Markov chain model of residence time distribution in a new type entrained-flow gasifier

A continuous-time Markov chain has been used to establish the residence time distribution (RTD) model in a new type entrained-flow gasifier, which is called entrained-flow gasifier with opposed multi-burner. According to the measurement results of the flow fields in the gasifier, the state transfer diagram of Markov chain formed in the case of the flow fields are simplified. The results show that this method is feasible in modeling the flow system which consists of ideal mixing cells and plug flow regions. The flow pattern of the gasifier is closed to continuous stirred tank reactor (CSTR). The simulation results are in good agreement with the experimental data. The established model has been applied to forecast the RTD in the industrial gasifier.     

撞击流气化炉内颗粒停留时间分布的随机模拟

根据多喷嘴对置式气化炉流场测试,将气化炉划分为若干区域,运用时间离散、状态离散的马尔可夫链随机模型,模拟了气化炉内颗粒相的停留时间分布(RTD)。当颗粒在撞击区和射流区间的回流比为0.5,向下撞击流股区和管流区为平推流模型,其他区域按全混流模型处理时,模拟值与实验值吻合较好。随着进料流量的增大,平均停留时间减小,量纲1方差减小;随着回流比的增加,平均停留时间增大;气固两相平均停留时间接近,但RTD存在一定差异。     

流化床-气流床耦合反应器中煤气化特性

利用化工动力学软件CHEMKIN建立了流化床-气流床耦合反应器等效网络模型,在φ300 mm反应器中的煤气化实验结果基础上,充分考虑耦合反应器不同区域物料间两相流动、传质传热,对耦合反应器各部分流体力学特征以及耦合反应器中不同区域的化学反应进行了分析。利用模型对飞灰的碳转化率、耦合反应器的碳转化率、耦合反应器内温分布及物料停留时间进行计算,结果表明,流化床耦合气流床反应器后,气流床可将出口飞灰碳转化64.1%,实现了耦合反应器对飞灰的再气化;耦合反应器煤气化系统的碳转化率由单独流化床的84.9%提高到92.2%。     

Production of ultrapure hydrogen from biomass gasification with air

An integrated process has been proposed for the production of ultrapure hydrogen from biomass gasification with air. The process consists of an air-blown bubbling fluidized bed gasifier, a steam reformer, and a water-gas-shift membrane reactor. A non-isothermal model has been developed to simulate the fluidized bed gasifier, and a one-dimensional model has also been developed to simulate the steam reformer. The simulation results are compared with the experimental data, and good agreement is obtained. Based on the simulation results, the thermodynamic analysis of the integrated process is carried out. The simulation and analysis provide a quantitative tool for gaining insight into the process.     

分级气流床气化炉模型研究

为了研究分级和气化炉结构对气化效果的影响,结合对分级气化炉内流动、燃烧和气化反应的分析,采用小室模型建立了分级气化炉的动力学模型,考虑了气化炉结构尺寸对气化过程和结果的影响。利用建立的模型,对等径结构、颈缩结构和渐扩结构3种形式的分级气化炉进行了计算,得到温度、气体组成及其体积分数、碳转化率等参数沿气化炉炉膛的分布情况,并和连续气化的结果进行了对比。结果表明氧气的分级给入加强了气化炉内的物料混和,提高了平均温度,有利于提高气化效率;同时最高点温度有所降低,有利于和延长耐火砖使用寿命。同样运行条件下分级气化得到的有效气体体积分数要高于连续气化。     

射流流化床体积效应对煤气化特性的影响

根据射流流化床内流体流动特性,在流体动力学行为相似的基础上,利用化学动力学软件Chemkin构建了射流床煤气化炉的动力学模型,通过体积放大引起物料停留时间及流体力学相似性的改变,研究其对射流床中物料特性的影响.分析了射流流化床几何相似放大与高径比减小放大对反应器特性的影响,认为等高径比放大停留时间较长,反应器内流体力学相似性较好,在后续工艺对出口组成要求较高时,采用此放大原则能满足要求.     

Numerical simulation of coal gasification at circulating fluidised bed conditions

This paper presents modelling results for a new pressurised fluidised bed gasifier concept, called the Power High-Temperature Winkler gasifier (PHTW gasifier). The numerical simulation of the steam/oxygen blown and lignite-fuelled power plant gasifier is performed on the 4800 t/day (1000 MW) at a pressure of 33 bar. The formation of flow pattern, turbulence, product gas composition, temperature, and radiation heat transfer were investigated. Influence of diameter variation on the flow patterns at constant operating conditions is presented. A comparison between the calculation and literature data of similar fluidised bed systems shows good conformance. To anticipate the solid's behaviour, particle concentration, particle size change due to pyrolysis and surface reactions, and particle tracks were modelled using an Eulerian–Lagrangian approach. While varying the total particle mass flow, the pressure drop as a function of reactor height was observed.     

Numerical study on the coal gasification characteristics in an entrained flow coal gasifier

The coal gasification process of a slurry feed type, entrained-flow coal gasifier was numerically predicted in this paper. By dividing the complicated coal gasification process into several simplified stages such as slurry evaporation, coal devolatilization and two-phase reactions coupled with turbulent flow and two-phase heat transfer, a comprehensive numerical model was constructed to simulate the coal gasification process. The k– turbulence model was used for the gas phase flow while the Random-Trajectory model was applied to describe the behavior of the coal slurry particles. The unreacted-core shrinking model and modified Eddy break-up (EBU) model, were used to simulate the heterogeneous and homogeneous reactions, respectively. The simulation results obtained the detailed information about the flow field, temperature and species concentration distributions inside the gasifier. Meanwhile, the simulation results were compared with the experimental data as a function of O₂/coal ratio. It illustrated that the calculated carbon conversions agreed with the measured ones and that the measured quality of the syngas was better than the calculated one when the O₂/coal ratio increases. This result was related with the total heat loss through the gasifier and uncertain kinetics for the heterogeneous reactions.     

基于锥型煤气炉应用中若干问题的探讨

从系统阻力、物料平衡、热量平衡、炉渣过渡区、灰盘直径、防流板、炉下带出物、气化强度等方面阐述了造气煤气炉由直筒形改为锥形炉后生产中存在的问题;论述了煤气炉阀径与工艺流程的选配原则;阐明了锥形煤气炉的生产水平低于直筒形炉气炉的观点。     

Numerical Simulation and Assessment of a Two‐Stage Gasifier Modified from an Opposed Multi‐Burner Gasifier

An opposed multi‐burner (OMB) entrained‐flow gasifier with coal water slurry feeding is developed by the East China University of Science and Technology. A 3D model is employed to numerically simulate the gas flow field, motion of char particles, and distributions of temperature and gaseous components in an OMB gasifier and in a conceptual two‐stage gasifier modified from the OMB gasifier (TS‐OMB gasifier). Results show that the TS‐OMB gasifier produces higher concentration and productivity of the effective gases (CO+H₂) with a slightly higher carbon conversion than the OMB gasifier. The reasons for the differences between these two types of gasifier are discussed by means of numerical simulation. This information is valuable for guiding the design of an advanced OMB gasifier.     

On the scaling-up of a two-stage air blown entrained flow coal gasifier

A two-stage air blown entrained flow gasifier is being developed in Japan for the IGCC process. However, its scale-up up faces significant difficulties because of ash/slag deposition problems. The ash/slag deposition in the gasifier depends on both the ash properties and entrainment produced by the swirling gas flow. Therefore, the flow hydrodynamics are critical issues for the control of the ash behavior. In this paper, a comprehensive simulation model is used to examine the effects of the gasifier geometry and jet configuration on the flow hydrodynamics in order to control the ash deposition on the gasifier walls. A swirl number for the multi-stage injection swirling gas flow is defined and proved to be the most important hydrodynamic scaling law for the entrained flow gasifier.     

多喷嘴对置式气化炉炉口塞的设计优化与改造应用

多喷嘴对置式气化炉的炉顶封堵砖——炉口塞严重制约着气化炉的长周期运行，通过设计优化提高了炉口塞的寿命，解决了制约气化炉运行周期的问题。     

应用炉膛压力诊断气流床气化炉的火焰状态

气化炉是煤气化技术中的关键设备 .气化炉内火焰燃烧稳定性下降 ,会出现燃烧噪音增加、气化燃烧效率降低及熄火等现象 ,对安全性和经济性产生严重的影响 .对气流床气化炉内不同气化燃烧状态下的火焰压力信号进行了小波分析 .结果表明 ,压力信号在一定频段内的分布与气化炉内火焰燃烧的状态密切相关 ,发现随着火焰燃烧稳定性加强 ,气化炉内压力信号向高频方向移动 ,以此可以建立气流床气化炉燃烧诊断模型 .     

基于平衡常数法的Texaco气化模型

分析了Texaco气化技术的特点，建立了基于多个化学反应的平衡常数法的气化模型．在模型中，根据组分平衡、化学平衡和能量平衡，利用平衡常数法，可以由燃料性质和运行条件计算出口气体化学成分，得到了Texaco气化炉的一维模型．并通过实验数据，对模型进行了校核讨论．结果表明，模型计算值和实验值吻合得较好．     

基于双组分PDF模型的GSP气化炉数值模拟

GSP气化炉是国内最近引进的西门子公司开发的粉煤气化技术,由于对其炉膛内气固反应流动特性认识不足,运行中出现耐火砖烧穿、合成气含灰过高等问题。利用数值模拟方法,采用双组分PDF模型耦合湍流-化学反应、随机轨道法耦合湍流-颗粒运动,针对GSP气化炉内多相反应流场建立三维数值模型。计算结果与实验值及文献计算结果一致,表明该模型可用于GSP气化炉的模拟计算。研究发现,炉膛内流场主要分为旋转射流区、内回流区、外回流区和管流区。高温区位于发生氧化反应的旋转射流区和内回流区上部,而外回流区和管流区主要发生还原反应,温度较为均匀;炉膛高度1/3位置处为高温火焰直接冲刷处,在运行时需重点考虑该位置的热防护。     

气流床气化炉的CPFD数值模拟

利用CPFD(computational particle fluid dynamics)模拟方法对三维、全尺寸的气流床气化炉进行了模拟计算,建立起了适用于CPFD模拟方法的气化模拟模型。模拟结果与实验数据相一致,说明模型基本准确且CPFD模拟方法适用于气流床气化过程的模拟。借由CPFD模拟方法给出了颗粒相在气化炉中的具体反应历程及颗粒停留时间的概率分布;结果表明,在单喷嘴顶喷的气化炉中,同时存在颗粒相的轴向流动短路及返混,短路主要发生在炉中心区域;颗粒在炉中心区域反应剧烈而边壁区域反应则很缓慢,而且从气化炉流出的第一股短路颗粒主要由充分反应了的粉煤颗粒构成。     

Techno‐Economic Comparison of a 7‐MWth Biomass Chemical Looping Gasification Unit with Conventional Systems

The chemical looping process is an alternative method to provide conventional gasification (CG) systems with the required oxygen. The syngas produced via chemical looping has a higher calorific value than that generated by a conventional process with air. For comparison, a conventional gasification unit with pure oxygen (CGPO) and a chemical looping gasification (CLG) system were simulated with Aspen Plus. The CGPO reactor consisted of a bubbling fluidized bed and sand as bed material with oxygen supplied via a pressure swing adsorption unit. The CLG comprised a bubbling fluidized‐bed gasifier working in parallel with a fast fluidized‐bed oxidizer. The total capital investment (TCI) of the CLG unit was higher than that of the CGPO unit but the annual operating cost of the former was less which repays the difference in TCI in less than six years.     

Modeling of an oxygen-staged membrane wall gasifier: effects of secondary oxygen

A new type of entrained flow gasifier with membrane wall and two-stage oxygen supply is being developed in China. The fraction of the secondary oxygen in total oxygen (FSO) is an important parameter for this kind of gasifier. A dynamic reduced order model (ROM) based on a reactor network model (RNM) is developed for this gasifier, which is used to investigate the effects of FSO on the slag layer thickness profile on the wall and explore the potential of FSO in dynamic slag control. The ROM adopts a flexible RNM blocking method, which varies with FSO to account for the influence of FSO on the flow pattern in the gasifier. Available industrial data was used to validate the model and a detailed sensitivity analysis for the calculation of slag layer thickness was performed. Static analyses show that FSO has a marked effect on the slag thickness distribution and higher FSO leads to lower heat loss through the wall. Finally, a slag control system, which introduced FSO as an auxiliary regulator, is proposed. Dynamic simulation shows that the new control system offers an improved performance in slag control and can broaden the regulating range of operating temperature.     

鲁奇加压气化工艺优化设计

对鲁奇炉气化进行了数学模拟 ,通过了工程实际数据的检验 ,可对各型号的鲁奇炉进行优化设计。     

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。