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%。     

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.     

炭化气氛对黑液煤浆及不同煤种气化反应特性的影响

煤气化前阶段的炭化气氛(温度、时间)影响到煤焦的气化反应特性.采用不同的炭化温度和炭化时间制备了黑液水煤浆、普通水煤浆以及其他5种煤的焦样,得到了各种煤焦气化反应的碳转化率;同时,通过扫描电子显微镜分析手段鉴别焦炭表面孔隙分布情况.试验结果表明,相同炭化气氛下得到的7种不同煤焦中,黄陵煤焦的气化活性最高,说明煤化程度越高反应性越低;由于黑液中有机物和无机物钠盐的影响,黑液水煤浆焦的气化特性高于普通水煤浆焦和新汶煤焦.煤焦的气化反应性,不仅与煤阶有关,还和煤焦中含氧官能团和无机化合物的含量有关,同时煤浆中外在添加的无机物组分也影响到煤焦的气化活性.     

O_2/CO_2条件下生物质焦和煤焦燃烧动力学特性

为得到富氧条件下生物质焦和煤焦的燃烧动力学特性规律,利用热重研究了麦秆焦,木屑焦以及烟煤焦在富氧气条件下的燃烧特性。实验结果表明:无论是生物质焦还是煤焦,相同的O2浓度下,O2/CO2气氛下焦样的着火相对于O2/N2气氛均发生了延迟,燃烧特性指数也均低于O2/N2气氛下对应值;在O2/CO2气氛和O2/N2气氛下,随着O2浓度的增加,焦样的着火温度均降低,燃烧特性指数增大,且提高O2浓度对煤焦着火的改善程度显著优于木屑焦。     

氧对宜宾煤中燃料氮迁移特性的影响

利用X射线光电子能谱，研究了宜宾煤与煤焦中氮的形态，探讨了氧对煤中燃料氮迁移规律的影响．制焦气氛为高纯氩气中的惰性热解和氧／氩混合气氛．制焦温度为700℃和900℃．结果表明，煤焦中氮官能团的存在形式受温度控制，与气氛无关，但是温度和氧量对各官能团量的变化都有影响．氧的参与造成热解时燃料氮迁移规律的改变，这种改变随温度的升高愈加明显．有氧存在时，焦中氮的总含量随温度的升高迅速减少．实验结果分析说明，煤焦N-X中氧的来源是煤本身结合的燃料氧，而热解气氛中氧的参与不会造成N-6和N-Q转变为吡啶酮和N-X．各种氮官能团形式随温度的升高都有不同程度的减少，惰性热解条件下的各官能团相互转化现象在有氧存在时不明显．     

秸秆焦的表面特征及CO2气化反应性的研究

在700～1000℃热解温度条件下制备了稻秸秆和麦秸秆焦并进行了SEM和BET表面积测试分析,采用等温热重法研究了这些秸秆焦的CO2气化反应特性.结果表明:在较低热解温度(700℃)下,秸秆热解焦中尚含有一定量未析出的焦油;在700～1000℃范围内,随热解温度上升秸秆焦的BET表面积逐渐增加,而气化反应活性却有所下降;在800～1100℃气化温度范围内,秸秆焦的气化反应性随气化温度明显增加,两种秸秆焦的表观活化能则随热解温度稍有增加,稻秸秆和麦秸秆焦的表观活化能范围分别为183.58～196.50kJ/mol和147.27～184.01kJ/mol.     

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%.     

浑源煤焦CO_2气化反应的影响因素及动力学特性分析

研究了热解温度、热解时间以及气化温度对浑源煤焦CO2气化反应的影响,并获得了气化反应的动力学模型.结果表明：浑源煤焦的气化活性随热解温度的提高而降低;每个热解温度都对应着一个最佳热解时间,且存在最佳热解时间随温度升高而缩短的趋势;提高气化温度能够显著提高煤焦的气化反应性能,气化温度对气化反应的影响大于热解温度的影响;低温度煤焦的气化活性随气化温度的提高而增加更为剧烈;900℃及以上的高温使活性点数增加,从而使煤焦间的活性差距分布均匀;浑源煤焦的气化反应适宜用体积模型来描述,所求取的动力学参数之间存在补偿效应,其等动力学温度约为1 199.6℃.     

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.     

Effect of CO2 and steam gasification reactions on the oxy-combustion of pulverized coal char

For oxy-combustion with flue gas recirculation, elevated levels of CO₂ and steam affect the heat capacity of the gas, radiant transport, and other gas transport properties. A topic of widespread speculation has concerned the effect of gasification reactions of coal char on the char burning rate. To asses the impact of these reactions on the oxy-fuel combustion of pulverized coal char, we computed the char consumption characteristics for a range of CO₂ and H₂O reaction rate coefficients for a 100 μm coal char particle reacting in environments of varying O₂, H₂O, and CO₂ concentrations using the kinetics code SKIPPY (Surface Kinetics in Porous Particles). Results indicate that gasification reactions reduce the char particle temperature significantly (because of the reaction endothermicity) and thereby reduce the rate of char oxidation and the radiant emission from burning char particles. However, the overall effect of the combined steam and CO₂ gasification reactions is to increase the carbon consumption rate by approximately 10% in typical oxy-fuel combustion environments. The gasification reactions have a greater influence on char combustion in oxygen-enriched environments, due to the higher char combustion temperature under these conditions. In addition, the gasification reactions have increasing influence as the gas temperature increases (for a given O₂ concentration) and as the particle size increases. Gasification reactions account for roughly 20% of the carbon consumption in low oxygen conditions, and for about 30% under oxygen-enriched conditions. An increase in the carbon consumption rate and a decrease in particle temperature are also evident under conventional air-blown combustion conditions when the gasification reactions are included in the model.     

Experimental simulate on hydrogen production of different coals in underground coal gasification

Research on hydrogen production from coal gasification is mainly focused on the formation of CO and H₂ from coal and water vapor in high-temperature environments. However, in the process of underground coal gasification, the water gas shift reaction of low-temperature steam will absorb a lot of heat, which makes it difficult to maintain the combustion of coal seams in the process of underground coal gasification. In order to obtain high-quality hydrogen, a pure oxygen-steam gasification process is used to improve the gasification efficiency. And as the gasification surface continues to recede, the drying, pyrolysis, gasification and combustion reactions of underground coal seams gradually occur. Direct coal gasification can't truly reflect the process of underground coal gasification. In order to simulate the hydrogen production laws of different coal types in the underground gasification process realistically, a two-step gasification process (pyrolysis of coal followed by gasification of the char) was proposed to process coal to produce hydrogen-rich gas. First, the effects of temperature and coal rank on product distribution were studied in the pyrolysis process. Then, the coal char at the final pyrolysis temperature of 900 °C was gasified with pure oxygen-steam. The results showed that, the hydrogen production of the three coal chars increased with the increase of temperature during the pyrolysis process, the hydrogen release from Inner Mongolia lignite and Xinjiang long flame coal have the same trend, and the bimodality is obvious. The hydrogen release in the first stage mainly comes from the dehydrogenation of the fat side chain, and the hydrogen release in the second stage mainly comes from the polycondensation reaction in the later stage of pyrolysis, and the pyrolysis process of coal contributes 15.81%–43.33% of hydrogen, as the coal rank increases, the hydrogen production rate gradually decreases. In the gasification process, the release of hydrogen mainly comes from the water gas shift reaction, the hydrogen output is mainly affected by the quality and carbon content of coal char. With the increase of coal rank, the hydrogen output gradually increases, mainly due to the increasing of coal coke yield and carbon content, The gasification process of coal char contributes 56.67–84.19% of hydrogen, in contrast, coal char gasification provides more hydrogen. The total effective gas output of the three coal chars is 0.53–0.81 m³/kg, the hydrogen output is 0.3–0.43 m³/kg, and the percentage of hydrogen is 53.08–56.60%. This study shows that two-step gasification under the condition of pure oxygen-steam gasification agent is an efficient energy process for hydrogen production from underground coal gasification.     

煤与稻草共热解特性研究

用热重法研究不同煤化程度煤与稻草共热解特性.结果表明：煤与稻草共热解的TG曲线随稻草掺混比例的增加向低温区移动,趋近稻草单独热解的TG曲线;DTG曲线主要热解阶段的两个区间曲线和特征参数分别与稻草、煤单独热解的相似.通过对热解特征参数实际值和理论值的对比,稻草对共热解过程有一定的促进作用,而煤对共热解过程则没有表现出明显作用.     

掺混生物质焦和煤焦共气化的热重分析

采用热重分析法对煤焦和几种生物质焦及其混合物的气化过程及动力学规律进行了分析,分析结果表明煤焦的失重与生物质焦相比差别明显,混合物中的生物质焦所占比重越大、发生失重的温度越低。进一步采用Coats—Redfern方法对样品气化过程进行了动力学分析,得到了生物质焦、煤焦及其混合物表观活化能。     

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.     

CaO和Fe（N03）3复合催化锦界煤焦-C02气化的实验研究

在搭建的固定床实验台上对CaO和Fe（NO3）3复合催化锦界煤焦-CO2常压等温气化的反应特性进行了研究．结果表明：复合催化剂最佳质量添加比例为1％Ca、29／6Fe,且在最佳添加量下气化时间比原煤焦和单组分催化剂下的气化时间分别缩短了103rain和18rain,催化强度系数分别是原煤焦、单组分催化剂CaO和Fe（N03）3的5．71倍、1．65倍和2．04倍,气化温度降低了100K,气化温度降低程度介于单组分催化剂CaO和Fe（NO3）3之间;复合催化过程生成的部分Ca（NO3）2与CaO的活性不同,即Ca的催化强度与其前驱物的形式有一定关系;添加单组分催化剂的煤焦活化能与原煤焦的活化能基本相同,不同添加比例的复合催化剂的煤焦活化能增加的程度不同,且在最佳添加比例下增加程度最小,其值为15．4％．     

Syngas yield during pyrolysis and steam gasification of paper

Main characteristics of gaseous yield from steam gasification have been investigated experimentally. Results of steam gasification have been compared to that of pyrolysis. The temperature range investigated were 600–1000 °C in steps of 100 °C. Results have been obtained under pyrolysis conditions at same temperatures. For steam gasification runs, steam flow rate was kept constant at 8.0 g/min. Investigated characteristics were evolution of syngas flow rate with time, hydrogen flow rate and chemical composition of syngas, energy yield and apparent thermal efficiency. Residuals from both processes were quantified and compared as well. Material destruction, hydrogen yield and energy yield is better with gasification as compared to pyrolysis. This advantage of the gasification process is attributed mainly to char gasification process. Char gasification is found to be more sensitive to the reactor temperature than pyrolysis. Pyrolysis can start at low temperatures of 400 °C; however char gasification starts at 700 °C. A partial overlap between gasification and pyrolysis exists and is presented here. This partial overlap increases with increase in temperature. As an example, at reactor temperature 800 °C this overlap represents around 27% of the char gasification process and almost 95% at reactor temperature 1000 °C.     

Influence of pyrolysis pressure on structure and combustion reactivity of Zhundong demineralized coal char

The investigation on evolution of coal char structure during pressurized pyrolysis can reveal the combustion reactivity of coal char in thermal utilization at elevated pressure. In this study, Zhundong subbituminous coal was demineralized and a pressurized drop tube reactor (PDTR) was used to prepare coal char under different temperature and pressure conditions. The physicochemical structures of raw and demineralized coal chars were characterized by the application of nitrogen adsorption analyzer, automatic mercury porosimeter, and Fourier transform infrared spectroscopy (FTIR). The change mechanism of char infrared structure with pyrolysis pressure is revealed on the molecular level in this paper. The results show that the N₂ adsorption quantity of raw coal char increases with the increase of pyrolysis temperature, while that of demineralized coal char decreases. Because of the difference in molecular volume and steric hindrance between aliphatic and aromatic structure in char, the increasing pressure has less inhibition effect on the escape of the former than the latter. With the increase of pyrolysis pressure, the combustion reactivity of char is related to the infrared structure at 700 and 800 °C while to macropore structure at 900 and 1000 °C.