United States Environmental Protection Agency Industrial Environmental Research Laboratory Research Triangle Park NC 27711 Research and Development EPA-600/S7-82-054 Dec. 1982 Project Summary Coal Gasification/Gas Cleanup Test Facility: Volume III. Environmental Assessment of Operation with New Mexico Subbituminous Coal and Chilled Methanol J. K. Ferrell, R. M. Felder, R. W. Rousseau, R. M. Kelly, M. J. Purely, and S. Ganesan This report concerns the second major study carried out on a pilot- scale coal-gasification/gas-cleaning test facility: the steam-oxygen gasifi- cation of a New Mexico subbituminous coal using refrigerated methanol as the acid gas removal solvent. The report briefly describes the facility; summarizes gasifier operation using the New Mexico coal; gives results of mathematical modeling of the gasifier, detailed chemical analyses of gasifier effluent streams, and operation of the acid gas removal system using the gasifier make gas as feed; and sum- marizes results of mathematical model development for the acid gas absorber column. Several trace sulfur com- pounds and aliphatic hydrocarbons were found to distribute among all exit streams from the acid gas removal system. In addition, a wide range of simple aromatic hydrocarbons were found to accumulate in the recir- culated methanol. This Project Summary was devel- oped by EPA's Industrial Environ- mental Research Laboratory. Research Triangle Park, NC. to announce key findings of the research project that is fully documented in a separate report of the same title (see Project Report ordering information at back). Introduction As a part of a continuing research program on the environmental aspects of fuel conversion, the EPA has spon- sored a research project on coal gasification at North Carolina State University. The facility used for this research is a small coal-gasification/ gas-cleaning pilot plant. The overall objective of the project is to characterize the gaseous and condensed phase emissions from the gasification/gas- cleaning process, and to determine how emission rates of various pollutants depend on adjustable process pa- rameters. The plant, described in detail in Volume I (EPA-600/7-80-046a; NTIS PB80-188378) consists of a fluidized- bed reactor, a cyclone and venturi scrubber for particulates, condensables, and solubles removal, and absorption and stripping columns for acid gas removal and solvent regeneration. The plant has a nominal capacity of 23 kg/hr (50 Ib/hr) of coal feed for steady state operation. Figure 1 is a schematic of the gasifier, the acid gas removal system (AGRS), and other major components. In an initial series of runs on the gasifier, a pretreated Western Kentucky No. 11 coal was gasified with steam and ------- Syn Gas NtPui Coal Feed Hopper NX Purg ge e _ I Gasifier NX Purge Plor not < > rh 1 :xc/onelNX1 ^ a p k> J :har Receiver /V2 Purpe tf are/- ol Steam -u [ fei 'cr . 1 1 V^ 1 7rur/ fc 6/>e/- [y Dehydrator ^ Sour-Gas T Compressor D T~ iMist Eliminator r*! Y /"\ ^ Heat Exchanger PCS Tank H Excr -© Acid Gas I L Circulation Pump Solvent Pump S = Sample Port Figure 1. Pilot plant facility. oxygen. The results of this work and a detailed list of project objectives are in Volume II (EPA-600/7-82-023). This report concerns the second major study carried out on the facility, the steam-oxygen gasification of a New Mexico subbituminous coal using refrigerated methanol as the AGRS solvent. This coal, from the Navaho mine of the Utah International Co., was ground and screened by the Morgan- town Energy Technology Center of the Department of Energy. Table 1 shows an average analysis of the char and coal used in studies to date. This report briefly describes the facili- ty; summarizes gasifier operation using New Mexico coal; gives results of math- ematical modeling of the gasifier, de- tailed chemical analyses of gasifier ef- fluent streams, and operation of the AGRS using the gasifier make gas as feed; and summarizes results of mathe- matical model development for the AGRS absorber. Results and Discussion Fifteen gasification runs were made using the pilot plant facility with New Mexico coal. Six runs made use of the gasifier-PCS system only, and nine runs were integrated and included the acid gas removal system. To evaluate the ability of the system to handle the tars associated with the coal feedstock, gasifier runs were com- menced by feeding mixtures of the sub- bituminous coal and devolatilized West- ern Kentucky coal char used in previous studies. The first four runs used 10, 30, 30, and 50 wt % subbituminous coal; the rest used char. After some system Table 1. Coal and Char Analysis modification to accommodate tars, these runs indicated that 100% New Mexico subbituminous coal could be used as a feedstock, so 100% coal was used for the rest of the runs. Sampling and chemical analysis methods were developed for all feed and effluent streams. Methods used to sample and analyze gaseous streams were satisfactory for the major gases and for all minor components of the gaseous streams in concentrations Coal Char New Mexico Coal wt% Proximate Analysis % Fixed Carbon Volatile Matter Moisture Ash 86.0 2.4 0.9 10.7 36.2 31.1 9.7 23.0 Ultimate Analysis % Carbon Hydrogen Oxygen Nitrogen Sulfur Ash 83.8 0.6 2.2 O.1 2.6 10.7 50.2 4.2 20.7 1.1 0.8 23.0 ------- greater than a few parts per million. Detailed chemical compound analyses for solid and liquid streams are gener- ally satisfactory, but are still under development. A major effort was made to develop methods to detect trace metal elements in the feed and effluent streams. Methods now used for As analysis are satisfactory, both for ease of application and reliability. The main problem with As is the ineffectiveness of the impinger solutions in trapping it from the gas stream. Reproducibility of Pb concentration measurements has been less than satisfactory, although considerable improvement has been made recently by diluting all samples to fall within the linear range of the atomic absorption spectrometer calibration, and by adding dibasic ammonium phosphate to the injected sample, thereby binding the Pb and enabling higher charring temperatures. The cold- vapor technique used for Hg is satisfac- tory; the main difficulty with Hg is its volatility: samples must be analyzed soon after they are taken. The most important quality assurance test for the evaluation of the experimen- tal data was good closures on the mass balances for total mass and for all major elements. In general, the mass balance results for both the gasif ier-PCS and the acid gas removal systems are excellent: they indicate no gross errors in either chemical analyses or mass flow mea- surements. Frequent calibration checks were necessary to achieve the mass balance results shown. Reactor temperature and steam-to- carbon feed ratio were the main operating parameters varied for the gasifier: results show that the make gas flow rate and the carbon conversion both increase with increasing tempera- ture. This increase is expected: the degree of devolatilization and the gasification reaction rates all increase with increasing temperature. Although the effects of operating parameters on reactor performance are not easily determined directly from the experimen-' tal data, a mathematical model devel- oped in this study correlates run results reasonably well, and is useful in evaluating the effects of operating parameters. Previous studies with a char feed indicated that the sulfur conversion could be roughly estimated by assuming it to equal the carbon conversion. For New Mexico coal, this crude approxima- tion also seems applicable. In addition. results of a detailed analysis of the reactor make gas for the various sulfur gases indicate that the distribution between H2S and COS may be predicted by assuming that the reaction, COS + H2O = H2S + C02 is at equilibrium at the temperature above the fluidized bed. Figure 2 shows the equilibrium constant (Ki) for this reaction plotted versus the temperature at the top of the f lu idized bed for both the char and the coal runs. The gasification of New Mexico coal produces many hydrocarbon gases. Aliphatics up to butene and butane and simple aromatic compounds have been detected in the gasifier make gas stream. Analyzing these hydrocarbon emission rates indicates that they generally increase with increasing reactor bed temperature. Table 2 shows the gas compositions measured at six gas sample locations shown on Figure 1. After leaving the PCS system, the reactor make gas is compressed to about 3610 kPa (525 psig) and then cooled to approximately 10°C. During this process higher molecular weight compounds in the gas stream in very low concentrations are condensed and separated from the gas in a knockout drum. This drum eliminates pressure fluctuations at the sour gas flow meter and also collects liquids which may condense after compression and cooling. A sample of this liquid was collected after Run GO-79 and was analyzed by GC-MS. The mass spectrogram is shown in Figure 3; results of compound identification are listed in Table 3. While a variety of hydrocarbon compounds were found in this liquid, no aromatic compounds heavier than substituted benzenes were found. This fact, together with results of analyses of the methanol AGRS solvent, indicates that no detect- able polynuclear aromatic compounds are in the gases leaving the PCS system. No unusual results were noted from the proximate and ultimate analyses of the solid streams; however, the ultimate analysis of the spent char generally correlates with gasifier run conditions. For example, higher temperatures result in higher carbon conversions and a lower carbon content in the spent char. The tars collected from the cold trap downstream from the cyclone were subjected to a solvent partitioning scheme to separate them into groups of compounds of varying polarities. The groups were then quantified as to their wt % contribution to total tar compo- sition. In addition to the partitioning 25 20 15 10 From Kohl and Riesenfeld (COS)(H20) Char O New Mexico Coal O 1400 (760) Figure 2. 1500 (815) 1600 1870) 170O 4925) 1800 (980) Temperature at Top of Bed. °F(°C) Comparison of experimental values of Riesenfeld. with data of Kohl and ------- Table 2. Gas Analysis Summary for AMI-60/GO-79 Species H2 COs Ethylene Ethane HzS COS N, CHt CO Benzene Toluene Ethyl Benz. Xylenes Thiophene* CHaSH*, CzHsSH* Carbon disulfide* Propylene* Propane* Butane* Methanol** Sample Train 32.13 21.68 0.30 0.33 0.206 0.0084 21.33 6.78 17.06 N/A N/A N/A N/A 99 37 1 2 925 273 451 PCS Tank 32.57 21.82 0.30 0.33 0.174 0.0078 20.62 6.65 17.17 0.0272 0.0278 N/A N/A 97 29 1 2 940 277 1730 Sour Gas 32.60 21.68 0.32 0.36 0.214 0.0084 20.71 6.61 17.25 0.0391 0.0393 N/A N/A 83 35 2 2 1012 314 224 Sweet Gas 43.01 0.065 0.081 0.026 0.0019 27.62 7.44 21.90 N/A N/A 212 66 Flash Gas 21.55 27.16 0.69 0.82 0.108 0.0044 24.40 25.18 N/A N/A 7 381 364 145 Acid Gas 63.82 0.95 1.03 0.597 0.0233 24.71 2.60 2.06 0.0592 N/A N/A 13 26 65 5 1053 5004 434 3.49 * Parts per million (volume) ** Estimated ULA (NOTE: Peaks identified in Table 3.) 8 16 24 32 40 48 56 64 72 Figure 3. GC/MS scan of compressor knockout condensate forAMI-60/GO-79. analysis, the tars were analyzed for polynuclear aromatic hydrocarbons (PAHs) and organic sulfur compounds. The PAHs were analyzed by glass capillary gas chromatography with a flame ionization detector; the sulfur- containing species were analyzed by gas chromatography with a flame photo- metric detector. Tables 4,5, and 6 show results of these analyses. Table 3. Compressor Knockout Sample from AMI-60/GO- 79 Peak Numbers from Figure 3 1. 1-pentene 2. Hydrocarbon 3. Benzene 4. Hydrocarbon 5. Toluene 6. Cyclo C4-C5 7. Hydrocarbon 8. Ethyl benzene 9. Dimethyl benzene 10. Substituted benzene 11. CB hydrocarbon 12. C9 hydrocarbon 13. Propyl or ethyl methyl substituted benzene 14. Propyl or ethyl methyl substituted benzene 15. 1-decene 16. 2-propyl benzene 17. 1 -ethyl-4-methyl benzene The analyses of the tars indicate that a significant amount of PAHs is in the gas stream as it leaves the reactor, and emerge primarily in the stream con- densed by the venturi scrubber. Com- pounds with boiling points higher than that of naphthalene do not seem to be in the gas stream past the PCS system. The concentrations of various species in the water condensate from the sample train were normalized to deter- mine rates of evolution in milligrams per kilogram of coal fed to the gasifier. No clear trends with reactor temperature are evident, indicating that (for the temperature range covered) the reactor temperature has little effect on the emission rates of wastewater species. Water samples were analyzed by high-performance liquid chromatog- raphy (HPLC) for phenolics. The sam- ple preparation consisted of filtering to remove particulates prior to direct injection into the HPLC. The results, shown in Table 7, are not reported as specific phenolic compounds, but are categorized as phenols, cresols, and xylenols. Also, the samples (except GO- 70) were analyzed for total organic extractables. A methylene chloride extraction was performed and the extract evaporated to dryness to deter- mine the weight percent of organic extractables in the sample. In addition, both the trap water and water from the PCS tank were analyzed by standard methods. Table 8, summa- rizing these results, shows average values for all runs, general levels of ------- Table 4. Tar Partition Results* GO-69B GO-70 PCS PCS Acids 10.9 34.7 Bases 20.9 27.5 TOTAL NEUTRALS 68.3 37.7 Non polar 25.1 5.5 PAHs 36.0 26.7 Polar 7.2 5.5 Cyclohexane Insolubles *wt% Table 5. Capillary GC Tar Analyses* GO-69B No. Compound PCS 1 Phenol 0. 15 2 Indene 0.87 3 Naphthalene 3.50 4 Benzothiophene 0.13 5 Quinoline 0.08 6 2-Methylnaphthalene 1.60 7 1 -Methylnaphthalene 1.10 8 Biphenyl 0.36 9 Acenaphthylene 1.50 10 Acenaphthene 0.57 1 1 Dibenzofuran 0. 74 12 Fluor ene 1.00 Dibenzothiophene 0.09 13 Phenanthrene 1.30 14 Anthracene 0.73 15 Fluoranthene 0.45 16 Pyrene 0.32 17 Benzo(a)anthracene 0.09 18 Chrysene 0. 14 19 Triphenylene 0. 14 20 Benzo(b)Fluoranthene 0.04 21 Benzo(k)F/uoranthene 0.02 22 Benzo(e)Pyrene 0.05 23 Benzo(a)Pyrene 0.04 24 Perylene 0.02 Total Wt% 15.03 *wt% concentrations found, and differences between the two kinds of samples collected. Efforts continued to determine the fate of several of the more volatile trace metal elements in the feed coal. Closures on As mass balances consis- tently vary between 35% and 70%, suggesting that a significant fraction of this substance is passing undetected from the system, either in the gas phase or adsorbed on fine particles that are not trapped by the cold trap or impingers. Similar results are obtained for Pb, for which closures never exceeded 34%, GO-76 GO-76 GO-78 Trap PCS Trap 16.5 11.2 17.29 4.7 6.7 6.05 78.8 80.1 76.66 24.7 30.0 11.53 10.7 11.5 26.85 15.3 15.2 16.45 28.1 23.4 21.83 GO-76 GO-76 GO-78 Trap PCS Trap 2.11 1.30 2.10 0.09 0.06 0.08 0.16 0.09 0.13 0.79 0.60 0.97 0.52 0.37 0.81 0.16 0.14 0.28 0.71 0.53 0.60 0.34 0.30 0.26 0.53 0.46 0.53 0.53 0.51 0.43 0.07 0.08 0.09 0.62 0.67 0.47 0.38 0.32 0.49 0.36 0.32 0.23 0.26 0.25 0. 1 7 0.16 0.07 0.05 0.13 0.09 0.04 0.06 0.03 0.02 0.11 0.05 0.013 0.06 0.01 0.007 0.05 0.01 0.007 0.11 0.03 0.015 0.05 0.01 0.01 8.36 6.30 7.802 indicating a higher volatility for this element. The problem with Hg is reproduc- ibility, rather than failure to detect a portion of the total emitted element. The quantity of Hg appearing in the trapped tar and solids varies dramatically from one run to another. In some instances the apparent amount of Hg in one stream or other exceeds the quantity fed in with the coal. To aid in formulating gasifier perform- ance correlations, a simple mathemati- cal model of the fluidized bed gasifier has been developed which considers the gasification process in three stages: instantaneous devolatilization of coal at the top of the fluidized bed, instanta- neous combustion of carbon at the bottom of the bed, and steam/carbon gasification and water gas shift reaction in a single perfectly mixed isothermal stage. The model is significant in and of itself, but its particular importance to the project is that it enables the specification of gasifier conditions required to produce a feed to the acid gas removal system with a predeter- mined flow rate and composition. Using optimal parameter values, the model was run for all gasifier runs and gave excellent predictions of carbon conversion, dry make gas flow rate, and the production rate of all major gases. Figure 4 shows an example. The model does a good job of correlating data on the evolution of individual species and may be used to predict the composition of the gasifier make gas for a specified set of reactor conditions, and also to study the effects of individual reactor variables on yield. Results from the acid gas removal system show that refrigerated methanol is an effective solvent for cleaning gases produced by coal gasification. COa, COS, and H2S can be removed to sufficiently low levels with proper choice of operating conditions and effective solvent regeneration. The presence of several trace sulfur compounds, mercaptans, thiophenes, organic sulfides, and CS2, complicates the gas cleaning process. These com- pounds were found to distribute among all exit streams from the AGRS. Since no provision was made to treat these sulfur gases, they may be emitted to the atmosphere and must be dealt with to avoid significant environmental prob- lems (see Table 2). A wide variety of aliphatic and aromatic hydrocarbons are present in the gas stream fed to the AGRS. The aliphatic hydrocarbons, from methane to butane, cover a wide range of solubilities. Their presence in all AGRS streams must be anticipated to prevent their emission to the atmosphere. While a wide range of simple aromat- ics were identified in the gas stream fed to the AGRS, essentially no polynuclear aromatic compounds were found. Apparently, the gas quenching process effectively removes these compounds from the gasifier product gas. However, significant quantities of simple aromatics were found to accumulate in the recirculating methanol increasing the ------- Table 6. Quantitative Analysis of Sulfur Species* (Tar Sample, Run GO-69B) No. Compound 1 Thiophene 2 Methylthiophenes 3 Cz-thiophenes 4 C3-thiophenes 5 Benzothiophene 6 Ci-benzothiophenes 7 Cz-benzothiophenes 8 C3-benzothiophenes 9 Dibenzothiophenes 10 Naphthothiophenes 1 1 Phenanthrothiophenes 12 Naphthobenzothiophenes Total *wt% Table 7. Water Analyses* GO-69B GO-70 GO-76 PCS PCS Trap Phenols 870 637 1250 Cresols 690 398 693 Xylenols 230 881 161 Organic extractables 1620 2040 *mg/l Table 8. Water Analysis for All Runs* PCS water Ammonia 700 Carbon 725 Chloride 20 COD 1,500 - 3,OOO Cyanate 500 Cyanide 45 Fluoride 5 Nitrogen 600 pH 7.7 Phenolics 20O - 400 Sulfate 35 Sulfite 15 Thiocyanate 50 TOC 400 - 600 TVC 325 Concentration 0.01 0.02 0.03 0.03 0.13 0.05 0.06 0.05 0.09 0.08 0.06 0.09 0.70 GO-76 GO-78 PCS Trap 220 1584 166 783 97 510 460 1900 Trap water 6,000 3,200 40 6,000 - 10.000 2.000 - 5.000 25 - 200 10 6.000 8.5 6OO - 1,100 40 - 300 40 250 2,600 1,500 pollutants throughout the AGRS. The nature and design of these polishing steps will depend on the required discharge levels of specific pollutants manufactured in the gasification process. As a part of the AGRS research program, a mathematical model of the absorber was developed. The model assumes adiabatic operation of the column and uses appropriate mass and energy balances, physical and transport property information, and phase equi- librium relationships to simulate steady- state behavior of the absorber. The model was tested by comparing its predictions with experimental data for runs made with a mixture of nitrogen and CO2 only (syngas runs) and with reactor make gas from the PCS system. For the syngas runs the measured and predicted liquid temperature profiles showed excellent agreement. For runs using reactor make gas there was very good agreement between the predicted and experimental concentrations for most compounds. However, experimen- tal data and model predictions for H2S, C2H4, and CaHe show some small differences. These differences were bllUWil l\J UG fclcJLcU LU II Ic ldl*L 11 Id 1 lilt? entering methanol was not adequately stripped and contained some H2S (input data to the model assumed that clean methanol was fed to the column). The difference between the values for C2H4 and C2He may be related to the fact that Henry's law does not provide an accurate correlation of vapor/liquid equilibrium data for these species. Figure 5 gives examples. ^ *mg/l (except pH); values shown are averages or minimum-maximum values. potential for their discharge to the atmosphere. Provision must be made to purge the solvent of these compounds or to remove them prior to the AGRS through cold traps. Table 9 shows results of a GC/MS scan of a sample of the methanol solvent taken at the stripper exit after Run GO-76. In an environmental context, use of refrigerated methanol as an acid gas removal solvent for coal gas cleaning must be accompanied by safeguards to avoid several potential problems. The need for polishing steps on any discharge stream appears necessary because of the wide distribution of several potential ------- 2.6 " §2.0 1.4 1.4 1.6 1.8 2.0 2.2 2.4 Experimental, Ib/hr 2.6 Figure 4. Predicted vs. experimental production rate of H2 from gasification of New Mexico coal. Table 9. AMI-57/GO-76 Stripper Exit Methanol 1 . 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 1 7. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 3 1 . 32. 33. 34. 35. 36. S at'd hydrocarbon CO2 CtHg isomer Tetramethylsilane Trichlorofluromethane isomer Unknown Freon 113 Cyclopentadiene CeH-iz isomer isomer isomer Benzene C7Hi4 isomer C?Wie isomer C7Hie isomer C7Hi 2 isomer isomer isomer Unknown hydrocarbon Toluene Methyl thiophene isomer isomer isomer Ca/Ae isomer Cs/Ae isomer (trace) CeHi4 isomer (trace) Hexamethyl cyclotrisiloxane CgA/20 isomer Cg//is isomer Ethyl benzene Xylene (M.P) Styrene Xylene (O) CgHia isomer CgA/20 isomer Table 9. (Continued) 37. C3 alkyl benzene 38. CioHzz isomer 39. Unknown hydrocarbon 40. Unknown hydrocarbon 41. Ci i#24 isomer 42. C3 alkyl benzene 43. C3 alkyl benzene 44. CioHzz isomer 45. CwHzs isomer 46. CA alkyl benzene 47. Ci(//22 isomer 48. CioW2o isomer 49. Unknown hydrocarbon 50. C9#io 51. CgHa isomer 52. Alkyl benzene isomer 53. Ci i/y^ isomer 54. CsHwO isomer 55. CnHZ4 isomer 56. CaHioO isomer 57. Unknown siloxane 58. Unknown siloxane 59. Unknown siloxane 60. Ci tHao isomer 61. CuHw isomer 62. Unknown 63. CisW32 isomer 3.0- (91.4) ,2.0 (61 t 1.0 5 ln = -34.07°F(-36.71 (30.5) COZ H2S COS MEOH H2 CO N* CH4 C*H4 C2H6 Inlet* 20. 150 0.300 0.010 32.570 21.230 18.790 6.200 0.310 0.510 Outlet* trace 0.022 0.001 trace 43.400 25.790 23.010 7.530 0.062 0.112 Predicted Outlet* 0.257 0.014 41.155 26.800 23.748 7.576 0.163 0.281 *AII Values in Mole Percent -35 -25 -15 -5 5 (-37) (-32) (-26) (-21) (-15) Solvent Temperature, °F t°C) Figure 5. AMI-43/GO-68B ONDA correlation. 7 &U.S. GOVERNMENT PRINTING OFFICE: 1983/659-095/559 ------- J. K. Ferrell, R. M. Felder. R. W. Rousseau. R. M. Kelly, M. J. Purdy. andS. Ganesan are with North Carolina State University, Raleigh, NC 27650. N. Dean Smith is the EPA Project Officer (see below). The complete report, entitled "Coal Gasification/Gas Cleanup Test Facility: Volume III. Environmental Assessment of Operation with New Mexico Sub- bituminous Coal and Chilled Methanol," (Order No. PB 83-107 417; Cost: $19.00, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Industrial Environmental Research Laboratory U.S. Environmental Protection Agency Research Triangle Park, NC 27711 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati OH 45268 Postage and Fees Paid Environmental Protection Agency EPA 335 Official Business Penalty for Private Use $300 PS 0000329 ------- |