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Hydrogen is an outstanding source of energy and plays very important part in energy system. Hydrogen is one of the best energy carrier alternatives to fossil fuels because of its high energy density. It is very important to produce clean and renewable energy sources due to increasing population and pollution day by day. In 2018, the maximum hydrogen (94%) is manufactured from fossil fuels by steam reforming of natural gas, partial oxidation of the methane gas as well as coal gasification. The hydrogen production plays important role in any industrialized society, since hydrogen is required for many essential chemical processes. Several designed metal-based ideas can be employed as an efficient catalyst for hydrogen production for the alternate source of energy and society benefits. Proposed review is highlighting the different efficient strategies for hydrogen production.

Hydrogen is an important chemical commodity and plays a key role in the clean, secure and affordable energy scenarios of the future. There is a significant interest in the development of small plants for hydrogen generation besides other plants where hydrogen has been consumed as raw material and it is because of the very high cost of compression and transportation of hydrogen. Thermal methane cracking (TMC) is an alternative process for high purity hydrogen manufacturing along with the traditional commercial processes such as steam reforming, coal gasification, partial oxidation, and water electrolysis. Employing the TMC process for very high purity hydrogen production on a small or medium-scale plant with the minimum requirement of separation units is the main incentive of this review. Given the results of the review, using catalysts for TMC can decrease the working temperature to below 800 °C but it could create some significant issues, especially catalyst deactivation (a low catalyst life due to carbon deposition), so it is not yet a viable method to employ on the production plants. On the other hand, supplying the heat of reaction and reactor blockages are two basic challenges for a non-catalytic reaction way.

Inert powders played an important role in the explosion inhibition of dust removal equipment and coal gasification process. In this paper, SiO2, dry water, carrageenan dry water, and NaHCO3 were adopted to explore the influences of inert powders on the deflagration flame propagation characteristics of mixed pulverized coal by a vertical pipeline. The results showed that the flame brightness of the mixed pulverized coal decreased with the irregularly discrete of flame front after the addition of inert powders. As the increasing of pulverized coal mesh number, the peak flame temperature first increased and then decreased, while the drop value of peak flame velocity and temperature increased with the increasing of mass concentration. In addition, the inerting rate affected the propagation of pulverized coal composite flame. When the inerting rate exceeded 1.0, the peak temperature drop increased rapidly and dry water exhibited the best inhibition performance.

Hydrogen (H2) energy has come to the fore as a significant role of chemical industry in achieving a sustainable energy sector under serious environmental problems. Therefore, research for using H2 as an energy carrier has been actively conducted. However, H2 has very low volumetric energy density making it require conversion to other forms to acquire higher volumetric energy density. In this paper, the promising compound methanol (MeOH) was considered as a H2 carrier owing to carbon-neutral in environmental terms. The two main overall H2 supply scenarios were considered. The first case covers the use of MeOH produced from various types of H2 (from steam methane reforming (SMR), coal gasification (CG), and water electrolysis (WE)), indirectly, and CO2 electrolysis, directly, as a H2 carrier, further converted to H2 at desired locations. The second case covers the conversion of MeOH from four production pathways into H2 followed by the transportation of the produced H2 via various H2 transportation methods such as compressed H2 (CH2), liquefied H2 (LH2), liquid organic hydrogen carrier (LOHC), and ammonia (NH3). In this work, diverse H2 supply scenarios considering various MeOH production methods, capacities, pathways, and distances were analyzed with unit H2 supply cost via economic analysis.

Catalytic steam hydrogasification of coal is a direct method for methane production. Calcium looping concept is usually used in coal gasification process for in-situ carbon dioxide removal and heat supply. In this paper, a new process combining catalytic steam hydrogasification and calcium looping was proposed and investigated using a self designed instantaneously feeding reactor under high-temperature and pressurized conditions. The effects of operation conditions (including hydrogen concentration with a range of 0–50 vol%, gasification pressure with a range of 0.1–3.5 MPa, gasification temperature with a range of 700–800 °C, and gasification-calcination cycle number up to six) on the performance of the new process have been studied. The results show that: (i) increasing H2 concentration is beneficial to methane products; (ii) high temperature and low pressure are not conducive to methane production and carbon dioxide capture as well as the self-sustained heat supply in gasifier; (iii) the methane content and carbon conversion can be maintained at 30–40 vol% and 75–80% for the durability tests. According to the performance of gas products, 750 °C 3.5 MPa and Ca/C = 0.5 are suggested for the new process. In addition, the gasification reactivity can be affected by the Ca–K-Char interaction as indicated by the XRD, FT-IR and SEM-EDX analysis.

Dihydrogen (H-2), commonly named 'hydrogen', is increasingly recognised as a clean and reliable energy vector for decarbonisation and defossilisation by various sectors. The global hydrogen demand is projected to increase from 70 million tonnes in 2019 to 120 million tonnes by 2024. Hydrogen development should also meet the seventh goal of 'affordable and clean energy' of the United Nations. Here we review hydrogen production and life cycle analysis, hydrogen geological storage and hydrogen utilisation. Hydrogen is produced by water electrolysis, steam methane reforming, methane pyrolysis and coal gasification. We compare the environmental impact of hydrogen production routes by life cycle analysis. Hydrogen is used in power systems, transportation, hydrocarbon and ammonia production, and metallugical industries. Overall, combining electrolysis-generated hydrogen with hydrogen storage in underground porous media such as geological reservoirs and salt caverns is well suited for shifting excess off-peak energy to meet dispatchable on-peak demand., Environmental Chemistry Letters, 20 (1), ISSN:1610-3653, ISSN:1610-3661

Environmental consequences of polycyclic aromatic hydrocarbons (PAHs) were studied to evaluate possible human health risks, subsequent cancer probabilities and remediation tools for their eradication. Polycyclic aromatic hydrocarbons (PAHs) are generated globally through incomplete combustion of organic materials and emitted in the environment by various anthropogenic routes including residential heating, coal gasification, liquefying plants, cooking practices, thermal distillation of petroleum and coal, oil spills, ships embankments, incomplete burning of fossil fuels, forest fires, asphalt, engines and vehicles exhaust. Their high lipophilicity and marked tendency for localization in body fats made them easily absorbed through dermis, nasal mucosa and gastrointestinal tract of mammals. The reviewed data show estimated carcinogenic potency equivalent concentrations exceeding the screened value for food stuffs including fish species indicating significant carcinogenic health risks associated with the consumption of fishes. Many remedial measures have been taken to exterminate persistent organic pollutants including PAHs out of which bio-remediation being comparatively safer and economical methodology. Keywords

The production of olefins by catalytic transformation of methanol on zeolites and zeotypes is of great interest to scientists and specialists in various fringe areas of national economy. Due to implementation of this process on industrial level, the attention gradually shifts from scientific studies devoted to the synthesis and modification of zeolites and zeotypes with different structure to investigation of pilot and industrial plants and determination of the main economic and environmental characteristics of both the existing and the future plants. In 2019, the development of 26 production sites in China with the annual output of 14 million tons of ethylene and propylene was licensed and 14 plants with the total capacity of 7.67 million tons of ethylene and propylene were launched. The created plants provide a complete cycle of coal processing, which consists of coal gasification units yielding syngas, units for the synthesis of methanol and olefins, their refinement and production of polyethylene and polypropylene. The total output of ethylene and propylene at the launched plants was more than 21 million tons. The paper presents a review of publications on the development and modification of catalysts as well as the technological, economic and environmental aspects of olefins production from methanol, which appeared in foreign journals in the recent five years.

Underground Coal Gasification (UCG) is the process of converting the materials used to make synthetic gas in a feasible and economically attractive manner as a method for harnessing energy from underground coal sources. Coal gasification will produce a gas producer in the form of synthetic gas (syngas) with the main components consisting of carbon monoxide (CO), hydrogen (H2), carbon dioxide (CO2) and nitrogen (N2) and low pollutants. The highest temperature produced with MT 47 lignite coal using an oxygen velocity of 5 liters/minute was 2400 C at the 35th minute, while the lowest temperature was 950 C at the 95th minute. For Subbituminous AL 51 coal using an oxygen velocity of 5 liters/minute, the highest temperature is 3540 C at 75 minutes, while the lowest temperature is 1060 C at 130 minutes. At an oxygen velocity of 5 liters/minute the flash point / burn test is on the MT 47 lignite coal type in the 10th minute and at a temperature of 1700 C. Meanwhile, the AL 51 subbituminous coal type is in the 30th minute and at a temperature of 3130 C. Based on the discussion and analysis of data from the gasification test of lignite and subbituminous coal with variations in oxygen velocity of 5 liters/minute, the results obtained are that lignite coal burns faster (burn test) in the 10th minute at a temperature of 1700 C, in the subbituminous type it has higher temperature 3130 C and longer burn test at 30 minutes.

The aim was to assess the technological feasibility of generating sodium cyanide by coal gasification, to study the effects of the process parameters (temperature, experiment duration, coal type) on the concentration of sodium cyanide in the resulting solutions, as well as to identify optimal modes of the process. Experiments were carried out on a laboratory setup consisting of a tubular cylindrical furnace equipped with a working compartment in the form of a corundum tube. Lignite and charcoal, preliminarily crushed to increase the specific surface area, were investigated. A solution of sodium cyanide was produced by sorption of gaseous hydrocyanic acid (a syngas component) with a sodium carbonate solution. A NaOH solution (pH = 10) installed in an ice bath was used in the system of absorbers. The content of sodium cyanide in the solution was determined by the titrimetric method. The HSC Chemistry 5.1 software package was used for thermodynamic calculations. During the gasification of charcoal in the temperature range 600–800oC, sodium cyanide solutions with a concentration of 0.03–0.08 wt% were obtained. An increase in temperature from 600 to 900oC led to a 4-fold decrease in the concentration of sodium cyanide in an alkaline solution, under the same duration of the experiments. A regression equation was derived for the dependence of the NaCN concentration in solution on the temperature of coal gasification and the duration of the process. It was shown that the generation of sodium cyanide by coal gasification under laboratory conditions yields sodium cyanide concentrations in solution comparable to those used for gold cyanidation at gold recovery plants. The installation of sodium cyanide generation lines directly at the production areas of gold recovery plants will reduce the production costs by eliminating expenses for purchasing, transporting and storing reagents.

In this work, a model of hydrogen production by double chemical looping is introduced. The efficiency benefit obtained was investigated. The chemical looping hydrogen generation unit is connected in series to the downstream of a chemical looping gasification unit as an additional system for 100 MW·h coal gasification, with the function of supplementary combustion to produce hydrogen. Using Aspen Plus software for process simulation, the production of H2 and N2 in the series system is higher than that in the independent Chemical looping gasification and Chemical looping hydrogen generation systems, and the production of hydrogen is approximately 25.63% and 12.90% higher, respectively; The study found that when the gasification temperature is 900 °C, steam-carbon ratio is 0.84 and oxygen-carbon ratio is 1.5, the hydrogen production rate of the system was the maximum. At the same time, through heat exchange between logistics, high-pressure steam at 8.010 × 104 kg·h−1 and medium-pressure steam at 1.101 × 104 kg·h−1 are generated, and utility consumption is reduced by 61.58%, with utility costs decreasing by 48.69%. An economic estimation study found that the production cost of ammonia is 108.66 USD·(t NH3)−1. Finally, cost of equipment is the main factors influencing ammonia production cost were proposed by sensitivity analysis.

The aim of this study is to assess the influence of oxygen-to-steam ratio, wall boundary conditions, coal feeding rate, and static bed height on the concentrations, heating values, and efficiencies of the product gas in a tapered fluidized bed reactor. Results show that lower and higher heating values slightly vary with increasing the oxygen-to-steam ratio in the range of 0.25–0.35. It is found that cold gas efficiency and carbon conversion efficiency goes up with increased ratio of oxygen to steam; however, both efficiencies decline as a result of increasing the coal feeding rate. As static bed height rises, lower and higher heating values diminish for tapered angle of 5°. For tapered angle of 5°, slight changes in concentrations of the product gas are observed with the increased coal feeding rate while the gas concentrations remarkably vary for the tapered angle of 9°.

Waste gasification has the potential to contribute to China's transition towards carbon neutrality and zero waste cities via the recirculation of waste as secondary carbon feedstock for the production of chemicals with lower/and or zero carbon footprint, green hydrogen with zero carbon footprint and CO2-neutral synthetic liquid fuels. With China's significant coal gasification capacity and associated experiences and expertise, Coal-to-X could act as a bridge to Waste-to-X for carbon intensive sectors such as the waste management, chemical production and mobility sectors. To illustrate the opportunities in these areas, this article presented highlights from dynamic global developments in waste gasification, focusing on pioneering industrial developments in Germany between 1980–2000's as well as current international developments. Lessons learnt from previous and current waste gasification project deployment are shared and enabled the identification of problems which will have to be addressed in the transition from coal gasification towards mono-waste gasification technologies. Additionally, a qualitative evaluation of gasification technologies pointed to the strengths and weaknesses of fixed-bed, fluidized-bed and entrained-flow gasification principles in their application for waste gasification.

The paper considers a staged conversion process of pulverized coal fuel in the MHPS-type gasifier, which uses mixtures of oxygen and carbon dioxide as a gasifying agent instead of air. Similar conversion processes can be applied in the process diagrams with the capture and disposal of carbon dioxide. The research tool is a reduced-order mathematical model of coal particles' conversion in a reacting gas flow. Replacement of nitrogen with carbon dioxide leads to significant changes in the gasification process characteristics: the average reaction temperature decreases, but this decrease is partially compensated by an increase in the concentration of gaseous reactants. Thus, the gasification process efficiency and the fuel conversion degree increase. Calculations make it possible to identify a range of parameters with the highest cold gas efficiency values. The influence of oxygen concentration is estimated, the dependence of the fuel conversion degree on the reaction temperature is analyzed.

The high-temperature syngas and molten slag droplets discharged from entrained-flow coal gasifiers contain a large amount of heat energy, which can be efficiently recovered by radiant syngas coolers (RSCs). However, it is hard to know the solidification degree of molten slag droplets at the outlet of an RSC during industrial operations. In this work, the industrial-scale RSC and molten slag droplet models are established to predict the solidification degree of slag droplets at the outlet of the RSC. Then, the effects of slag diameter, syngas flow field, slag initial temperature, slag porosity, and slag pore structure are investigated by numerical simulations, and residence time as well as complete solidification time are calculated by coupling of a discrete-phase model and a solidification model. The results indicate that as the slag droplet diameter increases, the residence time of the slag droplet shortens, but the complete solidification time increases. When the slag droplet diameter is greater than or equal to 3.0 mm, the complete solidification time is larger than the residence time, and the slag droplet cannot solidify completely at the outlet of the RSC. The solidification degree in the windward zone is greater than that in the leeward zone. Although the slag initial temperature has little effect on the solidification, a lower slag initial temperature is still conducive to a greater solidification degree. Additionally, the pore structure facilitates solidification, and the promoting effect of penetrated pores is more remarkable than that of closed pores. A larger porosity is also beneficial to accelerate the solidification of molten slag droplets and increase the solidification degree.

The characteristics of the energy structure of rich coal, less oil and less gas, coupling with a high external dependence on oil and natural gas and the emphasis on the efficient and clean utilisation of coal, have brought opportunities for coal chemical industry. However, with the large-scale popularisation of coal gasification technology, the production and resulting storage of coal gasification slag continue to increase, which not only result in serious environmental pollution and a waste of terrestrial resources, but also seriously affect the sustainable development of coal chemical enterprises. Hence, the treatment of coal gasification slag is extremely important. In this paper, the production, composition, morphology, particle size structure and water holding characteristics of coal gasification slag are introduced, and the methods of carbon ash separation of gasification slag, both domestically and abroad, are summarised. In addition, the paper also summarises the research progress on gasification slag in building materials, ecological restoration, residual carbon utilisation and other high-value utilisation, and ultimately puts forward the idea of the comprehensive utilisation of gasification slag. For large-scale consumption to solve the environmental problems of enterprises and achieve high-value utilisation to increase the economic benefits of enterprises, it is urgent to zealously design a reasonable and comprehensive utilisation technologies with simple operational processes, strong adaptability and economic benefits.

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.

Fine slag (FS), which is a by-product from coal gasification, is composed of inorganic minerals and residual carbon. Acid treatment has high efficiency to separate the residual carbon in FS but the changes of properties of FS treated by acid remain unclear. To have a deep understanding of effects of acid treatment on physicochemical properties and gasification activity of FS, FS was subjected to different acid treatment, and then were characterized using Nitrogen adsorption technique, Raman spectroscopy and thermo-gravimetric analyzer. The results showed that the combined treatment with hydrochloric acid and hydrofluoric acid can remove the almost all mineral matters. Acid treatments did not modify the continuous and complete pores structure of FS. While, hydrochloric acid has a major influence on carbon structure, which produces the highest carbon actives and amorphous carbon. Nitric acid has positive influence on carbon structure transformation to crystalline structure. Notably, the gasification time can be shortened by the reduction of ash content. The carbon active sites in samples governed the initial reactivity while at the late stage of gasification the amount of inorganic elements controlled the gasification rate.

The conventional hydrogen production methods, primarily steam methane reforming and coal gasification, produce massive amounts of greenhouse gas emissions which significantly cause impacts on the environment. An alternative hydrogen production method is high-temperature electrolysis using Solid Oxide Electrolyzer that combines both high conversion efficiency and saleable high purity hydrogen production. The produced hydrogen can feed the various industrial processes at different scales in addition to offering an environmentally friendly storage option. The scope of this paper is to examine the economic feasibility of this technology through the utilization of the exergoeconomic concept, which traces the flow of exergy through the system and price both waste and products. Therefore, a standalone solid oxide electrolyzer of a 1MWe is considered for hydrogen production using renewably generated electricity. Having the detailed exergy analysis conducted in earlier studies, the focus of this article is on the costing of each exergy stream to determine the exergy cost and the potential changes outcomes as a result of the system operating or design parameters optimization. It is found that the cost of hydrogen production through the modular high-temperature electrolyzer varies between $3-$9/kg with an average of about $5.7/kg, respectively.

Indonesia's coal reserve is abundant with its lower price and widely distributed than oil and natural gas. However, the coal emits high carbon dioxide gas (CO2) and sulfur compounds (H2S, SOx) to the environment during utilization. Plasma gasification can overcome those lacks using the external electric energy through a plasma torch. The chemical properties of coal have impacts on the energy content and environmental benchmarking. Using steam as a gasifying agent should be adequate to produce H2 and CO syngas. A research has been carried out to analyze and understand the benefit of using different gasifying agent for maximizing the H2 production and minimizing the environmental impact. Pure Steam (PS) gasifying agent to coal ratio of 0.4 has shown 43.76% H2 composition in syngas and cold gasification efficiency (CGE) with 37.71%. The PS to coal ratio of 0.2 has a significant carbon conversion efficiency of 4.75% and the PS to coal ratio of 0.6 has a gross energy potential of 86.5 kW. Using such the PS is significantly better than the mixture of steam oxygen (SO) as the gasifying agent since it needs to have a greater SO flow rate to have the SO to coal ratio of 1.00.

Mercury (Hg), a kind of heavy metal pollutant, has a great impact on the environment and human health. The highly efficient technology for Hg removal has attracted widespread attention from researchers. In this study, the coal gasification slag (CGS) and the slag after sorting were used as sorbents, and the Hg0 removal performance of the sorbents were investigated through the fixed-bed reactor and entrained flow reactor. The characterization methods such as N2 adsorption-desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) were performed to analyze the physical and chemical characteristics of the sorbents. According to the results of fixed-bed Hg0 removal experiment, the Hg0 removal efficiency of the origin slag (OS) and high carbon slag (HCS) could maintain more than 91% at 60–120°C. The high ash slag (HAS) showed the highest Hg0removal efficiency of 97% at 60°C, which was greatly affected by the Hg0 removal temperature. The Hg-TPD (Hg-temperature program desorption) and XPS results indicated that the chemisorbed oxygen on the sorbent participated in the Hg0 oxidation process with HgO formed on the surface of the sorbent. According to the results of entrained flow Hg0 removal experiments, the Hg0 removal efficiencies of OS and HCS were 56% and 57% at C/Hg ratio of 40000 and the Hg0 removal temperature of 60°C, respectively. When the C/Hg ratio was 80000 and the Hg0 removal temperature was 60°C, the Hg0 removal efficiencies of OS and HCS were 100% and 82%, respectively.

Co-gasification of renewable biomass and coal is a promising technique to reduce greenhouse gas emission beside increasing gasification performance instead of individual coal gasification. In this study, the co-gasification performance of pine bark (PB) biomass and Barapukurian bituminous coal (BBC) have been assessed using a high-temperature entrained flow gasifier using CO2 reactant. Results show that increasing biomass concentration increases the carbon conversion, syngas quality and cold gas efficiency (CGE), while reduces emission. For example, an addition of 20% biomass with coal increased the carbon conversion by 21.5, 10.6 and 4.5%-point at temperatures of 1000, 1200 and 1400 °C compared to pure coal gasification. Similarly, increasing biomass ratio in the blend increased the yield of CO by 11–36 vol% under different temperatures. Also, the CGE, fragmentation index ( F I = ∑ i n F D o ) and alkali and alkaline earth minerals in ash were increased with increasing biomass ratio in the blend. Overall, at least 50% of coal can be replaced with renewable biomass considering performance and emission characteristics, making the technology more sustainable.

The article presents results from analyzing the state of the art achieved in the coal gasification technologies developed around the world and the demand for them. It is shown that such technologies have presently arrived at a crossroad in their development. Their future will be determined by the development prospects of coal energy as a whole. Coal still continues to play the most important role in the world energy. In recent years, external factors have become extremely negative for the development of coal energy. Among other fuels, coal produces the largest specific emissions of CO2 during its combustion, in view of which it may become the first victim of the unfolding energy decarbonization policy. Under such conditions, there is a need to diversify the coal utilization fields, primarily through manufacturing a wide range of chemical products with a high added value. This generates the need to develop the appropriate technologies, and, first of all, gasification technologies, the use of which opens the possibility of making almost the entire range of products from coal that are obtained from petroleum and natural gas. It has been determined that gasification technologies have already reached a high level of technical maturity, and a large number of gasifier designs have been proposed. It has been determined that the majority of operating coal gasification plants are presently used for manufacturing various chemical products, first of all, natural gas substitute (which is then forwarded to gas networks) and also methanol and ammonia. It is pointed out that only a few integrated gasification combined cycle plants have been implemented and planned for construction, which means that the private sector shows little interest in this technology. At the same time, such plants have quite a high potential for being used in low-carbon energy, of course, provided that the problem of disposing the captured CO2 is solved. It is shown that a large number of gasifier equipment manufacturers are available around the world. However, gasifiers are produced in single units or in a small series, which unavoidably leads to the high cost of this equipment. For the further innovative development of the gasification technology, combined efforts should be taken by the private sector and the state.

The technology of supercritical water gasification (SCWG) of coal has a great prospect because it converts coal into hydrogen-rich gas products efficiently and cleanly. However, there are bottlenecks affecting the complete gasification of coal in supercritical water (SCW) without catalyst under moderate conditions. This work is to explore the restricted factor for complete gasification of coal in SCW by investigating the conversion mechanism. The conversion mechanism of SCWG of coal with and without K2CO3 is proposed. Polycyclic aromatic hydrocarbons (PAHs) with graphite phase structures are formed by the condensation of aromatic structures at 550–750 °C. It is the restricted factor due to its characteristic of difficulty to be gasified. There is no condensation of aromatic structures in the process of SCWG of coal with K2CO3, which effectively inhibited the formation of PAHs with graphite phase structures. K2CO3 dramatically promoted the SCWG of coal, leading to carbon gasification efficiency (CE) reaching 98.43%.

Developing underground coal gasification (UCG)-based hydrogen production (UCG-H2) is expected to alleviate hydrogen supply and demand contradiction, but its energy consumption and environmental impact need to be clarified. In this paper, comparative study of energy consumption and greenhouse gas (GHG) emissions between UCG-H2 and typical surface coal gasification (SCG)-based hydrogen production (SCG-H2) is carried out using life cycle assessment method. Result shows energy consumption of UCG-H2 is only 61.2% of that of SCG-H2, which is 1,327,261 and 2,170,263 MJ respectively, reflecting its obvious energy saving advantage. 80% capture rate can achieve an appropriate balance between energy consumption and emissions. Under this capture rate, emissions of UCG-H2 and SCG-H2 are roughly equivalent, which are 207,582 and 197,419 kg CO2-eq respectively. Scenario analysis indicates energy consumption in hydrogen industry can reduce by 38.8% when hydrogen production is substituted by UCG with CCS to fully meet demand of 21 Mt in 2030.

Coal gasification is a popular method for the optimization of coal utilization and the reduction of environmental pollutant emissions. However, the reductive atmosphere of its products is disadvantageous for removing elemental mercury (Hg0). Activated cokes (AC) was employed in this work for mercury capture in a reducing atmosphere. The high-temperature heating decreases the mercury-removal capability of carbon sorbents because the carbonaceous surface is becoming oxygen-depleted and micropore-decreased after the heating treatment. The mechanism of mercury adsorption in pure nitrogen follows the Mars-Maessen mechanism over the carbon sorbents. To identify the effects of carbon monoxide (CO) and carbon dioxide (CO2) on Hg0 removal, the Hg0-adsorption and thermal desorption experiments were carried in a fixed-bed reaction system. CO inhibits both the chemisorption and physisorption of Hg0. CO2 competes for the active sites, lactone groups and hydroxyl groups, and occupies the micropores, which is beneficial to adsorb Hg0 physically. When CO and CO2 coexisted, the removal efficiencies show steadier than those in monocomponent gas (only CO or CO2). CO2 can resist the negative effect of CO on Hg0 removal, to some extent, because CO2 can inhibit the oxidation and disproportionation of CO. This experimental study provides practical guidance for the development of mercury-removal technology with carbon materials in the coal gasification plant.

Hydrogen is the core source to both refinery and synthetic plant of chemicals. Refinery consumes high purity hydrogen while synthetic plant of chemicals needs syngas consists of hydrogen and carbon oxides. As main hydrogen production technologies, industrial coal gasification and steam methane reforming based pathways generate H2, CO and CO2, which is actually the mixture of hydrogen and carbon oxides. Hence, the gases demand of refinery and synthetic plant of chemicals and their supply from hydrogen production can form hybrid hydrogen networks. On the basis of complementary reuse, this paper firstly proposes integration of hybrid hydrogen network for refinery and synthetic plant of chemicals. Superstructures of individual and hybrid hydrogen networks are employed as problem illustration and corresponding linear programming (LP) mathematical models are formulated. Practical refinery and synthetic plant of chemicals cases are employed to demonstrate its application. Compared with individual networks, the natural gas conservation case can recover 8660.4 Nm3·h-1 hydrogen in purge gas, reduce 1386.6 Nm3·h-1 CO2 emission, equaling to reduction of 278.11 kmol·h-1 natural gas feedstock and 14.8% of total gas production load; the coal conservation case can even waive the total coal consumption and extra 104.1 kmol·h-1 natural gas, recover 8660.4 Nm3·h-1 hydrogen in purge gas, reduce 5255.8 Nm3·h-1 of CO2 emission and decrease 21.2% of the total gas production load. Furthermore, economic evaluation is also placed to account for the economic advantage of hybrid network.

Chemical looping gasification (CLG) is a recommended method for lignite gasification, and the product syngas is a mixture of H2, CO, and other gases. Much attention has been paid to coal gasification using a fluidized bed for syngas production. In this study, the performance of syngas preparation from CLG using a fluidized bed and CaSO4–CuO as the oxygen carrier was evaluated. To better understand the fluidization process, coal fluidized bed experiments were carried out. Based on the cold-state, syngas obtained from CLG under hot-state conditions was analyzed. The results show that a reaction time of 5 min is recommended for more CO generation. At the same time, a H2/CO molar ratio of around 1 can be achieved. The energy consumption of syngas generation using CaSO4–CuO CLG with lignite is 399.75 kJ mol−1, lower than that of syngas generation using the traditional coal reaction with pure oxygen and steam. This indicates that this is an advanced method for preparing syngas, providing a basis for industrial amplification operations.

A technological scheme has been developed for the utilization of a water–tar mass containing toxic organic compounds from the phenol series formed in the course of coal gasification. Coal tar pitch was obtained based on the multiple distillation of the separated tar mass, and its application to the production of carbon electrodes was investigated.

Violates containing polycyclic aromatic hydrocarbons (PAHs) were precipitated in the process of fast pyrolysis and gasification of coal and organic substances. PAHs are one of bottlenecks of entire coal gasification for hydrogen production. In current work, the solubility of PAH oil droplets in supercritical water/hydrogen circumstances were investigated based on molecular dynamics simulation, which was beneficial for understanding the solubility behaviors of PAHs in supercritical water/hydrogen environment. The results showed that heavy PAHs were rather stable in the water phase. Supercritical water along with hydrogen promoted the miscibility of PAHs compared with that of pure supercritical water. Furthermore, high density and high temperature facilitated the rapid solvation of PAHs in supercritical water/hydrogen environment. This paper is expected to provide a theoretical support for the development of complete coal gasification technology for hydrogen production.

In this work, the effect of an iron-based catalyst from coal liquefaction on coal gasification was studied. Two catalyst loading methods and three catalyst loading contents were taken into consideration. Besides, the carbon structure, surface morphology, and element distribution of coal char and gasified semi-char were investigated, and the interactions between the catalyst and internal minerals of coal were studied. The results showed that the coal char prepared by wet impregnation had higher reactivity than that prepared by a dry mixing method. From the perspective of improving the coal reactivity, the optimal addition method should be wet impregnation with a 2% catalyst. The model-free and model-fitting methods were applied to study the catalytic gasification kinetics. The iron-based catalyst would be broken during wet impregnation, and the catalyst fragments could stick to the surface of coal char, resulting in higher reactivity. The graphitization of char increased with the addition of the iron-based catalyst. This can imply that the carbon structure cannot effectively represent the gasification reactivity in the presence of the iron-based catalyst. The Iron-based catalyst can accelerate the gasification rate alone and can also provide higher catalytic activity with the internal minerals of coal.

Low-Rank Coal (LRC) gasification utilising Fluidised Bed Gasifier (FBG) is more efficient for LRC that has higher reactivity, moisture, tar, volatile, and ash content but lower calorific value compared to other types of coals. This work investigated the application of Computational Fluid Dynamics (CFD) in simulating LRC gasification under different temperatures which is lower (873K), normal (973K) and higher (1073K) temperature atmosphere. Besides that, the effect of LRC type and gasifying agents on the producer gas CO+H2 composition, Lower Heating Value (LHV) and Cold Gas Efficiency (CGE) were also studied using High-rank Coal (HRC) as comparison. The results obtained showed that LRC gasification using oxygen increased LHV and CGE. Lower temperature gasification using oxygen at 873 increased CO+H2, LHV and CGE for LRC compared to higher temperatures at 973K and 1073K. This prediction suggests that LRC gasification using oxygen at lower temperature increases the LRC gasification efficiency.

Gaseous sulfur is released during fluidized bed coal gasification, and control the yield of gaseous sulfur or the conversion between gaseous organic sulfur and inorganic sulfur at source is necessary, because it can economically satisfy the requirements of industrial production and protect the environments. In this study, sulfur release behaviors of a middle-sulfur coal called Guizhou coal were quantitatively determined through controlled experiments in a lab-scale fluidized bed during oxygen rich-steam gasification. The measured gaseous sulfur species were H2S, SO2, COS and CS2. The effects of temperature (850OC-950OC) and limestone (Ca/S = 2) on the sulfur release behaviors were investigated. Among the above four gaseous sulfur, the yield of H2S is the highest, followed by COS, while only less than 1.5% of sulfur in coal is released as SO2 and CS2. With the increase in temperature, the yield of H2S increases while that of SO2 decreases, and the change of COS yield and CS2 yield is not obvious. The molar ratio of H2S/COS increases with increasing temperature, which is qualitatively matched by thermodynamic analysis. The addition of limestone reduces the released sulfur but not change the distribution of gaseous sulfur forms. Meanwhile, the molar ratio of H2S/COS increases after adding limestone, while the trend with temperature of H2S/COS does not change. The removal rate of H2S is between 23% and 28%, which increases with temperature. The distributions of sulfur in bottom char and fly ash are similar. The main sulfur species in the bottom char is organic sulfur, and thiophene dominates the organic sulfur. The increase of temperature and the addition of limestone will both promote the increase of inorganic sulfur content, and the decrease of organic sulfur content.

This study classifies the evolutionary properties of coal char pore structure which occur during coal gasification. CO2 gasification of various coal samples was carried out in a fixed bed reactor. The resulting chars were analysed using N2 isothermal adsorption/desorption and scanning electron microscopy (SEM), coupled with fractal theory. Analytical results indicate that the pore structure of coal char underwent micropore evolving, enlarging and overlapping, while more mesopores and macropores developed with continued gasification. The surface area of coal char increased to its maximum value when carbon conversion reached approximately 50%. Fractal calculation results showed that two types of fractal structures associated with the coal char surface and pore structure underwent stereome development and elapsing. However, the evolutionary properties were unique for different coal samples. High rank coal had a complex spatial structure with more micro-pores, whereas lower rank coal had a much flatter spatial structure.