CHARACTERIZATION TRACE
ORGANIC
OF AIRBORNE SPECIES
FROM
TRACE COAL
METAL
AND
GASIFICATION
J A M E S F. O S B O R N , S U R E S H S A N T H A N A M , and C L I F F I. D A V I D S O N Departments of Civil Engineering, Biomedical Engineering, and Engineering and Public Policy, Carnegie-Mellon University, Pittsburgh, PA 15213, U.S.A.
R I C H A R D D. F L O T A R D and J O S E P H R. STETTER Geochemistry Section, Energy and Environmental Systems Division, Argonne National Laboratory, Argonne, IL 60939, U.S.A.
(Received 7 September, 1983) Abstract. Fugitive emissions from a slagging fixed-bed coal-gasification pilot plant were analyzed by flameless atomic absorption spectrophotometry, gas chromatography, and mass spectrometry for trace metal and trace organic species. Analysis of the size distributions of airborne particulate matter inside the plant showed an abundance of large metal-containing particles; outdoor distributions in the vicinity of the plant resembled the indoor distributions, suggesting the importance of the gasifier in influencing ambient air quality. This conclusion was further supported by identification of similar organic compounds inside and outside the plant. Trace element enrichment factors based on the earth's crustal composition were greater than those based on the composition of the lignite used in the gasifier, showing the importance of characterizing the proper source material when investigating chemical fractionation during aerosol formation. Enrichments in the present study were much greater than those found in previous sampling during aborted start-up and cleaning procedures, where normal operating temperatures had not yet been reached. Both studies showed evidence of enrichment factors which decreased with increasing particle size. Although much of the airborne mass was associated with large particles having low respirability, the high concentrations of some metals indoors suggests that further assessment of potential occupational exposures is warranted.
I. Introduction The size distribution a n d chemical c o m p o s i t i o n o f airborne particulates emitted by the c o m b u s t i o n o f coal have been r e p o r t e d in the literature. M a n y studies have shown that submicron particles c o n t a i n volatile species such as Pb, Cd, and b e n z o ( a ) p y r e n e (Lee and von L e h m d e n , 1973; T o c a et al., 1973; K a t z a n d Chan, 1980). Less volatile, and m o r e benign, species such as F e a n d M g are usually found in larger particles. The presence o f toxic substances in small particles is a potential health h a z a r d , since these particles are preferentially d e p o s i t e d in the lower lung ( L i p p m a n n , 1977). The danger is e n h a n c e d b e c a u s e o f the p r e d o m i n a n c e o f toxic species on particle surfaces rather than in particle interiors (Linton et al., 1976; Van C r a e n e t a L , 1983). In general, a large fraction o f the pollutant emissions from coal c o m b u s t i o n is released to the environment through stacks. Fugitive emissions are often smaller, though still significant for m a n y pollutants. Coal gasification emissions, in contrast, are mostly fugitive. These fugitive emissions include dust resulting from coal handling operations, Environmental Monitoring and Assessment 4 (1984) 317- 333. 0167-6369/84/0044-0317 $ 02.55. 9 1984 by D. Reidel Publishing Company.
318
AIRBORNE TRACE METAL AND TRACE ORGANIC SPECIES
and uncontrollable releases of fine particles and gases at various locations throughout the system of valves and pipes at coal combustion and coal gasification facilities. Although stack and fugitive emissions from coal combustion processes have been studied, data are lacking for fugitive emissions from coal gasification operations. Commercial-scale gasifiers may be constructed to meet future energy requirements. Therefore it is desirable to study emissions from existing coal gasification pilot plants during regular operation; previous sampling of the type reported here pertained to gasifier emissions during an aborted start-up procedure (Davidson et aL, 1982). The objective of the present study was to collect data on the chemical composition and size distributions of fugitive aerosol emissions at a pilot-scale gasifier using lignite. The gasifier is located at the University of North Dakota Energy Research Center in Grand Forks. The project focused on trace metal and trace organic species. Sampling was conducted simultaneously inside the gasifier complex and at a nearby outdoor location. From these data, one can obtain qualitative information on the influence of gasifier emissions on outdoor air quality in the vicinity of the plant, as well as information on potential health hazards associated with the emissions.
2. Experimental Methods 2.1. TRACE METALS Size-fractionated samples for trace metal analysis were collected using two Sierra Model 235 impactors with 25 x 20 cm cellulose acetate backup filters having a pore size of 0.45/~m (Millipore Corp. HAWP). The impactors incorporated 20-mil FEP Teflon substrates that had been washed in three successive baths of concentrated HNO 3 (G. Frederick Smith, redistilled) for 24 hr each, followed by a 24-hr soak in purified water (supplied by a Coming MP3A still with LD2A demineralizer). To minimize particle bounceoff, the substrates were coated with a mixture of Vaseline and spectrograde hexane (Davidson et al., 1984). All washing and preparation of equipment for sampling was conducted in the Carnegie-Mellon University (C-MU) clean laboratory (Shaeffer and Davidson, 1979). Custom explosion-proof sampling motors (Amatek) assembled in housings made at Argonne National Laboratory were used for all indoor sampling. The filters were unsheltered. Standard high-volume vacuum pumps (General Metal Works) were used for the outdoor runs. The filters operated outdoors were enclosed in standard highvolume sampling shelters. Indoor sampling was conducted at the second level of the gasifier, one story above ground, for a 24-hr period during November 4-5, 1981. The Sierra impactor and backup filter were operated at 5.8 m 3 hr -1, measured with a Singer DTM 325 dry test meter calibrated at C-MU. Outdoor sampling with the other Sierra impactor was conducted simultaneously at a location approximately 25 m from the gasifier building. The average flow rate was 15 m 3 hr -x.
J . F . OSBORN ET AL.
319
The gasifier was started shortly before the sampling run began. The first 4 hr of sampling took place while the gasifier was in a start-up mode. The following 13 hr coincided with gasifier operation under normal steady-state conditions. For the final 7 hr, the gasifier was shut down due to slag solidification. At the end of these runs, both impactors were triple-bagged in polyethylene (Clean Room Products UCF-POLY). The backup filters were transferred into airtight PFA Teflon jars (Savillex 0110) and triple-bagged. The samples were transported to the C-MU clean laboratory, and digested in a solution of 5.25 ml concentrated HNO3 (G. Frederick Smith, redistilled) and 2.25 ml concentrated H F (Ultrex), diluted to 8 N. After several hours of gentle heating, the samples were further diluted to 4 N and analyzed by flameless atomic absorption spectrophotometry with a Perkin-Elmer 703 AA unit and H G A 2200 graphite furnace. The analytical procedures were identical to those described by Davidson et al. (1982).
2.2. TRACE ORGANICS All solvents used in these experiments except for acetone and ethanol were chromatography grade, distilled-in-glass (Burdick and Jackson, Muskegon, MI, or Waters Associates, Milford, MA). The acetone, used only for glass washing, and ethanol, used for initial cleaning of the Amberlite XAD-2 resin, were chemically pure grade. The Amberlite XAD-2 resin was laboratory grade (Mallincrodt, St. Louis, MO) and was cleaned prior to use by exhaustive Soxhlet extraction. The filters used to collect particle samples were Zefluor Teflon filters with a pore size of 2/~m (Membrana Corp. P5PJ001). Both 25 x 20 cm and 76-ram diameter filters were used. Soxhlet extractors used to extract samples and Kuderna Danish evaporative condensers used to reduce extract volumes were obtained from Kontes of Illinois (Evanston, IL) or Ace Glass Co. (Vineland, N J). Three separate sampling runs were used for trace organics measurement. The first run was conducted simultaneously with the trace metal sampling on November 4-5, 1981, and included one filter operated indoors at a flow rate of 36 m 3 hr -1. The second run included simultaneous indoor and outdoor filters operated at 34 and 40 m 3 hr -I, respectively. The final experiment consisted of one indoor filter run at 44 m 3 hr -1. All three sampling periods were 24 hr in duration, coinciding with steady-state operation of the gasifier. At the completion of sampling, the filters were immediately weighed in an adjacent laboratory, rolled with tweezers, placed in a glass Soxhlet extractor thimble, and extracted with CH2C12 for 4 hr. The extract was removed from the collection flask, filtered through a syringe-type 0.45 #m Millipore filter, and reduced to 4-5 ml in a Kuderna Danish evaporative condenser. The extract was transferred to a glass vial, capped, and stored in the dark until returned to Argonne. Upon arrival at Argonne, the extracts were further reduced in volume if necessary and analyzed by GC. The chromatographic data were analyzed using the RRI/Conc computer program (Stamoudis, 1982) and were compared to aromatic and aliphatic hydrocarbon standards. Simultaneously with the trace organic particulate sampling, vapor samples were
320
AIRBORNE
TRACE METAL AND TRACE ORGANIC
SPECIES
collected by passing the air through a 120-g bed of Amberlite XAD-2 resin. The resin was enclosed in an all-glass holder, topped by a 2/am Zefluor filter that prevented particulate matter from being entrained in the resin. The design and operation of the equipment have been reported elsewhere (Flotard, 1980). Samples were collected during 90-min periods for total sample volumes of 2-2.3 m 3. The sampler was located on the second-floor control room and in the third-floor laboratory where sidestream oil/tar samples were being collected. The resin was transferred to glass extractor thimbles, and was Soxhlet extracted for 2-hr periods within a few hours after the vapor was collected. The extract was transferred to a Kuderna Danish evaporative condenser and reduced to approximately 4 ml. The extracts were then sealed in glass vials, stored in the dark, and returned to Argonne for analysis. Upon arrival at Argonne, the vials were refrigerated. If necessary, further volume reductions were made before analysis. Analyses of the extracts from particulate and vapor sampling were conducted with a Hewlett-Packard 5880A gas chromatograph equipped with a level-4 computer control and data handling system, split/splitless injector system, 50 m • 0.31 mm OV-101 fused silica capillary column, and a flame ionization detector. The identity of compounds in the extracts was confirmed using a Hewlett-Packard 5985A mass spectrometer interfaced with a 5840A gas chromatograph equipped with the same injector system and fused silica capillary column as the 5880A. A 5934A data system was used to control the mass spectrometer and collect data. 3. Data Presentation and Discussion
3.1. TRACE METALS The Sierra impactor AA data served as input to a F O R T R A N program developed at C-MU. The program generated AA calibration curves based on a polynomial interpolation of standard concentrations, computed concentrations in each sample, and calculated the normalized mass distribution function (AC/Cx)/A log dp. Here AC is the airborne concentration corresponding to an impactor stage or backup filter in ng m -3, Cris the total concentration summed over all six stages, and A log dp is the particle size interval with dp representing the aerodynamic diameter in /~m. When the mass distribution function is plotted against log dp, the area under the curve between any two diameters is proportional to the fraction of airborne mass between those diameters. The value of dp with equal areas under the curve on both sides is termed the mass median aerodynamic diameter (MMD). Size distributions of A1, Ba, Ca, Fe, Mg, Mn, Na, Ag, As, Cd, Cu, and Pb for the indoor and outdoor impactor runs are shown in Figures 1 and 2, respectively. The elements graphed in the left columns are found in high concentrations in the earth's crust and in lignite. The elements in the right columns are less abundant, and are generally enriched in the atmosphere relative to the earth's crustal composition (Rahn, 1976). Standard deviations, not shown in the figures, are similar to those reported previously (Daddson et al., 1982). Shading below the curve in a given size interval denotes an
J . F . OSBORN ET AL.
321
A1 Ag 2.5q
2~
0.01
0.1
1
10
100
Be
1.50q
1,25t
o.7~ 0.50-{ o.2 1
F-L
~
........
0.01
0,1
1
10
p 0 1
001
I0
I00
1
10
100
I
10
100
1
10
100
1
10
100
As
lq
100
I
0,75]
Ca
0.50 0 25 0
.~112L
0.01
0.1
1
10
Fe
1.25 0.75
......... , ~
....
0.50
.........
0.01
1
0,1
10
100
Mg
0.25 0
1.25q
4
J
001
01
Cu
0.75~
1.5o 1
0.504 0.25 4
1.25
0.01
0.1
1
10
100
0.75 0,50
Mn
1.50q
!
0.251 ol
1.254
0,75 0.50 0:25
1'257/ 001
0.01
0,1
1
10
100
0.75
o.751~
0.50 4
0,50 ~
0.25
1,25W
0.01
0.1
dp, ~m
0,1 Pb
1 -]
Na
1.50 q
Fig. 1.
0.1 Cd
ORGANIC
OF AIRBORNE SPECIES
FROM
TRACE COAL
METAL
AND
GASIFICATION
J A M E S F. O S B O R N , S U R E S H S A N T H A N A M , and C L I F F I. D A V I D S O N Departments of Civil Engineering, Biomedical Engineering, and Engineering and Public Policy, Carnegie-Mellon University, Pittsburgh, PA 15213, U.S.A.
R I C H A R D D. F L O T A R D and J O S E P H R. STETTER Geochemistry Section, Energy and Environmental Systems Division, Argonne National Laboratory, Argonne, IL 60939, U.S.A.
(Received 7 September, 1983) Abstract. Fugitive emissions from a slagging fixed-bed coal-gasification pilot plant were analyzed by flameless atomic absorption spectrophotometry, gas chromatography, and mass spectrometry for trace metal and trace organic species. Analysis of the size distributions of airborne particulate matter inside the plant showed an abundance of large metal-containing particles; outdoor distributions in the vicinity of the plant resembled the indoor distributions, suggesting the importance of the gasifier in influencing ambient air quality. This conclusion was further supported by identification of similar organic compounds inside and outside the plant. Trace element enrichment factors based on the earth's crustal composition were greater than those based on the composition of the lignite used in the gasifier, showing the importance of characterizing the proper source material when investigating chemical fractionation during aerosol formation. Enrichments in the present study were much greater than those found in previous sampling during aborted start-up and cleaning procedures, where normal operating temperatures had not yet been reached. Both studies showed evidence of enrichment factors which decreased with increasing particle size. Although much of the airborne mass was associated with large particles having low respirability, the high concentrations of some metals indoors suggests that further assessment of potential occupational exposures is warranted.
I. Introduction The size distribution a n d chemical c o m p o s i t i o n o f airborne particulates emitted by the c o m b u s t i o n o f coal have been r e p o r t e d in the literature. M a n y studies have shown that submicron particles c o n t a i n volatile species such as Pb, Cd, and b e n z o ( a ) p y r e n e (Lee and von L e h m d e n , 1973; T o c a et al., 1973; K a t z a n d Chan, 1980). Less volatile, and m o r e benign, species such as F e a n d M g are usually found in larger particles. The presence o f toxic substances in small particles is a potential health h a z a r d , since these particles are preferentially d e p o s i t e d in the lower lung ( L i p p m a n n , 1977). The danger is e n h a n c e d b e c a u s e o f the p r e d o m i n a n c e o f toxic species on particle surfaces rather than in particle interiors (Linton et al., 1976; Van C r a e n e t a L , 1983). In general, a large fraction o f the pollutant emissions from coal c o m b u s t i o n is released to the environment through stacks. Fugitive emissions are often smaller, though still significant for m a n y pollutants. Coal gasification emissions, in contrast, are mostly fugitive. These fugitive emissions include dust resulting from coal handling operations, Environmental Monitoring and Assessment 4 (1984) 317- 333. 0167-6369/84/0044-0317 $ 02.55. 9 1984 by D. Reidel Publishing Company.
318
AIRBORNE TRACE METAL AND TRACE ORGANIC SPECIES
and uncontrollable releases of fine particles and gases at various locations throughout the system of valves and pipes at coal combustion and coal gasification facilities. Although stack and fugitive emissions from coal combustion processes have been studied, data are lacking for fugitive emissions from coal gasification operations. Commercial-scale gasifiers may be constructed to meet future energy requirements. Therefore it is desirable to study emissions from existing coal gasification pilot plants during regular operation; previous sampling of the type reported here pertained to gasifier emissions during an aborted start-up procedure (Davidson et aL, 1982). The objective of the present study was to collect data on the chemical composition and size distributions of fugitive aerosol emissions at a pilot-scale gasifier using lignite. The gasifier is located at the University of North Dakota Energy Research Center in Grand Forks. The project focused on trace metal and trace organic species. Sampling was conducted simultaneously inside the gasifier complex and at a nearby outdoor location. From these data, one can obtain qualitative information on the influence of gasifier emissions on outdoor air quality in the vicinity of the plant, as well as information on potential health hazards associated with the emissions.
2. Experimental Methods 2.1. TRACE METALS Size-fractionated samples for trace metal analysis were collected using two Sierra Model 235 impactors with 25 x 20 cm cellulose acetate backup filters having a pore size of 0.45/~m (Millipore Corp. HAWP). The impactors incorporated 20-mil FEP Teflon substrates that had been washed in three successive baths of concentrated HNO 3 (G. Frederick Smith, redistilled) for 24 hr each, followed by a 24-hr soak in purified water (supplied by a Coming MP3A still with LD2A demineralizer). To minimize particle bounceoff, the substrates were coated with a mixture of Vaseline and spectrograde hexane (Davidson et al., 1984). All washing and preparation of equipment for sampling was conducted in the Carnegie-Mellon University (C-MU) clean laboratory (Shaeffer and Davidson, 1979). Custom explosion-proof sampling motors (Amatek) assembled in housings made at Argonne National Laboratory were used for all indoor sampling. The filters were unsheltered. Standard high-volume vacuum pumps (General Metal Works) were used for the outdoor runs. The filters operated outdoors were enclosed in standard highvolume sampling shelters. Indoor sampling was conducted at the second level of the gasifier, one story above ground, for a 24-hr period during November 4-5, 1981. The Sierra impactor and backup filter were operated at 5.8 m 3 hr -1, measured with a Singer DTM 325 dry test meter calibrated at C-MU. Outdoor sampling with the other Sierra impactor was conducted simultaneously at a location approximately 25 m from the gasifier building. The average flow rate was 15 m 3 hr -x.
J . F . OSBORN ET AL.
319
The gasifier was started shortly before the sampling run began. The first 4 hr of sampling took place while the gasifier was in a start-up mode. The following 13 hr coincided with gasifier operation under normal steady-state conditions. For the final 7 hr, the gasifier was shut down due to slag solidification. At the end of these runs, both impactors were triple-bagged in polyethylene (Clean Room Products UCF-POLY). The backup filters were transferred into airtight PFA Teflon jars (Savillex 0110) and triple-bagged. The samples were transported to the C-MU clean laboratory, and digested in a solution of 5.25 ml concentrated HNO3 (G. Frederick Smith, redistilled) and 2.25 ml concentrated H F (Ultrex), diluted to 8 N. After several hours of gentle heating, the samples were further diluted to 4 N and analyzed by flameless atomic absorption spectrophotometry with a Perkin-Elmer 703 AA unit and H G A 2200 graphite furnace. The analytical procedures were identical to those described by Davidson et al. (1982).
2.2. TRACE ORGANICS All solvents used in these experiments except for acetone and ethanol were chromatography grade, distilled-in-glass (Burdick and Jackson, Muskegon, MI, or Waters Associates, Milford, MA). The acetone, used only for glass washing, and ethanol, used for initial cleaning of the Amberlite XAD-2 resin, were chemically pure grade. The Amberlite XAD-2 resin was laboratory grade (Mallincrodt, St. Louis, MO) and was cleaned prior to use by exhaustive Soxhlet extraction. The filters used to collect particle samples were Zefluor Teflon filters with a pore size of 2/~m (Membrana Corp. P5PJ001). Both 25 x 20 cm and 76-ram diameter filters were used. Soxhlet extractors used to extract samples and Kuderna Danish evaporative condensers used to reduce extract volumes were obtained from Kontes of Illinois (Evanston, IL) or Ace Glass Co. (Vineland, N J). Three separate sampling runs were used for trace organics measurement. The first run was conducted simultaneously with the trace metal sampling on November 4-5, 1981, and included one filter operated indoors at a flow rate of 36 m 3 hr -1. The second run included simultaneous indoor and outdoor filters operated at 34 and 40 m 3 hr -I, respectively. The final experiment consisted of one indoor filter run at 44 m 3 hr -1. All three sampling periods were 24 hr in duration, coinciding with steady-state operation of the gasifier. At the completion of sampling, the filters were immediately weighed in an adjacent laboratory, rolled with tweezers, placed in a glass Soxhlet extractor thimble, and extracted with CH2C12 for 4 hr. The extract was removed from the collection flask, filtered through a syringe-type 0.45 #m Millipore filter, and reduced to 4-5 ml in a Kuderna Danish evaporative condenser. The extract was transferred to a glass vial, capped, and stored in the dark until returned to Argonne. Upon arrival at Argonne, the extracts were further reduced in volume if necessary and analyzed by GC. The chromatographic data were analyzed using the RRI/Conc computer program (Stamoudis, 1982) and were compared to aromatic and aliphatic hydrocarbon standards. Simultaneously with the trace organic particulate sampling, vapor samples were
320
AIRBORNE
TRACE METAL AND TRACE ORGANIC
SPECIES
collected by passing the air through a 120-g bed of Amberlite XAD-2 resin. The resin was enclosed in an all-glass holder, topped by a 2/am Zefluor filter that prevented particulate matter from being entrained in the resin. The design and operation of the equipment have been reported elsewhere (Flotard, 1980). Samples were collected during 90-min periods for total sample volumes of 2-2.3 m 3. The sampler was located on the second-floor control room and in the third-floor laboratory where sidestream oil/tar samples were being collected. The resin was transferred to glass extractor thimbles, and was Soxhlet extracted for 2-hr periods within a few hours after the vapor was collected. The extract was transferred to a Kuderna Danish evaporative condenser and reduced to approximately 4 ml. The extracts were then sealed in glass vials, stored in the dark, and returned to Argonne for analysis. Upon arrival at Argonne, the vials were refrigerated. If necessary, further volume reductions were made before analysis. Analyses of the extracts from particulate and vapor sampling were conducted with a Hewlett-Packard 5880A gas chromatograph equipped with a level-4 computer control and data handling system, split/splitless injector system, 50 m • 0.31 mm OV-101 fused silica capillary column, and a flame ionization detector. The identity of compounds in the extracts was confirmed using a Hewlett-Packard 5985A mass spectrometer interfaced with a 5840A gas chromatograph equipped with the same injector system and fused silica capillary column as the 5880A. A 5934A data system was used to control the mass spectrometer and collect data. 3. Data Presentation and Discussion
3.1. TRACE METALS The Sierra impactor AA data served as input to a F O R T R A N program developed at C-MU. The program generated AA calibration curves based on a polynomial interpolation of standard concentrations, computed concentrations in each sample, and calculated the normalized mass distribution function (AC/Cx)/A log dp. Here AC is the airborne concentration corresponding to an impactor stage or backup filter in ng m -3, Cris the total concentration summed over all six stages, and A log dp is the particle size interval with dp representing the aerodynamic diameter in /~m. When the mass distribution function is plotted against log dp, the area under the curve between any two diameters is proportional to the fraction of airborne mass between those diameters. The value of dp with equal areas under the curve on both sides is termed the mass median aerodynamic diameter (MMD). Size distributions of A1, Ba, Ca, Fe, Mg, Mn, Na, Ag, As, Cd, Cu, and Pb for the indoor and outdoor impactor runs are shown in Figures 1 and 2, respectively. The elements graphed in the left columns are found in high concentrations in the earth's crust and in lignite. The elements in the right columns are less abundant, and are generally enriched in the atmosphere relative to the earth's crustal composition (Rahn, 1976). Standard deviations, not shown in the figures, are similar to those reported previously (Daddson et al., 1982). Shading below the curve in a given size interval denotes an
J . F . OSBORN ET AL.
321
A1 Ag 2.5q
2~
0.01
0.1
1
10
100
Be
1.50q
1,25t
o.7~ 0.50-{ o.2 1
F-L
~
........
0.01
0,1
1
10
p 0 1
001
I0
I00
1
10
100
I
10
100
1
10
100
1
10
100
As
lq
100
I
0,75]
Ca
0.50 0 25 0
.~112L
0.01
0.1
1
10
Fe
1.25 0.75
......... , ~
....
0.50
.........
0.01
1
0,1
10
100
Mg
0.25 0
1.25q
4
J
001
01
Cu
0.75~
1.5o 1
0.504 0.25 4
1.25
0.01
0.1
1
10
100
0.75 0,50
Mn
1.50q
!
0.251 ol
1.254
0,75 0.50 0:25
1'257/ 001
0.01
0,1
1
10
100
0.75
o.751~
0.50 4
0,50 ~
0.25
1,25W
0.01
0.1
dp, ~m
0,1 Pb
1 -]
Na
1.50 q
Fig. 1.
0.1 Cd
