The performance of nickel-loaded lignite residue for steam reforming of toluene as the model compound of biomass gasification tar

Tars should be removed from biomass gasification systems so as not to damage or clog downstream pipes or equipment. In this paper, lignite insoluble residue (LIR) after extraction of humic acids was used as the support to prepare a nickel-loaded LIR (Ni/LIR) catalyst. This novel catalyst Ni/LIR was tested in steam reforming of toluene as a model compound of biomass tar conducted in a laboratory-scale fixed bed reactor. When compared to the reactions without catalyst or with Ni/Al₂O_3, Ni/LIR was confirmed as an active catalyst for toluene conversion at a relatively low temperature of 900 K. The investigated reforming parameters during the experiments in this research were selected as reaction temperature at a range of 850–950 K, steam/carbon molar ratio at a range of 2–5 mol/mol, and a space velocity from 1696 to 3387 h^?1. It was concluded that, under optimum conditions, significant amount of syngas yields, acceptable Ni/LIR consumption and more than 95% of toluene conversion can be obtained from the biomass Ni/LIR catalytic gasification system.     

Catalytic decomposition of biomass tars: use of dolomite and untreated olivine

Although biomass is getting increased attention as a renewable energy source, one of the remaining problems still to be solved is the reduction of the high level of tar present in the product gas from gasification of biomass. The purpose of the present work is to study the activity of olivine and dolomite for tar destruction. Some researchers investigated olivine as bed material for biomass gasification. But it is not yet known how tars behave in the presence of olivine and whether olivine has some activity towards tar destruction. A slipstream from a lab-scale atmospheric bubbling-fluidised-bed gasifier (located at ECN) is passed through a secondary fixed-bed reactor where the additives are placed. For easy understanding, the results are represented in terms of the following tar classes; GC-undetectable tars (class 1), heterocyclic compounds (class 2), aromatic compounds (class 3), light polyaromatic compounds (class 4), heavy polyaromatic compounds (class 5). The general observation is that the conversion of all tar classes increases as the temperature was raised from 800 to 900 °C for both additives. The water-soluble heterocyclic compounds can be easily converted by thermal treatment. At the temperature of 900 °C, the water-soluble heterocyclic compounds are completely converted. A 48% decrease in heavy PAHs is observed with pure sand. Addition of 17 wt% olivine to the sand leads to a 71% decrease of PAHs at 900 °C, whereas addition of 17 wt% (pre-calcined) dolomite converted 90%. Also improvement in conversion of other tar classes is observed when olivine and dolomite are added during hot gas cleaning. A total tar amount of 4.0 g m₀⁻³ could be reduced to 1.5 and 2.2 g m₀⁻³ using dolomite and olivine, respectively, at a temperature of 900 °C. Inspite of this reduction in total tar concentration, a limited impact on the tar dewpoint is observed.     

The influence of preparation method of char supported metallic Ni catalysts on the catalytic performance for reforming of biomass tar

The char‐supported nickel catalysts prepared by wet impregnation and precipitation‐deposition methods under different nickel loadings and catalytic temperatures for catalytic reforming of rice husk tar were investigated. The influences of preparation methods on the physicochemical properties of catalysts and catalytic activity towards tar conversion and gas yield were studied. The results showed that char‐supported metallic Ni catalysts can be directly used without a reduction process because of carbon thermal reaction during calcination. The preparation method had a significant influence on the porosity and Ni dispersion of catalysts. The addition of Ni to char improved the specific surface area from 60 m² g^?1 to 346.8 m² g^?1 because of activation effect of nickel nitrate on char pore structure. The precipitation‐deposition method produced higher surface area, smaller Ni nanoparticulates with more corner and step sites, as well as more concentrated size distribution than those of wet impregnation method, leading to higher catalytic activity, in terms of high tar conversion efficiency (83%) and increasing syngas yield. The selectivity to phenols and naphthalene for precipitation‐deposited catalysts was strengthened, and the relative content of heavy tars was decreased remarkably. The increasing H₂ yield and concentration were indicative of efficient conversion of macromolecular organic matters into small molecules gases. In addition, the precipitation‐deposited catalyst exhibited weaker Ni sintering after reaction. The catalytic cracking temperature of 800° C and Ni loading of 10 wt% exhibited the best catalytic effects on gas distribution and tar conversion.     

The characteristics of syngas production from bio-oil dry reforming utilizing the waste heat of granulated blast furnace slag

A two-stage utilization of the waste heat of granulated blast furnace slag (BFS) was proposed, and the characteristics of bio-oil dry reforming under different conditions were investigated. For the bio-oil dry reforming utilizing granulated BFS as the heat carrier, when the temperature was higher than 800 °C, changes in the characteristics as bio-oil conversion and lower heating value (LHV) were not pronounced in response to the increasing temperature. The bio-oil conversion reached its maximum value with a CO₂/C (molar ratio of CO₂ to carbon in bio-oil) of 0.85. When the liquid hourly space velocity (LHSV) was higher than 0.45 h^?1, the bio-oil conversion and LHV dropped quickly as the LHSV increased. At the optimal condition with a temperature of 800 °C, a CO₂/C of 0.85 and an LHSV of 0.45 h^?1, the bio-oil conversion and LHV reached 90.15% and 511.02 kJ per mole of bio-oil, respectively. Granulated BFS could be beneficial for the bio-oil dry reforming process. Combining biomass pyrolysis and bio-oil dry reforming, a feasible industry application utilizing the waste heat of granulated BFS was presented systematically.     

Fundamental study on biomass‐fuelled ceramic fuel cell

Recent development in the advanced intermediate temperature (400 to 700°C) ceramic fuel cell (CFC) research brings up feasibility and new opportunity to develop innovative biomass‐fuelled CFC technology. This work focuses on fundamentals of the biomass‐fuelled CFCs based on available biofuel resources through thermochemical conversion technologies. Both real producer gas from biomass gasification and imitative compounded gas were used as the fuel to operate the CFCs in the biomass CFC testing station. The composition of the fuel gas was varied in a wide range of practices of the present conversion technology both in KTH and Shandong Institute of Technology (SDIT). CFC performances were achieved between 100 and 700 mW cm^?2 at 600–800°C corresponding to various gas compositions. A high performance close to 400 mW cm^?2 was obtained at 600°C for the gas with the composition of H₂ (50 per cent)+CO (15 per cent)+CO₂ (15 per cent)+N₂ (20 per cent) and more than 600 mW cm^?2 for the H₂ (55 per cent)+CO (28 per cent)+CO₂ (17 per cent) at 700°C. This paper presents the experimental results and discusses the fundamentals and future potentiality on the biomass fuelled CFCs. Copyright © 2002 John Wiley & Sons, Ltd.     

Biomass to hydrogen-rich syngas via tar removal from steam gasification with La1-XCeXFeO3/dolomite as a catalyst

Biomass gasification produces hydrogen, which is a clean and promising technology. One of the most important aspects of the biomass gasification process is choosing the right catalyst. In this study, 10% La_1-XCe_XFeO₃/Dolomite (X = 0,0.2,0.4,0.6,0.8) synthesized using the sol-gel method was used as a catalyst in biomass gasification for the production of hydrogen-rich syngas. Gasification tests were carried out in a fixed bed reactor. The effects of an elemental substitution in LaFeO₃, temperature on the product were examined. Ce-substitution boosted the activity of LaFeO₃/DOL according to the data. Among the prepared catalysts, La_0.8Ce_0.2FeO₃/DOL performed the best, yielding a greater H₂ production and tar with a higher naphthalene concentration. As the temperature rises, so does the H₂ yield, at 850 °C, the highest H₂ yield is 0.69Nm³/Kg. Furthermore, the aromatization of phenols in tar is more likely to occur at high temperatures.     

Desulfurization and tar reforming of biogenous syngas over Ni/olivine in a decoupled dual loop gasifier

For the production of bio-SNG (substitute natural gas) from syngas of biomass steam gasification, trace amounts of sulfur and tar compounds in raw syngas must be removed. In present work, biomass gasification and in-bed raw gas upgrading have been performed in a decoupled dual loop gasifier (DDLG), with aggregation-resistant nickel supported on calcined olivine (Ni/olivine) as the upgrading catalyst for simultaneous desulfurization and tar elimination of biogenous syngas. The effects of catalyst preparation, upgrading temperature and steam content of raw syngas on sulfur removal were investigated and the catalytic tar reforming at different temperatures was evaluated as well. It was found that 850 °C calcined Ni/olivine was efficient for both inorganic-sulfur (H₂S) and organic-sulfur (thiophene) removal at 600–680 °C and the excellent desulfurization performance was maintained with wide range H₂O content (27.0–40.7%). Meanwhile, tar was mostly eliminated and H₂ content increased much in the same temperature range. The favorable results indicate that biomass gasification in DDLG with Ni/olivine as the upgrading bed material could be a promising approach to produce qualified biogenous syngas for bio-SNG production and other syngas-derived applications in electric power, heat or fuels.     

Performance evaluation of 10 kWe pilot scale downdraft gasifier with different feedstock

Gasification is a thermochemical conversion of carbonaceous biomass into the producer gas. Gasification of lignite, wood, sawdust briquette and their mixtures are investigated on a 10 kWe laboratory scale downdraft gasifier at atmospheric pressure. The air is used as a gasifying medium. The gasifier was operated on different particle sizes of lignite and lignite-wood ratio; 22–25 mm lignite particle size and lignite – wood ratio (70:30, w/w) were found to be optimum to overcome clinker formation and higher Cold Gas Efficiency (CGE). To avoid unwanted maintenance, it is essential to diminish the producer gas pollutants such as tar and particulate matter (PM) before injecting the producer gas into a turbine or a gas engine. A setup was developed to measure tar and PM from the producer gas. The gasifier performance was evaluated on various parameters such as tar, PM, fuel consumption, gas yield, gas composition, gas calorific value and CGE for all selected feedstock. The tar in the producer gas was found in the range of 201.30 mg Nm^?3 to 617.80 mg Nm^?3 whereas PM was found in the range of 36.76 mg Nm^?3 to 68.35 mg Nm^?3. CGE and gas calorific value were observed in the range between 64.99% and 71.62% and 4.64 MJ Nm^?3 to 5.29 MJ Nm^?3, respectively. Specific fuel consumption (SFC) was obtained in the range of 1.52 kg kWh^?1 to 1.84 kg kWh^?1. CGE with lignite – wood or sawdust briquette ratio (70:30, w/w) is found maximum whereas tar and PM are found minimum with wood and sawdust briquette feedstock in the present study.     

Co–gasification of coal/biomass blends in 50 kWe circulating fluidized bed gasifier

This paper reports gasification of coal/biomass blends in a pilot scale (50 kWe) air-blown circulating fluidized bed gasifier. Yardsticks for gasification performance are net yield, LHV and composition and tar content of producer gas, cold gas efficiency (CGE) and carbon conversion efficiency (CCE). Net LHV decreased with increasing equivalence ratio (ER) whereas CCE and CGE increased. Max gas yield (1.91 Nm³/kg) and least tar yield (5.61 g/kg of dry fuel) was obtained for coal biomass composition of 60:40 wt% at 800 °C. Catalytic effect of alkali and alkaline earth metals in biomass enhanced char and tar conversion for coal/biomass blend of 60:40 wt% at ER = 0.29, with CGE and CCE of 44% and 84%, respectively. Gasification of 60:40 wt% coal/biomass blend with dolomite (10 wt%, in-bed) gave higher gas yield (2.11 Nm³/kg) and H₂ content (12.63 vol%) of producer gas with reduced tar content (4.3 g/kg dry fuel).     

Hydrogen-rich gas production from pyrolysis of wet sludge in situ steam agent

A series of wet sludge samples with different moisture contents were pyrolyzed in situ steam in a bench-scale fixed bed reactor in order to examine the influence of moisture and temperature on product distribution and gas composition. The results demonstrated that inherent moisture in wet sludge had a great effect on the product yield. The pyrolysis of wet sludge (43.38% moisture content) at 800 °C exhibited maximum H₂ yield (7.76 mol kg^?1 dry basis wet sludge) and dry gas yield (0.61 Nm³ kg^?1) and H₂ content of 42.13 vol%. When the moisture exceeded 43.38%, H₂ yield and gas yield both tended to decline. It was also shown that the elevated temperature exhibited a significant influence on gas content increase and tar reduction; at the same time, H₂ yield and H₂ content were increased from 1.83 mol kg^?1 dry basis wet sludge and 16.67 vol% to 9.15 mol kg^?1 dry basis wet sludge and 45.67 vol%, respectively, as temperature increased from 600 °C to 850 °C. LHV of fuel gas varies from 15.49 MJ Nm^?3 to 11.65 MJ Nm^?3 because of decrease in CH₄ and C₂H₄ content as temperature increasing. In conclusion, hydrogen rich gas production by pyrolysis of wet sludge which avoided pre-drying process and utilized in situ steam agent from wet sludge is an economic method.     

Evaluation of regenerative function and activity of reforming toluene by composite catalyst containing spinel oxide

Catalysts that can maintain the activity for a long time are indispensable for the distributed power generation consisting of biomass gasifier and Solid Oxide Fuel Cell (SOFC). This study aims to reveal and develop the regenerative function of composite catalysts containing NiAl₂O₄ that can be regenerated by reduction and oxidation (Red-Ox) for converting tar from biomass. Regenerative function of composite oxide catalyst containing NiAl₂O₄ spinel (NAO) and Ru added to NAO (RNAO) by Red-Ox cycles and their activity of autothermal reforming of toluene were examined. Regenerating function of NAO and RNAO were investigated by temperature programmed reduction (TPR) and oxidation at 850 °C repeatedly. After 7th times Red-Ox cycles at 850 °C, though the regenerated amount of Ni in NAO decreased by 70%, that in RNAO was maintained. By Red-Ox of NAO and RNAO, Ni was oxidized to NiO at 350–650 °C and dissolved into γ-Al₂O₃ to form the NiAl₂O₄ spinel at above 750 °C. In RNAO, RuO₂ particles were more dispersed, decreasing its particle size than the initial, with the Red-Ox cycles, since Ru was dissolved into the Ni particles exsoluted from NiAl₂O₄. By evaluating the activity of autothermal reforming of toluene, NAO and RNAO showed 1.5–3.0 times higher activity than Pt/γ-Al₂O₃, due to the highly dispersive active sites unoccupied by CO. Since the active metals can be redispersed by oxidation and reduction at the range from 750 °C to 850 °C, NAO and RNAO would contribute the maintenance free system for reforming tar from biomass gasification.     

One-step synthesis of biochar-supported potassium-iron catalyst for catalytic cracking of biomass pyrolysis tar

In this work, K–Fe bimetallic catalyst supported on porous biomass char was synthesized via a one-step synthesis method by pyrolysis of biomass (peanut shells) after impregnation of a small amount of potassium ferrate (PSC–K₂FeO₄), and was evaluated for the cracking of biomass pyrolysis tar. Control experiments using the pure char (PSC) and char-supported catalysts after impregnation of KOH (PSC–KOH) and FeCl₃ (PSC–FeCl₃) were also performed for comparison. The as-prepared PSC-K₂FeO₄ possessed a porous structure with the dispersion of particles/clusters of Fe metal, K₂CO₃ and KFeO₂ on the char support. Tar cracking experiments showed that the PSC-K₂FeO₄ exhibited excellent catalytic activity on the cracking of biomass pyrolysis tar in the temperature range of 600–800 °C, and the obtained tar conversion efficiencies were obviously higher than that in the control experiments, particularly at relatively lower temperatures (600 and 700 °C). The yields of combustible gas compounds including CO, H₂ and CH₄ increased significantly using PSC-K₂FeO₄ as the catalyst due to the enhanced tar cracking and reforming reactions. The porous structure and the active crystal structures of the spent catalyst were well retained, indicating the potential for efficient and long-term utilization of the catalyst in tar cracking. PSC-K₂FeO₄ exhibited excellent reusability during the five times reuse under the same conditions without regeneration, which showed almost no obvious decrease in the tar conversion efficiency and gas yields.     

Nickel supported over MCM-41 coated ceramic membrane for steam reforming of real tar

A novel catalyst, Nickel supported over MCM-41 coated ceramic membrane (NMC), was developed using coating method and deposition-precipitation method and applied for steam reforming of real tar in fixed bed. The effects of reaction conditions such as Ni loading amount, reaction temperature and mass ratio of steam to tar were also studied. The good dispersion of Ni nanoparticles and the strong interaction between Ni particles and the support were identified by BET, XRD, H₂-TPR and SEM/EDS, resulting in the excellent performance of NMC catalysts. Maximum tar conversion of 96.4% and H₂ yield of 98.7 mmol g^?1 were obtained using 20NMC with a mass ratio of steam to coal tar of 2 at 800 °C. Moreover, 20 NMC exhibited a good stability in 10 h of lifetime test and the resistance of graphitic carbon formation prone to easier regeneration of catalysts illustrated by Raman spectroscopy. It indicates that the utilization of NMC catalysts for tar steam reforming is a promising way.     

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

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

Hydrogen-rich gas production from biomass steam gasification in an updraft fixed-bed gasifier combined with a porous ceramic reformer

This paper investigates the hydrogen-rich gas produced from biomass employing an updraft gasifier with a continuous biomass feeder. A porous ceramic reformer was combined with the gasifier for producer gas reforming. The effects of gasifier temperature, equivalence ratio (ER), steam to biomass ratio (S/B), and porous ceramic reforming on the gas characteristic parameters (composition, density, yield, low heating value, and residence time, etc.) were investigated. The results show that hydrogen-rich syngas with a high calorific value was produced, in the range of 8.10–13.40 MJ/Nm³, and the hydrogen yield was in the range of 45.05–135.40 g H₂/kg biomass. A higher temperature favors the hydrogen production. With the increasing gasifier temperature varying from 800 to 950 °C, the hydrogen yield increased from 74.84 to 135.4 g H₂/kg biomass. The low heating values first increased and then decreased with the increased ER from 0 to 0.3. A steam/biomass ratio of 2.05 was found as the optimum in the all steam gasification runs. The effect of porous ceramic reforming showed the water-soluble tar produced in the porous ceramic reforming, the conversion ratio of total organic carbon (TOC) contents is between 22.61% and 50.23%, and the hydrogen concentration obviously higher than that without porous ceramic reforming.     

Optimization of hydrogen production from steam reforming of biomass tar over Ni/dolomite/La2O3 catalysts

Industrially, the endothermic process of steam reforming is carried out at the lowest temperature, steam to carbon (S/C) ratio, and gas hourly space velocity (GHSV) for maximum hydrogen (H₂) production. In this study, a three-level three factorial Box-Behnken Design (BBD) of Response Surface Methodology (RSM) was applied to investigate the optimization of H₂ production from steam reforming of gasified biomass tar over Ni/dolomite/La₂O₃ (NiDLa) catalysts. Consequently, reduced quadratic regression models were developed to fit the experimental data adequately. The effects of the independent variables (temperature, S/C ratio, and GHSV) on the responses (carbon conversion to gas and H₂ yield) were examined. The results indicated that reaction temperature was the most significant factor affecting both responses. Ultimately, the optimum conditions predicted by RSM were 775 °C, S/C molar ratio of 1.02, and GHSV of 14,648 h⁻¹, resulting in 99 mol% of carbon conversion to gas and 82 mol% of H₂ yield.     

In-situ IR study for elucidating the adsorption cracking mechanism of toluene over calcined olivine catalyst

In order to improve the energy conversion efficiency of hydrogen production from biomass gasification and reduce environmental pollution, it is necessary to study the mechanism of tar catalytic cracking. In present work, in-situ infrared spectroscopy has been used to study the adsorption cracking of toluene on calcined olivine catalyst from room temperature to 500 °C. The experimental results indicate that there is no chemical adsorption of toluene on calcined olivine catalyst from room temperature to 200 °C. When the temperature is higher than about 300 °C, the toluene is chemically adsorbed on α-Fe₂O₃, which is the surface active site of the calcined olivine catalyst. The chemical adsorption occurs between the benzene ring and Fe³⁺, and it promotes the breakage of methyl from the benzene ring. With the increasing of reaction temperature, the delocalization large π bond in the benzene ring is destroyed by Fe³⁺, which makes the benzene ring easier to break into smaller products or intermediate products.     

Transient analysis and performance studies of two tubular photobioreactors for outdoor culture of spirulina

A mathematical model to make a transient thermal analysis and to estimate the incident solar energy for two designs of tubular photobioreactor installed outdoors is presented here. In the first photobioreactor design the tubes were arranged in one plane, whereas in the second the tubes were arranged in two planes. The model was validated by comparing the experimental data and predicted values of culture temperature. Both the input solar energy and culture temperature in a tubular photobioreactor may be predicted with a reasonable degree of accuracy by employing the model. The performance of the two photobioreactors for mass culture of Spirulina was also studied in relation to their design and culture temperature. The average biomass yield obtained in one-plane and two-plane photobioreactors were (dry weight) 23.7 g m^?2 day^?1 and 27.8 g m^?2 day^?1 respectively. Such biomass yields corresponded to a volumetric productivity of (dry weight) 0.466 g litre^?1 day^?1 in the one-plane reactor and 1.5 g litre^?1 day^?1 in the two-plane reactor. We further observed that biomass yield could be increased by about 21% when the culture temperature was maintained at the optimal value of 35°C compared to another culture in which temperature changed according to the ambient temperature from 20 to 39°C during the day.     

Influence of catalyst and temperature on gasification performance of pig compost for hydrogen-rich gas production

The catalytic steam gasification of pig compost (PC) for hydrogen-rich gas production was conducted in a fixed-bed reactor. The influence of the catalyst and reactor temperature on yield and product composition was studied at the temperature range of 700–850 °C, for weight hourly space velocity (WHSV) in the range of 0.30–0.60 h⁻¹. The results indicate that the developed NiO on modified dolomite (NiO/MD) catalyst reveals better catalytic performance on the tar elimination and hydrogen yield than calcined MD or NiO/γ-Al₂O₃ catalyst. Meanwhile, the lower WHSV and higher reactor temperature can contribute to more hydrogen production and gas yield. Moreover, the char from catalytic steam gasification of PC has a highest ash content of 75.84% at 850 °C. In conclusion, pig compost is a potential candidate for hydrogen gas production through catalytic steam gasification technology.     

Iron and nickel doped alkaline-earth catalysts for biomass gasification with simultaneous tar reformation and CO2 capture

The tar reforming catalytic activity of iron and nickel based catalysts supported on alkaline-earth oxides CaO, MgO and calcined dolomite [a (CaMg)O solid solution] has been investigated in a fixed bed reactor operating at temperatures ranging from 650 to 850 °C; toluene and 1-methyl naphthalene were used as model compounds for tar generated during biomass gasification. The CO₂ absorption capacities of Fe/(CaMg)O and Ni/(CaMg)O were also investigated at the lower temperature condition (650 °C) at which the sorption process is thermodynamically favoured. It was found that iron and nickel may be optimised in the substrate particles to enhance both the catalytic activity and the carbon deposition resistance during catalytic tests, at the same time reducing critical limitations on CO₂ capture capacity.