Reduction of primary tar vapor from biomass by hot char particles in fixed bed gasification

This study investigated the reduction of primary tar vapor from biomass pyrolysis over a bed of hot char particles, focusing on the effect of different operating conditions and char properties. The char samples were prepared from wood, paddy straw, palm kernel shell, and activated carbon. The primary tar was produced from fir wood by pyrolysis at 500 °C and passed through a reactor filled with char particles with different lengths and temperatures.The tar cracking reactions became active above 700 °C, and the presence of hot char particles promoted more tar reduction compared with thermal cracking alone. The mass yield of the primary tar was reduced from 24.8% by pyrolysis to 13.7% by thermal cracking at 800 °C, and further to 7.7% by hot char particles in a reactor volume of 1.48 cm³/g_wood. In terms of carbon yield, these values correspond to 32.1%, 19.9% and 11.8%, respectively. The tar with smaller molecular weights was quickly decomposed to gases, whereas the heavy tar was resistant to cracking, even when the reactor volume was increased to 6.90 cm³/g_wood. The tar cracking behaviors were similar for four char types despite differences in microscopic surface areas, pore-size distributions, and inorganic contents. The results suggest that creating a tar-cracking zone using char particles situated between the pyrolysis and gasification zones could be helpful in converting the primary tar vapor in a downdraft fixed-bed gasifier, but the degree of conversion is not high enough to eliminate tar issues completely.     

Components and potential utilization of oil sands semicoke

Retorting is one of the above-ground methods available for producing oil from oil sands, which also releases solid wastes such as oil sand semicoke. Although some oil sand retorting technologies have been explored and developed, such as rotary kilns and fluidized beds (FBs), there is little information on the components of their semicoke. Considering the semicoke to be a potential hazardous waste, this work first prepared the semicoke from retorting Indonesian oil sands, and then analyzed its components using different techniques, such gas chromatograph–mass spectrometer and X-ray diffractometer (XRD). The obtained results reveal that semicoke is a combustible fuel with a major proportion of toxic aromatic hydrocarbons and calcite. Based on the studies on the components of the semicoke and the characteristics of the FB retorting technology, a new oil sand utilization system with dual FBs is finally recommended for retorting oil sands in one fluidized bed and burning the semicoke in the other one.     

Effect of admixing different carbon structural variants on the decomposition and hydrogen sorption kinetics of magnesium hydride

The effect of admixing catalysts comprised of carbon nanostructures, specifically planar, helical and twisted carbon nanofibers, spherical carbon particles and multi-walled carbon nanotubes, on the hydrogen storage properties of magnesium hydride has been investigated. Optimum results were achieved with the mixture containing twisted carbon nanofibers (TCNF) synthesized by Ni catalyst derived by oxidative dissociation of catalyst precursor LaNi₅. The desorption temperature of 2 wt.% TCNF admixed MgH₂ is ∼65 K lower than that of pristine MgH₂ milled for the same duration. The enhancement in hydrogen absorption capacity of MgH₂ admixed with 2 wt.% TCNF has been found to be two-fold in the first 10 minutes at 573 K and under a hydrogen pressure of 2 MPa, i.e. 4.8wt% as compared to 2.5 wt% for MgH₂ alone. The increase in capacity by a factor of about two within the first 10 minutes as a result of the catalytic activity of TCNF is one of the exciting results obtained for hydrogen absorption in catalyzed MgH₂.     

Thermodynamic analysis of combined unit of biomass gasifier and tar steam reformer for hydrogen production and tar removal

A combined unit of biomass gasifier and tar steam reformer (CGR) was proposed in this study to achieve simultaneous tar removal and increased hydrogen production. Tar steam reforming calculations based on thermodynamic equilibrium were carried out by using Aspen Plus software. Thermodynamic analysis reveals that when selecting appropriate operating conditions, exothermic heat available from the gasifier could sufficiently supply to the heat-demanding units including feed preheaters, steam generator and reformer. The effects of gasification temperature (T_gs), reforming temperature (T_ref) and steam-to-biomass ratio (S:BM) on percentages of tar removal and improvement of H₂ production were investigated. It was reported that the CGR system can completely remove tar and increase H₂ production (1.6 times) under thermally self-sufficient condition. The increase of H₂ production is mainly via the water–gas shift reaction.     

Tar removal from biomass pyrolysis gas in two-step function of decomposition and adsorption

Tar content in syngas pyrolysis is a serious problem for fuel gas utilization in downstream applications. This paper investigated tar removal, by the two-step function of decomposition and adsorption, from the pyrolysis gas. The temperature of the tar decomposition process was fixed at 800 °C both with and without steam, with air as the reforming agent. Both steam and air had a strong influence on the tar decomposition reaction. The reduction of the gravimetric tar mass was 78% in the case of the thermal cracking, whereas, it was in the range of 77–92% in the case of the steam and air forming. Under conditions of tar decomposition, the gravimetric tar mass reduced, while the yield of the combustible gaseous components in the syngas increased. Synchronously, the amount of light tars increased. This should be eliminated later by fixed-bed adsorption. Three adsorbents (activated carbon, wood chip, and synthetic porous cordierite) were selected to evaluate the adsorption performance of light tars, especially of condensable tar. Activated carbon showed the best adsorption performance among all light tars, in view of the adsorption capacity and breakthrough time. On the other hand, activated carbon decreased the efficiency of the system due to its high adsorption performance with non-condensable tar, which is a combustible substance in syngas. Synthetic porous cordierite showed very low adsorption performance with almost all light tars, whereas, wood chip showed a high adsorption performance with condensable tar and low adsorption performance with non-condensable tar. When compared with other adsorbents, wood chip showed a prominent adsorption selectivity that was suitable for practical use, by minimizing the condensable tar without decreasing the efficiency of the system.     

On properties of royalty and tax regimes in Alberta’s oil sands

Simulation models that include royalty and tax provisions are used to examine the distribution between developers and governments of net returns from the development of Alberta’s oil sands deposits. A specific focus is to assess the effects on the level and distribution of net revenues associated with a number of changes in assumed revenue and expenditure conditions. Developers typically bear a greater share of the consequences of variations in capital expenditures than they do of changes in operating expenditures, prices, and exchange rates. A comparison across royalty and tax regimes suggest that there is a positive relationship between the level of net revenues estimated to accrue to either developers or governments and the share of the consequences of changes in conditions borne by that party. Some differences across production technologies are noted. The role of the federal government as a fiscal player in oil sands development has shrunk over time. In contrast, under the current regime, the Government of Alberta captures a higher share of net returns and typically bears a greater proportion of the consequences of changes in conditions than at any time since the introduction of an explicit royalty and tax regime in 1997.     

Should Alberta upgrade oil sands bitumen? An integrated life cycle framework to evaluate energy systems investment tradeoffs

The inclusion of greenhouse gas (GHG) emissions costs in energy systems investment decision-making requires the development of a framework that accounts for GHG and economic tradeoffs. This paper develops such a framework by integrating partial cost–benefit analysis with life cycle assessment to explore the question of whether bitumen should be upgraded in the Canadian province of Alberta to produce synthetic crude oil (SCO), or blended with light hydrocarbons to produce lower-quality diluted bitumen (dilbit). The net present value (NPV) of these options is calculated from the stakeholder perspectives of the oil sands industry, the Alberta public, and a climate-concerned Alberta resident. This calculation includes monetized GHG emissions costs stemming from a hypothetical economy-wide GHG price, and a sensitivity analysis explores the effects of variations in technical and economic conditions on stakeholders’ preferences. We find that under most plausible sets of conditions, industry would prefer the dilution option, while the climate-concerned Alberta resident would prefer the upgrading option. In contrast, the preferences of the general Alberta public depend on the values of key variables (e.g., the SCO-dilbit price differential). Key drivers of differences among stakeholders’ preferences include different perceptions of risks and responsibilities for life cycle GHG emissions.     

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.     

Changes of components and chemical structure of bitumen-derived liquids during retorting Indonesian oil sands

It is very important to explore the changes of components and chemical structure of bitumen-derived liquids during retorting oil sands. In order to reveal that, this work prepared natural bitumen and pyrolytic oil samples by the extraction and the retorting of Indonesian oil sands, respectively, and employed GC-MS (gas chromatograph-mass spectrometer) and ¹³C NMR (nuclear magnetic resonance) to analyze them. Due to the thermal decomposition of organic macromolecules of natural bitumen, the yield of pyrolytic oil from the retorting is only 62.86~63.05% on the basis of the amount of the extracted natural bitumen, among which the content of low-molecular-weight compounds (C7–C10) increases largely from 25.59% to above 50%. Further increase of the retorting temperature from 450°C to 520°C slightly increases the oil yield. ¹³C NMR analysis was used to compare the organic carbon structure characteristics between natural bitumen and pyrolytic oil. Obvious changes in both methylene chain length and aliphatic methyl content also support the intense thermal cracking of organic carbon components during the retorting of oil sands.     

Catalytic decomposition of tar derived from biomass pyrolysis using Ni-loaded chicken dropping catalysts

The Ni-loaded chicken droppings (Ni/CD) and chicken dropping ash (Ni/CDA) were prepared by the impregnation method and applied as catalysts for biomass tar decomposition at low temperature (450 °C) under N₂ and steam/N₂ conditions. The prepared samples and the supports were characterized by N₂ adsorption measurements, X-ray diffraction, H₂ temperature-programmed reduction, and X-ray photoelectron spectroscopy. The results reveal that Ni/CD and Ni/CDA showed higher catalytic activity for tar decomposition, in terms of producing hydrogen-rich gas, relative to commercial Ni/Al₂O₃ under N₂ conditions. This higher activity was caused by lower interactions of Ni with the support and the presence of additional reduced Ni. In the case of steam reforming, Ni/CDA also showed higher hydrogen yield and a lower amount of carbon deposition than Ni/Al₂O₃. This result indicates that a hydrophilic hydroxyapatite in the CDA support promoted the water–gas shift reaction to suppress carbon deposition and increase hydrogen yield.     

Effects of H2O and CO2 on the homogeneous conversion and heterogeneous reforming of biomass tar over biochar

The effects of H₂O and CO₂ reforming agents on the homogeneous conversion and heterogeneous reforming of biomass tar were studied in the presence of a biochar catalyst to better understand the transformation pathway between tar and biochar. Catalysis was performed in a two-stage fluidized bed/fixed bed reactor while Raman analysis and Gas Chromatograph-Mass Spectrometry were used to investigate biochar and tar characteristics. The results show temperatures of 700–900 °C are required for the homogeneous transformation of tar in the presence of H₂O/CO₂, which especially affect polycyclic aromatic hydrocarbons. The tar homogeneous reforming effect of 15 vol.% H₂O is significantly higher than that of 29 vol.% CO₂. During heterogeneous reforming of tar over biochar at 800 °C, the tar yield decreases in varying degrees with the H₂O and CO₂ concentration increasing. H₂O and CO₂ not only directly affect the tar transformation on biochar, but also indirectly influence the reforming of tar through changing the structure of biochar catalyst. The formation of additional oxygen-containing functional groups and transformation of small aromatic rings to larger aromatic rings in the biochar structure are promoted with the concentration of H₂O and CO₂ increasing. Under a H₂O/CO₂ atmosphere, a higher degree of aromatic ring heterogeneous reforming occurs over biochar than for non-aromatic tar components. Heterogeneous reforming reactivity of tar is promoted by the biomass tar structure (e.g the substituents, large aromatic ring size and five-carbon ring structures) over biochar under H₂O/CO₂ atmospheres. Further increasing H₂O and CO₂ concentration enhances this effect.     

Evaluating tar production via the release of volatile matters for H2-rich syngas production

Tar measurement and calculation is crucial for understanding the in-situ tar elimination and hydrogen-rich syngas production during the biomass gasification process. In this study, the method of evaluating tar production was proposed and studied on a two-stage fixed-bed reactor. Two different groups of oxidized and reduced oxygen carriers were investigated for comparison. The collected tar was tested on a gas chromatography–mass spectrometry (GC-MS) system. The types of the tar were all belonged to aromatic hydrocarbons. The H₂ composition in the syngas was over 34% in three reduced-OC conditions. The carbon percentage identified by the GC-MS was at the range of 93.75–95.05 wt%. The average carbon from the char combustion period was 2.85 mmol. The tar yield in the three oxidized-OC conditions was 43 ± 22 mg/g, 53 ± 11 mg/g, and 62 ± 8 mg/g, respectively. The result indicated that the reduced OC had a catalytic effect for increasing the H₂ composition in syngas. On the other hand, the oxidized OC influenced the reactions by providing with lattice oxygen. The evaluation of the produced tar was beneficial for a further understanding of the mechanism for producing the H₂-rich syngas.     

Hydrogen-rich syngas production by catalytic cracking of tar in wastewater under supercritical condition

This paper presents the results from experimental study of syngas production by catalytic cracking of tar in wastewater under supercritical condition. Ni/Al₂O₃ catalysts were prepared via the ultrasonic assisted incipient wetness impregnation on activated alumina, and calcined at 600 °C for 4 h. All catalysts showed mesoporous structure with specific surface area in a range of 146.6–215.3 m²/g. The effect of Ni loading (5–30 wt%), reaction temperature (400–500 °C), and tar concentration (0.5–7 wt%) were systematically investigated. The overall reaction efficiency and the gas yields, especially for H₂, were significantly enhanced with an addition of Ni/Al₂O₃ catalysts. With 20%Ni/Al₂O₃, the H₂ yield increased by 146% compared to the non-catalytic experiment. It is noteworthy that the reaction at 450 °C with the addition of 20%Ni/Al₂O₃ had a comparable efficiency to the reaction without catalyst at 500 °C. The maximum H₂ yield of 46.8 mol/kg_tar was achieved with 20%Ni/Al₂O₃ at 500 °C and 0.5 wt% tar concentration. The catalytic performance of the catalysts gradually decreased as the reuse cycle increased, and could be recovered to 88% of the fresh catalyst after regeneration. 20%Ni/Al₂O₃ has a potential to improve H₂ production, as well as a good reusability. Thus, it is considered a promising catalyst for energy conversion of tar in wastewater.     

Perovskite-based catalysts for tar removal by steam reforming: Effect of the presence of hydrogen sulfide

One of the greatest problems in biomass gasification processes is the conditioning of the produced synthesis gas, which contains various contaminants, including tar and hydrogen sulfide. Nickel catalysts, designed for steam reforming of aliphatic hydrocarbons (natural gas and nafta), are usually deactivated by coke deposition and sulfur poisoning. In this work, nickel and/or manganese catalysts derived from perovskites were prepared by the citrate method and characterized by X-ray diffraction, N₂ physisorption and temperature programmed reduction. The catalysts were evaluated in the steam reforming of toluene, used as tar model compound, in the absence of H₂S at 700 °C and in the presence of 50 ppm H₂S at 800 °C. LaNi_0.5Mn_0.5O₃ catalyst showed higher activity and stability in the absence of H₂S. LaMnO₃ catalyst, although less active in the absence of H₂S, showed increased stability in the presence of H₂S, with conversion of about 60%. H₂ production was only observed in the absence of H₂S.     

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.     

Roles of AAEMs in catalytic reforming of biomass pyrolysis tar and coke accumulation characteristics over biochar surface for H2 production

Coke formation is a significant challenge in catalytic tar reforming. AAEMs are essential in the conversion and decomposition of tar catalyzed by biochar. In this paper, four biochar catalysts with different K and Ca contents were prepared by acid washing and loading, and the coke accumulation characteristics in catalytic tar reforming at 650 °C were investigated using a single-stage reaction system. The gas-liquid-solid products were characterized by GC-MS, Raman, N₂ adsorption, FTIR and TG. The results suggest that K-loaded biochar has a maximum tar reforming capacity of 94.9%, while H-form biochar has a tar removal efficiency of only 27.8%. The micropore area in biochar is considerably reduced and the average pore size is increased after coke deposition. While K-loaded biochar retains the highest micropore area, it also exhibits a smaller increase in average pore size. The loading of K/Ca affects the growth structure of the coke, resulting in an increased number of O-containing structures in it. The coke on the Raw biochar surface is mainly small aromatic ring structures and aliphatic structures, thus increasing the intensity of the vibrational peaks corresponding to aromatic = C–H and aliphatic C–H on it. The coke on K-loaded biochar has a large proportion of aliphatic structures, which also contributes to the reduced graphitization of it after reforming. The AAEMs-free biochar surface preferentially removes tar components carrying O-containing groups. K-loaded biochar preferentially catalyzes the reforming of mono-aromatic ring components in tar. Ca-loaded biochar preferentially removes the mono-aromatic ring components, while being less selective for the removal of tar components containing hydroxyl groups and polyaromatic ring components. The loading of K/Ca promotes the dehydrogenation of the tar fraction during reforming, while only K catalyzes the deoxygenation of tar components. H-form biochar has no appreciable catalytic activity on CH₄ cracking. AAEMs have a catalytic activity on CH₄ cracking. K is particularly effective in improving tar conversion and hydrogen production of biochar.     

A parametric study on the factors affecting the froth floatation of Jordanian tar sand utilizing a fluidized bed floatator

Different parameters affecting the behavior of froth flotation of Jordanian tar sand, obtained from the Dead Sea area, were studied. This study was performed in a modified fluidized bed floatator. The effects of the addition of a flotation agent, NaOH, temperature and flotation time on the beneficiation of bitumen in the froth were investigated. It was found that the beneficiation factor in the froth increased with the increase of temperature and flotation time. However, the amount of base (NaOH) and the flotation agent were found to have a negative effect on that factor. A regression model based on a full factorial experimental design results was obtained with a significant correlation coefficient. The optimum beneficiation factor was found to be 7.2 and the bitumen content in the froth was found to be 79% in the froth, which was obtained at 0.2 gNaOH/L, zero agent, 80 °C, and 30 min.     

Evaluation of the uncertainty associated to tar sampling with solid phase adsorption cartridges

The uncertainty evaluation associated with the quantification of tar with the use of solid phase adsorption for tar sampling and gas chromatography analysis is present. The study shows that the major contribution to the overall uncertainty is related to the extraction step. Relevant tar compounds are selected and used as model to quantify the uncertainty and for comparison with the uncertainty associates to the traditional methodology for tar sampling. The study indicates that the uncertainty associated to the tar sampling with solid phase adsorption cartridges is lower than the uncertainty associated to the tar sampling with impinger bottles.     

The influence of different chemical compositions in biomass on gasification tar formation

To elucidate the relationship between biomass composition and tar formation, forest residue sawdust, rich in lignin, and agriculture waste cornstalks, rich in cellulose, were gasified in a spout-fluidized bed reactor from 700 °C to 900 °C. Gel permeation chromatography (GPC) coupled with a photodiode array detector (PDA) and gas chromatography – mass spectrometry (GC–MS) were used to analyze the tar character. The GPC results showed that the molecular mass distribution of the gasified tars were unchanged, only the amount of each component changed when the temperature increased during gasification. The amount of heaviest molecular mass components decreased, while the lighter components increased with temperature. Sawdust tar and cornstalks tar both showed aromatic character, while cornstalks tar contained more aliphatic compounds than sawdust tar. The tar formation mechanism has been proposed from the experimental data analysis.     

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.