生物质半焦气化反应动力学参数研究

为了得到升温速率对生物质半焦气化反应的影响。利用热重分析仪对玉米秸秆半焦和松木半焦在不同的升温速率(10、20、40、50℃/min)条件下的反应进行研究,得到这两种半焦TG曲线和DTG曲线,曲线表明反应速率会随着升温速率增大而加快。采用未反应收缩核模型得到反应机理函数,分析计算动力学参数。分析发现,随着升温速率的增大,生物质焦发生CO2气化反应的活化能也增加,同时指前因子也随之增大。     

不同热解温度下落叶松半焦特性的演变规律

为探究热解温度对生物质半焦特性的影响规律,文章以落叶松为原料,采用管式电阻炉制取200～1 000℃的热解半焦,利用元素分析、XRD、BET、SEM等测试手段,结合碳-氢-氧相图及Scherrer方程,深入分析了热解温度对生物焦元素组成、石墨化程度、孔隙结构及表观形貌的影响。结果表明:热解温度升高,热解半焦的H/C,O/C原子比减小,芳构化程度加深,碳微晶结构更趋于有序化,片层状碳骨架结构逐渐凸显,石墨化程度增加;400℃下的半焦比表面积最高,微孔对比表面积的贡献大;300℃和500℃是热解半焦结构发生明显变化的两个特殊的温度点。     

升温速率和水分含量对木屑热解过程和特性的影响

以木屑为研究对象进行热重分析试验,利用TG/DTG曲线分析了木屑热解的基本特性,包括热解区间、最大热解速率对应的温度、不同加热速率和水分含量对热解过程的影响.试验结果表明:木屑的失重过程主要由干燥、预热、挥发分析出和炭化4个阶段组成;随着升温速率的增大,TG和DTG曲线移向高温区,半焦产率降低;水分含量的增大在一定程度上促进了木屑热解反应的进行,使半焦产率升高.     

非等温热重分析玉米芯半焦CO_2气化特性

采用非等温热重法对玉米芯热解半焦CO2气化行为和动力学特性进行研究。结果表明:升温速率对整个气化过程有重要影响。随着升温速率的增大,完成反应所需的温度提高,反应速率增加,反应时间缩短,而且升温速率越大,反应速率的峰值越高且向高温区偏移。利用Kissinger微分法和Coats-Redferm积分法分别计算动力学参数,所得不同升温速率下的平均活化能为180.77kJ/mol;升温速率越大,活化能越小。研究发现,玉米芯热解半焦CO2非等温气化的活化能E和频率因子A之间存在动力学补偿效应,两者满足lnA=0.09384E+2.604。     

烟煤煤焦的CO2气化反应

采用TG-FTIR方法,在反应温度为950～1300℃时,研究了几种典型煤种及其在高温下慢速和快速热解煤焦的CO2气化反应特性.对4种原煤及其1200℃快、慢速热解条件下煤焦气化产物CH4和CO进行了实时检测和分析.同时对煤焦的孔隙结构和化学组成进行了分析.结果表明,各种热解煤焦的反应速率随气化温度的升高而增大,当达到最大值后随温度的升高而下降;4种煤焦的活化能随热解和气化温度的升高而增大;煤焦气化过程释放CH4和CO的特性与原煤的趋势相似,但原煤热解气化过程中释放CH4的质量浓度比不同热解速率制得煤焦的热解气化释放CH4的质量浓度高出2个数量级,快焦相比慢焦释放出更高质量浓度的CH4;各种煤焦的BET比表面积都较小(除神府慢焦外都小于2 ㎡/g);快焦的气化活性比慢焦的好.     

热解温度对污泥热解半焦产率与特性影响的研究

利用固定床反应器对3种不同来源的污泥进行热解,研究了热解终温对污泥热解半焦产率、热值和比表面积的影响。研究结果表明：随着热解终温的提高,污泥热解半焦的产率逐渐降低;随着半焦中挥发分的减少和灰分含量的增加,半焦的热值降低;半焦的比表面积呈现先增加后降低的趋势,3种污泥在热解终温分别为900,800,700℃时获得的半焦比表面积达到最大值,分别为64．88,44．26,23．75m^2／g。     

制备温度对芒草热解焦CO2气化反应动力学的影响

利用热重分析仪进行了芒草热解焦与CO_2气化反应实验研究,选取均相反应模型、颗粒反应模型和随机孔模型计算了芒草热解焦的CO_2气化反应动力学参数,探讨了3种动力学模型的适用性.为进一步探讨制备温度对热解焦CO_2气化反应的影响机理,利用扫描电镜(SEM)和Brunauer-Emmett-Teller(BET)分析了芒草热解焦的孔隙结构和表面形态.研究表明,随着制备温度的升高,热解焦表面结构被逐渐加深,表面粗糙度提高,比表面积相对增大,制备温度为600℃的热解焦具有最大的微孔容积与总孔容积之比,使得其更容易发生气化反应;制备温度为400℃时,芒草热解焦在3种模型下具有最小的平均活化能,随机孔模型对芒草热解焦实验数据拟合效果最好,其模拟的相关性系数R2均大于0.97.     

生物质热解半焦特性及其水蒸气吸附规律

选择杨木和松木两种木材作为热解原料,在常压下250~550℃内选取4个温度进行热解,并对生物半焦的性质进行分析。通过对生物半焦比表面积、表面官能团、孔隙率、氧碳比、氮碳比等性质的分析,研究热解得到的生物质半焦水蒸气吸附的影响规律。研究发现:生物半焦对水蒸气的吸附并非由单一性质所决定,而是受到比表面积、表面官能团、孔隙率等因素共同决定。     

生物质热解参数对焦碳生成特性及产氢率的影响

选取一定量筛分干燥后的松木屑作为实验材料,同时选取煅烧白云石粉及橄榄石粉作为实验反应催化剂.在石英管式炉上650～900℃温度范围内分别完成松木屑、松木屑与催化剂混合物的快速热解过程以及热解焦碳的气化反应过程.木屑低温热解时焦碳产生量多、比表面积大、气化活性好;白云石与木屑混合热解后焦碳产生量显著增多,优于橄榄石,低温热解产物潜在产氢率高.较低温度热解焦碳与水蒸气气化反应产气中氢体积含量可超过70%.     

分段式热解工艺2种高温模式下牛粪热解与气化产物特性

为确定牛粪连续分段式热解高温段热解模式和中高温段分界温度点,利用煤气分析仪、压汞仪和扫描电镜分析研究在管式气氛炉内中温段干馏、高温段干馏热解和水蒸气气化2种模式(在不同温度点通入水蒸气)下,牛粪热解与气化产物产率变化以及生物炭孔隙结构特征的演变。结果表明:随着温度的升高,在2种模式下均出现固相产率下降、气相产率升高、气相热值增大的趋势;与干馏相比,水蒸气气化模式可明显改善生物燃气安全利用性能;水蒸气气化模式下固相产物总孔隙度明显大于干馏模式,平均孔径差异不明显,除700℃外,其他温度条件下干馏模式固体比表面积明显高于水蒸气气化模式;在800℃及以下温度时,固相产物保持明显的骨架及纹理结构,其SiO_2基本处于无定形态,宏观上也表现出良好的散粒体特性,在900℃时,水蒸气气化模式下的固相产物出现明显的熔融结晶状态,炭中存在严重的团聚渣块现象,渣块坚硬且密实,干馏模式下产物未出现熔融结渣状况,但出现结构变形。     

Kinetic characteristics of in-situ char-steam gasification following pyrolysis of a demineralized coal

This study aims to examine the char-steam reactions in-situ, following the pyrolysis process of a demineralized coal in a micro fluidized bed reactor, with particular focuses on gas release and its kinetics characteristics. The main experimental variables were temperatures (925 °C?1075 °C) and steam concentrations (15%–35% H₂O), and the combination of pyrolysis and subsequent gasification in one experiment was achieved switching the atmosphere from pure argon to steam and argon mixture. The results indicate that when temperature was higher than 975 °C, the absolute carbon conversion rate during the char gasification could easily reach 100%. When temperature was 1025 °C and 1075 °C, the carbon conversion rate changed little with steam concentration increasing from 25% to 35%. The activation energy calculated from shrinking core model and random pore model was all between 186 and 194 kJ/mol, and the fitting accuracy of shrinking core model was higher than that of the random pore model in this study. The char reactivity from demineralized coal pyrolysis gradually worsened with decreasing temperature and steam partial pressure. The range of reaction order of steam gasification was 0.49–0.61. Compared to raw coal, the progress of water gas shift reaction (CO + H₂O ? CO₂ + H₂) was hindered during the steam gasification of char obtained from the demineralized coal pyrolysis. Meanwhile, the gas content from the char gasification after the demineralized coal pyrolysis showed a low sensitivity to the change in temperature.     

Distribution of Nitrogen Species During Vitrinite Pyrolysis and Gasification

The formation of HCN and NH₃ during pyrolysis in Ar and gasification in CO₂ and steam/Ar was investigated. Vitrinites were separated and purified from different rank coal from lignite to anthracite. Pyrolysis and gasification were carried out in the drop-tube/fixed-bed reactor at temperatures of 600–900°C. Results showed that with increase of reaction temperature the yield of HCN increased significantly during pyrolysis and gasification. Decrease of coal rank also increased the yield of HCN. Vitrinite from lower rank of coal with high volatile content released more HCN. The yield of NH₃ was the highest at 800°C during pyrolysis and gasification. And the yield of NH₃ from gasification in steam/Ar was far higher than that from gasification in CO₂, where the hydrogen radicals play a key role. Nitrogen retained in char was also investigated. The yield of char-N decreased with an increase of pyrolysis temperature. Vitrinite from lower rank coal had lower yield of char-N than that from the high rank coal.     

CO2 gasification characteristics of nascent pyrolyzed particles from coals and oil shale

In this work, the co‐pyrolysis characteristics of oil shale with two typical coals, bitumite and lignite, and the co‐gasification characteristics of the mixture pyrolyzed fuels were studied via thermo‐gravimetric analysis. The individual fuels and mixture fuels were first pyrolysis in N₂ atmosphere to specified temperature (450, 550, and 620 °C) at the heating rate of 20, 30 and 40 °C/min, respectively, and then maintained at the given temperature for 20 min before converted to CO₂ ambient to conduct the CO₂ gasification tests. The kinetic behavior and effects of both fuel types and pyrolysis temperature were investigated. The shoulder peak at around 550 °C observed in the derivative of weight loss derivative thermogravimetry analysis (DTG) curve during the pyrolysis of oil shale has confirmed the existence of specific reactions of oil shale at around 550 °C that leads to a sharp trough in the differential curves of co‐pyrolysis with coals and the unusual change in activation energies of gasification. In isothermal pyrolysis stage, oil shale lost its vast majority of organic matters at the temperature lower than 550 °C. The escape of pyrolysis gas and liquids in the coals is much harder than that in oil shale. The interaction between oil shale and bitumite was too weak to discriminate both in the pyrolysis and CO₂ gasification process. The variation of the particle surface structure caused by the releasing of volatile gases is strongly affected by the reaction rate and temperature. Quick volatile decomposition and gas releasing lead to the increase of surface area, decrease of the average pore diameter as well as the uniformization of the pore structure, while the higher temperature results in the blockade and merging of fine pores. The two factors lead to the greatest mass loss rate in the pyrolyzed particles obtained at 550 °C in temperature programmed CO₂ gasification stage. Two model‐free methods, Friedman method and Flynn–Wall–Ozawa method, were used to extract kinetic parameters from the experimentally determined pyrolyzed fuel conversions. The volatile contend has a significant influence on the fixed carbon conversion during the partially pyrolyzed particles' CO₂ gasification. In this study, significant interactions existed in co‐thermal utilization, both pyrolysis and CO₂ gasification, of oil shale and lignite. It is therefore surmised that co‐gasification of pyrolyzed lignite and oil shale may represent a feasible, practical route to high‐efficiency utilization of these fuels. Copyright © 2017 John Wiley & Sons, Ltd.     

Gasification of woody biomass under high heating rate conditions in pure CO2: Experiments and modelling

The present paper focuses on the gasification of thin wood particles in pure CO₂ at 850 °C under high heating rate conditions (similar to fluidized bed gasifiers). The aim is to assess the potential use of CO₂ as gasifying medium and to learn more about its effects on the pyrolysis as well as on the char gasification stages. Experimental and numerical modelling results provide answers on the unfolding of the whole CO₂ biomass pyro-gasification process. It was found that despite the CO₂ is present inside the particle during the pyrolysis stage, it has no noticeable impacts neither on the reaction rate nor on the char yield due to the relatively low temperature inside the particle. The CO₂ char gasification is the rate limiting step of the global pyro-gasification reaction as its duration is near to 95% of the entire biomass conversion time.     

Experimental analysis of pyrolysis of sewage sludge

Pyrolysis is a thermal process where organic materials such as biomass and oil are decomposed and lighter materials such as gas, vapor, liquid products, and char are produced. The aim of this study was to investigate the pyrolysis behavior of sewage sludge in different operating conditions. Using a fixed bed, the influence of some important parameters such as pyrolysis temperature, heating rate, particle size, and N₂ flow rate on product yields was studied. Results showed that with increase in temperature from 400 to 700°C, the char yield decreased from 30.1 to 7.50%, while the gas yield increased from 35.8 to 52.4%. The gas yield also increased from 46.9 to 49.1% as the heating rate increased from 20 to 60°C/s, while the oil yield increased from 45.2 to 46.8% as heating rate increased to 40°C/s and then the increase leveled off.     

Product distribution from solar pyrolysis of agricultural and forestry biomass residues

Solar pyrolysis of pine sawdust, peach pit, grape stalk and grape marc was conducted in a lab-scale solar reactor for producing fuel gas from these agricultural and forestry by-products. For each type of biomass, whose lignocellulose components vary, the investigated parameters were the final temperature (in the range 800°C–2000 °C) and the heating rates (in the range 10–150 °C/s) under a constant sweep gas flow rate of 6 NL/min. The parameter influence on the pyrolysis product distribution and syngas composition was studied. The experimental results indicate that the gas yield generally increases with the temperature and heating rate for the various types of biomass residues, whereas the liquid yield progresses oppositely. Gas yield as high as 63.5wt% was obtained from pine sawdust pyrolyzed at a final temperature of 2000 °C and heating rate of 50 °C/s. This gas can be further utilized for power generation, heat or transportable fuel production.     

Characteristic of hydrogen and syngas evolution from gasification and pyrolysis of rubber

The characteristics of syngas evolution during pyrolysis and gasification of waste rubber have been investigated. A semi-batch reactor was used for the thermal decomposition of the material under various conditions of pyrolysis and high temperature steam gasification. The results are reported at two different reactor temperatures of 800 and 900 °C and at constant steam gasifying agent flow rate of 7.0 g/min and a fixed sample mass. The characteristics of syngas were evaluated in terms of syngas flow rate, hydrogen flow rate, syngas yield, hydrogen yield and energy yield. Gasification resulted in 500% increase in hydrogen yield as compared to pyrolysis at 800 °C. However, at 900 °C the increase in hydrogen was more than 700% as compared to pyrolysis. For pyrolysis conditions, increase in reactor temperature from 800 to 900 °C resulted in 64% increase in hydrogen yield while for gasification conditions a 124% increase in hydrogen yield was obtained. Results of syngas yield, hydrogen yield and energy yield from the rubber sample are evaluated with that obtained from woody biomass samples, namely hard wood and wood chips. Rubber gasification yielded more energy at the 900 °C as compared to biomass feedstock samples. However, less syngas and less hydrogen were obtained from rubber than the biomass samples at both the temperatures reported here.     

Modeling of beech wood pellet pyrolysis under concentrated solar radiation

A two-dimensional, unsteady CFD (Computational Fluid Dynamics) single particle model was developed and used to simulate the solar pyrolysis process of beech wood pellets (10 mm in diameter and 5 mm in height). Pseudo-stoichiometric coefficients about the mass fraction of primary tar converted by the reaction into gas and secondary tar were determined at different temperatures and heating rates for the first time. The 2D model predictions were successfully validated with tests performed at 600 °C to 2000 °C final temperature, with 10 and 50 °C/s heating rates. The evolution of the final products and mass losses of pyrolyzed biomass are enhanced with temperature and heating rate. Moreover, the higher the temperature and heating rate, the higher the gas yield. This emphasizes the intra-particle tar secondary reaction into gas for pyrolysis of large size sample under high temperature and heating rate.     

Performance of active nickel loaded lignite char catalyst on conversion of coffee residue into rich-synthesis gas by gasification

Performance of nickel-loaded lignite char catalyst on conversion of coffee residue into synthesis gas by catalytic steam gasification was carried out at low reaction temperatures ranging from 500 °C to 650 °C in the two-stage quartz fixed bed reactor. The effects of steam pressures (30, 36 and 50 kPa corresponding to S/B = 2.23, 2.92 5.16, respectively) and catalyst to biomass ratios (C/B ratio = 0, 1, 3) were considered. Nickel-loaded lignite char was prepared as a catalyst with a low nickel loading amount of 12.9 wt%. The gas yields in the catalytic steam gasification process strongly depended on the reaction temperature and C/B ratio. The total gas yields obtained in catalytic steam gasification was higher than that of catalytic pyrolysis, steam gasification and non-catalytic pyrolysis with steam absence by factors of 3.0, 3.8 and 7.7, respectively. To produce the high synthesis gas, it could be taken at 600 °C with total gas yields of 67.13 and 127.18 mmol/g biomass-d.a.f. for C/B ratios of 1.0 and 3.0, respectively. However, the maximum H₂/CO ratio was 3.57 at a reaction temperature of 600 °C, S/B of 2.23 and C/B of 1.0. Considering the conversion of coffee residue by catalytic steam gasification using the nickel-loaded lignite char catalyst, it is possible to covert the coffee residue volatiles into rich synthesis gas.     

Hydrogen enriched syngas production via gasification of biofuels pellets/powders blended from olive mill solid wastes and pine sawdust under different water steam/nitrogen atmospheres

In this work, we study the gasification of pellets produced, after densification, by blending olive mill solid wastes, impregnated or not by olive mill waste water, and pine sawdust under different steam/nitrogen atmospheres. The charcoals necessary for the gasification tests were prepared by pyrolysis using a fixed bed reactor. The gasification technique using steam was chosen in order to produce a hydrogen-enriched syngas. Gasification tests were performed using macro-thermogravimetric equipment. Tests were carried out at different temperatures (750 °C, 800 °C, 820 °C, 850 °C and 900 °C), and at different atmospheres composed by nitrogen and steam at different percentages (10%, 20% and 30%). Results show that the mass variation profiles is similar to the usual lingo-cellulosic gasification process. Moreover, the increase of temperatures or water steam partial pressures affects positively the rate of conversion and the char reactivity by accelerating the gasification process. The increase of the gasification yields demonstrates the promise of using olive mill by-products as alternative biofuels (H₂ enriched syngas).