Study on biomass gasification under various operating conditions

An Aspen Plus model of biomass gasification with different gasifying agents has been developed. Due to lack of kinetic data, the developed model is based on Gibbs free energy minimization. The main objective of this study is to study the influence of gasifying agent (pure oxygen; oxygen-enriched air and air), gasification temperature and equivalence ratio (ER) on gas composition, gas lower heating value (LHV), and energy/exergy efficiencies. The developed model was validated with experimental data which was found to be in well agreement. Increase in gasification temperature led to a significant increase in H₂ content. On the other hand, an increase in ER led to a significant reduction in H₂, CO, and CH₄ and a significant increase in CO₂. Also, a gradual downward trend of exergy efficiency (EE) was found, as ER increased from 0.15 to 0.21, while it basically kept constant as the gasification temperature was varied.     

Characteristics of hydrogen-rich gas production of biomass gasification with porous ceramic reforming

In the present study, an updraft biomass gasifier combined with a porous ceramic reformer was used to carry out the gasification reforming experiments for hydrogen-rich gas production. The effects of reactor temperature, equivalence ratio (ER) and gasifying agents on the gas yields were investigated. The results indicated that the ratio of CO/CO₂ presented a clear increasing trend, and hydrogen yield increased from 33.17 to 44.26 g H₂/kg biomass with the reactor temperature increase, The H₂ concentration of production gas in oxygen gasification (oxygen as gasifying agent) was much higher than that in air gasification (air as gasifying agent). The ER values at maximum gas yield were found at ER = 0.22 in air gasification and at 0.05 in oxygen gasification, respectively. The hydrogen yields in air and oxygen gasification varied in the range of 25.05–29.58 and 25.68–51.29 g H₂/kg biomass, respectively. Isothermal standard reduced time plots (RTPs) were employed to determine the best-fit kinetic model of large weight biomass air gasification isothermal thermogravimetric, and the relevant kinetic parameters corresponding to the air gasification were evaluated by isothermal kinetic analysis.     

Syngas production by chemical looping gasification of rice husk using Fe-based oxygen carrier

The chemical looping gasification (CLG) of rice husk was conducted in a fixed bed reactor to analyze the effects of the ratio of oxygen carrier to rice husk (O/C), temperature, residence time and preparation methods of Fe-based oxygen carriers. The yield of gas, H₂/CO, lower heating value of syngas (LHV), conversion efficiency and performance parameters were analyzed to obtain CLG reaction characterization and optimal reaction conditions. Results showed that when O/C increased from 0.5 to 3.0, the gas production, H₂/CO, CO₂ yield and carbon conversion efficiency gradually increased, while the yield of H₂, CO and CH₄ and LHV gradually decreased. At the same time, a highest gasification efficiency was obtained when O/C was 1.5. As increasing temperature, the gas production, CO yield, carbon conversion efficiency and gasification efficiency gradually increased, while the yield of H₂, CH₄ and CO₂, H₂/CO and LHV gradually decreased. Sintering and agglomeration was obvious when the temperature was higher than 850 °C. When the reaction time increased from 10 min to 60 min, the gas production, CO yield, carbon conversion efficiency and gasification efficiency gradually increased, but the yield of H₂, H₂/CO and LHV decreased, among which 30 min was the best reaction residence time. In addition, coprecipitation was the best preparation method among several preparation methods of oxygen carrier. Finally, O/C of 1.5, 800 °C, 30 min and coprecipitation preparation method of oxygen carrier were the optimal parameters to obtain a gasification efficiency of 26.88%, H₂ content of 35.64%, syngas content of 56.40%, H₂/CO ratio of 1.72 and LHV of 12.25 MJ/Nm³.     

Syngas production from algae biomass gasification: the case of China

A kinetic model of algae gasification for hydrogen production with air and steam as gasification agent and was developed. The developed model was based on kinetic parameters available in the literature. The objective was to study the effect of critical parameters such as reaction temperature, stoichiometric ratio (SR) and steam flow rate (SFR) on H₂/CO ratio in the syngas, hydrogen yield, and lower heating value (LHV) of the produced syngas. Model formulation was validated with experimental results on air-steam gasification of biomass conducted in an atmospheric fluidized bed gasifier. The results showed that higher temperature contributed to lower H₂/CO, while higher SFR resulted in higher H₂/CO. The LHV of producer gas increased with SFR and gasification temperature.     

Oxy–steam gasification of biomass for hydrogen rich syngas production using downdraft reactor configuration

The paper focuses on the use of oxygen and steam as the gasification agents in the thermochemical conversion of biomass to produce hydrogen rich syngas, using a downdraft reactor configuration. Performance of the reactor is evaluated for different equivalence ratios (ER), steam to biomass ratios (SBR) and moisture content in the fuel. The results are compared and evaluated with chemical equilibrium analysis and reaction kinetics along with the results available in the literature. Parametric study suggests that, with increase in SBR, hydrogen fraction in the syngas increases but necessitates an increase in the ER to maintain reactor temperature toward stable operating conditions. SBR is varied from 0.75 to 2.7 and ER from 0.18 to 0.3. The peak hydrogen yield is found to be 104 g/kg of biomass at SBR of 2.7. Further, significant enhancement in H₂ yield and H₂ to CO ratio is observed at higher SBR (SBR = 1.5–2.7) compared with lower range SBR (SBR = 0.75–1.5). Experiments were conducted using wet wood chips to induce moisture into the reacting system and compare the performance with dry wood with steam. The results clearly indicate the both hydrogen generation and the gasification efficiency (η_g) are better in the latter case. With the increase in SBR, gasification efficiency (η_g) and lower heating value (LHV) tend to reduce. Gasification efficiency of 85.8% is reported with LHV of 8.9 MJ Nm^?3 at SBR of 0.75 compared with 69.5% efficiency at SBR of 2.5 and lower LHV of 7.4 at MJ Nm^?3 at SBR of 2.7. These are argued on the basis of the energy required for steam generation and the extent of steam consumption during the reaction, which translates subsequently in the LHV of syngas. From the analysis of the results, it is evident that reaction kinetics plays a crucial role in the conversion process. The study also presents the importance of reaction kinetics, which controls the overall performance related to efficiency, H₂ yield, H₂ to CO fraction and LHV of syngas, and their dependence on the process parameters SBR and ER. Copyright © 2013 John Wiley & Sons, Ltd.     

Evolution of syngas from cardboard gasification

Evolutionary behavior of syngas characteristics evolved during the gasification of cardboard has been examined using a batch reactor with steam as a gasifying agent. Evolutionary behavior of syngas chemical composition, mole fractions of hydrogen, CO and CH₄, as well as H₂/CO ratio, LHV (kJ/m³), hydrogen flow rate, and percentage of combustible fuel in the syngas evolved has been examined at different steam to flow rates with fixed mass of waste cardboard. The effect of steam to carbon ratio as affect by the steam flow rate on overall syngas properties has therefore been examined. A new parameter called coefficient of energy gain (CEG) has been introduced that provides information on the energy gained from the process. This new parameter elaborates the importance of optimizing the sample residence time in the reactor.     

Coal gasification in CO2 atmosphere and its kinetics since 1948: A brief review

Numerous coal gasification studies have been found in the literature those employed various kinds of gasifying agents such as steam and carbon dioxide. These studies are featured with wide variations in the parametric conditions and the usage of equipments. Steam is frequently employed as a gasifying agent, however, in several studies carbon dioxide has also been used as a gasifying agent either pure or in combination with other gasifying agents (H₂O, O₂, CO, H₂). This paper is a brief review of the coal gasification with CO₂ as a diluent. Different factors were studied over the coal gasification with CO₂ such as coal rank, pressure, temperature, gas composition, catalyst and the minerals present inside the coal, heating rate, particle size, and diverse reactor types. It also deals with the application of the gas-solid models developed in the literature and the combustion and gasification mechanisms for O₂/CO₂ streams. Moreover, it reviews the kinetics and the reaction rate equations (Arrhenius and Langmuir-Hinshelwood types) for coal-char gasification both in the reaction kinetic control region (low temperature) and the diffusion control region (high temperature) and at both low and high pressures.     

Thermodynamic analysis of glycerol-steam reforming in the presence of CO2 or H2 as carbon gasifying agent

This paper deals with the thermodynamic analysis of glycerol-steam reforming with H₂ or CO₂ co-fed as carbon gasifying agents in order to mitigate carbon deposition. Thermodynamic calculations were carried out at temperatures from 500 to 800 K and steam-to-glycerol ratios of 0:1–20:1 at atmospheric pressure. Carbon deposition was significant (1.0–1.7 mol C/mol C₃H₈O₃) at low steam-to-glycerol ratio (<4.0) within the reaction temperature range (500–800 K). Carbon-free regime can only be achieved at temperatures above 700 K at steam-to-glycerol ratio of 3:1. Beyond the steam-to-glycerol ratio of 4:1, carbon deposition is essentially zero. The addition of H₂ (as co-reactant) reduced the carbon deposition (down to 0.58 mol C/mol C₃H₈O₃ from 1.70 mol C/mol C₃H₈O₃) even at steam-to-glycerol ratio of 0:1 and reaction temperature of 500 K. Above 5 mol H₂/mol C₃H₈O₃, thermodynamic analysis showed undetectable carbon deposition. Significantly, this could be attributed to the H₂-gasification of carbon species to produce CH₄ and hence, the concomitant increase in the latter. The introduction of CO₂ into the glycerol-steam system, however, led to increased carbon deposition at all temperatures considered in this study due to the reaction between CO₂ and CH₄ in forming carbon deposits. Nevertheless, the carbon yield can be reduced through reforming at higher temperatures. It was further concluded from the current work that H₂ co-feeding linearly increased the exothermicity of reforming system.     

Evaluation of biomass gasification in a ternary diagram

The present paper addresses the development of an alternative approach to illustrate biomass gasification in a ternary diagram which is constructed using data from thermodynamic equilibrium modeling of air-blown atmospheric wood gasification. It allows the location of operation domains of slagging entrained-flow, fluidized-bed/dry-ash entrained-flow and fixed/moving-bed gasification systems depending on technical limitations mainly due to ash melting behavior. Performance parameters, e.g. cold gas efficiency or specific syngas production, and process parameters such as temperature and carbon conversion are displayed in the diagram depending on the three independent mass flows representing (1) the gasifying agent, (2) the dry biomass and (3) the moisture content of the biomass. The graphical approach indicates the existence of maxima for cold gas efficiency (84.9%), syngas yield (1.35 m³ (H₂ + CO STP)/kg (waf)) and conversion of carbon to CO (81.1%) under dry air-blown conditions. The fluidized-bed/dry-ash entrained-flow processes have the potential to reach these global maxima since they can operate in the identified temperature range from 700 to 950 °C. Although using air as a gasifying agent, the same temperature range posses a potential of H₂/CO ratios up to 2.0 at specific syngas productions of 1.15 m³ (H₂ + CO STP)/kg (waf). Fixed/moving-bed and fluidized-bed systems can approach a dry product gas LHV from 3.0 to 5.5 MJ/m³ (dry STP). The ternary diagram was also used to study the increase of gasifying agent oxygen fraction from 21 to 99 vol.%. While the dry gas LHV can be increased significantly, the maxima of cold gas efficiency (+6.5%) and syngas yield (+7.4%) are elevated only slightly.     

Waste glycerol gasification to syngas in pure DC water vapor arc plasma

In this experimental study, the conversion of waste glycerol, derived from industrial biodiesel production process, to syngas in water vapor DC thermal arc plasma was carried out. Pure water vapor was used as a gasifying agent, a heat carrier and a plasma-forming gas. This enabled to avoid undesirable ballast products, such as nitrogen oxide, and obtain higher hydrogen and carbon monoxide concentration. It was found that a higher process efficiency (the concentration of H₂ 57.9 vol% and CO 21 vol%, the H₂/CO ratio 2.76, the yield of H₂ 70 mol.% and CO 37 mol.%, the tar content 0.822 g/m³, the carbon conversion efficiency 68%, the energy conversion efficiency 39.5%) with a lower specific energy requirement (227.8 kJ/mol) was obtained at the highest H₂O/C₃H₈O₃ ratio of 1.9 (or water vapor flow rate of 14.76 kg/h, waste glycerol content of 7.88 kg/h, and the plasma torch power of 57 kW). This study is expected to provide an effective and advanced waste-to-energy solution.     

Hydrogen rich fuel gas production by gasification of wet biomass using a CO2 sorbent

Hydrogen rich fuel gas production by gasification of wet biomass accompanied by CO₂ absorption is proposed. The paper addressed this topic, and experiments were conducted to investigate the effects of the moisture content (M), the molar ratio of Ca(OH)₂ to carbon in the biomass ([Ca]/[C]) and the reactor temperature (T) on hydrogen production and CO₂ absorption by CaO. Measurement of the calcium compounds in solid residues was carried out with XRD and SEM. The results show that directly gasifying of wet biomass not only favors hydrogen production but also promotes CO₂ absorption by CaO. For the experiment with wet biomass (M = 0.90), the H₂ yield is increased by 51.5% while the CO₂ content is decreased by 28.4% than that for experiments with dry biomass (M = 0.09). CaO plays the dual role of catalyst and sorbent. It is noteworthy that CaO reveals a stronger effect on the water gas shift reaction than on the steam reforming of methane. The increase of the reactor temperature contributes to produce more H₂, but goes against CO₂ absorption by CaO. XRD spectrum and SEM image of the solid residues further confirmed that high temperature is unfavorable to CO₂ absorption by CaO. For the new method, the optimal operating temperature is in the 923–973 K range.     

Steam gasification of Greek lignite and its chars by co-feeding CO2 toward syngas production with an adjustable H2/CO ratio

Low-rank lignite is among the most abundant and cheap fossil fuels, linked, however, to serious environmental implications when employed as feedstock in conventional thermoelectric power plants. Hence, toward a low-carbon energy transition, the role of coal in world's energy mix should be reconsidered. In this regard, coal gasification for synthesis gas generation and consequently through its upgrade to a variety of value-added chemicals and fuels constitutes a promising alternative. Herein, we thoroughly explored for a first time the steam gasification reactivity of Greek Lignite (LG) and its derived chars obtained by raw LG thermal treatment at 300, 500 and 800 °C. Moreover, the impact of CO₂ addition on H₂O gasifying agent mixtures was also investigated. Both the pristine and char samples were fully characterized by various physicochemical techniques to gain insight into possible structure-gasification relationships. The highest syngas yield was obtained for chars derived after LG thermal treatment at 800 °C, due mainly to their high content in fixed carbon, improved textural properties and high alkali index. Steam gasification of lignite and char samples led to H₂-rich syngas mixtures with a H₂/CO ratio of approximately 3.8. However, upon co-feeding CO₂ and H₂O, the H₂/CO ratio can be suitably adjusted for several potential downstream processes.     

Hydrogen-rich gas production from biomass air and oxygen/steam gasification in a downdraft gasifier

Biomass gasification is an important method to obtain renewable hydrogen. However, this technology still stagnates in a laboratory scale because of its high-energy consumption. In order to get maximum hydrogen yield and decrease energy consumption, this study applies a self-heated downdraft gasifier as the reactor and uses char as the catalyst to study the characteristics of hydrogen production from biomass gasification. Air and oxygen/steam are utilized as the gasifying agents. The experimental results indicate that compared to biomass air gasification, biomass oxygen/steam gasification improves hydrogen yield depending on the volume of downdraft gasifier, and also nearly doubles the heating value of fuel gas. The maximum lower heating value of fuel gas reaches 11.11 MJ/N m³ for biomass oxygen/steam gasification. Over the ranges of operating conditions examined, the maximum hydrogen yield reaches 45.16 g H₂/kg biomass. For biomass oxygen/steam gasification, the content of H₂ and CO reaches 63.27–72.56%, while the content of H₂ and CO gets to 52.19–63.31% for biomass air gasification. The ratio of H₂/CO for biomass oxygen/steam gasification reaches 0.70–0.90, which is lower than that of biomass air gasification, 1.06–1.27. The experimental and comparison results prove that biomass oxygen/steam gasification in a downdraft gasifier is an effective, relatively low energy consumption technology for hydrogen-rich gas production.     

Coupling the solvent-based CO2 capture processes to the metal water-splitting for hydrogen generation in a semi-continuous system

Hydrogen is considered as the future energy vector. Due to scarceness in materials, obtaining hydrogen from common metals and metallic residues is gaining interest. The present work aims at coupling for the first time solvent-based CO₂ capture processes with the hydrogen generation from the metal-water splitting reaction, using common elements such as Al, Zn, Mn and Fe. To do so, a novel semicontinuous facility is developed. In the process, both the CO₂-Rich stream (CO2RS) and CO₂ Capture-Solvent Lean stream (CO2LS) are considered. The production of H₂ increased in the order Al < Mn < Fe < Zn. For pure Al, aqueous NaOH (CO2LS) showed the highest H₂ yield, up to 85.5%, while Al chips (residue) showed outstanding performance. The experimental study showed that small particle sizes improve the H₂ yield. This technology represents an opportunity for bringing about value-added to CO₂ capture by generating at the same time green hydrogen.     

Application of response surface methodology to assess the combined effect of operating variables on high-pressure coal gasification for H2-rich gas production

Coal gasification was performed by means of a high-pressure fixed bed gasifier fitted with a solids feeding system in continuous mode, using oxygen and steam as gasifying agents. The main aim of the paper was to assess the combined effects of the operating variables (temperature, oxygen and steam concentrations) on high-pressure coal gasification. To this end a face centered central composite design (FCCCD) based on response surface methodology (RSM) was used. The response variables studied were: H₂, CO and syngas production, H₂/CO ratio, cold gas efficiency (η), and carbon conversion (X). The study was carried out at temperatures of 900, 950 and 1000 °C, using oxygen concentrations of 5, 10 and 15 vol.%, and steam concentrations of 25, 40 and 55 vol.%. The gasification temperature was found to be the most influential variable, with high temperatures leading to an increase in all the response variables studied. An increase in the oxygen content of the gasifying agent led to a decrease in H₂ and CO production, and cold gas efficiency, whilst carbon conversion was favoured. An increase in steam concentration, on the other hand, favoured the production of H₂ and syngas production, whereas CO production underwent a reduction; cold gas efficiency and carbon conversion were observed to increase. Response surface methodology (RSM) revealed the effects of interaction between the operating variables, which would not have been identified by the traditional “one-factor-at-a-time” method. The models developed successfully fitted the experimental results for all the response variables studied.     

Hydrogen production via steam reforming of methanol over Cu/(Ce,Gd)O2−x catalysts

Hydrogen production via steam reforming of methanol is carried out over Cu/(Ce,Gd)O_2−x catalysts at 210–600 °C. The CO content in reformate is about 1% at 210–270 °C, which are the typical temperature for hydrogen production via steam reforming of methanol. Largest H₂ yield and CO₂ selectivity and smallest CO content are obtained at 240 °C. The formation rate of CO increases with increasing temperature. The average formation rate of CO becomes larger than that of CO₂ at about 450 °C. The H₂ yield, the CO₂ selectivity and the CO content become constant at about 550 °C. At 240 °C, the smallest CO content is obtained with a catalyst weight of 0.5 g and a Cu content of 3 wt%. The H₂ yield, defined as H₂/(CO + CO₂) in formation rates, at 240 °C is always 3 and not affected by the variations of either the catalyst weight or the Cu content.     

Performance assessment of thermochemical CO2/H2O splitting in moving bed and fluidized bed reactors

In this paper, we present the assessment of moving bed reactors and fluidized bed reactors operating in different fluidizing regimes for solar thermochemical redox cycles (STRC) for syngas production. The reduction reactor with a moving bed (MB_RED) while the oxidation reactor (OXI) is either a moving bed reactor (MB_OXI) or bubbling bed (BB_OXI) yields higher performance. It was observed that only water splitting is suitable at 1400 °C and 10⁻³ bar reduction conditions. The higher reduction temperature and pressure improved the efficiency of the CO₂/H₂O splitting unit. The requirement of the H₂/CO ratio drives the gas feed (CO₂/H₂O) into OXI. To achieve an H₂/CO ratio of 1, MB_OXI and BB_OXI require an equimolar mixture of CO₂ and H₂O at 1600 °C. However, to achieve a similar H₂/CO ratio at a lower temperature of 1500 °C, the gas feed of the CO₂/H₂O ratio required is 3. A similar H₂/CO ratio is achieved for OXI operating in a turbulent and fast fluidizing, but the selectivity is lower due to lower reaction rates. OXI as a transport bed is least suited based on solid conversion (X_OXI), H₂/CO, or efficiency. The results are useful in designing the redox reactors for syngas.     

Effect of agglomeration/defluidization on hydrogen generation during fluidized bed air gasification of modified biomass

This study presents the effect of particle agglomeration on syngas emission during the biomass air gasification process. Various operating conditions such as operating temperature, equivalence ratio (ER), and amount of bed materials are employed. The concentrations of H₂ and CO increase along with the operating time as agglomeration begins, while CO₂ decreases at the same time. However, there is no significant change in the emission concentration of CH₄ during the defluidization process. The lower heating value increases while the system reaches the agglomeration/defluidization under various operating parameters. When the system reaches the agglomeration/defluidization process, the LHV value sharply increases. The results are obtained when the system reaches agglomeration/defluidization. The temperature increases while bed agglomeration occurs. A higher temperature increases the production of H₂ and CO, contributing to the LHV calculation.     

Kinetic characterizations of biomass char CO2-gasification reaction within granulated blast furnace slag

The reactions of biomass char CO₂-gasification within granulated blast furnace slag (BFS) were systematically conducted by the non-isothermal program using a thermogravimetric analyzer. At the same time during reaction proceeded, the conversion of biomass char CO₂-gasification reaction increased with the increasing heating rate. However, at the same temperature during reaction proceeded, the conversion of biomass char CO₂-gasification reaction decreased with the increasing heating rate. The granulated BFS could be used as a catalyst in the biomass char CO₂-gasification reaction and its catalytic effect became more obvious with the increasing content of BFS in the mixture. The A₄ model (nuclei production (m = 4) model) selected through the novel two-step method firstly proposed in the study was the best match with all the gasification reactions. The activation energy was from 52.75 kJ/mol to 64.42 kJ/mol and was lower with the increase of heating rate and the content of BFS in the mixture. The kinetic equations of biomass char CO₂-gasification reaction within granulated BFS were developed through the selected model and calculated kinetic parameters.