Coal Gasification Characteristics Research Articles

Experiment and simulation assessment of supercritical underground coal gasification in deep coal seam

To explain the impact of geological and process factors on underground coal gasification in deep coal seam (>2200 m) and promote the efficient and clean extraction and conversion of coal, this study employs the orthogonal experimental design method to investigate the impact of CO2 coefficient (0–1), moisture content (30–80 wt%), calcite content (0–10 wt%), albite content (0–10 wt%), kaolinite content (0–20 wt%), reaction temperature (550–650 °C), and reaction pressure (23–27 MPa) on the characteristics of coal underground gasification under supercritical H2O/CO2 conditions. Furthermore, range analysis and variance analysis are utilized to determine the degree of influence of each factor and the interaction between factors. Finally, the Gibbs free energy minimization method is used to conduct a thermodynamic equilibrium analysis of coal supercritical H2O/CO2 gasification at high temperatures (750–1000 °C). The results indicate that the three most significant factors affecting the process of coal supercritical H2O/CO2 gasification are the CO2 coefficient, moisture content, and reaction temperature. The maximum carbon gasification efficiency at 650 °C in experimental cases and 1000 °C in simulation cases is 22.2% and 88.1%, respectively. Although the addition of CO2 at lower temperatures reduces the carbon gasification efficiency, at high temperatures (>900 °C), a higher initial CO2 concentration increases the carbon gasification efficiency. The addition of CO2 under conditions of low moisture content increases the mole fraction of H2, but reduces it under conditions of high moisture content (≥70 wt%). Among the three minerals, calcite has the most significant influence on the gasification process.

Gasification study of Meulaboh coal under limited synthetic air and carbon dioxide environments

Gasification characteristics of Meulaboh coal have been investigated using chemical, petrographical, and thermogravimetry–mass spectrometry (TG-MS) approaches. The coal is classified as sub-bituminous C and dominated by huminite maceral (77% vol.). Based on proximate analysis, the coal comprises 12.56% moisture, 17.36% ash, 38.92% volatile matter, and 31.16% fixed carbon (adb). The coal is low in rank and dominated by reactive maceral. Thus, it is suitable for gasification study. TG-MS measurement revealed that the main pyrolysis product consists of H2O, CO2, and CH4, which generated significantly in slow and fast pyrolysis stages (180-294°C and 194-529°C, respectively). Gasification was performed using limited synthetic air and CO2 environments. TG and DTG thermograms show that gasification using CO2 resulted a higher mass loss rate than that using limited synthetic air. Moreover, gasification in a limited air atmosphere produced higher contents of H2O and CO2, while gasification in a CO2 atmosphere produced primarily CO.

Entrained-flow pyrolysis and (co-)gasification characteristics of Indian high-ash coals

Co-utilization in entrained-flow gasifiers is a potential solution to address the high ash-related problems persistent in fluidized-bed gasifiers. This work presents the hitherto unreported high-temperature (1000–1400 °C) entrained-flow pyrolysis and (co-) gasification characteristics of Indian high-ash coals and two candidate fuels (indigenous bituminous coal and petcoke) for possible co-utilization. Char analyses – TGA, FTIR, Raman, and SEM − are also performed to characterize the pyrolysis-induced structural changes. Volatile yields of candidate fuels matched with proximate values while those of high-ash coal exceeded by ∼12 wt%. Thermal deactivation was more pronounced for coal chars. High-ash coals achieved 100% carbon conversion at conditions exceeding 1300 °C and 20 vol% CO2. Bituminous coal showed comparable conversions, 70−90%, at identical conditions; further increase in conversion potential may be possible through steam addition due to enhanced char deactivation and pore diffusion effects at higher temperatures. Petcoke achieved lowest conversion of ∼30% even at the severest conditions; decreasing the average particle size by half showed an improvement of only ∼15%. Co-gasification of high-ash coal and petcoke blends showed no synergy. Considering closely matching carbon conversion, volatile release potential, and industry-standard slag tapping temperatures (1300−1500 °C), indigenous bituminous coals are more promising for co-utilization with high-ash coals in autothermal entrained-flow gasifiers.

K2CO3-catalyzed gasification of coal of different ranks in supercritical water for hydrogen production: A general kinetic model with good coal adaptability

Supercritical water gasification (SCWG) of coal provides a new solution for the green transformation and upgrading of traditional coal industry. Considering the good coal adaptability of SCWG and the excellent catalytic performance of K2CO3, a new kinetic model was developed in this work for predicting the catalytic gasification characteristics of coal of different ranks in supercritical water (SCW). In this model, various ranks of coal are characterized by the combination of three types of primary coal in different proportions, and the proportions can be obtained based on elemental analysis data and matrix computation. The SCWG of various ranks of coal can be considered as a combination of reactions of three types of primary coal in SCW. The model contains a total of 18 reactions, and various intermediates are represented by phenol and a high-carbon hydrocarbon. K2CO3-catalyzed SCWG experimental data of three different coal samples obtained in an improved quartz tube reactor system were used for the determination of model kinetic parameters. Then the experimental results of catalytic SCWG of other coal samples were used for the model validation, and it was found that the model can effectively predict the variations of gaseous products within an acceptable error. Afterward, the model was used to predict carbon gasification efficiency and gas compositions for coal of different ranks and to analyze carbon distribution and reaction rates for specific coal. The proposed kinetic model fits well with the good coal adaptability of SCWG technology, and it has great significance for the promotion of SCWG technology.

Characteristics of coal gasification with CO2 after microwave irradiation based on TGA, FTIR and DFT theory

Characteristics of coal gasification with CO2 after microwave irradiation based on TGA, FTIR and DFT theory

Study on characteristics of coal gasification fine slag-coal water slurry slurrying, combustion, and ash fusion

In this study, the effects and mechanisms of coal gasification fine slag-coal water slurry (CGFS-CWS) preparation, combustion and ash fusion (AF) were assessed. As the CGFS content increased, the viscosity of the slurry increased, but the stability of the slurry improved significantly. The improvement in the slurry stability is due to the negative charge on the surface of CGFS is significantly stronger than that coal particles. This stronger charge provides strong electrostatic repulsion, which facilitates particle dispersion. The slurry combustion experiments revealed that the incorporation of CGFS significantly reduced the burnout temperature of the slurry and increased the maximum combustion rate. When the mixing amount was less than 8%, the flammability index, combustion stability index, and comprehensive combustion characteristic index significantly improved. Such finding may be due to the formation of activation centers by the alkali metals in CGFS, which promote combustion reactions. The AF temperature of the CGFS-CWS ash decreased as the CGFS blending amount in the slurry increased. This result is due to the melting-assisting effect produced by the Fe2O3 and sulfate contained in the CGFS ash. Albite crystallization with a lower fusion temperature also appeared in the CGFS-CWS, which may be generated by the reaction of nepheline in coal ash and sodium-containing compounds in CGFS ash at high temperatures.

Gasification kinetics of Barapukurian coal char using carbon dioxide and steam reactants

Gasification of coal is a cost-effective and sustainable technology to produce syngas and hydrogen with integrated carbon capture and storage system. This study investigates the gasification characteristics of Barapukurian bituminous coal (BBC) char under carbon dioxide (CO2) and steam atmosphere using a thermogravimetric analyser (TGA). The char was prepared through a rapid pyrolysis process in a high temperature entrained flow gasifier at a temperature of 1200 °C. TGA experiments were conducted under atmospheric pressure over 700–1200 °C. Factors affecting intrinsic gasification kinetics, such as diffusion and mass transfer limitations, were optimised before conducting TGA experiments at various temperatures. Three established kinetic models of the volumetric model (VM), grain model (GM) and random pore model (RPM) fitted well with the experimental data. The activation energy determined from CO2 gasification was 1.20–1.25 times higher than that of steam gasification, indicating a higher reactivity under steam than CO2. The order of reaction using CO2 and steam was determined to be 0.67 and 0.95 at 900 °C.Graphical abstract

Sequential transformation study of minerals during underground coal gasification: Promising to indirectly reflect the actual reaction condition

AbstractThe mineralogical characteristics of underground coal gasification (UCG) residuals are closely related to the gasification conditions. The study of the mineral composition and transformation of ash and slag under different gasification conditions has important scientific significance for understanding the real gasification conditions, improving the utilization efficiency of coal, and identifying and controlling the environmental impact. In this paper, the sequential transformation of minerals under different temperature and atmosphere are studied by X‐ray diffraction (XRD) and FactSage software, and the elemental composition of the surface of the UCG ash and slag is characterized by SEM‐EDX. The results show that the main minerals in the semicoke are quartz (SiO2), illite (K1.5Al4(Si6.5Al1.5)O20(OH)4), and sanidine (KAlSi3O8). In the 900–1300°C reduction, ash, quartz, sanidine, hercynite (FeAl2O4), anorthite (CaAl2Si2O8), and mullite (Al6Si2O13) are the main minerals. The minerals in the oxidation residuals (1100–1500°C) are quartz, anorthite, hematite (Fe2O3), hercynite, cordierite (Fe2Al4Si5O18), and cristobalite. The reaction temperature has a significant effect on the changes in mineralogy. The reaction temperature is low during the pyrolysis process, and most changes involve only structural changes. With the reaction temperature increases, a series of reactions occur between different minerals. The reaction atmosphere also has a significant effect on the mineralogy. The research on the transformation of minerals in UCG residues can indirectly reflect the actual process of UCG, which can provide suggestions for the stable operation of the UCG process.

Effect of pre-treatment on catalytic coal gasification characteristics of sub-bituminous coal

Sintering or agglomeration is formed in the process of the gasification of coal when fluxing K2CO3, which leading to the entire bed defluidization. In order to study the catalytic coal gasification reactivity and agglomeration properties in pressurized fluidized bed, Wangjiata raw coal, demineralized coal with HCl-HF treatment, and raw coal with different amounts of clay mineral addition were selected. The catalytic coal gasification reactivity, the agglomeration and sintering properties were studied. As well as water-soluble catalyst recovery from the gasification residue was also determined. The results show that for potassium-catalyzed steam gasification, not only coal ash content but also composition affected the gasification reactivity, agglomeration, and catalyst recovery. The carbon conversion increased varying degrees with increasing K2CO3 loadings, K2CO3 impregnated coal showed a high degree of agglomeration, and agglomeration increased with increasing K2CO3 amount. Demineralized coal couldn't improve the agglomeration property. The addition of Clay mineral, was found to be very efficient in anti-sintering. However, compared with demineralized coal, the carbon conversion and water washing catalyst recoveries decreased obviously for those samples with the addition of clay minerals. The test verifies that part of potassium catalyst irreversibly reacted with coal ash to form relatively water-insoluble potassium compounds such as kaliophilite and sanidine.

Influences of Ash-Existing Environments and Coal Structures on CO2 Gasification Characteristics of Tri-High Coal

Two kinds of tri-high coals were selected to determine the influences of ash-existing environments and coal structures on CO2 gasification characteristics. The TGA results showed that the gasification of ash-free coal (AFC) chars was more efficient than that of corresponding raw coal (RC) chars. To uncover the reasons, the structures of RCs and AFCs, and their char samples prepared at elevated temperatures were investigated with SEM, BET, XRD, Raman and FTIR. The BET, SEM and XRD results showed that the Ash/mineral matter is associated with coal, carbon forms the main structural framework and mineral matters are found embedded in the coal structure in the low-rank tri-high coal. The Raman and FTIR results show that the ash can hinder volatile matters from exposing to the coal particles. Those results indicate that the surface of AFC chars has more free active carbon sites than raw coal chars, which are favorable for mass transfer between C and CO2, thereby improving reactivity of the AFC chars. However, the gasification reactivity was dominated by pore structure at elevated gasification temperatures, even though the microcrystalline structure, functional group structure, and increase in the disorder carbon were improved by acid pickling.

Experimental Study on Coal Gasification in a Full-Scale Two-Stage Entrained-Flow Gasifier

In this paper, coal gasification characteristics in the reductor were investigated in a full-scale two-stage pressurized entrained-flow gasifier, which has been seldom conducted previously. The present study aimed at elucidating the effects of gasifying agent concentration, coal input rate, and operation period under full reductor load on the performance of a utility two-stage pressurized entrained-flow gasifier for the first time. When the steam input in the combustor was raised from 3318 kg/h to 5722 kg/h, the total outputs of H2, CO, and CO2 were increased by 1765 Nm3/h and 2063 Nm3/h, respectively, while the CH4 output was decreased by 49 Nm3/h. The coal conversion rate was minimal at low steam input. In addition, more coal gasified in the reductor could increase the output of CH4, while CH4 could reach 1.24% with the coal input in the range of 8000–10,000 kg/h. The present work can offer a further understanding of the gasification performance in the reductor of the full-scale two-stage pressurized entrained-flow gasifier, and motivates the potential for clean utilization of coal resource.

Petrographic Characteristics of Coal Gasification and Combustion by-Products from High Volatile Bituminous Coal

The coal was gasified in a fluidized bed reactor with CO2 as a gasifying agent at 889–980 °C. The coal and gasification residue produced during gasification was burned at temperatures up to 900 °C. The petrographic analysis, gasification residues, and fly and bottom ash resulting from the combustion of coal and chars showed the efficiency of the gasification and combustion processes. The gasification residue primarily comprised inertoids and crassinetwork, which accounted for 60% of the sample. The analysis of the petrographic composition of fly ash revealed that the fly ash formed during the combustion of gasification residue had a higher mineral content. The fly ash from the combustion of gasification products contained significantly less unburned coal compared to that from coal. The samples of the bottom ash from coal combustion were composed of approximately 25% organic matter, most of which was chars. The bottom ash formed from the combustion of coal gasification products was composed mainly of mineral matter (95% or higher). The obtained results have significant implications in determining future waste management strategies.

Study on petrographic characteristics of devolatilization char/coke related to coal rank and coal maceral

Char/coke is the medium product of coal gasification, combustion, and metallurgy, whose morphological and optical characteristics are determined by coal rank and pyrolysis conditions. Twelve coals varying in coal rank from lignite to anthracite, collected in China, were used to study morphological and optical characteristics of char/coke upon different pyrolysis conditions systematically, specifically the char/coke structure and texture influenced by coal rank and coal maceral. Coke and char are distinguished by their caking ability. The morphology of the chars derived from low rank coals and high rank coals are closely related to coal maceral composition, whereas the morphology of cokes derived from high volatile bituminous A, medium, and low volatile bituminous is closely related to coal rank. In lignite, subbituminous, high volatile bituminous C, semianthracite, and anthracite, macerals are infusible during the heating process, but cavities generated in the low rank coals are related to the shapes of the liptinite macerals in the raw coals. Morphological changes of chars derived from high rank coals are difficultly to identify microscopically using an oil-immersion objective with a 1-lambda gypsum plate. in addition, the random reflectance (Rr) range of the chars becomes narrower as pyrolysis temperature increases. Overall, the Rr range of cokes is much larger than that of the chars, which is a result of the optical anisotropy of the caking coals. Although the Rr of vitrinite/huminite in the low and high ranks is distinct, the Rr of their chars is always similar when the pyrolysis conditions are the same. The Rr of char/coke is closely related to both coal rank and the final pyrolysis temperature. Longer residence time of the char/coke at the same pyrolysis temperature did not show a relevant difference in the reflectance of char/coke.

Improvement of resource recovery rate for underground coal gasification through the gasifier size management

Underground coal gasification is one of the most vital technical directions for the future development of the coal industry. Currently, numerous small-scale underground coal gasification industrial tests of different processes have been successively conducted, which has laid a solid foundation for further large-scale experiment and production. However, with the expansion of underground coal gasification experiment scale and promoting application, the surrounding rock stability and surface subsidence must be considered. Moreover, there exists a bottleneck problem, which should be solved urgently, that how to design underground gasification production for different geological conditions to improve resource recovery rate. To solve this issue, this paper analyzed the existing situation of resource recovery rate of industrial experiment for underground coal gasification without shaft. Also, the improvement method for resource recovery rate of underground coal gasification with considering of the gasifier safety and surface subsidence was proposed in combination with the technology characteristics of underground coal gasification. Meanwhile, the influence rule of gasifier parameters on the coal pillars stability and surface subsidence was revealed. From the findings in this research, it can be expected that the resource recovery rate of underground coal gasification without shaft can be increased from about 40% to more than 60% under the both conditions of the safe production of underground gasifiers and surface subsidence control. These research results are of great significance for enhancing the economic benefits of underground coal gasification and promoting its industrialization and large-scale production.

Numerical study of coal gasification in a dual-CFB Plant based on the generalized drag model QC-EMMS

The gas-solid fluidization and coal gasification reactions in a newly-designed dual circulating fluidized bed (CFB) plant were analyzed by full-loop numerical simulation to provide support for industrial applications. The generalized drag model, QC-EMMS, was used in the Eulerian-Eulerian approach to model the entire coal gasification process in a 60 m high dual-CFB pilot plant with a capacity of 100 tons coal per day. The predicted pressures, temperatures, and syngas compositions are more consistent with field test data compared with the results predicted by using the conventional Gidaspow drag model. The unmeasured solid mass circulation rates were accurately predicted by the QC-EMMS model. The characteristics of gas-solid fluidization and coal gasification were estimated by analyzing the flow and reaction details in the plant. These results show that the QC-EMMS drag model has advantages in simulating the complicated gas-solid flows and reactions in large-scale CFB plants.

Investigation of Chemical-looping Gasification Characteristics of Chinese Western Coals with Hematite-CuO Oxygen Carrier

In order to realize highly efficient conversion of Chinese western bituminous coals into syngas, a series of chemical-looping gasification experiments was conducted with hematite-CuO oxygen carrier in a laboratory-scale fluidized-bed reactor. The results indicated that the gasification rate of Chinese western bituminous increased by 2-3 times after addition of a hematite-CuO oxygen carrier. Meanwhile, the syngas yields of Chinese western bituminous ranged from 1.84–2.04 m3/kg, three times higher than that of lignite. This shows that the combination of chemical-looping technology and gasification of coal can achieve efficient conversion of Chinese/western bituminous coals. The temperature and the supply oxygen coefficient (O/C) all demonstrated a clear effect on the gasification rates and the gas yields. 10 cycles of redox experiments indicated that the hematite-CuO oxygen carriers have good recycled reaction characteristics. Those results provide theoretical guidance for the efficient conversion of Chinese western bituminous coals into syngas via chemical-looping gasification.

Gasification of Jhama Coal using Statistical Design of Experiment

In the present investigation, an attempt has been made to explore the effect of ash content on the gasification characteristics of Jhama coal. The two levels of ash content were selected for this study. The samples were obtained by gravity separation of Jhama coal. These two samples (clean Jhama coal: low ash and reject Jhama coal: high ash) were subjected to gasification at different temperatures for different time intervals, and carbon dioxide gas was used as a gasifying agent. The effect of temperature and residence time on gasification of two samples with different ash contents has been investigated. The values of activation energy of low-ash and high-ash Jhama coal samples have been obtained in the range of 51–66 kJ/mol and 37–43 kJ/mol, respectively. In addition, design of experiments was performed using response surface methodology (RSM) under 23 full factorial designs. RSM-based empirical models were developed for low-ash and high-ash Jhama coal samples to correlate process variables to the response of interest.

New Slag–Char Interaction Mode in the Later Stage of High Ash Content Coal Char Gasification

In this work, characteristics of single brown coal char particle gasification at around the ash fusion temperature was investigated. The particle size of gasification residue decreased with the inc...

Experimental and simulation studies on gasification characteristics of a low-rank coal by rapid heating under CO2-rich condition

In this investigation, an environmentally benign and efficient way for gasification of low-rank coal under CO2 rich condition, rapid heating, and high pressure was investigated. Series of experimental and simulation studies were carried out to compare the combustion characteristics of the Shandong (SD) low rank coal and Datong (DT) bituminous coal. It was found that the gasification potential of the SD coal sample was higher than that of the DT coal sample under the conditions investigated. A gasification model was developed and validated to predict the gasification characteristics of the low rank coal based on the experimental and the gasification kinetic parameters. It was found that the gasification conditions resulting in effective gasification of the low rank coal (in terms of CH4, CO and H2 gases production) are 100% CO2 concentration, 37.5 J/s heating rate, and 0.5 – 1 MPa pressure range.

Effects of hydrothermal upgrading on the physicochemical structure and gasification characteristics of Zhundong coal

It is difficult to directly use Zhundong (ZD) coal because of its high alkali metal content and the associated slagging and fouling problems. Therefore, in this study, hydrothermal (HT) treatment was introduced to remove the alkali metals and upgrade ZD coal at 150–350°C. The physicochemical structure and gasification characteristics of ZD coal were investigated. The results showed that the properties of the upgraded coal were effectively improved and the coal rank increased after HT upgrading. Additionally, alkali metals Na and K were notably removed, reaching approximately 98% and 82% at 350°C, respectively. BET analysis indicated that the pore structure was initially enriched at 150–300°C and then deteriorated at 300–350°C. The XRD and Raman results revealed that the microcrystalline structure tended to be more aromatic and graphitized, and the chemical structure became dense, orderly and stable. In addition, the CO2 gasification reaction curve shifted to the high-temperature region as the HT temperature increased. The gasification reactivity exhibited a decreasing trend, and the results were verified by dynamic analysis. Moreover, the comprehensive influence of different factors on the gasification reactivity was explored via a potential mechanism analysis, and a multiple linear regression model of gasification reactivity was established.