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%.     

Inhibition of steam gasification of biomass char by hydrogen and tar

The influence of hydrogen and tar on the reaction rate of woody biomass char in steam gasification was investigated by varying the concentrations in a rapid-heating thermobalance reactor. It was observed that the steam gasification of biomass char can be separated into two periods. Compared with the first period, in the second period (in which the relative mass of remaining char is smaller than 0.4) the gasification rate is increased. These effects are probably due to inherent potassium catalyst. Higher hydrogen partial pressure greatly inhibits the gasification of biomass char in the first and second periods. By calculating the first-order rate constants of char gasification in the first and second periods, we found that the hydrogen inhibition on biomass char gasification is caused by the reverse oxygen exchange reaction in the first period. In the second period, dissociative hydrogen adsorption on the char is the major inhibition reaction. The influence of levoglucosan, a major tar component derived from cellulose, was also examined. We found that not only hydrogen but also vapor-phase levoglucosan and its pyrolysates inhibited the steam gasification of woody biomass char. By mixing levoglucosan with woody biomass sample, the pyrolysis of char proceeds slightly more rapidly than with woody biomass alone, and gas evolution rates of H₂ and CO₂ are larger in steam gasification.     

Steam co-gasification of Japanese cedarwood and its commercial biochar for hydrogen-rich gas production

In this study, steam gasification and co-gasification of Japanese cedarwood and its commercial biochar were performed in a lab-scale fixed-bed reactor to investigate the feasibility for producing H₂-rich syngas. Ultimate analysis, proximate analysis, Brunauer-Emmett-Teller (BET) surface area analysis, and scanning electron microscopy (SEM) were conducted to understand the changes caused by the carbonization process. The effects of gasification temperature and steam flow rate on gas production yield from the steam gasification of the individual samples were investigated at first, which showed larger gas production yield and less tar yield for the steam gasification of the commercial biochar than that of raw cedarwood, indicating that the commercial biochar obtained from the carbonization process was more beneficial for the gasification. The co-gasification of raw Japanese cedarwood and its commercial biochar with different mixing ratios was conducted at different reaction temperatures. The synergistic effect was obviously observed. Especially, the commercial biochar with the highly porous structure and high content of alkali and alkaline earth metal (AAEM) species might provide the catalytic effect on cracking and reforming of tar derived from the raw cedarwood, resulting in a larger H₂ yield. However, the catalytic effect and gasification reactivity of biochar would decrease by increasing the amount of raw-cedarwood in the blends due to the coke deposition on the surface of biochar.     

Synergistic effects during co-pyrolysis of biomass and plastic: Gas,tar, soot,char products and thermogravimetric study

Synergistic effects of biomass and plastic co-pyrolysis on gas, tar, soot and char production and pyrolysis kinetics were studied using a fixed-bed reactor and a thermogravimetric analyzer, respectively. These pyrolysis products' yields and compositions were measured during the individual pyrolysis of biomass and plastic at 800–1100 °C, and synergistic effects were explored under non-sooty (900 °C) and sooty (1100 °C) conditions. Results shows that the soot starts to form from tar at 900–1000 °C for both biomass and plastic and that the soot from plastic pyrolysis is of greater yield and size than the biomass pyrolysis. Under non-sooty conditions, the synergistic effect of co-pyrolysis results in higher char yields but lower tar yields, while under sooty conditions co-pyrolysis inhibits the gas and soot formation, resulting in higher tar yields and different soot morphologies. The synergistic effect observed by the thermogravimetric analysis agrees with that in a fixed-bed reactor.     

气化参数对高温空气气化的影响

介绍了生物质高温空气气化思想和系统的工作原理及其过程，并就气化参数对生物质高温空气气化的影响进行了深入的分析，结畏发现：随蒸汽消耗率的增加气化温度降低，而气化所得的煤气热值增大；气化温度随氮碳比的增大而升高，而气化所得的煤气热值却随氮碳比的增加而降低；煤气热值随气化温度的增加而增大，但是增加量不大。     

Steam gasification of biochars derived from pruned apple branch with various pyrolysis temperatures

In this study, the gas production behavior from the steam gasification of the biochar derived from the pruned apple brunch was investigated using a fixed-bed reactor. The optimal biochar obtained at the pyrolysis temperature of 550 °C was gasified under different operating conditions for the hydrogen rich gas production. The experimental results indicated that high reaction temperature and high water flow rate were both beneficial to the hydrogen gas yield, but excess steam had a negative impact contrarily. Besides, the small size particles (0.5–1.0 mm) showed better performance in the hydrogen gas production at the low water flow rates (0.05–0.20 g/min); while the large size particles (1.0–2.8 mm) showed better performance at the high water flow rates (0.25–0.30 g/min). The suitable operating conditions for the gasification of the biochar were determined as the reaction temperature of 850 °C, water flow rate of 0.25 g/min, and particle size of 1.0–2.8 mm.     

Combined slow pyrolysis and steam gasification of biomass for hydrogen generation—a review

Hydrogen, the inevitable fuel of the future, can be generated from biomass through promising thermochemical methods. Modern‐day thermochemical methods of hydrogen generation include fast pyrolysis followed by steam reforming of bio‐oil, supercritical water gasification and steam gasification. Apart from the aforementioned methods, a novice technique of employing combined slow pyrolysis and steam gasification can be also engaged to produce hydrogen of improved yield and quality. This review paper discusses in detail about the existing hydrogen generation through thermochemical methods. It elaborates the merits and demerits of each method and gives insight about the combined slow pyrolysis and steam gasification process for hydrogen generation. The paper also elaborates about the various parameters affecting integrated slow pyrolysis and steam gasification process. Copyright © 2014 John Wiley & Sons, Ltd.     

Production of hydrogen-rich syngas from absorption-enhanced steam gasification of biomass with conch shell-based absorbents

In this study, steam gasification of pine sawdust is conducted in a fixed-bed reactor in the temperature range 650–700 °C with calcined conch shell (CS) serving as a starting absorbent. The CS is further subjected to hydration (HCS) and calcination (CHCS) to prepare a modified absorbent. It is found that the hydration-calcination treatment of CS causes smaller CaO crystal grains with a larger BET surface area and more porous surface. As a consequence, CHCS exhibits higher catalytic activity for tar reforming, faster reaction rate for CO₂ absorption and better performance for H₂ selectivity than CS. Elevating the temperature contributes to tar reduction but results in lower H₂ content and higher CO₂ content, while an increase in Ca/C leads to higher H₂ content. And the H₂ content can reach approximately 76% with the use of CHCS when temperature and Ca/C ratio are 650 °C and 2, respectively.     

Hydrogen-rich gas from catalytic steam gasification of biomass in a fixed bed reactor: Influence of temperature and steam on gasification performance

The catalytic steam gasification of biomass was carried out in a lab-scale fixed bed reactor in order to evaluate the effects of temperatures and the ratio of steam to biomass (S/B) on the gasification performance. The bed temperature was varied from 600 to 900 and the S/B from 0 to 2.80. The results show that higher temperature contributes to more hydrogen production.     

Exergy analysis of hydrogen production from steam gasification of biomass: A review

Exergy analysis of hydrogen production from steam gasification of biomass was reviewed in this study. The effects of the main parameters (biomass characteristics, particle size, gasification temperature, steam/biomass ratio, steam flow rate, reaction catalyst, and residence time) on the exergy efficiency were presented and discussed. The results show that the exergy efficiency of hydrogen production from steam gasification of biomass is mainly determined by the H₂ yield and the chemical exergy of biomass. Increases in gasification temperatures improve the exergy efficiency whereas increases in particle sizes generally decrease the exergy efficiency. Generally, both steam/biomass ratio and steam flow rate initially increases and finally decreases the exergy efficiency. A reaction catalyst may have positive, negative or negligible effect on the exergy efficiency, whereas residence time generally has slight effect on the exergy efficiency.     

生物质气化洗焦废水处理技术的研究进展

对国内外生物质气化洗焦废水的主要处理技术进行了综述,阐述了各种方法和工艺的优缺点及其研究现状,并提出生物处理技术以及相关的新工艺将是今后气化洗焦废水处理技术的发展趋势。     

Multifaceted analysis of products from the intermediate co-pyrolysis of biomass with Tetra Pak waste

This study investigates the co-pyrolysis of two types of biomass (pine bark and wheat straw) with Tetra Pak waste (TPW). The experiments were performed using a fixed-bed reactor equipped with an innovative system, where a sample was rapidly heated to 600 °C before being rapidly cooled. The multifaceted analysis included the determination of the i) physical and chemical properties of the feedstocks and chars, ii) aqueous phase, tars, and waxes, iii) char ignition and burnout temperature, iv) chemical composition of gas, and v) distribution of carbon and hydrogen in the obtained products. The results showed that the addition of TPW to the both types of biomass significantly reduced the char mass and aqueous phase, decreased the carbon, hydrogen, and nitrogen contents of the char, and increased the wax and tar yields retained in the water cooler. Different organic compounds such as alkenes, aromatic hydrocarbons, and acids were found in tars and waxes. The chemical composition of the released gases was detected in situ (by a flue-gas analyser) and ex-situ (using gas chromatography). Changes in the concentrations of H₂, CH₄, CO, CO₂, and C2–C4 were observed. The addition of Tetra Pak to the two types of biomass had an evident and positive effect on the hydrogen content of the pyrolysis gas.     

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.     

Hydrogen-rich gas from catalytic steam gasification of biomass in a fixed bed reactor: Influence of particle size on gasification performance

The catalytic steam gasification of biomass was carried out in a lab-scale fixed bed reactor in order to evaluate the effects of particle size at different bed temperatures on the gasification performance. The bed temperature was varied from 600 to 900 °C and the biomass was separated into five different size fractions (below 0.075 mm, 0.075–0.15 mm, 0.15–0.3 mm, 0.3–0.6 mm and 0.6–1.2 mm). The results show that with decreasing particle size, the dry gas yield, carbon conversion efficiency and H₂ yield increased, and the content of char and tar decreased. And the differences due to particle sizes in gasification performance practically disappear as the higher temperature bound is approached. Hydrogen and carbon monoxide contents in the produced gas increase with decreasing particle size at 900 °C, reaching to 51.2% and 22.4%, respectively.     

不同因素对生物质气化产出气特性的影响

将木屑、花生壳和稻草等生物质放在流化床气化反应器内,采用空气作为气化介质,通过添加白云石、菱镁矿和橄榄石3种炉内催化剂,在温度为750,800,850℃,当量比(ER)为0.15,0.25,0.35的条件下进行气化,研究了各种因素的不同水平值对生物质气化气成分和热值的影响规律.     

生物质气化技术应用的问题及对策

阐述了当前生物质气化技术应用中人们普遍关心的气体焦油含量,气化站全年运行,经济效益以及综合利用等问题。提出了该技术在我国应用的发展对策。     

在碱金属催化作用下煤焦与CO2的气化反应

利用固定床实验装置、以CO2作为气化剂，进行煤焦气化反应动力学的研究，分析了碱金属的含量及气化温度对煤焦-CO2气化反应的影响。采用未反应核收缩模型对试验数据进行处理，得到气化反应动力学参数。发现气化温度对煤焦与CO2的气化反应影响显著，碱金属作为煤焦-CO2气化反应的催化剂，能够降低反应过程的活化能，提高反应速率，用未反应核收缩模型能够很好地描述煤焦。CO2的气化反应过程。     

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

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

生物质气化发电的经济效益分析

应用财务评价的方法分析了影响生物质气化发电经济效益的主要因素，从项目规模、出售电价和原料成本三个方面阐述了提高生物质气化发电经济效益的方法，提出了发展生物质气化发电技术的相关建议。