CO_2气氛下准东煤化学链燃烧特性研究

我国准东煤储量丰富,钠含量高。以高钠准东煤为燃料,CO_2为气化介质,铁矿石为载氧体,基于鼓泡流化床反应器开展准东煤化学链燃烧特性的实验研究,考察了煤粒径、温度、流化风速和煤焦粒径对煤及煤焦化学链燃烧过程中可燃气体逃逸规律的影响;同时研究了煤中矿物质对煤焦气化过程的影响。结果表明,在基于鼓泡流化床实施的煤化学链燃烧过程中,由于煤颗粒和载氧体床料流化特性差异大,存在离析现象;离析影响煤化学链燃烧过程中挥发分和焦炭的转化;较高流化风速可显著增强载氧体与煤/焦炭颗粒的混合,有效改善离析对可燃气体转化的影响,降低可燃气体逃逸,并加快焦炭气化速率;煤焦中的矿物质能够维持煤焦较快的气化速率。     

高钠煤化学链燃烧特性及煤焦气化反应动力学研究

采用连续提取法对新疆准东高钠煤进行萃取处理，制备含有不同存在形式钠元素的准东煤样品，在小型流化床上考察了水溶性钠、醋酸铵溶性钠和稀盐酸溶性钠对于准东煤化学链燃烧特性的影响。结果表明，去除水溶性钠后准东煤化学链燃烧产物中含碳气体相对浓度显著提高，相同时刻碳转化率明显提高。而经过醋酸铵和稀盐酸处理后的准东煤相比未处理的准东煤，其化学链燃烧反应性能显著降低。对四种不同处理程度准东煤焦的等温气化反应进行动力学分析表明，WW-ZDJ与水蒸气的气化反应的活化能最小，HAW-ZDJ的气化反应活化能最大。水溶性钠对于准东煤化学链燃烧过程具有抑制作用，而醋酸铵和稀盐酸溶性的钠在准东煤的化学链燃烧过程中促进作用显著。     

高钠煤化学链燃烧特性及煤焦气化反应动力学研究

采用连续提取法对新疆准东高钠煤进行萃取处理,制备含有不同存在形式钠元素的准东煤样品,在小型流化床上考察了水溶性钠、醋酸铵溶性钠和稀盐酸溶性钠对于准东煤化学链燃烧特性的影响。结果表明,去除水溶性钠后准东煤化学链燃烧产物中含碳气体相对浓度显著提高,相同时刻碳转化率明显提高。而经过醋酸铵和稀盐酸处理后的准东煤相比未处理的准东煤,其化学链燃烧反应性能显著降低。对四种不同处理程度准东煤焦的等温气化反应进行动力学分析表明,WW-ZDJ与水蒸气的气化反应的活化能最小,HAW-ZDJ的气化反应活化能最大。水溶性钠对于准东煤化学链燃烧过程具有抑制作用,而醋酸铵和稀盐酸溶性的钠在准东煤的化学链燃烧过程中促进作用显著。     

基于3kW塔式串行流化床差异燃料的化学链燃烧解析

化学链燃烧反应器具有广泛的燃料适应性，可同时兼顾气、液、固多类型燃料的运行。本文依托耦合内构件的3kW塔式串行流化床反应器，分别开展异丙醇、污泥以及煤炭的化学链燃烧实验，探究燃料物化属性对化学链燃烧过程与反应器运行的影响，揭示面向目标燃料的反应器针对性设计、载氧体性能选择与流化操作策略，助力形成指向性强、碳捕集效率高与操作灵活的化学链燃烧技术。面对碳化程度低、有机质含量高的固体燃料，焦炭气化速率已非强化重点，如污泥在3kW塔式反应器910℃与150s停留时间内，可实现大于99%的CO₂捕集效率，化学链燃烧反应器应侧重改善可燃气体转化与旋风分离器对轻质焦炭颗粒的捕捉。当采用异丙醇等高CH₄含量的燃料时，Fe基矿石载氧体的反应性能不足，3kW反应器的额外耗氧率高达10%～19%，其中未燃尽CH₄对额外耗氧率的贡献占比超80%。化学链燃烧反应器需依据热解反应气的物化特性，选择或掺混功能性载氧体，以针对性改善气固转化。在煤等高碳化燃料的化学链燃烧过程中，焦炭气化是反应的限制性步骤，简化循环结构的3kW塔式反应器停留时间不足，仅可...     

煤化学链转化技术研究进展

化学链技术为化石能源的清洁高效利用提供了新思路。本文在综述煤化学链燃烧和气化转化工艺现状及特点的基础上,对煤化学链转化的载氧体以及煤-载氧体反应和化学链反应器强化等进行了评价及展望。指出煤化学链转化的研究重点为以下3方面：①载氧体-煤-煤灰-气化剂等反应体系中氧传递过程及反应机理;②载氧体应围绕多活性组分载氧体、耦合催化-载氧-捕C/S多功能复合载氧体和具有特定储氧功能和高稳定性结构载氧体等3方面进行研究;③针对载氧体和煤反应慢的瓶颈,应揭示反应器优化和操作强化的理论基础。     

铁基载氧体与干化市政污泥二元混合物流化特性

化学链燃烧技术处置污泥可有效抑制有害气体排放，但干化污泥与铁基载氧体的物理性质相差较大，在流化床内会产生混合分离等问题。在内径(φ)为100 mm的有机玻璃冷态流化床装置上，进行了干化污泥与载氧体二元颗粒流化实验，讨论了颗粒粒径大小、干化污泥与载氧体质量比和操作风速对二元颗粒流化特性的影响。结果表明，污泥与平均粒径为0.66 mm的载氧体能实现混合流化，最小流化速度 和最小混合操作风速Um相等；污泥与平均粒径为1.46 mm的载氧体流化时，随操作风速增大，逐渐由分离流化状态过渡到混合流化状态，Um? ；污泥与平均粒径为2.43 mm的载氧体流化时，始终保持分离流化状态。基于提出的表征混合/分离流化状态的无量纲数Gd，当00.8时处于分离流化。     

基于NiO载氧体的煤化学链燃烧实验

采用流化床反应器并以水蒸气作为气化-流化介质,研究了以NiO为载氧体在800～960℃内的煤化学链燃烧反应特性。实验结果表明,载氧体与煤气化产物在反应器温度高于900℃体现了高的反应活性。随着流化床反应器温度的提高,气体产物中CO₂的体积浓度(干基)呈单调递增;CO、H₂、CH₄的体积浓度(干基)呈单调递减;煤中碳转化为CO₂的比率逐渐递增,碳的残余率逐渐递减。反应器出口气体CO₂、CO、H₂、CH₄的生成率随反应时间呈单峰特性,H₂生成率的峰值远小于CO的峰值;且随反应器温度升高,CO₂生成率升高,CO、H₂、CH₄的生成率降低。反应温度高于900℃时,流化床反应器NiO载氧体煤化学链燃烧在9 min之内就基本完成,CO₂含量高于92%。     

铁基载氧体对煤中汞释放行为的影响

采用Ontario-Hydro方法,在管式炉中考察了煤化学链燃烧/气化过程中Fe₄Al₆载氧体对煤中汞释放率、气态汞形态分布及汞在两反应器内释放行为的影响。结果表明,载氧体对煤中汞释放率具有显著的影响,在500~700℃,与无载氧体相比,化学链燃烧过程煤中汞释放率减少,化学链气化过程煤中汞释放率增大,而在900℃时,无论化学链燃烧过程还是化学链气化过程,煤中汞释放率均减小。Fe₄Al₆载氧体能够显著增加燃料反应器出口气态Hg²⁺的相对含量,其含量随温度的升高而逐渐升高。燃料反应器的温度也是影响煤中汞在两反应器中的分布以及空气反应器中不同价态汞百分含量的重要因素。此外,相同条件下不同煤种的汞释放率不同,主要与煤的组成不同有关。该研究对揭示载氧体对煤中汞迁移的影响机理以及煤化学链转化过程汞的控制提供了实验依据。     

煤化学链燃烧载氧体研究进展

煤的化学链燃烧是清洁煤燃烧的重要技术之一。化学链中载氧体的使用可以避免煤和空气直接接触,从而避免氮氧化物等污染物的产生并提高能量转化效率。一般来说,煤的化学链燃烧有2种反应途径:煤气化化学链燃烧和氧解耦化学链燃烧;不同反应途径将极大影响载氧体组分以及结构设计。详细论述了2015-2020年煤化学链燃烧中固态金属载氧体的研究进展,包括铁基、锰基、铜基、镍基、硫酸钙以及其他复合金属载氧体。总结了不同金属载氧体的优缺点、反应路径、气-固和固-固反应机理、金属与载体的相互作用以及载氧体失活原理。铁基载氧体被广泛应用于气化化学链燃烧中,但单一铁基载氧体的反应速率较低。适量添加碱金属或碱土金属可以提升载氧体的反应活性。锰基载氧体在化学链燃烧中具有两面性:一方面可以在高温缺氧气氛中释放气态氧,另一方面也可以与还原性气体发生气-固反应。通过使用惰性载体以及碱金属添加剂可以提高锰基载氧体的机械强度和氧解耦能力。含铜载氧体具有出色的氧解耦能力和反应活性而被广泛关注,然而铜及其氧化物低熔点所带来的金属聚集导致载氧体的失活问题亟需克服。研究发现使用铁、锰和铜矿石制得的载氧体具有良好的反应性能。硫酸钙载氧体具有较好的反应活性,但煤的化学链燃烧时潜在的二氧化硫和硫化氢副产物需要引起重视。镍基载氧体虽然在煤的化学链燃烧中反应性能较好,但硫毒化、成本较高和环保性能不佳等缺点导致近年来镍基载氧体的研究较少。新型双金属或多金属载氧体可以同时结合2种金属的反应特性,从而显著提高载氧体的整体反应活性。基于载氧体的研究现状,对未来的发展方向提出了4点建议:结合2种煤的化学链燃烧机理设计新型氧解耦辅助化学链燃烧载氧体;发展新型材料和金属组分的载氧体;利用冶金工业废料制得载氧体;开发新型结构的载氧体。     

无烟煤化学链燃烧过程燃料氮转化释放特性

基于赤铁矿石载氧体,在小型单流化床反应器上,开展煤挥发分和焦炭的化学链燃烧研究,探讨挥发分氮和焦氮在化学链燃烧过程中的转化特性。研究表明:燃料氮释放的中间产物HCN和NH₃与铁矿石载氧体具有较高的化学反应亲和性,易于被载氧体氧化生成N₂和NO。淮北无烟煤挥发分氮转化过程中,NO是唯一的氮氧化物,反应器出口中间产物NH₃的释放份额略高于HCN。在煤焦化学链燃烧还原过程中,部分燃料氮释放的中间产物HCN和NH₃被铁矿石氧化导致少量NO的生成,还原过程中无N₂O的释放;较高的还原反应温度加速了NO的生成。减少进入载氧体氧化再生过程的焦炭量可减少空气反应器NO和N₂O的生成。     

复合流化床低阶煤热解制备兰炭的工艺条件

以不同粒径范围的新疆准东煤为原料,在耦合下部流化床和上部输送床的复合流化床中热解制备兰炭,考察了热解温度、过量氧气系数、气化温度、煤颗粒停留时间等对热解产物分布和热解半焦性质的影响. 结果表明,随过量氧气系数、气化温度和颗粒平均停留时间增加,气体产率升高,半焦和焦油产率降低;半焦的比表面积随气化温度升高而增大,而随过量氧气系数增大先增大后减小. 当煤从下部流化床进料时,在过量氧气系数0.11、流化床气化温度850℃、输送床热解温度750℃、流化床内煤颗粒停留时间90 s的操作条件下,可制备出固定碳含量超过83%(w)、挥发分含量低于9%(w)的兰炭.     

钠修饰铁矿石载氧体的串行流化床煤化学链燃烧试验

利用1 kW_th串行流化床反应器对钠修饰铁矿石载氧体进行试验研究,考察燃料反应器温度对煤化学链催化燃烧特性的影响。结果表明,钠在820～920℃温度下显著促进了煤气化反应的进行,随着燃料反应器温度的提高,使用Na-铁矿石时燃料反应器出口CO₂浓度明显增大,CO浓度明显降低,在920℃时CO₂捕集效率和碳捕集效率分别达到78.60%和80.54%,而使用纯铁矿石时CO₂捕集效率和碳捕集效率仅为40.27%和45.65%。在高温950℃时Na-铁矿石活性下降,出现烧结和团聚现象,燃料反应器出现滞流态化现象,这可能是钠的化合物熔点较低和载氧体过度还原所导致的。XRD和SEM分析结果显示钠修饰铁矿石促使更多的Fe₂O₃被还原为Fe₃O₄。     

Effect of fuel particle size on reaction rate in chemical looping combustion

Chemical looping combustion (CLC) uses an oxygen carrier circulating between an air and a fuel reactor to replace direct burning of fuels in air. The very low energy penalty for CO₂ separation in CLC gives it the potential to become an important technology on the way to a CO₂ neutral energy supply. In this work, the influence of the particle size of coal on the rate of reaction of the coal was investigated in a bed of oxygen carrier. In order to do this, a method to quench the reaction of coal with oxygen carriers at a specified time and measure the particle size distribution of the remaining coal was developed. Three size fractions of coal were used in the experiments: 90–125, 180–212 and 250–355 μm. Particle size distributions of the fuel show a decrease in particle size with time. The influence of devolatilisation of the coal on the coal particle size was measured, showing that coal particles do not break in the fluidized bed reactor used for the experiments. Reaction rates based on measurements of gas phase concentrations of CO₂, CO and CH₄ showed that the reaction rate is independent of the particle size. These results are in line with literature findings, as studies have shown that carbon gasification is size-independent at conditions similar to those in the performed CLC experiments.     

Multiphase CFD Modeling for a Chemical Looping Combustion Process (Fuel Reactor)

There are growing concerns about increasing emissions of greenhouse gases and a looming global warming crisis. CO₂ is a greenhouse gas that affects the climate of the earth. Fossil fuel consumption is the major source of anthropogenic CO₂ emissions. Chemical looping combustion (CLC) has been suggested as an energy‐efficient method for the capture of carbon dioxide from combustion. A chemical‐looping combustion system consists of a fuel reactor and an air reactor. The air reactor consists of a conventional circulating fluidized bed and the fuel reactor is a bubbling fluidized bed. The basic principle involves avoiding direct contact of air and fuel during the combustion. The oxygen is transferred by the oxygen carrier from the air to the fuel. The water in combustion products can be easily removed by condensation and pure carbon dioxide is obtained without any loss of energy for separation. With the improvement of numerical methods and more advanced hardware technology, the time required to run CFD (computational fluid dynamic) codes is decreasing. Hence, multiphase CFD‐based models for dealing with complex gas‐solid hydrodynamics and chemical reactions are becoming more accessible. To date, there are no reports in the literature concerning mathematical modeling of chemical‐looping combustion using FLUENT. In this work, the reaction kinetics models of the (CaSO₄ + H₂) fuel reactor is developed by means of the commercial code FLUENT. The effects of particle diameter, gas flow rate and bed temperature on chemical looping combustion performance are also studied. The results show that the high bed temperature, low gas flow rate and small particle size could enhance the CLC performance.     

Characteristics of fluidization at high pressure

Experiments were conducted to investigate fluidization fundamentals at pressures up to 6485 kPa using nitrogen as the fluidizing gas. The particles under study were coal, char and Ballotini. Both a three-dimensional bed (10.16-cm-i.d.) and a two-dimensional bed (1.9x 10.16cm) were used in the experiments. The fundamentals of high pressure fluidization examined in this study include minimum fluidization velocity, bed voidage at minimum fluidization, bed expansion, and bubbling behavior. An empirical correlation was developed for determining minimum fluidization velocity. The effects of pressure upon bed voidage at minimum fluidization and expanded bed height were analyzed for several types of particles. High speed photographs were studied to describe bubbling behavior in a fluidized bed over a range of pressures.     

A model on chemical looping combustion of methane in a bubbling fluidized-bed process

We developed a mathematical model to discuss the performance of chemical looping combustion (CLC) of methane in continuous bubbling fluidized-beds. The model considers the particle population balance, oxidation and reduction rate of particles in fluidized beds. It also considers utilization efficiency of oxygen carrier (OC) particles, residence time of particles in each reactor, and particle size in reaction rate. The model was applied for a bubbling coreannulus fluidized-bed process. The core bed was the fuel reactor (0.08 m-i.d., 2.1 m-height) and the annulus bed was the air reactor (0.089 m-i.d., 0.15 m-o.d., 1.6 m-height). The process employed a type of Ni-based OC particles. The present model agrees reasonably well with the combustion efficiency measured in the process. Simulation was performed to investigate the effects of some variables for the process. The present model revealed that the range of circulation rate of OC particles for achieving complete combustion determined the operating range of the CLC system. The minimum circulation rate of OC particles for complete combustion decreased in the considered operating range as temperature or bed mass increased in the fuel reactor. A large mass of the fuel bed was necessary to obtain complete combustion at low fuel reactor temperature. The fresh feed rate of OC particles for steady state operation increased in complete combustion condition as temperature or static bed height or gas velocity increased.     

Pressurized gasification of woody biomass—Variation of parameter

Pressurized gas produced from biomass is a renewable resource that is attracting a great deal of attention due to its wide range of industrial applications, such as the production of hydrogen, chemicals or high grade fuels. Therefore, the Vienna University of Technology in cooperation with BioEnergy 2020+ is operating a bubbling pressurized gasification plant. The pressurized research unit (PRU) is able to perform the gasification of wood chips, wood pellets, coal and other solid fuels with gasification agents air, steam, oxygen or carbon dioxide. This paper gives the results of parameter variation at this plant with regard to the producer gas composition. The feedstock was wood pellets and as bed material olivine was used with an average particle size of 0.5 mm. The parameters varied were temperature (720-900 °C), pressure (1-5 bar), air ratio (0.2-0.4), gasification agent (air, steam, oxygen), biomass feed input (4.5-8 kg/h) and the fluidization conditions of the reactor fluidized bed (fluidization number (3-7)).