Experimental Simulation on Chemical-looping Combustion of Cold Model（英文）

The pressure profiles, gas velocities, solid circulation rate, solids flux, residence time distribution of gas and particles in chemical-looping combustion reactors and gas leakage were studied in a cold flow model unit. And these parameters in both air and fuel reactors were measured in the experimental stage. The experimental results show that gas fluidization velocity in the air reactor is 1.8 m/s, gas fluidization velocity in the fuel reactor 0.5 m/s, and the bed materials inventory of the two reactors between 1.2 to 3.15 kg. The first cold flow model results show that the solid circulation rates are sufficient. The appropriate operating conditions are optimized and the summary of final changes is made the on cold model. The proposed design solutions are currently being verified in a cold flow model simulating the actual reactor(hot) system. This paper presents an overview of the research performed on a cold flow model and highlights the current status of the technology.     

塔式化学链燃烧反应器系统的气固流动特性

目前,化学链燃烧技术主要局限于不充分的燃料转化和低效的碳捕集率。为了解决这一问题,本文提出了一种基于多腔室塔式鼓泡床的化学链燃烧反应器系统。该系统由塔式燃料反应器、空气反应器、旋风分离器、返料器、提升管和下降管组成循环回路。采用压力测量和气体检测的方法,基于冷态模型研究在不同风量下该系统内的压力分布、气固分布、固体循环量以及窜气规律等气固流动特性。结果表明：返料器可以弥补两个反应器间存在的压差,保持系统内的压力平衡;燃料反应器内流化数应控制在3.5~4.0之间,在保证反应器内气固均匀分布的同时,减弱隔板处的压力损失;固体循环量与提升管内压降成正比,最高可达0.013kg/s,主要影响因素为反应器内流化数;返料器至反应器的窜气率为4%~8%,而两个反应器间几乎没有气体窜混,这为热态反应器的设计与运行提供了良好的实验基础。     

大颗粒三相环隙气升式环流反应器流体力学行为

研究了大颗粒体系气升式环流反应器的流体力学行为,考察了表观气速和颗粒质量分数对床层膨胀高度、循环液速和固含率分布的影响。实验结果表明,按颗粒的运动状态不同可以将反应器内的流动分为3个区域,即固定床区域、膨胀床区域和循环床区域,各流动区域内的流动行为存在显著差异。随着颗粒质量浓度的增大,起始流化气速和最小循环气速均显著增大。基于三相流化床的流化模型和环流反应器的特点建立了相应的数学模型,对大颗粒三相气升式环流反应器的起始流化气速和最小循环气速进行了预测,模型预测值与实验测量值吻合良好。     

Innovative Internally Circulating Reactor Concept for Chemical Looping‐Based CO2 Capture Processes: Hydrodynamic Investigation

An experimental hydrodynamic investigation has been carried out for a novel internally circulating chemical looping (ICCL) reactor concept proposed to reduce the technical complexities encountered in conventional chemical looping combustion (CLC) and reforming (CLR) technologies. The concept consists of a single reactor with internal physical separations dividing it into two sections, i.e., the fuel and air sections. The trade‐off for this reduction in process complexity is increased gas leakage between the two reactor sections, so a pseudo‐2D cold‐flow experimental unit was designed. The ICCL concept remains highly efficient in terms of CO₂ separation while ensuring significant process simplifications. The solids circulation rate also proved easy to control by adjusting the fluidization velocity ratio and the bed loading. In the light of the excellent hydrodynamic performance, the ICCL concept appears to be well‐suited for further development as a CLC/CLR reactor model.     

A Two‐Compartment Fluidized Bed Reactor for CO2 Capture by Chemical‐Looping Combustion

Chemical‐looping combustion (CLC) is a combustion method for a gaseous fuel with inherent separation of the greenhouse gas carbon dioxide. A CLC system consists of two reactors, an air reactor and a fuel reactor, and an oxygen carrier circulating between the two reactors. The oxygen carrier transfers the oxygen from the air to the fuel. The flue gas from the fuel reactor consists of carbon dioxide and water, while the flue gas from the air reactor is nitrogen from the air. A two‐compartment fluidized bed CLC system was designed and tested using a flow model in order to find critical design parameters. Gas velocities and slot design were varied, and the solids circulation rate and gas leakage between the reactors were measured. The solids circulation rate was found to be sufficient. The gas leakage was somewhat high but could be reduced by altering the slot design. Finally, a hot laboratory CLC system is presented with an advanced design for the slot and also with the possibility for inert gas addition into the downcomer for solids flow increase.     

Characterization of an airlift reactor with helical flow promoters

The helical flow promoter (HFP), inserted in the downcomer of an airlift reactor (ALR), generates a helical flow pattern in the circulating gas–liquid (solid) mixture. Data on the fluidization capacity, gas holdup, liquid velocity and mass transfer rate for two- and three-phase systems with two different carboxymethylcellulose solutions collected in a 58 L ALR-HFP are presented and compared with those of common pneumatic reactors. Generally, an increasing solid concentration led to a slight decrease in gas holdup and liquid velocity but to a considerable decrease in mass transfer rates. Insertion of HFPs produced a significantly enhanced fluidization capacity of solid particles compared to the common systems.     

Effect of ring‐type internals on solids distribution in a dual circulating fluidized bed system—cold flow model study

The redistribution of solids in a counter‐current circulating fluidized bed (CFB) by effect of ring‐type internals was investigated in a downscaled cold‐flow model. The system consists of two interconnected CFB reactors, in which the primary reactor operates like a common riser while the secondary reactor operates in counter‐current. The unit works without circulation rate control devices and the inventory splits inherently between the two reactors by pressure balance and depending on the fluidization velocities. Previous studies showed an increment in the total pressure drop in the secondary reactor as result of the internals installation. With the purpose of obtaining comparable inventory in the secondary reactor with and without rings, a device for adjustment of total inventory was designed and installed. Effects of the aperture ratio, number of rings, fluidization velocity, and particles circulation rate were studied. The results obtained approach a guideline for the detailed design of similar configurations. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3612–3623, 2013     

Regime classification of macroscopic gas—solid flow in a circulating fluidized bed riser

A conceptual flow regime diagram for a circulating fluidized bed riser is proposed, combining existing investigations with experimental data obtained under idealized conditions in which a fully independent control of gas velocity and solid circulation rate was conducted by use of a screw feeder for solid feed into the riser. The diagram classifies the flow state into five regimes by qualitative transition lines which describe the relationship between gas velocity and solid circulation rate. These regimes are particulate fluidization, bubbling fluidization, turbulent fluidization, dense-phase transport and dilute-phase transport. The diagram suggests that S-shaped bed-density distribution or dense/dilute region interface appears only at limited conditions in the bubbling and turbulent fluidization regimes. These experimental findings were generalized by further experiments in a conventional circulation system with a ball valve between the riser and the downcomer which permits changes in the solid circulation rate and the bed height in the downcomer. The experimental results showed that the bed height in the downcomer has no particular effect on the bed density distribution or the height of the dense/dilute region interface, but an appreciable effect on the lowest gas velocity to maintain steady solid circulation at a given rate. These results are consistent with the above diagram.     

CFB煤燃烧／热解双反应器立管内气固流动模型分析

在循环流化床（CFB）煤燃烧／热解双反应器冷态实验装置上,以硅胶和电厂锅炉灰为实验物料,考察了立管内的气固流动特性,其中立管的内径44mm、高3m。研究结果表明,立管内的气固流动形态为移动床流动,Leung的立管流动模型适合对该系统中立管内移动床流动的描述,经拟合分别得到了立管内气、同速率以及气同相对速率与固体速率之间的经验方程,对热态实验过程中判断立管内的气固流动型态以及料封的稳定性均具有一定的参考价值。     

Design and operation of a 10 kWth chemical-looping combustor for solid fuels - Testing with South African coal

This paper presents the results obtained for the operation of a 10 kW_th chemical-looping combustor using a South African coal as the solid fuel and an oxygen carrier of ilmenite, a natural iron titanium oxide. A chemical-looping combustor for solid fuels was designed and built. It consists of two interconnected fluidized beds, an air reactor where the oxygen carrier is oxidized and a fuel reactor where the coal is gasified by steam and the syn-gases react with the oxygen carrier. A constant coal flow corresponding to a thermal power of 3.3 kW was introduced into the fuel reactor. The tests were conducted at temperatures above 850 °C and for a total test duration of 22 h. The particle integrity of ilmenite and the particle circulation between the two reactors were investigated and verified. The effects of particle circulation on coal conversion, gas conversion of the fuel reactor and carbon separation or CO₂ capture between the air and fuel reactors were investigated. The actual CO₂ capture ranged between 82.5% and 96% while the gas conversion from the fuel reactor was in the range 78-81%, based on measurements of unconverted CO and CH₄.     

Cold Flow Model Study of an Oxyfuel Combustion Pilot Plant

The fluid‐dynamic behavior of a circulating fluidized bed pilot plant for oxyfuel combustion was studied in a cold flow model, down‐scaled using Glicksman's criteria. Pressures along the unit and the global circulation rate were used for characterization. The analysis of five operating parameters and their influence on the system was carried out; namely, total solids inventory and the air velocity of primary, secondary, loop seal and support fluidizations. The cold flow model study shows that the reactor design allows stable operation at a wide range of fluidization rates, with results that agree well with previous observations described in the literature.     

Liquid velocity in a high‐solids‐loading three‐phase external‐loop airlift reactor

BACKGROUND: Airlift reactors are of interest for many different processes, especially for three‐phase systems. In this study the behavior of a high‐loading three‐phase external‐loop airlift reactor was examined. In particular, the effect of parameters such as airflow rate (riser superficial gas velocities between 0.003 and 0.017 m s^?1), solids loading (up to 50%, v/v) on liquid circulation velocity in the air‐water‐alginate beads system as a crucial hydrodynamic parameter was studied. RESULTS: It was observed that increase of the airflow rate resulted in increase of the liquid velocity in the system. The same result but less pronounced was observed by introducing small amounts of solid particles up to 7.5% v/v. However, further introduction of solids caused decrease of the liquid velocity. Laminar regime for the liquid circulation was observed for low gas velocities. Minimum gas velocities for recirculation initiation in the reactor were determined for all solid loadings and linear dependence on the solid content was found. Gas holdups for the three‐phase system were larger than for the two‐phase system in all experiments. A simple model for predicting the liquid circulation velocity in the three‐phase system with high solid loading of low‐density particles was developed. This model is based on the viscosity of integrated medium (solid + liquid) which is a new aspect to analyze this phenomenon. CONCLUSIONS: The developed model shows very good agreement with the experimental results for all solid loadings. It also includes the influence of reactor geometry on the liquid circulation velocity thus enabling optimization. Copyright © 2012 Society of Chemical Industry     

Bed density and circulation mass flowrate in a novel annulus-lifted gas–solid air loop reactor

Air loop reactors (ALR) have been widely used as promising and high-efficiency gas–liquid and gas–liquid–solid reactors. Extensive research on ALR has been conducted, but mostly limited to gas–liquid and gas–liquid–solid systems. Work associated with gas–solid systems has been rare and mainly focused on draft tube-lifted spouted bed treating coarse Geldart B, D particles. The present paper proposed a novel gas–solid air-loop reactor treating fine Geldart A particles and operating in a new annulus-lifted mode, with bubbling or turbulent bed upward flow in the annulus in parallel with bubbling bed downward flow in the draft tube. In view of these differences, distinct hydrodynamic behaviour can be anticipated for the gas–solid annulus-lifted air-loop reactor. The influence of operating conditions and geometric configuration on the distribution of bed density is discussed in a cold model annulus-lifted air loop reactor. A mechanistic model for the circulation mass flowrate is established based on an energy balance and resistance analysis. Nearly 50% and 30% of the energy dissipation rate occurs in the bottom and top regions, respectively. With increasing draft tube height, the energy dissipation rate increases in the annulus and draft tube regions, while it decreases in the top and bottom regions. The circulation mass flowrate decreases with increasing draft tube height. Analysis of the distribution of bed density and energy dissipation rate leads to suggestions regarding optimization of the design and axial location of the ring distributor and gap height.     

大型径向流反应器中流体均布参数的研究

文中研究了工业规模径向反应器中流体的变质量流动规律,在直径3 m,高7 m的大型径向反应器冷模装置中测定了流道静压变化和穿孔阻力,通过数学拟合获得了动量交换系数和侧流穿孔阻力系数。实验结果表明,大型径向反应器冷模装置测得分流和集流动量交换系数Kd和Kc与前人众多的实验室小试单管结果十分相近;而大型冷模的分流和集流侧流穿孔阻力系数dξ和cξ在穿孔流速与主流道流速之比大于2之后分别比实验室小试结果提高了35%和16%左右。上述大型冷模实验研究结果对工业径向流反应器的开发有参考价值。     

串行流化床内气体串混特性

串行流化床反应器间的气体串混是影响化学链燃烧过程的关键因素之一,采用串行流化床冷态试验装置,通过改变各反应器入口流化数,考察反应器间的串混量及串混率。反应器之间的气体串混路径可能有空气反应器和燃料反应器之间的气体串混、燃料反应器内气体向旋风分离器串混、隔离器气体在空气反应器和燃料反应器内的分布。结果表明,在空气反应器和燃料反应器之间加设隔离器能有效阻止两个反应器之间发生气体串混;燃料反应器内少许气体通过反应器内料腿向上串混到旋风分离器排气中,串混率约为2%,这使得该串行流化床化学链燃烧的理论碳捕集效率可以达到98%;燃料反应器流化风速对隔离器内气体在两个反应器的分布影响较小,采用水蒸气流化可避免隔离器气体向空气反应器和燃料反应器内串混所带来的影响。     

Transition from Low Velocity to High Velocity in a Three Phase Fluidized Bed

The onset liquid velocity demarcating the conventional and the circulating fluidization regimes of three‐phase fluidized beds was determined by measuring the time required to empty all particles in a batch fluidized bed at various liquid and gas velocities. Experiments were performed in a gas‐liquid‐solid circulating fluidized bed of 2.7 m in height using glass beads of 0.508 mm in diameter as solid phase and air and tap water as the fluidizing gas and liquid, respectively. The results show that gas velocity is a strong factor on the onset liquid velocity. Higher gas velocity yields a lower onset liquid velocity. It is also demonstrated that the onset liquid velocity has the same value as particle terminal velocity in a gas‐liquid mixture. Within the gas‐liquid‐solid circulating fluidization regime, the solids circulation rate is increased with the total liquid velocity and the auxiliary liquid velocity.     

Predicting axial pressure profile of a CFB

The numerical simulation of CFBs is an important tool in the prediction of its flow behavior. Predicting the axial pressure profile is one of the major difficulties in modeling a CFB. A model using a Particle Based Approach (PBA) is developed to accurately predict the axial pressure profile in CFBs. The simulation model accounts for the axial and radial distribution of voidage and velocity of the gas and solid phases, and for the solids volume fraction and particle size distribution of the solid phase. The model results are compared with and validated against atmospheric cold CFB experimental literature data. Ranges of experimental data used in comparisons are as follows: bed diameter from 0.05 to 0.305 m, bed height between 5 and 15.45 m, mean particle diameter from 76 to 812 μm, particle density from 189 to 2600 kg/m³, solid circulation fluxes from 10.03 to 489 kg/m² s and gas superficial velocities from 2.71 to 10.68 m/s. The computational results agreed reasonably well with the experimental data. Moreover, both experimental data and model predictions show that the pressure drop profile is affected by the solid circulation flux and superficial velocity values in the riser. The pressure drop increases along the acceleration region as solid circulation flux increases and superficial velocity decreases.     

Hydrodynamic Modelling of Internal Loop Airlift Reactor Applying Drift‐Flux Model in Bubbly Flow Regime

A new model for the liquid circulation rates in airlift reactor (ALR) is presented. The model is based on the energy balance for the flow loop (riser, turn riser‐downcomer, downcomer, and turn downcomer‐riser) coupled with a drift flux theory of two‐phase flow gas‐liquid system, considering a bubbly flow regime. The predicted values of the liquid circulation rates by the developed model are compared with experimental results performed in a 22 dm³ internal loop airlift reactor and with the results obtained in the literatures. The proposed model predicted the experimental results very well. Slip velocity relationship based on the drift flux model was proposed; including the gas holdup, bubble size and the liquid physical properties. The predicted slip velocity was similar to that obtained from the literature. The study revealed that appropriate arrangements of internal bioreactor parts can positively influence the liquid circulation velocity at the same energy consumption. The proposed models are useful in the design; scale up and characterization of the internal loop airlift reactors, and provides a direct method of predicting hydrodynamic behaviour in gas‐liquid airlift reactors.     

垂直筛板流化床中FCC催化剂的流化性能

以FCC催化剂颗粒研究垂直筛板流化床内构件对气固两相流化性能的影响,考察了板孔气速、颗粒循环量和帽罩开孔比等筛板结构对流化床压降和提升量强度的影响. 结果表明,气固两相总体逆流流动条件下,帽罩内气速达4 m/s,气固高速并流喷射无气泡,两相接触好、返混小,属快速流态化. 由于没有气泡,床层压力波动小,在塔板上颗粒返混小. 垂直筛板压降随板孔气速、帽罩底隙高度增大而增大,随帽罩开孔比、板孔径增大而减小,颗粒提升量大,床层压降大. 提升量强度随板孔气速、帽罩底隙高度、颗粒循环量增加而增大,随帽罩高度与塔节高度比增大而减少,随帽罩筛孔孔径变化存在最大值. 当帽罩开孔比为1.2~2.5、板孔面积与帽罩截面积比为0.42、帽罩底隙高与板孔孔径比为0.36~0.64时帽罩流化性能较好.     

高硫焦用强混反应器流动特性

根据炼油工业近年来流态化技术的发展及相关新技术的应用,设计了一套适合高硫焦燃烧特点的新型强混反应器冷态实验装置. 强混反应器主要由混合段和提升段两部分构成,两部分的设备结构尺寸分别为f240 mm′3000 mm和f70 mm ′9000 mm. 选取了适合工业应用的实验操作条件：提升段操作表观线速度6~20 m/s,颗粒循环速率20~230 kg/(m2.s). 系统考察了高硫焦模拟颗粒在混合段的流动特性. 通过对强混反应器轴、径向颗粒浓度和速度分布的实验测定,将强混反应器的混合段沿轴向分为两个区,沿径向分为两个或三个区,并提出用径向分布指数来表征颗粒浓度和速度的径向不均匀性.