生物质炭水蒸气气化制取富氢合成气

以生物质炭为原料在上吸式固定床气化炉中进行水蒸气气化制备富氢合成气,考察了不同原料、粒径和催化剂对生物质炭水蒸气气化影响。结果表明,不同类型炭气化结果存在较大差异,其中木片炭气化结果最优,其次是玉米芯炭和稻壳炭,秸秆炭气化结果最差,木片炭产氢率最大为222.8g/kg。粒径的改变主要影响炭转化率,炭转化率随着粒径的增加呈增加趋势。通过炭吸收方式负载催化剂为有效的方法,其中在相同钾盐质量分数下,KOH催化能力较优于K₂CO₃,且气化速率为未加催化剂条件下的两倍。炭转化率随着碱液浓度的增加而增加,但浓度过高会增加灰分含量从而不利于产氢率,玉米芯炭催化气化最高产氢率为197.8g/kg,在碱质量分数为6%下获得。     

Comparison of steam-gasification characteristics of coal char and petroleum coke char in drop tube furnace

The steam-gasification reaction characteristics of coal and petroleum coke (PC) were studied in the drop tube fur-nace (DTF). The effects of various factors such as types of carbonaceous material, gasification temperature (1100–1400 °C) and mass ratio of steam to char (0.4:1, 0.6:1 and 1:1 separately) on gasification gas or solid products were investigated. The results showed that for al carbonaceous materials studied, H2 content exhibited the larg-est part of gasification gaseous products and CH4 had the smal est part. For the two petroleum cokes, CO2 content was higher than CO, which was similar to Zun-yi char. When the steam/char ratio was constant, the carbon con-version of both Shen-fu and PC chars increased with increasing temperature. When the gasification temperature was constant, the carbon conversions of al char samples increased with increasing steam/char ratio. For al the steam/char ratios, compared to water gas shift reaction, char-H2O and char-CO2 reaction were further from the thermodynamic equilibrium due to a much lower char gasification rate than that of water gas shift reaction rate. Therefore, kinetic effects may play a more important role in a char gasification step than thermodynamic ef-fects when the gasification reaction of char was held in DTF. The calculating method for the equilibrium shift in this study wil be a worth reference for analysis of the gaseous components in industrial gasifier. The reactivity of residual cokes decreased and the crystal layer (L002/d002) numbers of residual cokes increased with increasing gasification temperature. Therefore, L002/d002, the carbon crystallite structure parameter, can be used to evaluate the reactivity of residual cokes.     

Reaction kinetics and producer gas compositions of steam gasification of coal and biomass blend chars, part 2: Mathematical modelling and model validation

In gasification of biomass, coal and blended biomass and coal, there are two steps including an initial pyrolysis process followed by gasification of solid char. The latter process is a slow process and thus dominates the whole gasification. In our previous paper (Xu et al., in press), the differences between steam gasification of biomass chars and that of coal chars have experimentally been investigated and the results show that these differences are mainly due to the difference in microstructures of these two fuels. In this work, a mathematical model of char gasification is developed based on reaction kinetics and gas transportation of both the producer gas and the gasification agent (steam). The model also includes mass conservation equations for each of the gas components and solid carbon involved in the gasification process. This has resulted in a set of highly nonlinear differential equations which have been solved using a numerical technique to predict gas production rate, gas compositions and carbon consumption rate during the gasification.The developed mathematical model is validated using experimental results reported in previous paper (Xu et al., in press), and close agreement between the simulation results and the experimental values have been observed. From the modelling, it has been confirmed that the char gasification is mainly determined by the characteristics of char matrix including the exposed surface area and the micro-pore size. The former determines intrinsic reaction rate and the latter influences the intra-particle mass transportation. Biomass char has more amorphous structure, thus the intrinsic reaction rate is enhanced. For coal char, the larger pore size enables the high transport rate of the gasification agent (water vapour) into the char particles but the resultant gases have higher resistance to transfer through compact clusters. For simulation of the blended biomass and coal, the blend properties were determined based on the blend proportion of each fuel. The close agreement between the simulation results and experimental data suggests that the approach in this work can adequately quantify the gasification kinetics and the gas composition.     

Steam gasification reactivity of char from rapid pyrolysis of bio-oil/char slurry

A slurry of bio-oil and char originating from wood pyrolysis is a promising gasifier feed-stock because of its high energy density. When such a slurry is injected into a high temperature gasifier it undergoes a rapid pyrolysis yielding a char which then reacts with steam. The char produced by pyrolysis of an 80 wt% bio-oil/20 wt% char mixture at heating rates of 100-10,000 °C/s was subjected to steam gasification in a thermogravimetric analyzer. The original wood char from the bio-oil production was also tested. Gasification was conducted with 10-50 mol% steam at temperatures from 800 to 1200 °C. Reactivity of the slurry chars increased with pyrolysis heating rate, but was lower than that of the original chars. Kinetic parameters were established for a power-law rate model of the steam-char reaction, and compared to values from the literature. At temperatures over 1000 °C, the gasification rates appeared to be affected by diffusional resistance.     

On the intrinsic reaction rate of biomass char gasification with carbon dioxide and steam

The gasification of beech wood char and oil palm shell char with carbon dioxide and steam was studied. To avoid heat and mass transport limitations during gasification, the amount of char, particle size and flow rate were varied in isothermal experiments. A rate expression of the Langmuir–Hinshelwood-type was applied to match the experimental data at different partial pressures and reaction temperatures in the intrinsic regime. Furthermore, the reactive surface area (RSA) of the biomass chars was determined as a function of the degree of conversion by the temperature-programmed desorption technique (TPD). The results show that the reaction rate is in general proportional to the RSA. The surface related reaction rates for the studied biomass chars are comparable to surface related reaction rates for coal chars at similar reaction temperatures.     

Steam gasification of coal char catalyzed by K2CO3 for enhanced production of hydrogen without formation of methane

Steam gasification of coal char catalyzed by potassium carbonate was investigated on a laboratory fixed-bed reactor to examine the catalytic effects not only on the reaction rate but also on the reaction selectivity, and non-catalytic gasification of coal char was performed by way of contrast. It was observed that the catalytic gasification of coal char with steam occurred significantly in a temperature range of 700-750 °C, producing a hydrogen-rich gas with slight formation of carbon monoxide and virtually no formation of methane. An oxygen transfer and intermediate hybrid mechanism of the catalytic char gasification with steam is proposed for understanding of the experimental data regarding both the kinetic behaviors and reaction selectivity. The study has highlighted the advantages of the catalytic gasification of coal char over the conventional coal gasification with respect to the reaction selectivity. The catalytic steam gasification of coal char makes it possible to eliminate or simplify the methane reforming and water-gas shift processes in the traditional gas-to-hydrogen purification system.     

Reaction kinetics and producer gas compositions of steam gasification of coal and biomass blend chars, part 1: Experimental investigation

Biomass and coal are important solid fuels for generation of hydrogen-rich syngas from steam gasification. In this work, experiments were performed in a bench-scale gasifier to investigate the effect of coal-to-biomass ratio and the reaction kinetics for gasification of chars of biomass, coal and coal–biomass blends. In the gasification of these chars, steam was used as the gasification agent, while nitrogen was used as a gas carrier. The gasification temperature was controlled at 850, 900 and 950 °C. Gas produced was analysed using a micro-GC from which carbon conversion rate was also determined. From the experiments, it is found that the coal and biomass chars have different gasification characteristics and the overall reaction rate decreases with an increase in the ratio of coal–to-biomass.The microstructure of the coal char and biomass char was examined using scanning electronic microscopy (SEM), and it was found that the biomass char is more amorphous, whereas the coal char has larger pore size. The former enhances the intrinsic reaction rate and the latter influences the intra particle mass transportation. The difference in mass transfer of the gasification agent into the char particles between the two fuels is dominant in the char gasification.     

Gasification rate analysis of coal char with a pressurized drop tube furnace

Two coal chars were gasified with carbon dioxide or steam using a Pressurized Drop Tube Furnace (PDTF) at high temperature and pressurized conditions to simulate the inside of an air-blown two-stage entrained flow coal gasifier. Chars were produced by rapid pyrolysis of pulverized coals using a DTF in a nitrogen gas flow at 1400°C. Gasification temperatures were from 1100 to 1500°C and pressures were from 0.2 to 2 MPa. As a result, the surface area of the gasified char increased rapidly with the progress of gasification up to about six times the size of initial surface area and peaked at about 40% of char gasification. These changes of surface area and reaction rate could be described with a random pore model and a gasification reaction rate equation was derived. Reaction order was 0.73 for gasification of the coal char with carbon dioxide and 0.86 for that with steam. Activation energy was 163 kJ/mol for gasification with carbon dioxide and 214 kJ/mol for that with steam. At high temperature as the reaction rate with carbon dioxide is about 0.03 s⁻¹, the reaction rate of the coal char was controlled by pore diffusion, while that of another coal char was controlled by surface reaction where reaction order was 0.49 and activation energy was 261 kJ/mol.     

煤焦与水蒸气加压气化反应活性的研究

采用填充床热天平反应器（ＰＢＢＲ）系统,于０．０９８ＭＰａ～２．４５ＭＰａ压力和７５０℃～１０００℃温度下进行了煤焦与水蒸气气化反应的活性研究,以基碳转化率（Ｘ）和比气化速率（Ｂ）作为反应活性的评价指标。结果表明,煤焦的Ｘ和Ｂ随着温度和压力的增加而增加;煤焦的气化反应活性顺序为：褐煤焦＞气煤焦＞贫煤焦。     

Reaction kinetics of pulverized coal-chars derived from inertinite-rich coal discards: Gasification with carbon dioxide and steam

An investigation was undertaken to determine the kinetics of gasification of coal-chars (pulverized) derived from typical South African inertinite-rich (high-ash) coals involving char reactions with carbon dioxide and steam and the effects of carbon monoxide and hydrogen. The chars used were characterized with respect to structural, chemical, mineralogical and petrographic (maceral content) properties and gasification experiments were conducted in a TGA at atmospheric pressure with different gas mixtures within a temperature range of 1073–1223 K. The shrinking core model with a controlling surface reaction was shown to be applicable for the gasification of pulverized coal-chars consisting of essentially of carbon-rich particles. The validity of this model can be attributed to the core having an exceptional low porosity (high inertinite parent coal) and consequently negligible penetration of the gases. It was found that the gasification intrinsic reaction rates could be adequately described by Langmuir–Hinshelwood type rate equations and that established equations have been validated with corresponding constants according to new data processing procedures. It was found that the reaction rate constants for coal-chars derived from inertinite-rich (76–80%) coal discards were different to results published in the literature and that the intrinsic reaction rates differed only slightly (order of magnitude) for coal-chars with similar maceral (inertinite) compositions and different total ash contents. The marked inhibiting effect of the carbon monoxide and hydrogen on the carbon dioxide/carbon monoxide and steam/hydrogen gasification reactions is shown and relevant constants are reported. Experiments were done and models evaluated for a multi-component gasification mixture consisting of a feed mixture of carbon dioxide, carbon monoxide, steam and hydrogen. Reaction constants determined with results from binary mixtures were used to predict results and it was found that the overall rate is best described with the assumption that the important reactions proceed on separate sites.     

煤的水蒸汽及二氧化碳高温气化活性评价

选用燃料比(固定碳/挥发份)1到8,变质程度从褐煤到无烟煤(包括粘结性的和非粘结性的)的六种煤焦为试样,在1100—1400℃下,用热重量法进行了含O_2、H_2O、CO_2气化剂的实验室气化,用修正体积反应模型式进行了数据处理和活性评价.并将高温区的结果与低温区(1000℃以下)的实验结果进行了比较.     

The catalytic steam gasification of chars from various sources by K2CO3

Gasification of a char prepared from hydrocracked residuum was compared with the gasification of chars prepared from bituminous and sub-bituminous Canadian coals, wood and graphite. Each material was mixed with 10 mass per cent K₂CO₃ and pyrolyzed up to 900°C. The yield of char was inversely proportional to the amount of volatile matter in the original material. The char prepared from hydrocracked residuum was different from the others. The other chars all followed zero-order gasification kinetics. Gasification of char prepared from the residuum was first-order in the solid. The development of a liquid phase during the pyrolysis of the residuum to char may explain this difference. The gasification rate of the char. from residuum was slower than the rates with the two coal chars and the wood char, but faster than the gasification rate of graphite. A combination of transient experiments and X-ray photoelectron spectroscopic (XPS) measurements indicated that hydrogen was formed almost instantaneously when steam reacted with the char. XPS spectra at liquid nitrogen temperature indicated that during gasification the formation of carbon oxygen bonds proceeded in the following sequence: COH, CO and CO.     

Effect of pressure on gasification reactivity of three Chinese coals with different ranks

The gasification reactivities of three kinds of different coal ranks (Huolinhe lignite, Shenmu bituminous coal, and Jincheng anthracite) with CO₂ and H₂O was carried out on a self-made pressurized fixed-bed reactor at increased pressures (up to 1.0 MPa). The physicochemical characteristics of the chars at various levels of carbon conversion were studied via scanning electron microscopy (SEM), X-ray diffraction (XRD), and BET surface area. Results show that the char gasification reactivity increases with increasing partial pressure. The gasification reaction is controlled by pore diffusion, the rate decreases with increasing total system pressure, and under chemical kinetic control there is no pressure dependence. In general, gasification rates decrease for coals of progressively higher rank. The experimental results could be well described by the shrinking core model for three chars during steam and CO₂ gasification. The values of reaction order n with steam were 0.49, 0.46, 0.43, respectively. Meanwhile, the values of reaction order n with CO₂ were 0.31, 0.28, 0.26, respectively. With the coal rank increasing, the pressure order m is higher, the activation energies increase slightly with steam, and the activation energy with CO₂ increases noticeably. As the carbon conversion increases, the degree of graphitization is enhanced. The surface area of the gasified char increases rapidly with the progress of gasification and peaks at about 40% of char gasification.     

Factors affecting steam gasification rate of low rank coal char in a pressurized fluidized bed

A high-pressure bubbling fluidized bed reactor was used to study the steam gasification of coal char under pressure. Indonesian sub-bituminous coal char (Adaro) and Australian lignite char (Loy Yang) were gasified with steam in the reactor at temperatures below 1173 K and at total pressures ranging from 0.1 to 0.5 MPa. The steam gasification rates of the coal chars were determined by analysis of the gaseous products. Activation energies for the steam gasification of the chars were as high as about 250 kJ/mol, which suggests that the temperature dependence of the gasification was substantial. The apparent gasification rates under the study conditions were described by a Langmuir–Hinshelwood (L–H)-type equation. Analysis of the reaction kinetics on the basis of the L–H equation indicated that increasing steam pressure effectively increased the gasification rate.     

煤焦加压化学链气化反应特性和机理

采用机械混合法制备的Fe₂O₃/膨润土为载氧体,在加压固定床中进行煤焦化学链气化试验和动力学研究,借助拉曼和N₂吸附等温线表征手段,分析压力对煤焦反应活性及煤焦碳结构和孔结构的影响,讨论煤焦加压化学链气化反应机理。结果表明：系统总压从0.46MPa增加至0.80MPa时,煤焦化学链气化反应速率从0.0159min^-1提高至0.0309min^-1;水蒸气分压增加75%,H₂/CO摩尔比值增加74%。煤焦加压化学链气化过程可以用随机孔模型（RPM）描述,系统总压增加有利于内部扩散。系统总压增大煤焦的比表面积增加,水蒸气分压增大煤焦的反应活性提高,因而提高了煤焦化学链气化反应速率。     

Fe/赤泥催化水蒸气气化煤焦的反应性与微结构特性

利用固定床反应器和自制Fe/赤泥（RM）、RM催化剂,进行了900℃煤焦/催化剂不同质量比的水蒸气气化实验,并采用原位红外（FTIR）、物理吸附仪（BET）、拉曼光谱（Raman）等测试手段,分析了催化气化过程中不同阶段煤焦的气化反应性、表面官能团、孔隙结构和碳微晶结构的演变规律。结果表明,Fe1/RM2催化剂可显著提高煤焦-水蒸气的气化反应性。在Fe1/RM2/煤焦-水蒸气反应过程中,煤焦表面形成-CH₂、-COOH、酚羟基等活性官能团并与Fe1/RM2活性组分相互作用,形成新的小分子基团或化合物;煤焦的比表面积先增大后减小（6.98～323.22m²/g）,平均孔径呈现相反的变化趋势（2.91～11.25nm）;碳有序化程度先降低后提高,碳转化率为36%煤焦中无定形碳的相对含量最高（0.371）。在煤焦-Fe1/RM2-水蒸气反应初期（X_C<36%）,煤焦表面活性基团增多、比表面积增大、有序化程度降低,综合提高了煤焦-水蒸气气化反应性;降低36%≤X_C≤62%阶段的碳有序化程度,对煤焦气化反应性的提高具有显著意义。     

煤焦的水蒸汽气化反应速率解析

为得到煤的气化技术开发的基础数据,在固定床微分反应器中,于常压、动力学控制条件下,对国内外七种煤半焦进行水蒸汽气化实验.将煤的气化反应速率用水蒸汽分压及煤的未转化率的幂函数型式表示时,其结果是与水蒸汽分压及细孔表面积的一次方成正比.从理论上推导出了在反应过程中包括考虑煤的细孔结构变化的动力学方程,并且导出了含碳组分气体的生成速率与煤的气化速率的相关式.用Bhatia等人的随机细孔模型表示反应过程中的细孔表面积变化时,计算结果与实测值相当吻合.     

滴管炉内不同煤阶煤焦水蒸气气化反应特性

在滴管炉内对煤焦与水蒸气气化反应进行了实验研究,考察了煤阶、气化温度、水蒸气与进料煤焦质量比（气焦比）对气化气体产物释放特性以及煤焦转化率的影响。实验温度为1100、1200、1300和1400℃,气焦比分别为0.4：1、0.6：1和1：1。研究发现：滴管炉内不同煤焦的水蒸气气化气体产物以H₂含量最高,CH₄含量最低。不同煤阶热解焦、气化温度以及气焦比的变化影响滴管炉内水蒸气气化产物气体组成和转化率的高低。随气化温度的升高,神府煤焦和北宿煤焦气化气体产物中H₂和CO产率不断增大,H₂/CO的比值则逐渐减小,碳转化率有不断增加的趋势。在气化温度大于1200℃的条件下,当气焦比从0.4：1增至0.6：1,神府煤焦和北宿煤焦的碳转化率变化幅度不大（5%以内）;当气焦比从0.6：1增至1：1,北宿煤焦的碳转化率略微降低,而神府煤焦的碳转化率增幅则在15%以上。     

Gasification of wood char and effects of intraparticle transport

Kinetic parameters for gasification of hybrid poplar spp. char have been measured. A differential reactor was used to obtain rate data for catalytic and non-catalytic reactions of small wood char particles (1–2 mm in size) at 100 kPa for temperatures in the range 400–700 °C, steam partial pressures between 45–100 kPa, and space velocities in the range 2.0–7.3 s^?1 During pyrolysis of wood without the addition of either K₂CO₃ or Na₂CO₃, the cellular structure of the wood was preserved. Additionally, this cellular structure remained intact during most of the gasification process. Addition of K₂CO₃ and Na₂CO₃ before pyrolysis caused a degradation of the regular cellular structure and an increase in the rate of gasification of the resulting char. Effectiveness factor calculations were made for particles of various sizes and results indicate that diffusion control of the gasification reaction becomes important for particles larger than 0.5 CM.     

升温速率及水蒸气分压改变对神华煤焦及其显微组分焦气化反应性的影响

用非等温热重法考察了神华煤焦及其显微组分富集物焦的水蒸气气化反应,分析了升温速率、水蒸气分压改变对煤焦及其显微组分富集物焦气化反应性的影响。利用最大反应速率和半衰期两种方法评价了所选样品的气化反应性。结果表明：对神华煤而言,在相同的气化反应条件下,当升温速率和水蒸气分压发生改变时,其气化反应性顺序均为,镜质组富集物焦〉原煤焦〉惰质组富集物焦。