Experimental and Numerical Study of Gas-Liquid Flow in a Sectionalized External-Loop Airlift Reactor

The external loop airlift reactor(ELALR)is widely used for gasliquid reactions.It’s advantage of good heat and mass transfer rates compared to conventional bubble column reactors.In the case of fermentation application where a medium is highly viscous and coalescing in nature,internal in riser helps in the improvement of the interfacial area as well as in the reduction of liquidphase back mixing.The computational fluid dynamic(CFD)as a tool is used to design and scaleup of sectionalized external loop airlift reactor.The present work deals with computational fluid dynamics(CFD)techniques and experimental measurement of a gas holdup,liquid circulation velocity,liquid axial velocity,Sauter mean bubble diameter over a broad range of superficial gas velocity 0.0024≤UG≤0.0168 m s 1.The correlation has been made for bubble size distribution with specific power consumption for different plate configurations.The effects of an internal on different mass transfer models have been completed to assess their suitability.The predicted local mass transfer coefficient has been found higher in the sectionalized external loop airlift reactor than the conventional ELALR.

Influence of external circulation on sludge characteristics during start-up of internal circulation reactor

The start-up of external circulationadded internal circulation(IC) reactor was finished in 26 d, 32 d fewer than that of IC reactor. To evaluate the influence of the added external circulation on the development of granular sludge, the characteristics of the granular sludge taken from the two tested laboratory-scale reactors during start-up were studied. The results show that the added external circulation can enhance biomass granulation, accelerate granule development and improve sludge characteristics. At the end of start-up, the granular size of sludge in external circulation-added IC reactor greatly increases with a size distribution much better than that of sludge in IC reactor. The granular sludge originated from external circulationadded IC reactor contains more extracellular polymers and has a greater settling velocity than that from IC reactor. Methanogenic activity of the granular sludge from the external circulationadded IC reactor started 26 d ago reaches 358.23mL·g -1 ·d -1 , 1.66 and 1.20 times as great as that of the sludge from the IC reactor started 26 d and 58 d ago respectively.

Treatment of methanol wastewater in external circulation anaerobic reactor with different inoculums

In order to guide the inoculums selection for the anaerobic treatment of methanol wastewater in the engineering application,two 7 L bench-scale external circulation (EC) anaerobic reactors were operated to investigate the inoculums of anaerobic granular sludge and anaerobic digested sludge,focusing on the efficiency and process stability.The effect of impact concentration and temperature on the performance was studied.The results demonstrated that anaerobic granular sludge as the inoculums could complete the start-up more rapidly than the anaerobic digested sludge,and above 90% COD removal were achieved at the organic loading rate of 10 to 15 kgCOD/(m3·d).The effect of impact COD on the methanogenic activity of sludge was weak and the removal efficiencies recovered gradually in the two reactors.The COD removal efficiencies reduced swiftly to 50%-60% due to the impact temperature.The results indicated that the complex bacterial groups in anaerobic digested sludge benefited to enhance the reactor's capacity for withstanding the temperature shock at some extent.

Influences of top clearance and liquid throughput on the performances of an external loop airlift slurry reactor integrated mixing and separation

A new developed external loop airlift slurry reactor, which was integrated with gas–liquid–solid three-phase mixing, mass transfer, and liquid–solid separation simultaneously, was deemed to be a promising slurry reactor due to its prominent advantages such as achieving continuous separation of clear liquid from slurry and cyclic utilization of solid particles without any extra energy, energy-saving, and intrinsic safety design. The principal operating parameters, including gas separator volume, handling capacity, and superficial gas velocity, are systematically investigated here to promote the capabilities of mixing, mass transfer, and yield in the pilot external loop airlift slurry reactor. The influences of top clearance and throughput of the clear liquid on flow regime and gas holdup in the riser, liquid circulating velocity, and volumetric mass transfer coefficient with a typical high solid holdup and free of particles are examined experimentally. It was found that increasing the gas separator volume could promote the liquid circulating velocity by about 14.0% at most. Increasing the handling capacity of the clear liquid from 0.9 m3·h-1 to 3.0 m3·h-1 not only could increase the output without any adverse consequences, but also could enhance the liquid circulating velocity as much as 97.3%. Typical operating conditions investigated here can provide some necessary data and guidelines for this new external loop airlift slurry reactor to upgrade its performances.

Modeling of Continuous Cross-flow Microfiltration Process in an Airlift External-loop Slurry Reactor

New modified combination mathematical models including the pores blocking models and the cake layer models were developed to describe the continuous cross-flow microfiltration in an airlift external loop slurry reactor. The pores blocking models were created based on the standard blocking law and the intermediate blocking law, and then the cake layer models were developed based on the hydrodynamic theory in which the calculation method of porosity of cake layer was newly corrected. The Air-Water-FCC equilibrium catalysts cold model experiment was used to verify the relevant models.Results showed that the calculated values fitted well with experimental data with a relative error of less than 10%.

Removal of Real Textile Dyes by Electrocoagulation/Electroflotation in a Pilot External-Loop Airlift Reactor

This paper studied the efficiency of electrocoagulation/electroflotation in removing colour from real textile wastewater by using aluminum and iron electrodes in an innovative pilot external-loop airlift reactor of 150 L. The reactor was designed to operate in batch and continuous modes. The real effluent contained 90% of disperse dye and 10% of reactive dye. A complete flotation of pollutants with acceptable mixing was achieved in this reactor using only the overall liquid recirculation induced by H2 microbubbles. The treatment of these discharges was easier using electrodes of iron rather than aluminum. The optimal initial pH was 10 for both aluminum and iron electrodes. By using iron electrodes, the maximum decolourisation efficiency and COD reduction efficiency reached respectively 96% and 65% for 90 minutes of treatment. Similarly, by using aluminum electrodes, the maximum decolourisation efficiency reached 90%, COD reduction reached 51% for 120 minutes of treatment. In the case of an initial pH slightly different to 10, the required time to reach 90% ranged from double to triple.

Hydrodynamics and Mass Transfer of Oily Micro-emulsions in An External Loop Airlift Reactor

This study reports an experimental investigation on hydrodynamics and mass transfer characteristics in a 15.6x10-3 m3 external loop airlift reactor for oil-in-water micro-emulsions with oil to water volume ratio （φ） rang- ing from 3% to 7% （by volume）. For comparative purposes, experiments were also carried out with water. Increase in φ of micro-emulsion systems results in an increment in the gas holdup and a decrease in the volumetric gas-liquid oxygen transfer coefficient and liquid circulation velocity, attributed to the escalation in the viscosity of mi- cro-emulsions. The gas holdup and volumetric mass transfer coefficient for micro-emulsion systems are signifi- cantly higher than that of water system. Two correlations are developed to predict the gas holdup and oxygen trans- fer coefficient

Determination of External Mass Transfer Model for Hydrolysis of Jatropha Oil Using Immobilized Lipase in Recirculated Packed-Bed Reactor

In this study, a simple and effective technique for establishing an external mass transfer model in a recirculated packed-bed batch reactor (RPBBR) with an immobilized lipase enzyme and Jatropha oil system is presented. The external mass transfer effect can be represented with a model in the form of Colburn factor JD = K Re-(1–n). The value of K and n were derived from experimental data at different mass flow rates.The experiment shows an average increment of 1.51% FFA for calcium alginate and 1.62% FFA for carrageenan after the hydrolysis took place. Based on different biopolymer material used in immobilized beads, JD = 1.674 Re-0.4 for calcium alginate and JD = 1.881 Re-0.3 for k-carrageenan were found to be adequate to predict the experimental data for external mass transfer in the reactor in the Reynolds number range of 0.2 to 1.2. The purposed model can be used for the design of industrial bioreactor and scale up. Besides, the external mass transfer coefficients for the hydrolysis of Jatropha oil reaction and the entrapment efficiency for the two biopolymer materials used were also investigated.

Liquid Circulation in a Multi-tube Air-lift Loop Reactor

A multi-tube air-lift loop reactor (MT-ALR) is presented in this paper. Based on the energy conservation, a mathematical model describing the liquid circulation flow rate was developed, which was determined by gas velocity, the cross areas of riser and downcomer, gas hold-up and the local frictional loss coefficient. The experimental data indicate that either increase of gas flow rate or reduction of the downcomer diameter contributes to higher liquid circulation rate. The correlation between total and the local frictional loss coefficients was also established.Effects of gas flowrate in two risers and diameter of downcomer on the liquid circulation rate were examined. The value of total frictional loss coefficient was measured as a function of the cross area of downcomer and independent of the gas flow rate. The calculated results of liquid circulation rates agreed well with the experimental data with an average relative error of 9.6%.

Severe accident risks from external events

This paper reviews the early development of design requirements for seismic events in USA early developing nuclear electric generating fleet. Notable safety studies,including WASH-1400,Sandia Siting Study and the NUREG1150 probabilistic risk study,are briefly reviewed in terms of their relevance to extreme accidents arising from seismic and other severe accident initiators. Specific characteristic about the nature of severe accidents in nuclear power plant (NPP) are reviewed along with present day state-of-art analysis methodologies (methods for estimation of leakages and consequences of releases (MELCOR) and MELCOR accident consequence code system (MACCS)) that are used to evaluate severe accidents and to optimize mitigative and protective actions against such accidents. It is the aim of this paper to make nuclear operating nations aware of the risks that accompany a much needed energy resource and to identify some of the tools,techniques and landmark safety studies that serve to make the technology safer and to maintain vigilance and adequate safety culture for the responsible management of this valuable but unforgiving technology.

生化-超滤-纳滤组合工艺在餐厨垃圾废水处理中的应用

采用除渣预处理+厌氧反应器+二级AO+外置式超滤+NF(双膜法)组合工艺进行餐厨垃圾废水处理,研究结果表明,当进水COD为72315~78562 mg/L时,NF系统产水COD为264~347 mg/L,对有机物的去除率达到99.5%~99.7%,研究了NF系统压力、温度、pH和运行时间对膜分离性能的影响。NF出水可以达到《污水排入城镇下水道水质标准》(GB/T 31962-2015)标准B等级指标,NF系统浓水用于静脉产业园垃圾焚烧炉飞灰固化。最后,对工程投资、运行费用和经济效益进行了分析和讨论。

气升式浆态床外环流反应器流体力学性能研究

针对气含率和浆液循环流速两个关键流体力学参数,系统研究了气升式浆态床外环流反应器的流体力学特性,掌握了气含率与浆液循环流速的变化规律。验证了体积膨胀法、压差法和电导探针法测量气含率的方法准确性。研究了气体分布器结构对气升式浆态床外环流反应器流体力学特性的影响,结果表明开孔向下双环管分布器的综合性能最优。气含率与浆液循环液速之间存在线性关系,建立了预测浆液循环流速的计算式,计算误差基本小于20%。

双轴自清洁反应器“8”字壳开孔接管结构外压稳定性研究

针对双轴自清洁反应器“8”字壳开孔接管结构承受外压过大时易发生失稳的问题,课题组提出采用有限元分析方法进行双轴自清洁反应器“8”字壳开孔接管结构外压稳定性研究,当接管中心线和“8”字壳垂直中心线的距离X分别取0.0a,0.4a和0.5a,径厚比D_(o)/δ_(e)分别取30,40,50,60和70,长径比L/D_(o)分别取2,3,4,5和6,开孔率d/D分别取010,0.25,0.40,0.55和0.70,接管壁厚和筒体壁厚比δ_(e)t/δ_(e)分别取0.2,0.6,1.0,1.4和1.8时,探究各结构参数与临界失稳压力削弱系数K的关系。研究结果表明:接管壁厚和筒体壁厚比δ_(e)t/δ_(e)和长径比L/D_(o)较小及开孔率d/D和径厚比D_(o)/δ_(e)较大时,开孔接管对“8”字壳外压承载能力削弱严重。

铅冷快堆主换热器内冷却剂流动换热特性研究

铅冷快堆由于其优秀的热工水力性能和安全性能,在商业发电和动力装置应用上具有良好的应用前景。以液态铅铋合金(LBE)和超临界二氧化碳(SCO_(2))为工质的主换热器作为连接铅冷快堆一、二回路的关键设备,其热工及安全性能对反应堆的运行效率及运行安全有重要影响。为了研究铅冷快堆主换热器内流动换热优化方案,针对铅冷快堆主换热器编写了设计和校核计算程序,借助等换热功率分段模型获得了设计工况下主换热器的关键热工水力参数;基于相似原理构建了缩比模型,对使用外置式导流筒时换热器内的流动情况进行了数值模拟;对比分析了换热器分别使用直管和螺旋扁管时流体的流场、温度场分布。研究结果表明,增设外置式导流筒减小了LBE在换热器壳侧流动的最大流速,改善了流场;螺旋扁管相较于直管换热器增大了总换热功率约1.68倍,管侧和壳侧的温度和速度分布更加均匀,改善了换热器的整体换热性能。

Insights into sludge granulation during anaerobic treatment of high-strength leachate via a full-scale IC reactor with external circulation system

In this study, a full-scale internal circulation（IC） reactor coupled with an external circulation system was developed to treat high-strength leachate from a municipal solid waste（MSW）incineration plant, in which anaerobic sludge granulation was intensively investigated. Results showed that the IC reactor achieved excellent treatment performance under high organic loading rates（OLR） of 21.06–25.16 kg chemical oxygen demand（COD）/（m3？ day）. The COD removal efficiency and biogas yield respectively reached 89.4%–93.4% and 0.42–0.50 m3/kg COD.The formation of extracellular polymeric substances（EPS） was closely associated with sludge granulation. Protein was the dominant component in sludge EPS, and its content was remarkably increased from 21.6 to 99.7 mg/g Volatile Suspended Solid（VSS） during the reactor operation. The sludge Zeta potential and hydrophobicity positively correlated with the protein/polysaccharide ratio in EPS, and they were respectively increased from-26.2 m V and 30.35% to-10.6 m V and 78.67%, which was beneficial to microbial aggregation. Three-dimensional fluorescence spectroscopy（3 D-EEM） and Fourier transform infrared spectroscopy（FT-IR）analysis further indicated the importance of protein-like EPS substances in the sludge granulation. Moreover, it was also found that the secondary structures of EPS proteins varied during the reactor operation.

新型流化床外取热器的性能验证试验

针对目前工业流化床反应器普遍采用的传统外取热器设备复杂、长周期可靠性差、传热效率低等问题,提出一种基于热管、具有更高设备可靠性的新型流化床外取热器。为考察新型外取热器的传热和流化特性,设计并建造一套小型热态性能验证试验装置,研究热管启动特性、流化特性以及不同因素对热管密相传热系数的影响规律。结果表明:热管具有非常高的传热效率,这表现在新型外取热器测得的传热特性规律总体与前人报道的密相流化床对流传热特性变化规律总体一致,也具有相近的数值范围;试验范围内热管在催化裂化(FCC)颗粒流化床的最大密相传热系数可达620 W/(m^(2)·K),高于所有文献报道中工业FCC外取热器的实测传热系数,充分验证热管作为新型外取热器传热元件的可行性;在影响传热系数的众多因素中,表观气速的影响最大,床高次之,床温最小。

闭式循环氦气轮机技术特点研究及应用前景展望

该文介绍常规热力发动机的定义与分类,并由此引入外燃机与广义上的内燃机的技术区别,归纳现有主流热力发动机及其遵循的热力循环。其中,燃气轮机是一类在发电、航空及舰船动力等领域得到广泛应用的热力涡轮机械,其与汽轮机相比有着其独到的技术优势。但在核动力领域,为确保安全性,多采用闭式循环燃气轮机。与常规的开式循环燃气轮机不同,闭式循环燃气轮机并不属于广义上的内燃机,其采用外部加热方式,并且有着更好的燃料适应性,在工质的选择上,也曾有过多种方案。与二氧化碳及氮气等气体相比,氦气具有较好的热物理性质,以其作为工质的氦气轮机同样得到业界重视。目前,氦气轮机多作为高温气冷堆的发电主机。随着相关技术的发展,除核电产业之外,高温气冷堆与氦气轮机有望应用于舰船动力等其他领域。

反应堆核热耦合松耦合数值仿真研究综述

在反应堆运行过程中,包含多个性质不同却相互联系的物理现象,涉及反应堆物理、热工水力、材料、系统控制等专业。本文主要探讨堆芯反应堆物理与热工水力间的相互作用,且主要关注对反应堆安全运行具有重要意义的耦合现象,对核热耦合的松耦合数值仿真研究进展进行广泛综述。本文先简要介绍核热耦合的原理方法和主流数值仿真程序,随后依据仿真程序自身特点进行科学分类,最后着重研究四类松耦合数值仿真方法现阶段的实际应用情况,给出了典型算例,并分析其计算效果及实用价值。

Computational fluid dynamics simulation of hydrodynamics in the riser of an external loop airlift reactor

Local hydrodynamics in the riser of an external loop airlift reactor （EL-ALR） are identified and the performances of three drag models are evaluated in computational fluid dynamics simulation. The simulation results show that the Schiller-Naumann drag model underestimated the local gas holdup at lower superficial gas velocity whereas the Tomiyama drag model overestimated that at higher superficial gas velocity. By contrast, the dual-bubble-size （DBS）-local drag model gave more reasonable radial and axial distri-butions of gas holdup in all cases. The reason is that the DBS-local drag model gave correct values of the lumped parameter, i,e., the ratio of the drag coefficient to bubble diameter, for varying operating conditions and radial positions. This ratio is reasonably expected to decrease with increasing superficial gas velocity and be smaller in the center and larger near the wall. Only the DBS-local drag model correctly reproduced these trends. The radial profiles of the axial velocity of the liquid and gas predicted by the DBS-local model also agreed well with experimental data.

池式供热堆厂址设计中的基准地震探讨

小型核反应堆具有较好的安全特性和广泛的应用领域,并获得越来越多的关注。相对于大型核电站而言,外部约束条件对小型堆的推广有很大影响,对需要靠近公众用户的核能供热堆更是如此。该文针对固有安全性较高的池式低温供热堆,论证其能够实际消除明显厂外放射性释放,厂址设计基准地震可以合理优化,作为核能供热设施能够适应我国采暖区大部分厂址条件。