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Mercury emissions from a modified in-situ oil shale retort
VOI IS. No 11. PP 2559-2563.
ooo4-6981,84 f3 00 + 0.00 Pngamon Press Ltd
19x4
DISCUSSIONS MERCURY EMISSIONS FROM A MODIFIED IN-SITU OIL SHALE RETORT The results reported, by Hodgson et al. are significant because they clearly demonstrate the presence of organo-mercury compound(s) together with elemental mercury in the untreated off-gasesfrom the oil shale process.It was disappointing to note that the authors chose not to concurrently collect and analyze such samples after the incinerator and scrubber. Since the off-gasses are further treated by these control devices, prior to release into the atmosphere, the data as presented does not assistreaders to evaluate the effectiveness of the control devices for collection, retention, or removal of these organo-mercury compounds. In our opinion, this paper has the following other limitations: (i) apparently, concurrent sampling between the three analytical techniques was not carried out; (ii) the authors’ efforts fell short in determination of the mercury compounds or speciesand (iii) little information on mercury collection by the pollution control equipment is presented in the paper. Comparatively, very little, if any, work so far appeared to have been done on mercury speciation for combustion sources in general. In fact, reports dealing with sampling for mercury (mostly elemental mercury) in coal-fired flue gas have inherently suffered due to lack of efficient collection substrates. This may be, in part, reasons for poor mass balances for mercury around the process (Billings and Matson, 1972; Cato and Venezia, 1976; Klein er al., 1975). There are a variety of metal sorbants and absorbing solutions that are available and commonly used for collection of mercury and its compounds in the air and, also, in source testing (Shendrikar et al., 1984). Such substrates have been evaluated in the laboratory for optimum collection efficiencies including evaluations of elemental mercury and various organomercury compounds. In spite of this, poor mercury mass balances and poor collection efficiencies from the flue gas environment have been reported as early as in the 1970s. It is our opinion that this may be due to any one or a combination of the following reasons: (i) sampling environment contains chemical components, all of which have not been simulated in the laboratory, that may poison the mercury collection substrate(s); (ii) sampling environment contains mercury compounds other than those for which collection efficiency studies in the laboratory are performed; (iii) incomplete recovery of mercury and/or its compounds from the collection medium and (iv) problems during analytical quantification of collected samples. Because of the above discussed reasons and the well documented mercury collection meffeciencies,we were rather disappointed to see that Hodgson et 01. did not attempt to investigate the collection efficiency of their sampling devices such as gold-coated glass beads and Carbosieve B, followed by gold amalgamation column, in the field environment. In fact, a systematic study of collection efficiency/mefficiency of mercuryand other volatile traceelementsin thefluegasdue to coal combustion still does not exist in the open literature. It is our thinking that extrapolations of laboratory results of sampling techniques without field validation may be risky since laboratory studies are just not capable ofaccounting for all of the sampling difficulties of the flue gases in the field.
Granted that the agreement, from diKerent sampling methods such as the on-line monitor, gold-coated beads, and the Carbosieve B, provide total mercury concentrations that are comparable to each other within process variation. However, a direct proof by using two or three of each of these sampling devices, in series, particularly the last two, would have greatly increased the significance of this work. The paper, as written, simply demonstrates the analytical application of the Zeeman Spectrometer to continuously measure mercuryconcentrations in the off-gases.It isour thinking that the method development process is not complete unless attempts are made to validate the data using another, but well-established, sampling method. To achieve this objective, samplesneed to be collected concurrently rather than sequentially, as in the paper (see Table I). This becomes imperative becauseany processstream is a dynamic and stratified system. In terms of data interpretation to assessthe environmental impact of oil shale retorting and/or developing a control strategy, we think the data included in Tables I and 2 could be further interpreted by the following line of reasoning: (i) The gold amalgamation method and the on-line monitor provided mercury concentrations in the off-gases that are essentially the same (Table I) with the exception of sampling days 297 and 306. (ii) The on-lineplonitor analyzes both elemental mercury and organo-mercury compounds because of conversion of organic to elemental mercury in the furnace and the absorption chamber of the monitor. (iii) The gold-coated glassbeads collect elemental mercury and only dimethyl mercury quantitatively (Braman and Johnson, 1974). Since, in essence,there is agreement between total mercury concentration (see Table I) obtained by the on-line monitor and gold-coated glass beads, the off-gases most likely are deduced to contain only elemental mercury and dimethyl mercury. The data obtained by the other manual technique tends to support the same conclusion: (i) The mercury concentrations obtained with gold-coated glassbeadsand Carbosieve B coupled to a gold amalgamation column are essentially the same (Tables I and 2). (ii) Carbosieve B in the laboratory evaluation studies has shown to be quite efficient for collection of methyl mercury, ethyl mercury, dimethyl mercury (Trujillo and Campbell, 1975). Since total mercury concentrations included in Table I, under gold amalgamation method, and Table 2 are essentially the same, the data from these tables could be interpreted to state that gases primarily contained elemental mercury and dimethyl mercury. If significant quantities of other organomercury compounds were present, such an agreement would not have been possible. Becauseof the importance of the chemical species,we think that Hodgson et al. should have attempted to interpret the data in Tables I and 2 from the standpomt of mercury speciation. Alternatively, they could have used the sampling device developed by Braman and Johnson (1974) which mav have provided additional information on’ the presence of other mercury compounds present in the off-gases. Such information is generally considered of importance, particularly because many organo-mercurial compounds are more toxic than the elemental mercury (D’ltri, 1982). The main objectives of stack testing of any processesare to evaluate health effectsof the emission, quantify control device
2559
2560
DiscussIons
performance, and, if required, develop a control strategy. In our opimon, the authors should have collected and reported data of samples obtained concurrently, i.e. before and after the control devices. With the exception of sampling day 300 and that too not concurrently and with only the gold amalgamation method, control device data are not taken. Even then here an attempt has been made to further extrapolate the data mostly from the samples collected and analyzed before the control devices and a value for daily mercury emissions from this retort type IS calculated. Additionally, such a calculated value is compared with mercury emissions from a coal-fired power plant, ore processing facility, chlor-alkali plant, etc. Are the authors assuming no mercury collection efficiency by the control devices? This may be true for the coal-fired power plants controlled by electrostatic precipitators where 98 per cent of the coalbound mercury is emitted into the atmosphere (Diehl et al., 1972; Billings and Matson, 1972). In our opinion, this assumption coupled with one day sampling results for control devices unique to the oil shale process may not be without risks. Historically, our attempts to regulate stationary source emissions appeared to have concentrated on removal/control of particulate matter and gaseous pollutants such as SO,, NO,, POM, etc. In comparison, little attention to date has been focused specifically on the trace element emissions in the form of particulate matter or vapors due to fossil fuel combustion. However, work performed clearly indicates that such particulate matter emission is essentially an aggregate of trace elements/or their compounds; many of these show carcinogenic and toxic potentials to humans, animals, and to our biological systems. Therefore, it is our opinion that advances in ‘control technology’ should not only be concerned with the physical and engineering principles but also consider chemical aspects of the emission problem. Since toxicity potentials of trace elements are dependent on the chemical nature, attempts should be made to identify/quantify trace element species in the flue gases. Such mformation in the future may prove to be valuable in developing a total emission control strategy. Limitations of available analytical methodologies prohibits determination of chemical species for many of the trace elements of current interest; however, mercury is one of the few elements for which speciation methodology is relatwely well documented In the open ltterature and should be attempted when possible.
element discharge from coal combustion for power production. War. Air Soil PoUur. 5, 71. Shendrikar A. D., Damle A. and Gutknecht W F. (1984) Collection efficiency evaluation of mercury-trappmg media for the SASS train impinger assembly EPA Contract No 68-02-3626. Trujillo P. E. and Campbell E. E (1975) Development of a multistageaalr sampler for mercury. Analvf. Chem. 47, 1629
AUTHORS’
REPLY
In their comments on our paper “Mercury Enusslons from a Modified In-Situ Oil Shale Retort”. Shendrikar and Ensor Ignore the major objectives of the study and demonstrate their unfamiliarity with thecomplex nature of oil shale offgas. Due to their misconstruction. it is necessary to reiterate the objectives and significant results of the study*. First, we demonstrated the efficacy ofa new continuous online gas monitor for the quantitation of Hg in an extremely difficult to analyze industrial gas stream. Our prior work had shown that the standard techniques for measuring gaseous Hg were inadequate in the oil shale offgas environment. U.S. EPA reference method 101 failed comoletelv. and Auamalgamation methods were found to &qui& two-stage thermal desorption and a background-corrected spectrameter. In part due to the lack of adequate methods, data on the mass emissions of Hg from large oil shale retorts were previously limited to a few discrete sample measurements of undetermined accuracy. The on-line gas momtor allowed us to overcome the difficulties of working in the offgas environment. The validity of the method was demonstrated m laboratory studies using a 5-kg Fischer assay type retort; closure of a Hg mass balance equation was obtained along with agreement with discrete measurements made by the Auamalgamation method. We are confident that the data obtained with the gas monitor on Hg emissions from the Rio Blanc0 retort are of high accuracy. Calibrations were by standard additions, and the small nonconcurrence between the gas monitor measurements and the Au-amalgamation measurementsdoes not significantly detract from the fact that good agreement was obtained between two independent methods under difficult sampling and analytical conditions. Second, our results demonstrated the potential magnitude lnorgamcs Laborator ARUN D. SHENDRIKAR of Hg emissions from the modified in-situ oil shale process Although the mass of Hg contained in the retort is unknown, CompuChem Laboratories, Inc. extrapolation of available data suggests the majority of the P. 0. Box 12652 Hg in the retort partitioned to the offgas. This occurred Research Tnangle Pad, despite the probable existence of several major loss mechanNC 27709, U.S.A. Research Triangle lnsrrrure DAVIDS. ENSOR isms. It was not our intention, nor did the sampling situation allow us, to evaluate the stack-gas scrubber for the removal of P. 0. Box 12194 Hg. The development of commercial technology for the Research Triangle Pad. NC 27709. C’.S.A extraction of shale oil is still in the formative stage, and several sulfur removal processes are being evaluated. We suggest that efficiency of Hg removal be one of the parameters that IS REFERENCES determined for these processes. It seems likely that some Hg would be removed by a flue-gas scrubber such as used at Rio Blanc0 since the offgas bubbles through an aqueous slurry, Billings C. E. and Matson W. R. (1972) Mercury emissions however, the limited data we collected downstream from the from coal combustion. Science, Wash. 176, 1232. scrubber do not support this. Braman R. S. and Johnson D. L. (1974) Selective absorption Third, since we were able to measure Hg m the offgas on a tubesand emission technique for determination ofambient continuous real-time basis, we observed large temporal forms of mercury in air. EnL;lr.SCI.Technol. 8, 996. variations in the Hg mass emission rate. This variability has Cato C. A. and Venezia R. A. (1976) Trace Element and important implications for the development of future samOrganic Emissions from Industrial Boilers. Presented at pling strategies for the oil shale industry. It IS now apparent the 69th APCA Annual Meeting, Portland, Oregon. Dichl R. C., Hattman E. A., Schultz H. and Haren R. T. (1972) that any strategy which attempts to characterize Hg emissions from a few discrete sample measurements will be inadequate. Fate of Mercury in the Combustion of Coal. Bureau of Mines Technical Progress Report No. 54. D’ltri F. M. (1972) The envlronmental mercury problem. Chemical Rubber Company Press, Cleveland, OH 44129. *Work supported by U.S. DOE, Contract No. DE-AC0376SFOOO98. Klein D. H., Anderson A. W. and Bottom N. E. (1975) Trace
ooo4-6981,84 f3 00 + 0.00 Pngamon Press Ltd
19x4
DISCUSSIONS MERCURY EMISSIONS FROM A MODIFIED IN-SITU OIL SHALE RETORT The results reported, by Hodgson et al. are significant because they clearly demonstrate the presence of organo-mercury compound(s) together with elemental mercury in the untreated off-gasesfrom the oil shale process.It was disappointing to note that the authors chose not to concurrently collect and analyze such samples after the incinerator and scrubber. Since the off-gasses are further treated by these control devices, prior to release into the atmosphere, the data as presented does not assistreaders to evaluate the effectiveness of the control devices for collection, retention, or removal of these organo-mercury compounds. In our opinion, this paper has the following other limitations: (i) apparently, concurrent sampling between the three analytical techniques was not carried out; (ii) the authors’ efforts fell short in determination of the mercury compounds or speciesand (iii) little information on mercury collection by the pollution control equipment is presented in the paper. Comparatively, very little, if any, work so far appeared to have been done on mercury speciation for combustion sources in general. In fact, reports dealing with sampling for mercury (mostly elemental mercury) in coal-fired flue gas have inherently suffered due to lack of efficient collection substrates. This may be, in part, reasons for poor mass balances for mercury around the process (Billings and Matson, 1972; Cato and Venezia, 1976; Klein er al., 1975). There are a variety of metal sorbants and absorbing solutions that are available and commonly used for collection of mercury and its compounds in the air and, also, in source testing (Shendrikar et al., 1984). Such substrates have been evaluated in the laboratory for optimum collection efficiencies including evaluations of elemental mercury and various organomercury compounds. In spite of this, poor mercury mass balances and poor collection efficiencies from the flue gas environment have been reported as early as in the 1970s. It is our opinion that this may be due to any one or a combination of the following reasons: (i) sampling environment contains chemical components, all of which have not been simulated in the laboratory, that may poison the mercury collection substrate(s); (ii) sampling environment contains mercury compounds other than those for which collection efficiency studies in the laboratory are performed; (iii) incomplete recovery of mercury and/or its compounds from the collection medium and (iv) problems during analytical quantification of collected samples. Because of the above discussed reasons and the well documented mercury collection meffeciencies,we were rather disappointed to see that Hodgson et 01. did not attempt to investigate the collection efficiency of their sampling devices such as gold-coated glass beads and Carbosieve B, followed by gold amalgamation column, in the field environment. In fact, a systematic study of collection efficiency/mefficiency of mercuryand other volatile traceelementsin thefluegasdue to coal combustion still does not exist in the open literature. It is our thinking that extrapolations of laboratory results of sampling techniques without field validation may be risky since laboratory studies are just not capable ofaccounting for all of the sampling difficulties of the flue gases in the field.
Granted that the agreement, from diKerent sampling methods such as the on-line monitor, gold-coated beads, and the Carbosieve B, provide total mercury concentrations that are comparable to each other within process variation. However, a direct proof by using two or three of each of these sampling devices, in series, particularly the last two, would have greatly increased the significance of this work. The paper, as written, simply demonstrates the analytical application of the Zeeman Spectrometer to continuously measure mercuryconcentrations in the off-gases.It isour thinking that the method development process is not complete unless attempts are made to validate the data using another, but well-established, sampling method. To achieve this objective, samplesneed to be collected concurrently rather than sequentially, as in the paper (see Table I). This becomes imperative becauseany processstream is a dynamic and stratified system. In terms of data interpretation to assessthe environmental impact of oil shale retorting and/or developing a control strategy, we think the data included in Tables I and 2 could be further interpreted by the following line of reasoning: (i) The gold amalgamation method and the on-line monitor provided mercury concentrations in the off-gases that are essentially the same (Table I) with the exception of sampling days 297 and 306. (ii) The on-lineplonitor analyzes both elemental mercury and organo-mercury compounds because of conversion of organic to elemental mercury in the furnace and the absorption chamber of the monitor. (iii) The gold-coated glassbeads collect elemental mercury and only dimethyl mercury quantitatively (Braman and Johnson, 1974). Since, in essence,there is agreement between total mercury concentration (see Table I) obtained by the on-line monitor and gold-coated glass beads, the off-gases most likely are deduced to contain only elemental mercury and dimethyl mercury. The data obtained by the other manual technique tends to support the same conclusion: (i) The mercury concentrations obtained with gold-coated glassbeadsand Carbosieve B coupled to a gold amalgamation column are essentially the same (Tables I and 2). (ii) Carbosieve B in the laboratory evaluation studies has shown to be quite efficient for collection of methyl mercury, ethyl mercury, dimethyl mercury (Trujillo and Campbell, 1975). Since total mercury concentrations included in Table I, under gold amalgamation method, and Table 2 are essentially the same, the data from these tables could be interpreted to state that gases primarily contained elemental mercury and dimethyl mercury. If significant quantities of other organomercury compounds were present, such an agreement would not have been possible. Becauseof the importance of the chemical species,we think that Hodgson et al. should have attempted to interpret the data in Tables I and 2 from the standpomt of mercury speciation. Alternatively, they could have used the sampling device developed by Braman and Johnson (1974) which mav have provided additional information on’ the presence of other mercury compounds present in the off-gases. Such information is generally considered of importance, particularly because many organo-mercurial compounds are more toxic than the elemental mercury (D’ltri, 1982). The main objectives of stack testing of any processesare to evaluate health effectsof the emission, quantify control device
2559
2560
DiscussIons
performance, and, if required, develop a control strategy. In our opimon, the authors should have collected and reported data of samples obtained concurrently, i.e. before and after the control devices. With the exception of sampling day 300 and that too not concurrently and with only the gold amalgamation method, control device data are not taken. Even then here an attempt has been made to further extrapolate the data mostly from the samples collected and analyzed before the control devices and a value for daily mercury emissions from this retort type IS calculated. Additionally, such a calculated value is compared with mercury emissions from a coal-fired power plant, ore processing facility, chlor-alkali plant, etc. Are the authors assuming no mercury collection efficiency by the control devices? This may be true for the coal-fired power plants controlled by electrostatic precipitators where 98 per cent of the coalbound mercury is emitted into the atmosphere (Diehl et al., 1972; Billings and Matson, 1972). In our opinion, this assumption coupled with one day sampling results for control devices unique to the oil shale process may not be without risks. Historically, our attempts to regulate stationary source emissions appeared to have concentrated on removal/control of particulate matter and gaseous pollutants such as SO,, NO,, POM, etc. In comparison, little attention to date has been focused specifically on the trace element emissions in the form of particulate matter or vapors due to fossil fuel combustion. However, work performed clearly indicates that such particulate matter emission is essentially an aggregate of trace elements/or their compounds; many of these show carcinogenic and toxic potentials to humans, animals, and to our biological systems. Therefore, it is our opinion that advances in ‘control technology’ should not only be concerned with the physical and engineering principles but also consider chemical aspects of the emission problem. Since toxicity potentials of trace elements are dependent on the chemical nature, attempts should be made to identify/quantify trace element species in the flue gases. Such mformation in the future may prove to be valuable in developing a total emission control strategy. Limitations of available analytical methodologies prohibits determination of chemical species for many of the trace elements of current interest; however, mercury is one of the few elements for which speciation methodology is relatwely well documented In the open ltterature and should be attempted when possible.
element discharge from coal combustion for power production. War. Air Soil PoUur. 5, 71. Shendrikar A. D., Damle A. and Gutknecht W F. (1984) Collection efficiency evaluation of mercury-trappmg media for the SASS train impinger assembly EPA Contract No 68-02-3626. Trujillo P. E. and Campbell E. E (1975) Development of a multistageaalr sampler for mercury. Analvf. Chem. 47, 1629
AUTHORS’
REPLY
In their comments on our paper “Mercury Enusslons from a Modified In-Situ Oil Shale Retort”. Shendrikar and Ensor Ignore the major objectives of the study and demonstrate their unfamiliarity with thecomplex nature of oil shale offgas. Due to their misconstruction. it is necessary to reiterate the objectives and significant results of the study*. First, we demonstrated the efficacy ofa new continuous online gas monitor for the quantitation of Hg in an extremely difficult to analyze industrial gas stream. Our prior work had shown that the standard techniques for measuring gaseous Hg were inadequate in the oil shale offgas environment. U.S. EPA reference method 101 failed comoletelv. and Auamalgamation methods were found to &qui& two-stage thermal desorption and a background-corrected spectrameter. In part due to the lack of adequate methods, data on the mass emissions of Hg from large oil shale retorts were previously limited to a few discrete sample measurements of undetermined accuracy. The on-line gas momtor allowed us to overcome the difficulties of working in the offgas environment. The validity of the method was demonstrated m laboratory studies using a 5-kg Fischer assay type retort; closure of a Hg mass balance equation was obtained along with agreement with discrete measurements made by the Auamalgamation method. We are confident that the data obtained with the gas monitor on Hg emissions from the Rio Blanc0 retort are of high accuracy. Calibrations were by standard additions, and the small nonconcurrence between the gas monitor measurements and the Au-amalgamation measurementsdoes not significantly detract from the fact that good agreement was obtained between two independent methods under difficult sampling and analytical conditions. Second, our results demonstrated the potential magnitude lnorgamcs Laborator ARUN D. SHENDRIKAR of Hg emissions from the modified in-situ oil shale process Although the mass of Hg contained in the retort is unknown, CompuChem Laboratories, Inc. extrapolation of available data suggests the majority of the P. 0. Box 12652 Hg in the retort partitioned to the offgas. This occurred Research Tnangle Pad, despite the probable existence of several major loss mechanNC 27709, U.S.A. Research Triangle lnsrrrure DAVIDS. ENSOR isms. It was not our intention, nor did the sampling situation allow us, to evaluate the stack-gas scrubber for the removal of P. 0. Box 12194 Hg. The development of commercial technology for the Research Triangle Pad. NC 27709. C’.S.A extraction of shale oil is still in the formative stage, and several sulfur removal processes are being evaluated. We suggest that efficiency of Hg removal be one of the parameters that IS REFERENCES determined for these processes. It seems likely that some Hg would be removed by a flue-gas scrubber such as used at Rio Blanc0 since the offgas bubbles through an aqueous slurry, Billings C. E. and Matson W. R. (1972) Mercury emissions however, the limited data we collected downstream from the from coal combustion. Science, Wash. 176, 1232. scrubber do not support this. Braman R. S. and Johnson D. L. (1974) Selective absorption Third, since we were able to measure Hg m the offgas on a tubesand emission technique for determination ofambient continuous real-time basis, we observed large temporal forms of mercury in air. EnL;lr.SCI.Technol. 8, 996. variations in the Hg mass emission rate. This variability has Cato C. A. and Venezia R. A. (1976) Trace Element and important implications for the development of future samOrganic Emissions from Industrial Boilers. Presented at pling strategies for the oil shale industry. It IS now apparent the 69th APCA Annual Meeting, Portland, Oregon. Dichl R. C., Hattman E. A., Schultz H. and Haren R. T. (1972) that any strategy which attempts to characterize Hg emissions from a few discrete sample measurements will be inadequate. Fate of Mercury in the Combustion of Coal. Bureau of Mines Technical Progress Report No. 54. D’ltri F. M. (1972) The envlronmental mercury problem. Chemical Rubber Company Press, Cleveland, OH 44129. *Work supported by U.S. DOE, Contract No. DE-AC0376SFOOO98. Klein D. H., Anderson A. W. and Bottom N. E. (1975) Trace