Measurement of Gaseous Hydrogen Chloride Emissions from Municipal Refuse Energy Recovery Systems in the United States Roosevelt Rollins" and James B. Homolya Gaseous Emissions Research Section, Environmental Sciences Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, N.C. 2771 1
Measurements were carried out a t two refuse energy recovery systems to assess the atmospheric emissions of HC1. Flue gas measurements data were used to establish both emission factors and mass emission rates. The latter were used as inputs to an elevated point source dispersion model to estimate maximum surface concentrations of HC1 under a variety of meteorological conditions. The projected ambient HC1 levels associated with refuse energy recovery processes raise a question regarding the potential for significant materials damage resulting from uncontrolled emissions. T h e use of refuse as fuel for heat or electric power generation has become an economical venture because of the rising cost of conventional fuels and t h e need for dealing with a n ever-increasing volume of solid waste. Several of the existing and planned refuse-to-energy recovery facilities are located near or interdispersed among large urban populations ( I , 21, a n d , if emissions are not properly controlled, they could impose an unnecessary environmental hazard. Potential pollutants from refuse incineration systems include particulate matter, sulfur oxides, nitrogen oxides, hydrogen chloride, hydrocarbons, carbon monoxide, and trace elements ( 3 ) . T h e Environmental Protection Agency has promulgated standards of performance for particulate emissions from incineration facilities built since 1971 ( 4 ) . At the present time, there are no standards for gaseous emissions from these facilities. However, as more US.cities turn to refuse-to-energy recovery technology to help cope with their solid waste disposal problem and to supplement their energy needs, the question of environmental impact needs to be assessed. Some studies (c5,6) have indicated that significant quantities of HC1 may be emitted during incineration of normal refuse. HC1 emissions from incinerators are expected to increase in the future because of the increasing poly(viny1 chloride) (PVC) content in refuse. Based upon a projected compositional change in US. urban refuse, plastics will comprise 13 wt 9% of refuse in the year 2000 as compared to about a 2% value established for 1970 (7). Refuse energy recovery technology has been utilized in Europe for several years. T h e Federal Republic of Germany has established a chloride mass emission rate of 6 kg/h for incinerators firing refuse in excess of 18 tons per day (8).As a result, many incinerators have been retrofitted with alkali scrubbers and emissions monitors to comply with emissions regulations. In the United States, refuse incinerators operated solely to dispose of solid waste usually incorporate some form of water spraying system t o cool the exhaust gases and control particulate emissions. Because of the high solubility of HC1 in water, HCI emissions are also effectively controlled in the process (9).However, modern incinerators designed and operated for waste heat recovery are generally subject to stringent particulate control regulations, and electrostatic precipitators are used in place of low efficiency scrubbing. Consequently, higher HCI emission levels would be expected. Environmental data on gaseous emissions from newly constructed waste-to-energy recovery systems are extremely limited. T o help remedy this situation, a source measurement 1380
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program was conducted at two refuse-burning, steam-generating facilities. T h e facilities selected for this program burn normal residential, commercial, and nonhazardous industrial refuse. During the measurements, no attempt was made t o establish the physical composition of the refuse being burned, since the primary goal of the program was to acquire information on typical gaseous HC1 emission levels.
The Incinerator Facilities T h e two incinerators tested were of the continuous-fed, mechanically stoked-grate type with water-walled boilers. They represent the best of typical modern designs. At both facilities, electrostatic precipitators ( E S P ) are installed to control particulate emissions. T h e operations of both facilities are basically identical. Figure 1 shows a cross-sectional view of the process. Refuse generated by the associated metropolitan area is delivered by truck to the dumping pit. Crane grapple buckets transfer the refuse from the dumping pit into feed hoppers. T h e feed hoppers open into a feed chute equipped a t the top with a hydraulically operated shut-off gate; the gate is used to prevent air infiltration into the system when the furnace is out of service. T h e refuse is then fed, by gravity, onto the stoker grates where combustion takes place. T h e movement of the grate forces the refuse downward through the combustion chamber and provides tumbling action to increase combustion efficiency. Underfire air is used t o cool the grates and control the hed Combustion rates. Overfire air above the grate promotes efficient burn-out and oxidation of the bed combustion products. T h e ash residue is discharged a t the end of the grate into an ash pit partially filled with water, thus quenching the ash. T h e ash is then carried via belt conveyors to a screening area where salvageable metals are recovered. The hot (1500-2000 O F ) flue gases from the combustion pass through a series of boiler tube banks before being discharged to the ESP. By the time the flue gases have reached the ESP, the temperature has been reduced to 450-550 O F . From the E S P unit, flue gases are discharged through an induced draft fan into the stack. T h e major differences between the two facilities are the number and size of furnace units. Incinerator A has two identical furnaces, each designed for firing a maximum of 750 tons of refuse per day. T h e associated boilers are capable of generating 185 000 lb of steam/h a t 690 Iblin.' pressure. One 33.4-m high stack serves both furnaces. This facility became operational in 1975 and provides steam for a local industry. Incinerator B became operational in 1971 and has four furnaces; each is designed for firing u p to 400 tons of refuse per day. T h e boiler unit generates u p to 110 000 lb of steam/h a t 250 lblin.' pressure. Each of the 75-m high stacks accommodates two furnaces, also. At the time of this study, the facility did not have a customer for the excess steam generated. At both facilities, each furnace exhausts through a separate E S P unit, fan, and associated duct work. Sampling ports are installed in each duct following the E S P as well as on the stack. Both plants generally operated 24 h per day. T h e number of units being fired a t any one time varied, depending upon
This article not subject to U.S. Copyright. Published 1979 American Chemical Society
ELECTROSTATIC
STOKER GRATE ASH O I S C H A R G E R
Figure 1. Cross-sectional view of the incinerator facility
steam requirements and refuse inventory. Each unit is normally operated a t or near its design capacity.
Teht Procedures T h e test program involved manual sampling for the determination of HC1 concentrations and ancillary measurements of stack oxygen, moisture, temperature, and velocity. All of these measurements were made in t h e outlet duct following t h e E S P unit. When t h e two furnaces t h a t shared a common stack were being fired simultaneously, parallel testing was conducted on the two units. At t h e beginning of each test day, a complete velocity transverse was performed on each duct. An average gas velocity was determined and this value used to select a sampling point having this average velocity. HC1 gas samples were collected with a heated, glass-lined probe coupled to a four-midget impinger train. T h e first three impingers contained a solution of dilute sodium hydroxide (NaOH) as the absorbing solution for HC1. For particulate filtering, a glass-wool plug was placed in t h e front end of t h e probe. Sampling was conducted nonisokinetically, a t a single point, and a t a n average rate of 1 t / m i n .
Table 1. Emission Data for Incinerator A
date
run
3/22
A B
3/23
C D E F
3/24
HCI cpncn, ppmv unit unit no. 1 no. 2
282 258 205 328 207 289
G H I
9/25 9/26
9/27
1 2 3 4 5 6 7 8 9 10 11
122 382 318 20 1 180 110 78 244 164 43
HCI mass emisslpn rate, kg/h unjt unit no. 1 no. 2
HCI mass emission rate at stack exit, kg/h
88.7 81.2 61.9 95.0 65.1 92.3 131 172 125 307 188 255 137 182 395 312 366 352 69
31.7 98.9 82.8 52.8 46.6 28.0 20.8 63.9 48.2 13.0
Moisture and oxygen measurements were made immediately following the HCl sampling run. T h e moisture analysis was performed by drawing a gas sample through a preweighed silica gel drying tube and determining its weight gain. Oxygen levels were determined via Orsat procedures or a Teledyne Model 320P Oxygen Analyzer. Temperatures were measured continually by a thermocouple, which was connected t o a digital readout device. T h e analysis of a gas sample for its HC1 concentration involved pretreatment of t h e impinger catch by passing a n aliquot of absorbing solution through a n ion exchange column (Rexyn 101-H) to remove possible interfering species such as heavy metals, and then adding hydrogen peroxide to oxidize sulfite ions. T h e sample aliquots were then titrated using a standard solution of mercuric nitrate [Hg(NO&]. Previous studies have shown this methodology to be t h e most suitable for determining t h e HCl concentration in emissions from a combustion source ( 1 0 ) . Results a n d Discussion Source measurements were performed during t h e periods of March 22-24, July 18-20, and September 26-27,1978, and, thus, should include the effect of seasonal variations in refuse composition. T h e test results obtained from these measurements are presented in Tables I and 11. HC1 concentrations and mass emission rates are reported on a dry basis a t standard conditions. HCl mass emission rates a t stack exits are given for those periods when two furnaces t h a t shared a common stack were operating simultaneously. These values
Table II. Emission Data for Incinerator B
48.2 52 8 38.4 78.7 52.0 64.5 34.9
83.7 163.4 117.7
46.1 99.3 78.5 95.2 93.2 18.0
92.7 127.3 99.3 159.1 141.4 31.0
date
7/18 7/19
7/20
run
1 2 3 4 5 6 7 8 9 10 11 12 13
HCI concn, ppmv unit unit no. 1 no. 2
246 338 319 129 212 192 231 280 350 285 299 193 324 ~~
227 416
190 186 216 299 237 264 ~
HCI mass emission rate, kg/h unit unit no. 1 no. 2
26.9 36.3 37.0 14.8 24.3 26.1 26.9 33.2 38.3 30.2 32.1 21.0 36.6
HCI mass emission rate at stack exit, kg/h
23.3 42.2
50.2 78.5
24.9 24.7
51.8 57.9
29.1 37.2 29.4 32.6
59.3 69.3 50.4 69.2
~
Volume 13, Number 11, November 1979
1381
should be treated as approximations, since all of the measurements were actually made a t a single point in the duct leading into the stack. T h e test period averages for moisture, oxygen, and temperature ranged from 7 to 15%,6 to 1270,and 230 to 270 “C, respectively. On a given day these variables remained nearly constant, varying by less than 1%with successive close samples. Stack gas volumetric flow rates averaged about 6000 m.’/min for incinerator A and 2800 m ’/min for incinerator B. T h e average HC1 concentrations ranged from 142 to 262 PPW Significant variations in HC1 concentrations were measured for a single unit during a test period and between two identical units operating simultaneously. Two explanations can be given for the variations in results. First, fluctuation in refuse firing rates during a test period and between t h e two units would result in variations in the HCl emissions. Second, some variations likely existed in refuse composition on a day-to-day basis as well as on a unit-to-unit basis. T h e day-to-day variations on refuse composition became apparent at the beginning of the last test period, when a yellowish oily material was observed to collect in t h e HCl sampling train. This unknown material condensed and formed a distinct layer on top of the aqueous NaOH absorbing solution. Similar occurrences had not been observed for any of the other tests. The unknown material was not positively identified; but, based on Fourier transform infrared spectral analysis, it appeared to be a heavy, saturated oil, similar t o t h a t used for household cooking. Because the unknown organic material was observed in the flue gas, normal sampling and analysis procedures were slightly modified. Some of the samples were collected with an extra glass-wool filter plug placed at the back end of the probe, or with an added impinger, containing distilled water only, a t t h e front end of the impinger train. For these samples, t h e catch was first passed through a charcoal column to remove the organic material; samples were then subjected to normal analytical procedures. T h e modified analytical procedure was subsequently tested in the laboratory with a known C1- solution and showed no effect on the results. T h e HCl mass emission rate averages for each unit were approximately 60 kg/h for incinerator A and 30 kg/h for incinerator B. Given refuse firing rates of 750 and 400 tons/day for the units, HC1 emission factors are calculated to be 2.11 and 1.98 g of acid/kg of refuse fired for A and B, respectively. In essence, the good agreement between the emission factors reflects the general uniform composition of municipal refuse from large US.cities. The two sources studied in this program are about 900 miles apart and located in metropolitan centers with populations in excess of one million. T h e measured chlorine content of municipal refuse in St. Louis was reported t o vary between 0.13 and 0.32 wt 90( I ] ) , which compares favorably with a calculated value of0.20 wt % based on the flue gas HCI measurements of the present study. The mass emission rate data were used as inputs to a plume dispersion model for estimating ambient HC1 concentrations attributable to the sources. T h e model selected is termed PTMAX (12)and estimates maximum surface concentrations of elevated source emissions as a function of wind velocity and atmospheric stability. This model has been used a t EPA to provide estimated peak maximum, 1-h, surface concentrations ( 1 3 ) .Source A is normally operated with both units in use, which results in a combined HCl mass emission rate of 120 kg/h. At source B, three of the four units are in continuous use, giving an emission rate of 90 kg/h. The results of the PTMAX projections over a range of atmospheric stabilities are summarized in Table 111. T h e stability categories range from “extremely unstable” (low surface wind speeds, strong incoming solar radiation) to “most stable” (night hours with
Table 111. Estimated Maximum Surface Concentrations of HCI Emitted from Refuse-Energy Recovery Sources atrn stability
wind speed, rn/s
1 (unstable)
0.5 1.5 3.0 1.o 2.5 5.0 3.0 10.0 15.0 5.0 10.0 20.0 2.0 3.0 5.0 2.0 3.0 5.0
2
f
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Environmental Science &. Technology
3
4 (neutral)
5
6 (stable)
rnax concn. wg/rn3 source A source B
25.6 36.7 42.8 12.3 21.6 29.2 17.7 29.0 29.6 9.7 15.1 17.5 21.0 18.1 14.8 10.1 9.5 8.5
21.0 28.8 31.8 10.1 16.4 20.1 13.1 17.2 16.1 6.5 8.5 8.3 12.0 10.0 7.8 4.8 4.3 3.6
dlstance of rnax, krn source A source B
1.6 1.o 0.8 4.6 2.2 1.3 3.9 1.5 1.2 9.1 4.3 2.5 14.2 12.1 10.0 38.6 31.3 24.5
1.6 1.o 0.8 4.4 2.2 1.4 3.9 1.7 1.4 9.8 5.2 3.4 16.9 14.7 12.5 51.3 42.9 34.9
little cloud cover). T h e neutral class, 4, can be assumed for overcast conditions during day or night, regardless of wind speed. Under extremely unstable conditions, the highest peak concentrations of HC1 were estimated to be 42.8 and 31.8 pg/m.’ a t 800 m downwind for sources A and B, respectively. Although we have estimated ground-level concentrations of HC1, undoubtedly the acid emissions undergo some transformation upon mixing and dilution in the ambient air. I n particular, the formation of ammonium chloride aerosols in the vicinity of the source may be a major secondary reaction. In aerosol form, HC1 is a very corrosive agent. In fact, one of the most serious operational maintenance problems a t this type of source is the continual replacement of alloyed steel material in the furnace wall tubes and convective pass tubes. Acidic corrosion has been reported (14) in the E S P and stack breechings of several incinerators. Therefore, it is conceivable that a significant environmental consequence of such source emissions is materials deterioration a t chronic exposure levels. In order to be economically viable, energy recovery installations would be sited in the proximity of large accumulations of refuse to minimize transportation costs. Also, the effective utilization of the steam produced by the incinerators would dictate a location in industrialized areas. Since most U.S. refuse energy recovery systems have been operational for only the past few years, it is unlikely that any measurable materials degradation has been noted. However, the need for energy conservation, coupled with the increasing proportion of plastics in refuse, will result in a greater utilization of this technology concomitant with higher emissions levels. Therefore, aerometric surveys in the vicinity of such sources are warranted; these surveys would establish levels of HC1 and other chloride species attributable to incinerator emissions, and they would monitor the extent of materials damage over continued, low-level exposures. Only in this sense can we properly evaluate the net benefits t o the public from this particular form of energy conservation. Summar> Two energy recovery sources have been studied to determine emission rates of HCl generated from the incineration o f plastic materials contained in municipal refuse. The sources
were found to emit about 2 g of gaseous HCl for every kg of refuse fired. Under typical operating conditions, the daily mass emissions of HC1 from two sources were calculated to be 2900 and 2200 kg. Using a point source dispersion model, maximum surface concentrations of HC1 were estimated t o range between 10 and 43 pg/m3 a t distances of up to 5 km from t h e emissions sources. Acknowledgment T h e authors wish to thank Mike Pleasant, Northrop Services, Inc., and Larry Cottone, Engineering Sciences, Inc., for their efforts in carrying out many of the arduous tasks involving field measurements for this program. Literature Cited ( 1 ) St. Clair, C. LV., F’ollut. Eng. (Sept 1978).
(2) Freeman, H., lintsiron. Sei. Technol., 12, 1252-6 (1978). (:’I) Corey, R. C., in “Air Pollution, Vol. IV, Engineering Control of Air Pollution”. Stern, A. C., Ed., Academic Press, New York, 1977,
( 4 ) U.S. Environmental Protection Agency, Fed Reg., 36(247), 24876-95 (1971). (5) Robertson, C. A. M., Solid Wastes Management, 64(3), 139-54 (1974). (6) Carotti, A. A,, Kaiser, E. R., J . Air Pollut. Control Assoc , 22(4), 248-53 (1972). ( 7 ) .Jackson, F. R., ”Energy from Solid Waste”, Noyes Data Corporation, Park Ridge, N.J., 1974, p 6. (8) Federal Republic of Germany Federal Laws, Air Pollution Control, par. 3.2.1.1, “Facilities LVhich Are Designed Primarily t o E n tirely or Partially Eliminate Refuse from Households and Similar Materials by Combustion”, Bonn, Aug 28, 1974. (9) dahnke, .J. A,, Cheney, J . L., Fortune, C. R., J . 4ir. Pollut. Control Assoc., 2 7 ( 8 ) ,747-53 (1977). (10) Cheney, .J. L., Fortune, C. R., Sci. Total Ent’iron,, in press. (11) See ref 7, p 21. (121 Farmer. S.B., “Workbook of Atmospheric Dispersion Estimates”, Office of Air Programs Publication No. AP-26, Environmental Protection Agency, Research Triangle Park, N.C., 1970. (18) Hosler, C. R., H u l / . Am. M e t . SOC., 56, 1261-70 (1975). (11) Rubel. F. N., “Incineration of Solid LVaste”, Noyes Data Corporation. Park Ridge, N.J., 1974, pp 108-37.
Receiced for recieic. M a y 7, 1979. AcceptPd J u l y 19, 1979
pp 5:31-9:3,
Oxidative Control of Organosulfur Pollutants David C. Ayres” and Catherine M. Scott Chemistry Department, Westfield College, Hampstead, London, NW3 7ST, England Ruthenium tetroxide is a powerful primary oxidant and may he generated economically using chlorine or hypochlorite as a secondary oxidant. I n this initial study of its possible application to pollution control we determined its effectiveness against a group of thiophenes and related odorants. Rates of oxidation of these substances in saturated potassium permanganate solution have been determined at p H 1 2 and 22 “C. These results showed t h a t a considerable residue would survive wet scrubbing with permanganate since half-life times were in the range 12.5-1215 min. With aqueous ruthenium tetroxide solutioiis, the oxidation rates were at least 100 times those found for permanganate. When control of air pollutants is attempted by means of wet scrubbing, then sodium hypochlorite ( I ) or potassium permanganate is the preferred reagent. Nucleophilic substrates may become stabilized t o oxidation by hypochlorite through their capture of chlorine; the formation from thiophene of chlorothiophenes and their chlorine adducts (2) affords an example of this. Permanganate, although more expensive, is generally more effective (3);nevertheless, its application t o odor control commonly requires better than 99% destruction of a n odorant. This optimum level is difficult to achieve, as Anderson and Adolf have shown ( 4 ) for a range of organosulfur and other odorants from rendering and food processing. T h e efficiency of wet scrubbers is limited by short contact times. We have therefore investigated t h e rates of oxidation of some common odorants by permanganate, as compared t o t h e rates achieved with hypochlorite in t h e presence of ruthenium salts. Salts such as the commercially available hydrate of ruthenium trichloride ( 5 ) are oxidized (6) by hypochlorite to ruthenium tetroxide:
+ +
+
-
[ R U ( O H ) ~ C I ~ . H ~ O 2C10]20H- --* R u 0 4 5C1- 3H20 whence R u 0 4 RuOp
+
Ruthenium tetroxide has been shown ( 7 )t o be both rapid and of wide application in its oxidation of organic compounds; numerous applications of the reagent to pollution control are implicit in the literature. We selected organosulfur compounds and thiophenes in particular for this initial study because these odorants are currently emitted by a variety of large-scale industrial processes. Thus, post-vulcanization gases contain 33% of organosulfur compounds with benzothiophene forming 12°C of the trapped oils from tire production ( 8 ) ,while it has been established (9)t h a t organosulfur release occurs during the reducing stages of brick production from Oxford clays. An extensive investigation of shale oils by Pailer and Grunhaus ( 1 0 ) showed t h a t some fractions contain 15%of sulfur comhined as thiophene and its alkyl and phenyl derivatives. Thirteen substituted thiophenes were identified (11) in t h e products of the hydrogenation of coal, and these compounds are known (12) to form part of the volatile organosulfur products from carbonization of coal. Difficulties in the treatment of organosulfur odorants emitted from coke ovens a t a concentration of 300 mg.m-3 have been described (13) where an oxidative procedure gave only 30-6070 removal. T h e problem posed by these substances in coal conversion processes has also attracted comment recently (14).
+ 2[0]
This compound is the primary oxidant and it persists at a n effective concentration as it is continuously regenerated by the action of hypochlorite (2 equiv) on t h e dioxide. 0013-936X/79/0913-1383$01.00/0
@ 1979 American Chemical Society
Experimental
Source of Materials. 2-Phenylthiophene ( m p 40 “C, ref 2 5 ) was prepared by adaption of a n existing procedure (16). Steam-distilled product was further separated by alumina chromatography using first benzene and then 5% ethanol in benzene as eluant. Final purification of these fractions was effected by preparative GLC using a 3-m column having 10% SE30as the stationary phase on Chromosorb W (60/80) a t 180 “C. T h e same procedure was used a t t h e appropriate column temperature for t h e purification of commercial samples of thiophene (110 “C), dimethyl sulfide (80 “C), 2-n-butylthiophene (130 “C), and 2-ethylthiophene (110 “C). Diphenyl disulfide (1 7 ) was prepared by concentration of an ammoniacal solution of thiophenol in ethanol; the product ( m p 60 “C) was pure by GLC standards on recrystallization Volume 13, Number 11, November 1979 1383
