Cycle performance of Cu-based oxygen carrier based on a chemical-looping combustion process

The cycle life of oxygen carrier（OC） is crucial to the practical applications of chemical looping combustion（CLC）. Cycle performance of Cu/SiO2 prepared with a mechanical mixing method was evaluated based on a CLC process characterized with an added methane steam reforming step. The Cu/SiO2 exhibited high redox reactivity in the initial cycles, while the performance degraded with cycle number. Through characterization of the degraded Cu/SiO2, the performance degradation was mainly caused by the secondary particles＇ fragmentation and the fine particles＇ local agglomeration, which worsened the distribution and diffusion of the reactive gases in the packed bed. A regeneration method of the degraded OC based on re-granulation has been proposed, and its mechanism has been illustrated. With this method, the performance of the degraded OC through 420 redox cycles was recovered to a level close to the initial one.

Theoretical study of reduction mechanism of Fe_(2)O_(3) by H_(2) during chemical looping combustion

An atomic-level insight into the H_(2)adsorption and oxidation on the Fe_(2)O_(3)surface during chemicallooping combustion was provided on the basis of density functional theory calculations in this study.The results indicated that H_(2)molecule most likely chemisorbs on the Fe_(2)O_(3)surface in a dissociative mode.The decomposed H atoms then could adsorb on the Fe and O atoms or on the two neighboring O atoms of the surface.In particular,the H_(2)molecule adsorbed on an O top site could directly form H_(2)O precursor on the O_(3)-terminated surface.Further,the newly formed H-O bond was activated,and the H atom could migrate from one O site to another,consequently forming the H_(2)O precursor.In the H_(2)oxidation process,the decomposition of H_(2)molecule was the rate-determining step for the O_(3)-terminated surface with an activation energy of 1.53 eV.However,the formation of H_(2)O was the ratedetermining step for the Fe-terminated surface with an activation energy of 1.64 eV.The Feterminated surface is less energetically favorable for H_(2)oxidation than that the O_(3)-terminated surface owing to the steric hindrance of Fe atom.These results provide a fundamental understanding about the reaction mechanism of Fe_(2)O_(3)with H_(2),which is helpful for the rational design of Fe-based oxygen carrier and the usage of green energy resource such as H_(2).

Reactivity Investigation on Iron-Titanium Oxides for a Moving Bed Chemical Looping Combustion Implementation

Ilmenite-type natural ore which is constituted mainly of iron-titanium oxide is an interesting candidate as an oxygen carrier in chemical looping combustion (CLC) process. Its reactivity was investigated using methane as reducing gas and air as oxidizing gas. Experiments were carried out in a coupled thermogravimetric–thermo differential analyzer (TGA-DTA). When temperature increases from 700℃ to 1000℃, the reaction rate increases by 50 times while the oxygen transfer capacity passes from 1.8% to 12%. TG-DT analyses showed that the overall mass loss due to ilmenite reduction reached at most 12%. It corresponds to 87% of theoretical mass loss due to the transformation of Fe2TiO5 into Fe and TiO2. It is established that the reduction for the iron-titanium oxides occurs in two steps: Fe2TiO5→ FeTiO3→ Fe + TiO2. The titanium reduction from the state TiO2 to the stage Ti3O5 was observed as well. This behavior is supported by XRD analysis. Subsequent oxidation of the reduced mineral led to recover the starting oxide. The stability of iron-titanium oxides was established over 35 looping cycles of oxidation-reduction, with an increase of 5% of oxygen transfer capacity and reactivity in the first 5 cycles and after that, ilmenite reactivity remained constant. At high temperatures, catalytic effect of ilmenite on methane decomposition leading to carbon deposition is observed. The deposited carbon participates in the reactivity of the oxide.

铈改性CuMn/Al_(2)O_(3)/堇青石整体催化剂的甲苯催化燃烧性能研究

本研究以堇青石为载体,采用超声浸渍法制备了一系列CuMnCe_(x)/Al_(2)O_(3)/堇青石整体式催化剂,同时,通过N_(2)吸附-脱附、XRD、SEM、EDX、H_(2)-TPR、O_(2)-TPD、XPS和EPR等方法对样品的物理、化学性质进行了系统的表征分析。实验结果表明,CuMnCe_(x)/Al_(2)O_(3)/堇青石整体式催化剂中的Ce含量明显影响甲苯催化燃烧性能。其中,CuMnCe_(2)/Al_(2)O_(3)/堇青石整体式催化剂对甲苯氧化具有最高活性,当甲苯浓度为1 g/L、空速为78000 mL/(g·h)、温度为263℃时甲苯转化率达到90%,究其原因为CeO_(2)在CuMnO_(x)上分散均匀,不仅提高了氧空位的浓度和氧物种的迁移率,还增强了催化剂的低温还原性。同时,CuMnCe_(2)/Al_(2)O_(3)/堇青石整体式催化剂在长期评价和循环测试中呈现良好的稳定性。

Reduction Kinetics of Fe-based Oxygen Carriers Using Syngas in a Honeycomb Fixed-Bed Reactor for Chemical-Looping Combustion

Chemical-looping combustion(CLC)is considered to be a vital method for utilizing hydrocarbon fuel with low carbon emissions.A honeycomb fixed-bed reactor is a new kind of reactor for CLC.However,the further application of the reactor is limited by the inadequacy of the kinetic equations for CLC.In this paper,the experimental studies on the kinetic of Fe-based oxygen carriers were carried out by the CLC experiments using syngas which was obtained from one typical type of coal gasification products.The experimental results show that there were two individual stages for the kinetic characteristics during the fuel reaction process.Therefore,the CLC fuel reaction process could be described by a two-stage unreacted-core shrinking model and the reaction rate equations for each of the two phases were provided.In both stages,the dominant resistances were analyzed.The activation energy and the reaction order in both stages were calculated respectively as well.Comparing the experimental results of reaction rate with the calculated results of the obtained rate equations,it could be clearly seen that the reaction kinetics model was appropriate for the CLC in the honeycomb reactor.This work is expected to provide a guideline for the future development and industrial design of the honeycomb CLC reactors from the perspective of kinetics.

Three-dimensional multiphase full-loop simulation of directional separation of binary particle mixtures in high-flux coal-direct chemical-looping combustion system

Coal-direct chemical-looping combustion(CDCLC)is a promising coal combustion technique that provides CO2 capture with a low energy penalty.In this study,we developed a three-dimensional Eulerian-Eulerian multiphase full-loop model for simulating the circulation and separation of binary particle mixtures in a novel high-flux CDCLC system.This model comprised a high-flux circulating fluidized bed as the fuel reactor(FR),a counter-flow moving bed as the air reactor(AR),a high-flux carbon stripper,two downcomers,and two J-valves.This model predicted the main features of complex gas-solid flow behaviors in the system.The simulation results showed that quasi-stable solid circulation in the whole system could be achieved,and the FR,AR,and J-valves operated in a dense suspension upflow regime,a near-plug-flow regime,and a bubbling fluidization regime,respectively.The multiphase flow model of binary particle mixtures was used to predict the mechanisms of directional separation of binary particle mixtures of an oxygen carrier(OC)and coal throughout the system.A decrease in the baffle aspect ratio of the inertial separator improved the coal selective separation efficiency but resulted in a slight decline in the OC selective separation;this is believed to be the result of weakening of particle collisions with the baffle.A higher FR gas velocity had a slightly negative effect on the OC selective separation efficiency,but improved the coal selective separation efficiency;this can be attributed to an increase in the particle-carrying capacity of the gas stream.A decrease in the coal particle size led to better entrainment of the coal particles by the gas stream and this increased the coal selective separation efficiency.In real CDCLC applications,the operating variables for separation of binary particle mixtures should be comprehensively assessed to determine their positive and negative effects on the carbon capture efficiency,OC regeneration efficiency,gas leakage restraint,energy consumption,and fuel conversion.

Simultaneous syngas production with different H_2/CO ratio in a multi-tubular methane steam and dry reformer by utilizing of CLC

For syngas production, the combustion of fossil fuels produces large amounts of CO2 as a greenhouse gas annually which intensifies global warming. In this study, chemical looping combustion （CLC） has been utilized for the elimination of CO2 emission to atmosphere during simultaneous syngas production with different H2/CO ratio in steam reforming of methane （SR） and dry reforming of methane （DR） in a CLC-SR-DR configuration. In CLC-SR-DR with 184 reformer tubes （similar to an industrial scale steam reformer in Zagros Petrochemical Company, Assaluyeh, Iran）, DR reaction occurs over Rh-based catalysts in 31 tubes. Also, SR reaction is happened over Ni-based catalysts in 153 tubes. CLC via employment of Mn-based oxygen carriers supplies heat for DR and SR reactions and produces CO2 and H2O as raw materials simultaneously. A steady state heterogeneous catalytic reaction model is applied to analyze the performance and applicability of the proposed CLC-SR-DR configuration. Simulation results show that combustion efficiency reached 1 at the outlet of fuel reactor （FR）. Therefore, pure CO2 and H2O can be recycled to DR and SR sides, respectively. Also, CH4 conversion reached 0.2803 and 0.7275 at the outlet of SR and DR sides, respectively. Simulation results indicate that, 3223 kmol.h-l syngas with a H2/CO ratio equal to 9.826 was produced in SR side of CLC-SR-DR. After that, 1844 kmol.h-1 syngas with a H2/CO ratio equal to 0.986 was achieved in DR side of CLC-SR-DR. Results illustrate that by increasing the number of DR tubes to 50 tubes and considering 184 fixed total tubes in CLC-SR-DR, CH4 conversions in SR and DR sides decreased 2.69% and 3.31%, respectively. However, this subject caused total syngas production in SR and DR sides （in all of 184 tubes） enhance to 5427 kmol-h-1. Finally, thermal and molar behaviors of the proposed configuration demonstrate that CLC-SR-DR is applicable for simultaneous syngas production with high and low Hx/CO ratios in an environmental friendly process.

Emission characteristics of flue gas during the chemical-looping combustion process for multi-component solid waste

Solid waste has interactions with its flue-gas products during combustion,which offers the possibility of regulating its pollutant emissions.Especially,these interaction pathways would be clearer under anaerobic conditions when the chemical-looping combus-tion(CLC)process is used.The CLC experiments of multi-component solid waste were conducted on a homemade twin-bed reactor and the characteristics of flue gas were investigated for the effect of the mixing ratio of sewage sludge and polyvinyl chloride(PVC).The results indicated that the combustion efficiency was>99.9%for these CLC processes;the highest carbon-conversion rate was obtained at 96.3%for PVC with 60%sludge.The highest NO and SO_(2)emissions were 26%and 19%,respectively,when the sludge was mixed with 20%PVC.As the proportion of PVC blended into the sludge increased,the time when the concentration of NO in the flue-gas peaks moved backwards,while peak SO_(2)concentration moved forward.The general trend was to increase first and then de-crease.In addition,there were multiple peaks in carbon emissions,corresponding to~10%,30%and~70%of the carbon-conversion rate;nitrogen emissions reached 90%of total emissions before the carbon-conversion rate was 40%;sulphur emissions had a longer cycle and were mainly emitted between 10%and 60%of the carbon-conversion rate.The results are expected to provide a reference for solid-waste source suppressing to inhibit the generation of pollutants.

化学链燃烧技术的研究进展

化学链燃烧是一种新型的燃烧方式,具有高效、内分离CO2、低NOx等特点。本文阐述了化学链燃烧的基本技术原理,并从氧载体的筛选与制备、化学链燃烧反应器的发展、化学链燃烧系统分析与数值模拟、化学链燃烧与其它技术的耦合、化学链燃烧技术的拓展等方面对当前化学链燃烧技术的发展现状和存在不足进行了总结分析,指出了化学链发展的5个重点方向:筛选制备性能优异的的氧载体、探讨反应历程和反应机理、设计优化反应器、开展系统分析和数值模拟、拓展应用范围。

CaSO_4氧载体煤基合成气化学链燃烧模拟研究(英文)

相对于金属氧载体,CaSO4作为氧载体用于化学链燃烧,具有成本低、来源广泛和氧传递容量大等诸多优点,但是气相SO2以及各种固相硫沉积物对CaSO4用于化学链燃烧过程造成很大的障碍。基于热力学模拟,对CaSO4氧载体与以合成气为燃料的化学链燃烧进行了模拟研究,结果表明就CaSO4与合成气的反应而言,在燃料反应器中,100℃~400℃的低温反应条件下,主要发生的是合成气中CO和H2的甲烷化反应以及硫酸盐热化学还原反应,反应产物主要是H2S和CaCO3;在400℃~915℃,主要发生的是CO和H2与CaSO4的还原反应,还原产物是CaS和CO2;当反应温度高于915℃时,诸多副反应开始发生,反应物相除了CaS和CO2外,CaO等副产物开始出现;而在空气反应器中,在CaS的整个氧化过程中,CaS再生形成CaSO4的反应都是主要的,但是当空气过量系数ФAR<0.8时,CaSO4与CaS的固相反应以及CaS氧化形成CaO的两个副反应也同时起作用。在燃料反应器中,最优的反应条件是反应温度915℃、常压并严格控制CaSO4的加入量并确保CaSO4氧载体过量系数ФFR^1;而在空气反应器中,提供充足的空气量对于CaS的氧化非常重要,空气过量系数ФAR≥1不仅能确保CaS的充分氧化,而且还能避免CaS氧化过程中SO2的排放和CaO的产生。

固定床上Fe_2O_3载氧燃烧特性实验研究

Fe2O3作为载氧体可以在载氧燃烧过程中实现CO2的分离。在固定床试验台(内径40mm,高1600mm)上,通过改变载氧体在反应器中所处的还原氧化氛围模拟载氧燃烧过程,研究载氧体Fe2O3的载氧燃烧特性。实验载氧体量385g,CO+CO2+N2为还原气体,O2+N2为氧化气体。在900℃下针对CO2对反应的影响进行研究,对载氧体粒径和反应温度的影响进行探讨。为了分析载氧体的反应活性与稳定性,在900℃下对载氧体颗粒进行多次还原氧化循环实验。结果表明,在纯CO的氛围下,Boudouard反应会导致还原过程发生析碳,CO还原气中加入CO2可以抑制析碳的产生。还原反应中载氧体颗粒的比表面积和孔隙率越大,CO的转化率越高。在Fe2O3-Fe3O4阶段,高温不利于CO的转化,但有助于CO在Fe3O4-Fe0.947O/Fe阶段中的转换。通过5～6次的循环实验发现,载氧体在经过第1次反应后会出现一定程度的失活,此后性质保持稳定。

燃煤CO_2减排技术

燃煤CO2等温室气体的大量排放是造成全球气候变暖的一个重要原因。阐述了我国CO2的排放状况,概括了减少燃煤CO2排放的3种途径:提高能源效率、改革传统的煤炭燃烧利用方式、烟气中CO2的捕获与储存。综述了国际社会减排CO2的努力以及各国新一代的洁净煤技术计划。着重介绍了几种燃煤CO2减排的新技术,包括CaO碳酸化-煅烧循环的CO2分离(CCR)技术、O2/CO2循环燃烧技术及化学链燃烧(CLC)技术。比较了CaO碳酸化-煅烧循环的CO2分离技术与使用MEA的吸收技术的经济性。提出了一类用于化学链燃烧的新型非金属氧载体,给出了这些氧载体在与不同气体燃料组成的反应系统的热力学以及动力学特性的一些初步结论。

化学链燃烧技术中载氧体的最新研究进展

介绍了化学链燃烧(CLC)技术的基本概念,指出了其具有在燃烧过程中捕获高浓度CO2,同时消除大气污染物(NOx)等优点。载氧体的性能对其应用非常关键。总结了该领域最近几年新开发的单金属氧化物、复合金属氧化物以及非金属氧化物载氧体的最新研究进展。对具有广泛应用前景的固体燃料化学链燃烧技术及其合适的载氧体做了综述。最后,对化学链燃烧技术中与载氧体相关的重点问题做了展望。

新型节能CO_2零排放工艺——化学循环燃烧技术

介绍了一种新型节能CO2零排放工艺——化学循环燃烧技术中几个热点研究问题,包括热力学分析、氧载体及反应器的设计与选用,探讨了化学循环燃烧技术在我国乃至国际清洁煤燃烧领域的发展前景。还对由化学循环概念发展而来的化学循环重整过程以及水分解制氢过程做了简要的概述,最后展望了化学循环燃烧技术的研究发展趋势。

化学链燃烧国内外研究发展现状

阐述了化学链燃烧的基本技术原理、常见的动力学模型及其载氧体应具备的条件,并从载氧体的选取、化学链燃烧反应器的发展两个方面对当前化学链燃烧技术的发展现状和存在不足进行了总结分析。指出了化学链燃烧反应器应探索的方向和提出采用磷石膏作为载氧体的新想法。

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NH_3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N_2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NH_3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NH_3被铁矿石氧化导致少量NO的生成,还原过程中无N_2O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N_2O的生成。

基于Fe基载氧体的生物质化学链燃烧试验研究

化学链燃烧技术(CLC)是一种含有CO2内分离的新型燃烧技术。以Fe2O3为载氧体,在10 kWth级串行流化床上进行了生物质化学链燃烧的试验研究,探讨了燃料反应器温度、生物质进料量和水蒸气量对2个反应器(燃料反应器+空气反应器)气体产物组成的影响。结果表明较高的反应器温度虽然有助于速控步(即气化反应)的进行,但是受载氧体的载氧率和颗粒循环速率的影响反而不利于CO2捕集。随着生物质进料量的增加,燃料反应器需氧量的上升,不利于燃料反应器CO2的捕集。而水蒸气量的增加有利于燃料反应器CO2的捕集,但是同时也导致H2的出现。

CaO加入条件下煤与CaSO_4氧载体化学链燃烧的反应性能研究

以小型流化床为反应器、水蒸气为气化介质,在CaSO4氧载体中加入CaO颗粒进行煤气化—氧载体还原反应实验。实验结果表明,添加CaO改善了煤气化—CaSO4还原反应性能,提高了煤气化—CaSO4还原反应速率和CO2生成速率。但CaO添加剂的催化作用随反应温度的提高而减弱。900℃是较适宜的反应温度,此温度下加入适量CaO(CaO/CaSO4物质的量比1.18),气态硫化物释放得到显著抑制,SO2和H2S降幅分别为63.19%和27.37%;同时,还能控制CO2被吸收固化成CaCO3的比例低于2%。

新型煤气化间接燃烧联合循环研究

以煤为燃料,通过气化和间接燃烧等技术,实现燃煤发电的CO2分离。水煤浆增压后,利用间接燃烧过程热源气化。以金属氧化物为载氧体,实现间接燃烧(CLC),即载氧体与煤气的“燃烧”和载氧体与空气的再生,“燃烧” 气相产物为H2O(汽)+CO2,冷凝水后,可分离出CO2。结合燃气蒸汽联合循环技术,构成新型煤气化间接燃烧联合循环,实现燃煤高效和CO2分离。文中通过数学建模方法,对系统特性进行仿真计算,预测煤气成分,研究载氧体还原比率、循环倍率、煤气成分等参数对间接燃烧性能的影响,为间接燃烧技术的实验研究和系统概念设计提供基础数据。

煤化学链燃烧装置中串联分离器的数值模拟与性能优化

由于煤化学链燃烧技术中煤灰对载氧体活性具有较强抑制作用,本文提出了通过双级串联旋风分离器分别对载氧体及煤灰进行分离的新方法,并应用雷诺应力RSM(SSG)湍流模型以及DPM颗粒随机轨道模型,考虑气固两相的相间耦合,对煤化学链燃烧装置中的双级旋风分离器进行了数值模拟,根据模拟结果对一级、二级分离器进口尺寸及结构形式进行了优化,并通过实验对分离性能进行了验证。优化后模型的模拟及实验结果均表明:相比原模型,优化模型中90%以上的CaSO_4载氧体从一级分离器排尘口返回炉膛,降低了载氧体流失率;约50%的煤灰颗粒从二级分离器排尘口分离,仅13%左右的煤灰随气流从其排气口排出,有效降低炉膛返灰率,保持载氧体活性,并实现排气的相对清洁。最后指出本文研究结果对煤化学链燃烧装置的高效运行具有重要的参考价值。