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.     

Syngas production from biomass gasification in China: A clean strategy for sustainable development

Biomass gasification, which can be categorized as a set of relatively clean processes, is a good option for hydrogen production. The main purpose of the present work was to focus on the use of natural olivine as a bed material to minimize the tar content and enhance the hydrogen yield. The catalytic gasification tests were carried out in a fluidized bed gasifier using steam as the fluidizing medium. Hydrogen yield slightly increased from 51.9 to 53.1 g/kg biomass, as biomass particle size (BP) decreased from 5.0 to 2.0 mm. The yield of tar also decreased from 0.15 to 0.07 g/Nm³ with BP decreasing from 5.0 to 2.0 mm. With an increase in the catalyst-to-biomass ratio (C/B) from 0.2 to 0.8, HY increased from 47.8 to 51.9 g/kg biomass and tar content (TC) decreased from 0.8 to 0.15 g/Nm³. Temperature and steam/biomass ratio (S/B) were also affected the syngas composition and HY, significantly.     

Enhanced trace pollutants removal efficiency and hydrogen production in rice straw gasification using hot gas cleaning system

This study investigates the enhancement of tar and trace gaseous pollutants (e.g. hydrogen sulfide (H₂S) and hydrogen chloride (HCl) removal efficiency derived from rice straw gasification using an integrated hot-gas cleaning system. A bubbling fluidized bed gasifier was used by controlling the temperature at 800 °C and equivalence ratio (ER) ranging 0.2 to 0.4. The hot gas cleaning system was operated at 250 °C and designed to combine three types of absorbents including zeolite, calcined dolomite, and activated carbon. Tar, H₂S, and HCl removal efficiency and enhanced hydrogen production were also discussed. The experimental results indicated that light fraction tar removal efficiency was higher than 90% and the overall tar removal efficiency was approximately 70%. In the case of ER 0.4, the syngas tar content was decreased from 71.88 g/Nm³ (without hot gas cleaning system) to 16.53 g/Nm³ (with hot gas cleaning system). The tar removal efficiency is nearly 77% using the hot gas cleaning system. The HCl and H₂S removal efficiency ranged from 94% to 98% and from 80.7% to 83.92%, respectively. In the case of ER 0.3 and with the hot gas cleaning system, the HCl and H₂S concentrations in cleaned syngas gas were less than 40 ppm and 100 ppm, respectively. Meanwhile, the hydrogen concentration of produced gas was also increased from 6.82% to 9.83% with hot gas cleaning system used. It means that the hot gas cleaning system can effectively remove HCl and H₂S from produced gas in gasification, but also it has good potential for improving syngas quality and enhancing gas turbine application in the future.     

Biomass gasification as the first hot step in clean syngas production process – gas quality optimization and primary tar reduction measures in a 100 kW thermal input steam–oxygen blown CFB gasifier

Syngas production based on biomass gasification is an attractive, feasible alternative to fossil fuel feedstock for the production of transportation fuels. However, the product gas from biomass gasification must be cleaned and tailored to comply with strict syngas quality requirements, as it consists of a wide variety of major and minor components and impurities. The characterization of such species is important to determine downstream gas treatment steps, and to assess the efficiency of the gasification process.This paper gives an overview of the results obtained during experiments on steam–oxygen gasification of biomass using 100 kW maximal thermal input circulating fluidized bed gasifier (CFBG) that have been performed at Delft University of Technology during the CHRISGAS project. The unit is also equipped with a high-temperature ceramic gas filter and downstream reactors for upgrading of the gas.In the experiments biomass types of both woody and agricultural origin have been used. They were represented by clean wood, demolition wood, an energy crop species (miscanthus) and a true residue (Dutch straw), respectively. Moreover, different bed materials have been applied, namely quartz sand, treated and untreated olivine and magnesite. During the experiments extensive measurements of gas composition have been carried out throughout the integrated test rig. The gas characterization included major gas components as well as certain minor species and tar.The results show that with the use of magnesite as bed material, remarkable increases of hydrogen yield were attained, as compared to sand or olivine; up to a volume fraction of almost 40% (dry, nitrogen-free basis). Also the H₂:CO ratio increased from values near or lower than 1 to 2.3–2.6. This is near the values needed, for e.g., Fischer–Tropsch diesel production, indicating a potential for simplification of the gas upgrading. Furthermore, by using magnesite tar content of the raw gas was reduced to values near 2 g m^?3 (STP). Moreover, magnesite complied with the expectation to have a positive impact on agglomeration prevention for the agricultural fuels containing alkali and chlorine in the ash. The kind of olivine applied during the experiments did not yield the expected tar reduction; the measured tar concentration was even higher than when quartz sand was used as bed material. Finally kaolin proved to be an effective additive to counteract the agglomeration when fuels with high alkali content in the ash are gasified using bed material that is rich in silica, as it is the case with quartz sand and olivine.     

Chemical looping dry reforming of benzene as a gasification tar model compound with Ni- and Fe-based oxygen carriers in a fluidized bed reactor

Gasification tar during a fluidized bed operation impedes syngas utilization in downstream applications. Among tar constituents sampled during biomass gasification, benzene was the most abundant species. Thus, benzene was used as a model compound for chemical looping dry reforming (CLDR) over iron (Fe) and nickel (Ni) metals impregnated on silicon carbide (SiC) in a lab-scale fluidized bed reactor to convert it into hydrogen and carbon monoxide (H₂ and CO). A high benzene conversion rate (>90%) was observed at a higher experimental temperature (above 730 °C). Catalytic conversion of benzene using NiFe/SiC catalyst resulted in higher H₂ production whereas higher levels of CO were produced with Fe/SiC catalyst at an elevated temperature. Control experiments using an empty bed and SiC bed showed the formation of both the biphenyls and excessive carbon deposits. Air oxidation was also performed for the regeneration of oxygen carrier during the chemical looping operation.     

Experimental study of torrefied pine as a gasification fuel using a bubbling fluidized bed gasifier

Torrefied biomass has higher C/O ratio, resulting in improved heating value and reduced hygroscopic nature of the biomass, thus enabling longer storage times. In the southeastern United States, pine is has been identified as a potential feedstock for energy production. The objective of this study was to understand the performance of torrefied pine as a gasification fuel in a bench-scale bubbling fluidized bed gasifier. The gasification of torrefied pine was carried out at 790, 935 and 1000 °C and three equivalence ratios (ERs: 0.20, 0.25 and 0.30). The effect of process variables were studied based on i) products yield, ii) syngas composition iii) syngas energy content, and iv) contaminants. The mean concentration of CO increased with an increase in temperature, but was not statistically significant. On the other hand, H₂ concentration increased whereas CH₄ concentration decreased significantly with an increase in temperature from 790 to 935 °C. Further, with an increase in ER from 0.20 to 0.30, only CO₂ concentrations increased in the syngas. Results from torrefied pine were compared with raw pine gasification, and it was observed that torrefied pine gasification led to much higher char yield (more than twice) than pine; however, it produced less than half as much tar.     

Influences of equivalence ratio,oxygen concentration and fluidization velocity on the characteristics of oxygen-enriched gasification products from biomass in a pilot-scale fluidized bed

The influences of equivalence ratio (ER), oxygen concentration (OC) and fluidization velocity (FV) on the gasification performance in a pilot-scale fluidized bed with capacity of 1 ton biomass (the mixture of agricultural residue) per day were investigated using oxygen-enriched air as gasification agent and high-alumina bauxite as bed material. The characteristics of syngas (lower heating value (LHV), gas yield (Y), carbon conversion (CC) and cold gas efficiency (CGE)), bio-char (LHV and Proximate analysis) and tar (tar yield and LHV) were used to evaluate the gasification performance in this study. The results showed that 0.161 was the optimal ER due to the high quality of syngas produced and relatively lower tar generation with ER changing from 0.115 to 0.243 at OC ≈ 40% and FV ≈ 1.20.29.7% was the optimal OC due to the highest Y and CC and relatively low tar generation when OC varied from 21% to 44.7% at ER ≈ 1.40 and FV ≈ 1.15. Although higher FV could improve syngas quality, it also resulted in the higher tar yield and heavier wear, therefore, the optimal gasification performance was achieved at moderate FV (FV = 1.13). This study proved that oxygen-enriched gasification in a large-scale fluidized bed was an effective option to produce gaseous biofuels with high quality.     

Two-dimensional numerical modeling of combustion of Jordanian oil shale

A two-dimensional (2-D) modeling of the burning process of Jordanian oil shale in a circulating fluidized bed (CFB) burner was done in this study. The governing equations of continuity, momentum, energy, mass diffusion, and chemical combustion reactions kinetics were solved numerically using the finite volume method. The numerical solution was carried out using a high-resolution 2-D mesh to account for the solid and gaseous phases, k-ε turbulence, non-premixed combustion, and reacting CFD model with the same dimensions and materials of the experimental combustion burner used in this work. The temperature distribution and evolution of species were also computed.

Proximate and ultimate analyses were also performed to evaluate the air–fuel ratio and ash content. The required thermophysical properties, such as heating value, density, and porosity were obtained experimentally, while the activation energy was obtained from published literature.

It was found that the temperature contours of the combustion process showed that the adiabatic flame temperature was 1080 K in a vertical burner, while the obtained experimental results of maximum temperature at various locations of the burner in actual, non-adiabatic, non-stoichiometric combustion reached 950 K, showing good agreement with the model.     

Performance evaluation of an innovative 100 kWth dual bubbling fluidized bed gasifier through two years of experimental tests: Results of the BLAZE project

In this work, the results of two years of experimental tests on an innovative dual bubbling fluidized bed gasifier are reported. These are related to the activities of the BLAZE project (Horizon 2020) for the integration of steam biomass gasification and solid oxide fuel cell. Several tests were carried out on the pilot-scale reactor at various operating conditions, and in this work the results are reported in terms of dry gas composition and yield, organic and inorganic contaminants (tar, particulate matter, H₂S). The compact design of the gasifier (a single reactor with two concentric chambers and in-situ hot gas cleaning and conditioning) reduces the heat losses and produces close to nitrogen-free syngas. Preliminary tests using a filter candle filled with conventional catalyst, installed in the freeboard of the gasifier, show that the tar content dropped to about 2 g/Nm³, and the H₂ concentration increased up to 41%_vol,dry.     

Steam gasification of Miscanthus X Giganteus with olivine as catalyst production of syngas and analysis of tars (IR, NMR and GC/MS)

Steam gasification of Miscanthus X Giganteus (MXG) at high heating rate in a fluidised bed reactor with the use of olivine as catalyst was investigated. The effects of temperature (815-880 °C) on the yields and the compositions of syngas and tars were determined. The experimental results show that the gas yields and the content of H₂ increase with the temperature, while the yields of tar, char and the content of CO, CO₂ and CH₄ in the product gas decrease. Noteworthy is that about 1.1 m³ of dry gas (at ambient conditions) per kg of dry ash free biomass were obtained with about 46% of H₂ and 24% of CO by volume at 880 °C.The tars composition was determined by FTIR, NMR and GC/MS. The identification of different compounds shows mainly the presence of simple molecules. This may be facilitating the possibility of complete tar reforming process (hot gas cleaning), to improvement of the syngas yield and the decrease of the formation of pollutants.     

Hydrogen‐rich gas production from catalytic gasification of pine sawdust over Fe‐Ce/olivine catalyst

In order to improve hydrogen production and reduce tar generation during the biomass gasification, a catalyst loaded Fe‐Ce using calcined olivine as the support (Fe‐Ce/olivine catalysts) was prepared through deposition‐precipitation method. The characteristics of catalysts were determined by XRF, BET, XRD, and FTIR. Syngas yield, hydrogen yield, and tar yield were used to evaluate the catalyst activity. Meanwhile, the stability of catalysts was also studied. The results showed that the specific surface area and pore volume of olivine after calcined at high temperature were improved which was beneficial for the load of metals. α‐Fe₂O₃ and CeO₂ were the main active component of Fe‐Ce/olivine catalyst. The Fe‐Ce/olivine catalyst displayed a good performance on the catalytic gasification of pine sawdust with a syngas yield of 0.93 Nm³/kg, H₂ yield of 21.37 mol/kg, and carbon conversion rate of 55.14% at a catalytic temperature and gasification temperature of 800°C. Meanwhile, the Fe‐Ce/olivine catalyst could maintain a good stability after 150 minutes used.     

Hydrogen gas yield and trace pollutant emission evaluation in automotive shredder residue (ASR) gasification using prepared oyster shell catalyst

This work examines the hydrogen gas yield and trace pollutants partitioning in automobile shredder residue (ASR) catalytic gasification by fixed bed and fluidized bed gasifier with controlling at equilibrium ratio (ER) 0.2, temperature 900 °C, and 5%–15% prepared catalyst addition. Oyster shell (OS) is a valuable resource due to its higher calcium content that it could prepare as a catalyst for enhancing the hydrogen production in ASR gasification. In the case of the fixed bed gasifier experiments, the highest lower heating value (LHV) and syngas production were found at 900 °C and 10% OS catalyst addition. The maximum H₂ and CO composition were 6.57% and 5.97%, respectively. The LHV of syngas was approximately 4.43 MJ/Nm³. The fluidized bed gasifier could provide a good ASR decomposition and heat transfer behavior. The syngas yield results indicated the maximum H₂ and CO composition were 12.12% and 10.59%, respectively. It was obviously showed that the syngas production and energy conversion efficiency were enhanced by applying fluidized bed gasifier. The maximum produced gas LHV was 10.77 MJ/Nm³ as well as the cold gas efficiency (CGE) of produced gas was 71.62%. On the other hand, the volatile sulfur and chlorine speciation formed in ASR gasification were mainly partitioned in the solid and/or liquid phase. It implied that tested OS catalysts could inhibit the volatile sulfur and chlorine speciation emission in the produced gas as well as enhance the produced gas quality. In summary, this research could provide basic insight into enhanced syngas production and quality in ASR catalytic gasification using the prepared OS catalyst.     

Utilization of bifunctional catalyst for upgrading petroleum residue via cracking and gasification: Effect of catalysts

Vacuum residue is stepwise and high-efficient converted by the base cracking and coke gasification process. Cracking effect of vacuum residue was carried out with different bifunctional catalysts in a fluidized bed reactor, respectively. Calcium aluminate catalyst specialized for cracking and gasification procedure is selected with the activities of cracking and gasification. In comparison with silica sand, calcium aluminate catalyst showed the higher vacuum residue cracking activity, and cracking activity gradually increased with increasing the Ca/Al ratios. The results indicated that C2C4 olefinicity of above 60.4%, cracking-generated coke of about 5.0 wt%, and light oil yields is over 84.0 wt% at 650 °C with a catalyst-to-oil ratio of 7.0. Moreover, it was also found that calcium aluminate catalyst synthetized with the Ca/Al molar ratio of 12:7 and carbon black as pore-forming agent displayed a better cracking properties than that of the other catalysts. VR cracking properties over calcium aluminate catalysts was closely related to their basicity, as indicated by the Hammett indicators method. Cracking-generated coke on the base catalyst was well gasified with pure steam at 800 °C and produced the syngas with the total content of H₂ and CO₂ up to 81.5 vol%, the coke conversion over the tested catalysts is of above 93.6% in 30 min. Also, the alternating base cracking and gasification operations were performed three times to verify the stability of the optimal calcium aluminate catalyst. The selected catalysts presented high hydrothermal stability and stable cracking activity, which could be potentially used for vacuum residue stepwise and high-efficient utilization via vacuum residue catalytic cracking and gasification regeneration process.     

Combustion characteristics of solid waste biomass,oil shale,and coal

In this study, a developed two-dimensional mathematical model was used to represent the physical model of the combustion process of olive cake and date seed, and solve the governing equations using finite-volume method. The simulation was performed using ANSYS/Fluent software in order to estimate maximum temperature, heating values and pollutants concentrations. The obtained results were compared with experimental results, and corresponding values of oil shale and coal. The experimental work of direct burning of olive cake and date seeds was performed using an existing circulated fluidized bed (CFB) unit.

It was found that the adiabatic flame temperatures were 1380 K and 839 K for olive cake and date seed, and 2260 K and 1080 K for coal and oil shale, respectively. The experimental results showed that the maximum temperatures were 1126 K and 723 K for olive cake and date seed, respectively. The lower heating values were 19,500 kJ/kg and 16,400 kJ/kg for olive cake and date seed, and 29,000 kJ/kg and 7000 kJ/kg for coal and oil shale, respectively.

Thus, biomass such as date seed and olive cake may be used as an alternative fuel in electrical power plants in olive- or date-producing countries, which may save 40% of fuel cost.     

Enhancement of the quality of syngas from catalytic steam gasification of biomass by the addition of methane/model biogas

In this study, methane and model biogas were added during the catalytic steam gasification of pine to regulate the syngas composition and improve the quality of syngas. The effects of Ni/γ-Al₂O₃ catalyst, steam and methane/model biogas on H₂/CO ratio, syngas yield, carbon conversion rate and tar yield were explored. The results indicated that the addition of methane/model biogas during biomass steam gasification could increase the H₂/CO ratio to about 2. Methane/model biogas, steam and Ni/γ-Al₂O₃ catalyst significantly affected the quality of syngas. High H₂ content syngas with H₂/CO ratio of about 2, biomass carbon conversion >85% and low tar yield was achieved under the optimum condition: S/C = 1.5, α = 0.2 and using Ni/γ-Al₂O₃ catalyst. According to ANOVA, methane and catalyst were the key influencing factors of the H₂/CO ratio and syngas yield, and the tar yield mainly depended on the Ni/γ-Al₂O₃ catalyst. Biogas, as a more environmentally friendly material than methane, can also regulate the composition of syngas co-feeding with biomass.     

Hydrogen rich syngas production from biomass gasification using synthesized Fe/CaO active catalysts

Biomass gasification for hydrogen rich syngas production was investigated using the Fe/CaO catalysts in a fluidized bed reactor. The synthesized catalysts were prepared by an impregnation method with different Fe/CaO mass ratios (5%, 10%, 15%, 20%) for enhancing H₂ concentration and syngas yields and then characterized using X-ray diffraction (XRD), nitrogen adsorption and desorption isotherms test, scanning electron microscopy (SEM) and CO₂ absorption capacity test. The results showed that the Fe load had significant influences on the composition, textural properties and CO₂ adsorption capacity. Results of gasification experiments verified that the presence of Fe enhanced the concentration and yield of H₂. The highest syngas yield of 38.21 mol/kg biomass, H₂ yield of 26.40 mol/kg biomass, LHV values of 8.69 MJ/kg and gasification efficiency of 49.15% were obtained at an optimized mass ratio of Fe/CaO = 5%. In addition, the characterization results indicated that Ca₂Fe₂O₅ phase was formed. The Ca₂Fe₂O₅ had less CO₂ absorption capacity and effect on the gasification, but was considered to be a catalyst for tar cracking thus preventing the CaO deactivation.     

The development of a real-time thermogravimetric analyzer on the gasification of pine sawdust in a simulated fluidized bed gasifier

In this study, a real-time thermogravimetric analyzer was developed for providing insight into the reactivity and gasification process of pine sawdust. The mass loss rate of pine sawdust, syngas composition, and tar compounds in the gasification process were analyzed at different gasification conditions. According to the real-time thermogravimetric analysis, 800°C of the gasification temperature, 0.25 of the equivalence ratio, and 600 kg/(m²·h) of the gasification throughput were regarded as an optimum conditions for the gasification of pine sawdust in a fluidized bed gasifier.     

Air gasification of dried sewage sludge in a two-stage gasifier: Part 1. The effects and reusability of additives on the removal of tar and hydrogen production

Air gasification of dried sewage sludge was conducted in a two-stage gasifier. In the experiments, natural occurring materials, such as natural zeolite, olivine and dolomite, as well as biomass-based and coal-based activated carbons, were applied to the upper reactor of a two-stage gasifier, while sand and calcined dolomite were used as the fluidized bed material in the lower reactor. The reusability of the spent coal-based activated carbon and spent calcined dolomite was also investigated. The combination of calcined dolomite as the bed material and coal-based activated carbon in the upper reactor produced the highest H₂ (28 vol.%) and CO (21 vol.%) contents. Furthermore, total amount of tar generated with the combination was 91% less than that generated with no additive in the upper reactor and sand in the lower reactor. The H₂ content and tar removal efficiencies in the experiments with the spent activated carbons and spent calcined dolomites were shown to be better than those without additives in the upper reactor.     

Effect of fluidization/gasification parameters on hydrogen generation in syngas during fluidized-bed gasification process

This study discusses the influence of fluidization and gasification parameters on the hydrogen composition in syngas. For gasification conditions, when Stage 1 and Stage 2 gasifier temperature is 900 °C, the hydrogen content in syngas is 35.59 mol.% when the activated carbon is used as bed material. For using zeolite as bed material, the hydrogen content is 38.25 mol.%. The hydrogen content is higher than that under other conditions, but if the Steam/Biomass ratio is increased to 0.6, the hydrogen content resulted from zeolite as bed material is the highest 39.38 mol.%. For fluidization parameters, when Stage 2 bed material size is changed to 0.46 mm, no matter the bed material is activated carbon or zeolite, the hydrogen content in syngas is the best among three particle sizes. In terms of operating gas velocity, when gas velocity is 1.5 U_mf, the hydrogen content is higher. For fluidization parameters, the two bed materials can increase hydrogen content in syngas effectively in Stage 2 fluidized bed, and their effects are similar to each other. However, considering the fluidization parameters, the hydrogen content in syngas when activated carbon is used as bed material is better than that when the zeolite is used.     

Reactivity tests of the water–gas shift reaction on fresh and used fluidized bed materials from industrial DFB biomass gasifiers

The dual fluidized bed gasification process, offers various advantages for biomass gasification as well as the utilization of other solid feedstocks. In order to improve the knowledge of the reactions in fluidized bed gasifier, different types of bed material used in the gasifier were tested in a micro-reactivity test rig. It has been previously observed that during long-term operation, the surface of the bed material used (calcined olivine) undergoes a modification that improves catalytic activity. The main reaction of interest is the water–gas shift reaction. Olivine taken from long-term operation at the 8 MW biomass gasifier at Güssing (Austria), fresh olivine as a reference, and calcite, which is commonly used for enhancing in-bed catalytic tar reduction, were tested using the micro-reactivity test rig. Tests were carried out at temperatures of 800, 850, and 900 °C and space velocities of 40,000 to 50,000 h⁻¹ were applied. CO conversions of up to 61.5% were achieved for calcite. Used olivine showed a similar behavior, representing a large improvement compared to fresh olivine, which had CO conversion rates of less than 20%.