Continuous lignite char combustion in a spouted bed

A simulation model of continuous lignite char combustion in a spouted bed has been developed to predict bed oxygen concentrations, bed particle size distribution, bed carbon loading, mean diameter of bed char, and the fractional combustion in spout, annulus, and fountain. The approach involves taking into account the spouted bed hydrodynamics, a burning law for individual particles, and the combines mass balances for bed char and oxidant in the three typical regions. The predicted results for various operating conditions are compared with some experimental data.     

Attrition of lignite char in a spouted bed combustor

The generation of carbon fines by attrition during burning of Thai lignite char has been studied experimentally by means of a 92 mm i.d. continuous spouted bed combustor at different values of spouting gas velocity, bed temperature, and char feed size. Both inert particle size and static bed depth were fixed for all experimental runs. The collected data were used to analyse size distributions of both in-bed particles and elutriated fines, and to generate the suitable correlations for carbon attrition rate. Results obtained showed that attrition rate in the spouted bed is proportional to the excess of gas velocity above the minimum spouting gas velocity and the overall bed carbon surface exposed to attrition. The attrition rate constant is slightly dependent on operating bed temperature. Its values for the char studied were 1.6511 × 10^?6 for 707°C operating bed temperature, and 1.1222 × 10^?6 for 850°C, with the average for all tested runs being 1.224 × 10^?6.     

Equilibrium modeling of gasification: Gibbs free energy minimization approach and its application to spouted bed and spout-fluid bed gasifiers

Spouted beds have been found in many applications, one of which is gasification. In this paper, the gasification processes of conventional and modified spouted bed gasifiers were considered. The conventional spouted bed is a central jet spouted bed, while the modified spouted beds are circular split spouted bed and spout-fluid bed. The Gibbs free energy minimization method was used to predict the composition of the producer gas. The major six components, CO, CO₂, CH₄, H₂O, H₂ and N₂, were determined in the mixture of the producer gas. The results showed that the carbon conversion in the gasification process plays an important role in the model. A modified model was developed by considering the carbon conversion in the constraint equations and in the energy balance calculation. The results from the modified model showed improvements. The higher heating values (HHV) were also calculated and compared with the ones from experiments. The agreements of the calculated and experimental values of HHV, especially in the case of the circular split spouted bed and the spout-fluid bed were observed.     

贴体坐标系下喷动床内气固两相流体动力特性的数值模拟

采用稠密固相动力-摩擦应力模型,建立喷动床内气固两相双流体模型．应用贴体坐标系使得计算网格与喷动床的倒锥体边界相一致．通过数值模拟获得喷动床内喷射区、环隙区和喷泉区内颗粒速度及浓度分布．计算结果表明,喷泉区具有强烈的气固两相质量和动量交换．当倒锥体倾斜角度达到60°,在射流入口处形成一瓶颈．研究表明颗粒间滑动-滚动摩擦应力对环隙区颗粒流动具有明显的影响．     

Combustion in crater beds

A preliminary study of a new type of heat-recirculating particulate bed combustor has been carried out with a view to overcoming some limitations arising in the scaling up of spouted bed combustors. A fountain of particles, somewhat similar to that produced in spouted beds, is raised by a jet of gaseous reactants flowing downward into a crater formed below the bed surface. Reactants are preheated prior to combustion both by heat transfer from the products across the walls of the inlet tube and by the interaction of reactants with the inert particles heated by the flame. Combustion characteristics are studied for single and multiple inlet tubes in small laboratory burners and in a much larger 50 KW system. Crater beds are compared with other two-phase combustors, especially spouted beds. They readily lend themselves to scaling up by the use of multiple jets, from one or from several inlets, and recirculate heat between products and reactants both within the craters and by heat transfer to the inlet tubes. Tests show that they can be used either with gaseous reactants entering through the jet or with only oxidant introduced in that way, fuel being included within the bed. Stability limits established for the laboratory burners show a leaner burning capability than is achievable in spouted or fluidized beds and the device offers several advantages over other circulating two-phase systems.     

导流管喷动床流体动力特性的实验研究

对以小米为物料的常规喷动床及导流管喷动床全床压降随表观气速变化规律进行了实验研究．结果表明，与常规喷动床相比，导流管喷动床不仅最小喷动速度、操作压降和最大压降均大幅减小，而且夹带高度较小时会在达到稳定喷动之前发生有利于操作的不稳定喷动现象．此外，导流管喷动床的流体动力特性受料床高度影响不大，但受导流管内径和夹带高度的影响显著．最后，依据实验结果提出了导流管喷动床最小喷动速度的关联式．     

Spouted and spout-fluid bed combustors 1: Devolatilization and combustion of coal volatiles

The devolatilization and volatile combustion of a single coal particle in spouted and spout-fluid beds have been studied. The results showed that the flame extinction time increases with the particle diameter, and decreases with the bed temperature. When the bed temperature and the air flow rate were fixed, the operation modes (spouted or spout-fluid bed) showed less effect on the mean flame extinction time. A mathematical model of the spouted bed mode for preignition and postignition periods has also been developed assuming the devolatilization rate to be controlled by heat transfer and multireaction pyrolysis kinetics based on volatile products. Ignition, heat transfer back from the volatile flame to the particle surface, variation in flame temperature, and the hydrodynamics of SB are taken into account. The model predictions, with some adjusting parameters, were in good agreement with experimental results.     

Experimental Study on Oxy-Fuel Combustion and NO Emission in a Spouted-Fluidized Bed with under Bed Feeding

The spouted-fluidized bed is modified from the classical fluidized bed device, which combines the features of spouted and fluidized beds. In the present work, the performance of oxy-fuel spouted-fluidized bed combustion with under bed feeding and its effect on NO emission were systematically investigated. The results revealed that it was feasible to use a spouted-fluidized bed combustor for oxy-fuel combustion with real flue gas recycling. The transition from air combustion to oxy-fuel combustion was smooth and the concentration of CO_2 in the flue gas could be as high as 90% steadily(dry base). Increasing the reaction temperature exhibited a negative effect on NO emission. Compared with that under the shallow bed, the concentration of NO in the flue gas was lower under the deep bed condition. Besides, the utilization of crush particles was favorable for suppressing NO emission because of the promoted mixing between coal particles and solid bed materials. Furthermore, the addition of limestone was proven to undesirably increase the NO emission during oxy-fuel spouted-fluidized bed combustion.     

Fuel characteristics of gasified coconut shell in a fluidized and a spouted bed reactor

In this study, an attempt has been made to gasify coconut shell in a fluidized and a spouted bed reactor. The effects of the gasification temperature on individual gas components, their yields and heating values for both types of beds have also been studied. The fluidized bed appears slightly superior to the spouted bed both in respect to heating value and gas yield over the temperature range studied.     

The flash pyrolysis of cellulosic materials using concentrated visible light

The radiant flash pyrolysis of Avicel cellulose and kraft paper particles using concentrated visible light is described. The particles circulate in a clear quartz spouted bed reactor while undergoing pyrolysis in an incident radiant flux of up to 200 W/cm². This flux is supplied by an arc image furnace which uses a 5 kW Xenon bulb as its light source. The volatile pyrolysis products are quenched by the steam flow used to spout the bed and are entrained out of the reactor before secondary reactions can occur, ensuring a high sirup yield (63 per cent from cellulose). The major sirup component is levoglucosan.     

喷动床反应器内流体动力特性的数值模拟

采用欧拉-欧拉双流体模型,颗粒动理学理论模拟颗粒相流动,对喷动床核反应器内的流体动力行为进行了数值模拟.模拟得到了喷动床核反应器内颗粒浓度标准方差、空隙率和颗粒速度分布.研究结果表明喷动床核反应器内颗粒浓度标准方差先逐渐增大至最大值后下降.分析了摩擦应力模型和倒锥体角度等影响因素对喷动床核反应器内的流体动力特性的影响.     

单颗粒海藻在流化床内燃烧试验及灰色关联分析

在流化床内进行了单颗粒海藻(条浒苔)的燃烧试验,研究了床高、床温和流化风速对条浒苔颗粒燃烧后剩余质量和固定碳残留率的影响,并对各因素的影响程度进行了灰色关联分析.结果表明:床温和流化风速对条浒苔颗粒燃烧后剩余质量和固定碳残留率的影响较大,而床高对其的影响较小;各工况因素影响固定碳燃尽的主次依次为:床温>流化数>床高,在研究工况范围内床温是影响燃烧的最主要因素.     

Spouted BED combustion of paddy husk

This communication reports the results of an experimental study of spouted bed combustion of paddy husk. The results indicate that husk combustion intensity of the order of 350 kg/h — m² of reactor area is possible with a combustion efficiency of over 85 per cent. Selection of sand size and bed-depth for the spouted bed have emerged to be important parameters in view of pressure drop across bed and entrainment from combustor. The changes in efficiency of combustion were insignificant for different particle size and different bed depths. However there seems to be an optimum combustion intensity i.e. 350 kg/h — m² below and above which combustion efficiency decreases.     

Superheated steam drying of sawdust in continuous feed spouted beds – A design perspective

Spouted bed drying technology shows promising results for the drying of unscreened sawdust in superheated steam. In this paper, the experiences from designing, running and evaluating two spouted bed continuous feed dryers are presented. Stable running conditions and drying results have been achieved. This has been particularly important for sawdust that will be compressed into pellets or briquettes. The spouted bed superheated steam dryer also shows high potential for energy efficient integration into sawmills. Our recommendation is thus, to use the outlet steam temperature as the control parameter for the outlet moisture content. A drying rate above and one below the fibre saturation level, can be identified. Visual observations through the viewing glass in the drying zone in both the dryers clearly showed that not all of the material participated in the spout at all times; there were, however, no indications of dead zones. A heat transfer analysis indicated that only about 70% of the surface area of the material was in thermal contact with the steam. This paper sums up the experiences regarding drying properties, control and system properties obtained when sawdust is dried using superheated steam as the drying medium. Further work on standardised dryers in series or in parallel is necessary to increase the capacity in the spouted bed dryer.     

Modeling and countermeasures of combustion characteristics of char particles in CFBC

INTRAODUCTIONAsahigh-efficiencyandcleancoalcombustiontechnology,circulatingfluidizedbed(CFB)combustiontechnologyachievesrapiddevelopmentinChinaforburningvariouslow--gradefuels.ThescalerupofCFBboilersbecomesakeypointconcernedbytheCFBboilerdesigners.At...     

固宝床层中四种不同粒径柱状活性炭流动阻力特性

采用活性炭脱硫制酸,床层阻力是活性炭床层在工程技术设计中一个重要的特征数据,通过测量4种不同粒径活性炭的阻力特性,为工程设计提供了依据.实验表明在层流区时,平均阻力系数随Re数的增大而减小,层流向紊流过渡区时,平均阻力系数随Re数的增大而增大.入口效应仅在低Re数、床层总阻力较小时对床层平均阻力系数影响较大.在层流区时小颗粒直径的活性炭(1mm)床层平均阻力系数随床层高度增大而增大,大颗粒直径活性炭(3mm,6mm,10mm)床层平均阻力系数随床层高度的增大而减小.过渡区中大颗粒直径活性炭的平均阻力系数随床层高度增大而增大.     

无烟煤流化床燃烧中热破碎现象的研究综述

归纳用于衡量破碎程度的参数,分析产生破碎的机理,研究影响热破碎的因素,讨论破碎现象对燃烧的作用。总结认为。流化床燃烧中。无烟煤的破碎具有较大随机性,受煤质影响极大,粒径、炉床温度、停留时间、流化介质及流化速度等对破碎也有重要影响。煤的破碎有利于提高煤焦颗粒的燃烧速率,但同时也会增加炉床内可扬析颗粒数量,导致飞灰未燃碳含量增加的后果。实现破碎物料的准确快速取样和建立破碎前后颗粒平均粒径之间的关系是今后破碎研究工作尚待解决的问题。     

Studies on the carbon reactions in the anode of deposited carbon fuel cells

The carbon reactions in the anode of deposited carbon fuel cells were studied experimentally and theoretically. Deposition experiments were conducted by decomposing methane in a thermogravimetric analyzer at 800 °C, with both NiO or YSZ powders and small chips of an unused anode-supported SOFC button cell used separately as bed materials. The carbon tended to deposit on the Ni surfaces with the NiO or YSZ powders, while with the anode chips, the deposited carbon formed particles comparable in size to the Ni or YSZ particles with little carbon deposited near the electrolyte where the electrochemical reactions occur. Thus, the results infer that the deposited carbon has little opportunity to participate in the electrochemical reactions. A two-dimensional isothermal model was then developed to examine the influence of the deposited carbon on the cell performance. The results show the diffusion coefficient of CO has the largest influence, followed by the gasifying reactivity and the electrochemical reactivity of the carbon. Finally, a short deposition time and a high methane concentration are favored to improve the performance of deposited carbon fuel cells.     

底饲进料循环喷动床进料与回料混合特性及影响因素

分别以石英砂和消石灰模拟进料和回料,对一台0.6m×15m底饲进料循环喷动床脱硫塔内颗粒混合特性进行了研究。利用石英砂和消石灰在水中溶解度的差异计算得到底饲进料与回料在不同位置的混合熵和不同高度上的混合指数,并分析不同操作参数对塔内颗粒混合行为的影响。研究结果表明:混合指数能够很好地反映塔内进料与回料颗粒的混合质量;随着流化速度的提高,塔内不同高度上的混合指数呈上升趋势;喷射速度和循环倍率对塔内尤其是反应塔底部的颗粒分布特性有明显影响,采用较高的喷射速度和循环倍率,混合指数随之上升,说明塔内颗粒的混合质量得到改善。     

旋涡流化床旋风燃烧的动力学研究

以旋涡流化床悬浮空浮空间喷入二次风形成一强放流场和气固悬浮流动为物理模型,试验研究了床面夹带到悬浮空间颗粒群的运动行为及气固两相浓度场的匹配,指出在气相强旋湍流的作用下,在近壁区形成一稳定的高浓度的颗粒悬浮层,颗粒在炉内的平均停留时间延长,气固滑移速度增大,两相混合强并充分接触,良好的空气动力结构对提高炭粒在悬浮空间的燃尽度,降低场析可燃物质损失十分有利,本文研究结果,对降低常规鼓泡床及抛煤机链条炉内的飞灰可燃物损失,提高悬浮空间的气流横向混合速率有重要参考价值。