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Petrological characteristics and trace elements partitioning of gasification residues from slagging entrained-flow gasifiers in Ningdong, China Yuegang Tang, Xin Guo, Qiang Xie, Robert B. Finkelman, Shoucheng Han, Binbin Huan, and Xi Pan Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b03647 • Publication Date (Web): 12 Feb 2018 Downloaded from http://pubs.acs.org on February 15, 2018

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Petrological characteristics and trace elements partitioning of gasification residues from slagging entrained-flow gasifiers in Ningdong, China Yuegang Tang,*† Xin Guo,† Qiang Xie, ‡ Robert B. Finkelman,§ Shoucheng Han,† Binbin Huan,† and Xi Pan† † College of Geoscience and Surveying Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China ‡ School of Chemical & Environmental Engineering, China University of Mining & Technology (Beijing), D 11, Xueyuan Road, Haidian District, Beijing 100083, P. R, China § Department of Geosciences, University of Texas at Dallas, Richardson, TX, USA Abstract: In order to better understand the petrological characteristics of gasification residues and trace elements partitioning during entrained-flow gasification processes, oil-immersion microscopy, X-ray diffraction (XRD), scanning electron microscopy combined with an energy dispersive detector (SEM-EDX), inductively coupled plasma mass spectrometry (ICP-MS), Milestone DMA-80 Hg analyzer and pyrohydrolysis in conjunction with a fluorine ion-selective electrode, were employed to study samples collected from three commercial-scale slagging entrained-flow gasifiers in Ningdong, China. Petrological analysis indicated that dominant organic components in the residues were inertiods, fusinoids, tenuinetworks, and crassisnetworks. In addition, vitroplast and cenosphere were observed in coarse residues produced from water-slurry coal gasification. The main inorganic components were quartz, calcite, spinel, and a large amount of Al-Si glass. After gasification, most trace elements were significantly enriched in the residues. Critical trace elements, Li, Be, Sc, V, Cr, Sr, REEs, Th, Nb, Ta, Zr, and Hf were enriched in the coarse residues. Critical trace elements, Zn, Sb, Pb, and Bi were enriched in the fine residues, which was in accord with volatilization-condensation mechanism. The partitioning of trace elements was elucidated based on their relative enrichment (RE). Fluorine showed various partitioning behavior in three gasification processes. Mercury was the most volatile element. Generally, trace elements from the GE gasification process were less volatile, elements from the OFB gasification were more volatile, and the volatile behavior of trace elements from the GSP was intermediate. Key words: coal; gasification residue; petrological characteristics; partitioning of trace elements

1. INTRODUCTION Coal is a complex flammable sedimentary rock consisting primarily of macerals (vitrinite, inertinite, and liptinite), discrete organic components derived from the precursor plants, and mineral matter containing a range of crystalline minerals and non-mineral inorganic elements1-3. Coal is still the dominant fuel in China, accounting for 62% of the primary energy consumption in 2016, although this is historically the lowest percentage4, this fossil fuel will continue to be a major source of energy in China and around the world for the foreseeable future5. Utilizing coal cleanly and effectively will be increasingly important as countries try to mitigate climate change and other environmental and health impacts caused by coal use. Liquefaction is one method of using coal as an energy source while minimizing its environmental and human health impacts. However, liquefaction of coal usually requires higher quality coal which are becoming 1

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scarcer6. Gasification is another option that utilize coal and aims for “zero emissions”. Entrained-flow coal gasification has become one of the leading clean technologies, by reducing particle size and residence time of feed coal in the gasifiers, increasing carbon conversion efficiency compared with fixed-bed gasification and fluidized bed gasification technologies7-9. Coal pyrolysis, which is the devolatilization of coal in an inert atmosphere, is the fundamental process of coal combustion and gasification. Macerals in the coal primarily devolatilize and form char that will be gasified under high temperature and pressure conditions, whereas, mineral matter in the coal transforms into ash that will be removed from the gasifiers (dry-bottom gasifier) where the temperature is lower than the ash fusion temperature (AFT) or become liquid slag at temperature higher than the coal ash fusion temperature (slagging gasifier). Crystalline structures will be developed with downstream if these liquid phases cool slowly, while a mixture of glassy material will be formed with rapid cooling10. The macerals and mineral matter could interact with each other under the rapid and complicated gasification process, and minerals in the char could also act as a catalyst contributing to carbon conversion11. Under ideal conditions, macerals in the coal transforms into usable energy while the slag is removed as a by-product of the mineral matter melting12-14. In the light of the appearance of feed coal, entrained-flow coal gasification technology is divided into coal-water-slurry pressured gasification, such as GE (former Texaco), OMB (Opposed multi-burner gasification technology), and pulverized coal gasification, such as Shell, GSP (Gaskombimat Schwarze Pumpe gasifier) 7, 15, 16. The coal-water-slurry gasifier is furtherly divided into mono-nozzle gasifier (GE, former Texaco) and multi-nozzle gasifier (OMB, opposed multi-burner gasifier) according to the number of the nozzle. The gasifying agents used for the coal-water-slurry gasification is oxygen and for the pulverized coal gasification is oxygen and steam. The coal will be prepared as coal-water-slurry (CWS) before feeding into the coal-water-slurry gasifier. Then feed coal is high-speed injected into the entrained-flow gasifiers where the operating temperature is typically around 1500℃ with the gasification agents through the nozzles 16, 17. Atomized coal particles (-75µm) simultaneously undergo drying, devolatilization, and gasification within a few seconds18, 19. The entrained-flow gasifiers described in this paper are slagging gasifiers. Gasification residues can be divided into two types based on the formation process: coarse residue and fine residue. Molten ash particles are deposited on the internal wall of the gasifier and then form a layer of solid slag. Liquid slag flows along the furnace wall under the force of gravity and out of the gasifier into a water-quench section and then to the lock-hopper where the coarse residue is collected. The fine residue is removed from the filter of the gasifier and black water from the quench section20, 21. Figure1 shows the schematic process of entrained-flow gasification. Previous studies22-24 have shown that the coarse residue is a vitreous, dense, and abrasive solid that has relatively low carbon content but high carbon reactivity compared to the fine residue, while the fine residue consists of irregular particles with a higher level of residual carbon and a relatively high developed pore structure, having graphitized in the high-temperature reducing atmosphere. The pore structure of the residual carbon in the fine residues is the main factor for absorbing trace elements during the gasification processes25-27. Compared with studies of the petrographic classification of fly-ash components from coal combustion and co-combustion28-40, research on the petrographic characteristics of coal gasification residue is relatively rare21, 41-48. Two distinct systems were used to describe petrological characteristic of fly ash. The nomenclature used at the University of Kentucky Center for Applied Energy Research28, 33, 35-37, 39, 49 emphasizes the forms of 2


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the carbon, as well as the type of inorganic matter, in the combustion fly ash, and not the overall texture. A system proposed by Bailey et al.50 and modified by Lester et al.29 emphasizes the textural description of the char structure. This classification of char is the basis for the system adopted by the International Committee for Coal and Organic Petrology (ICCP). Bielowicz41 studied petrographic characteristics of lignite gasification chars on basis of this classification scheme (Lester et al.29). A new system for the petrographic classification of fly-ash components has been developed after three round robins exercises successively performed by petrographers involved in this task by the Fly-Ash Working Group, Commission III of the ICCP30. In recent years, several attempts have been made to describe the behavior of mineral matter during coal gasification2, 7, 13, 31, 51-67. Matjie et al.51, 53-61, 67 systematically investigated the mineralogical characteristic of coal and coal ash from Sasol coal gasification. Using a combination of SEM (scanning electron microscopy), HR-TEM (high resolution transmission electron microscopy), XRD (X-ray diffraction) and Roman spectroscopy technologies, a number of high temperature solid crystalline phases i.e. anorthite, cristobalite, diopside, goethite, mullite, and muscovite were identified in the gasification residues derived from high volatile bituminous coals31, 43, 53, 55 . Amorphous material bearing a large amount Ca-Si-Al-Fe is the main composition of the residues. Studies on trace elements in coal and coal combustion are abundant, but there has not been an explicit classification of the volatile behavior of trace elements during coal gasification25-27, 68-73. Trace elements emitted from integrated gasification combined-cycle (IGCC) in the vapor phase may become air pollutants or they may contaminate soil and groundwater as part of the emitted residues. Clarke26 summarized the fate of trace elements during coal combustion and gasification, indicating that trace elements partitioning behavior during coal gasification is similar to their distribution in the combustor. Barium, Be, Cr, Cu, Mo, Sr, and U belong to Group 1, Group 2 elements are concentrated more in fine residues compared with coarse residues, such as Sb, Zn, As, Tl, and Pb. Group 3 elements mainly volatilize during the coal combustion process and are concentrated in the vapor or gas phase, such as Hg. Meij74 used relative enrichment factor to describe trace elements characterization in coal-fired power plants. The relative enrichment was cited by Duchesne and Hughes75 to assess the partitioning of inorganic elements in pilot-scale and demonstration-scale entrained-flow gasifiers. Studies26, 27, 69, 71, 75 show that partitioning of trace elements are affected not only by their modes of occurrences but also by gasification conditions. Hence, the objective of this work is: (1) to characterize the microstructure of organic matter in coarse and fine gasification residues from three different commercial entrained-flow gasifiers; (2) to characterize minerals and amorphous material in residues; and (3) to elucidate the portioning of trace elements during entrained-flow gasification processes.

2. EXPERIMENTAL SECTION 2.1. Samples. Ten samples consisting of three feed coals, four coarse residues, and three fine residues were collected from three commercial-scale entrained-flow gasifiers from the Ningdong Energy and Chemical Industry Base, Ningxia Hui Autonomous Region, China 76. The three different gasification technologies are OFB (Opposed four-burner gasification technology), GE (former Texaco) and GSP (Gaskombimat Schwarze Pumpe gasification technology), of these the OFB and GE are water-slurry coal gasification processes and the GSP is a pulverized coal gasification process. Feed coals (-75µm) characterized by high volatile matter are bituminous coals from the Jurassic 3


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Yan’an Formation. The coal was made into a coal-water-slurry (CWS) and pulverized grains before the gasification processes. Then feed coal and gasifying reagents oxygen (oxygen and steam) were fed into the gasifiers simultaneously resulting in synthesis gas (methane) as well as gasification by-products, coarse residue and fine residue. According to the Chinese standard GB/T6678-200377, the feed coals, coarse residues, and fine residues were sampled from the continuously-running conveyor belt, outlet of the lock-hopper, and black water filter of each gasifier (Figure1), respectively. The feed coals for the OFB and GE were from the Yangchangwan mine (YCW) and the feed coal for the GSP was from the Meihuajing mine (MHJ). Samples from the OFB, GE, and GSP were identified as series 1 (Coal-1, CR-1, and FR-1), series 2 (Coal-2, CR-2-A, CR-2-B, and FR-2), and series 3 (Coal-3, CR-3, and FR-3), respectively. CR-2-A and CR-2-B were similar in origin but different in particle size. The CR-2-A contains more particles with the particle size ＞ 5 mm than the CR-2-B. Sample information and gasification operation parameters are shown in Table 1. 2.2. Analytical Methods. Proximate analysis was performed on the feed coals and gasification residues following ASTM standards D3173-1178, D3174-1179, and D3175-1180, respectively. The total sulfur was determined according to the ASTM standard D3177-02 (Reapproved 2007)81. Ultimate analysis was determined following ASTM standard D5373-0882. Ash fusion temperature of the feed coal ash were performed according to ASTM Standard D1857M-0483. The feed coals and the coarse residues were ground into a fine powder (20 mesh) following ASTM Standard D5671-95 (Reapproved 2011)84, mounted in resin and then polished to meet the requirements of microscopic analysis, the particle size of the fine residue had already met the requirements of microscopic analysis without further grinding. The loss on ignition (LOI) was performed following the ASTM standard D7348-1385 heating the samples to 950 ℃. The optical petrological characterization of the samples and coal maceral nomenclature follows the International Committee for Coal and Organic Petrography system86-88, using a magnification of 500 ×, oil-immersion, and reflected-light optical microscopy. Quantitative analysis of maceral and mineral composition of the feed coal was determined optically by counting at least 500 points for each sample pellet. The components in the gasification residues was characterized on the basis of the classification scheme developed for the Combustion Chars-Commission III Combustion Working Group of the International Committee for Coal and Organic Petrology29, 30, 39(Table 2). The maximum reflectance of vitrinite (Ro, max %) was determined according to ASTM Standard D2798-2011a89, using a Leitz Orthoplan microscope equipped with a Daytronic mainframe 9005 spectrophotometer. The average random reflectance of residual carbon in the residues was determined using the same standard and method as for the feed coals. Samples of the feed coals, the coarse residues, and the fine residues were prepared as polished sections. A TESCAN-VEGA \\ LMU scanning electron microscope (SEM) with associated energy-dispersive X-ray (EDX) element analyzer was used on the polished sections according to Chinese standard GB/T17361-199890 to determine the components in the feed coals and gasification residues. The mineral components of the samples were also analyzed using XRD (D/max-2500/TTR powder diffractometer) following Chinese oil and gas industry standard SY/T 5163-201091. All solid samples were crushed and ground to pass 200-mesh sieve for geochemical analysis. X-ray fluorescence spectrometry (XRF, AB-104L, PW2404) was used to determine the major element oxides including SiO2, Al2O3, CaO, K2O, Na2O, Fe2O3, MnO, MgO, TiO2, and P2O5 of the feed coal ash as well as the residues at 815 °C. Forty-six trace elements were determined in this study, 4


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of which forty-four trace elements were determined by inductively coupled plasma mass spectrometry (ICP-MS, ELEMENT XR), based on the methods for coal and coal-related materials outlined by Dai et al.92 The content of Hg was determined using DMA-80 Mercury Analyzer as outlined by Dai et al.93 and fluorine was determined using pyrohydrolysis in conjunction with a fluorine ion-selective electrode as outlined by Wang et al. 94

3. RESULTS AND DISCUSSION 3.1. Chemical Analyses. Proximate and ultimate analyses results (Table 3) basically fitted the previous studies95. The ash yield of the feed coals was between 10.21 and 12.70 (wt. %, d), and the total sulfur content was between 0.47 and 0.90 (wt. %, d). The coal used for gasification were middle-low ash and low sulfur according to the classification for quality of coal in China (GB/T 15224. 1-9496 and GB/T 15224.2-199497). The volatile matter ranged from 31.77 to 34.26 (wt. %, daf). The moisture content of the fine residues (Table 3) was extremely high. As mentioned before, the fine residues were collected from the black water filter (Figure 1), so external water may not have been removed completely when drying the samples. The volatile matter in the fine residues was distinct, of which volatile matter in FR-2 was highest (Table 3). Carbon content (Cd, wt %) of the fine residues were relatively high compared with that in the coarse residues (Table 3), which is consistent with the results that unburned carbon in the fine residues was higher compared to the coarse residues21, 24. Major elements (reported as oxides, determined by XRF analysis) in samples are shown in Table 4. Proportions of alkaline oxides (CaO, MgO, Fe2O3) in Coal-1 and Coal-2 were higher than that in Coal-3, resulting in ash fusion temperature (AFT) of Coal-1 and Coal-2 was lower than that of Coal-3. This is due to free silicon oxide that could combine with alkaline oxides and generate eutectic crystals lowering the AFT98. 3.2. Mineralogical characteristics. 3.2.1. Mineral matter in the feed coals. The minerals determined by XRD in the feed coals (Table 5) indicates that the feed coals consisted primarily of clay minerals (9.4-18.9, wt. %), followed by quartz (3.5-7.9, wt. %), with minor amounts of calcite (1.2-2.5, wt. %), pyrite (0.4-1.5, wt. %), and siderite (0.9-1.0, wt. %). Minerals in feed coals were “included minerals” occurring in intimate association with the coal matrix. Because ‘excluded minerals’ occurred as rock fragments or as cleat and fracture fillings may had been removed when the feed coals were prepared. Examples of, minerals determined by the SEM-EDX are shown in Figure3. Calcite determined in Coal-1 occurred in the cell structure of fusinite (Figure 2 a), and clay observed in Coal-1 occurred in bands (Figure 2 b). Barite (Figure 2 c) observed in Coal-3 occurred as irregular grain, and gypsum (Figure 2 d) observed in Coal-3 was euhedral crystals, but the content of barite and gypsum were too low to be determined by XRD. 3.2.2 Mineralogical characteristics of gasification residues. According to the results from XRD (Table 5), gasification residues consisted of a large amount of Al-Si glass (amorphous phase), followed by clay minerals, calcite, and quartz. Examples of, inorganic matter determined by SEM-EDX are shown in Figure 3. In our residue samples, the quartz (Figure 3 a, and b) probably represented the unreacted quartz in the feed coals. During coal gasification, mineral particles will be released as the coal particle crushing, and molten ash could capture the quartz particle which was relative small and light in the feed coal. These quartz particles could be determined in the residues (Table 3) because the ash fusion temperature (AFT) of quartz (1800 ℃) is higher than the temperature in the gasifiers1, 3, 99.SEM observation showed the Al-Si glass (amorphous phase) occurred as irregular aggregates and the quartz were set in the Al-Si glass (Figure 3 a, and b, dark 5


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grey). This phenomenon indicated that some larger mineral particles may be only partially melted and form ash particles with non-spherical shapes due to the short residence time in the high temperature zone71. During coal gasification processes, quartz will also take part in the formation of silicates with other components (e.g. alkaline oxides) or minerals (e. g. pyrite, and siderite) when temperature is higher than 1300 °C100. It is unreasonable to determine calcite in gasification residues because calcite in coal will disintegrate when heating at temperature higher than 900 °C. However, calcite was identified in both the coarse and fine residues (Table 5). Kim and Kazonich10 indicate that crystalline structures will be developed with downstream if liquid phases cool slowly. Therefore the calcite determined in the residues probably formed from recrystallization during residues cooling1, 54, 55, 99. Moreno et al.101 also reported that calcite in coal fly ashes when they characterized European pulverized coal combustion fly ashes. Pyrite is the most common sulfide mineral in coal102, the thermal transformation of which has been widely studied103-105. Iron-bearing minerals may react to form discrete iron oxide particles when heating106. Hematite (Fe2O3) and magnetite (Fe3O4) are typically the main products of the oxidation of pyrite and siderite through a series of complex reactions105, 107. In our samples, Fe-oxide was observed by SEM-EDX in CR-1 and CR-2-A (Figure 3 c and d). In our study pyrite was identified in CR-2-B and FR-3 (Table 5). This may be explained by that coal particles fed into coal gasifiers had its own composition and internal texture, which provided different opportunities for them to interact with gasifying agents57. So it is possible to consider that pyrite occurred in intimate association with the coal matrix may still be present in gasification ash31. During slagging entrained-flow coal gasification processes, minerals transformed to ash primarily and then the ash melted to form liquid slag at the temperature higher than AFT106. Metakaolin transformed from kaolinite may interact with other elements released from mineral matter, such as Ca, Na, K, or Fe, to produce a number of new Al-Si glass54, 99, 108, 109. Figure 3 f shows the clay minerals in CR-2-B, in this study it is difficult to identify whether the clay minerals was from the feed coal or from the recrystallization during residues cooling. In our residue samples, a large amount of Al-Si glass were observed by SEM-EDX (Figure 3 a, b, and f). It was indicated from Table 5 that Al-Si glass (amorphous material) ranged from 78.5 to 89.2 (wt, %) in the coarse residues and from 85.4 to 88.1 (wt, %) in the fine residues. Comparing Figure 3 a with Figure 3 e, it was obvious that the Al-Si glass (amorphous material) in the CR-1 were irregular and grey (Figure 3 a), and in the FR-1 were spherical with bright grey (Figure 3 f). In addition, Fe and Si which were released from minerals, such as pyrite, siderite, and kaolinite, could form Fe-Si (Figure 3 g). Sulfur was determined in CR-3 (Figure 3 h), which was probably formed in a reducing environment in the GSP gasifier. Celsian (Figure 3 i) which may be transformed from barite in Coal-3 was determined in the CR-3. 3.3 Petrological characteristics. 3.3.1 Petrological characteristics of the feed coals. Petrological analysis of the feed coals (Table 6) show that content of vitrinite in the feed coals ranged from 49.8-52.9 (Vol. %), inertinite from 43.3-46.4 (Vol. %), and liptinite from 1.5-3.0 (Vol. %), with a low mineral matter content of 1.8-2.4 (Vol. %). Collodetrinite (25.0-27.4 Vol %, Figure3 a) was the main vitrinite maceral and semifusinite (22.5-24.6 Vol %, Figure 2 b) was the main inertinite maceral. The relatively high content of inertinite could induce burnout problems54, however a high inertinite content is advantageous when gasifying in the entrained-flow gasifiers because it suppresses excessive caking and swelling110. The max reflectance of vitrinite ranges of the feed coals were from 6


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0.50 to 0.57 % (Table 6). The max reflectance of inertinite in feed coals were 1.15 %, 1.56 %, and 1.90 % (Table 6). 3.3.2 Petrological characteristics of the residues. Macerals and minerals were altered with the rapidly increasing temperature in the installations, to a peak temperature of 1250-1400 °C14, 21. In coal combustion, unburned carbon in fly ash is measured by loss on ignition (LOI), although the LOI is usually higher than the actual content of unburned carbon in coal ash or residue due to the CO2 released from carbonates, structural water released from clay minerals, etc39. Unburned carbon in the ash/ residues indicates inefficiency of the coal utilization process and will impede its utilization in cement or ceramic industries. In our study, we also used LOI to represent residual carbon in gasification residues. LOI in CR-2-A, CR-2-B, CR-3 and FR-1, FR-2, and FR-3 were relatively high (Table 4). Carbon content (Cd, wt %) in CR-2-B, CR-3 and FR-1, FR-2, and FR-3 were correspondingly high (Table 3). Notably FCd (about 18%) of the fine residue (FR-1) from OFB gasifier was lower compared to FCd (more than 30%) of the fine residues from GE and GSP gasifiers. It is the same for residual carbons too (LOI in Table 4). The residual carbon in the residues from OFB were relatively lower than ones from other two gasifiers (Table 3), this is due to structure of the gasifier. OFB gasifier has four nozzles which could inject the feed coals from four different directions with oxygen (Table 1). Gas flows from four directions could form the impinging streams which could intensify heat and mass transfer, and consequently facilitate gasification reaction 16. It should be considered to reuse residual carbon in residues to reduce coal resource wasting and to improve quality of residues which will be used for cement and ceramic39. In Ningdong Energy and Chemical Industry Base, Ningxia, China, 4.737 million tons of coal are consumed for coal gasification every year resulting in 1.046 million tons of residues (the data was from the annual statistical data). Residual carbon should be taken attention to its added-value application, like preparing carbon nanotubes, and active carbon. The petrological analysis of the gasification residues is shown in Table 8. Examples of different constituents are presented in Figure 4. We classified inorganic matter in the gasification residues into glass (Figure 4 a) and mineroid (Figure 4 a, b, and c). Spinel is a broad category of minerals, including magnetite105, it comes from the decomposition of Fe-sulfides and other Fe-bearing minerals in the feed coals. In CR-1, spinel was formed as delicate dendrites in a glass matrix (Figure 4 b). When counting the percentage of petrological constituents, spinel was classified into the mineroid in our study. In gasification residues glass (Figure 4 a) was the most abundant constituent (Table 7). The dominant organic components were tenuispheres, crassispheres, tenuinetworks, crassinetworks, fusinoids, and inertoids (Table 2 and Table 7). In our residue samples, tenuisphere had a highly porous structure with thin walls (the tenuisphere in Figure 4 d is half round). Tenuinetwork was char with an abundant internal network structure (Figure 4 e). Crassisphere chars (Figure 4 f) were characterized by thick external walls and a strong porosity within the particles. Crassinetwork chars had internal area that were partially porous (Figure 4 g). In our samples, the amount of mixed porous and mixed density particles were low (Table 7, Figure 5 h and k). Fusinoid was unfused particle presenting cellular structure of fusinite (Figure 4 i). The small cavity in fusinoid indicated that it had reacted with gas (Figure 4 i). Fusinoids in the fine residues (0.2-4.2 Vol %) were far less common than that in the coarse residues (3.6-16.6 Vol %). The particles classified as inertoids are fused or unfused, characterized by low porosity. They were usually small fragments (Figure 4 j). Original maceral debris included completely unreacted vitrinite debris and inertinite debris (Figure 4 l). When the feed coals and gasifying reagents (oxygen or oxygen and H2O (g)) were 7


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injected into the gasifiers, not all the feed coal particles could react with the gasifying reagents due to the short residence time. As a consequence, some feed coal debris came down directly without reacting with the oxygen or oxygen and H2O (g). From the data of Cd (%) in Table 3, it could be estimated that about 20% carbon was wasted during OFB gasification process and more than 30% carbon was wasted during GE and GSP coal gasification processes. However, the accurate data of coal debris came down directly without reacting with the gasifying agents need to be study by the microscope and SEM-EDX further. Except for the char types which could be observed in coal combustion fly ash, vitroplast and cenosphere (Figure 4 m, n, and o) were observed in the coarse residues produced from the GE and OFB gasification processes (water-slurry gasification processes). Considering the complex gases in gasifiers, the vitroplast and cenosphere observed in the CR-1, CR-2-A, and CR-2-B may be products of vitrinite or semifusinite with hydrogen, formed similarly to the formation of vitroplast and cenosphere during coal liquefaction111, 112. Currently few research about the origin of residual carbon during coal gasification, this study only supply the petrological characteristics of residual carbon right now. If more data about the origin of residual carbon obtained, it will help to guide adjust the proportions of different macerals of feed coals used for gasification and reduce the organic matter in the residues. 3.4. Partitioning of trace elements. Concentrations of 46 trace elements in the samples were determined (Table 8). The concentration coefficients (CC) for the feed coals are shown in Figure 5. The concentrations of most trace elements in the feed coals were, on average, equal to (0.5< CC < 2) or lower than (CC < 0.5) the average concentrations in Chinese coal70. Strontium (296-345 µg/g) in the three feed coals, Ba (457 µg/g) in Coal-3, and Cu (49.4 µg/g) in Coal-1 were slightly enriched (2< CC< 5) compared to the average values of Chinese coal70. Our SEM-EDX results show that the Ba occurred in barite (BaSO4) in Coal-370. During gasification processes, the coal particles experience complex changes including char formation, agglomeration of melted minerals, and vaporization of volatile elements. Physical and chemical processes, such as turbulence, pollution control devices, and temperature profile in the gasifiers, can affect the distribution of trace elements. After the gasification processes, trace elements in the feed coals migrated into the coarse residues and fine residues unevenly. The results in Table 8 show that the concentrations of the hazardous trace elements (such as Pb, Cr, Cd, Sb, Tl, U, Cu, and F) and critical elements113 (such as Ga, Zn, V, Co, and Ni) in the fine residues were higher than that in the coarse residues. Bunt et al.25 and Yoshiie et al.27 indicated that volatile trace elements tended to go into the gas phase and condensed on the surface of the finer particles during the gas cooling process. Trace elements tended to enrich in smaller particles because finer ones contained more residual carbon which has a greater surface area26, 114, 115. Compared with average values of trace elements in coal ash116, the concertation of Ba in CR-1, FR-1, CR-3, and FR-3 (Table 8) was higher than the average content of Ba in coal ash (980 ± 60 µg/g ) and the concertation of Sr (Table 8) in the seven residues was higher than the average content of Sr in coal ash (730 ± 50 µg/g ), indicating that Ba and Sr were prominently enriched in gasification residues though they were just slightly enriched in feed coals. Thus, the residues from these entrained-flow gasifiers might be utilized for extracting useful alkaline earth metal elements117, 118. In addition, concentrations of trace elements, such as, Co, Ga, In, Sb, Pb, and Zn in FR-1, and Zn, and Pb in FR-2 (Table 8) were higher than their corresponding average concentrations in word hard coal ash, concentrations of other trace elements (Table 8) determined in our study were lower than the corresponding average concentrations in word 8


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hard coal ash116. Trace elements vaporization behavior determines their partitioning in the emission stream to some extent. Trace elements were classified into three groups according to their vaporization behavior during coal combustion26, 119, and Clarke26 proposed that the partitioning behavior of trace elements in the gasification process was similar to that in coal combustion, which was confirmed by Helble et al.120 Barium, Be, Cr, Cu, Mo, Sr, and U belong to Group 1, Group 2 elements are concentrated more in fine residues compared with coarse residues, such as Sb, Zn, As, Tl, and Pb. Group 3 elements mainly volatilize during the coal combustion process and are concentrated in the vapor or gas phase, such as Hg. In order to establish the relationship between the elements in the different process streams of coal combustion, Meij74 used a relative enrichment factor (RE) to classified elements based on their behavior in a coal-fired combustion system. Meij74 normalized concentrations with respect to the ash yield, because the contamination in complex gasification system could affect trace elements enrichment. This relative enrichment was cited by Duchesne and Hughes75 to assess the partitioning of inorganic elements in pilot-scale and demonstration-scale entrained-flow gasifiers. The RE is defined as follows:

RE =

×

①

where, is the trace element concentration in the residues, µg/g; is the trace element concentration in the feed coal, µg/g; A !"#$%&" is the ash yield in the residue, %; A is the ash yield in the feed coal, %.

According to this formula and concentrations of trace elements in the gasification residues, the REs of all our gasification residues were calculated (Table 8).The partitioning of trace elements in residues in these three different gasification processes were different due to the different temperatures, pressures, and gasification conditions (Table 1)25, 26, 121. In the current study, Meij’s classification criteria74, 75 have been adapted to the gasification system in order to compare element classifications for combustion and gasification systems (Table 9). We have defined four Classes of elements based on relative enrichment (RE). Class 1 elements have an RE for the coarse residues which is greater than or equal to 0.7. Trace elements in Class 1 are non-volatile and are slightly enriched in the coarse residues. In the OFB gasification process, 35 trace elements (such as, Be, Sc, V, Cr, Co, Ni, Ga, Sr, Mo, Cs, Ba, REEs, and U) had the RE in the coarse residues greater than 0.7 (Table 8), which shows non-volatile in OFB gasification process (Table 9). Twenty-six trace elements (such as, Be, Cr, V, Sr, U, and REEs) from the GSP gasification process had REs in the coarse residues greater than 0.7 (Table 8), which showed non-volatile in GSP gasification process (Table 9). In the GE process, F was slightly enriched in the coarse residue, which was different from its partitioning in both of the other processes and combustion systems. Temperature, pressure, and reducing condition can all affect the emission of trace elements75. Notably, the partitioning behavior of F contrasts to its behavior in bench-scale experiments by Helble et al.120 where higher volatility was observed in reducing conditions compared to oxidizing conditions. Class 2 elements have an RE for the coarse residues less than 0.7, and an RE for the fine residues greater than 1.3. Trace elements in Class 2 devolatilize and condense in the gasifiers. Volatile 9


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elements preferentially condense on the surface of smaller particles in the gases as cooling occurs. These particles have a greater ratio of surface area to volume26, 114, 115. Enrichment of more volatile elements on the smaller ash particles is also due to the process of vaporization and re-condensation122. Partitioning behavior of Zn, Sb, Pb, and Bi in all three gasification processes was in accord with the volatilization-condensation mechanism (Table 9). Previous investigations123-125 on the characteristics of pulverized coal-fired power plant fly-ash emission reveals that concentrations of certain elements, notably the toxic elements, As, Sb, Zn, Pb, and Cr are systematically enriched in the finer sized fly-ash particulates and, in some cases, on the surface layers of the particulates. In addition, trace elements Cd, In, Re, F, and Tl in the OFB process; Li, Cr, Co, Ga, Rb, Cs, Tl, U, In, Be, Cu, and Cd in the GE process; and Cu, and Ga in the GSP process were grouped in Class 2.These elements corresponded to the elements in Class II in coal combustion behavior26. The partitioning behavior of trace elements during coal utilization, including combustion and gasification are primarily determined by their modes of occurrence. Vejahati et al.71, Yoshiie et al.27, Clarke26 and Xu et al.126 concluded that some elements have an organic affinity and those trace elements (As, Se, Hg, Pb, and Ti) associated with the sulfide minerals tend to vaporize first, and are easily adsorbed on fine particles during ash cooling due to larger specific surface area of the finer particles. We have determined the modes of occurrence of 14 trace elements (Be, V, Cr, Co, Ni, Cu, Zn, Mo, Cd, Sb, Ba, Tl, Pb, and U) in samples from the GSP gasification process using selective chemical leaching. The results showed that part of the Pb was associated with organic matter in the feed coal, the modes of occurrence of which was described by Querol et al.127; Sb, Zn, and part of Pb were associated with inorganic matter, and Xu126 indicated that Pb and Bi were in clay minerals and feldspars and that Sb was in the iron sulfides. With the high temperature in the gasifiers, Pb, Sb, Bi, and Zn vaporized and then condensed on the surfaces of the fine residues during the cooling process. Class 3 elements have an RE for the coarse residues less than 0.7, and an RE for the fine residues between 0.7 and 1.3. Elements in this Class (Table 9) vaporize and then condense on the finer particles, but they also continue to vaporize. This phenomenon can be explained by complex gasification conditions affecting partitioning behavior of elements27, 69, 120, 128, 129. Class 4 elements have an RE for the coarse residues which is less than 0.7and an RE for the fine residues which is much lesser than 1.0. Elements in Class 4 devolatilize but do not condense on the fine residues in the gasifiers. In our study, mercury was the element belongs to Class 4. It is indicated that the volatile behavior of trace elements is affected not only by their modes of occurrence in coal but also by the gasification conditions. Considering the impact on volatile behavior of trace elements from different gasification conditions, it is generally concluded that trace elements from the GE gasification process were less volatile, elements from the OFB gasification were more volatile, and the volatile behavior of trace elements from the GSP was intermediate (Figure 6). Nevertheless, it is noteworthy that gasification temperature in OFB gasifier was not the highest among these three gasifiers, therefore, multi-factor in gasifiers affect the volatile behaviors of trace elements in complicated ways.

4. CONCLUSIONS Petrological analysis indicated that dominant organic components in the residues were inertiods, fusinoids, tenuinetworks, and crassisnetworks. In addition, vitroplast and cenosphere were observed in coarse residues produced from water-slurry coal gasification. The main inorganic components were quartz, calcite, spinel, and a large amount of Al-Si glass. 10


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Concentrations of forty-six trace elements were determined. Although most trace elements in the feed coals are equal to or less than the average values of Chinese coal, some are enriched in the gasification residues. Some critical elements (such as Ga, Zn, V, Co, Ni, and Cu) and hazardous trace elements (such as Cr, Cd, Sb, Tl, U, and F) were enriched in the fine residues compared with Ba and Sr enriched in the coarse residues. The critical elements Ba and Sr are highly enriched compared with their average value in coal ash, which means that the gasification residues from Ningdong could be the utilized for extracting some useful elements. Partitioning of trace elements were summarized according to their volatile behaviors based on their relative enrichment (RE) calculated from the concentration of trace elements in the gasification residues. In this study, critical trace elements, Li, Be, Sc, V, Cr, Sr, REEs, Th, Nb, Ta, Zr, and Hf, showed non-volatile in the OFB and GSP processes. Critical race elements, Zn, Sb, Pb, and Bi were depleted in the coarse residues and enriched in the fine residues in all three gasification processes, which was in accord with volatilization-condensation mechanism. Fluorine were volatile in OFB gasification process, non-volatile in GE gasification process, and more volatile in GSP gasification process. Mercury was the most volatile element in all three gasification processes. Generally, trace elements from the GE gasification process were less volatile, elements from the OFB gasification were more volatile, and the volatile behavior of trace elements from the GSP was intermediate.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS The authors gratefully acknowledge the financial and other support from the National Key Basic Research Program of China (NO. 2014CB238905). The authors also express special and sincere thanks to Professor James C. Hower and Professor Shifeng Dai for their kind constructive suggestions. The authors would like to express great gratitude to Engineer Jianrong Yang for his assistance in the sampling. We appreciate the help of the Analytical Laboratory of Beijing Research Institute of Uranium Geology, Lab of Sinopec Petroleum Exploration and Production Research Institute, Shanxi Coal Geological Bureau and State Key Laboratory of Coal Resources and Safe Mining (CUMTB) for their testing work.

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Figure 1. Schematic process of the entrained-flow gasification.

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Figure 2. Minerals (observed by SEM-EDX) and macerals (observed by reflected light, oil-immersion microscope, and × 500) in the feed coals. a), Calcite filled in cell in Coal-1; b), Clay in Coal-1; c), Barite in Coal-3; d), Gypsum in Coal-3; e), Collodetrinite in Coal-2; f), Semifusinite in Coal-3.

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Figure 3. SEM-EDX results. a), Al-Si glass and quartz in CR-2-A; b), Al-Si glass and quartz in CR-2-A; c), Fe-oxide and Al-Si glass in CR-1; d), Fe-oxide and clay minerals in CR-2-A; e), Clay minerals in CR-2-B; f), Al-Si glass in FR-1; g), Fe-Si in CR-3; h), S in CR-3; i), Celsian in CR-3. 21


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Figure 4. Examples of residual carbon in gasification residues. a), Glass and mineroid in CR-2-B; b), Spinel in CR-2-B; c), Mineroid in CR-1; d), Tenuisphere (Ts) in FR-3; e), Tenuinetwork (Tn) and Crassinetwork (Cn) in CR-3; f), Crassisphere (Cs) in CR-1; g), Crassinetwork in CR-2-A; h), Mixed porous (Mp) and mixed dense (Md) in CR-1; i), fusinoid (F) in CR-2-B; j), Inertoid in CR-1; k), Mixed dense (Md) and Mineroid in CR-2-A; l), Unchanged maceral fragment (fragment of inertinite (I) and vitrinite (V)) in CR-2-B; m), Vitroplast and cenosphere in CR-1; n), Vitroplast In CR-2-A; o), Cenosphere in CR-2-B (reflected light, oil-immersion, and × 500).

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Energy & Fuels

CC＜＜ 0.5

0.5＜＜ CC＜＜2

2＜＜ CC＜＜5

Figure 5. Concentration coefficients (CC) for the feed coals. CC, ratio of investigated samples vs. average concentrations in Chinese coal.

Figure 6. Relative enrichment of trace elements in gasification residues (data of coarse residue used for GE was CR-2-A). 23


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Energy & Fuels

Table 1 Sample information and gasification operation parameters Samples Feed

Status of the

Gasification

Feed coal

feed coal

agents

Mine

Number of

Temperature

Pressure

nozzle

(℃)

(MPa)

CWS

Oxygen

YCW

OFB

4

1300

3.8

CWS

Oxygen

YCW

GE

1

1250

4.3

MHJ

GSP

1

1350-1450

3.8-4.0

Gasifiers

Residue

coal Coal-1 CR-1 FR-1 Coal-2 CR-2-A CR-2-B FR-2 Coal-3 CR-3 FR-3

PC

Oxygen+ Steam

CWS: coal-water slurry; PC: pulverized coal; CR: coarse residue; FR: fine residue. YCW: Yangchangwan mine; MHJ: Meihuajing mine. OFB: Opposed four-burner gasification technology; GE: former Texaco gasification technology; GSP: Gaskombimat Schwarze Pumpe gasification technology.

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Table 2 The classification system for combustion chars [27] Char

Description

Tenuisphere

Spherical to angular, porosity > 80%, > 50% of wall area > 3 µm.

Crassisphere

Spherical to angular, porosity > 60%, > 50 % of wall area > 3 µm.

Tenuinetwork

Internal network structure, porosity> 70%, > 50% of wall area < 3 µm.

Crassinetwork

Char with internal network structure, porosity > 40%, > 50% of wall area > 3 µm.

Mixed porous

Char with fused and unfused parts, porosity > 60%. > 25% unfused (otherwise it would be Ceno-or Net-) but < 75% (if > 75% unfused, it would be inertoid or solid/fusinoid).

Mixed dense

Char with fused and unfused parts, porosity 40–60%. > 25% unfused (otherwise Ceno or Net) but < 75% (if so, it would be inertoid or solid/fusinoid).

Inertoid

Dense, porosity 5–40%, can be either fused or unfused.

Fusinoid/Solid

Inherited cellular fusinite structure or solid particle with < 5% porosity.

Mineroid

Particle with > 50% inorganic matter.

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Table 3 Results of proximate, ultimate analyses, and sulfur for samples (wt. %). Samples

Mad

Coal-1

12.20

Coal-2

9.86

Coal-3

13.43

CR-1

0.01

CR-2-A

0.18

CR-2-B

1.53

CR-3

1.00

FR-1

32.68

FR-2

35.06

FR-3

15.98

Ad

V

12.7

32.4

0

5a

10.2

31.7

1 11.53 97.3 5 97.1 8 89.3 7 95.2 1 81.8

7

a

34.2 6

a

0.31b 1.74 b

2.76 b

0.88 b

0.36

9

b

57.2

10.0 b

2

1

65.0

3.69

3

b

FCd

St, d

Sp, d

Ss, d

S*o, d

54.85

0.57

0.39

0.02

0.16

58.02

0.47

0.28

0.02

0.17

54.21

0.90

0.62

0.02

0.25

3.03

0.16

0.12

0.02

0.02

1.62

0.18

0.10

0.04

0.04

7.87

0.20

0.13

0.04

0.03

4.23

0.52

0.10

0.03

0.39

18.28

0.36

0.10

0.12

0.14

32.77

0.40

0.14

0.14

0.12

31.28

0.62

0.15

0.12

0.35

Cd 68.30 69.74 69.00 2.09 2.23 10.15 3.89 16.20 37.55 34.09

Cdaf

Hdaf

Ndaf

So, daf

78.24

3.96

0.92

0.18

77.67

4.07

0.89

0.19

77.99

4.32

1.07

0.29

78.87

3.40

5.28

0.75

79.08

6.38

4.96

1.41

95.48

2.73

1.13

0.26

81.21

2.71

2.92

8.11

89.45

1.55

0.77

0.76

87.77

1.68

0.72

0.29

97.48

0.17

0.49

0.99

M: moisture; A: ash; V: volatile matter; FC: fixed carbon; St: total sulfur; Sp: pyritic sulfur; Ss: sulfate sulfur; So: organic sulfur; C: carbon; H: hydrogen; N: nitrogen; O: oxygen. ad: air-dried basis; d: dry basis; daf:, dry and ash-free basis. a

dry and ash-free basis; b dry basis; * by difference.

27


O*daf 16.70 17.18 16.33 11.70 8.17 0.40 5.05 7.47 9.54 0.87

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Table 4 Major elements (determined by XRF analysis) and LOI in the feed coals and residues (wt, %) and coal ash fusion temperature. Samp les Coal1 Coal2 Coal3 CR-1 CR-2 -A CR-2 -B CR-3 FR-1 FR-2 FR-3

Si O2

Al2 O3

4.3

1.7

3

0

6.4

2.0

2

8

6.5

2.8

4

1

37. 95 24. 42 23. 98 48. 88 31. 57 22. 08 34. 41

16. 21 10. 61 10. 38 19. 50 15. 54 10. 77 14. 22

Ti O2 0. 10 0. 14 0. 16 0. 69 0. 47 0. 47 0. 83 0. 73 0. 52 0. 69

Ca O 1.6 2 1.8 8 1.3 1 14. 66 10. 65 10. 99 7.0 1 10. 61 9.0 6 5.6 1

M gO 0. 68 0. 71 0. 66 5. 42 3. 92 4. 01 2. 89 5. 72 4. 58 2. 90

Fe2 O3

K2O

Na2 O

1.82

0.19

0.30

1.93

0.26

0.33

1.69

0.24

0.22

1.34

2.75

0.83

1.66

0.80

1.61

7.64

1.56

1.15

8.97

1.31

3.09

6.10

0.93

2.05

5.49

1.24

1.05

13.5 0 9.90 10.5 5

P2 O5 0. 01 0. 02 0. 06 0. 05 0. 04 0. 04 0. 17 0. 09 0. 08 0. 37

DT

HT

MnO2

LOI

0.04

89.18

1150

1170

1180

1190

0.04

86.14

1150

1160

1170

1180

0.02

86.12

1180

1220

1230

1240

0.30

6.52

0.23

36.78

0.24

36.76

0.10

9.68

0.19

21.71

0.14

43.12

0.06

33.41

DT: deformation temperature; ST: softening temperature; HT: hemispherical temperature; FT: flow temperature. LOI: loss on ignition.

28


（℃）

ST（℃）

（℃）

FT（℃）

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Table 5 Mineralogical results of the feed coal and residue samples using XRD analysis (wt, %). Minerals Samples

Coal-1

Amorphous phase

Quartz

Orthoclase

Calcite

Pyrite

Siderite

Clay minerals

4.3

-

2.5

0.6

0.9

9.4

82.3

Coal-2

3.5

-

1.2

0.4

1.0

10.2

83.7

Coal-3

7.9

0.4

1.2

1.5

-

11.9

77.1

CR-1

5.2

1.0

3.6

-

-

1.0

89.2

CR-2-A

5.3

-

7.8

-

-

8.4

78.5

CR-2-B

5.6

-

10.5

1.7

-

7.8

74.4

CR-3

7.3

-

5.1

-

-

4.6

83.0

FR-1

3.1

-

4.3

-

-

7.2

85.4

FR-2

3.0

-

5.0

-

-

4.9

87.1

FR-3

3.8

-

3.3

1.3

-

3.5

88.1

-: undetected.

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Table 6 Petrological analyses of the feed coals (vol. %) and max reflectance of vitrinite and inertinite. Sample s

T

CT

CG

CD

VD

V

F

SF

Ma

Mi

ID

I

Coal-1

11.2

6.6

0.2

26.7

5.7

50.3

2.9

22.5

5.8

10.4

4.9

46.4

Coal-2

9.1

12.7

0.2

27.4

3.6

52.9

3.4

24.6

1.5

5.7

8.0

43.3

Coal-3

9.2

11.3

0.4

25.0

3.9

49.8

3.2

24.1

3.0

3.8

10.7

44.7

Sample

Sp

Cut

Sub

Res

Alg

L

Cl

Py

Q

M

RVmax,

RImax,

Coal-1

0.2

0.5

0.6

0.2

-

1.5

1.1

0.6

-

Coal-2

0.5

0.5

0.3

0.2

0.2

1.5

1.4

0.8

Coal-3

1.5

1.1

0.2

0.2

-

3.0

1.3

0.9

%

%

1.8

0.56

1.15

0.2

2.3

0.57

1.56

0.2

2.4

0.5

1.9

T: telinite; CT: collotelinite; CG: corpogelinite; CD: collodetrinite; VD: vitrodetrinite; V: vitrinite; F: fusinite; SF: semifusinite; Ma: macrinite; Mi: micrinite; ID: inertodetrinite; I: inertnite; Sp: sporinite; Cut: cutinite; Sub: suberinite; Res: resinite; Alg: alginite; L: liptinite; Cl: clay; Py: Pyrite; M: Mineral; -: undetected.

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Energy & Fuels

Table 7 Results of petrological analysis of gasification residues (Vol. %). Inorganic components

Organic matter Samp les

Origi nal maceral

Tenuisphe

Crassispher

re

e

Tenuinetwor k

Crassinetwor k

Mixe d porous

debris

Mix ed

Fusinoi

dense

d

Inerto id

Vitropl ast

Cenosph ere

CR-1

2.0

1.6

2.2

0.6

1.2

0.8

1.4

3.4

21.2

3.2

0.2

CR-2

0.4

-

-

5.2

3.8

-

0.4

6.4

12.8

8.8

4.6

-

2.2

0.4

10.2

7.6

-

0.6

10.4

17.6

1.2

0.6

44.8

12.4

28.4

9.6

34.4

-

0.4

1.4

3.8

5.6

-

-

13.2

21.8

-

-

10.2

33.6

-B CR-3

Glassy grains

15.8

-A CR-2

Mineriod

FR-1

-

3.6

7.2

16.4

6.6

-

-

4.2

17.6

-

-

5.2

22.6

FR-2

12.8

-

-

19.6

0.8

-

-

0.2

20.6

-

-

8.8

37.2

FR-3

-

11.4

0.2

22.4

3.2

3.2

-

10.2

9.4

-

-

3.4

26.6

-: undetected.

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Table 8 Concentrations of trace elements in the feed coal and different residue samples (µg/g). TEs

Coal-1

CR-1

RE

FR-1

RE

Coal-2

CR-2-A

RE

CR-2-B

RE

FR-2

RE

Coal-3

CR-3

RE

FR-3

RE

Li

2.63

34.4

1.5

31.5

2.48

3.76

14.9

0.4

21.0

0.57

22.3

1.45

4.15

39.1

1.06

38.9

1.63

Be

0.506

3.82

0.87

4.11

1.68

0.529

2.29

0.44

2.77

0.54

3.4

1.57

0.344

3.76

1.23

3.71

1.88

Sc

1.81

20.5

1.3

20.4

2.34

2.23

10.4

0.47

13.8

0.64

12.8

1.4

2.57

17.8

0.78

16.3

1.1

V

14.5

122

0.96

123

1.76

15.4

61.7

0.41

77.2

0.52

77.4

1.23

15.8

102

0.73

105

1.16

Cr

8.58

98.9

1.32

107

2.59

9.88

56.6

0.58

60.0

0.63

73.6

1.82

10.5

65.0

0.7

68.1

1.13

Co

2.73

28.6

1.2

40.7

3.09

3.43

16.9

0.5

20.1

0.6

26.1

1.86

4.1

22.3

0.61

24.9

1.06

Ni

5.11

50.5

1.13

54.3

2.2

10.2

30.9

0.31

35.1

0.35

40.1

0.96

4.98

27.3

0.62

34.1

1.19

Cu

49.4

64.3

0.15

82.3

0.35

9.11

35.9

0.4

45.3

0.51

56.8

1.52

9.49

49.5

0.59

100

1.83

Zn

19.8

20

0.12

238

2.49

16.3

21.5

0.13

31.6

0.2

174

2.61

8.05

17.9

0.25

77.9

1.68

Ga

2.11

16.4

0.89

40.7

4.00

2.72

9.54

0.36

13.2

0.5

30.4

2.73

3.18

7.7

0.27

27.9

1.53

Rb

6.43

72.8

1.3

70.00

2.26

8.63

36.1

0.43

41.5

0.5

46.1

1.31

9.8

55.4

0.64

67.2

1.19

Sr

345

3190

1.06

2792

1.68

305

1896

0.63

2386

0.81

2281

1.83

296

2400

0.92

1726

1.01

Y

4.03

45.8

1.3

44.8

2.31

5.77

25.2

0.44

30.8

0.55

28.1

1.19

5.69

42.9

0.85

38.8

1.19

Mo

0.208

2.17

1.2

2.33

2.32

0.177

0.934

0.54

0.98

0.57

1.26

1.74

0.368

1.98

0.61

2.18

1.03

Cd

0.047

0.004

0.01

0.717

3.16

0.009

0.006

0.07

0.015

0.17

1.27

34.49

0.067

0.081

0.14

0.304

0.79

In

0.009

0.01

0.13

0.345

7.95

0.009

0.014

0.16

0.026

0.3

0.245

6.65

0.015

0.008

0.06

0.088

1.02

Sb

0.287

0.387

0.15

7.00

5.06

0.2

0.305

0.15

0.662

0.34

5.22

6.38

0.126

0.387

0.35

1.37

1.89

Cs

0.779

7.72

1.14

7.86

2.09

0.729

4.17

0.58

4.73

0.67

5.19

1.74

1.55

8.67

0.63

9.02

1.01

Ba

138

1410

1.17

979

1.47

141

644

0.46

756

0.55

598

1.04

457

2674

0.66

1199

0.46

La

4.98

67.6

1.56

56.9

2.37

8.19

36.5

0.45

43.9

0.55

34.7

1.04

7.52

65.7

0.99

50.8

1.18

Ce

8.16

106

1.49

94.6

2.4

13.8

59.2

0.44

72.6

0.54

60.9

1.08

12.8

90.7

0.8

84.8

1.15

Pr

1.07

14.0

1.5

12.1

2.34

1.81

7.66

0.43

9.19

0.52

7.48

1.01

1.67

14.7

0.99

11.2

1.17

Nd

3.96

52.8

1.53

45.1

2.36

6.91

27.8

0.41

34.1

0.51

28.3

1.02

6.34

54.1

0.96

40.6

1.11

Sm

0.767

9.63

1.44

8.34

2.25

1.25

5.21

0.42

6.21

0.51

5.35

1.05

1.2

10

0.94

7.58

1.1

Eu

0.171

2.07

1.39

2.01

2.44

0.266

1.15

0.44

1.43

0.55

1.28

1.18

0.201

1.8

1.01

1.62

1.4

Gd

0.805

8.25

1.17

7.61

1.96

0.975

4.24

0.44

4.95

0.52

4.76

1.19

0.937

8.25

0.99

6.36

1.18

Tb

0.128

1.43

1.28

1.3

2.11

0.171

0.825

0.49

0.893

0.54

0.827

1.18

0.189

1.43

0.85

0.993

0.91

Dy

0.643

7.69

1.37

6.77

2.18

0.915

4.06

0.45

5.03

0.57

4.5

1.2

0.893

7.04

0.89

6.21

1.21

Ho

0.155

1.69

1.25

1.38

1.85

0.22

0.844

0.39

0.991

0.46

0.874

0.97

0.177

1.47

0.94

1.12

1.1

Er

0.303

4.21

1.59

3.79

2.59

0.508

2.06

0.41

2.57

0.52

2.41

1.16

0.48

3.91

0.92

3.18

1.15

Tm

0.066

0.629

1.09

0.531

1.67

0.086

0.358

0.42

0.448

0.54

0.431

1.22

0.088

0.62

0.8

0.565

1.12

Yb

0.443

4.09

1.06

3.88

1.82

0.577

2.34

0.41

2.53

0.45

2.63

1.11

0.553

4.07

0.83

3.67

1.15

Lu

0.043

0.555

1.48

0.505

2.44

0.083

0.29

0.36

0.351

0.44

0.306

0.9

0.085

0.539

0.72

0.49

1

W

0.318

2.05

0.74

2.21

1.44

0.289

1.07

0.38

1.23

0.44

1.28

1.08

0.39

1.86

0.54

2.64

1.18

Re

0.004

0.019

0.54

0.026

1.35

0.008

0.007

0.09

0.02

0.26

0.009

0.27

0.007

0.023

0.37

0.017

0.42

Tl

0.165

0.161

0.11

4.11

5.17

0.179

0.261

0.15

0.514

0.3

3.39

4.63

0.695

1.17

0.19

4.56

1.14

Pb

4.03

4.63

0.13

168

8.64

5.01

6.64

0.13

11.1

0.23

126

6.15

5.28

3.43

0.07

45.4

1.5

Bi

0.11

0.041

0.04

3.65

6.88

0.102

0.042

0.04

0.12

0.12

3.05

7.31

0.123

0.033

0.03

0.973

1.38

Th

2.01

22.7

1.29

21.5

2.22

2.94

12

0.41

14.4

0.5

13.2

1.1

3.25

23.4

0.81

18.5

0.99

U

0.687

5.75

0.96

7.21

2.18

0.713

3.05

0.43

3.74

0.54

4.7

1.61

0.891

4.38

0.56

6.14

1.2

Nb

1.03

11.8

1.31

12

2.42

1.55

6.45

0.42

7.33

0.49

7.62

1.2

1.7

13.1

0.87

11

1.13

Ta

0.062

0.868

1.6

0.85

2.84

0.123

0.448

0.37

0.526

0.44

0.492

0.98

0.152

1.12

0.83

0.739

0.85

Zr

11.2

163

1.67

119

2.2

24.1

77.5

0.33

93

0.4

70.3

0.71

18.2

205

1.27

122

1.17

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Energy & Fuels

Hf

0.286

5.04

2.02

3.69

2.68

0.781

2.47

0.32

2.86

0.38

2.39

0.75

0.561

6.54

1.32

3.54

1.1

F

0.030

301.36

0.37

700.46

1.58

0.029

524.48

0.71

588.55

0.8

907.95

2.94

0.037

204.93

0.14

831.72

0.88

Hg

92.11

0.01

0.04

0.009

0.06

75.44

0.009

0.03

0.009

0.03

0.024

0.2

164.95

0.004

0.01

0.009

0.04

TEs: trace elements; RE: relative enrichment. Fluorine was determined using pyrohydrolysis in conjunction with a fluorine ion-selective electrode, and mercury was determined by DMA-80 Mercury Analyzer. Other trace elements were determined by ICP-MS.

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Page 34 of 34

Table 9 Partitioning of trace elements during entrained-flow coal gasification processes.

Classes

CR

FR

Behavior in the gasifiers

OFB

GE

Li, Be, Sc, V, Cr, Co, Ni, Ga, Rb, Sr, 1

≥0.7

Non-volatile

Mo, Cs, Ba, REEs, Th, U, Nb, Ta,

F

Zr, Hf

2

＜0.7

＞1.3

Volatile (volatilization-condensation)

GSP

Li, Be, Sc, V, Cr, Sr, REEs, Th, Nb, Ta, Zr, Hf

Li, Be, Sc, Cr, Co, Cu, Zn, Ga, Zn, Cd, In, Sb, Re, Tl, Pb, Bi, F

Rb, Sr, Mo, Cd, In, Sb, Cs, Tl ,

Cu, Zn, Ga, Sb, Pb, Bi

Pb, Bi, U

3

＜0.7

0.7-1.3

More volatile

-

4

＜0.7

＜＜1

most volatile

Cu, Hg

34


V, Ni, Y, Ba, REEs, W, Th, Nb,

Co, Ni, Rb, Mo, Cd, In, Cs, Ba,

Ta, Zr, Hf

W, Re, Tl. U, F

Re, Hg

Hg

Petrological characteristics and trace elements partitioning of

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