球型热载体回转窑褐煤热解过程的传热模型

为了了解热载体球煤粉热解过程的传热机理,建立了热载体球回转窑褐煤热解的传热模型并进行了模拟。结果表明:在热载体和煤的初始温度分别为973.15K和373.15K,煤粒径为6mm,热载体与煤质量比为6时,在330s后系统温度达到平衡,约786K。煤颗粒密度的变化以及热解气与热载体对流换热对系统的温度变化的影响较小,反应热对传热速率和平衡温度影响较大。     

球型固体热载体煤粉热解过程传热计算及分析

为了优化球型固体热载体煤粉热解反应器和操作条件,建立了热载体球煤粉热解过程的传热模型。计算了不同热载体与煤质量比、热载体初始温度及煤粒径下的煤颗粒温度分布。结果表明:增加质量比、提高热载体的初始温度能够提高煤热解平衡温度,缩短达到平衡温度所需时间;减少煤粒径同样可以缩短达到热解平衡温度所需时间。在热载体初始温度973.15 K,煤初始温度373.15 K,热载体与煤质量比大于4时,煤热解温度才能高于732 K。     

褐煤固体热载体热解提质工艺进展

介绍了国内外几种典型的褐煤固体热载体热解提质工艺,并从原理、操作条件、原料、热解产品、能量利用率、局限性等方面对各种工艺进行了分析对比;分析了工业上常用的固体热载体的优缺点,提出了褐煤固体热载体热解技术的发展方向。     

固体热载体热解中传热行为的Fluent模拟和实验

固体热载体热解(SHC)和外热式普通热解(CP)由于传热方式和热解挥发物经历温度场的不同,其传热行为和热解行为存在较大差异。采用小型密闭固定床反应器,以核桃壳(WS)为原料、石英砂(QS)为固体热载体,在石英砂预热温度800℃、QS与WS质量比9∶1条件下研究了传热行为和热解规律。采用实验和Fluent模拟两种方式研究了固体热载体热解过程的传热行为,并将温度场解耦为热解温度(T_WS)和挥发物温度(T_QS-h)。研究结果表明:相比于模拟所得的T_WS和T_QS-h最大值(490和612℃),实验数据(460和508℃)更小,实验过程存在散热现象。T_WS平均值■和T_QS-h平均值■的温差的实验值和模拟值分别为39和72℃,说明低温挥发物在逸出过程中经过高温石英砂层时发生剧烈的二次反应。相比于CP,SHC热解方式下的焦炭得率和气体得率更高,分别为67.42%和12.51%;油得率和水得率更低,分别为8.69%和11.38%。同时,SHC热解方式下的油中极轻馏分(VL...     

褐煤低温热解分级利用现状分析及展望

我国"富煤,贫油,少气"的能源现状,决定了很长时间我国仍将以煤炭为主。其中中低阶煤占目前煤炭总探明储量的50%以上,为高效利用褐煤等中低阶煤炭资源,笔者对我国褐煤资源的分布特点、物理特性及其干燥脱水、压缩成型和低温热解加工利用现状进行了分析,重点综述了褐煤低温热解技术研究现状,对目前广泛应用的固体热载体热解技术、气体热载体和气-固热载体进行了总结,并从反应器类型、热载体类型、适用范围、进料粒度、目标产品、工业化程度等方面对热解工艺进行了对比,指出了现阶段褐煤分级利用过程中存在的产品附加值不高、焦油收率低、余热回收和粉尘处理等关键技术问题,并对未来褐煤热解分级炼制工艺进行了展望,提出了通过提高焦油等热解产物的附加值来延伸产品链、开发与其他物质的共热解工艺、完善现有反应器并开发新的热解反应器、通过工艺调整提高褐煤中氧等元素利用率及大型化发展的必要性。提出未来褐煤等中低阶煤综合利用的建议,将褐煤热解提质技术与现有的煤气化、液化、MTO、MTP等煤化工技术集成,并通过设置适宜的产品目标和设计合理的工艺路线,得到多种高附加值清洁燃料、化工原料以及热能、电力等产品,有效延长褐煤产业链,实现低阶煤分级分质利用,促进我国煤炭转化产业结构调整和优化升级。     

褐煤提质技术研究进展与展望

介绍了褐煤提质的必要性以及褐煤提质工艺的发展现状,列举了蓄热式无热载体旋转床干馏工艺、输运床气化炉(TRIGTM)、固体热载体煤热解工艺等几种提质干燥工艺流程及其特点;提出了我国褐煤干燥提质技术的发展方向。     

浅析褐煤的煤化工技术与应用

论述了褐煤热解提质、褐煤液化和气化的工艺技术和实际应用情况,重点分析了褐煤固体热载体法快速热解技术和褐煤低温干馏改质技术的特点。     

低阶煤无热载体快速热解炉工艺试验研究

为实现煤炭热解分质梯级利用,提出了低阶煤无热载体粉煤快速热解炉工艺,以印尼褐煤为研究对象,对无热载体粉煤快速热解工艺所产焦油、热解气、半焦等进行分析,验证低阶煤无热载体热解炉工艺的技术可行性。结果表明,试验煤种经低阶煤无热载体粉煤快速热解炉工艺处理后热解焦油产率达11.84%、热解气产率14.08%,半焦产率64.97%,其中焦油产率比格金干馏试验提高了1.49%,半焦发热量较原煤提高了2.63 MJ/kg,热解气有效气体含量达80%以上。表明该低阶煤无热载体粉煤快速热解炉工艺具有热解温度可区域精确控制、热解速度快、焦油产率高、产品品质好等优点。     

固体热载体煤热解过程中氮的迁移

在固体热载体煤热解实验装置上考察了石英砂、燃烧灰和气化半焦为热载体对煤热解过程中氮迁移的影响.固体热载体煤热解过程中,热解温度升高有利于煤中挥发分析出,可以促进煤中含氮官能团发生断键,利于氮的脱除.快速热解可促进煤中氮脱除生成HCN和NH3.分别以石英砂、燃烧灰和气化半焦为热载体,研究表明:热载体中矿物质可促进焦油氮分...     

塑料与蜡(重油)催化共热解相互作用研究

采用低密度聚乙烯(LDPE)和固体石蜡(WAX)分别作为塑料及重油的模型化合物,以HZSM-5为反应催化剂,通过热重实验进行热解特性及动力学分析,研究了二者在热解行为上的相互作用;并结合固定床反应器对比研究单独热解及不同原料配比下共热解的产物分布,考察了共热解过程相互作用对热解产物的影响规律。结果表明,LDPE与WAX共热解过程二者间相互作用增强,表现为促进反应物的热解失重,降低了原料的特征热分解温度及反应活化能,显著提高了热解油中C_(21-)轻油馏分及芳烃的选择性,而油中C_(21+)重油馏分的选择性及固体残渣产率均降低;而且随着共热解原料中WAX比例的增加二者间的相互作用不断增强;基于模型化合物水平初步验证了塑料与裂解重油共热解制备高品质轻质燃油工艺的可行性与技术优势。     

A model of devolatilization behavior in lignite pyrolysis with solid heat carriers

To elucidate the influence of the process conditions on pyrolytic products, the interactions between transport phenomena and pyrolysis kinetics are quantitatively analyzed at the level of a single coal particle. A comprehensive mathematical model is formulated to predict intraparticle multiphysics and devolatilization behaviors; the model contains two correlative one-dimensional unsteady heat conservation equations and ternary mass conservation equations in conjunction with the simplified dusty-gas model. Moreover, a multistep kinetic model of coal devolatilization is adopted to predict the generating rates of the lumped pyrolytic products. Validation of the model against experimental and literature data showed that can predict the transient temperature profiles of a coal particle and the yields of volatiles. Finally, the effects of the main process conditions on the intra- and extra-temperature history of lignite during pyrolysis with solid heat carriers are analyzed. The interactions between physical transport and the pyrolysis reaction are also examined.     

松木屑颗粒热解过程中的热/质传递规律

为探索在固定床反应器中有机固废颗粒热解过程中的热量、质量传递机理,本研究从颗粒尺度上对有机固废松木屑颗粒热解过程建模分析,模型中考虑了焦油的二次裂解反应及挥发分在颗粒孔隙中的质量、动量传递过程,并采用达西定律模拟了挥发分在颗粒孔隙内的流动现象,对颗粒热解过程的吸热反应以及挥发分逸出时的对流换热对颗粒温度的影响进行考察。基于两步反应动力学模型,探讨了不同颗粒尺寸、热解温度对有机固废松木屑颗粒热解过程的影响。结果表明,热解吸热反应和挥发分的对流换热阻碍了热量向颗粒中心的传递,延长了颗粒达到均温的时间;松木屑颗粒热解时,颗粒内会存在明显的温度梯度,在颗粒表面主要受化学反应动力学限制,在颗粒内部则主要受热量传递过程限制。此外,热解温度越低,粒径越大,颗粒内部的传热阻力越大。松木屑颗粒完全热解所需时间会随着颗粒粒径的增大而增加,但当颗粒粒径在10mm以上时,随着颗粒粒径的增大,颗粒完全热解所需时间的增量要大于10mm以下颗粒。     

Experimental studies on pyrolysis of Datong coal with solid heat carrier in a fixed bed

An experimental apparatus was set up for batch simulation of coal pyrolysis with solid heat carrier in a fixed bed. Quartz sand as heat carrier preheated to about 700–800°C was mixed with Datong bituminous coal by an agitator. The thermal history of the coal particle has been followed by a K-type thermocouple. The effects of particle size, pyrolysis time and temperature on the gas yield during pyrolysis of coal with solid heat carrier were examined for different conditions. The experimental results showed that a dominant percentage of the gas product is produced during the first 1–3 min, although gas evolution would last for as long as 10 min. The total gas yield, insensitive to particle size of the heat carrier, depends on carrier temperature and coal particle size under tested conditions. The contact heat transfer of cold and hot particles was analyzed.     

Experimental and numerical investigation on the pyrolysis of single coarse lignite particles

This paper reports on the mathematical modeling of the pyrolysis of single coarse lignite particles using a kinetics model coupled with a heat transfer model. The parallel reaction kinetics model of the lignite pyrolysis makes no assumptions about the activation energy distribution and the conversion of sub-reactions. The pyrolysis kinetics parameters were obtained on the basis of experimental data from thermogravimetric analysis (TGA) tests. The heat transfer model includes diffusive, convective and radiative heat transfer modes. The experimental investigations were carried out for single lignite particles in an electrically heated reactor. Measurements of the temperature and mass loss were performed during the pyrolysis in a nitrogen atmosphere. The model predictions for the temperature and mass loss histories agree well with the experimental data, verifying that the mathematical model accurately evaluates the pyrolysis of lignite particles. The effects of temperature and particle size on the pyrolysis time and final residual mass fraction were evaluated using the numerical model.     

Modelling of the pyrolysis of biomass particles. Studies on kinetics,thermal and heat transfer effects

The present work provides a rationally-based model to describe the pyrolysis of a single solid particle of biomass. As the phenomena governing the pyrolysis of a biomass particle are both chemical (primary and secondary reactions) and physical (mainly heat transfer phenomena), the presented model couples heat transport with chemical kinetics. The thermal properties included in the model are considered to be linear functions of temperature and conversion, and have been estimated from literature data or by fitting the model with experimental data. The heat of reaction has been found to be represented by two values: one endothermic, which prevails at low conversions and the other exothermic, which prevails at high conversions. Pyrolysis phenomena have been simulated by a scheme consisting of two parallel reactions and a third reaction for the secondary interactions between charcoal and volatiles. The model predictions are in agreement with experimental data regarding temperature and mass-loss histories of biomass particles over a wide range of pyrolysis conditions.     

Pyrolysis of single large biomass particle: Simulation and experiments

Pyrolysis and heat transfer characteristics of single large biomass particle were investigated using three-dimensional unsteady heat transfer model coupled with chemical reactions. The consumption of biomass and the production of products were simulated. Some experiments were designed to provide model parameters for simulation calculations. The simulation was verified by pyrolysis experiments of large biomass particle in a vertical tube furnace. The simulation results show the internal heat and mass transfer law during the pyrolysis of large biomass particle. When the biomass particle diameter is between 10 and 30 mm, for every 5 mm increase in particle diameter, the time required for complete pyrolysis will increase on average by about 50 s. When the pyrolysis temperature is between 673 K and 873 K, a slight decrease in the pyrolysis temperature will cause the time required for the biomass to fully pyrolyze to rise significantly. And the phenomenon is more obvious in the low temperature range. The results indicate that the numerical simulation agrees well with the experimental results.     

气固流化床外取热器内流动和换热特性分析

外取热器是维持催化裂化反应-再生系统热平衡和保持装置平稳运行的关键设备之一。外取热器的优化设计和合理调控,要求深入理解外取热器内的流动特性、换热特性及两者之间关系。在一套大型冷模热态实验装置上,分别考察了表观气速、颗粒质量流率对换热管附近的局部固含率和气泡频率、床层与换热管间传热系数的影响。结果表明:增加表观气速可以降低局部固含率、增加局部气泡频率、强化床层与换热管间换热;随着颗粒质量流率增加,局部固含率和局部气泡频率均增加;在较低表观气速下,增加颗粒质量流率不利于换热,而在较高表观气速下,传热系数随颗粒质量流率逐渐增加。不同流型下,气固流动特性对换热特性的影响不同。在鼓泡床流型下,过高的局部固含率不利于颗粒在换热表面的更新,增加换热管附近的局部气泡频率可以明显强化换热;而在湍流床流型下,换热管附近的局部固含率和气泡频率的增加,均使传热系数逐渐增大。建立了针对不同流型的换热经验关联式,预测值与实验值的平均相对偏差分别为6.9%和1.3%。     

Simulation of coal pyrolysis by solid heat carrier in a moving-bed pyrolyzer

A one-dimensional, steady state, numerical model for coal pyrolysis by solid heat carrier in moving-bed has been developed. The multiple-reaction model of coal pyrolysis and the gas–solid–solid three phases heat transfer theory in packed bed have been applied to account for the pyrolysis process. The results show that the axial temperature distribution of the coal particles increase with a heating rate more than 600 K/min. Coal particle size has significant influence on the heating rate, while blending ratio is the determinant factor of pyrolysis temperature. Given the main operating parameters, product distributions (H₂, CO, CH₄, tar, etc) are calculated by the model. The modeling results are found to agree the experimental data using a moving-bed pyrolyzer with processing capacity 10 kg h^?1 of coal.