气流床气化炉综合模型及颗粒粒径对气化结果的影响研究

采用颗粒停留时间分布表征炉内颗粒流动,建立了一种考虑了炉体结构、颗粒粒径以及煤焦反应动力学的气流床气化炉综合模型,其中包含了煤脱挥发份、均相反应、非均相反应、气-固相能量方程、相间传热等子模型。模拟结果与多喷嘴对置式水煤浆气化炉工业运行数据吻合良好,考察了气相组分、温度以及不同粒径颗粒的碳转化率和温度在炉内的一维无因次分布。对模拟结果的分析表明:煤颗粒的预热、脱挥发份和燃烧过程在约30 ms内完成,气化过程占颗粒反应历程的绝大部分;气化炉内100μm以下的小颗粒升温速率快,且温度较高,碳转化率基本接近100%;而200μm以上的大颗粒升温速率较慢,碳转化率较低,影响了气化炉整体碳转化率。     

水冷壁气化炉内熔渣流动特性模型

通过将3D气化炉模型、熔渣一维流动传热模型和颗粒壁面捕捉模型耦合,对工业水煤浆水冷壁气化炉内的熔渣流动特性进行模型研究。重点分析了颗粒壁面行为对气化炉结渣的影响以及氧煤比变化对于渣层厚度的影响,并简要分析了水冷壁气化炉和耐火砖气化炉的差异。研究结果表明:大粒径颗粒易于被壁面捕捉,利于穹顶和直筒段渣层的形成,但不利于碳转化率的提高;小粒径颗粒具有高碳转化率,是下游细灰的主要来源,容易加剧下游受热面和灰黑水系统的负担;水冷壁气化炉内形成的固态渣层是气化炉热阻的主要组成部分,能够起到"以渣抗渣"的作用。     

气流床煤气化炉壁面反应模型

建立了气流床煤气化炉煤灰渣颗粒沉积和壁面反应模型,相应完善了渣层流动、传热传质和相变模型,发展了数值模拟方法,并以国内某型两段式干煤粉加压气流床煤气化中试炉为对象进行了模拟。利用建立的模型可以得到壁面反应速率、渣层含碳量、固态渣层厚度、液态渣层厚度、渣层平均温度和液态渣层平均速度等。结果表明:氧煤比升高,渣层平均温度升高,固态渣层厚度、液态渣层厚度和气化炉出口灰渣含碳量降低。计算得到的灰渣含碳量在14%左右,整体碳转化率为95.2%左右,与实际值相近。通过模拟发现壁面反应对于所分析气化炉的碳转化率、排渣含碳量、壁面渣层流动和温度状态具有重要影响,进而影响气化炉的安全稳定运行。     

载气对两段式干煤粉加压气化炉气化特性的影响

相比于N_2,CO_2作为气化炉煤粉载气会降低合成气中N_2的含量而有利于后续CO_2捕集,但O_2在CO_2中较小的扩散系数会影响焦炭的反应特性,进而影响气化炉运行结果。为此,考虑到气化炉中较高的CO含量及其对煤气化反应的抑制作用,将Langmuir-Hinshelwood动力学模型与缩核模型相结合,提出一个改进的焦炭反应模型,并对两段式干煤粉气化炉内的流场、温度场和组分浓度场进行了模拟分析,结果与实炉实测数据一致。在此基础上,模拟分析了气化炉在不同煤粉载气(N_2、CO_2)、两种二段给煤量下的气化特性。结果表明,煤粉载气由N_2改为CO_2后,由于O_2在CO_2中较低的扩散速率,一段气化室喷嘴区域气体温度和碳转化率降低,该区域CO_2增多对焦炭-CO_2反应的促进作用对提高碳转化率的影响较小;在一段气化室喷嘴区域之上,O_2浓度较低导致O_2扩散性影响减弱,同时CO_2增多促进焦炭-CO_2反应进而提高碳转化率。研究结果还证实,煤粉载气由N_2改为CO_2会促进CO的生成,抑制H_2的生成。     

煤粉柔和气化炉冷态和热态流场特性数值模拟

基于煤粉柔和气化炉工况特征,设计了热负荷0.5 MW的煤粉气化炉模型,采用数值模拟手段研究了冷态情况下射流喷嘴相对位置、射流速度、煤粉粒径对烟气回流、停留时间、颗粒浓度的影响,以及热态情况下变工况条件对炉膛温度场、组分场分布和碳转化率的影响,并将热态模拟结果与实验结果进行了对比,验证了模拟结果的正确性。     

煤颗粒对化学热回收二段式煤气化工艺的影响

基于碳和水蒸气、CO2气化的吸热化学反应原理,开发出回收煤气显热的高效化学热回收二段式煤气化工艺,可有效提高现有气流床气化技术的热效率.文中在实验室规模的热态反应平台上,对二段气化床层内煤颗粒粒径对二段床层内的温度分布、二段气化效率及煤渣层残炭率的分布规律进行了实验.研究优选出二段气化炉内煤颗粒粒径范围为10-15 m...     

煤气化技术工业应用概况及工艺选择(下)

正1.3气流床气化工艺气流床气化工艺有干法进料和湿法进料2种形式,将煤粉(粒度100μm)或煤浆与气化剂一起由喷嘴高速喷入气化炉,气化炉内气流速率超过颗粒夹带气速,气固并流运动并发生高温燃烧和气化反应(约1 500℃),煤灰呈熔融状排出气化炉。气流床气化的高温、高压、强混合过程有利于提高气化强度,具有生产能力大、碳转化率高、煤气     

基于CPFD方法的流化床生物质气化数值模拟

基于计算颗粒流体动力学（CPFD）建立了三维鼓泡流化床水蒸气-空气混合气化的数值模型，并进行了模型验证，结果表明模拟和实验具有良好的一致性。在该模型的基础上，研究了气化炉内气体分布以及温度分布；同时探究了生物质属性（颗粒粒径、含水率、种类）以及操作条件（气化温度、床料高度）对气化特性的影响。结果表明，生物质颗粒粒径对气化性能的影响存在一个最优值，平均粒径为0.6 mm是最佳的；较高的含水率会降低可燃气体产量，不利于气化反应的进行；四种生物质中，锯末气化的效率最高、可燃气体产量最大、气体热值最高，稻壳仅次于锯末但其碳转化率高于锯末；提高气化温度可以增加可燃气体的比例、提高气化效率；而初始床层高度的变化可以改变H₂/CO的比例。本实验为生物质水蒸气/空气气化提供了理论参考，有助于生物质原料的选取和处理，也有助于气化炉的放大和优化。     

灰熔聚气化炉内气体与固体混合特性的研究

气化炉内的气化剂与煤粉的混合特性直接影响着气化炉内的碳转化率和灰熔聚流化床气化炉的热效率。研究气化炉内气体和固体颗粒的混合特性,掌握炉内气体和固体颗粒的轴向和径向的运动规律,对认识床内传热和传质机理具有重要的意义。基于欧拉双流体模型,结合颗粒动力学理论,应用商用FLUENT软件,对太原化学工业集团有限公司运行的灰熔聚流化床气化炉内的气体与固体的混合特性进行了数值模拟。     

多喷嘴对置式水煤浆气化炉炉渣特性研究

为实现多喷嘴对置式水煤浆气化炉炉渣资源化、减量化、无害化利用,对兖矿集团陕西未来能源化工有限公司气化炉粗渣和细渣进行分析,研究气化渣的粒度分布、烧失量、化学组成、显微结构、残碳分布、表面形态等特性,并对其综合利用方向提出建议。结果表明,气化细渣、粗渣烧失量均较高,粗渣为18.79%,细渣为30.57%,未燃碳是烧失量的主要成分,细渣未燃碳高于粗渣。未燃碳在粗、细渣中的分布具有一定规律性,细渣的碳含量随粒径增大而增加,粗渣碳主要分布在0.500~0.125 mm中等粒径。SEM结果表明,气化残渣中的物质由多孔不规则颗粒、黏结球形颗粒和孤立的大球形颗粒组成。其中,多孔不规则颗粒的主要成分为碳,球形颗粒主要成分为硅铝矿物。粗渣、细渣孔隙以4~10 nm介孔为主,细渣的孔结构和比表面积优于粗渣。试验炉渣可作为循环流化床掺烧燃料、废水处理吸附材料、建材掺混材料使用。     

Operation characteristics of 1 ton/day-scale coal gasifier with additional stage

A one-stage coal gasifier was modified to accommodate the two stages of coal feeding. Operating characteristics were compared between the one-stage and two-stage gasification in terms of syngas composition, carbon conversion, shape and inner structure of produced slags, characteristics of particle size distribution in entrained fines, and effects on particulate removal facilities. Temperature at the second stage of the gasifier resulted in lower values, which confirms the performance of the second stage as a reduction area by endothermic reactions. The results suggest that the 10–20% increase in coal feeding to the second stage might not cause much loss in carbon conversion. Produced slag and the performance of metal filters and water scrubber were similar with the earlier results from one-stage gasification tests. The two-stage gasification appears to help in increasing the cold gas efficiency for the certain operating range. Two-stage gasification had an impact on the 0.1–1 μm size of entrained fines, which appear to be cenospheres that occur during the rapid quenching in temperature.     

The influence of geometrical factors and feedstock on gasification in a high temperature fluidised bed

Results are presented for gasification of coal and char by means of air or air-steam mixtures in fluidised bed reactors of three different volumes. Two sizes of coal feedstock particles, 0.5-1.0 mm and 1.0-1.5 mm, and one size of char particles, 0.5-1.5 mm, were used. The calorific value of generated gas and the carbon conversion are presented as a function of particle residence time. For coal gasification higher carbon conversion has been obtained at the same particle residence time than for char gasification. For the steam gasification, a lower gas heating value of about 4 MJ/m³ (S.T.P.) was obtained.     

Dynamic modeling and simulation of reaction,slag behavior,and heat transfer to water-cooling wall of shell entrained-flow gasifier

A mathematical model is developed to simulate a pilot Shell entrained-flow coal gasifier. Submodels of specific structures of the gasifier are established to simulate the complicated gasification process. The model includes the total energy conservation equation and mass conservation equations for the gas components, solid flow, and gas flow. It simulates the influence of the gasifier structure and dimensions and can calculate the effects of changing almost every important operation parameter, e.g., the syngas composition, gasification temperature, carbon conversion ratio, walllayer temperature, and slag mass flow rate. The model can predict the syngas composition under a limited residence time condition. Furthermore, it considers the heat transfer coefficient of each layer of the water wall to calculate its heat loss and temperature. Thus, the model also reflects the influence of performance parameters of the gasifier’s water wall. The slag mass flow rate on the wall is calculated using a slag submodel.     

Numerical simulation of coal gasification in entrained flow coal gasifier

This paper presents modeling of a coal gasification reaction, and prediction of gasification performance for an entrained flow coal gasifier. The purposes of this study are to develop an evaluation technique for design and performance optimization of coal gasifiers using a numerical simulation technique, and to confirm the validity of the model. The coal gasification model suggested in this paper is composed of a pyrolysis model, char gasification model, and gas phase reaction model. A numerical simulation with the coal gasification model is performed on the CRIEPI 2 tons/day (T/D) research scale coal gasifier. Influence of the air ratio on gasification performance, such as a per pass carbon conversion efficiency, amount of product char, a heating value of the product gas, and cold gas efficiency is presented with regard to the 2 T/D gasifier. Gas temperature distribution and product gas composition are also presented. A comparison between the calculation and experimental data shows that most features of the gasification performance were identified accurately by the numerical simulation, confirming the validity of the current model.     

水煤浆气化炉内飞灰的形成机理

基于实验室规模的多喷嘴对置式水煤浆气化炉,利用SEM、马尔文激光粒度仪和XRD表征气化炉内飞灰的粒径分布和组成,并分析了气化炉内飞灰的形成机理。结果表明,喷嘴平面处飞灰与气化炉出口处飞灰的粒径分布及化学组成存在显著差异,不同气化阶段飞灰的形成机理也不同。气化燃烧阶段飞灰的形成机理为部分固定碳燃烧和外在矿物转化,而在焦炭气化反应阶段,飞灰的形成机理为焦炭破碎和内在矿物释放及转化。     

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.     

Carbon particle type characterization of the carbon behaviour impacting on a commercial-scale Sasol-Lurgi FBDB gasifier

Char-form analysis, whilst not yet an ISO standard, is a relatively common characterization method applied to pulverized coal samples used by power utilities globally. Fixed-bed gasification coal feeds differ from pulverized fuel combustion feeds by nature of the initial particle size (+6 mm, −75 mm). Hence it is unlikely that combustion char morphological characterization schemes can be directly applied to fixed-bed gasifier chars. In this study, a unique carbon particle type analysis was developed to characterize the physical (and inferred chemical) changes occurring in the particles during gasification based on coal petrography and combustion char morphology. A range of samples sequentially sampled from a quenched commercial-scale Sasol-Lurgi fixed-bed dry-bottom (FBDB) Gasifier were thus analysed.It was determined that maceral type (specifically vitrinite and inertinite) plays a pivotal role in the changes experienced by carbon particles when exposed to increasing temperature within the gasifier. Whole vitrinite particles and vitrinite bands within particles devolatilized first, followed at higher temperatures by reactive inertinite types. By the end of the pyrolysis zone, all the coal particles were converted to char, becoming consumed in the oxidation/combustion zone as the charge further descended within the gasifier.The carbon particle type results showed that both the porous and carbominerite char types follow similar burn-out profiles. These char types formed in the slower pyrolysis region within the pyrolysis zone, increasing to around 10% by volume within the reduction zone, where 53% carbon conversion occurred. Both of these char forms were consumed by the time the charge reached the ash-grate at the base of the reactor, and therefore did not contribute to the carbon loss in the ash discharge. It would appear as if the dense char and intermediate char types are responsible for the few percent carbon loss that is consistently obtained at the gasification operations.The carbon particle type analysis developed for coarse coal to the gasification process was shown to provide a significant insight into the behaviour of the carbon particles during gasification, both as a stand alone analysis and in conjunction with the other chemical and physical analyses performed on the fixed-bed gasifier samples.     

气流床煤气化的Aspen Plus建模：平衡模型和动力学模型

基于Aspen Plus软件建立了GE气流床煤气化的平衡模型和动力学模型,计算了气化的煤气组成和碳转化率。模型分为热解、气化和气液分离三个阶段。其中,气化阶段又分为初步气化和气化重整,从而获得气化产物在恒定温度下的分布。平衡模型的气化阶段使用了吉布斯反应器RGIBBS,基于吉布斯自由能最小化原理对体系内的气化产物进行计算;动力学模型的气化阶段使用了全混流反应器RCSTR,基于煤气化反应的动力学机理对体系内的气化产物进行计算。模拟值与GE气化炉的实际工程数据进行了对比,结果表明,平衡模型可在一定程度上反映气化结果的变化趋势,但预测结果的准确性有所欠缺,而基于气化反应机理建立的动力学模型能很好地预测GE气化炉的气化结果。对动力学模型中的全混流反应器进行反应时间设定,可以对GE气化炉生产提供一定的指导,结果表明：反应停留时间为3.5s时就可以达到很好的气化效果。温度是影响气化反应速率及产物分布的重要因素,利用煤气化的动力学模型模拟了气化温度对气体组成及碳转化率的影响,结果表明：随着气化温度的升高,CO含量逐渐增加,H₂含量基本不变,CO₂含量逐渐减小,碳转化率逐渐升高。     

Thermophoresis effects on gas-particle phases flow behaviors in entrained flow coal gasifier using Eulerian model

A numerical model based on the Eulerian–Eulerian two-fluid approach is used to simulate the gasification of coal char inside an entrained flow gasifier. In this model, effects of thermophoresis of coal char particles are thoroughly investigated. The thermophoresis is due to the gas temperature gradient caused by absorpted heat of coal char gasification. This work, firstly, calculates the gas temperature gradient and thermophoretic force at1100 °C,1200 °C,1300 °C and 1400 °C wall temperatures. Then, the changes of particle volume fraction and velocity in the gasifier are studied in the simulation with thermophoresis or not. The results indicate that considering the particle thermophoresis has some effects on the calculation of particle volume fraction in the gasifier, especially at wall temperature of 1400 °C, and the maximum particle volume fraction variance ratio reaches up to 1.38% on wall surface of the gasifier. These effects are mainly caused by large gas temperature gradient along the radial direction of the gasifier. For the particle velocity, the changes are small but can be observable along radial direction of the gasifier, which has good agreement with the distributions of radial gas temperature gradient and thermophoretic force. These changes above may have certain effects on gasification reaction rates in this Eulerian model. So the change of gasification reaction rates in the simulation with thermophoresis or not is studied finally.     

Experiment and mathematical modeling of a bench-scale circulating fluidized bed gasifier

The gasification of two different coals and chars with CO₂ and CO₂/O₂ mixture in a 48-mm-i.d. circulating fluidized bed (CFB) gasifier is investigated. The effects of operation condition on gas composition, carbon conversion and gasification efficiency were studied. A simple CFB coal gasification district mathematical model has been set up. The effects of coal type and CFB operating conditions on CFB coal gasification are discussed based on the CFB gasification test and model simulation. The main operation parameters in CFB gasification system are coal type, gas superficial velocity, circulating rate of solids and reaction temperature. It is found that CO concentration and carbon conversion increase with increasing solids circulating rate and decreasing gas velocity due to the increase in gas residence time and solids holdup in the CFB. The carbon conversion increases with increasing temperature and O₂ concentration in the inlet gas. The experimental results prove that the CFB gasifier works well for high volatile, high reactivity coal.