Thermogravimetric analysis of gasification reactivity of coal chars with steam and CO2 at moderate temperatures

Comparative study on the gasification reactivity of the three types of Chinese coal chars with steam and CO₂ at 850–1050 °C was conducted by isothermal thermogravimetric analysis. The effects of coal rank, pore structure, ash behavior, and gasification temperature on the gasification reactivity of coal chars were investigated. It is found that the gasification reactivity difference between different coal chars changes with reaction degree and gasification temperature, and has no immediate connection with coal rank and initial pore structure. Ash behavior plays an important role in the char reactivity, and changes with gasification temperature and reaction degree due to the variation in the compositions and relative amount. The influence of pore structure is more noticeable during a relatively moderate reaction process. The relative reactivity ratio of steam to CO₂ gasification generally decreases with the increasing temperature, and is related with the catalytic effect of inherent minerals. The characteristic parameters of the chars were analyzed, finding that the value of half reaction specific rate is approximate to the average specific rate under the same conditions. The nth-order distributed activation energy model is proposed to describe the coal char gasification process, and the results show that the activation energy increases with the increasing carbon conversion.     

不同彬县焦的水蒸气气化反应动力学研究

在常压,900℃～1050℃考察了彬县煤的三种焦样（常规方法制焦、快速热解焦和脱灰快速热解焦）在热天平上的水蒸气气化反应。考察了温度和焦种对水蒸气气化反应的影响。对比了三种焦的动力学参数和比表面积。结果表明,气化温度是影响煤焦气化反应速率的主要因素,提高50℃,反应速率增加一倍。快速热解焦的反应速率在相同反应条件下明显大于慢速焦。三种焦的表观活化能以快速焦最大,因而反应速率受温度的影响也最大,快速脱灰焦次之,慢速焦最小。     

重油残渣焦水蒸气气化反应特性的研究

采用常压热重分析仪,研究了重油残渣焦的水蒸气气化反应性,主要考察了热解温度、升温速率、停留时间及气化反应温度、气化剂分压对重油残渣焦水蒸气气化反应的影响,并借助XRD对残渣焦进行了分析表征。结果表明,气化温度950℃,60%水蒸气分压条件下,快速热解焦比慢速热解焦的气化反应性高;随制焦温度(500~900℃)的提高及停留时间的延长,焦的气化反应性降低。气化温度是影响重油残渣焦气化反应的主要因素,在900~1 050℃,温度每提高50℃,重油残渣焦气化反应时间几乎减半;随着水蒸气分压的提高,气化反应速率增加,但当气化剂分压高于60% 时,其对气化反应影响较小。采用均相模型和缩核模型对重油残渣焦气化曲线进行模拟,结果发现,缩核模型模拟相关性较好,其活化能为195.0 kJ/mol,指前因子A₀为2.6×10⁷min^-1。     

稻秆半焦与CO2气化反应特性的研究

利用三种热解炉装置,分别在热解终温550℃～950℃、加热速率0.1K/s～500K/s下热解制取稻秆半焦。采用等温热重法,在STA409综合热分析仪上进行了稻秆半焦与CO₂的气化实验,考察了热解终温、热解速率以及气化温度对半焦气化反应性的影响。研究表明,热解条件对稻秆半焦的反应性影响很大。在热解终温为550℃～950℃时,随着热解温度的提高,其气化反应性呈下降趋势;热解速率越高,其气化反应性越好。在850℃～950℃,提高气化温度能提高稻秆半焦与CO₂的反应性。采用扫描电镜技术观测了0.1K/s和500K/s 两种热解速率下半焦的表面形貌。结果显示,后者具有更加丰富的孔隙结构,且大孔结构明显多于前者。采用混合反应模型描述了稻秆半焦与CO₂的气化反应过程,求取了反应动力学参数。     

CO2 gasification of woody biomass chars: The influence of K and Si on char reactivity

Although the influence of metallic and alkaline elements on biomass char reactivity is well known, a quantitative assessment of this catalytic effect is hard to obtain because of the chemical and textural complexity of biomass. The effect of K and Si on the CO₂ gasification reactivity of a biomass char was studied using thermogravimetric analysis. A beech sample was pyrolyzed at 800 °C and then impregnated with known amounts of silicon or potassium allowing to obtain a wide range of K/Si ratios. The reactivity of the impregnated samples was studied under a CO₂ (20% vol.) atmosphere. The results show that at low conversion ratios, the char reactivity depends on its textural properties, with strong diffusional limitations. When conversion reaches 60%, the presence of a catalyst (K) and an inhibitor (Si) becomes the major parameter influencing reactivity. From these experiments, a general trend was obtained between K/Si ratio and reactivity as a function of conversion.     

生物质焦制备条件对其燃烧反应特性的影响

在热重分析仪上,研究了生物质焦的制备条件对其燃烧反应特性的影响。生物质焦由闪速裂解技术制得,裂解温度为 748 K、773 K和823 K;原料含水质量分数为0、7.0%和11.3%。研究发现,生物质焦中挥发性物质的质量分数和H/C质量比随裂解温度的增加而降低,其燃烧反应性随裂解温度的增加而降低;与高裂解温度条件下制得的生物质焦相比,低裂解温度条件下制得的生物质焦具有较高的反应活化能和对燃烧温度更敏感。原料含水量对生物质焦的燃烧反应特性影响很小;但对高裂解温度条件下制得的生物质焦中的挥发性组分含量有较大的影响。简化的生物质焦本征燃烧反应幂函数动力学模型可以很好地描述其燃烧行为。     

高温下热解温度对煤焦孔隙结构的影响

利用高温沉降炉在1500K～1800K制备京西无烟煤煤焦,使用化学吸附法测定不同热解温度下煤焦比表面积及孔容积与孔径的分布特征,并采用SEM观察煤焦颗粒表面的形态,分析了高温下热解温度对煤焦孔隙结构的影响规律。结果表明,煤焦的比表面积主要由孔径小于10nm的微孔和中孔构成,而其孔容积则主要由孔径为2nm~50nm的中孔构成。高温下煤焦比表面积和孔容积随热解温度的升高,呈现先增大后减小的非单调变化现象,转折温度约为1600K。出现这种变化的主要原因是煤焦在热解温度超过1600K后开始烧结,产生较为光滑致密的表面结构,部分孔隙封闭。     

不同水蒸气浓度下褐煤气化半焦的活化及机理

以胜利褐煤为原料,利用流化床/固定床石英反应器,进行褐煤气化实验,采用BET、Raman、FT-IR、微波消解ICPAES、TGA等技术表征半焦。结果表明,在800℃水蒸气气氛中,醚基裂解造成芳环间短链或无定形碳含量减少,从而削弱石墨化进程,进而提高芳香结构的缺陷程度,是半焦活化的内在原因。提高水蒸气浓度(10%-25%),半焦的反应性降低,是因为气化过程中半焦的活性位再生能力变弱,而反应(Ar,R-CO-Ar,R+2H_2O→Ar,R-O-Ar,R+2H_2+CO_2)增强,导致醚基含量增加,是半焦活性位再生能力变弱的内在原因。继续提高水蒸气浓度(25%-40%),半焦的反应性略有提高,是因为芳香小环(3-5环)缺陷结构含量增加,而反应(Ar,R-CH=CH_2+H_2O→Ar,R-CO-CH_3+H_2)和反应(Ar,R-+H-→Ar,R-H)增强是芳香小环缺陷结构含量增加的内在原因。     

中国无烟煤焦气化活性的研究--水蒸气与二氧化碳气化活性的比较

在常压和920℃~1050℃下,采用热重方法,进行了六种中国典型无烟煤焦水蒸气与二氧化碳气化活性比较的研究。结果表明,无烟煤焦与水蒸气气化反应的活性与无烟煤的煤化程度相对应,无烟煤煤化程度越高,水蒸气气化反应活性越小。无烟煤焦与二氧化碳气化反应的活性与煤中矿物质的催化作用有密切关系,煤中矿物质的催化作用越大,二氧化碳气化反应活性越大。无烟煤焦与二氧化碳气化反应活性明显小于与水蒸气气化反应活性,后者比前者大10倍左右。初步探讨了无烟煤焦与水蒸气和二氧化碳的气化机理。     

热解压力对生物质焦结构及气化反应性能的影响

利用加压固定床反应器、吸附仪、X射线衍射仪、元素分析仪、电感耦合等离子原子发射光谱仪等考察了热解压力对生物质半焦(以下简称半焦)产率、物化结构、元素组成的影响规律。同时,利用热天平对不同热解压力下所制半焦的气化行为进行了考察。结果表明,随热解压力升高,半焦产率增大,当压力升至1.0 MPa后,半焦产率基本不变;半焦中C元素含量随热解压力的升高而增加,而H元素含量和BET比表面积则减小;此外,随热解压力升高,玉米秸秆焦和锯末焦的石墨化程度增强,而稻壳焦的石墨化程度则基本不受热解压力影响。气化反应的研究表明,玉米秸秆焦及锯末焦的平均气化反应速率随热解压力的提高而减小,而稻壳焦的平均气化反应速率基本不受热解压力的影响。热解压力对半焦BET比表面积及碳微晶结构的影响规律与气化反应速率变化规律的对比研究表明,热解压力引起半焦微晶结构的变化是造成热解压力对半焦气化反应速率影响的主要原因。     

An experimental investigation into the gasification reactivity and structure of agricultural waste chars

The gasification reactivity as well as physical and chemical structure of chars generated from two kinds of agricultural waste (i.e. corn straw and wheat straw) were studied to better understand the role of lower pyrolysis temperatures and lower heating rates on the gasification characteristics of agricultural waste chars. Char samples were generated in a one-stage quartz fixed-bed reactor. The carbon dioxide (CO₂) gasification reactivity of chars was measured by thermogravimetric (TGA) analysis. Scanning electron microscopy (SEM) analysis, surface area (BET) analysis, Fourier transform infrared spectroscopy (FTIR) analysis and X-ray diffractometry (XRD) analysis were employed to determine the effect of operating conditions on the char structure. Char gasification reactivities decreased with increasing pyrolysis temperatures. The char particles generated under high pyrolysis temperatures had many smaller pores with thinner cell walls, larger surface areas, and some melting. Results indicated that many functional groups’ bands decreased and even disappeared with an increasing pyrolysis temperature. The chars’ microcrystalline became larger at high pyrolysis temperatures. The reactivity of wheat straw char is higher than corn straw char. The difference in the gasification reactivity of agricultural waste chars generated at different pyrolysis temperatures correlated well with the effect of pyrolysis temperatures on the agricultural waste char structure.     

Kinetic models comparison for steam gasification of different nature fuel chars

The reactivity in steam of five different types of solid fuels (two coals, two types of biomass and a petcoke) has been studied. The fuel chars were obtained by pyrolysis in a fixed-bed reactor at a temperature of 1373 K for 30 min. The gasification tests were carried out by thermogravimetric analysis (TG) at different temperatures and steam concentrations. The reactivity study was conducted in the kinetically controlled regime and three representative gas-solid models, volumetric model (VM), grain model (GM) and random pore model (RPM), were applied in order to describe the reactive behaviour of the chars during steam gasification. The kinetic parameters of these models were derived and the ability of the models to predict conversion and char reactivity during gasification was assessed. The best model for describing the behaviour of the samples was the RPM. The effect of the partial pressure of steam in gasification was studied, and the reaction order with respect to steam was determined. The reactivity of the chars was compared by means of a reactivity index. Biomass exhibited a higher reactivity than coals and petcoke. However, significant differences in reactivity were observed between the two types of biomass used, which could be due to catalytic effects.     

Preparation and characterization of pyrolytic chars from different biomass samples

In the present work four different biomass samples (pine cone, soybean cake, corn stalk and peanut shell) were pyrolyzed to 550 °C in an inert gas atmosphere and a comparison between the properties of chars produced has been performed. Characterization of biomass samples was carried out with FT-IR, ¹³C NMR, SEM and EDX. The influence of the parent material on char quality was investigated. The chars were characterized by their proximate and ultimate analysis and surface areas by N₂ adsorption at 77 K using BET equation. The morphological changes in carbonaceous solids were observed by scanning electron microscopy (SEM), and FT-IR spectra were obtained to evaluate the functional groups. The results obtained from the different techniques were combined to give an overview of the chemical and physical properties of the biomass char samples.     

高碳转化率下热解神府煤焦-CO2高温气化反应性

用热天平等温热重法研究了6种不同热解速率和热解终温的神府煤焦在反应温度1200℃～1400℃的CO2气化反应性。研究了高碳转化率下,反应温度、热解终温和热解速率对快速和慢速热解焦高温反应性的影响。结果表明,快速热解焦比慢速热解焦的反应性好;随气化温度的提高,煤焦反应性的总体趋势增强,反应温度1300℃～1400℃时,3种快速热解焦的反应速率出现重叠;碳转化率为90%～98%时,慢速和快速热解焦的平均表观活化能为59.64kJ/mol～105.92kJ/mol和34.47kJ/mol～40.87kJ/mol,且气化反应以扩散控制步骤为主。     

棕榈壳焦CO2气化过程中反应性及结构特性研究

850℃下,利用管式炉制备了不同转化率的棕榈壳CO₂气化焦,通过热重分析仪研究了气化焦的CO₂气化反应性,采用比表面积分析、拉曼光谱、X射线荧光光谱和扫描电镜-能谱等分析手段,考察了气化焦孔隙结构、碳组成、矿物元素含量与分布随转化率的变化。结果表明,在CO₂气化过程中,随着转化率的提高,棕榈壳气化焦固定碳的含量逐渐降低,有序化碳的相对含量为0.30~0.33,对气化过程起到一定的抑制作用;灰分含量逐渐增加,但气化反应指数R_s呈现先降低后升高的过程。转化率小于23%时,R_s与气化焦比表面积的变化趋势一致;23%< 转化率< 31%时,R_s基本不变;31%< 转化率< 68%时,比表面积随转化率线性增加,R_s取决于孔隙比表面积、矿物元素催化2个因素的协同作用,当转化率> 56 %时,该催化作用变得明显,同时碳的有序化程度开始降低;转化率> 68%时,R_s主要受矿物元素的催化作用控制。     

Investigation into the kinetics of pressurized steam gasification of chars with different coal ranks

The steam gasification of coal chars derived from three different ranks of typical Chinese coals was studied in a pressurized fixed-bed differential reactor at elevated pressure (up to 2.0 MPa). Three mathematical models [volumetric model (VM), grain model (GM), and random pore model (RPM)] for the gasification kinetics of different chars were validated, through which the kinetic parameters were obtained and discussed. The results show that the evolution trend of the coal char gasification rate with carbon conversion differs from coal ranks and has little change with pressure and temperature. The pressurized gasification process of the Shenmu sub-bituminous coal char (SM char) and the Jingcheng anthracite char (JC char) can be well-predicted by the RPM, while that of the Huolinhe lignite char can be better described by the VM. The pressure has little effect on the options of the reaction kinetic models for the three chars. The kinetic parameter E is almost a constant independent of pressure, while k ₀ changes with pressure, and it seems that k ₀ would be almost a constant over 1.0 MPa for SM and JC chars. The reaction order decreases with increasing the total system pressure and differs from different coal types.     

Catalytic gasification of Pakistani Lakhra and Thar lignite chars in steam gasification

采用热重法在常压与700℃~900℃条件下的水蒸气气化过程,对两种巴基斯坦Lakhra和Thar褐煤半焦进行了单一和混合催化剂(即3%钙和5%钠-黑液单一催化剂及一种3%钙和5%钠-黑液混合催化剂)对碳转化率、气化反应速率常数及活化能、有害污染含硫气体相对量的催化效应研究.两者Lakhra和Thar褐煤半焦经直接气化就可获得高的碳转化率,但采用纸浆黑液催化剂可使气化速率变得很快.含灰高的Thar褐煤半焦在纸浆黑液催化气化过程更易生成一些复杂的硅酸盐,从而导致比含灰低的Lakhra褐煤半焦出现一个更低的转化率.在水蒸气气化过程由半焦和纸浆黑液自身所产生的SO2 和 H2S含硫气体可为存在于纸浆黑液中的Ca盐所捕获而完成脱硫过程,但这一过程在低于900℃时更有效.缩芯模型 (SCM)可较好地用来关联转化率与时间的关系并给出不同温度下的反应速率常数k.基于阿累尼乌斯方程预测了反应活化能Ea 和指前因子A.在纸浆黑液和钙混合催化及纸浆黑液催化剂时,Lakhra褐煤半焦的Ea分别为44.7kJ/mol和 59.6kJ/mol明显小于Thar褐煤半焦的Ea=114.6kJ/mol 和 Ea=100.8kJ/mol,同样也小于无催化剂纯半焦气化时Lakhra褐煤半焦的Ea=161.2kJ/mol和Thar半焦的Ea=124.8kJ/mol.     

High-pressure reactivity of propene

The phase diagram of propene has been investigated at high pressure by using the diamond anvil cell technique and Fourier transform infrared spectroscopy. The pressure conditions necessary to induce a spontaneous reaction of the sample have been found at different temperatures, allowing the stability boundary of propene to be drawn. The reaction is diffusion controlled and seems to occur only in the fluid phase, implying a slope inversion of the stability boundary at about 250 K. The product of the reaction is a mixture of linear oligomers independently of the P-T conditions. The activation volume and energy of the process have been obtained from the kinetic data. Also the activation of the reaction by laser absorption has been carefully studied. A high proton mobility has been identified as the likely reason that limits the lengthening of the chain up to six to eight monomeric units preventing the polymer formation.     

The kinetics of CO2 gasification of coal chars

The gasification reactivities of three char samples derived from coals of varying ranks (“Turów” lignite, “Piast”, and “Wieczorek” sub-bituminous coals) toward CO₂ were investigated isothermally using thermogravimetric analysis. Kinetic behavior was studied at temperatures of 900, 950, and 1,000 °C under atmospheric pressure. Conditions for the chemical-controlled regime were established at these temperatures and pressure. In this paper, four kinetic models were applied to describe the varying conversion rate: volumetric model, grain model, modified volumetric model, and random pore model. From these models, only the random pore and the volumetric models positively corresponded to nearly the entire range of experimental results. Calculated values of activation energy for study samples were in the range of 180–250 kJ mol^?1, which is in accordance with other reported data. Moreover, the obtained results confirmed the significant impact of parent coal rank on its char reactivity, offering possibilities in the approximation of coal char kinetic behavior after further more detailed studies with a larger number of samples.     

高温下煤焦的碳微晶及孔结构的演变行为

以贵州煤为原料,在热解温度950℃~1400℃制备了各种慢速和快速热解焦,主要对高温热解过程中煤焦的碳微晶和孔结构的演变行为进行了研究,同时也研究了高温气化过程中煤焦的孔结构变化规律。结果表明,慢速热解焦和快速热解焦的C和H含量明显不同;随热解温度的升高,煤焦的碳微晶结构向有序化方向发展,但慢速热解煤焦比快速热解煤焦的"石墨化"程度大;快速热解煤焦的微孔比表面积和微孔容积明显高于慢速热解煤焦,即快速热解煤焦的孔隙结构明显比慢速热解煤焦发达;在气化反应初期,煤焦的微孔比表面积下降,微中孔比表面积增加,反应后期煤焦的总比表面积快速下降。