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.     

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。     

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.     

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。     

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。     

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。     

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。     

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.     

家用生物质颗粒燃料炉的研制

为解决农村秸秆焚烧污染问题，研究以生物质颗粒为燃料的家用生物质颗粒燃料炉供农家炊事使用。在充分研究、分析生物质颗粒燃料燃烧动力学特性的基础上，根据生物质颗粒燃料挥发分含量高、燃点低的特点，在生物质颗粒燃料炉的设计中采用了气化、燃烧一体化结构。测试结果表明，生物质颗粒燃料在生物质颗粒燃料炉内能气化燃烧，残碳也能够完全燃尽。该炉的主要技术指标均符合国家标准，燃烧稳定、高效、清洁，提高了秸秆的能源利用率。     

Influence of pyrolysis temperature and residence time on available nutrients for biochars derived from various biomass

To study the effect of pyrolysis temperature and residence time on properties and nutrient values, biochars were produced from corn stalk, rice hull, peanut hull and tobacco stalk at 200°C–700°C for one minute and 60 minutes, respectively. When temperatures and residence times increase, yields of biochars decrease accompany with higher pH values of biochars, changing the acidity of biochars from acidic to alkaline, and increasing total C and parts of the available N and K contents of biochars. These results indicate that feedstock and preparation technology are important factors affecting available nutrients of biochars.     

The impact of steam and current density on carbon formation from biomass gasification tar on Ni/YSZ, and Ni/CGO solid oxide fuel cell anodes

The combination of solid oxide fuel cells (SOFCs) and biomass gasification has the potential to become an attractive technology for the production of clean renewable energy. However the impact of tars, formed during biomass gasification, on the performance and durability of SOFC anodes has not been well established experimentally. This paper reports an experimental study on the mitigation of carbon formation arising from the exposure of the commonly used Ni/YSZ (yttria stabilized zirconia) and Ni/CGO (gadolinium-doped ceria) SOFC anodes to biomass gasification tars. Carbon formation and cell degradation was reduced through means of steam reforming of the tar over the nickel anode, and partial oxidation of benzene model tar via the transport of oxygen ions to the anode while operating the fuel cell under load. Thermodynamic calculations suggest that a threshold current density of 365 mA cm⁻² was required to suppress carbon formation in dry conditions, which was consistent with the results of experiments conducted in this study. The importance of both anode microstructure and composition towards carbon deposition was seen in the comparison of Ni/YSZ and Ni/CGO anodes exposed to the biomass gasification tar. Under steam concentrations greater than the thermodynamic threshold for carbon deposition, Ni/YSZ anodes still exhibited cell degradation, as shown by increased polarization resistances, and carbon formation was seen using SEM imaging. Ni/CGO anodes were found to be more resilient to carbon formation than Ni/YSZ anodes, and displayed increased performance after each subsequent exposure to tar, likely due to continued reforming of condensed tar on the anode.     

Numerical and experimental study on laminar burning velocity of syngas produced from biomass gasification in sub-atmospheric pressures

The laminar burning velocity of syngas mixtures has been studied by various researches. However, most of these studies have been conducted in atmospheric conditions at sea level. In the present study, the effect of sub atmospheric pressure was evaluated on the laminar burning velocity for a mixture of H₂, CO and N₂ (20:20:60 vol%) in real sub atmospheric condition. The measurements was conducted in an altitude of 2130 m.a.s.l (0.766 atm) and 21 m.a.s.l (0.994 atm) to evaluate the effect of pressure, the temperature and relative humidity were controlled using an air conditioning unit and was maintained in 295 ± 1 K and 62.6 ± 2.7% respectively. The Flames were generated using contoured slot-type nozzle burner, and an ICCD camera was used to capture chemiluminescence emitted by OH∗-CH∗ radicals present in the flame and thus obtain the flame front and determinate the laminar burning velocity using the angle method. The experimental results were compared with numerical calculations, conducted using the detailed mechanisms of Li et al. and the GRI-Mech 3.0. It was found that the laminar burning velocity increases at lower pressure, for an equivalence ratio of 1.1, the laminar burning velocity increases by almost 23% respect to the sea level conditions.