Life-cycle performance of indirect biomass gasification as a green alternative to steam methane reforming for hydrogen production

The environmental performance of hydrogen production via indirect gasification of poplar biomass was evaluated following a Life Cycle Assessment approach. Foreground data for the study were provided mainly from process simulation. The main subsystems and processes that contribute to the environmental impacts were identified. Thus, poplar production and direct emissions to air from the processing plant were found to be the main sources of environmental impact. Furthermore, a favourable (positive) life-cycle energy balance was estimated for the gasification-based system.     

Research needs for coal gasification and coal liquefaction

We describe essential features of developing coal-gasification and coal-liquefaction technologies and summarize the current development status and important R&D needs for these processes.     

Detonation-induced coal gasification

A preliminary experimental and theorotical investigation of the feasibility of detonation-induced pulverized coal gasification is described. The concept envisions a closed annular detonation duct through which a hydrogen/oxygen gasphase detonation propagates continuously. Coal particles injected into the violent and rapidly changing atmosphere produced by the detonation would undergo gasification reactions and be subsequently expelled from the duct. These events would occur in a time period compatible with one revolution of the detonation. A one-dimensional analysis of the response of a single coal particle within the expansion-wave region behind the detonation front is presented. Independent variables include particle diameter, initial H₂/O₂ stoichiometry and expansion wavelength (at the time the particle is overtaken by the detonation front). The most significant result of this analysis is the prediction of relative gas/particle velocities ranging between 125 and 1500m/s, which are sustained throughout particle residence times of 1–15 ms corresponding to 10–1000 μm diameter particles. An experimental facility comprising a 47 m ‘single-shot’ detonation duct that was built for this study is discussed. The duct was 2.54 cm square and was terminated at each end by a 0.36 m diameter × 2.44 m long cylindrical tank which contained helium gas during a test. Sized coal particles were placed at a point within the first 3.7 m length of the duct, and thin brass diaphragms initially separated the duct from the two helium-filled tanks. Detonation was initiated at the duct, end closest to these particles. The diaphragm at that end burst, allowing combustion and gasification products to exhaust into the adjoining tank where they were quenched and decelerated. When the detonation reached the far end of the duct the second diaphragm burst, minimizing wave reflections which would otherwise return to the ‘test section’ end and interfere with the flow field there. After a test the contents of both tanks and the duct were circulated and mixed. A gas sample was then drawn and analysed for yield. Results from preliminary experiments using this facility are presented. Although too few tests were conducted for conclusive observations to be reported, in two experiments yields of CO + CH₄ representing 40 per cent of the total initial carbon content in the coal samples were obtained.     

Solar coal gasification

A preliminary evaluation of the technical and economic feasibility of solar coal gasification has been performed. The analysis indicates that the medium-Btu product gas from a solar coal-gasification plant would not only be less expensive than that from a Lurgi coal-gasification plant but also would need considerably less coal to produce the same amount of gas. A number of possible designs for solar coal-gasification reactors are presented. These designs allow solar energy to be chemically stored while at the same time coal is converted to a clean-burning medium-Btu gas.     

Catalytic coal gasification for SNG manufacture

Exxon Research and Engineering Company is engaged in research and development on catalytic coal gasification (CCG) for the production of substitute natural gas (SNG). the catalysts being studied are the basic and weak acid salts of potassium. the use of a gasification catalyst allows the gasifier temperature to be reduced, reduces the tendency for swelling and agglomeration of caking coals and promotes gas phase methanation equilibrium. These features of the catalyst are utilized in a novel processing sequence which involves separation of product gas into methane (SNG) and a CO/H₂ stream which is recycled to the gasifier. the predevelopment phase of research on this process concept was completed in early 1978 and included bench-scale research on catalyst recovery and kinetics, the operation of a 6 in diameter × 30 ft long fluid bed gasifier and supporting engineering studies. As part of the engineering programme, a conceptual design has been developed for a pioneer commercial CCG plant producing SNG from Illinois No. 6 bituminous coal. the paper reviews the status of research and development on the CCG programme and describes the conceptual design and economics for the commercial scale CCG plant.     

A steam process for coal gasification

A gasification process has been studied using steam as a reactant as well as a heat source to generate hydrogen, carbon monoxide, and methane by using carbon in coal as a reducing agent. Economical operation (60–70% efficiency based on the heating value of coal) can be maintained by using a large excess in steam at 1300 C level (more than 4 mole of H₂O to 1 mole C). This steam is produced by burning a fraction of the product gas in a pebble-heater system. A high percentage of H₂ can be produced in the product gas without the need for shift conversion. Depending on the reactor pressure and temperature, other components of varying percentages are CO, CH₄ with CO₂ and H₂S removed by absorption; excess H₂O is removed by condensation. Heat removed in condensation is recovered in steam heating and feed water heating. Ash is removed in the reactors and fines in the condensate as condensation nuclei. Large excess steam converts all sulfur to H₂S with final removal as raw sulfur. Charcoal and Illinois No. 6 coal were gasified in our laboratory facility at pressures up to 10 atm. Steam was heated in an electric arc heater to simulate the pebble heaters in the prototype. All flyash and tar was removed with the condensate.     

Prospects for coal gasification in Pakistan

Pakistan is currently facing serious energy supply problems. Energy demand has been increasing by about 8% per year during the last 12yr and this trend is likely to continue. Since 1980–1981 the oil import bill has been consuming more than 50% of yearly export earning. As there is not much scope for a sizeable increase in the domestic supply of gas, oil, or hydroelectric power, increasing the use of domestic coal is necessary to avoid excessive dependence on imported energy. Coal gasification to produce substitute natural gas (SNG) is not economical at present coal production costs, due to the low cost of indigenous gas and subsidized furnace oil and kerosene and the high SNG production costs from the technology available at present. If domestic prices of gas and liquid fuels are increased to the level of current international oil prices and developments in coal gasification technologies can bring about expected reductions in capital costs and improvements in efficiency, coal gasification may become economical in Pakistan. It is estimated that indigenous coal resources can potentially supply 3–6 million TCE/yr of SNG by 2000—about 10–20% of the substitutable fossil fuels demand for that year—along with meeting about 9% of the electricity demand.     

Plasma catalytic reforming of methane

Thermal plasma technology can be efficiently used in the production of hydrogen and hydrogen-rich gases from methane and a variety of fuels. This article describes progress in plasma reforming experiments and calculations of high temperature conversion of methane using heterogeneous processes. The thermal plasma is a highly energetic state of matter that is characterized by extremely high temperatures (several thousand degrees Celsius), and a high degree of dissociation and a substantial degree of ionization. The high temperatures accelerate the reactions involved in the reforming process. Hydrogen-rich gas (40% H₂, 17% CO₂ and 33% N₂, for partial oxidation/water shifting) can be efficiently made in compact plasma reformers. Experiments have been carried out in a small device (2–3 kW) and without the use of efficient heat regeneration. For partial oxidation/water shifting, it was determined that the specific energy consumption in the plasma reforming processes is 16 MJ/kg H₂ with high conversion efficiencies. Larger plasmatrons, better reactor thermal insulation, efficient heat regeneration and improved plasma catalysis could also play a major role in specific energy consumption reduction and increasing the methane conversion. A system has been demonstrated for hydrogen production with low CO content (1.5%) with power densities of 30 kW (H₂ HHV)/l of reactor, or 10 m³/h H₂ per liter of reactor. Power density should further increase with increased power and improved design.     

Microwave-assisted dry reforming of methane

The microwave-assisted dry reforming of methane over an activated carbon, which acted as catalyst and microwave receptor, was investigated. As a preliminary study, the CO₂ reforming of CH₄ was carried out using conventional heating and microwave heating in order to compare both heating devices. Higher conversions of CH₄ and CO₂ were achieved by microwave heating. Under microwave heating, various operating variables were studied in order to determine the best conditions for performing dry reforming with high conversions and the most suitable H₂/CO ratio. Thus, the dry reforming reaction was studied at different temperatures. An optimum range of working temperatures (between 700 °C and 800 °C) was established. In this range of temperatures, the dry reforming reaction is believed to take place as a combination of CH₄ decomposition and CO₂ gasification. Carbonaceous deposits from CH₄ decomposition are gasified by CO₂ and, as a result, active centres for the dry reforming reaction are constantly regenerated. The effect of the proportion of CO₂ fed in on the CH₄ and CO₂ conversions was also investigated. Small increases in the percentage of CO₂ fed in gave rise to large increases in both conversions, but especially in the case of CH₄. The volumetric hourly space velocity was also studied. It was found that the lower the space velocity, the higher the conversions obtained.     

Supported catalysts for induction-heated steam reforming of methane

Ni₆₀Co₄₀ nanoparticles supported on γ-Al₂O₃ capable of simultaneously catalysing the steam reforming reaction of methane and supplying in-situ the heat necessary to activate the reaction by induction heating, have been synthesized and characterized. Energy is remotely and promptly supplied by an alternating radiofrequency magnetic field (induction heating system) to supported nanoparticles that act as dissipating agents by virtue of their ferromagnetic properties. The temperature reached on the Ni–Co based catalyst surface is high enough to obtain good catalytic performances for the steam methane reforming (SMR). By varying synthesis conditions, samples with two different metal loading (17 wt% and 30 wt%) and different particle size distribution were prepared and characterized. Experimental results evidence that the temperature reached on the catalyst surface is related to the metal loading and to the particles size distribution that strongly affect the ability of ferromagnetic nanoparticles to convert the externally applied radio frequency field into heat. Catalyst pellets proved their effectiveness reaching the temperature of 720 °C during SMR reaction and 80% methane conversion.     

Experimental and in-situ estimation on hydrogen and methane emission from spontaneous gasification in coal fire

In order to quantitatively understand the wasteful and combustible gas resources which are released from underground coal fires caused by spontaneous combustion, the emission characteristics of hydrogen and methane in the thermochemical process of coal oxidation are investigated by both laboratory tests and on-site measurements. Employing an adiabatic oxidation test, the releasing rules of index gases in limited space were estimated with programmed temperature rising up to 200 °C. Experimental results demonstrate that the releasing concentrations of methane and hydrogen preform an exponential trend with oxidation temperature, while the release rates are significantly influenced by the metamorphic degrees and oxygen supplement conditions. Field survey was also operated to trace the gaseous products in a typical coal fire area in Xinjiang Region, China via gas monitoring at surface emission vents and fractures. Measurement data illustrate a good consistency between the index gases and the stage of coal spontaneous combustion, and the exhaust hydric gases are estimated at more than 1000 tons per year. The presented method and results could provide a useful reference to gaseous products estimation for coal spontaneous combustion.     

Effect of Ni precursor salts on Ni-mayenite catalysts for steam methane reforming and on Ni-CaO-mayenite materials for sorption enhanced steam methane reforming

In view of climate change containment, sorption enhanced steam methane reforming (SESMR) appears as an interesting production route for H₂ with the additional advantage of CO₂ capture application performed by high-temperature solid sorbents. CaO is largely employed as CO₂ sorbent because of its low-cost mineralized forms (limestone and dolomite), of its high sorption capacity in the high temperature range compatible with steam methane reforming (SMR). Many recent studies have proposed purposely synthesized Ni-based reforming catalysts, used with high-temperature CO₂ solid sorbents, or combined sorbent-catalyst materials (CSCM). For this last purpose, we studied the effect of Ni salt precursor (Ni nitrate hexahydrate or Ni acetate tetrahydrate) on properties and reactivity of Ni-mayenite catalysts or Ni-CaO-mayenite CSCM, synthesized by an already validated sequence of wet mixing (for sorbents synthesis) and wet impregnation (for catalysts and CSCM synthesis) methods. Although Ni acetate tetrahydrate was often reported as the best choice to improve textural properties, our study identified Ni nitrate hexahydrate as a definitely more suitable precursor than Ni acetate tetrahydrate in the purpose of developing efficient materials for SESMR. The dissimilar behaviors observed in reforming reactivity are related and explained by the differences in textural properties, Ni species dispersion, and reducibility.     

La-doped supported Ni catalysts for steam reforming of methane

Ni-La/α-Al₂O₃ catalysts at different Ni/La ratio of respectively 7/3, 8/2 and 9/1 to obtain a material with total loading of 10 wt% as used in industrial methane steam reforming field are prepared with incipient wetness impregnation method. Various techniques including TGA-DTA, XRF, XRD, particles size, H₂-RTP and BET are used to characterize materials and their catalytic performance is evaluated during the steam reforming reaction at different temperatures ranging from 500 to 800 °C. Only NiO and α-Al₂O₃ phases are evidenced by DRX indicating probably the presence of small lanthanum crystallites in high dispersion state. Addition of La may cause strong change at the surface of NiO sites. Substitute Ni by La leads to smaller and well dispersed NiO particles sizes with strong metal support interaction (SMSI). TPR analysis reveals the reduction of Ni species with high Ni-La-Al interactions particularly well observed with 3 wt%La catalyst. The small Ni particles sizes highly dispersed on the support enhance the dissociative adsorption of CH_x species. The highest H₂ yield is obtained with 7Ni-3La/Al catalyst reaching 94% at 800 °C.     

Highly-efficient hydroxyapatite-supported nickel catalysts for dry reforming of methane

Ni-based catalysts were prepared using two hydroxyapatites (Ca-HA1, S_BET = 7 m²/g and Ca-HA2, S_BET = 60 m²/g) with different physico-chemical properties. The objective of the study was to evaluate the performance of these two materials as promising supports for dry reforming reaction (DRM) as well as to investigate the influence of different process parameters, such as temperature, pressure, time and catalyst pretreatment on the performance of these two catalysts. Thermodynamic calculations were performed to determine the conditions that would limit solid carbon deposit and favor the reactants conversion. Then, an experimental parametric study was carried out to investigate the impact of the temperature, pressure, catalyst pretreatment and support thermal treatment on the catalysts performance. The results showed that the catalyst pretreatment allowed the reduction of the nickel particles in a higher extent, which resulted in better catalytic performance when compared to the catalysts without pretreatment. High temperatures around 700 °C and low pressures around 1.6 bar were required to attain high CH₄ and CO₂ conversions around 70–80% as well as high H₂ and CO selectivity around 90% for 90 h of time on stream. In all cases, Ni/Ca-HA2 catalyst presented better catalytic performance than Ni/Ca-HA1 due to the presence of smaller nickel particles (10–20 nm), stronger basicity, higher density of basic sites (0.23 mmol g⁻¹) as well as higher specific surface area (S_BET = 60 m²/g) of the Ca-HA2 support. Ni/Ca-HA2 catalyst was highly active (initial methane conversion: 75%) and relatively stable during 90 h of TOS and its catalytic behavior was comparable with the performance of Ni-based catalysts prepared with conventional supports reported in the literature.     

In situ generation of nickel/carbon catalysts by partial gasification of coal char and application for methane decomposition

Catalytic methane decomposition (CMD) has a good potential to develop environmentally friendly hydrogen economy, and the catalyst plays a vital role on its applications. In this work, a novel strategy was proposed to fabricate efficient and effective nickel/carbon catalysts for CMD by introducing some additional nickel and K₂CO₃ into partial steam gasification of coal char. The gasification process is conducive to in situ synthesize nickel crystallites with high reduction degree (the value of Ni⁰/(Ni⁰+Ni²⁺) up to 76%–81%) on the catalyst surface, and it is competent for co-generation of hydrogen-rich gas and nickel/carbon hybrids with large surface areas (around 86–149 m²/g after washing off the residual potassium salts). The nickel/carbon hybrid as the gasification residue could serve as the catalyst for CMD, showing high and stable methane conversion (up to 80%–87%) at 850 °C. It is observed that co-production of hydrogen and filamentous carbons can be achieved in the 600-min process of CMD, thanks to the positive effect of K₂CO₃ on formation and activity improvement of the nickel/carbon catalyst.     

煤的气化反应活性对常压固定床气化的影响

简要介绍了煤的气化反应活性及其影响因素,提出了根据煤的气化反应活性界定气化用煤灰熔融性温度指标的方法,并就煤的气化反应活性对常压固定床气化炉内氧化层、还原层、干馏层、干燥层及炉出煤气温度的影响进行了系统分析。     

Status of coal gasification processes

The current status of a number of processes which have been or are being developed to produce high-Btu, medium-Btu, and low-Btu gas from coal is given.     

The coal gasification plant for the developing country

An attempt has been made to discuss various design aspects of the coal gasification plant for the developing country on effective utilization of coal as a fuel there, where coal is used at the moment as the energy raw material for local cement, lime and brick manufacturers. This includes economic exploitation, economic justification and the IGCC technology proving to be an effective method of coal utilization and environmentally safe and clean design. The present work suggests the material with higher resistance to minimise crack failure for the transportation, storage and utilization of hydrogen fuels desired there. For this the soft soldered composite laminates made from 4340 steel were tested under plane strain conditions in the environments of hydrogen especially at 700 torr. This all is supported by the fracture behaviour of the soft soldered composite laminates which remains same with and without hydrogen during final stage of fracture there.     

Underground coal gasification: A new clean coal utilization technique for India

Energy demand of India is continuously increasing. Coal is the major fossil fuel in India and continues to play a pivotal role in the energy sector. India has relatively large reserves of coal (253 billion tonnes) compared to crude oil (728 million tonnes) and natural gas (686 billion cubic meters). Coal meets about 60% of the commercial energy needs and about 70% of the electricity produced in India comes from coal, and therefore there is a need for technologies for utilization of coals efficiently and cleanly. UCG offers many advantages over the conventional mining and gasification process. UCG is a well proven technology. Due to the site-specific nature of the process, possibility of land subsidence and surrounding aquifer water contamination, this technology is still in a developing stage in India. Potential for UCG in India is studied by comparing the properties of Indian coals with the properties of coal that are utilized by various UCG trials. The essential issues are elaborated for starting UCG in India based on the reported information from the successful field trials conducted all over the world. Indian industries are in the process of initiating pilot studies of UCG at various sites. This study will help to motivate both applied and theoretical research work on UCG sites in India and after detailed analysis it will provide basic data to interested industries.