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.     

Thermodynamic analysis of hydrogen production via autothermal steam reforming of selected components of aqueous bio-oil fraction

From a technical and economic point of view, autothermal steam reforming offers many advantages, as it minimizes heat load demand in the reformer. Bio-oil, the liquid product of biomass pyrolysis, can be effectively converted to a hydrogen-rich stream. Autothermal steam reforming of selected compounds of bio-oil was investigated using thermodynamic analysis. Equilibrium calculations employing Gibbs free energy minimization were performed for acetic acid, acetone and ethylene glycol in a broad range of temperature (400–1300 K), steam to fuel ratio (1–9) and pressure (1–20 atm) values. The optimal O₂/fuel ratio to achieve thermoneutral conditions was calculated under all operating conditions. Hydrogen-rich gas is produced at temperatures higher than 700 K with the maximum yield attained at 900 K. The ratio of steam to fuel and the pressure determine to a great extent the equilibrium hydrogen concentration. The heat demand of the reformer, as expressed by the required amount of oxygen, varies with temperature, steam to fuel ratio and pressure, as well as the type of oxygenate compound used. When the required oxygen enters the system at the reforming temperature, autothermal steam reforming results in hydrogen yield around 20% lower than the yield by steam reforming because part of the organic feed is consumed in the combustion reaction. Autothermicity was also calculated for the whole cycle, including preheating of the organic feed to the reactor temperature and the reforming reaction itself. The oxygen demand in such a case is much higher, while the amount of hydrogen produced is drastically reduced.     

Exergy analysis of hydrogen production from biomass gasification

For a given set of operating conditions, the hydrogen production from biomass gasification can be improved through optimization of the operating parameters and efficiencies. The present approach can predict hydrogen production via biomass gasification in a range of 10–32 kg/s from biomass (sawdust wood). The biomass is introduced to a gasifier at an operating temperature range of 1000–1500 K. Also, 4.5 kg/s of steam at 500 K is used as gasification medium. Results indicate that improvement in hydrogen production from biomass steam gasification depending on the amount of steam and quantity of biomass feeding to the gasifier as well the operating temperature. Over the range of feeding biomass, the hydrogen yield reaches 80–130 g H₂/kg biomass while in the operating temperature examined, the hydrogen yield reaches 80 g H₂/kg biomass. On mole basis it is found that, in the first range of H₂ varies from 51 to 63% in the studied range of feeding biomass in existing 4.5 kg/s from steam while H₂ gets to 51–53% in existing of 6.3 kg/s from steam.     

High temperature steam-only gasification of woody biomass

We have studied a high temperature steam gasification process to generate hydrogen-rich fuel gas from woody biomass. In this study, the performance of the gasification system which employs only high temperature steam exceeding 1200 K as the gasifying agent was evaluated in a 1.2 ton/day-scale demonstration plant. A numerical analysis was also carried out to analyze the experimental results. Both the steam temperature and the molar ratio of steam to carbon (S/C ratio) affected the reaction temperature which strongly affects the gasified gas composition. The H₂ fraction in the produced gas was 35–55 vol.% at the outlet of the gasifier. Under the experimental conditions, S/C ratio had a significant effect on the gas composition through the dominant reaction, water–gas shift reaction. The tar concentration in the produced gas from the high temperature steam gasification process was higher than that from the oxygen-blown gasification processes. The highest cold gas efficiency was 60.4%. However, the gross cold gas efficiency was 35%, which considers the heat supplied by high temperature steam. The ideal cold gas efficiency of the whole system with heat recovery processes was 71%.     

Hydrogen-rich gas production by air–steam gasification of rice husk using supported nano-NiO/γ-Al2O3 catalyst

The air–steam catalytic gasification of rice husk for hydrogen-rich gas production was experimentally investigated in a combined fixed bed reactor with the newly developed nano-NiO/γ-Al₂O₃ catalyst. A series of experiments have been performed to explore the effects of catalyst presence, catalytic reactor temperature, the equivalence ratio (ER), and steam to biomass ratio (S/B) on the composition and yield of gasification gases. The experiments demonstrated that the developed nano-NiO/γ-Al₂O₃ catalyst had a high activity of cracking tar and hydrocarbons, upgrading the gas quality, as well as yielding a high hydrogen production. Catalytic temperature was crucial for the overall gasification process, a higher temperature contributed to more hydrogen production and gas yield. Varying ER demonstrated complex effects on rice husk gasification and an optimal value of 0.22 was found in the present study. Compared with biomass catalytic gasification under air only, the introduction of steam improved the gas quality and yield. The steam/biomass ratio of 1.33 was found as the optimum operating condition in the air–steam catalytic gasification.     

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.     

Integrated catalytic adsorption (ICA) steam gasification system for enhanced hydrogen production using palm kernel shell

This paper investigates the integrated catalytic adsorption (ICA) steam gasification of palm kernel shell for hydrogen rich gas production using pilot scale fluidized bed gasifier under atmospheric condition. The effect of temperature (600–750 °C) and steam to biomass ratio (1.5–2.5 wt/wt) on hydrogen (H₂) yield, product gas composition, gas yield, char yield, gasification and carbon conversion efficiency, and lower heating values are studied. The results show that H₂ hydrogen composition of 82.11 vol% is achieved at temperature of 675 °C, and negligible carbon dioxide (CO₂) composition is observed at 600 °C and 675 °C at a constant steam to biomass ratio of 2.0 wt/wt. In addition, maximum H₂ yield of 150 g/kg biomass is observed at 750 °C and at steam to biomass ratio of 2.0 wt/wt. A good heating value of product gas which is 14.37 MJ/Nm³ is obtained at 600 °C and steam to biomass ratio of 2.0 wt/wt. Temperature and steam to biomass ratio both enhanced H₂ yield but temperature is the most influential factor. Utilization of adsorbent and catalyst produced higher H₂ composition, yield and gas heating values as demonstrated by biomass catalytic steam gasification and steam gasification with in situ CO₂ adsorbent.     

Hydrogen production from biomass combining pyrolysis and the secondary decomposition

An efficient method of hydrogen production from biomass was studied in this paper. The pyrolysis of biomass was combined with the secondary decomposition of gaseous intermediate for hydrogen-rich gas production, with the avoidance of N₂ and CO₂ dilution to the energy density of gaseous effluents. In order to acquire the optimum conditions for hydrogen generation, effects of operating parameters on this two-step decomposition of biomass were analyzed through simulation of thermodynamic equilibrium and experiments using Ni/cordierite catalyst. The results indicate that the operating parameters, including pyrolysis temperature 923 K, 18 min of residence time, the secondary decomposition temperature 1123 K and molar steam to carbon ratio 2, satisfy all the criteria for high hydrogen content and energy efficiency. Hydrogen content of above 60% and hydrogen yield of around 65 g/kg biomass were achieved with optimized conditions. The hydrogen-rich gas is preferred for potential utilization in downstream fuel cells for the implementation of distributed energy supply, and is also practical for pure hydrogen production.     

Hydrogen-rich gas from catalytic steam gasification of municipal solid waste (MSW): Influence of catalyst and temperature on yield and product composition

In the present study the catalytic steam gasification of MSW to produce hydrogen-rich gas or syngas (H₂ + CO) with calcined dolomite as a catalyst in a bench-scale downstream fixed bed reactor was investigated. The influence of the catalyst and reactor temperature on yield and product composition was studied at the temperature range of 750–950 °C, with a steam to MSW ratio of 0.77, for weight hourly space velocity of 1.29 h⁻¹. Over the ranges of experimental conditions examined, calcined dolomite revealed better catalytic performance, at the presence of steam, tar was completely decomposed as temperature increases from 850 to 950 °C. Higher temperature resulted in more H₂ and CO production, higher carbon conversion efficiency and dry gas yield. The highest H₂ content of 53.29 mol%, and the highest H₂ yield of 38.60 mol H₂/kg MSW were observed at the highest temperature level of 950 °C, while, the maximum H₂ yield potential reached 70.14 mol H₂/kg dry MSW at 900 °C. Syngas produced by catalytic steam gasification of MSW varied in the range of 36.35–70.21 mol%. The char had a highest ash content of 84.01% at 950 °C, and negligible hydrogen, nitrogen and sulphur contents.     

Thermodynamic optimization of biomass gasification for decentralized power generation and Fischer–Tropsch synthesis

In recent years, biomass gasification has emerged as a viable option for decentralized power generation, especially in developing countries. Another potential use of producer gas from biomass gasification is in terms of feedstock for Fischer–Tropsch (FT) synthesis – a process for manufacture of synthetic gasoline and diesel. This paper reports optimization of biomass gasification process for these two applications. Using the non–stoichometric equilibrium model (SOLGASMIX), we have assessed the outcome of gasification process for different combinations of operating conditions. Four key parameters have been used for optimization, viz. biomass type (saw dust, rice husk, bamboo dust), air or equivalence ratio (AR = 0, 0.2, 0.4, 0.6, 0.8 and 1), temperature of gasification (T = 400, 500, 600, 700, 800, 900 and 1000 °C), and gasification medium (air, air–steam 10% mole/mole mixture, air–steam 30%mole/mole mixture). Performance of the gasification process has been assessed with four measures, viz. molar content of H₂ and CO in the producer gas, H₂/CO molar ratio, LHV of producer gas and overall efficiency of gasifier. The optimum sets of operating conditions for gasifier for FT synthesis are: AR = 0.2–0.4, Temp = 800–1000 °C, and gasification medium as air. The optimum sets of operating conditions for decentralized power generation are: AR = 0.3–0.4, Temp = 700–800 °C with gasification medium being air. The thermodynamic model and methodology presented in this work also presents a general framework, which could be extended for optimization of biomass gasification for any other application.     

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.     

Simulating the steam reforming of sunflower meal in Aspen Plus

Hydrogen is a clean energy carrier that has the potential to mitigate the environmentally hazardous effects of fossil fuels. Hydrogen is mainly produced through the steam reforming of natural gas however it is also possible to produce hydrogen through the thermochemical conversion of various biomasses. In this study, three Aspen plus simulation models were developed to obtain hydrogen-rich gas products from biomass through catalytic steam reforming. The results obtained in this modeling study were compared to the experimental data obtained by the steam reforming of the sunflower meal, which is a waste product of the seed oil industry. Out of all three models, model II, in which all of the reactions are assumed to occur simultaneously and all species except for biomass are assumed to undergo combustion reactions, was the most successful one at predicting close results (93% similar) to experimental findings. Using this model, the effect of water:biomass feed ratio on the product yields was tested and the highest possible H₂ yield (44.9 mol H₂/kg sunflower meal) was achieved with a 15:1 water:biomass feed ratio at the constant temperature of 800 °C and atmospheric pressure.     

Integrated adsorption steam gasification for enhanced hydrogen production from palm waste at bench scale plant

The generation of hydrogen-enriched synthesis gas from catalytic steam gasification of biomass with in-situ CO₂ capture utilizing CaO has a high perspective as clean energy fuels. The present study focused on the process modeling of catalytic steam gasification of biomass using palm empty fruit bunch (EFB) as biomass for hydrogen generation through experimental work. Experiment work has been carried out using a fluidized bed gasifier on a bench-scale plant. The established model integrates the kinetics of EFB catalytic steam gasification reactions, in-situ capturing of CO₂, mass and energy balance calculations. Chemical reaction constants have been calculated via the parameters fitting optimization approach. The influence of operating parameters, mainly temperature, steam to biomass, and sorbent to biomass ratio, was investigated for the hydrogen purity and yield through the experimental study and developed model. The results predicted approximately 75 vol% of the hydrogen purity in the product gas composition. The maximum H₂ yield produced from the gasifier was 127 gH₂/kg of EFB via experimental setup. The increase in both steam to biomass ratio and temperature enhanced the production of hydrogen gas. Comparing the results with already published literature showed that the current system enables to produce a high amount of hydrogen from EFB.     

An experimental investigation of hydrogen production from biomass gasification

An experimental study of hydrogen production from biomass was conducted using a benchscale fluidized bed gasifier. Parametric experiments were performed to determine the effects of reactor temperature, equivalence ratio, and steam to biomass ratio. Experimental measurements of gas composition and yield were used to calculate the hydrogen yield potential, the capacity of the gas stream for hydrogen production by shifting carbon monoxide and steam reforming higher hydrocarbons. Over the ranges of experimental conditions examined, hydrogen yield potential proved to be most sensitive to equivalence ratio, varying from 62 g H₂ kg⁻¹ of dry, ash-free biomass at an equivalence ratio of 0.37, to 128 g H₂ kg⁻¹ of dry, ash-free biomass at an equivalence ratio of 0.0. Of the conditions tested, the highest hydrogen yield potential, 128 g H₂ kg⁻¹ of dry, ash-free biomass, was achieved at a reactor temperature of 850 °C, equivalence ratio of 0.0, and a steam to biomass ratio of 1.7. This is 78% of the theoretical maximum yield of 165 g H₂ kg⁻¹ of dry, ash-free biomass for this feedstock.     

Thermodynamic analysis of hydrogen production via steam reforming of selected components of aqueous bio-oil fraction

This work presents thermodynamics analysis of hydrogen production via steam reforming of bio-oil components. The model compounds, acetic acid, ethylene glycol and acetone, representatives of the major classes of components present in the aqueous fraction of bio-oil were used for the study. The equilibrium product compositions were investigated in a broad range of conditions like temperature (400–1300 K), steam to fuel ratio (1–9) and pressure (1–20 atm). Any of the three model compounds can be fully reformed even at low temperatures producing hydrogen with maximum yield ranging from 80% to 90% at 900 K. Steam to fuel ratio positively affect the hydrogen content over the entire range of temperature studied. Conversely, higher pressure decreases the hydrogen yield. The formation of solid carbon (graphite) does not constitute a problem provided that reforming temperatures higher than 600 K and steam to fuel ratios higher than 4 for acetic acid and ethylene glycol and 6 for acetone are to be used. Thermal decomposition of the bio-oil components is thermodynamically feasible, forming a mixture containing _C(s)${\mathrm{C}}_{(\mathrm{s})}$, CH₄, H₂, CO, CO₂, and H₂O at various proportions depending on the specific nature of the compound and the temperature. Material and energy balances of complete reforming system demonstrated that the production of 1 kmol/s hydrogen from bio-oil steam reforming requires almost the same amount of energy as with natural gas reforming.     

Utilization of NiO/porous ceramic monolithic catalyst for upgrading biomass fuel gas

Catalytic steam reforming for producing high quality syngas from biomass fuel gas was studied over monolithic NiO/porous ceramic catalysts in a fixed-bed reactor. Effects of reaction temperature, steam to carbon (S/C) ratio, and nickel loading content on catalyst performance were investigated. Results indicated that the NiO/porous ceramic monolith catalyst had a good ability to improve bio-fuel gas quality. H₂ yield, H₂ + CO content, and H₂/CO ratio in produced gas were increased when reaction temperature was increased from 550 to 700 °C. H₂ yield was increased from 28.1% to 40.2% with S/C ratio increased from 1 to 2. And the yield of hydrogen was stabilized with the further increase of S/C ratio. Catalyst activity was not always enhanced with increased nickel content, when NiO loading content reaches 5.96%, serious aggregation and sintering of active composition on catalyst surface occur. The best performance, in terms of H₂ yield, is obtained with 2.50% NiO content at reaction temperature of 700 °C and S/C ratio of 2.     

A study of combined biomass gasification and electrolysis for hydrogen production

An integrated system for the production of hydrogen by gasification of biomass and electrolysis of water has been designed and cost estimated. The electrolyser provides part of the hydrogen product as well as the oxygen required for the oxygen blown gasifier. The production cost was estimated to 39 SEK/kg H₂ at an annual production rate of 15?000 ton, assuming 10% interest rate and an economic lifetime of 15 years. Employing gasification only to produce the same amount of hydrogen, leads to a cost figure of 37 SEK/kg H₂, and for an electrolyser only a production cost of 41 SEK/kg H₂. The distribution of capital and operating cost is quite different for the three options and a sensitivity analyses was performed for all of these. However, the lowest cost hydrogen produced with either method is at least twice as expensive as hydrogen from natural gas steam reforming.     

生物质气化制氢的模拟

以秸秆为研究对象,利用Aspen P lus软件建立气化反应器模型,对生物质气化制氢进行模拟计算.探讨不同反应条件,包括气化温度、生物质与蒸汽质量配比以及催化剂对富氢气体成分的影响.计算结果表明,未加催化剂条件下,采用生物质蒸汽气化技术可获得体积分数为6000/以上的富氢燃料气,增大蒸汽与生物质质量配比有利于氢气产率的提高;添加CaO、MgO催化剂可较大幅度地提高氢气产率,氢气体积分数最大可达到9400/,其中CaO对生物质气化制氢过程的催化作用非常显著.     

Hydrogen-rich gas production from waste plastics by pyrolysis and low-temperature steam reforming over a ruthenium catalyst

Operating conditions for low-temperature pyrolysis and steam reforming of plastics over a ruthenium catalyst were investigated. In the range studied, the highest gas and lowest coke fractions for polystyrene (PS) with a 60 g h⁻¹ scale, continuous-feed, two-stage gasifier were obtained with a pyrolyzer temperature of 673 K, steam reforming temperature of 903 K, and weight hourly space velocity (WHSV) of 0.10 g-sample g-catalyst⁻¹ h⁻¹. These operating conditions are consistent with optimum conditions reported previously for polypropylene. Our results indicate that at around 903 K, the activity of the ruthenium catalyst was high enough to minimize the difference between the rates of the steam reforming reactions of the pyrolysates from polystyrene and polypropylene. The proposed system thus has the flexibility to compensate for differences in chemical structures of municipal waste plastics. In addition, the steam reforming temperature was about 200 K lower than the temperature used in a conventional Ni-catalyzed process for the production of hydrogen. Low-temperature steam reforming allows for lower thermal input to the steam reformer, which results in an increase in thermal efficiency in the proposed process employing a Ru catalyst. Because low-temperature steam reforming can be also expected to reduce thermal degradation rates of the catalyst, the pyrolysis-steam reforming process with a Ru catalyst has the potential for use in small-scale production of hydrogen-rich gas from waste plastics that can be used for power generation.     

Exergy analysis of biomass staged-gasification for hydrogen-rich syngas

Using Aspen Plus simulations, exergy analyses of hydrogen-rich syngas production via biomass staged-gasification are carried out for three configurations, namely, staged-gasification with pyrolysis gas combustion and char gasification (C-1), staged-gasification with pyrolysis gas reforming and char gasification (C-2), and staged-gasification with pyrolysis gas reforming and char combustion (C-3). The results show that, for the gasification and reforming processes, the exergy loss of pyrolysis gas with tar reforming is less than that of char gasification. As for the system, it is conducive to generating hydrogen by making full use of the hydrogen element (H) in biomass instead of the H in water. The benefits of C-1 are that it removes tar and produces higher yield and concentration of hydrogen. However, C-2 is capable of obtaining higher exergy efficiency and lower exergy loss per mole of H₂ production. C-3 theoretically has greater process performances, but it has disadvantages in tar conversion in practical applications. The appropriate gasification temperature (T_G) are in the range of 700–750 °C and the appropriate mass ratio of steam to biomass (S/B) are in the range of 0.6–0.8 for C-1 and C-3; the corresponding parameters for C-2 are in the ranges of 650–700 °C and 0.7–0.8, respectively.