR outlet, P P ~ ppm 1.88 1.34 1.81 1.34 1.24 0.31 1.23 0.73
FGD inlet,
FGD outlet/stack, P P ~ PPm 1.47 0.94 1.11 0.97 0.19 0.34
ticular trend observed for flue gas N 2 0 concentration related to unit output. Table I1 lists data for N20 concentrations before and after SCR and flue gas desulfurization (FGD) systems for coal-fired plants examined during this study. The concentrations of N 2 0 downstream of these systems were similar to or lower than the upstream concentrations. Past studies have found that the ratio of N 2 0 to total NO, was 0.2-0.3 and this value has been used in the development of N 2 0 emission inventories. In this study, the highest value observed for N20 to total NO, was 0.01. The results of this study support more recent findings (4-6) that emissions of N 2 0 by large utility boilers are probably
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Bolle, H. J.; Seiler, W.; Bolin, B. In The Greenhouse Effect: Climatic Change and Ecosystems; Bolin, B., Doos, B. R., Jager, J., Warrick, R. A., Eds.; John Wily & Sons: New York, 1987; pp 157-203. Hao, W. J.; Wofsy, S. C.; Beer, J. M.; Toquan, M. A. J . Geophys. Res. 1987, 92, 3098. Kavanaugh, M. J. Atoms. Environ. 1986, 21, 463. Munzio, L. J.; Kramlich, J. C. Geophys. Res. Lett. 1988, 15, 1369. Ryan, J. V.; Srivsastava, R. K. Project Summary for EPA/IFP European Workshop on Emissions of Nitrous Oxide from Fossil Fuel Combustion. EPA, January 1989 draft. Linak, W. P.; McSorley, J. A.; Hall, R. E.; Ryan, J. V.; Srivastava, R. K. K.; Wendt, J. 0. L.; Mereb, J. B. In 1989 Symposium on Stationary Combustion Nitrogen Oxide Control; EPRI GS-6423; Electric Power Research Institute: Palo Alto, CA, 1989; pp 1-37-1-54. Japan Industrial Standards Committee. Methods for Sampling o f Flue Gas JIS K 0095-1988; Japan Standards Association: Tokyo, 1988. Fuzii, T. Taihi Ossen Gahhai Shi 1980, 15, 53. Received for review August 14, 1990. Accepted November 12, 1990.
