Fossil Fuels Utilization - American Chemical Society

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Organic CompoundsfromCoal Combustion G. A. Junk, J. J. Richard, M. J. Avery, R. D. Vick, and G. A. Norton Ames Laboratory, Iowa State University, Ames, IA 50011 Organic compounds in the various effluents from the efficient combustion of coal at power plants do not appear to be an environmental problem. This conclusion is based on interpretation of results obtained during a four-year study of samples of stack gas and fly, grate and stack ashes from the combustion of coal alone and of mixtures of coal and refuse-derived fuel. Dioxins and furans were not present in these samples at the detection limit of 10 parts per trillion. Alkanes, chlorinated benzenes, polychlorinated biphenyls, polycyclic aromatic hydrocarbons, aliphatic acids and other miscellaneous compounds were identified, but the amounts were below those reported for ambient urban air. These low levels of organic compounds are obtained only under steady state conditions of high combustion temperature, excess oxygen, small fuel particles and sufficient residence time. The waters from the sluicing of the fly ash and grate ashes to settling ponds were also analyzed. The results of these analyses and separate adsorption and leaching experiments were used to conclude that fly and grate ashes were not a probable source of organic contamination of ground and surface waters. The release of organic pollutants into the environment from the burning of coal has been of periodic concern ever since the industrial revolution in England. This concern has resurfaced recently due to the shift to coal as the major fuel for generating electricity in the U.S. Because of this environmental concern, an extended study of the Ames power plant for generating electricity was begun in 1977. This study included all types of pollutants such as N0 , S0 , total suspended particles, fly ash, grate ash, and trace elements as well as the organic compounds from the combustion of coal alone and mixtures of coal and refuse derived fuel (RDF). The results in this report are confined to the organic compounds found in all of the X

X

0097-6156/86/0319-0109S06.00/0 § 1986 American Chemical Society

In Fossil Fuels Utilization; Markuszewski, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.


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s o l i d , l i q u i d and gaseous effluents related to the combustion processes. At the start of this study in 1977, the analytical methodology was inadequate f o r the characterization of organic compoundsinthe various e f f l u e n t s . Thus, p r i o r i t y was given to: 1) identifying the analytical d i f f i c u l t i e s ; 2) devising methods to resolve the most critical problems; and 3) using evolving methodologies to determine those components judged to pose a threat to the environment. As an aid in establishing the analytical problems, published data were compiled and reviewed for coal combustion and waste incineration ( 1_). Important conclusions drawn from this review were: 1) only a limited number of organic components had been i d e n t i f i e d in the e f f l u e n t s ; 2) the i d e n t i f i e d components reflected analytical c a p a b i l i t i e s and interests rather than a true d i s t r i b u t i o n ; 3) r e l i able quantitative data were not available; and 4) the data base was i n s u f f i c i e n t f o r predicting the probable environmental effects associated with the combustion of coal. A critical examination of the analytical procedures used prior to 1977 showed these to be inadequate f o r the determination of organic compounds in combustion effluents; of special concern were the short-comings in sample c o l l e c t i o n methods. These short-comings are delineated in a review published recently ( 2 ) . Because of these sampling uncertainties, the continuous development and validation of new procedures and sampling systems was an essential element of this study. Coincident with the development of sampling procedures were the constant i t e r a t i v e improvements in extraction, separation, i d e n t i f i cation and quantitation of organic compounds. Special emphasis was placed on selected compound classes such as the p o l y c y c l i c aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), chlorinated benzenes, and chlorinated dibenzo-p-dioxins ( d i o x i n s ) . The best available procedures were used to determine these components because they have known acute or chronic effects and previous studies suggested that they might be present in effluents from the combustion of coal alone and combination coal/RDF. Sampling Procedures Sampling points for a l l power plant influent and effluent streams are shown in Figure 1. The procedures used to c o l l e c t the stack e f f l u e n t s , the f l y and grate ash samples, and the waters are d i s cussed separately below. Stack Vapor. The major goal in sampling the stack effluent was to obtain large samples representative of the components presentinthe vapor phase and associated with suspended p a r t i c l e s . Vapor phase organic components present in the stack effluent were sampled by three d i f f e r e n t procedures. An EPA Method 5 t r a i n was equipped with an organic module and used during the early stages. This sampler allowed the stack gas to pass over the accumulated p a r t i c l e s during the entire sampling period and thus gave r i s e to the p o s s i b i l i t i e s of adsorption, sublimation and chemical transformations of organic components. When the equipment became available, the Method 5 t r a i n was supplanted by a Source Assessment Sampling System (SASS). This



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Organic Compounds from Coal Combustion

COAL

Or

111

STACK

±J

BOILER

l_l ESP

4

RDF

QRATË1 ASH

JÎHÎÔPPER

r \ i SLUICE WATER

A

S

H

SETTLING POND 9

Figure 1. Sampling points f o r fuels (1 and 2), ESP f l y ash (5), ash s l u r r i e s (6 and 8 ) , s l u i c e water (7), sediment and water (9), organic vapors (3 and 4 ) , and suspended particulate matter ( 4 ) .



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system allowed larger volumes of gas to be sampled and reduced the contact between accumulated p a r t i c l e s and the stack gas. The comp l e x i t y of the SASS made it undesirable for use when the only goal was to obtain a sample of vapor phase components. A t h i r d sampling system was the Ames Vapor Sampling System (AVSS) described by Junk and Richard ( 3 ) . This sampling system largely eliminated contact between vapor phase components and p a r t i c l e s . The AVSS provided a simple and e f f e c t i v e accunulation of organic components from very mild atmospheres such as ambient a i r and very severe atmospheres such as stack gas. Stack Ash. Four procedures were used f o r obtaining samples of stack ash. The EPA Method 5 t r a i n used i n i t i a l l y did not protect adequately the i n t e g r i t y of the samples because stack gas passed continuously over accumulated p a r t i c l e s . The magnitude of this problem could not be investigated because i n s u f f i c i e n t quantities of stack p a r t i c l e s were accumulated to allow for the accurate determination of adsorbed organic components. The SASS provided adequate quant i t i e s of p a r t i c l e s and simultaneously lessened the contact between accumulated p a r t i c l e s and stack gas. However, even the SASS did not c o l l e c t enough of the small respirable p a r t i c l e s to f a c i l i t a t e determinations of many organic components that might pose a potential health hazard. Two other procedures were used f o r obtaining large quantities of stack ash f o r scouting analyses. In one procedure, the p a r t i c l e s that had accumulated in unused sampling ports were simply r e t r i e v e d , sized, and used as samples representative of stack ash. Although these p a r t i c l e s were obviously not t r u l y representat i v e of those emitted from the stack, they were available in larger quantities f o r exploratory studies of analytical protocols and to establish the types of compounds present in the p a r t i c l e s . The second procedure f o r obtaining larger amounts of stack ash consisted of inserting a tray into the stack to c o l l e c t the p a r t i c l e s that s e t t l e d from the disturbed gas stream. As was the case with the p a r t i c l e s collected from sampling ports, the p a r t i c l e s collected in the tray were not t r u l y representative of the stack e f f l u e n t . However, these p a r t i c l e s were useful for determining changesinthe organic emissions when f i r i n g conditions and fuels were varied. Fly Ash. Fly ash samples were collected d i r e c t l y from the hoppers of the cyclone and e l e c t r o s t a t i c p r e c i p i t a t o r used for p a r t i c l e control. Grate Ash. Grate ash samples from stoker-fired units were c o l l e c t e d from hoppers located below the grates. Grate ash from the tangent i a l l y f i r e d units was removed from the boilers by s l u i c i n g . Samples were obtained by f i l t e r i n g the s l u i c e water c o l l e c t e d at the outlet of the pipe used to transport the sluiced ash to a s e t t l i n g pond. Additional ash samples were collected from the s e t t l i n g pond as sediment samples. Waters. Sluice and s e t t l i n g pond waters were collected as fourl i t e r grab samples.


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Extraction Procedures


The extractions of adsorbents, water condensates and ashes ( p a r t i cles) are described separately below. Adsorbents. A macroreticular r e s i n , XAD-2, was used as the adsorbent in the AVSS, the SASS and the EPA Method 5 sampling t r a i n . Organic compounds accumulated on the resin were recovered by e l u t i o n with methylene c h l o r i d e . Diethyl ether was used as an eluent, in stead of methylene c h l o r i d e , when subsequent determinations were performed by gas chromatography with electron capture detection. Other eluents and desorption techniques were tested and found to o f f e r no s i g n i f i c a n t advantages (3). Water Condensates. When stack gas was cooled during sampling, water vapor condensed. The organic components in these condensates were extracted with methylene c h l o r i d e . Diethyl ether, pentane and isooctane were used as a l t e r n a t i v e extraction solvents when subse quent gas chromatographic determinations required the use of e l e c tron capture detectors. Ashes ( P a r t i c l e s ) . Because there were no standard and accepted procedures among the many described in the l i t e r a t u r e for the ex t r a c t i o n of organic components from p a r t i c l e s , several techniques were c r i t i c a l l y evaluated. Soxhlet extraction with benzene, benzene-methanol, benzene saturated with hydrogen c h l o r i d e , toluene, toluene-methanol, and methylene chloride were evaluated. Sonic extractions using a probe or a bath with a v a r i e t y of solvents and pretreatment procedures using aqueous acids and water were also tested. No technique resulted in s i g n i f i c a n t improvement in the extraction of the cross-section of d i f f e r e n t organic components associated with the various p a r t i c l e e f f l u e n t s . Consequently, the t r a d i t i o n a l Soxhlet extraction using benzene-methanol was used most frequently. Class Separations Chromatographic and solvent p a r t i t i o n i n g procedures were used to separate organic components recovered from p a r t i c l e s into chemical classes to f a c i l i t a t e t h e i r ultimate determinations in less complex mixtures. The procedure included the separation of PAHs on Sephadex (4), the separation of components on the basis of p o l a r i t y using aTunina (5), s i l i c a gel (β), F l o r i s i l (7), the polystyrene-divinylbenzerife resin XAD-4 (8), and the t r a d i t i o n a l solvent p a r t i t i o n i n g into acid, base and neutral f r a c t i o n s . Preparatory s c a l e , normalphase, high-performance l i q u i d chromatography with amine and cyano col wins was also used to separate mixtures on the basis of p o l a r i t y and to p a r t i a l l y separate PAHs (9). The Soxhlet extraction of p a r t i c l e s with benzene-methanol yielded PAHs plus many polar and non-polar organic compounds which interfered with the gas chromatographic separations. The i n t e r f e r ing compounds were removed using standard solvent p a r t i t i o n i n g with dimethyl sulfoxide [DMSO] (10), dimethylformamide [DMF] (11), or nitromethane (12).


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Compound Separations Gas chromatography was used for the separation of individual organic components. Columns packed with Dexsil 300 (Supelco Inc., Bellefonte, PA) provided the separation of the high b o i l i n g point PAHs during the early stages of t h i s study. Later, as the col win technology advanced r a p i d l y , c a p i l l a r y columns coated with SE-52 and SE-54 (J&W S c i e n t i f i c , Rio Rancho, CA) were used almost e x c l u s i v e l y . These columns were found to be applicable to the e f f i c i e n t separat i o n of a diverse assortment of organic components in complex mixtures. I d e n t i f i c a t i o n and Quantitation Combination gas chromatography/mass spectrometry (GC/MS) was used for the i d e n t i f i c a t i o n of the organic components extracted from the various combustion e f f l u e n t s . Tentative i d e n t i f i c a t i o n s of the unknown compounds were obtained by computer l i b r a r y searching or manual i n t e r p r e t a t i o n of mass spectral data. Additional q u a l i t a t i v e information was obtained by gas chromatography on d i f f e r e n t p o l a r i t y col irons using element-specific detectors. Quantitations were performed by comparing the signal obtained for an i d e n t i f i e d peak with the signal obtained for a known amount of the same compound chromatographed under the same conditions in a s i m i l a r matrix. In specifi c instances, internal standards and the method of standard additions were used for quantitation. The quantitation by gas chromatography was p e r i o d i c a l l y checked on randomly chosen samples using appropriate techniques of combination GC/MS. Confirmations and Validations The presence of environmentally hazardous compounds, such as PCBs, in samples was confirmed using as many independent pieces of information as was possible. Ideally, each individual compound in a sample would exhibit NMR, IR, UV and MS data identical to authentic samples. In the real world of environmental samples, the compound in question is usually present in a complex matrix consisting of hundreds of other compounds in amounts far below those needed for most of the above mentioned techniques. Thus, gas chromatography/ mass spectrometry (GC-MS) data are often a l l that are a v a i l a b l e . For p o s i t i v e i d e n t i f i c a t i o n s by GC/MS, the f u l l mass spectrum of a t e n t a t i v e l y i d e n t i f i e d component was compared to the mass spectrim of an authentic sample. If the spectra were i d e n t i c a l , within experimental e r r o r , and i f the gas chromatographic retention times of standard and unknown components on a 30-meter SE-54 fused s i l i c a c a p i l l a r y column agreed within two seconds, the i d e n t i f i c a t i o n was considered p o s i t i v e . When the amount of material present was insuff i c i e n t for detection using f u l l scan GC/MS techniques, the more s e n s i t i v e single and multiple ion monitoring techniques were employed. Confirmation in these cases consisted of coincidences of retention times of mass chromatograms of the unknown and of the authentic sample. For chlorinated materials, the molecular ions contained additional information about the chlorine isotope d i s t r i bution. Confirmation in those cases included the correct isotope



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r a t i o s for the number of chlorines in the molecule. An additional piece of information for chlorinated materials was the coincidence of retention times of standards and unknown components coupled with response towards the electron capture detector. Validation of the methodology used for components that could not be detected in extracts of p a r t i c l e samples was obtained by extraction of surrogate samples. The surrogate sample for PAHs was soot generated from an air-starved methane flame. The p o s i t i v e r e s u l t s obtained from this soot sample have been reported elsewhere (13). The surrogate sample for dioxins was an incinerator ash obtained from Dow Chemical Company. Results obtained from analysis of extracts of t h i s ash sample were ±50* of the published values f o r the t e t r a - , hexa-, hepta- and octachloro- isomers (14). This agreement substantiated the v a l i d i t y of the analytical protocol used to screen the e f f l u e n t samples for dioxin compounds. Results and Discussions Results on the i d e n t i f i c a t i o n and quantitation of organic components in effluents from coal and coal/RDF combustion and on the analyses of s l u i c e and s e t t l i n g pond water are presented and discussed below. I d e n t i f i e d Components A combined l i s t i n g of a l l the compounds i d e n t i f i e d in the vapor and on p a r t i c l e s emitted during the combustion of coal at the Anes power plant are l i s t e d in Table I. Similar compounds have been i d e n t i f i e d in the emissions from a second c o a l - f i r e d power plant located at Iowa State U n i v e r s i t y . Therefore, t h i s l i s t may be p a r t i a l l y representative of coal combustion in semi-modern b o i l e r s . C e r t a i n l y , many more organic compounds than the l i s t e d 78 are present in these e f f l u e n t s , but so f a r these have not been p o s i t i v e l y i d e n t i f i e d . Indeed, a 1980 review of organic compounds from coal combustion (I) taken from a l l the l i t e r a t u r e reports had only 106 compounds identified. Quantitation It was not possible to obtain exact quantitative values for a l l the i d e n t i f i e d components associated with each of the e f f l u e n t s from coal combustion. The amounts varied because of the analytical problems mentioned in the experimental section and d i f f e r e n t f i r i n g conditions. Even when special e f f o r t s were made to achieve constant f i r i n g conditions, r a d i c a l l y d i f f e r e n t amounts of gas chromatographable materials were obtained as shown by the two chromatograms in Figure 2. However, semi-quantitative values have been obtained for many of the components and these values are proposed to be reasonable estimates of the amounts of organic compounds expected from the e f f i c i e n t combustion of coal in a modern power plant. A discussion of some important compound classes and the amounts in the various effluents is given below. In general, the amounts are much lower than would be predicted from a review of the limited quantitative data a v a i l a b l e in the l i t e r a t u r e .


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Table I. L i s t of Organic Compounds Present in Effluents From Coal Combustion ALKANES AROMATICS PAHs Methane Toluene Benz(a) pyrene Decane Xylene Anthracene Undecane Propyl benzene Fluoranthene Hexadecane Butyl benzene Fluorene Heptadecane Bi phenyl Pyrene Octadecane Ter phenyl Naphthalene Nonadecane Methylindene 1-Methylnaphthalene Eicosane 2-Methylnaphthalene Heneicosane Acenaphthene Docosane Benz( a) anthracene Benz(ghi)anthracene Tricosane Pentacosane Hexacosane Octacosane T r i aeontane Dotriacontane Tr i m et hy1 eye1οh ex an e Dimethylcyclohexane ACIDS PHENOLS 2-Ethylbutanoic Phenol Nonanoic o-Cresol Decanoic Ethyl phenol Dodecanoic Butyl phenol 2,4-Dichlorophenol Tridecanoic 2,4,6-Trichlorophenol Tetradecanoic Pentadecanoic 9-Hexadecenoic Hexadecanoic Heptadecanoic Octadecanoic Benzoic 0, Ν, P, S COMPOUNDS CL COMPOUNDS Acetophenone Tetrachloroethylene Methylacetophenone Tetrachloroethane Phthalic Anhydride 1.2- Dichlorobenzene Methyl benzoate 1.3- Di chlorobenzene Indanone 1.4- Dichlorobenzene Dibenzofuran 1,2,4-Tr i chloroben zene Diethyl phthalate 1,2,3-Tri chloroben zene Dibutylphthalate 1.2.3.4- Tetrachlorobenzene Diisobutyl phthalate 1.2.3.5- Tetrachlorobenzene Di(2-ethylhexyl)phthalate Pentachlorobenzene Diphenyl amine Hexachlorobenzene 2,3,2',5·-Tetrachlorobiphenyl 2,5,3*,4'-Tetrachlorobiphenyl 2,4,5,2*,5'-Pentachlorobiphenyl 2,4,5,2',4',5'-Hexachlorobiphenyl 3

The c h a r a c t e r i s t i c Arochlor 1254 p r o f i l e was observed but only four isomers were p o s i t i v e l y confirmed.


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P o l y c y c l i c Aromatic Hydrocarbons (PAHs). The most highly studied class of compounds in combustion e f f l u e n t s is the PAHs. However, very l i t t l e information about the amounts present in the vapor phase and on p a r t i c l e s in the e f f l u e n t s from the e f f i c i e n t combustion of coal is a v a i l a b l e . The data in Table II p a r t i a l l y f i l l s this informational gap. The amounts in the vapor phase varied according to the f i r i n g conditions and the stack temperature that was - 170 C. Even i f a l l these PAHs were to condense on the p a r t i c l e s , the amounts are well below the multiple yg/g quantities present on ambient a i r p a r t i c l e s .


e

Table I I . Summary of PAHs in Effluents From Coal-Fired Power Plants Concentration Range (ng/g) Compound

Respirable Particles

Naphthalene Phenanthrene Anthracene Fluoranthene Pyrene Chrysene Benz( a) pyrene Benz(a) anthracene Benz(ghi)perylene

ND -18 NM NM 0.2-0.3 0.2-7 ND ND ND NM

b

a

Non-Respirable Particles 0.5-23 NM NM 0.05-1.5 0.08-1.1 ND-4 ND ND-0.3 NM

Cone. Range Vapor Phase (ng/M3) c

10-1800 26-640 0.4-100 0.5-240 0.2-2850 0.1-28 0.1-120 NM 3-22

Observed in 26 stack samples collected over a 4 year period. Not detected at the l i m i t of 0.05 ng/g. Includes values reported by Midwest Research Institute (15,16). NM = Not measured. Alkanes and Aromatics. The d i s t i n c t i o n between aromatic and polyc y c l i c was a r b i t r a r i l y set at three conjugated six-member rings in Table I. With t h i s d e f i n i t i o n the alkanes and aromatic hydrocarbons, with 25 e n t r i e s , dominate the l i s t of i d e n t i f i e d components. These compounds are also present in the highest concentration in the d i f f e r e n t e f f l u e n t s . O r d i n a r i l y their concentrations were not measured because of a low interest in these kinds of compounds but in those instances where measurements were made, the amounts ranged from 10-1500 ng/M in the vapor phase and from 10-90 ng/g on the suspended p a r t i c l e s in the stack e f f l u e n t s . These hydrocarbons were not quantitated f o r any of the f l y and grate ash samples. 3

A l i p h a t i c Acids and Phenols. Eleven a l i p h a t i c acids and six phenols were determined as constituents of the vapor phase and associated with p a r t i c l e e f f l u e n t s . These acidic compounds and the amounts are l i s t e d in Table I I I . A range of values from 20 d i f f e r e n t sampling runs is shown f o r the C9, C12, C14, C16 and C18 acids and phenol to i l l u s t r a t e the f l u c t u a t i o n s that can occur in the amounts of organic acids in the e f f l u e n t s . The extent of the v a r i a t i o n attributed to



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Β

30 MINUTES

60

Figure 2. Gas chromatograms of organic material emitted during two d i f f e r e n t sampling days, A and B, when supposedly similar f i r i n g conditions were employed.


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changes in f i r i n g conditions and analytical d i f f i c u l t i e s in the determinations is unknown and needs further study. Polychlorinated Biphenyls (PCBs). The PCBs were observed in the stack e f f l u e n t s during the combustion of coal but these compounds were not produced in the combustion process by a de novo synthesis or from precursor compounds. The source of the PCBs was the indoor air used to support the combustion. This indoor a i r contained 0.11 yg/M of PCBs; the concentration of PCBs in the stack gas was only 0.02 yg/M when coal containing no detectable level of PCBs was burned. For perspective, this emission level should be compared to the average ambient outdoor a i r level of about 0.006 yg/M . When the coal fuel was supplemented with RDF containing 8500 yg of PCBs/kg of RDF, the amount of PCBs in the stack remained at the low level of 0.02 yg/M .


3

3

3

3

Table I I I . Sunmary of A c i d i c Compounds in Effluents From Coal-Fired Power Plants Concentration Range

a

Acid

Vapor (ng/M )

Particles (ng/g)

2-Ethylbutanoic Nonanoic Decanoic Dodecanoic Tridecanoic Tetradecanoic Pentadecanoic 9-Hexadecenoic Hexadecanoic Heptadecanoic Octadecanoic Phenol o-Cresol Butyl phenol 2,4-Dichlorophenol 2,4,6-Trichlorophenol Pentachlorophenol

200 20-250 10 80-800 NM 100-300 90 50 40-300 NM 80 20-200 NM NM NM NM NM

NM NM 20 90 10 8-600 50 NM 40-270 20 40-150 25-1000 NM NM 0.1 0.05 0.2

3

b

a

Where a range is l i s t e d , these selected components were measured . in 26 extracts. NM = Not measured. D

Calculations based on fuel inputs, stack gas flow, support gas input and PCBs in a l l the inputs and e f f l u e n t s showed that >99* of the PCBs in the input RDF were destroyed in the combustion process. The d e t a i l s of t h i s investigation of the co-combustion of coal and RDF containing PCBs have been published elsewhere (17). The explanation of the high destruction e f f i c i e n c y f o r the PCBs in the RDF is e f f i c i e n t combustion based on a combination of high


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temperature (~ 2000 F), excess oxygen at 22%, and adequate residence time and s u f f i c i e n t turbulence f o r the small coal and RDF p a r t i c l e s in the combustion zone. This same combination of combustion conditions is the probable explanation f o r the undetectable levels of TCDD discussed below. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD). At the detection l i m i t of ten parts per t r i l l i o n , no TCDD was found in the e f f l u e n t s from the combustion of coal in three d i f f e r e n t boilers at the Ames power plant (see summary table in reference 16 f o r d e s c r i p t i o n of b o i l e r s ) . This observation was confirmed at a second smaller coalf i r e d power plant located at Iowa State U n i v e r s i t y . Even when the coal fuel was supplemented with RDF, which should contain the precursor compounds, no dioxins were observed in the vapor and p a r t i c l e samples taken from the e f f l u e n t s . Thus no de novo synthesis occurred during the combustion of coal alone and i f dioxins were formed from precursor compounds in the co-combustion of coal and RDF, they were destroyed in the e f f i c i e n t combustion as explained above f o r the thermal destruction of the PCBs present in the RDF. The PCBs are reported to be completely destroyed at 1200 F (18) and a similar destruction temperature is expected f o r the dioxins. This is well below the 2000 F operation of the boilers used for t h i s study (19). e

e

Chlorinated Benzenes. Ten chlorinated benzenes were targeted f o r analysis in the stack e f f l u e n t s . The analytical r e s u l t s when coal alone was combusted are shown in Table IV. When the coal fuel was supplemented with RDF up to 20%, no consistent increaseinthe amounts of the chlorinated benzenes occurred although barely detectable amounts of the t e t r a - , penta- and hexa- isomers were observed during some of eleven d i f f e r e n t combustions of coal with 20% RDF. Based on these r e s u l t s it appears as i f the dichlorobenzenes, reported to be present in the RDF at the 8000 yg/kg level (15,16), were thermally destroyed with high e f f i c i e n c y in much the same manner as that docunented above for the PCBs present in the RDF. This suggestion has not been supported so f a r by experimental r e s u l t s . An additional speculation is that the o r i g i n of the chlorobenzenes observed in the e f f l u e n t s when coal alone was combusted was the indoor a i r used to support the combustion. The environmental effects from the emission of these c h l o r i nated benzenes are estimated to be i n s i g i f i c a n t because of the low l e v e l s and the further d i l u t i o n by factors of 10 to 10 inthe atmosphere before any himan or plant exposure. 3

5

Summary of I d e n t i f i c a t i o n s and Quantitations From Vapor and P a r t i c l e E f f l u e n t s " The i d e n t i f i e d compounds in each chemical class and the range in concentrations for d i f f e r e n t vapor and p a r t i c l e e f f l u e n t s from the combustion of coal and mixtures of coal and RDF are summarized in Table V. The range in concentrations is of the order of 10 . This range occurs because of one or any combination of the following reasons: 1) individual compounds within a class are present at concentrations that vary by many orders of magnitude; 2) differences in f i r i n g conditions caused a real change in the emissions; 3) analytical and sampling methodologies changed over the 3


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Table IV. Chlorinated Benzenes in Stack Effluent From Coal-Fired Power Plants Concentrations ng/M


Chlorobenzene Isomer

3

1,2-Dichloro1,3-Dichloro1,4-Dichloro1,2,3-Trichloro1,2,4-Trichloro1,2,3,4-Tetrachloro 1,2,3,5-Tetrachloro 1,2,4,5-Tetrachloro PentachloroHexachloroa

0.5 ND 80 3.9 1.2 ND ND ND ND ND a

3

ND = Not detected at l i m i t of 0.03 ng/M ; average of three runs.

Table V. Summary of Compounds in Vapor and P a r t i c l e Effluents From the Combustion of Coal and Coal/RDF 3

Compound Class Alkanes Aromatics PAHs Acids Phenols CL Compounds 0, Ν, P, S Compounds

Number Identified 18 7 11 12 6 15 11

Estimated L e v e l s Vapors Particles (ng/M ) (ng/g) 3

10-1500 10-2000 0.1-400 20-800 5-7200 0.1-1000 70-2500

b

NM 10-90 0.1-110 8-600 0.05-1100 1-16 50-100

From 26 combustion episodes over a four year period. NM = Not measured. four-year duration of t h i s project; and 4) the p a r t i c l e e f f l u e n t s include f l y , grate and stack ash samples where the amounts vary considerably. Consequently, this summary table should be used only to get a very rough estimate of the kinds and amounts of compounds present in the vapor and p a r t i c l e e f f l u e n t s . Indeed, it was not possible to e s t a b l i s h any differences in the kinds and amounts of organic emissions when the data from the 26 combustion episodes were separated into coal only and coal/RDF groups. In addition to the rough estimate of emissions discussed above, the data in Table V can be used to show that the organic compounds in the stack e f f l u e n t s are emitted mostly in the vapor phase. S l u i c e Water, There is a legitimate concern over the release o f p o l lutants into the water environment following the u t i l i z a t i o n or




122

disposal of the huge amounts of f l y and grate ash produced during the combustion of c o a l . Our studies were r e s t r i c t e d to the i n v e s t i gation of the possible release of organic pollutants only when f l y and grate ash are sluiced to s e t t l i n g ponds and retained there as a disposal s i t e . The water in the s e t t l i n g pond was checked periodic a l l y f o r organic compounds known to be present at low concentrations on the ash. None of these known components were detected in the water at the conservative limit of one ppB. Indeed, this pond water did not contain any gas chromatographable organic compounds at the detection limit of 0.1 ppB even though the well water used f o r s l u i c i n g contained multiple ppB levels of aromatic compounds indicative of the coal t a r that had contaminated the aquifer (20). Thus, the ash e f f l u e n t s from coal combustion appear to adsorb rather than release organic compounds into the water. This adsorption feature was examined in an experiment where water containing 20 to 50 ppB of f i v e aromatic hydrocarbons was mixed with f l y ash f o r ten minutes at a water to ash weight r a t i o of 10 to 1. In t h i s short contact time, the f l y ash completely removed the organic components; t h i s is v i v i d l y i l l u s t r a t e d by the two capi l l a r y column gas chromatograms shown in Figure 3. Going from l e f t to r i g h t , the major peaks in the water sample prior to contacting the f l y ash are indan, 3-methylindene, naphthalene, 1-methylnaphthalene and acenaphthylene. The e f f e c t i v e adsorption is probably due to the active forms of carbon, aluminum and s i l i c o n expected to be present in f l y ash. For organic compounds then, f l y ash provided desirable clean-up rather than undesirable contamination of water. Conclusions Based on the r e s u l t s of t h i s study, the following conclusions can be made: 1) Organic emissions quantified in this study are much lower in general than predicted from the l i t e r a t u r e . 2) Organic compounds in the various effluents from the e f f i c ient combustion of coal at power plants do not appear to be an environmental problem. 3) Under e f f i c i e n t combustion conditions, organic compounds in the fuel are destroyed. 4) No s i g n i f i c a n t ground water contamination is expected t o occur as a result of f l y ash disposal and u t i l i z a t i o n . AFTER

BEFORE

V TIME —

Figure 3. Gas chromatograms of water containing 20 to 50 ppB of f i v e aromatic hydrocarbons before and after contact with coal combustion f l y ash.


10.

JUNK ET AL.


123

5)

Additional work is needed on the i d e n t i f i c a t i o n and quanti tation of organic emissions from coal combustion. 6) The low organic emissions from steady state combustion at power plants should not be extrapolated to small scale units such as woodstoves where the necessary conditions f o r e f f i c i e n t combustion are r a r e l y achieved.


Acknowledgments The technical assistance of Al Joensen, Jerry H a l l , Brian Jerome and Jennings Capellen is g r a t e f u l l y acknowledged. The administrative assistance of H. J . Svec, V. A. Fassel, R. W. Fisher and H. R. Shanks is also appreciated. In addition, the thoughtful assistance and cooperation of Wr. Donald Riggs, Mr. Gary T i t u s , Mr. Arnold Chantland, and other personnel from the City of Ames made t h i s study p o s s i b l e . This work was supported f i n a n c i a l l y by the U. S. Depart ment of Energy under Contract No. W-7405-Eng-82 through the O f f i c e of Health and Environmental Research, O f f i c e of Energy Research, and the Assistant Secretary f o r Fossil Energy, Division of Coal U t i l i z a t i o n , through the Morgantown Energy Technology Center. Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9.

10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20.

Junk, G. Α.; Ford, C. S. Chemosphere 1980, 9, 187. Junk, G. Α.; Jerome, B. A. Amer. Lab). 1983, 15, 16. Junk, G. Α.; Richard, J. J. In "Identification and Analysis of Organic Pollutants in Air"; Keith, L. H., Ed.; Butterworth Pub lishers: Boston, MA, 1984, Chap. 5. Klimisch, H. J. Z. Anal. Chem. 1973, 264, 275. Klemm, L. H.; Reed, D.; Miller, L. Α.; Ho, B. T. J . Org. Chem. 1959, 24, 1468. Cahnmann, H. J. Anal. Chem. 1957, 29, 1307. Dinneen, G. U.; Smith, J. R.; VanMeter, R. Α.; Albright, C. S.; Anthony, W. R. Anal. Chem. 1955, 27, 185. Spitzer, T. J. J . Chromatogr. 1978, 150, 381. Wise, S. Α.; Bonnet, W. J . ; May, W. E. In "Polynuclear Aromatic Hydrocarbons, Fourth International Symposium"; Bjorseth, Α.; Dennis, A. J., Eds., Battelle Press: Columbus, OH, 1980, p. 781. Bjorseth, A. Anal. Chim. Acta. 1977, 94, 21. Tomkins, Β. Α.; Kuboxa, H.; Griest, W. H.; Caton, J. E.; Clark, B.; Guerin, M. R. Anal. Chem. 1980, 52, 1331. Hoffman, D.; Wynder, E. L. Anal. Chem. 1960, 32, 295. Vick R. D.; Avery, M. J. "Extraction and Identification of Or ganic Materials Present in Soot from a Natural Gas Flame"; Iowa State University Journal, IS-4329, 1978. Lamparski, L. L.; Nestrick, T. J. Anal. Chem. 1980, 52, 2045. Haile, C., Midwest Research Institute, personal communication. Redford, D., US EPA, personal communication. Richard, J. J . ; Junk, G. A. Environ. Sci. Technol. 1981, 15, 1095. Sebastian, F. P.; Kronenberger, G. F.; Lombana, L. Α.; Napoleon, J. M. Proc. Am. Ind. Chem. Eng. Workshop, 1974, 5, 67. Joensen, A. L . , Iowa State University, personal communication. Burnham, A. K.; Calder, G. V.; Fritz, J. S.; Junk, G. Α.; Svec, H. J.; Willis, R. Anal. Chem. 1972, 44, 139.

RECEIVED March 6, 1986 In Fossil Fuels Utilization; Markuszewski, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

Fossil Fuels Utilization - American Chemical Society

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