膜蒸馏法分离易挥发溶质水溶液

本文以稀甲醇水溶液为实验物系,研究了易挥发溶质水溶液膜蒸馏过程的传质和传热性能。对比直接接触膜蒸馏和空气隙膜蒸馏的实验结果得出,以提浓易挥发溶质为目的的膜蒸馏,采用空气隙膜蒸馏为宜。影响通量的主要因素是空气隙的传质阻力,影响分离因子的主要因素是膜热侧蒸发表面和冷侧冷凝表面之间的温度差。     

Operation experience with solar powered 10 M3 per day MSF-plant in Kuwait and results of upscaling experiments

This paper reports on the progress which was made in the field of solar desalination in order to obtain reliable equipment capable to both operate under the severe requirements associated with the use of solar energy as a variable source of heat and to yield favourable economic conditions in view of larger scale utilisation of the undepletable source of energy for the generation of fresh water.The results of a 2 year experience with a selfregulating solar MSF desalination plant under the extreme environmental conditions in the middle east will be discussed. A new type of a solar selfregulating fluidized bed MSF desalination unit will be presented for the first time. The new development which has been carried to a mass-production-level is the result of the experience gained in this field over the last years.The operation of the Atlantis desalination unit with different types of solar collection systems, in particular the salt gradient solar pond energy collection and storage system, will be discussed from the technical and economical point of view to demonstrate the feasibility of future larger scale solar desalination.     

耦合溴化锂吸收式制冷与有机朗肯循环的合成气深冷分离工艺

从合成气中深冷分离液化天然气(LNG)可以在调峰中发挥重要作用,并显著提升企业的经济效益。然而深冷分离的高能耗是实际工业中的一大问题。本文提出了耦合溴化锂吸收式制冷与有机朗肯循环的甲烷深冷分离工艺。新工艺可以利用原压缩制冷系统的余热从而降低制冷能耗。又因为压缩级数与能耗和可利用余热量成正相关,为使得系统的能耗最低,需同时优化压缩级数与所耦合的余热利用系统。采用自适应遗传算法对新工艺中8种不同压缩级数组合进行优化,通过对比各模型的总能耗、性能系数和单位能耗确定了能耗最低的流程。其结果表明,相比于原工艺总能耗减少了34%;性能系数增加了0.07;单位能耗减少了0.89kW/kg。经济表现为操作费用减少了33%;新增设备投资2550万元,理论上一年即可回收投资成本。     

热电联产机组热电解耦技术对比分析

增加热电联产机组运行的灵活性可以提高可再生能源利用率,减小“弃风”和“弃光”率,然而对于灵活性改造技术的对比分析研究相对较少。本文基于Ebsilon建立了600MW案例机组的热力学模型,采用Matlab调用模拟数据构建了该机组的能耗模型。基于此模型对比分析了热泵、电锅炉、蓄热罐及采用汽轮机本体改造等热电解耦技术对机组供热可行域及可行域内机组热力性能的影响规律。研究结果表明,采用热电解耦技术可以扩大机组的供热可行域,当机组热负荷为500MW时,采用热电解耦技术后,机组最小调峰能力由大到小排列为：电锅炉>低压缸光轴运行>低压缸零出力>压缩式热泵>蓄热罐。但电锅炉的能量利用率与?效率在所有热电解耦技术中最低。综合对比分析,在热电联产机组中采用压缩式热泵或热泵与蓄热罐耦合运行是一种节能的热电解耦方式。     

反冲洗降膜式污水源热泵机组供热性能实验测试

污水源热泵供热是城市污水热能利用的重要途径。为提高原生污水源热泵机组回收城市污水余热的能效,本文提出反冲洗降膜式污水源热泵机组供热系统,建立了污水源热泵机组供热性能实验系统,可与满液式污水热泵机组的供热性能进行比较研究,为解决直接换热式污水源热泵系统遇到的原生污水堵塞问题,本文还设计了污水反冲洗系统,并测试了反冲洗频率和时长对机组换热性能的影响。实验结果表明：降膜式污水蒸发器的平均传热系数要显著高于满液式污水蒸发器,降膜式污水蒸发器的平均传热系数比满液式污水蒸发器高了60.17％;在文中工况下,利用降膜式污水蒸发器的污水源热泵机组的供热性能系数要显著高于满液式污水蒸发器的污水源热泵机组,降膜式污水源热泵机组的供热性能系数比满液式污水蒸发器高了9.52%;污水反冲洗方式可以有效解决直接换热式原生污水源热泵系统的堵塞问题,在使用反冲洗模式时,反冲洗的时间间隔应尽可能短,以确保平均传热系数不会减小。因此,利用反冲洗降膜式蒸发器的污水源热泵机组可以更加高效地利用污水热能。     

Parametric analysis to improve the performance of a solar desalination unit with humidification and dehumidification

A solar desalination unit with humidification and dehumidification, characterized by reusing some of somewhat concentrated saline water after evaporation, recovering condensation heat, and forced air flow, was expected to produce more fresh water. A mathematical model of the unit is presented. The model was experimentally validated for numerical simulation. Parametric analysis was conducted in order to optimize the unit performance. The effect of some of the operating conditions such as flow rates, temperatures of feed water, air and cooling water, etc., was studied in detail. The daily solar productivity corresponding to unit square meter of collector area is about 6 kg/m²/d with 20 MJ solar energy input a day under given conditions. The unit has proven to be an efficient device to utilize solar energy for obtaining fresh water from saline water.     

A HYBRID CFD COMPARTMENTALIZATION MODELING FRAMEWORK FOR THE SCALEUP OF BATCH COOLING CRYSTALLIZATION PROCESSES

Crystallizer design is often hindered by the lack of scaleup rules, hydrodynamic information, and predictive crystallization modeling tools. A hybrid CFD compartmentalization batch cooling crystallizer model is proposed to take into account localized mixing, heat transfer, and fluid hydrodynamics, combined with key process engineering information obtained on a laboratory scale. The compartments were identified using CFD simulations based on the crystallizer geometry and operating conditions. The population, mass, concentration, and energy balance of each compartment is modeled separately as a well-mixed MSMPR unit with input and output streams. The software gPROMS (Process Systems Enterprise Limited) is a process-modeling tool that can facilitate compartmental modeling and will be used for the prediction of the crystallization behavior upon scaleup.     

A HYBRID CFD COMPARTMENTALIZATION MODELING FRAMEWORK FOR THE SCALEUP OF BATCH COOLING CRYSTALLIZATION PROCESSES

Crystallizer design is often hindered by the lack of scaleup rules, hydrodynamic information, and predictive crystallization modeling tools. A hybrid CFD compartmentalization batch cooling crystallizer model is proposed to take into account localized mixing, heat transfer, and fluid hydrodynamics, combined with key process engineering information obtained on a laboratory scale. The compartments were identified using CFD simulations based on the crystallizer geometry and operating conditions. The population, mass, concentration, and energy balance of each compartment is modeled separately as a well-mixed MSMPR unit with input and output streams. The software gPROMS (Process Systems Enterprise Limited) is a process-modeling tool that can facilitate compartmental modeling and will be used for the prediction of the crystallization behavior upon scaleup.     

How to Improve the Energy Savings in Distillation and Hybrid Distillation‐Pervaporation Systems

Abstract

As the worldwide demand for energy is growing, engineers are facing a challenge to design plants with minimum energy requirements. Distillation is an energy intensive process regardless of the products being separated. Using as an example the separation of alcohol–aqueous mixture, this article describes some options applicable to both revamp and new installations where the reduction of energy consumption is achieved. The “Hybrid” application is represented by the Water‐Tetrahydrofurane (THF) separation comparing a conventional two column Pressure Swing Distillation(PSD) system with a pressure distillation using a membrane unit. The main focus is on energy savings for a given separation problem trough the introduction of membrane unit.     

降膜蒸发内回热型太阳能海水淡化装置的实验研究

对一台利用太阳能驱动的横管降膜蒸发内回热型海水淡化装置进行了实际天气条件下的动态测试。系统采用了多效内回热措施,在蒸发及冷凝过程中,大部分水蒸汽的凝结潜热被重复利用于海水的预热及蒸发过程,在相同的天气条件下,该装置的产水率比单级盘式太阳能蒸馏器提高了2～3倍。太阳辐射越强,产水率越大;启动温度越高,产水量越大。对影响淡水产量的其他因素也进行了分析讨论。     

苯乙烯装置塔系热集成

精馏作为过程工业中最重要和最常用的分离手段, 是耗能最大的单元操作。精馏塔一般从再沸器输入热量, 从冷凝器取走热量, 利用某些塔高温位的冷凝热加热其他塔的再沸器, 并将单塔节能技术与过程集成相结合, 实现塔系的热集成, 可充分挖掘系统内部的节能潜力, 达到减少公用工程消耗的目的。本文通过对某化工厂的苯乙烯装置精馏塔系的分析, 通过各个塔的温焓图之间的关系, 提出了精馏塔系内部热集成的措施, 包括直接热集成、调压热集成和双效精馏与间接热集成耦合等3种方案。对于后两个热集成方案, 采用Aspen Plus模拟改造后精馏塔的变化并验证了方案的可行性。结果表明, 苯乙烯装置采用该热集成措施能明显节省高品位蒸汽的消耗, 降低能量费用。     

HIGH-TEMPERATURE SOLAR CHEMICAL REACTORS FOR HYDROGEN PRODUCTION FROM NATURAL GAS CRACKING

This study deals with the thermal cracking of natural gas for the coproduction of hydrogen and carbon black from concentrated solar energy without CO₂ emission. A laboratory-scale solar reactor (1 kW) was tested and modeled successfully. It consists of a tubular graphite receiver directly absorbing solar radiation, in which a mixture of Ar and CH₄ flows. A temperature increase or a gas flow rate decrease results in chemical conversion increase. Methane conversion higher than 75% was obtained. Reaction occurred near the wall where temperature is maximal and gas velocity is minimal due to the laminar flow profile. The work focused also on the design of a medium-scale tubular solar reactor (10 kW) based on the indirect heating concept. A reactor model including gas hydrodynamics and heat and mass transfers coupled to the chemical reaction was developed in order to predict the reactor performances. Temperature and species concentration profiles and final chemical conversion were quantified. According to the results, temperature was uniform in the tubular reaction zone and the predicted chemical conversion was 65%, neglecting the catalytic effect of carbon particles.     

Saffron Drying with a Heat Pump–Assisted Hybrid Photovoltaic–Thermal Solar Dryer

Saffron is the most expensive spice and Iran is the largest producer of this crop in the world. Saffron quality is profoundly affected by the drying method. Recent research has shown that hybrid photovoltaic–thermal solar power systems are more efficient in comparison with individual photovoltaic and thermal systems. In addition, heat pump dryers are highly energy efficient. Furthermore, they are suitable for heat-sensitive crops such as saffron. Therefore, in the present study, the performance of a hybrid photovoltaic–thermal solar dryer equipped with a heat pump system was considered for saffron drying, in order to obtain a high-quality product and reduce fossil fuel consumption. The effect of air mass flow rate at three levels (0.008, 0.012, and 0.016 kg/s), drying air temperature at three levels (40, 50, and 60°C), and two different dryer modes (with and without the heat pump unit) on the operating parameters of the dryer was investigated. The results of the investigation showed that total drying time and energy consumption decreased as air flow rate and drying air temperature increased. Applying a heat pump with the dryer led to a reduction in the drying time and energy consumption and an increase in electrical efficiency of the solar collector. The average total energy consumption was reduced by 33% when the dryer was equipped with a heat pump. Maximum values for electrical and thermal efficiency of the solar collector were found to be 10.8 and 28%, respectively. A maximum dryer efficiency of 72% and maximum specific moisture extraction rate (SMER) of 1.16 were obtained at an air flow rate of 0.016 kg/s and air temperature of 60°C when using the heat pump.     

Morphological study of two‐phase polymer blends during compounding in a novel compounder on the basis of elongational flows

A new laboratory‐scale mixing device based on an original concept was built and tested. This device has important technical features such as tightness to liquids and gases, the possibility of direct specimen molding after mixing, and easy handling of reactive systems. In comparison with existing laboratory mixers, the flow in this mixer is characterized by a high contribution from elongational flow. Morphological data on model polystyrene/poly(methyl methacrylate) blend systems have proved the high distributive and dispersive mixing efficiency in comparison with a classical rotational batch mixer. The influence of different experimental parameters such as the flow rate, mixing time, mixing element geometry, and viscosity ratio of blends is characterized and discussed. Much finer dispersions have been obtained with this new device versus those obtained with a conventional mixer with equivalent specific energy input. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

SCALE-UP OF CONTACT DRYERS

The scale-up of contact dryers is still based on experimental drying curves. In order to keep the effort to a minimum the drying curve is determined using a small laboratory or pilot dryer of similar geometry to the production dryer.

This paper introduces a new scale -up method for contact dryers. The new scale-up method is based on the assumption that heat transfer is the controlling mechanism. The scale-up method is derived from the material balance, the energy balance, the kinetic equation of heat transfer and thermodynamic equilibrium. The scale up method can be used to convert the drying time required to achieve a certain residual moisture content from the laboratory or pilot dryer to the production dryer and/or different drying conditions.

The scale-up method was verified by drying test with four different products in conical mixer dryers of 1, 60, 250, 1000 I volume. Two products were free flowing and two products were non free flowing in the wet state. The products can be considered non-hygroscopic in the moisture range investigated.     

横管降膜蒸发闭循环式太阳能海水淡化装置的研制及性能测试

设计制造了一台能利用太阳能或其它余热驱动的横管降膜蒸发闭循环式海水淡化装置，并分别用稳态热源和实际太阳光对该装置进行了实验测试。实验结果表明，由于装置充分并反复利用了水蒸汽的凝结潜热，因而有较高的产水率。同时，由于在气流的闭式循环过程中，蒸发室内处于负压状态，冷凝室内处于正压状态，进一步强化了系统的产水性能。介绍了系统的工作原理、运行特性及在实际天气条件下的运行结果。     

基于内模控制的内部热耦合精馏策略

精馏过程约占工业总能耗的1/3,其节能控制潜力很大。内部热耦合精馏(ITCDIC)是迄今为止所提出的节能效果最好(比常规精馏节能40%以上)却没有商业化的节能技术。主要原因在于该过程具有较强的非线性、复杂的动态特性以及耦合性,给控制方案的设计带来了极大的困难。通过建立更为精确的二阶内部模型,提出了一种有效的ITCDIC内模控制方案。实例研究结果表明,与传统控制方案PID相比,控制品质更加稳定可靠;同时,与目前国际上公开报道的最好结果相比,该控制方案有更广泛的操作域,鲁棒性更强。     

HEAT EXCHANGER FOR IN-GROUND HEAT STORAGE

The first phase of a research project using undisturbed soil for sensible heat storage is described. A laboratory scale model of a heat exchange system was constructed and tested. Thermal charging and recovery rates, modes of heat transport and transient temperature conditions, as well as over-all heat storage performance of the unit are given. The experimental results are compared with predictions of a numerical model based on mass and heat transport. A prototype field installation has been constructed and preliminary results are presented.