make the particle transfer across the fluid interface less efficient, which is borne out by the displacement of the opposing-jet classification curve to a somewhat higher particle size. It appears from Figure 5 that the numerically calculated curves for solid-plate impaction may be used to estimate the performance of the opposing-jet classifier. Numerical calculations performed for the opposing-jet geometry will provide better predictions. Radial Scan. The particle separation efficiencies and losses for radial scans using four different sizes of liquid oleic acid aerosols are shown in Figure 6. Traverses. from wall-to-wall showed that a slight misalignment in the two opposing jets or in the separation plate resulted in somewhat different performance curves to either side of the center line. To facilitate interpretation, the data for equal radial positions on either side of the centerline are averaged in Figure 6. The radial scan data show some variations of size classification and particle loss as a function of radial position in the original airstream. It appears that particle losses are less for aerosols coming from the centerline because they can best clear the separation plate. These centerline particles also have a slightly higher than average size separation efficiency, which may be due to a somewhat higher than average velocity in the core of the nozzle. The performance near the wall also deviates from the average which may, in part, be caused by an interference of the needle feed with the wall. However, when all radial data are weighted relative to the area they represent, the calculated overall size classification and particle loss agrees closely with the data obtained through overall feed experiments, as seen in Figure 3. During initial testing the velocity of the needle feed was about 10 times that of the average air velocity and resulted in large radial variation of the performance curves. Although the needle flow changed the main flow, one may conclude from these initial observations that there appears to be a dependence of performance on radial position. Further tests with thinner plates and with different-sized separation holes will be performed and are likely to provide further information on these relationships. In conclusion, this new technique gives a sharp particle-size classification. Future work will concentrate on the reduction
of particle losses. Assuming that a minimum separation plate thickness is needed for mechanical strength, a device with a higher flow rate will have a higher ratio of deflected flow height to separation plate thickness, and should, therefore, have lower losses. The deflected flow entrains air in the collecting chamber, thus giving rise to a secondary flow pattern that may deposit some particles onto the surrounding walls and onto the separation plate itself. This phenomenon, common to all types of impaction devices, can generally be reduced by designing the collecting chamber to be relatively large.
Literature Cited (1) Dzubay, T. G., Hines, L. E., Atmos. Enuiron., 9,l-6 (1975). (2) Rao, A. K., Whitby, K. T., Am. Ind. Hyg. Assoc. J., 38, 174-9 (1977). (3) Marple, V. A., Liu, B.Y.H., Environ. Sci. Technol., 8, 643-54 (1974). (4) Marple, V. A., Willeke, K., Atmos. Enuiron., 10,891-6 (1976). (5) Willeke, K., Am. Ind. Hyg. Assoc. J., 36,683-91 (1975). (6) Willeke, K., McFeters, J. J., J. Colloid Interface Sci., 53,121-7 (1975). (7) Dzubay, T. G., Stevens, R. K., Enuiron. Sci. Technol., 9,663-8 (1975). ( 8 ) Luna, R. E., PhD thesis, Princeton University, Princeton, N.J., 1965. (9) Hall, R. E., MS thesis, University of Kentucky, Lexington, Ky., 1970. (10) Mears, C. E., MS thesis, University of Kentucky, Lexington, Ky., 1973. (11) Mercer, T. T., “Aerosol Technology in Hazard Evaluation”, Academic Press, New York, N.Y., 1973. (12) Willeke, K., Whitby, K. T., J. Air Pollut. Control Assoc., 25, 529-34 (1975). (13) Baron, P., NIOSH, Cincinnati, Ohio, private communication, 1977. (14) Reischl, G., John, W., Devor, W., J . Aerosol Sci., 8, 55-65 (1977). (15) Karamcheti, K., Bauer, A. B., SUDAER No. 162, Stanford University, Stanford, Calif., 1963. (16) May, K. R., J. Aerosol Sci., 6,403-11 (1975). Received for review September 9,1977. Accepted November 7,1977. Research was supported by Grant ENG 77-04667from the National Science Foundation and was part of a Center Program supported by Grant ES-00159-11from the National Institute of Enuironmental Health Sciences. Support of one of the authors (R.E.P.)by a PhD Outseruice Training Program, Bureau of Medicine and Surgery, U.S. Nauy.
Composition and Size Distributions of Particles Released in Refuse Incineration Robert R. Greenberg’, William H. Zoller, and Glen E. Gordon’ Department of Chemistry, University of Maryland, College Park, Md. 20742
In recent years there has been increasing concern about toxic elements in urban atmospheres. Some chemical forms of the following elements are generally considered to be toxic to humans when deposited in the lungs: Be, Cr, Ni, As, Se, Cd, Sn, Sb, Hg, and P b ( I , 2). Before optimum control strategies for toxic species can be devised, major sources of the elements must be identified. Several studies considered the release of toxic elements from coal combustion (3-7) or fossil-fuel combustion in general (8).Despite the large mass of material released from coal combustion, analyses by Gladney et al. ( 3 ) and Small (7) indicate that, aside from As and Se, coal cannot account for most toxic elements in urban particulate matter. Furthermore, few elements from coal-fired plants are predominantly associated with small, respirable particles, although some fractionation of volatile elements toward smaller particle sizes has been demonstrated (3, 6, 7). Present address, Analytical Chemistry Division, National Bureau of Standards, Washington, D.C. 20234. 566
Environmental Science & Technology
Little was known about the emissions of various elements from incinerators. This information is needed because of possible environmental effects of existing incinerators and because many communities are considering the use of refuse-derived fuel (RDF) for heat or electric power generation. Before plans for these systems become fixed, the possible release of toxic substances from refuse incineration must be understood. We have studied particles released by incineration of urban refuse in two municipal incinerators in the Washington, D.C., area: the Alexandria (Va.) Municipal Incinerator and the Solid Waste Reduction Center #1 in Washington, D.C.
Sites Studied The Alexandria incinerator has two identical furnace trains each capable of incinerating 140 metric tons of refuse daily. Refuse is fed into the primary combustion chamber where it passes over a series of rocking grates. The combustion gases and suspended particles pass into the secondary combustion
0013-936X/78/0912-0566$01 .OO/O
0 1978 American Chemical Society
Suspended-particle and fly-ash samples are collected from two municipal incinerators in the Washington, D.C., area and analyzed for up to 39 elements. Concentrations of most elements in these materials vary little as function of time. Concentrations of elements in the suspended particles from two incinerators are very similar. Many elements, including Na, C1, Br, Cu, Zn, As, Ag, Cd, In, Sn, Sb, W, and Pb, are primarily associated with small particles. Contributions of refuse incineration to observed elemental concentrations on urban
aerosols are estimated by assuming that municipal incinerators contribute 3% of the 80 kg/m3 total suspended-particle loading typical of many urban areas. This calculation indicates that refuse incineration can account for major portions of the Zn, Cd, Sb and, possibly, Ag, In, and Sn observed on urban aerosols. Emissions from power plants using refuse as fuel should be carefully considered before that use of refuse becomes widespread.
chamber with additional air, where combustion continues. The effluent passes through a water-spray baffle where fly ash impinges upon wet baffles and is partially removed. Remaining particles and gases enter the atmosphere through a 61-m stack a t a temperature of about 260 "C (9). The Solid Waste Reduction Center # 1 (SWRC # 1)contains six identical furnace trains, each capable of incinerating 230 metric tons daily. Each furnace train is similar to those a t the Alexandria incinerator, except for the pollution control devices. The SWRC # 1has both mechanical separators and electrostatic precipitators to remove fly-ash particles. The emitted material leaves the incinerator via a 61-m stack a t a temperature of about 210 "C (10).
Teflon films coated with G. E. Silicone Resin (AR-512) to prevent particle bounce-off and reentrainment. Fly-ash samples were collected from the fly-ash settling tanks. Most analyses were done by instrumental neutron activation analysis (INAA) (12) at the National Bureau of Standards (NBS) reactor. Lead and Ni were measured by atomic absorption spectrometry (AAS) on material leached from filters with HCl and "03, which removed >99% P b and >90% Ni as determined by complete dissolution of some filters. Cadmium and Zn were measured by both INAA and AAS. The accuracy of the analytical technique was checked by analyzing NBS Standard Reference Material 1633 (fly ash), which yielded results in good agreement with literature values (13).
Experimental
Three experiments were performed to seek time variations in concentrations of up to 39 elements in fly ash. Short-term variations were determined by analyzing 18 fly-ash samples collected every 6 h. Intermediate-term variations were determined from 23 weekly samples made up by combining samples collected twice daily. Long-term variations were determined from 10 monthly samples prepared by combining fly ash collected daily during a calendar month. Whole-filter and cascade-impactor samples (11)were collected isokinetically at the two incinerators. The high stackgas temperatures (260 and 210 "C) initially required the use of glass-fiber filters despite high blank values for many elements. Teflon-fiber filters (Du Pont Needled Felt) were used when they became available. Impactor collection surfaces were
Results and Discussion
Time Studies. At the outset of this study, there was a major question of the uniformity of the composition of particles emitted at different times. Since the feed material is a mixture of many components, there was concern that the particles emitted one day might differ in composition from those emitted the next, or that there might be seasonal changes. Observed variations of fly-ash composition over all three periods studied were reasonably small. Variations of concentrations of most major elements such as Al, Fe, and Na were quite small. In Figures 1-3 we show the concentrations of some less abundant elements, Cd and Sb, along with that of Zn. Fluctuations of Zn concentrations are quite small, and those of Cd and Sb were among the greatest for any elements,
Municipal Incherator Weekly Fly Ash Samples
I
I
Alexandria Municipal Incinerator Six-Hour Fly Ash Samples 100
I-
c
50-
b
-
I
I
I
1
Friday
Monday I pm
Tuesday 7pm
Thursday lam
lam
Figure
1. Short-term variations In concentrations
of
2% Cd, and S b in fly ash from Alexandria Municipal
Incinerator
IO
I DEC. 1972
I
MAR inn
I
MAY 1171
I
Alexandria Municipa Incinerator Monthly Fly Ash
Samples
'.'/
l5o0
J
1
Figure 2. Intermediate-term variations in Figure 3. Long-term variations in concentraconcentrations of Zn, Cd, and Sb in fly ash tions of Zn, Cd, and S b in fly ash from Alexfrom Alexandria Municipal Incinerator andria Municipal Incinerator Volume 12, Number 5, May 1978
567
but one can still obtain meaningful average values. At first glance, the Cd data in Figure 3 appear to show a rising concentration with time, but this impression is based on only two points, the June 1973 point, which is low and the November 1973 point, which is unusually high. Considering all of the points, there does not appear to be an upward trend. Since the three fly-ash experiments were run consecutively, we followed elemental concentrations over about 15 months. Only two obvious long-term trends were observed. Beginning in June 1973, the Hf concentration increased fourfold over its previous value. The higher level was maintained for four months and then, between October and November 1973, it returned to its original value, as shown in Figure 4. The concentration of Mn also increased between June and July of 1973 by a factor of two to three. The Mn concentration maintained the higher concentration through the last sample analyzed (March 1974). The reasons for these concentration variations
I
i
I
I
Aleandria Municipal Incinerator Fly Ash
-
m-
4
h
20 IO
I
I
?:E
;",
i
I
R
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Figure 4. Longterm trends in concentrations of Mn and Hf in fly ash from Alexandria Municipal Incinerator
Table 1. Concentrations of Elements Observed in Alexandria Municipal Incinerator Fly Ash and Suspended Partlcles Concentration (pg/g unless 56 Indlcated) Suspended parllcles
Fly asha
Av f SD
1.45 f 0.19 0.76 f 0.19 1.3 f 0.5 4.3 f 1.0 610 f 300 2800 f 400 0.80 f 0.21 120 f 60 25 f 25 10.9 f 1.1 10.4 f 0.9 3.2 f 0.4 135 f 18 1330 f 170 4300 f 1800 5.2 f 1.2 35 f 5 740 f 100 980 f 440 1.08 f 0.14 4 0 f 13 3.4 f 1.9 85 f 22 42 f 24 0.71 f 0.49 0.143 f 0.026 270 f 140 34 f 6 78 f 17 4.2 f 1.0 1.07 f 0.17 0.22 f 0.10 1.5 f 0.6 14f2 6.8 f 5.9 3.1 f 0.9 16 f 4 1.1 f 0.8 0.40 f 0.13
Na (%) cs Mg (%) Ca (%) Sr Ba CI ( % ) Br
I AI (%) sc Ti ( % )
V Cr Mn Fe ( % ) co Ni cu Zn (%) As Se Ag Cd In Sn (%)
Sb La Ce Sm Eu Lu
Yb Th
Hf Ta W Au
Pb ( % ) 33 Samples.
568
26 Samples
Environmental Science & Technology
Range
1.12-1.94 0.21-1.2 0.5-2.1 3.3-8.6 260-1 100 1600-3600 0.30-1.12 61-250 5-80 9.0-14.2 8.9-13 2.6-4.2 110-166 1070-1 900 2700-8500 3.4-8.7 26-54 580-960 300-2000 0.78-1.36 9.4-74 1.4-11 52-140
