Steam Gasification Of Coal Research Articles

Steam gasification of co-pyrolysis chars from various types of biomass

Co-pyrolysis of two different types of biomass among apple tree branch (ATB), knotweed stem (KWS), seaweed (SW) and rice straw (RSt) was conducted to obtain co-pyrolysis char (co-char), and then the steam gasification of those co-chars was compared with the steam co-gasification of the physically mixed individual biochars to investigate the synergetic effect resulted from alkali and alkali earth metal (AAEM) in each biomass involved. It is found that the silica species in the RSt had negative effect on the activity of co-char due to the formation of alkali silicate compounds. However, combination of RSt with some non-woody biomass such as SW also showed promoting effect. In particular, the gasification of the co-char from the combination of various biomass with low or no silica content showed improved gasification efficiencies due to the synergetic effect AAEM species in the co-char from the different biomass. Therefore, the biomass selection should play a significant role in the co-pyrolysis of different biomass in the two-stage gasification system.

Investigation on carbide slag catalytic effect of Mongolian bituminous coal steam gasification process

Carbide slag may pollute the environment because it is difficult to handle. In this paper, carbide slag without pretreatment served as the new source of calcium and was added to bituminous coal for gasification experiments to realize waste utilization. The gasification experiment after adding carbide slag to bituminous coal enhances H2 production, which reduced the activation energy of the gasification reaction. The results show that the catalytic effect on steam gasification was evident when the carbide slag was added to Mongolian bituminous coal. The coal char at reaction temperature was prepared and characterized by X-ray diffraction (XRD), Raman, Scanning electron microscope (SEM), Transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and FT-IR spectroscopy. The carbon structure evolution and calcium structure changes of coal char under reaction temperature were studied, and the influence of coal char structure changes on gasification performance was analyzed. The results show that in the coal char added with carbide slag, the oxygen-containing functional groups generated by the polycondensation reaction interacted with calcium to form a calcium-oxygen-carbon complex. The existence of this structure not only leads to the highly uniform dispersion of CaO in the char but also hinders the graphitization process of the char. Highly dispersed CaO and disordered carbon structure significantly improved the reactivity of bituminous coal steam gasification. Si and Al in the bituminous coal affected the dispersion of Ca during steam gasification.

Spent Mushroom Substrate Performance for Pyrolysis, Steam Co-Gasification, and Ash Melting

Spent mushroom substrate is expected to be utilised as gasification feedstock in the future. This study investigated its performance in pyrolysis, steam co-gasification, and ash melting. Pyrolysis was performed by thermogravimetry-differential thermal analysis, and it was found that higher shoulder curves indicated higher hemicellulose content than timber waste. Steam co-gasification was evaluated using a laboratory-scaled fixed-bed downdraft gasifier. The results showed that blending the substrate with Erianthus enhanced carbon conversion to gas and hydrogen concentration (by 7.5–8.8 points) at a blend rate of 50 wt%, with lower H2S yield due to the formation of CaSO4 on the biomass surface. Furthermore, blending the substrate with Japanese cedar resulted in increased softening and fusion temperatures that can be explained by assuming the formation of calcium minerals (e.g., gehlenite and albite–calcian). Based on these results, spent mushroom substrate demonstrates high potential to serve as regional feedstock by co-gasification.

The effect of steam on air gasification of mechanically activated coal in a flow reactor

A combined steam-gas plant with in-cycle steam gasification of coal and hot gas purification is considered as a promising technology for increasing the efficiency of energy production with simultaneous reduction in environmental impact. To intensify steam-air gasification, mechanical activation of fuel is used; it consists in high-stress grinding in a mill-disintegrator. The supply of steam to the gasifier allows an increase in reactivity of fuel, suppression of sorbent decomposition in the unit of hot desulfurization, reduction in the steam load on the shift reactor, increase in useful external work of gas turbine expansion, reduction in nitrogen oxide formation, and general increase in the efficiency and ecological compatibility of energy generation. On the other hand, a significant amount of steam can deteriorate the heat balance and efficiency of the gasifier. In this work, the influence of the steam/fuel ratio on steam-air gasification of mechanically activated Kuznetsk coal in a flow reactor was studied experimentally. The excess air coefficient was maintained constant and equal to 0.51, which corresponded to a temperature at the reactor outlet of about 1100?C. When steam was supplied, the fuel and air-flow rates were adjusted to ensure a constant gas-dynamic regime. To evaluate the obtained regimes, the heat and material balances were compiled. A positive effect of steam on characteristics of the gasification process was revealed. For the studied coal, the maximum degree of coal conversion and the calorific value of synthesis gas are achieved with a steam/fuel ratio of about 0.4 kg/kg.

Production of H2-rich syngas from excavated landfill waste through steam co-gasification with biochar

Abstract Gasification of excavated landfill waste is one of the promising options to improve the added-value chain during remediation of problematic old landfill sites. Steam gasification is considered as a favorable route to convert landfill waste into H2-rich syngas. Co-gasification of such a poor quality landfill waste with biochar or biomass would be beneficial to enhance the H2 concentration in the syngas, as well as to improve the gasification performance. In this work, steam co-gasification of landfill waste with biochar or biomass was carried out in a lab-scale reactor. The effect of the fuel blending ratio was investigated by varying the auxiliary fuel content in the range of 15–35 wt%. Moreover, co-gasification tests were carried out at temperatures between 800 and 1000 °C. The results indicate that adding either biomass or biochar enhances the H2 yield, where the latter accounts for the syngas with the highest H2 concentration. At 800 °C, the addition of 35 wt% biochar can enhance the H2 concentration from 38 to 54 vol%, and lowering the tar yield from 0.050 to 0.014 g/g-fuel-daf. No apparent synergetic effect was observed in the case of biomass co-gasification, which might cause by the high Si content of landfill waste. In contrast, the H2 production increases non-linearly with the biochar share in the fuel, which indicates that a significant synergetic effect occurs during co-gasification due to the reforming of tar over biochar. Increasing the temperature of biochar co-gasification from 800 to 1000 °C elevates the H2 concentration, but decreases the H2/CO ratio and increases the tar yield. Furthermore, the addition of biochar also enhances the gasification efficiency, as indicated by increased values of the energy yield ratio.

Binary Blends Versus Ternary Blends in Steam Cogasification by Means of TGA–MS: Reactivity and H2/CO Ratio

Cogasification of olive pomace, almond shell, and petcoke was carried out by thermogravimetric analysis coupled with mass spectrometry. Binary and ternary blends were compared in terms of their rea...

Effect of the electronic state on low-rank coals with Ca2+ ion exchange

Ca2+-exchanged coal prepared from calcium hydroxide is a good catalyst for steam gasification of low-rank coal with a fixed-bed quartz reactor. However, it is difficult to clarify the effect of Ca2+ ion exchange on low-rank coal by experiment. To investigate the effect of Ca2+ ions on low-rank coals, this study determined the electronic states between Ca2+-exchanged and raw coal models and compared them by B3LYP/6-31G∗ and HF/6-311G∗ calculations. The experiments revealed that the Ca2+ ion exchange method significantly affects gasification of low-rank coal. It is considered that the molecular structure of low-rank coal presents significant changes in the electronic state before and after Ca exchange, even with a simple molecular structure. Therefore, a molecular model was created in which a COOH/OH H+ ion was exchanged with one Ca2+ ion, and quantum chemical calculations were subsequently performed. The results revealed that the –COOCa1/2 IR peak calculated from B3LYP/6-31G∗ appeared at approximately the same position as the experimental IR peak in low-rank coal after Ca exchange. The Ca structure was more stable following interaction with the O in the benzene OH group than with that in the OH group of the tetralin ring containing Ca. Furthermore, the increased negative charge of the benzene ring following Ca interaction was presumed to improve the reactivity between the low-rank coal and steam. In addition, weak bonds in the Ca2+-exchanged coal molecules were investigated by calculating the difference between the values of the Löwdin and Mulliken bond orders before and after Ca2+ exchange. The results indicated that the binding in the molecule was weakened by Ca coordination. From these facts, it is presumed that H+/Ca2+ ion exchange promotes the decomposition of low-rank coal.

Synergistic effect of mixing wheat straw and lignite in co-pyrolysis and steam co-gasification

Co-pyrolysis and steam co-gasification of wheat straw (WS) and lignite coal (LC) were studied in a tube furnace between 700 °C and 900 °C. Synergistic effect in co-pyrolysis is not always apparent. However, with the introduction of H2O vapor, synergetic effect is more obvious. Gas volume generated by co-gasification was higher than the prediction in all cases. Meanwhile, temperature played an important role and had a linear relationship with the excess gas volume when it exceeded 800 °C. These findings can be explained by that sufficient H2O vapor could enhance synergy according raising catalytic effect of alkali and alkaline earth metals (AAEMs), promoting free radical generated and increasing reactivity of half-chars. Moreover, co-gasification of WS and LC with several blending ratios were studied at 850 °C. It found H2O vapor could promote free radical formation stronger with higher ratio of WS during co-gasification, thus showing an enhancing effect on the reactivity of WS-derived chars.

Electronic State of Low-Rank Coals with Exchanged Sodium Cations.

Our previous experimental study showed that Na+-exchanged coal prepared from low-cost natural soda ash is an excellent catalyst for steam gasification of low-rank coals using fixed-bed quartz reactors. However, it is difficult to experimentally clarify the effect of Na ion exchange on low-rank coal. In order to investigate the influence of Na+ ions on low-rank coal, this study determined the electronic state between the Na+-exchanged coal model and raw coal model and compared them using RHF/6-311G* and B3LYP/6-31G*. The experiments revealed that Na ion exchange has a significant effect on low-rank coal gasification. The model structure of low-rank coal is considered to change significantly in terms of the electronic state before and after Na exchange even with a simple main molecular structure. Molecular models where H of COOH/OH was ion-exchanged with one, two, and three Na ions were developed, and quantum chemical calculations were performed. The results showed that when the number of Na+-exchanged sites is increased, the electron state on the coal molecule becomes more negatively charged in the case of the Na+-exchange coal model. It is presumed that this contributes to enhancing the reactivity of low-rank coal and water vapor. In addition, weak bonds in the Na+-exchanged coal molecule were examined by calculating the difference in the value of the Mulliken and Löwdin bond orders before and after Na+ exchange. The results showed that the increase in the number of exchanged Na+ in the low-rank coal molecule model increased the number of weak bonds in the molecule. It is presumed that this contributes to enhancing the decomposition of low-rank coal.

Steam co-gasification of horticultural waste and sewage sludge: Product distribution, synergistic analysis and optimization

In this study, horticultural waste (HW) and sewage sludge (SS) with different mass ratios were co-gasified with steam at different temperatures to investigate the product distribution, gas synergistic interaction, and optimal design for gas products from co-gasification process. Results showed that with the increase of SS ratio in blends, the H2 content was increased and the syngas yield was decreased. The synergistic interaction was more significant at higher temperature which promoted the H2 production probably due to the reduction and steam oxidation of Fe species in SS during co-gasification process. The optimized highest effective gas content (82.92 vol%) was achieved with the highest HHV (11.40 MJ/m3) at the conditions of SS ratio = 0.80 and temperature of 900 °C. It indicates that steam co-gasification of HW and SS is a promising technology to produce desired syngas towards a clean and efficient waste management process.

Studying the influence of the catalytic effect of transition metals and their oxides on the process of steam gasification of stone coal

Studying the process of steam gasification of stone coal continues. The study of the process occurs in the conditions of aerosol nanocatalysis technology (AnC). The aerosol nanocatalysis technology is a fundamentally new, simple and competitive catalysis technology without the use of a carrier. This is a technology for the implementation of heterogeneous catalytic processes, based on mechanochemical effects. Mechanochemical effects result from mechanical effects on the catalytically active component. The rotation reactor of aerosol nanocatalysis is a multipurpose purpose. The scheme of the laboratory installation with the rotating reactor has been modified to study the process of coal gasification. The main feature of this process is the formation and activation of catalyst nanoparticles. Which is realized by means of rotation of the reactor. Mechanochemical activation increases the reactivity of the catalyst particles, which leads to an increase in the rate of chemical reactions. The efficiency of gasification processes can be significantly improved by using suitable catalysts that allow to lower the temperature while maintaining the high speed of the process and to regulate the composition of the products. The effect of catalysts on the composition of the synthesis gas in the conditions of the aerosol nanocatalysis technology was investigated. For this purpose, were taken the catalysts, which are most widely used in the process of steam gasification of coal. The influence of each of the catalysts used in the study on the change in the content of hydrogen, carbon monoxide, carbon dioxide, methane, ethylene, ethane in the resulting synthesis gas is determined. Justification of the choice of catalyst to obtain a synthesis gas of one or another composition was given. The opportunity the obtaining of synthesis gas, the composition of which is favorable for the production of methanol, was considered. When processing the research data, the relative error, confidence probability and accuracy of approximation were calculated. Values of the obtained accuracy indicators show a satisfactory level of compliance of measurements with true values.

P-09 Effect addition of various biomass char on steam co-gasification with rice straw

P-09 Effect addition of various biomass char on steam co-gasification with rice straw

Examination of steam gasification of coal with physically mixed catalysts

Abstract The aim of this study was to analyse the steam gasification process of ‘Janina’ coal with and without Na-, K- and Ca-catalysts. The catalysts were physically mixed with the coal due to the simplicity of this method, short time of execution and certainty that the amount of catalyst is exactly as the adopted one. The isothermal measurements were performed at 800, 900 and 950°C and a pressure of 1 MPa using thermovolumetric method. The obtained results enabled assessment of the effect of analysed catalysts on the process at various temperatures by determination of: i) carbon conversion degree; ii) yield and composition of the resulting gas; and iii) kinetics of formation reactions of main gas components – CO and H2. The addition of catalysts, as well as an increase in operating temperature, had a positive effect on the coal gasification process – reactions rates increased, and the process time was reduced.

Catalytic steam co-gasification of biomass and coal in a dual loop gasification system with olivine catalysts

A dual loop gasification system (DLG) has been previously proposed to facilitate tar destruction and H2-rich gas production in steam gasification of biomass. To sustain the process auto-thermal, however, additional fuel with higher carbon content has to be supplied. Co-gasification of biomass in conjunction with coal is a preferred option. Herein, the heat balance of the steam co-gasification of pine sawdust and Shenmu bituminous coal in the DLG has been analyzed to verify the feasibility of the process with the help of Aspen Plus. Upon which, the co-gasification experiments in the DLG have been investigated with olivine as both solid heat carriers and in-situ tar destruction catalysts. The simulation results show that the self-heating of the DLG in the co-gasification is achieved at the coal blending ratio of 28%, gasification circulation ratio of 19 and reforming circulation ratio of 20 when the gasifier temperature 800 °C, reforming temperature 850 °C, combustor temperature 920 °C and S/C 1.1. The co-gasification experiments indicate that the tar is efficiently destructed in the DLG at the optimized reformer temperature and with olivine catalysts.

Modeling of gasification process of Indian coal in perspective of underground coal gasification (UCG)

In the present study, the steam gasification of Indian coal and its demineralized coal were investigated in a specially designed fixed-bed reactor, to determine the intrinsic kinetics parameters with optimum operating temperature and partial pressures of steam in the perspective of underground coal gasification (UCG). The gasification reactivity of a chosen coal was higher compared to the demineralized coal and the reason could be mineral content of ash present in the coal. A one-dimensional unsteady kinetic model was developed for the steam gasification process in a fixed-bed reactor. The intrinsic kinetic parameters for steam gasification and water–gas shift reaction are estimated by fitting the developed models with the experimental data.

Catalytic gasification of biomass and coal blend with Fe2O3/olivine in a decoupled triple bed

Steam co-gasification of pine sawdust and bituminous coal blend was performed in a pyrolysis-reforming-combustion decoupled triple bed gasification (DTBG) system with Fe2O3/olivine as both solid heat carrier and in-situ tar cracking/reforming catalyst. The effects of reformer temperature (RT) and circulation rate (CR) of catalyst on gasification performance were investigated. Besides, X-ray diffraction (XRD) and temperature programmed reduction (TPR) are employed to reveal the properties of Fe2O3/olivine catalyst during the continuous redox cycle between those decoupled reactors. The results indicated that, the configuration of the DTBG system favor tar cracking/reforming reaction to enhance H2 yield. Higher RT promotes the gas yield, H2 content in product gas, carbon conversion and cold gas efficiency of the process. Specifically, a gas yield of 0.66 Nm3/kg, tar content as low as 4.87 g/Nm3 with the H2 content of 42.2 vol% has been obtained at the RT of 850 °C. Lower CR of catalyst leads further reduction of Fe2O3 that allows increment on the gas yield and H2 content. The H2 content reduced from 44.5 vol% to 40.8 vol% and CO2 increased from 37.3 vol% to 41.4 vol% with increasing catalyst CR from 1.9 kg/h to 4.5 kg/h. Reduction level of Fe2O3/olivine increased with decreasing catalyst CR. Fe2O3/olivine not only has catalytic effect on tar cracking/reforming but also acts as an oxygen carrier transports oxygen from the combustor to the reformer.

Steam co-gasification of different ratios of spirit-based distillers’ grains and anthracite coal to produce hydrogen-rich gas

In this study, the gas release rate and gas composition in the steam gasification of blends of anthracite coal and spirit-based distillers’ grains (SDG) with mass ratios of 3:1, 1:1, and 1:3 were studied. The changes in the gasification reaction activity for different gasification temperatures and sample ratios were investigated, and the synergy between SDG and coal in terms of co-gasification was analysed. The results indicated that the instantaneous release rate of hydrogen was higher than that of other gases for all sample ratios. Upon the addition of SDG, the H2 content increased while CO and CO2 contents decreased. The gasification reactivity increased with decreased temperature and ratio of SDG. Furthermore, potassium and calcium in SDG ash played a synergistic catalytic role in the gasification reaction.

Thermochemical utilization of low rank coal and flotation concentrate

Abstract Flotation concentrates are waste material from coal mine operation. The process of steam gasification seems to be an attractive option for their economic utilization and an alternative to their potential combustion in boilers. The gasification process is characterized by both higher efficiency and lower emission of pollution than conventional combustion systems. In this paper the results of the steam gasification of low rank coal and flotation concentrate into hydrogen-rich gas at the temperature of 800 °C are presented. The reactivity for 50% carbon conversion as well as the maximum reactivity in this process were calculated for the samples studied.

Coal to substitute natural gas based on combined coal-steam gasification and one-step methanation

In the face of the requirement of clean coal utilization and greenhouse gas emission reduction, coal to substitute natural gas (SNG) production attracts increasing attention worldwide. This work proposed a coal-to-SNG process, which combines a high-efficiency coal-steam gasification and one-step methanation. Through regenerative unit, the sensible heat of the syngas can be recovered via the oxidant steam and then finally converted into chemical energy of syngas, and thereby the cold gas efficiency can be 8.8 percentage points higher than the traditional GE gasification. The H2/CO mole ratio of syngas leaving the gasifier is about 1.2 which can be used for one-step methanation directly and the traditional water gas shift process can be eliminated. Simulation and thermodynamic analysis of the whole plant are presented, and the experimental study of coke-steam gasification is carried out in a fixed bed reactor. Preliminary experiments show that when gasification temperature is higher than 1000 °C, the H2/CO ratio of the syngas is approximately 1.3–1.4. Thermodynamic analysis shows that the SNG conversion efficiency of the proposed process increases from 61.3% to 71.7% and the energy consumption for SNG product has been reduced from 84 GJ/t to 60.5 GJ/t, mainly due to the cold gas efficiency enhancement of gasification and elimination of water gas shift process. Besides, through the one-step methanation, the concentration of CO2 before CO2 separation unit increases from 31.1% to 43.2%, and the unit energy consumption in the CO2 capture decreases from 15.3 kJ/mol to 11.7 kJ/mol.

SNG production with CO2 capture based on coal-steam gasification and one-step methanation

Abstract In the face of energy crisis and greenhouse gas emission reduction, coal to synthetic natural gas (SNG) production attracts increasing attention worldwide. This work proposed a novel coal to SNG plant, in which the high-efficiency coal-steam gasification technology and one-step methanation method are adopted. In this novel system, the air separation unit and water gas shift process can be eliminated. Besides, through the one-step methanation, the CO2 concentration is much higher than the traditional SNG plant and the energy consumption of CO2 separation will be reduced. Via the coal-steam gasification and one-step methanation methods, the SNG output of the novel plant can be significantly improved and the total plant thermal efficiency increases by 15 percentage points.