An Experimental Investigation of Hydrogen Production from Biomass

In gaseous products of biomass steam gasification, there exist a lot of CO, CH4 and other hydrocarbons that can be converted to hydrogen through steam reforming reactions. There exists potential hydrogen production from the raw gas of biomass steam gasification. In the present work, the characteristics of hydrogen production from biomass steam gasification were investigated in a small-scale fluidized bed. In these experiments, the gasifying agent (air) was supplied into the reactor from the bottom of the reactor and the steam was added into the reactor above biomass feeding location. The effects of reaction temperature, steam to biomass ratio, equivalence ratio (ER) and biomass particle size on hydrogen yield and hydrogen yield potential were investigated. The experimental results showed that higher reactor temperature, proper ER, proper steam to biomass ratio and smaller biomass particle size will contribute to more hydrogen and potential hydrogen yield.     

Comparison of dual fluidized bed steam gasification of biomass with and without selective transport of CO2

A comparison of dual fluidized bed gasification of biomass with and without selective transport of CO₂ from the gasification to the combustion reactor is presented. The dual fluidized bed technology provides the necessary heat for steam gasification by circulating hot bed material that is heated in a separate fluidized bed reactor by combustion of residual biomass char. The hydrogen content in producer gas of gasifiers based on this concept is about 40 vol% (dry basis). Addition of carbonates to the bed material and adequate adjustment of operation temperatures in the reactors allow selective transport of CO₂ (absorption enhanced reforming—AER concept). Thus, hydrogen contents of up to 75 vol% (dry basis) can be achieved. Experimental data from a 120 kW_{Fuel input} pilot plant as well as thermodynamic data are used to determine the mass- and energy-balances. Carbon, hydrogen, oxygen, and energy balances for both concepts are presented and discussed.     

Sorption enhanced steam reforming (SESR): a direct route towards efficient hydrogen production from biomass‐derived compounds

OVERVIEW: Efficient conversion of biomass to hydrogen is imperative in order to realize sustainable hydrogen production. Sorption enhanced steam reforming (SESR) is an emerging technology to produce high purity hydrogen directly from biomass‐derived oxygenates, by integrating steam reforming, water‐gas shift and CO₂ separation in one‐stage. Factors such as simplicity of the hydrogen production process, flexibility in feedstock, high hydrogen yield and low cost, make the SESR process attractive for biomass conversion to fuels. IMPACT: Recent work has demonstrated that SESR of biomass‐derived oxygenates has greater potential than conventional steam reforming for hydrogen production. The flexibility of SESR processes resides in the diversity of feedstocks, which can be gases (e.g. biogas, syngas from biomass gasification), liquids (e.g. bioethanol, glycerol, sugars or liquid wastes from biomass processing) and solids (e.g. lignocellulosic biomass). SESR can be developed to realize a simple biomass conversion process but with high energy efficiency. APPLICATIONS: Hydrogen production by SESR of biomass‐derived compounds can be integrated into existing oil refineries and bio‐refineries for hydrotreating processing, making the production of gasoline and diesel greener. Moreover, hydrogen from SESR can be directly fed to fuel cells for power generation. Copyright © 2012 Society of Chemical Industry     

Process synthesis and economics of combined biomethanol and CHP energy production derived from biomass wastes

BACKGROUND: This paper reports on process synthesis and economics of combined methanol and CHP (combined heat and power) energy production from crude biooil, waste glycerol produced in biodiesel factories and biomass wastes using integrated reactor design for hydrogen rich syngas. This new process consists of three process steps: (a) pyrolysis of organic waste material to produce biooil, char and pyrogas; (b) steam assisted hydrogasification of the crude glycerol wastes, biooil mixed with pyrogas for hydrogen rich gas; and (c) a low temperature methanol synthesis process. The H₂‐rich gas remaining after methanol synthesis is recycled back to the pyrolysis reactor, the catalytic hydro‐gasification process and the heat recovery steam generator (HRSG). RESULTS: The breakeven price of the Hbiomethanol process yields positive net financial NPV and IRR above 600 USD per tonne. The total capital cost for a small‐scale methanol plant of capacity 2 tonne h^?1 combined with a cogeneration plant of capacity 2 MWe power is estimated to be 170.5 million USD. CONCLUSION: Recycling gas allows the methanol synthesis reactor to perform at a relatively lower pressure than conventionally while the plant still maintains a high methanol yield. The integrated hydrogasification reactor and energy recovery design process minimizes heat loss and increases the process thermal efficiency. The Hbiomethanol process can convert any condensed carbonaceous material and liquid wastes, to produce methanol and CHP. Copyright © 2012 Society of Chemical Industry     

The effect of steam on pyrolysis and char reactions behavior during rice straw gasification

Steam gasification of biomass can generate hydrogen-rich, medium heating value gas. We investigated pyrolysis and char reaction behavior during biomass gasification in detail to clarify the effect of steam presence. Rice straw was gasified in a laboratory scale, batch-type gasification reactor. Time-series data for the yields and compositions of gas, tar and char were examined under inert and steam atmosphere at the temperature range of 873-1173 K. Obtained experimental results were categorized into those of pyrolysis stage and char reaction stage. At the pyrolysis stage, low H₂, CO and aromatic tar yields were observed under steam atmosphere while total tar yield increased by steam. This result can be interpreted as the dominant, but incomplete steam reforming reactions of primary tar under steam atmosphere. During the char reaction stage, only H₂ and CO₂ were detected, which were originated from carbonization of char and char gasification with steam (C + H₂O→CO + H₂). It implies the catalytic effect of char on the water-gas shift reaction. Acceleration of char carbonization by steam was implied by faster hydrogen loss from solid residue.     

Potassium‐catalyzed steam gasification of ash‐free lignite coal with CO2 capture

The purpose of this research was to study steam gasification of ash‐free coal integrated with CO₂ capture in the presence of a K₂O catalyst for enhancement of the key water‐gas shift reaction and promotion of hydrogen production. To achieve this goal, gasification experiments on ash‐free coal (AFC) were carried out at varying temperatures (600, 650, 675, 700, and 750 °C) with a sorbent‐to‐carbon (CaO/C) ratio of 2 and a catalyst (K₂O) loading of 0.2 g/g (20 weight percent (wt%)) in a fixed‐bed reactor equipped with a gas chromatography analyzer. The sorbent‐to‐carbon (CaO/C) ratio of 2 is based on dry and ash‐free basis. The CaO/C ratio and K₂O wt% were chosen to maximize hydrogen production based on our previously determined optimal values. The AFC was originally extracted from raw lignite coal using organic solvents, which allowed the sorption‐enhanced gasification to be conducted with minimal ash‐catalyst interactions. The effect of temperature on the yield and the initial reaction rate were investigated. The optimal reaction temperature of 675 °C was determined. Carbon balance and final carbon conversions were calculated based on the residue analysis. Activation energy was also calculated using intrinsic kinetics of the reaction. In this study, using AFC offered the potential advantage of operating the gasification process with catalyst recycle.     

Analysis of Methanol Production from Biomass Gasification

A biomass‐based methanol production process was investigated. The process consists of a biomass gasifier, steam reformer, and methanol synthesis reactor as the main units. Reactors were simulated by applying the kinetic models previously developed and the process was analyzed based on the simulation results. The key parameters, the equivalence ratio in biomass gasification, the temperature in steam reforming, and the recycle of hydrogen in methanol synthesis were identified. These parameters affect the methanol production. The process analysis indicates that the optimal combinations of the parameters can greatly enhance the methanol production and the thermodynamic efficiency. Finally, the elemental analysis for carbon and hydrogen along the process was carried out.     

A study on the direct catalytic steam gasification of coal for the bench-scale system

Various techniques have been developed to increase the efficiency of coal gasification. The use of a catalyst in the catalytic-steam gasification process lowers the activation energy required for the coal gasification reaction. Catalytic-steam gasification uses steam rather than oxygen as the oxidant and can lead to an increased H₂/CO ratio. The purpose of this study was to evaluate the composition of syngas produced under various reaction conditions and the effects of these conditions on the catalyst performance in the gasification reaction. Simultaneous evaluation of the kinetic parameters was undertaken through a lab-scale experiment using Indonesian low rank coals and a bench-scale catalytic-steam gasifier design. The composition of the syngas and the reaction characteristics obtained in the lab- and bench-scale experiments employing the catalytic gasification reactor were compared. The optimal conditions for syngas production were empirically derived using lab-scale catalytic-steam gasification. Scale-up of a bench-scale catalytic-steam gasifier was based on the lab-scale results based on the similarities between the two systems. The results indicated that when the catalytic-steam gasification reaction was optimized by applying the K₂CO₃ catalyst to low rank coal, a higher hydrogen yield could be produced compared to the conventional gasification process, even at low temperature.     

Investigation on the reactions influencing biomass air and air/steam gasification for hydrogen production

Hydrogen could be the energy carrier of the next world scene provided that its production, transportation and storage are solved. In this work the production of an hydrogen-rich gas by air/steam and air gasification of olive oil waste was investigated. The study was carried out in a laboratory reactor at atmospheric pressure over a temperature range of 700 ­ 900 °C using a steam/biomass ratio of 1.2 w/w. The influence of the catalysts ZnCl₂ and dolomite was also studied at 800 and 900 °C. The solid, energy and carbon yield (%), gas molar composition and high heating value of the gas (kJ NL^− 1), were determined for all cases and the differences between the gasification process with and without steam were established. Also, this work studies the different equilibria taking place, their predominance in each process and how the variables considered affect the final gas hydrogen concentration. The results obtained suggest that the operating conditions were optimized at 900 °C in steam gasification (a hydrogen molar fraction of 0.70 was obtained at a residence time of 7 min). The use of both catalysts resulted positive at 800 °C, especially in the case of ZnCl₂ (attaining a H₂ molar fraction of 0.69 at a residence time of 5 min).     

Biomass gasification using capacitively coupled RF plasma technology

A laboratory-scale capacitively coupled radio frequency (RF) plasma pyrolysis reactor working in reduced pressure has been developed. Experiments have been performed to examine the characteristics of this RF plasma reactor and the products of biomass gasification. It was found that the electrode geometry, input power and reactor pressure were the key parameters affecting the plasma characteristics such as plasma length, temperature, and energy transfer efficiency. Biomass gasification using input power 1600-2000 W and reactor pressure 3000-8000 Pa produced a combustible gas consisted of H₂, CO, CH₄, CO₂ and light hydrocarbons as well as a pyrolytic char. On average, the gas yield can reach 66 wt% of the biomass feed. An energy balance analysis on the RF plasma pyrolysis system was also given.     

Financial and Ecological Evaluation of Hydrogen Production Processes on Large Scale

Hydrogen is widely seen as energy carrier of the future. Different technologies are under development to produce hydrogen at competitive cost but with significantly reduced carbon footprint. Two conventional technologies, namely, methane steam reforming and coal gasification, are compared based on product cost and carbon footprint with four new technologies, i.e., metal‐oxide cycle, water electrolysis, biomass gasification, and methane pyrolysis. To evaluate the carbon footprint for methane pyrolysis, system extension and differential methods are applied. For the boundary conditions selected here, methane pyrolysis yields very good values for product cost and carbon footprint. Therefore, a cross industry technology development of methane pyrolysis was initiated.     

Flax straw char‐CO2 gasification kinetics and its inhibition studies with CO

Char gasification has been studied in different ways with different feedstock; however, the fundamental studies about the variation of char reactivity with different combination of parameters are still required in order to design the biomass char gasification process in large scale unit. In this work, char from flax straw pyrolysis was used for gasification with different partial pressure of CO₂, different temperature and particle size. Results showed that 375‐µm particle sizes of char has higher reactivity compared to other particle sizes and the inhibition effect was also less at 375‐µm particle size. Kinetic parameters varied for gasification reaction with different particle sizes and the average activation energy was 196 kJ/mol and the order of the reaction was approximately 1. Inhibition studies with the addition of CO in the gasifying agent proved that CO molecules interfere significantly and reduced the reactivity. ANOVA test showed that the temperature plays a vital role in char reactivity. The particle sizes of 375 and 800 µm along with the CO₂ partial pressure of 0.35 bars are the best combination for achieving the maximum reactivity. © 2012 Canadian Society for Chemical Engineering     

Hydrogen Production by Sorption‐Enhanced Steam Glycerol Reforming: Sorption Kinetics and Reactor Simulation

Sorption‐enhanced glycerol reforming, an integrated process involving glycerol catalytic steam reforming and in situ CO₂ removal, offers a promising alternative for single‐stage hydrogen production with high purity, reducing the abundant glycerol by‐product streams. This work investigates this process in a fixed‐bed reactor, via a two‐scale, nonisothermal, unsteady‐state model, highlighting the effect of key operating parameters on the process performance. CO₂ adsorption kinetics was investigated experimentally and described by a mathematical reaction‐rate model. The integrated process presents an opportunity to improve the economics of green hydrogen production via an enhanced thermal efficiency process, the exothermic CO₂ adsorption providing the heat to endothermic steam glycerol reforming, while reducing the capital cost by removing the processing steps required for subsequently CO₂ separation. The operational time of producing high‐purity hydrogen can be enhanced by increasing the adsorbent/catalyst volume ratio, by adding steam to the reaction system and by increasing the inlet reactor temperature. © 2012 American Institute of Chemical Engineers AIChE J, 59: 2105–2118, 2013     

生物质下吸式气化炉气化制备富氢燃气实验研究

以制取富氢燃气为目标,在自热式下吸式气化炉反应器内,进行了生物质下吸式气化炉富氧/水蒸气及空气气化的制氢特性研究。实验结果表明,与空气气化相比,富氧/水蒸气气化可显著提高氢产率和产气热值。在实验条件范围内,最大氢产率达到45.16 g/kg;最大低位热值达到11.11 MJ/m3。在富氧/水蒸气气化条件下,燃气中H2+CO体积分数达到63.27%—72.56%,高于空气气化条件下的52.19%—63.31%。富氧/水蒸气气化条件下的H2/CO体积比比值为0.70—0.90,低于空气气化条件下的1.06—1.27。实验结果证实:生物质下吸式气化炉富氧/水蒸气气化是一种有效的制取可再生氢源的工艺路线。     

生物质气化模型的流程模拟

生物质能是一种重要的可再生能源。通过Aspen Plus软件平台,建立生物质气化反应器模型,对生物质气化过程进行模拟计算,探讨了不同反应条件,包括气化温度、压力以及水蒸气与生物质质量配比（S/B）对气化产物成分的影响。计算结果表明,采用生物质蒸汽气化技术可获得体积分数为60%以上的富氢燃料气,且增大水蒸气与生物质质量配比有利于氢气产率的提高。     

H2 rich product gas by steam gasification of biomass with in situ CO2 absorption in a dual fluidized bed system of 8 MW fuel input

The steam gasification of solid biomass by means of the absorption enhanced reforming process (AER process) yields a high quality product gas with increased hydrogen content. The product gas can be used for a wide range of applications which covers the conventional combined heat and power production as well as the operation of fuel cells, the conversion into liquid fuels or the generation of synthetic natural gas and hydrogen. On the basis of a dual fluidized bed system, steam gasification of biomass is coupled with in situ CO₂ absorption to enhance the formation of hydrogen. The reactive bed material (limestone) used in the dual fluidized bed system realizes the continuous CO₂ removal by cyclic carbonation of CaO and calcination of CaCO₃. Biomass gasification with in situ CO₂ absorption has been substantially proven in pilot plant scale of 100 kW fuel input. The present paper outlines the basic principles of steam gasification combined with the AER process the investigations in reactive bed materials, and concentrates further on the first time application of the AER process on industrial scale. The first time application has been carried out within an experimental campaign at a combined heat and power plant of 8 MW fuel input. The results are outlined with regard to the process conditions and achieved product gas composition. Furthermore, the results are compared with standard steam gasification of biomass as well as with application of absorption enhanced reforming process at pilot plant scale.     

Process modeling for parametric study on oil palm empty fruit bunch steam gasification for hydrogen production

Biomass steam gasification with in-situ carbon dioxide capture using CaO exhibits good prospects for the production of hydrogen rich gas. The present work focuses on the process modeling for hydrogen production from oil palm empty fruit bunch (EFB) using MATLAB for parametric study. The model incorporates the reaction kinetics calculations of the steam gasification of EFB (C_3.4H_4.1O_3.3) with in-situ CO₂ capture, as well as mass and energy balances calculations. The developed model is used to investigate the effect of temperature and steam/biomass ratio on the hydrogen purity, yield and efficiency. Based on the results, hydrogen purity of more than 76.1 vol.% can be achieved. The maximum hydrogen yield predicted at the outlet of the gasifier is 102.6 g/kg of EFB. It is found that increment in temperature and steam/biomass ratio promotes hydrogen production. However, it is also predicted that the efficiency decreases when using more steam. Due to the still on-going empirical work, the results are compared with published literatures on different systems. The comparison shows that the results are in agreement to some extent due to the different basis.     

Three‐stage well‐mixed reactor model for a pressurized coal gasifier

Three Canadian coals of different rank were gasified with air‐steam mixtures in a 0.1 m diameter spouted bed reactor at pressures to 292 kPa, average bed temperatures varying between 840 and 960°C, and steam‐to‐coal feed ratios between 0.0 and 2.88. In order to analyze gasifier performance and correlate data, a three‐stage model has been developed incorporating instantaneous devolatilization of coal, instantaneous combustion of carbon at the bottom of the bed, and steam/carbon gasification and water gas shift reaction in a single well mixed isothermal stage. The capture of H₂S by limestone sorbent injection is also treated. The effects of various assumptions and model parameters on the predictions were investigated. The present model indicates that gasifier performance is mainly controlled by the fast coal devolatilization and char combustion reactions, and the contribution to carbon conversion of the slow char gasification reactions is comparatively small. The incorporation of tar decomposition into the model provides significantly closer predictions of experimental gas composition than is obtained otherwise.     

Experimental Study on Catalytic Biomass Gasification in a Bubbling Fluidized Bed

A bubbling fluidized‐bed gasification system was selected for catalytic steam gasification of rice straw with four Ni‐based catalysts, i.e., Ni/Al₂O₃, Ni/CeO₂, Ni/MnO₂, and Ni/MgO. The effect of temperature, steam/biomass ratio (S/B), and catalyst/biomass ratio (C/B) on the gas composition, char conversion, and hydrogen yield was evaluated. It was found that higher temperature and S/B promote hydrogen production and char conversion. The results also demonstrated that the catalytic activity of Ni/Al₂O₃ under different S/B values is better than those of the other catalysts. Regarding the catalyst activity, all four catalysts exhibited good performance in terms of tar removal and carbon conversion. However, the performance of Ni/Al₂O₃ was superior to that of the other three catalysts.     

Steam Reforming of Bio‐Oil for Hydrogen Production: Effect of Ni‐Co Bimetallic Catalysts

Various Ni‐Co bimetallic catalysts were prepared by incorporating sol‐gel and wet impregnation methods. A laboratory‐scale fixed‐bed reactor was employed to investigate their effects on hydrogen production from steam reforming of bio‐oil. The catalyst causes the condensation reaction of bio‐oil, which generates coke and inhibits the formation of gas at temperatures of 250 °C and 350 °C. At 450 °C and above the transformation of bio‐oil is initiated and gaseous products are generated. The catalyst also can promote the generation of H₂ as well as the transformation of CO and CH₄ and plays an active role in steam reforming of bio‐oil or gaseous products from bio‐oil pyrolysis. The developed 3Ni9Co/Ce‐Zr‐O catalyst achieved maximum hydrogen yield and lowest coke formation rate and provided a better stability than a commercial Ni‐based catalyst.