不同种类生物质热解残焦的CO_2气化研究

在常压固定床反应器中,以不同种类生物质热解残焦为原料进行CO_2气化制取CO研究,并与煤焦的CO_2气化效果进行对比。实验在气化温度700~1000℃条件下进行,研究热解残焦制备温度、生物质热解残焦种类、气化温度对气化产气中CO浓度、热解残焦转化率的影响。研究结果表明:制备温度为550℃的生物质热解残焦的气化效果优于600℃时;生物质热解残焦的气化效果明显优于煤焦,且垃圾焦气化效果最佳;污泥焦、垃圾焦、秸秆焦的最佳气化温度为900℃,煤焦的最佳气化温度为1000℃。     

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.     

制焦条件对稻秆与大同烟煤共气化特性影响的实验研究

在自行设计搭建的气化实验装置上进行不同制焦条件下稻焦-大同烟煤焦的混合焦样气化特性实验。对比不同工况下气化特性曲线发现:在本实验工况下,稻-煤焦样经机械掺混后的气化特性优于相同工况下浸渍混合后的气化特性;混合后制焦所得焦样气化特性优于先制焦后混合处理所得焦样的气化特性;煤和稻焦热解温度对混焦的气化特性影响不同,热解温度对生物质焦以及随后气化特性的影响大于对煤焦的影响;无论是稻焦还是煤焦,热解时间对混焦的气化特性影响均不明显。通过上述热解条件对稻-煤气化特性的影响,为煤与生物质共气化的工业应用提供指导。     

兰炭生物质复合燃料热解实验分析

采用热重分析方法对生物质复合燃料、无生物质复合燃料、兰炭原料热解行为及其动力学规律进行研究,实验结果发现样品的失重过程分为脱水、脱挥发分,气化反应混合以及气化反应等3个阶段,实验样品的失重率会伴随着温度的变化而变化。对实验样品进行动力学分析,根据3种样品最佳反应温度得出升温速率拟合曲线,3种样品活化能分别为3 562.454、1 042.97、2 904.818 kJ/mol。对比分析得出生物质型炭的活化能大大增加,提高了能量利用率。     

锡林浩特褐煤气化特性研究

利用同步热分析仪研究了制焦温度、气化温度以及升温速率等因素对煤焦气化特性的影响。研究结果表明:随着制焦温度的升高,煤焦的气化失重量减少,气化反应的时间延长,气化反应性略有降低。随着气化温度的提高,锡林浩特褐煤煤焦在相同时间内的碳转化率增加,煤焦的气化时间缩短,气化温度对煤焦的气化反应性有较大的影响。随着升温速率的增大,TG曲线、DTG曲线均向高温侧偏移。升温速率越大,相同温度时煤焦的碳转化率越低,气化反应速率达到峰值对应的气化温度随升温速率的增大而升高。随着升温速率的增大,煤焦气化反应活性变好,气化反应进行的更加剧烈。     

生物质灰对煤-生物质混焦气化特性影响的实验研究

在自行设计搭建的气化实验装置上对稻灰和松灰2种生物质灰样对煤焦气化特性的影响进行实验,并对酸洗、水洗脱灰方式对生物质-煤混焦气化特性的影响进行研究。研究发现,松灰和稻灰对煤焦气化反应均有较好的催化作用,松灰催化的平均气化速率是稻灰催化的1.85倍;生物质酸洗脱灰后,煤-生物质焦的混焦气化特性出现一定程度的劣化,松木屑酸洗脱灰后混合焦样平均气化速率相对原值降低47.58%;稻秆水洗脱灰后的混合焦样平均气化速率相对原值降低46.65%,但松木屑水洗脱灰后的混合焦样平均气化速率相对原值增加29.21%。     

煤焦水蒸气催化气化动力学分析

利用固定床反应器研究了K、Ca、Ni和Fe金属对600～900℃内煤焦水蒸气气化的催化效果,分析了适用于原煤焦、脱灰煤焦和添加K、Ca、Ni和Fe金属后的煤焦水蒸气气化动力学模型。     

热解条件对生物质焦气化活性的影响及等温气化动力学参数求解方法

生物质气化是生物质利用研究的一个重点。生物质气化包含生物质的热解和热解所得焦炭的气化两个过程。不同的热解条件将得到具有不同气化活性的生物质焦炭,不同热解条件制取的焦炭的动力学参数也不相同。本文主要概述了热解条件对生物质焦气化活性的影响。同时基于阿伦尼乌斯公式介绍了生物质焦等温气化动力学参数的两种获取方法,非等转化率法是通过选择动力学模型中的结构因子f(x) 来获取动力学参数,而等转化率法是通过避开选择动力学模型中的结构因子f(x) 来获取动力学参数。基于简单碰撞理论提出了获取等温气化动力学参数的新方法,对阿伦尼乌斯公式中的指数项、指前因子A提出了明确的物理意义。基于简单碰撞理论的等温求解气化动力学参数方法类似于基于阿伦尼乌斯公式的等温求解气化动力学参数方法。     

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。     

纤维素和木质素含量对稻草、锯末热解及燃烧特性的影响

利用热重分析仪分析了生物质中纤维素和木质素含量对稻草、锯末热解及燃烧特性的影响。在热解过程中,生物质中纤维素含量较高的锯末,与纤维素含量较低的稻草相比,燃料失重要大。在燃烧过程中,通过实际生物质与纤维素和木质素混合物的对比,发现稻草和锯末的燃烧分为挥发分的脱除和焦的燃烧两个阶段,且燃烧特性与焦的形貌密切相关。     

煤和生物质床层燃烧氮氧化物生成规律的对比研究

为揭示和评估燃料特性对床层燃烧过程中氮氧化物生成规律的影响,选取了燃煤与生物质成型颗粒这两种代表性燃料,在单元体炉试验台上模拟层燃反应过程,并测定了床层表面和内部的温度及气氛.结果表明:无论燃煤还是生物质,床层内部的氮氧化物浓度峰值都显著高于床层表面,证实了炭层对氮氧化物优良的还原作用.生物质与燃煤相比火焰锋面处的氮氧...     

煤焦燃烧模型的热重实验研究

基于热重分析法对无烟煤和烟煤的两种煤焦在不同氧浓度下(100％、30％、20％和7％，其余为氩气)的燃烧模型进行了研究．比较和分析了几种主要燃烧动力学模型的特点，采用一种新的统一模型和动力学参数对上述煤焦的燃烧过程进行了模拟．分析了煤焦颗粒比表面积在燃烧过程中的变化规律，改进了原有煤焦模型中的表面积系数的选取办法，模拟结果与实验结果吻合程度较好．该模型能够较好地对煤焦的燃烧过程进行模拟，而且采用变氧浓度的实验方法是一种研究煤焦燃烧动力学参数的有效途径。     

Two-step steam pyrolysis of biomass for hydrogen production

In this study, different char based catalysts were evaluated in order to increase hydrogen production from the steam pyrolysis of olive pomace in two stage fixed bed reactor system. Biomass char, nickel loaded biomass char, coal char and nickel or iron loaded coal chars were used as catalyst. Acid washed biomass char was also tested to investigate the effect of inorganics in char on catalytic activity for hydrogen production. Catalysts were characterized by using Brunauer–Emmet–Teller (BET) method, X-ray diffraction (XRD) analyzer, X-ray fluorescence (XRF) and thermogravimetric analyzer (TGA). The results showed that the steam in absence of catalyst had no influence on hydrogen production. Increase in catalytic bed temperature (from 500 °C to 700 °C) enhanced hydrogen production in presence of Ni-impregnated and non-impregnated biomass char. Inherent inorganic content of char had great effect on hydrogen production. Ni based biomass char exhibited the highest catalytic activity in terms of hydrogen production. Besides, Ni and Fe based coal char had catalytic activity on H₂ production. On the other hand, the results showed that biomass char was not thermally stable under steam pyrolysis conditions. Weight loss of catalyst during steam pyrolysis could be attributed to steam gasification of biomass char itself. In contrast, properties of coal char based catalysts after steam pyrolysis process remained nearly unchanged, leading to better thermal stability than biomass char.     

Parameter for judging reactivity of coal and coke

To eliminate the judgment error of char reactivity arising from different carbon content of samples, a new parameter called specific maximum weight loss rate was introduced. It is defined as the quotient of the maximum weight loss rate in non-isothermal thermogravimetric analysis (TGA) experiment to the carbon content of the corresponding sample. The reactivity of different kinds of coal, the reactivity of the same coal type with different lithotype, and the reactivity of the char with different carbon conversion rates were checked by using the specific maximum weight loss rate, and the results were analyzed and compared with those obtained by using other criteria. The results show that the specific maximum weight loss rate can be used as a commonality parameter to evaluate and distinguish the reactivity of different coal and char. The heating rate selected in TGA experiment has no effect on the judgment. __________ Translated from Journal of Zhejiang University (Engineering Science), 2006, 40(11): 1998–2001 [译自: 浙江大学学报(工学版)]     

Comparison study of fuel characteristics of slow pyrolyzed chars with Neyveli lignite

As coals are fast depleting, suitable means of substituting coal need to be explored. In this work, a feasibility study of co-firing lignite with char was investigated. Some locally abundant biomass were slow pyrolyzed. The pyrolyzed chars were characterized and their fuel properties were compared with that of Neyveli lignite. The study indicated that the heating value of chars (except rice husk char) were higher than Neyveli lignite. The study also revealed that the properties of chars were on superior to Neyveli lignite and can be substituted to Neyveli lignite.     

天然气在煤焦表面的积碳行为

采用气相色谱(GC)和热重分析(TG)两种研究方法对天然气在高温制得煤焦的表面积碳特性进行了研究并发现:高煤阶煤种制备的普通焦有较好的抗积碳性能,而较低煤阶煤种制备的活性焦抑制积碳能力较好;活化后并不一定能提高煤焦的抗积碳性能。     

不同催化剂对脱矿煤焦还原NO的催化能力比较

通过实验研究了几种在煤灰中常见的金属 (K ,Na,Cu ,Fe ,Ca)氧化物对煤焦还原NO的催化作用 ,为了比较这些金属氧化物对焦炭还原NO反应的催化能力 ,对煤焦进行了脱矿处理。实验是在高温沉降炉内完成的。实验中使用的煤粉及其煤焦来自神府褐煤。实验结果表明 ,煤灰中的矿物质对煤焦异相还原NO具有催化作用。在实验条件下不同金属氧化物对煤焦还原NO的催化能力有如下顺序 :K >Na>Ca >Cu >Fe。实验结果还表明 ,实验工况 (温度 ,SR数 )和催化剂的添加量对NO的还原都具有不同程度的影响     

Initial moisture effects on herbal biomass torrefaction behavior: Gaseous products evolution and char structure analysis

Initial moisture effects on biomass torrefaction were investigated by thermogravimetric (TG) and Fourier transform infrared spectrometer (FTIR) methods. Mass degradation properties, gaseous products’ evolution characteristics, and biomass char chemical structural features were studied. Results show that during torrefaction process, the evaporation of water will create a porous structure inside the solid particles, hence extend the mass loss time intervals. Gaseous products’ evolutions were favored, while tar was reduced because of enhanced secondary decomposition. Char structure analysis suggested that –OH stretch was slightly strengthened through water molecule decomposition and other radical reactions, which would increase the reactivity of char gasification and combustion.     

Gasification reactivity and synergistic effect of conventional and microwave pyrolysis derived algae chars in CO2 atmosphere

This research focuses on the isothermal and non-isothermal CO₂ gasification of an algal (Chlorella) char prepared via two different thermal processing systems, i.e. conventional and microwave-assisted pyrolysis. It was found that chars prepared via microwave irradiation showed higher CO₂ gasification reactivity than that of chars prepared via the conventional method. Meanwhile, the activation energy of microwave char was found to be 127.89 kJ/mol, which was 46.3 kJ/mol lower than that of conventional char, indicating improved reactivity of microwave char. The systematic characterisation of both conventional and microwave chars shows that the higher reactivity of microwave char could be attributed to its large BET surface area, low crystalline index and high active sites. In addition, it was found that microwave heating contributed to high reactivity of chars through generating large amount of primary char, the formation of hot spot and high specific surface area and pore volume. Results of co-gasification under isothermal conditions revealed the existence of greater synergistic effects between coal char and microwave algae char than those of coal char and conventional algae char. Furthermore, based on the relative Rs (average gasification rate), a novel index proposed to quantify the interactions in co-gasification process, Australian coal char/microwave assisted char blend experienced 10% higher interactions compared to Australian coal char/conventional assisted char blend.