Experimental and theoretical study on the characteristics of vacuum residue gasification in an entrained-flow gasifier

About 200,000 bpd (barrel/day) vacuum residue oil is produced from oil refineries in Korea. These are supplied to use asphalt, high sulfur fuel oil, and upgrading residue hydro-desulfurization units. High sulfur fuel oil can be prepared by blending oil residue with light distillate to bring fuel oil characteristics in the range of commercial specifications, which will become more stringently restrictive in the near future in Korea. Vacuum residue oil has high energy content; however, due to its high viscosity, high sulfur content and high concentration of heavy metals are representative of improper low grade fuel, which is considered difficult to gasify. At present, over 20 commercial scale IGCC (Integrated Gasification Combined Cycle) plants using feedstocks with vacuum residue oil for gasification are under construction or operating stage worldwide. Recently, KIER (Korea Institute of Energy Research) has been studying the vacuum residue gasification process using an oxygen-blown entrained-flow gasifier. The experiment runs were evaluated under a reaction temperature of 1,200-1,250 C, reaction pressure of 1.0 kg/cm², oxygen/V.R ratio of 0.8-1.2 and steam/V.R ratio of 0.4-0.7. Experimental results show a syngas composition (CO+H₂), 77-88%; heating value, 2,300-2,600 kcal/Nm³; carbon conversion, 95-99, and cold gas efficiency, 68-72%. Also, equilibrium modeling was used to predict the vacuum residue gasification process and the predicted values reasonably well agreed with experimental data.     

Syngas combustion in a 500 Wth Chemical-Looping Combustion system using an impregnated Cu-based oxygen carrier

Chemical-Looping Combustion (CLC) is an emerging technology for CO₂ capture because separation of this gas from the other flue gas components is inherent to the process and thus no energy is expended for the separation. For its use with coal as fuel in power plants, a process integrated by coal gasification and CLC would have important advantages for CO₂ capture. This paper presents the combustion results obtained with a Cu-based oxygen carrier in a continuous operation CLC plant (500 Wth) using syngas as fuel. For comparison purposes pure H₂ and CO were also used. Tests were performed at two temperatures (1073 and 1153 K), different solid circulation rates and power inputs. Full syngas combustion was reached at 1073 K working at f higher than 1.5. The syngas composition had small effect on the combustion efficiency. This result seems to indicate that the water gas shift reaction acts as an intermediate step in the global combustion reaction of the syngas. The results obtained after 40 h of operation showed that the copper-based oxygen carrier prepared by impregnation could be used in a CLC plant for syngas combustion without operational problems such as carbon deposition, attrition, or agglomeration.     

Engine performance and emission characteristics of a three-phase emulsion of biodiesel produced by peroxidation

Biodiesel, which is produced from vegetable oils, animal fats or used cooking oils, can be used as an alternative fuel for diesel engines. The high oxygen content of biodiesel not only enhances its burning efficiency, but also generally promotes the formation of more nitrogen oxides (NO_x) during the burning process. Fuel emulsification and the use of NO_x inhibitor agents in fuel are considered to be effective in reducing NO_x emissions. In the study reported herein, soybean oil was used as raw oil to produce biodiesel by transesterification reaction accompanied by peroxidation to further improve the fuel properties of the biodiesel, which was water washed and distilled to remove un-reacted methanol, water, and other impurities. The biodiesel product was then emulsified with distilled water and emulsifying surfactant by a high-speed mechanical homogenizer to produce a three-phase oil-droplets-in-water-droplets-in-oil (i.e. O/W/O) biodiesel emulsion and an O/W/O emulsion that contained aqueous ammonia, which is a NO_x inhibitor agent. A four-stroke diesel engine, in combination with an eddy-current dynamometer, was used to investigate the engine performance and emission characteristics of the biodiesel, the O/W/O biodiesel emulsion, the O/W/O biodiesel emulsion that contained aqueous ammonia, and ASTM No. 2D diesel. The experimental results show that the O/W/O emulsion has the lowest carbon dioxide (CO₂) emissions, exhaust gas temperature, and heating value, and the largest brake specific fuel consumption, fuel consumption rate, and kinematic viscosity of the four tested fuels. The increase of engine speed causes the increase of equivalence ratio, exhaust gas temperature, CO₂ emissions, fuel consumption rate, and brake specific fuel consumption, but a decrease of NO_x emissions. Moreover, the existence of aqueous ammonia in the O/W/O biodiesel emulsion curtails NO_x formation, thus resulting in the lowest NO_x emissions among the four tested fuels in burning the O/W/O biodiesel emulsion that contained aqueous ammonia.     

NOx emission characteristics of counterflow syngas diffusion flames with airstream dilution

Syngas is produced through a gasification process using variety of fossil fuels, including coal, biomass, organic waste, and refinery residual. Although, its composition may vary significantly, it generally contains CO and H₂ as the dominant fuel components with varying amount of methane and diluents. Due to its wide flexibility in fuel sources and superior pollutants characteristics, the syngas is being recognized as a viable energy source worldwide, particularly for stationary power generation. There are, however, gaps in the fundamental understanding of syngas combustion and emissions, as most previous research has focused on flames burning individual fuel components such as H₂ and CH₄, rather than syngas mixtures. This paper reports a numerical investigation on the effects of syngas composition and diluents on the structure and emission characteristics of syngas nonpremixed flames. The counterflow syngas flames are simulated using two representative syngas mixtures, 50%H₂/50%CO and 45%H₂/45%CO/10%CH₄ by volume, and three diluents, N₂, H₂O, and CO₂. The effectiveness of these diluents is characterized in terms of their ability to reduce NO_x in syngas flames. Results indicate that syngas nonpremixed flames are characterized by relatively high temperatures and high NO_x concentrations and emission indices. The presence of methane in syngas decreases the peak flame temperature, but increases the formation of prompt NO significantly. Consequently, while the total NO formed is predominantly due to the thermal mechanism for the 50%H₂/50%CO mixture, it is due to the prompt mechanism for the 45%H₂/45%CO/10%CH₄ mixture. For both mixtures, CO₂ and H₂O are more effective than N₂ in reducing NO_x in syngas flames. H₂O is the most effective diluent on a mass basis, while CO₂ is more effective than N₂. The effectiveness of H₂O is due to its high specific heat that decreases the thermal NO, and its ability to significantly reduce the concentration of CH radicals, which decreases the prompt NO. The presence of methane in syngas reduces the effectiveness of all three diluents.     

Syngas combustion in a chemical-looping combustion system using an impregnated Ni-based oxygen carrier

Chemical-looping combustion (CLC) has emerged as a promising option for CO₂ capture because this gas is inherently separated from the other flue gas components and thus no energy is expended for the separation. This technology would have some advantages if it could be adapted for its use with coal as fuel. In this sense, a process integrated by coal gasification and CLC could be used in power plants with low energy penalty for CO₂ capture. This work presents the results obtained in the combustion of syngas as fuel with a Ni-based oxygen carrier prepared by impregnation in a CLC plant under continuous operation. The effect on the oxygen carrier behaviour and the combustion efficiency of several operating conditions was determined in the continuous CLC plant. High combustion efficiencies (～99%), close to the values limited by thermodynamics, were reached at oxygen carrier-to-fuel ratios higher than 5. The temperature in the FR had a significant influence, although high efficiencies were obtained even at 1073 K. The syngas composition had small effect on the combustion, obtaining high and similar efficiencies with syngas fuels of different composition, even in the presence of high CO concentrations. The low reactivity of the oxygen carrier with CO seemed to indicate that the water gas shift reaction acts as an intermediate step in the global reaction of the syngas in a continuous CLC plant. Neither agglomeration nor carbon deposition problems were detected during 50 h of continuous operation in the prototype. The obtained results showed that the impregnated Ni-based oxygen carrier could be used in a CLC plant for the combustion of syngas produced in an integrated gasification combined cycle (IGCC).     

NOx reduction from a large bore natural gas engine via reformed natural gas prechamber fueling optimization

Lean combustion is a standard approach used to reduce NO_x emissions in large bore (35–56 cm) stationary natural gas engines. However, at lean operating points, combustion instabilities and misfires give rise to high total hydrocarbon (THC) and carbon monoxide (CO) emissions. To counteract this effect, precombustion chamber (PCC) technology is employed to allow engine operation at an overall lean equivalence ratio while mitigating the rise of THC and CO caused by combustion instability and misfires. A PCC is a small chamber, typically 1–2% of the clearance volume. A separate fuel line supplies gaseous fuel to the PCC and a standard spark plug ignites the slightly rich mixture (equivalence ratio 1.1–1.2) in the PCC. The ignited PCC mixture enters the main combustion chamber as a high energy flame jet, igniting the lean mixture in the main chamber. Typically, natural gas fuels both the main chamber and the PCC. In the current research, a mixture of reformed natural gas (syngas) and natural gas fuels the PCC. Syngas is a broad term that refers to a synthetic gaseous fuel. In this case, syngas specifically denotes a mixture of hydrogen, carbon monoxide, nitrogen, and methane generated in a natural gas reformer. Syngas has a faster flame speed and a wider equivalence ratio range of operation than methane. Fueling the PCC with Syngas reduces combustion instabilities and misfires. This extends the overall engine lean limit, enabling further NO_x reductions.Research results presented are aimed at quantifying the benefits of syngas PCC fueling. A model is developed to calculate the equivalence ratio in the PCC for different mixtures and flowrates of fuel. An electronic injection valve is used to supply the PCC with syngas. The delivery pressure, injection timing, and flow rate are varied to optimize PCC equivalence ratio. The experimental results show that supplying the PCC with 100% syngas improves combustion stability by 21% compared to natural gas PCC fueling. A comparison at equivalent combustion stability operating points between 100% syngas and natural gas shows an 87% reduction in NO_x emissions for 100% syngas PCC fueling compared to natural gas PCC fueling.     

Use of syngas as an auto fuel additive: State of the art and prospects

A method for the production of a hydrogen-rich gas on board a vehicle was suggested and driving- and bench-tested for application in studies on energy-efficient internal combustion engines with minimum CO, CO₂, CH, and NO _x emissions. The generated gas is further added to the main fuel fed to the engine. Catalysts for hydrocarbon fuel conversion to syngas were developed. A compact on-board syngas generator mounted under the motor hood and a generator control system adapted to the engine control system were designed. It was shown experimentally that the suggested solution allows a reduction of 13–40% in the fuel rate depending on the operating mode under the urban cycle conditions and considerably decreases the release of CO, CO₂, and NO _x . Prospects for the applications of this technology for creating ecologically clean engines were assessed.     

A numerical and experimental study of counterflow syngas flames at different pressures

Synthesis gas or “Syngas” is being recognized as a viable energy source worldwide, particularly for stationary power generation due to its wide availability as a product of bio and fossil fuel gasification. There are, however, gaps in the fundamental understanding of syngas combustion and emissions characteristics, especially at elevated pressures that are relevant to practical combustors. This paper presents a numerical and experimental investigation of the combustion and NO_x characteristics of syngas fuel with varying composition, pressure and strain rate. Experiments were performed at atmospheric conditions, while the simulations considered different pressures. Both experiments and simulations indicate that stable non-premixed and partially premixed counterflow flames (PPFs) can be established for a wide range of syngas compositions and strain rates. Three chemical kinetic models, GRI 3.0, Davis et al., and Mueller et al. are examined. The Davis et al. mechanism is found to agree best with the experimental data, and hence used to simulate the PPF structure at different pressure and fuel composition. For the pressure range investigated, results indicate a typical double flame structure with a rich premixed reaction zone (RPZ) on the fuel side and a non-premixed reaction zone (NPZ) on the oxidizer side, with RPZ characterized by H₂ oxidation, and NPZ by both H₂ and CO oxidation. While thermal NO is found to be the dominant route for NO production, a reburn route, which consumes NO through NO + O + M→ NO₂ + M and H + NO + M → HNO + M reactions, becomes increasingly important at high pressures. The amount of NO formed in syngas PPFs first increases rapidly with pressure, but then levels off at higher pressures. At a given pressure, the peak NO mole fraction exhibits a non-monotonic variation with syngas composition, first decreasing to a minimum value, and then increasing as the amount of CO in syngas is increased. This implies the existence of an optimum syngas composition that yields the lowest amount of NO production in syngas PPFs, and can be attributed to the combined effects of thermal and reburn mechanisms.     

Potential for hydrogen generation from in situ combustion of Athabasca bitumen

The volume of heavy oil and bitumen in Alberta, Canada is estimated to be about 1.7 trillion barrels. The majority of the produced heavy oil and bitumen in Alberta is converted in surface upgraders to synthetic crude oil, a crude oil with API gravity typically between 31 and 33° API, which in turn can be converted to fuel, lubricant, and petrochemical products in standard refineries. To upgrade bitumen requires hydrogen. In current practice, much of this hydrogen is generated from catalytic steam reforming of methane together with the water-gas shift reaction. This means that heavy oil and bitumen upgrading, as is currently done, requires large amounts of natural gas to generate hydrogen. The potential for in situ generation of hydrogen by gasification of bitumen reservoirs offers an attractive alternative which can also have both economic and environmental benefits. For example, hydrogen generated from bitumen gasification can also be used for in situ upgrading as well as feedstock for ammonia and other chemicals. The water-gas shift reaction also generates carbon dioxide which could be potentially sequestered in an in situ gasification process so that emissions to the atmosphere are reduced. This technology provides a potential clean method to produce fuel and feedstock material from bitumen, a relatively “dirty” fuel and feedstock oil, in addition to more energy efficient ways of extracting in situ heavy oils. However, to design in situ bitumen gasification processes requires a reaction model that provides a reasonable representation of the gasification reactions. Here, a new kinetic model is developed to examine the potential for hydrogen generation from Athabasca bitumen. The kinetic model consists of thermal cracking, oxidation/combustion, hydrogen generation and hydrogen consumption reactions. A comparison of the simulation results and experimental data from the published literature reveal that the new model can predict hydrogen generation from gasification of methane, Athabasca bitumen, and coke.     

Electron beam flue gas treatment (EBFGT) technology for simultaneous removal of SO2 and NOx from combustion of liquid fuels

Electron beam flue gas treatment technology was applied for removal of SO₂ and NO_x from flue gas, emitted from combustion of high-sulfur fuel oils. The detailed study of this process was performed in a laboratory by irradiating the exhaust gas from the combustion of three grades of Arabian fuels with an electron beam from accelerator (800 keV, max. beam power 20 kW). SO₂ removal is mainly dependent on ammonia stoichiometry, flue gas temperature and humidity and irradiation doses up to 8 kGy. NO_x removal depends primarily on irradiation dose. High removal efficiencies up to 98% for SO₂ and up to 82% for NO_x were obtained under optimal conditions. The flue gas emitted from combustion of high-sulfur fuel oils, after electron beam irradiation, meets the stringent emission standards for both pollutants. The by-product, which is a mixture of ammonium sulphate and nitrate, can be used as a fertilizer as such or blended with other components to produce commercial agricultural fertilizer.     

Gasification of oil sand coke: Review

The production of synthetic crude from the tar sands in Western Canada has been steadily increasing. Most of the delayed coke produced by Suncor is combusted on site, whereas all fluid coke produced by Syncrude is stockpiled. The database on the chemical and physical properties of the oil sand coke, including the composition and fusion properties of the mineral matter, has been established. The reactivity of the coke was determined by oxygen chemisorption, fixed bed and fluid bed bench scale gasification and pilot plant gasification. The reactivity of the oil sand coke for gasification is rather low and comparable to high rank coals, such as anthracite. Slurrability tests revealed that a solid concentration in water, approaching 70 wt.%, can be achieved. Gasification is the front runner among clean technologies for the conversion of carbonaceous solids to useful products. Several commercial gasifiers are available to cover the wide range of severity. Because of the low reactivity of oil sands coke, high severity conditions are required to achieve high gasification conversion. Such conditions can be attained in entrained bed gasifiers. Gasifiers employing both dry and slurry feeding systems are suitable. A high efficiency, low SO_x and NO_x emissions, as well as a low solid waste production are among the key advantages of the gasification technology compared with the competing technologies. Commercial gasification of oil sands coke is delayed because of the availability of natural gas on the site of the upgrading plants. Potential for the transportation of the oil sand coke to USA for electricity generation using the integrated gasification combined-cycle (IGCC) technology was evaluated.     

Exploring the gas-phase anaerobic bioremoval of H2S for coal gasification fuel cell feed streams

An initial study was conducted to assess the potential feasibility of developing an anaerobic photobiofiltration process to remove trace concentrations of H₂S from gas streams such as syngas generated by coal gasification for fuel cells. Using the strain Heliobacterium chlorum, net removals of H₂S by the biomass on the order of 7–18% were obtained with a simple gas–biomass contactor energized by red light. Volumetric elimination capacities are 1–2 orders of magnitude lower than those obtained in liquid cultures under optimal conditions. This, combined with observed severe transport limitations, is an indication that the real residence time for biomass–gas contact in the photobioreactor is at least 1–2 orders of magnitude lower than the calculated value based on the ratio of the coke bed volume to gas flow rate. The quantity of aqueous medium that must be utilized to maintain active biocatalyst is shown to be quite small. Thus, the use of a gas/biocatalyst contactor should result in minimal water vapor addition to syngas streams. The challenge is designing an anaerobic photobioreactor with a significantly greater biomass surface-to-volume ratio than traditional biofiltration reactors.     

Effect of Gasifying Medium on the Coal Chemical Looping Gasification with CaSO4 as Oxygen Carrier

The chemical looping gasification uses an oxygen carrier for solid fuel gasification by supplying insufficient lattice oxygen. The effect of gasifying medium on the coal chemical looping gasification with CaSO₄ as oxygen carrier is investigated in this paper. The thermodynamical analysis indicates that the addition of steam and CO₂ into the system can reduce the reaction temperature, at which the concentration of syngas reaches its maximum value. Experimental result in thermogravimetric analyzer and a fixed-bed reactor shows that the mixture sample goes through three stages, drying stage, pyrolysis stage and chemical looping gasification stage, with the temperature for three different gaseous media. The peak fitting and isoconversional methods are used to determine the reaction mechanism of the complex reactions in the chemical looping gasification process. It demonstrates that the gasifying medium (steam or CO₂) boosts the chemical looping process by reducing the activation energy in the overall reaction and gasification reactions of coal char. However, the mechanism using steam as the gasifying medium differs from that using CO₂. With steam as the gasifying medium, parallel reactions occur in the beginning stage, followed by a limiting stage shifting from a kinetic to a diffusion regime. It is opposite to the reaction mechanism with CO₂ as the gasifying medium.     

Behaviour of heavy metals in the partial oxidation of heavy fuel oil

The behaviour of heavy metals in the partial oxidation of heavy fuel oils under a pressure of up to 100 bar (10 MPa) has been investigated. The tests were carried out in a 5 MW HP POX (High Pressure Partial Oxidation) test plant, that is operated by the IEC (Department of Energy Process Engineering and Chemical Engineering, TU Bergakademie Freiberg) in cooperation with Lurgi GmbH. In several test campaigns preheated oil with a viscosity of up to 300 cSt (= 300 mm²/s) at the burner inlet has been gasified. The heavy metals nickel Ni, iron Fe and vanadium V occur in heavy residual oils in considerable concentration and may seriously impact the gasification itself and the synthesis gas conditioning and usage. While iron is largely recovered in the gasification residue, the recovery rates of nickel and vanadium depend on the process conditions. Volatile nickel compounds were detected in the raw synthesis gas. It was found that an incomplete carbon conversion enables the capture of nickel Ni and vanadium V in the solid residue phase and can thus mitigate the problem of volatile metal compounds in the raw synthesis gas.     

Speciation and distribution of alkali,alkali earth metals and major ash forming elements during gasification of fuel cane bagasse

Gasification of fuel cane bagasse, the waste residue from fuel cane, a hybrid of wild and commercial clones of sugar cane, was carried out in a novel 50 kWe air-blown autothermal downdraft gasifier. The speciation and distribution of alkali, alkali earth metals and major ash forming elements during gasification were investigated to evaluate the extent of volatilisation of these elements into the syngas and to determine the likely impact on syngas fuelled solid oxide fuel cell systems. Also assessed was the potential for defluidisation of the fuel bed due to agglomerate and deposit formation. Chemical fractionation studies showed that 30% of the potassium was captured by aluminosilicates and was retained in the ash, thereby reducing the alkali loading in the syngas and that more than 50% of the alkali earth metals were released to the syngas. In contrast, although the major ash forming elements were transformed from acid insoluble to acid soluble forms during gasification they remained hard bound in the ash and less than 30% of each one was released into the gas phase. The composition of clinkers and agglomerates produced during gasification was investigated by SEM-EDX and XRD which confirmed the presence of the eutectic systems KAlSi₂O₆–SiO₂, KAlSi₂O₆–CaMgSi₂O₆–SiO₂ and CaMgSi₂O₆–NaAlSi₃O₈. A preliminary model of the distribution behaviour during gasification of the ash forming elements has been developed.     

Combustion of waste trap grease oil in gas turbine generator

The possibility of using waste trap grease in electric power generation is explored in this study. The performance and emissions of both diesel and waste trap grease oils were tested in a gas turbine generator at comparable operating conditions. The fuel system of the gas turbine was modified for dual fuel capability with a diversion valve and a heat exchanger with exhaust for elevating the temperature of trap grease. The viscosity of trap grease was measured as a function of temperature and it was determined that the trap grease oil should be heated up to nearly 80 °C in order to approach the viscosity of diesel fuel such that satisfactory injector atomization can be achieved. The heating values of the diesel and trap grease were measured using an oxygen bomb calorimeter to facilitate the calculations of engine performance on an energy input basis. The results showed that the trap grease exhibits less NO_x emission for high generator loads compared to diesel, whereas CO and CO₂ emissions are slightly to significantly higher than those of diesel as load decreases. The results of the performance and emissions testing indicate that trap grease can be satisfactorily used for power generation.     

Comparative environmental behavior of bus engine operating on blends of diesel fuel with four straight vegetable oils of Greek origin: Sunflower, cottonseed, corn and olive

An experimental study is conducted to evaluate the use of sunflower, cottonseed, corn and olive straight vegetable oils (SVO) of Greek origin, in blends with diesel fuel at proportions of 10 vol.% and 20 vol.%, in a fully instrumented, six-cylinder, turbocharged and after-cooled, heavy duty (HD), direct injection (DI), ‘Mercedes-Benz’, mini-bus engine installed at the authors’ laboratory. The series of tests are conducted using each of the above blends, with the engine working at two speeds and three loads. Fuel consumption, exhaust smokiness and exhaust regulated gas emissions such as nitrogen oxides (NO_x), carbon monoxide (CO) and total unburned hydrocarbons (HC) are measured. With reference to the corresponding neat diesel fuel operation, the vegetable oil blends show reduction of emitted smoke with slight increase of NO_x and effectively unaffected thermal efficiency. Theoretical aspects of diesel engine combustion, combined with the very widely differing physical and chemical properties of the vegetable oils against those for the diesel fuel, aid to the correct interpretation of the observed engine behavior.     

Experimental investigation of mineral diesel fuel, GTL fuel, RME and neat soybean and rapeseed oil combustion in a heavy duty on-road engine with exhaust gas aftertreatment

The effects of mineral diesel fuel, gas-to-liquid fuel, rapeseed methyl ester, neat soybean and neat rapeseed oil on injection, combustion, efficiency and pollutant emissions have been studied on a compression ignition heavy duty engine operated near full load and equipped with a combined exhaust gas aftertreatment system (oxidation catalyst, particle filter, selective catalytic NO_x reduction). In a first step, the engine calibration was kept constant for all fuels which led to differences in engine torque for the different fuels. In a second step, the injection duration was modified so that all fuels led to the same engine torque. In a third step, the engine was recalibrated in order to keep the NO_x emissions at an equal level for all fuels (injection pressure, injection timing, EGR rate). The experiments show that the critical NO_x emissions were higher (even behind the exhaust gas aftertreatment systems) for oxygenated fuels in case of the engine not being recalibrated for the fuel. GTL and the oxygenated fuels show lower emissions for some pollutants and higher efficiency after recalibration to equal NO_x levels.     

Hydrogen generation by catalytic gasification of motor oils in an integrated fuel processor

Catalytic gasification of waste motor oil (MO) for the generation of high purity of hydrogen and then integrated to a proton exchange membrane fuel cell (PEMFC) is economically and environmentally attractive. Thus, the objective of the present work was to investigate a MO catalytic gasification for generating high-purity hydrogen with 15 wt.% NiO/Al₂O₃ catalysts. In a lab-scale fixed-bed downdraft experimental approach, catalytic gasification of MO was accompanied by a substantial production of syngas at 760–900 K. From the XANES spectra, most of the Ni(II) reduced to Ni(0) was found in the MO catalytic gasification process. The EXAFS data also showed that the central Ni atoms have a Ni–O and a Ni–Ni with bond distances of 2.04 ± 0.05 Å and 2.48 ± 0.05 Å, respectively. In addition to over 85% of syngas generation, approximately 8.35 × 10⁵ kcal h⁻¹ of thermal energy was recovered and cold gas efficiency (CGE) was 77–84% when the catalytic gasifier was operated at O/C atomic ratios between 1.1 and 1.3. The proposed syngas production unit can be integrated in a fuel processor (e.g. PEMFC), in order to separate and purify the syngas to yield a 99.99% hydrogen stream. Moreover, cost or benefit analyses of MO catalytic gasifiers of 10- and 20-TPD (tons per day) were also performed.     

Recent advances in catalysts for hot-gas removal of tar and NH3 from biomass gasification

Biomass gasification produces a low to medium-BTU product gas (or syngas) containing primarily CO₂, H₂, CO, CH₄ and (C₂ + C₃), as well as some contaminants such as tars, NH₃, H₂S and SO₂. In order to achieve better efficiencies of the syngas applications, these contaminants must be removed before the syngas is used for internal combustion, gas engines, and in particular for fuel cells and methanol synthesis. Compared with the wet scrubbing technology, hot-gas cleanup technology to remove tar, ammonia and other contaminants at the “hot” state is more advantageous with respect to energy efficiencies. This paper provides an overview on recent advances in catalysts for hot-gas removal of tar and ammonia from biomass gasification. The review focuses on the recent development and applications of dolomite catalysts, iron-based catalysts, nickel and other metal supported catalysts, and the novel carbon-supported catalysts for hot-gas tar removal and ammonia decomposition. The barriers in applications of hot-gas cleanup processes and catalysts for full-scale biomass gasification, and areas for future research, are also discussed.