磁稳流化床研究与应用进展

磁稳流化床（MSFB）作为一种新型反应器,兼具固定床和流化床的众多优点,具有巨大的应用前景。本文综述了MSFB近年来在基础研究和应用上取得的进展。基础研究方面主要介绍了磁场强度和液相流速对床层结构的影响,以及床层空隙率、操作稳定性和传递特性等研究情况;应用方面介绍了MSFB在生物化工、能源和环境工程等领域的应用。最后分析了MSFB目前存在的不足,如对于一定的反应体系未找到相应合适的磁性催化剂、操作温度高于磁性载体的居里温度时,MSFB将无法操作、磁场发生装置释放出大量的热量对磁性载体和反应过程产生影响、难以确定稳定操作区域。并指出其今后的主要研究方向为磁性载体催化剂的研究与开发及对MSFB的稳定性判据、传热、传质、强化反应过程机理、反应器放大规律、工业化应用装置设计等方面的研究。     

Enhanced weathering to capture atmospheric carbon dioxide: Modeling of a trickle-bed reactor

Enhanced weathering (EW) of alkaline minerals can potentially capture CO₂ from the atmosphere at gigaton scale, but the reactor design presents great challenges. We model EW with fresh water in a counter-current trickle flow packed bed batch of 1–10 mm calcite particles. Weathering kinetics are integrated with the mass transfer of CO₂ incorporating transfer enhancement by chemical reaction. To avoid flooding, flow rates must be reduced as the particles shrink due to EW. The capture rate is mainly limited by slow transfer of CO₂ from gas to liquid although slow dissolution of calcite can also play a role in certain circumstances. A bed height of at least 7–8 m is required to provide sufficient residence time. The results highlight the need to improve capture rate and reduce energy and water consumption, possibly through enriching the feed with CO₂ and further chemical acceleration of the mass transfer.     

Multi-field synergy study of CO2 capture process by chemical absorption

Carbon dioxide capturing from the flue gas of power stations is an effective way to mitigate the global warming. In order to predict the performance from startup to stable operation in CO₂ absorption process, a multi-field synergy model was developed based on CO₂ capture process in a packed column by means of monoethanolamine (MEA). The model suggests that the integral diffusion–reaction coefficient plays an important role in the diffusion, fluid flow, heat transfer and chemical reaction processes. The influences of the fluid flow, heat transfer and chemical reaction can be justified using corresponding synergy numbers, quantifying multi-field interactive dynamic characteristics of the CO₂ capture process. The simulation shows a good agreement compared with data in the literature. The results show that the packing Reynolds number can be used as a criterion to choose the proper packing. The less the Reynolds number is, the more efficient the reaction absorption is. The average synergy number F_dc would be decreased by 20% with 6 K temperature drop and be descended by 7% with the 2.5% solvent weight percentage increment, which improved the efficiency of CO₂ capture by about 5% and 14%, and lowered the energy consumption by about 5%. The average synergy number F_dh would be decreased by about 8% with the 0.062 mol/molMEA lean solvent loading increment, which improved the efficiency by about 15% and lowered the energy consumption by 5%. After comparing with CMR-2, Raschig rings, Berl saddles and Pall rings, the 33% less average synergy number F_df of the CMR-2 packing with about 5% drop in energy consumption yields the highest efficiency of 71%, which is 10% higher than that of the Berl saddle packing. The results indicate that the proposed multi-field synergy model is an effective way to intensify the capture process as a guideline with the priority of precision and simplicity.     

Modeling the fischer-tropsch reactionin a slurry bubble column reactor

Reactant (CO and H 2 ) concentration and conversion profiles were determined as a function of axial distance for the Fischer-Tropsch reaction in a slurry bubble column reactor. Model equations were developed from the basic concepts, i.e., conservation of mass and momentum, and combined with iron catalyst reaction kinetics as well as mass transfer coefficients, gas, liquid, and solid phase holdup, Henry's Law constants, minimum fluidization velocity, and terminal velocity obtained from empirical correlations. Concentration profiles and conversion were determined for varying key process variables: liquid-phase velocity and rate constant. Results suggest that the reaction is kinetically limited and that conversion is proportional to liquid velocity. Thus, process improvements can be achieved by either maximizing liquid-phase velocity or increasing the rate constant by modifying the catalyst.     

低能耗化学吸收碳捕集技术展望

低能耗的CO₂捕集技术对“碳减排”有重要意义。化学吸收法是工业常用的CO₂捕集方法,过程能耗高、成本高,限制了大规模的工业应用。近年来,随着新型吸收剂的开发和吸收解吸装置的设计,过程能耗有所降低,在我国已有多套碳捕集示范装置。然而进一步降低捕集能耗,节约捕集成本是实现“碳中和”的不变追求。本文基于溶剂化学吸收CO₂研究,提出以下化学吸收法的研究方向：开发广泛的相变吸收理论,构建吸收体系数据库,建立定量预测模型,以实现吸收体系的分子设计;强化气液传质,设计液相传热部件和气液分离空间,研发高效吸收解吸设备,以提升碳捕集效率;耦合化学吸收和矿化,实现原位CO₂吸收固定,提升过程经济性。通过化学吸收技术的系统研发,以期促进低能耗的碳捕集,助力祖国实现“碳中和”。     

气固两相流内中空多孔催化剂性能的数值模拟

气固流态化过程中流体和颗粒分别聚集,形成稀密两相,严重限制其传质效率和反应速率的提高。针对此问题,本工作设计了一种中空多孔结构的催化剂颗粒,通过模拟方法研究该颗粒对稀密两相气相传质与反应的影响,及其在稀密相间转换的时间尺度。结果表明,一定的流动强度时,在颗粒稀密相转换的时间尺度内,中空多孔结构的颗粒能够有效地在稀相存储反应气体,并在密相释放,为密相提供额外的反应气体,增强体系的整体反应效率。当催化反应速率高于传质速率时,在所研究的流动条件下中空多孔颗粒体系的反应效率比实心球形颗粒体系高出26.92%~29.55%。可以预见在稀密相分布更广的大型气固流化床反应器中,中空多孔结构的催化剂颗粒能够更为有效地提高反应器的整体效率。     

多晶硅还原炉内流场及温度场的研究

多晶硅还原炉（CVD reactor）是西门子法生产多晶硅的主要设备。硅在多晶硅还原炉（CVD reactor）内的生长是一个复杂的过程,涉及动量、热量、质量传递以及化学反应,炉内流体流动分布是影响还原能耗的关键因素。在这项研究中主要考虑如何提高还原炉中流场和温度场的均匀性。提出了一种新的还原炉设计方案,与传统的多晶硅还原炉相比,在新的还原炉内加入了内罩,从而形成了一种不同的气体流动方式。在新的还原炉内,气体进口和气体出口被划分到不同的区域,气体从气体进口进入CVD reactor后向上流动同时参与气相沉积反应,反应后通过内罩的顶部,最后从气体出口流出。研究重点是内罩结构的设计,以期可以提高还原炉内部流场及温度的均匀性。通过计算流体力学研究,现在水平方向上温度梯度很小,同时有效地减小了回流区域面积。本研究提供了提高多晶硅还原炉内部流场及温度场均匀性的方法。     

MODELING THE FISCHER-TROPSCH REACTIONIN A SLURRY BUBBLE COLUMN REACTOR

Reactant (CO and H 2 ) concentration and conversion profiles were determined as a function of axial distance for the Fischer-Tropsch reaction in a slurry bubble column reactor. Model equations were developed from the basic concepts, i.e., conservation of mass and momentum, and combined with iron catalyst reaction kinetics as well as mass transfer coefficients, gas, liquid, and solid phase holdup, Henry's Law constants, minimum fluidization velocity, and terminal velocity obtained from empirical correlations. Concentration profiles and conversion were determined for varying key process variables: liquid-phase velocity and rate constant. Results suggest that the reaction is kinetically limited and that conversion is proportional to liquid velocity. Thus, process improvements can be achieved by either maximizing liquid-phase velocity or increasing the rate constant by modifying the catalyst.     

一氧化碳等温变换技术进展

对现代合成氨CO变换技术中发展起来的不同种类的固定床等温反应器进行了比较 ,从转化率、操作稳定性、结构复杂程度及发展前景等方面进行了论述。特别分析了另一类等温反应器———流化床反应器的特点 ,并结合其在传热、传质、处理量及操作等方面的优势和流态化技术的发展。流化床反应器在CO变换过程中的工业化应用很有前景     

基于太阳能蓄热过程的甲烷二氧化碳重整研究进展

热化学储能技术因为其储能密度高、热损小、能长距离运输等优点而成为保证太阳能长久稳定供应的关键技术。本文对基于甲烷二氧化碳重整反应的太阳能热化学储热系统研究现状进行了回顾,重点讨论了甲烷重整催化剂、重整反应器以及储能系统整体的传热特性等3个方向的研究进展。指出新型高效催化剂以及反应器开发和性能测试是目前该领域的主要研究方向。发现辐射热损失、非均匀温度分布特性、辐射热流的时变波动特性,以及由此造成的能量与化学反应的不匹配限制了热化学系统能量储存效率的进一步提高,并提出催化剂的催化特性与物性/结构参数依变关系,反应器辐射吸收特性、传热传质特性和反应特性之间的相互作用机制,以及系统时变动态特性与反应物流/辐射能流的匹配关系是建立甲烷重整热化学储能系统优化设计理论亟待解决的关键问题。     

耦合传质的羰基化固定床反应器传热模拟分析

固定床反应器中进行强放热反应时, 反应器的热点温度对操作参数变化敏感,容易引起飞温,导致转化率下降,影响催化剂寿命。为强化羰基化固定床反应器内热质传递与化学反应的协同性,建立考虑颗粒内扩散影响的羰基化固定床反应器拟均相一维传热模型,考察操作参数对床层热点温度、反应转化率、床层温升的影响。不仅体现传热传质和反应的协同作用,而且影响关系明晰、求解方便。为保证反应转化率,本实验条件下确定催化剂颗粒直径小于等于1.5 mm。反应器入口温度/冷却剂油温既要满足床层热稳定性需求,又要使反应转化率和床层温升都在合理范围内。模拟结果表明在床层入口温度升高的同时,可通过降低冷却剂油温获得良好的反应转化率和较小的床层温升。在此基础上,考察入口环氧乙烷浓度对反应转化率和床层温升的影响。本研究可为固定床反应器满足转化率要求、床层合理温升而选择催化剂颗粒直径、床层入口温度、冷却剂油温和床层入口浓度等操作参数提供计算依据。     

Mass transfer in trickle-bed reactors at low reynolds number

Mass transfer rates were determined in a 3.4 cm i.d. trickle-bed reactor in the absence of reaction by absorption measurements and in presence of reaction. Gas flow rates were varied from 0-100 l/h and liquid flow rates from 0-1.5 l/h. The catalyst particles were crushed to an average diameter of 0.054 and 0.09 cm. Mass transfer coefficients remained unaffected by change in gas flow rate but increased with liquid rate. The data from absorption measurements were evaluated with predictions based upon plug-flow and axial dispersion model. Mass transfer coefficients were found greater in case of axial dispersion model than that of plug-flow model specially at low Reynolds number (Re₁ < 1).Hydrogenation of α-methylstyrene to cumene using a Pd/Al₂O₃ catalyst was taken as a model reaction. Intrinsic kinetic studies were made in a laboratory-stirred-autoclave. Mass transfer coefficients were determined using these intrinsic kinetic data from the process kinetic measurements in trickle-bed reactor. Mass transfer coefficients under reaction conditions were found to be considerably higher than those obtained by absorption measurements.Correlations were suggested for predicting mass transfer coefficients at low Reynolds number.The gas to liquid mass transfer coefficients for lower gas and liquid flow rates were determined in a laboratory trickle-bed reactor. The effect of axial dispersion on mass transfer was considered in order to evaluate the experimental data. Three correlations were formulated to calculate the mass transfer coefficients, which included the effect of liquid loading, particle size and the properties of the reacting substances. The gas flow rate influences the gas to liquid mass transfer only in the region of low gas velocities. In the additional investigations of gas to liquid mass transfer without reaction in trickle-bed reactor, the mass transfer coefficients were determined under reaction conditions and the intrinsic kinetics was studied in a laboratory scale stirred autoclave with suspended catalyst. A few correlations are formulated for the mass transfer coefficients. A comparison with the gas-liquid mass transfer coefficient obtained by absorption measurements showed considerable deviations, which were illustrated phenomenologically.     

A novel reverse flow reactor coupling endothermic and exothermic reactions: Part II: Sequential reactor configuration for reversible endothermic reactions

The new reactor concept for highly endothermic reactions at elevated temperatures with possible rapid catalyst deactivation based on the indirect coupling of endothermic and exothermic reactions in reverse flow, developed for irreversible reactions in Part I, has been extended to reversible endothermic reactions for the sequential reactor configuration. In the sequential reactor configuration, the endothermic and exothermic reactants are fed discontinuously and sequentially to the same catalyst bed, which acts as an energy repository delivering energy during the endothermic reaction phase and storing energy during the consecutive exothermic reaction phase. The periodic flow reversals to incorporate recuperative heat exchange result in low temperatures at both reactor ends, while high temperatures prevail in the centre of the reactor. For reversible endothermic reactions, these low exit temperatures can shift the equilibrium back towards the reactants side, causing ‘back-conversion’ at the reactor outlet.The extent of back-conversion is investigated for the propane dehydrogenation/methane combustion reaction system, considering a worst case scenario for the kinetics by assuming that the propylene hydrogenation reaction rate at low temperatures is only limited by mass transfer. It is shown for this reaction system that full equilibrium conversion of the endothermic reactants cannot be combined with recuperative heat exchange, if the reactor is filled entirely with active catalyst. Inactive sections installed at the reactor ends can reduce this back-conversion, but cannot completely prevent it. Furthermore, undesired high temperature peaks can be formed at the transition point between the inactive and active sections, exceeding the maximum allowable temperature (at least for the relatively fast combustion reactions).A new solution is introduced to achieve both full equilibrium conversion and recuperative heat exchange while simultaneously avoiding too high temperatures, even for the worst case scenario of very fast propylene hydrogenation and fuel combustion reaction rates. The proposed solution utilises the movement of the temperature fronts in the sequential reactor configuration and employs less active sections installed at either end of the active catalyst bed and completely inactive sections at the reactor ends, whereas propane combustion is used for energy supply. Finally, it is shown that the plateau temperature can be effectively controlled by simultaneous combustion of propane and methane during the exothermic reaction phase.     

Dynamic simulation of a cascade fluidized-bed membrane reactor in the presence of long-term catalyst deactivation for methanol synthesis

In this work, a dynamic model for a cascade fluidized-bed hydrogen permselective membrane methanol reactor (CFBMMR) has been developed in the presence of long-term catalyst deactivation. In the first catalyst bed, the synthesis gas is partly converted to methanol in a water-cooled reactor, which is a fluidized-bed. In the second bed, which is a membrane assisted fluidized-bed reactor, the reaction heat is used to preheat the feed gas to the first bed. This reactor configuration solves some observed drawbacks of new conventional dual type methanol reactor (CDMR) and even fluidized-bed membrane dual type methanol reactor (FBMDMR) such as pressure drop, internal mass transfer limitations, radial gradient of concentration and temperature in both reactors. A dynamic two-phase theory in bubbling regime of fluidization is used to model and simulate the proposed reactor. The proposed model has been used to compare the performance of a cascade fluidized-bed membrane methanol reactor with fluidized-bed membrane dual-type methanol reactor and conventional dual-type methanol reactor. The simulation results show a considerable enhancement in the methanol production due to the favorable profile of temperature and activity along the CFBMMR relative to FBMDMR and CDMR systems.     

固定床煤气化过程的数学模型

根据气化原料与氧气、二氧化碳和水蒸气反应的动力学参数,在三传一反的基础上,建立了固定床煤气化过程的数学模型;对加压气化炉、水煤气炉等进行了模拟计算与分析。     

Strategies for size reduction of microreactors by heat transfer enhancement effects

One of the likely aims of reactor miniaturization in the field of chemical production and energy generation is to increase the conversion to the desired product and the selectivity of the process through better control of heat and mass transfer. In addition to the effects related to miniaturization, a further increase of the transfer coefficients is achieved by applying microstructuring techniques. In this context, three different approaches for heat transfer enhancement in miniaturized reaction systems are presented. The ideas put forward rely on entrance flow effects, inertial flows in meandering channels, and suppression of axial heat conduction. Among these ideas the entrance flow effect, realized by an arrangement of microfins with a typical dimension of a few hundred micrometers, provides the most efficient heat transfer. It is found that a heat transfer enhancement of at least one order of magnitude can be achieved compared to unstructured channels. On this basis, a miniaturized heat-exchanger reaction system is investigated, where a kinetic model of an endothermic, heterogeneously catalyzed gas-phase reaction is used. The miniaturized heat-exchanger reactor, both with and without heat transfer enhancement, is subsequently benchmarked against conventional fixed-bed technology. It is shown that, for the reaction system under study, a substantial reduction of the required amount of catalyst can be achieved in microsystems.     

STRATEGIES FOR SIZE REDUCTION OF MICROREACTORS BY HEAT TRANSFER ENHANCEMENT EFFECTS

One of the likely aims of reactor miniaturization in the field of chemical production and energy generation is to increase the conversion to the desired product and the selectivity of the process through better control of heat and mass transfer. In addition to the effects related to miniaturization, a further increase of the transfer coefficients is achieved by applying microstructuring techniques. In this context, three different approaches for heat transfer enhancement in miniaturized reaction systems are presented. The ideas put forward rely on entrance flow effects, inertial flows in meandering channels, and suppression of axial heat conduction. Among these ideas the entrance flow effect, realized by an arrangement of microfins with a typical dimension of a few hundred micrometers, provides the most efficient heat transfer. It is found that a heat transfer enhancement of at least one order of magnitude can be achieved compared to unstructured channels. On this basis, a miniaturized heat-exchanger reaction system is investigated, where a kinetic model of an endothermic, heterogeneously catalyzed gas-phase reaction is used. The miniaturized heat-exchanger reactor, both with and without heat transfer enhancement, is subsequently benchmarked against conventional fixed-bed technology. It is shown that, for the reaction system under study, a substantial reduction of the required amount of catalyst can be achieved in microsystems.     

冷凝液运动行为强化含有不凝气的蒸汽冷凝过程研究

基于场协同机制,对强化含有不凝气体的蒸汽冷凝过程的速度场与浓度梯度场协同作用进行了理论分析,提出利用冷凝液动态行为所产生的气液界面效应来强化混合蒸汽冷凝传热特性新思路.为进一步验证界面效应对气相传质扩散过程的影响,在不凝气摩尔含量为10%以内的混合蒸汽层流流动条件下,对冷凝液沿冷凝表面流动的常规膜状冷凝和冷凝液以液滴滴落方式定向脱离表面的两种排液方式下的膜状冷凝、冷凝液脉动的锯齿形滴膜共存冷凝和完全滴状冷凝四种模式下的冷凝传热特性进行了对比实验,比较分析了冷凝液运动行为影响传热特性的实质.实验结果表明,在不需要增加能耗的情况下,利用重力作用下冷凝液的运动行为产生的剪切作用和附加速度场,对气相边界层内的扩散传质过程能够产生协同作用,可以达到传热传质的无源强化效果.     

Kinetics and Heat Exchanger Design for Catalytic Ortho‐Para Hydrogen Conversion during Liquefaction

A major challenge for hydrogen liquefaction is the required catalytic ortho‐para hydrogen conversion. Efficient liquefaction plants use catalyst‐filled plate‐fin heat exchangers for the conversion. Kinetics of the allotropic reaction are determined using raw literature data on common first‐order and a Langmuir‐Hinshelwood kinetics, including temperature and molar concentration dependencies. Evaluation and comparison of the obtained kinetics results in the first‐order approach as the most stable model. A one‐dimensional continuum reactor model of the counterflow‐cooled, catalyst‐filled plate‐fin heat exchanger is developed and tested combining correlations for heat, mass, and momentum transfer as well as a state‐of‐the‐art equation‐of‐state.