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.     

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.     

Gasification of biomass to hydrogen-rich gas in fluidized beds using porous medium as bed material

Experiments were carried out to study the characteristics of biomass gasification in a fluidized bed using industrial sand and porous medium as bed materials. Analysis was conducted to investigate the effects of different operation parameters, including bed material, gasification temperature (600 °C–900 °C), oxygen enrichment in the gasifying agent (21 vol.% to 50 vol.%), and steam flow rate (1.08 kg/h to 2.10 kg/h), on product yields and gas composition. The results of gas chromatography show that the main generated gas species were H₂, CO, CO₂, CH₄, and C₂H₄. Compared with industrial sand as bed material, porous medium as bed material was more suitable for gasifying biomass to hydrogen-rich gas. The physical characteristics of porous structure are more favorable to heat transfer, producing the secondary crack of heavy hydrocarbons and generating more hydrogen and other permanent gases. The product yields of hydrogen-rich gas increased with increasing gasification temperature. The hydrogen concentration improved from 22.52 vol.% to 36.06 vol.%, but the CO concentration decreased from 37.53 vol.% to 28.37 vol.% with increasing temperature from 600 °C to 900 °C under the operation parameters of porous bed material at a steam flow rate of 1.56 kg/h. With increasing oxygen concentration, H₂ concentration increased from 12.36% to 20.21%. Over the ranges of the examined experimental conditions, the actual steam flux value (e.g., 1.56 kg/h) was found to be the optimum value for gasification.     

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.     

Research on the characteristics of biomass gasification in a fluidized bed

The depletion of fossil fuels and the increasing environmental problems, make biomass energy a serious alternative resource of energy. Biomass gasification is one of the major biomass utilization technologies to produce high quality gas. In this paper, biomass gasification was performed in a self-designed fluidized bed. The main factors (equivalence ratio, bed temperature, added catalyst, steam) influenced the gasification process were studied in detail. The results showed that the combustible gas content and the heating value increased with the increase of the temperature, while the CO₂ content decreased. The combustible gas content decreased with the increase of the equivalence ratio (ER), but CO₂ content increased. At the same temperature and at different ratios of CaO (from 0 to 20%), H₂ content was increased significantly, CO content was also increased, CH₄ content increased slightly, but CO₂ content was decreased. With the addition of steam at different temperature, the gas in combustible components increased, the content of H₂ increased obviously. The growth rate was 50% increased. As the bed temperature increased, gas reforming reaction increased, the CO and CH₄ content decreased, but CO₂ and H₂ content increased.     

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.     

Artificial neural network models for biomass gasification in fluidized bed gasifiers

Artificial neural networks (ANNs) have been applied for modeling biomass gasification process in fluidized bed reactors. Two architectures of ANNs models are presented; one for circulating fluidized bed gasifiers (CFB) and the other for bubbling fluidized bed gasifiers (BFB). Both models determine the producer gas composition (CO, CO₂, H₂, CH₄) and gas yield. Published experimental data from other authors has been used to train the ANNs. The obtained results show that the percentage composition of the main four gas species in producer gas (CO, CO₂, H₂, CH₄) and producer gas yield for a biomass fluidized bed gasifier can be successfully predicted by applying neural networks. ANNs models use in the input layer the biomass composition and few operating parameters, two neurons in the hidden layer and the backpropagation algorithm. The results obtained by these ANNs show high agreement with published experimental data used R² > 0.98. Furthermore a sensitivity analysis has been applied in each ANN model showing that all studied input variables are important.     

Investigation of a novel & integrated simulation model for hydrogen production from lignocellulosic biomass

Process simulation and modeling works are very important to determine novel design and operation conditions. In this study; hydrogen production from synthesis gas obtained by gasification of lignocellulosic biomass is investigated. The main motivation of this work is to understand how biomass is converted to hydrogen rich synthesis gas and its environmentally friendly impact. Hydrogen market development in several energy production units such as fuel cells is another motivation to realize these kinds of activities. The initial results can help to contribute to the literature and widen our experience on utilization of the CO₂ neutral biomass sources and gasification technology which can develop the design of hydrogen production processes. The raw syngas is obtained via staged gasification of biomass, using bubbling fluidized bed technology with secondary agents; then it is cleaned, its hydrocarbon content is reformed, CO content is shifted (WGS) and finally H₂ content is separated by the PSA (Pressure Swing Adsorption) unit. According to the preliminary results of the ASPEN HYSYS conceptual process simulation model; the composition of hydrogen rich gas (0.62% H₂O, 38.83% H₂, 1.65% CO, 26.13% CO₂, 0.08% CH₄, and 32.69% N₂) has been determined. The first simulation results show that the hydrogen purity of the product gas after PSA unit is 99.999% approximately. The mass lower heating value (LHV_mass) of the product gas before PSA unit is expected to be about 4500 kJ/kg and the overall fuel processor efficiency has been calculated as ～93%.     

Novel hydrogen‐rich gas production by steam gasification of biomass in a research‐scale rotary tubular helical coil gasifier

The concept of biomass steam gasification offers platform for production (i) of hydrogen, (ii) hydrocarbons and (iii) value added chemicals. Majority of these developments are either in nascent or in pilot/demonstration stage. In this context, there exists potential for hydrogen production via biomass steam gasification. Gaseous products of biomass steam gasification consist of large percentage of CO, CH₄ and other hydrocarbons, which can be converted to hydrogen through water‐gas‐shift reaction, steam reforming and cracking respectively. Although there are many previous research works showing the potential of production of hydrogen from biomass in a two stage process, challenges remain in extended biomass and char gasification so as to reduce the amount of carbon in the residual char as well as improve conversion of heavy hydrocarbon condensates to hydrogen rich gas. In the current work, the characteristics of biomass steam gasification in an in‐house designed rotary tubular helical coil reactor at temperatures less than 850 °C, in the presence of superheated steam, were presented. The objectives were to obtain high carbon conversion in the primary biomass steam gasification step (upstream) and high product gas yield and hydrogen yield in the secondary fixed bed catalytic step (downstream). The influence of temperature, steam‐to‐biomass ratio and residence time on product gas yield in the rotary tubular helical coil gasifier was studied in detail using one of the abundantly available biomass sources in India‐rice husk. Further, enhancement of product gas yield and hydrogen yield in a fixed bed catalytic converter was studied and optimized. In the integrated pathway, a maximum gas yield of 1.92 Nm³/kg moisture‐free biomass was obtained at a carbon conversion efficiency of 92%. The maximum hydrogen purity achieved under steady state conditions was 53% by volume with a hydrogen yield of 91.5 g/kg of moisture‐free biomass. This study substantiates overall feasibility of production of high value hydrogen from locally available biomass by superheated steam gasification followed by catalytic conversion. Copyright © 2016 John Wiley & Sons, Ltd.     

Numerical simulation of hydrogen production by gasification of large biomass particles in high temperature fluidized bed reactor

Biomass as a renewable fuel compared to fossil fuels usually contains high moisture content and volatile release. Hydrogen production by large particle biomass gasification is a promising technology for utilizing high moisture content biomass particle in the high temperature fluidized bed reactor. In the present work, simulation of large particles biomass gasification investigated at high temperature by using the discrete phase model (DPM). Combustible gases with homogeneous gas phase reactions, drying process with a heterogeneous reaction, primary and secondary pyrolysis with independent parallel-reaction by using two-competing-rate model to control a high and low temperature were used. During the thermochemical process of biomass, gaseous products containing of H₂, H₂O, CH₄, CO and CO₂ was obtained. The effects of concentration, mole and mass fraction and hydrodynamics effects on gaseous production during gasification were studied. The results showed that hydrodynamic effect of hot bed is different from cold bed. Concentration and molar fraction of CO and H₂ production by continually and stably state and small amount of CO₂, H₂O, and CH₄ was obtained. The hydrodynamic of bed plays the significant role on the rate of gaseous products.     

生物质与煤流化床催化气化制备燃气

基于单一流化床两步气化法,以煤作为热载体和发热体,水蒸气为气化剂,CaO为催化剂,在自行研制的流化床热态装置上对生物质（锯木）气化制备燃气进行了研究。探讨了温度和水蒸气与锯木比对燃气组分和低位热值的影响。在所研究的操作参数范围内,（H2 + CO）含量为67.58% ~ 74.9%,燃气低位热值为10719.09 kJ/Nm3 ~ 12002.44 kJ/Nm3。实验结果表明,含少量N2的中热值燃气可以被获得,H2和CO是燃气中最主要的两种气体。随着温度的升高,燃气中H2和CO含量增加,而CH4和CO2含量及燃气低位热值则呈现下降趋势。随着水蒸气与锯木比的增加,燃气中H2和CO2含量增加,而CH4和CO含量则相应的减小。     

Simulation of sorption enhanced staged gasification of biomass for hydrogen production in the presence of calcium oxide

A novel two-step sorption enhanced staged gasification of biomass for H₂ production was proposed and studied using Aspen Plus software. An equilibrium model based on Gibbs free energy minimization was developed and validated. The results showed that the two-step process was more advantageous for H₂ production compared with the conventional steam gasification and the one-step process. The independent control of each stage could realize a high temperature steam gasification in the first stage and a subsequent lower temperature steam reforming in the second stage, which thus promoted the gasification of biomass and benefited the water gas shift (WGS) reaction to produce more H₂. Meanwhile, the in situ CO₂ absorption of CaO in the second stage could enrich the H₂ concentration in the product gas, and also further shifted the WGS reaction equilibrium to convert more CO to H₂. With further introduction of catalyst for steam methane reforming (SMR), high-purity H₂ with the concentration of 99.7 vol% and yield of 142.8 g/kg daf biomass could be achieved.     

Evaluation of different biomass gasification modeling approaches for fluidized bed gasifiers

To develop a model for biomass gasification in fluidized bed gasifiers with high accuracy and generality that could be used under various operating conditions, the equilibrium model (EM) is chosen as a general and case-independent modeling method. However, EM lacks sufficient accuracy in predicting the content (volume fraction) of four major components (H₂, CO, CO₂ and CH₄) in product gas. In this paper, three approaches—MODEL I, which restricts equilibrium to a specific temperature (QET method); MODEL II, which uses empirical correlations for carbon, CH₄, C₂H₂, C₂H₄, C₂H₆ and NH₃ conversion; and MODEL III, which includes kinetic and hydrodynamic equations—have been studied and compared to map the barriers and complexities involved in developing an accurate and generic model for the gasification of biomass.This study indicates that existing empirical correlations can be further improved by considering more experimental data. The updated model features better accuracy in the prediction of product gas composition in a larger range of operating conditions. Additionally, combining the QET method with a kinetic and hydrodynamic approach results in a model that features less overall error than the original model based on a kinetic and hydrodynamic approach.     

Hydrogen and syngas production from catalytic steam gasification of char derived from ion-exchangeable Na- and Ca-loaded coal

Catalytic steam gasification of char derived from low-rank coal possesses substantial potential as a source of hydrogen energy and syngas feedstocks, and its performances are largely associated with the employed catalysts. Therein, ion-exchangeable Na or Ca species are always regarded as excellent in-situ catalysts in low-rank coal. In this paper, gasification of Na-Char, Ca-Char and a Na/Ca-Char mixture with different partial pressures of steam was performed within a temperature range of 700–900 °C using a micro fluidized bed reaction analyzer. The results indicate that Na and Ca species could accelerate the gas release rate during gasification and even significantly increase H₂ production, in sharp contrast to non-catalytic gasification. Variations in the product gases during Na-Char and Ca-Char gasification were completely different, which associated with the different deactivation pathways and catalytic reaction mechanisms of Na and Ca catalysts. With an increasing gasification temperature, the decreasing trend of H₂ production for Na-Char gasification was mainly due to the loss of Na during gasification. Conversely, the enhancement of Ca activity promoted the H₂ production. The H₂/CO ratio of Ca-Char gasification at 700 °C approximately ranged from 1.0 to 2.0 as a function of the partial pressure of steam, which suggested catalytic gasification can be suitable for hydrogen-rich production and subsequent synthesis reactions. In addition, gasification of Na/Ca-Char mixture produced a higher hydrogen content in the product gases than that of Na-Char or Ca-Char gasification alone, particularly for the 30%Na/70%Ca-Char mixture. It implies that the high H₂ production of 70%Ca30%Na-Char mixture was attributed to the cooperative effects of the Na and Ca species on the catalytic activity. This study provides comprehensive information regarding the effects of ion-exchangeable Na, Ca and a Na/Ca mixture on the hydrogen production and syngas composition during steam gasification, which provides new insight into the utilization of low-rank coal.     

Hydrogen production from steam gasification of tableted biomass in molten eutectic carbonates

The steam gasification of tableted biomass for H₂ production in molten salts was investigated under different conditions. The results showed that the ternary molten carbonates (32 wt% Li₂CO₃, 33 wt% Na₂CO₃ and 35 wt% K₂CO₃) acted as heat medium and catalyst in the gasification process. The use of molten salts could significantly increase total gas and H₂ production and simultaneously decrease the concentrations of CO and CH₄ in the product gas, and also decrease the yield of condensable tar. The increase in gasification temperature and mass ratio of steam to biomass (S/B) was beneficial for H₂ production process. However, excessive steam contributed slightly to the increase in H₂ production and largely increased the energy consumption. The optimal S/B ratio was found to be 1.0. The feedstock after tabletting could completely immersed in molten salts, which improved the contact between biomass and molten salts and thus favored the biomass gasification for H₂ production. When biomass particle size was 0.25 g/piece, the yield of H₂ reached 807.53 mL/g biomass.     

Air gasification of high-ash sewage sludge for hydrogen production: Experimental,sensitivity and predictive analysis

In this work, air gasification of sewage sludge was conducted in a lab-scale bubbling fluidized bed gasifier. Further, the gasification process was modeled using artificial neural networks for the product gas composition with varying temperatures and equivalence ratios. Neural network-based prediction will help to predict the hydrogen production from product gas composition at various temperatures and equivalence ratios. The gasification efficiency and lower heating values were also established as a function of temperatures and equivalence ratios. The maximum H₂ and CO was recorded as 16.26 vol% and 33.55 vol%. Intraileally at ER 0.2 gas composition H₂, CO, and CH₄ show high concentrations of 20.56 vol%, 45.91 vol%, and 13.32 vol%, respectively. At the same time, CO₂ was lower as 20.20 vol% at ER 0.2. Therefore, optimum values are suggested for maximum H₂ and CO yield and lower concentration of CO₂ at ER 0.25 and temperature of 850 °C. A predictive model based on an Artificial Neural network is also developed to predict the hydrogen production from product gas composition at various temperatures and equivalence ratios. The network has been trained with different topologies to find the optimal structure for temperature and equivalence ratio. The obtained results showed that the regression coefficients for training, validation, and testing are 0.99999, 0.99998, and 0.99992, respectively, which clearly identifies the training efficiency of the trained model.     

Adiabatic fixed-bed gasification of coal, dairy biomass, and feedlot biomass using an air–steam mixture as an oxidizing agent

Concentrated animal feeding operations, such as cattle feedlots and dairies, produce a large amount of manure, cattle biomass (CB), which can be included as renewable feedstock for locally based gasification for syngas (CO and H₂) production and subsequent use in power generation. Experimental results on effects of bed temperature and gas composition on the higher heating value (HHV) and energy recovery are presented for dairy biomass (DB) gasification using air and air–steam as oxidizers. Some experimental data are compared with adiabatic gasification modeling which includes atom balance conservation for assumed product species and chemical equilibrium analysis. Wyoming sub-bituminous coal (WYC) and Texas Lignite coal (TXL) are used as standard fuels for comparison purposes in modeling studies. Two main parameters are investigated in this study. One is the modified equivalence ratio (ER_M) defined as the ratio of stochiometric oxygen to total oxygen supplied in the oxidizing mixture of air and steam. The second is a measure of how much steam is in the oxidizer and is called the air steam ratio (ASTR), which is defined as the ratio of oxygen supplied in the air to the total oxygen supplied in the oxidizer. The results suggested that gasification of CB and coals under higher ER_M yield elevated concentrations of CO and CH₄, and low percentages of H₂ and CO₂, while higher ASTRs (less steam) produced mixtures poor in H₂, CO₂, and CH₄ and rich in CO with lower HHV. It was also found that FB and DB produced higher amounts of H₂ than WYC and TXL under the same ER_M and ASTR.     

The effect of biomass feeding location on rice husk gasification for hydrogen production

The objective of this study is to investigate the impact of biomass feeding location on rice husk gasification for hydrogen production. By comparing the results between top-feed and bottom-feed of the feedstock of the fluidized bed biomass gasification at the reaction temperature between 600～1000 °C and ER = 0.2, 0.27, and 0.33 without steam, the optimum low heating value was increase by 2.35 kJ/g-rice husk by the top-feed to gasifier. Although the yield of hydrogen was decreased by 42% for the rice husk gasification by the top-feed operation, the yield of CO, CO2, and CH4 were highly increased, which enhancing the heating value of the effluent gas. The study results suggested the potential route of the biomass gasification at the different feeding location.     

生物质流化床气化技术应用研究现状

按所得产品不同,可将生物质气化技术分为制氢、发电和合成液体燃料3大类。文章介绍了生物质流化床水蒸气气化制氢、催化气化制氢和超临界水气化制氢的工艺特点;分析了生物质流化床气化发电的技术、经济可行性;简述了生物质流化床气化合成液体燃料的研究现状;指出气化产出气化学当量比调变、焦油去除问题和合成气净化是生物质流化床气化技术应用的主要瓶颈,认为定向气化是今后研究的主要方向。     

Biomass gasification in a 100 kWth steam-oxygen blown circulating fluidized bed gasifier: Effects of operational conditions on product gas distribution and tar formation

Biomass gasification is one of the most promising technologies for converting biomass, a renewable source, into an easily transportable and usable fuel. Two woody biomass fuels Agrol and willow, and one agriculture residue Dry Distiller’s Grains with Solubles (DDGS), have been tested using an atmospheric pressure 100 kWth steam-oxygen blown circulating fluidized bed gasifier (CFB). The effects of operational conditions (e.g. steam to biomass ratio (SBR), oxygen to biomass stoichiometric ratio (ER) and gasification temperature) and bed materials on the composition distribution of the product gas and tar formation from these fuels were investigated. Experimental results show that there is a significant variation in the composition of the product gas produced. Among all the experiments, the averaged concentration of H₂ obtained from Agrol, willow and DDGS over the temperature range from 800 to 820 °C was around 24 vol.%, 28 vol.% and 20 vol.% on a N₂ free basis, respectively. A fairly high amount of H₂S (∼2300 ppmv), COS (∼200 ppmv) and trace amounts of methyl mercaptan (<3 ppmv) on a N₂ free basis were obtained from DDGS. Due to a relatively high content of K and Cl in DDGS fuel, an alkali-getter (e.g. kaolin) was added to avoid agglomeration during gasification. Higher temperatures and SBR values were favorable for increasing the mole ratio of H₂ to CO and the tar decomposition but less advantageous for the formation of CH₄. Meanwhile, higher temperatures and SBR values also led to higher gas yields, whereas a higher SBR caused a lower carbon conversion efficiency (CCE%), cold gas efficiency (CGE%) and heating values of the product gas due to a high steam content in the product gas. From solid phase adsorption (SPA) results, the total tar content obtained from Agrol was the highest at around 12.4 g/Nm³, followed by that from DDGS and willow gasification. The lowest tar content produced from Agrol, willow and DDGS using Austrian olivine (Bed 1) as bed materials was 5.7, 4.4 and 7.3 g/Nm³, values which were obtained at a temperature of 730, 820 and 730 °C, SBR of 1.52, 1.14 and 1.10, and ER of 0.36, 0.39 and 0.37, respectively.