单效蒸发机械压汽海水淡化系统热力性能分析

机械压汽蒸馏海水淡化是唯一消耗机械能的热蒸馏海水淡化方式。文中以单效蒸发机械压汽(SEE-MVC)系统为研究对象,建立了数学模型,分析了重要参数对热力性能的影响,结果表明:压缩机增压比越低、定熵效率越高、蒸发温度越低,则产水比功耗越低、系统回收率越高;综合考虑各种因素,系统蒸发温度在55—70℃、增压比在1.2—1.3为宜。文中还给出了典型条件下对应最小比功耗的系统参数,并讨论了参数特点,可供设计时参考。     

Analysis of a mechanical vapor compression desalination system

The mechanical vapor compression (MVC) desalination system is based on distillation of seawater. The system is basically a heat exchanger that is an evaporator/condenser. The heat required to evaporate water which flows on one side of a heat transfer surface is supplied through the simultaneous condensation of the distillate-producing vapor on the other side of the surface. That is, the latent heat is exchanged in the evaporation—condensation process within the system. A compressor is the driving force for this heat transfer and provides the energy required separating the solution and overcoming dynamic pressure losses and other irreversibilities. In this study, the operation characteristics of a low-temperature MVC desalination system are investigated. In the modeling, the overall energy balance and mass balance equations and LMTD method for heat transfer are used. The tube diameter and the tube length were taken at 0.025 m and 9 m, respectively. The main dependent parameters, the compressor work and the mass flow rate of the distilled water, were investigated against the independent parameters, the evaporation side pressure, the condensation side pressure, and the water inlet temperature.     

Enhanced-efficiency operating variables selection for vapor compression refrigeration cycle system

In this paper, a novel enhanced-efficiency selection of operating variables based on self-optimizing control (SOC) method for the vapor compression refrigeration cycle (VCC) system is proposed. An objective function is proposed to maximize the energy efficiency of the VCC system while meeting with the demand of indoor thermal comfort. With the detailed analysis of operating variables, three unconstrained degrees of freedom are selected among all the candidate operating variables. Then two SOC methods are applied to determine the optimal individual controlled variables (CVs) and measurement combinations as CVs. The model predictive control (MPC) method based controllers and PID controllers are designed for different sets of CVs, and the experimental results indicate that the proposed selection of CVs can achieve a good trade-off between optimal (or near optimal) stable operation and enhanced-efficiency of the synthesized control structure.     

Simulation and Analysis of a Single‐Effect Thermal Vapor‐Compression Desalination System at Variable Operation Conditions

A mathematical model is developed to analyze a single‐effect thermal vapor compression (TVC) desalination system. The effects of the variation of operation conditions such as the intake seawater temperature and the mass flow rate of cooling water on the system performance are investigated for a specific desalination unit. The system performance is found to decrease when the intake seawater temperature is different from the design value. By adjusting the mass flow rate of cooling water, a better system performance can be obtained when the intake seawater temperature differs from the design conditions. Decreasing the cooling water flow rate to values lower than the design value can lead to a better performance when the intake seawater temperature is lower than the design value, and the system performance reaches a peak point when the cooling water flow rate decreases to a definite level. A better performance can also be obtained by increasing the cooling water flow rate to values higher than design value, when the intake seawater temperature is higher than the design value and the system performance also reaches a peak point when the cooling water flow rate increases to a definite level.     

机械蒸汽压缩浓缩渗滤液热力过程数值模拟

介绍了我国渗滤液的基本成分及处理方法,着重分析机械蒸汽压缩浓缩渗滤液的热力过程,以质量、能量方程建立相应的数学模型.阐述了渗滤液入口温度与换热器面积的关系、蒸发倍数与蒸发器面积、压缩比的关系.结果表明:环境温度的提高有利于降低机械蒸汽压缩系统的投资成本.提高蒸发倍数,需要增加相应的压缩机功耗,提高整个系统的运行费用.     

可燃气云爆炸强度计算综述

综述了可燃气云爆炸强度的计算研究现状,对已提出的两种计算方法进行了讨论。     

Once-through and brine recirculation MSF designs — a comparative study

This study investigated the feasibility of the once-through (OT) MSF design for constructing large-capacity desalting plants rather than the conventional brine recycle (BR) MSF configuration. This was to explore the possibility of improving MSF process economics through the application of a simpler process design. It is known that the OT design is characterized by its simplicity and elimination of the brine recirculation pump as well as the rejection section. These features are expected to reduce capital and maintenance costs. The current study is based on comparing the two MSF plant configurations, OT and BR, from the standpoint of minimum heat transfer area, which is a major element in capital investment. Alternative tube layouts, long-tube (LT) and cross-tube (CT) arrangements, were considered. Design calculations were based on a plant capacity of 20 MGD, a gained output ratio of 10, a top brine temperature of 120°C, a feed temperature and concentration of 35°C and 48,000 ppm, respectively. The total number of stages was varied stepwise between 20 and 40. A rigorous mathematical model was developed to solve the optimization problem taking into consideration the nonlinearity of the thermo-physical properties of seawater and steam. The Solver tool of Microsoft Excel was used to determine the optimal solutions. Substantial savings in the heat transfer area can be realized through the application of the LT-OT design when the number of stages goes up to 40. However, comparison of the different MSF designs with the optimal number of stages and minimum heat transfer area tells us that the use of the OT designs is not likely to save more than 1% in heat transfer area relative to the conventional CT-BR configuration. Findings related to the specific chemical consumption are not in favor of OT plants where the consumption ratio varies between 1.7 and 1.9 relative to the CT-BR plants. Of course, excessive chemical consumption penalizes the operating cost of the OT plants. However, the increase in operating costs has to be weighed against the savings in capital cost and lower power consumption due to the elimination of the recycle pump and the heat rejection section. This will determine the use of the OT configuration for building MSF plants in the future. In this event, a detailed cost analysis will be needed.     

机械蒸汽再压缩技术在蒸发领域的应用

文章主要介绍了最近几年国内外机械蒸汽再压缩技术在蒸发领域的应用进展,重点阐述了在海水淡化、制盐、废水处理(硝酸铵废水、氯化铵废水、硫酸铵废水、油田污水等)、全卤制碱等领域的应用,进行了相关的能耗分析,并在此基础上分析了水蒸汽压缩机的研究现状,主要分析了目前应用最为广泛的罗茨式和离心式水蒸汽压缩机。综合分析当前阶段机械蒸汽再压缩技术应用的背景和前景,提出了该技术在蒸发领域的应用中要注意的问题,并给出了一些建议。     

单效热压缩蒸馏海水淡化热力过程数值模拟

建立了单效热压缩蒸馏海水淡化系统的热力学模型。分析了蒸发温度、压缩比和主动蒸汽压力等主要设计参数对系统造水比、单位造水换热面积和单位造水冷却水量的影响。结果表明,降低蒸发温度、减小压缩比和提高主动蒸汽压力将提高系统造水比,而单位产水换热面积将随蒸发温度和压缩比的减小而增加;提高蒸发温度和减小压缩比可以减小单位产水冷却水量;主动蒸汽压力对单位产水面积和冷却水量影响较小。研究成果将对系统优化设计提供有益的参考。     

机械蒸汽再压缩式热泵用于降膜蒸发系统的研究

介绍了一种机械蒸汽再压缩式(MVR)降膜蒸发系统的工艺流程,以水为介质,自主开发并搭建实验平台,采用罗茨风机驱动。使用理论分析和实验相结合的研究方法,探究了本系统在不同的蒸发压力及压缩比下合适的操作域,继而研究了二次蒸汽量、补充水量与压缩比及蒸发压力之间的关系,最后探讨了供热系数COP与压缩比的关系。结果显示,补充水量约占二次蒸汽量的3%~9%,且补充水的量随着压缩比的提高而提高;蒸发压力不变,蒸汽冷却冷凝放热量随着压缩比的增大而增大;压缩比不变,蒸汽冷却冷凝放热量随着蒸发压力的提高而提高;本系统最佳操作压缩比为1.9。     

低温多效压汽蒸馏海水淡化系统热力分析

低温多效压汽蒸馏(LT-METVC)海水淡化是一种很有发展前途的海水淡化方法,文中首先探讨了海水淡化系统中盐水焓、熵、的计算方法,然后对典型LT-METVC流程进行了详细的热力学分析,包括重要参数对系统性能的影响规律和系统的利用。结果表明:驱动蒸汽压力升高,会使造水比增加、效率下降,比传热面积则基本不变;系统效数增加或压缩比降低,都会使系统造水比和效率提高、比传热面积增大。LT-METVC系统的效率很低,在示例中仅为1.3%。提出并初步讨论了进一步改善性能的途径。     

Practical Methodology for Distillation Design using a Miniplant

Development of a model for a complex multi‐component distillation process is presented. Vapor‐liquid equilibria and distillation column models are developed individually, and further compiled together to yield a holistic distillation model tailored for an industrial example. Miniplant‐scale distillation hardware is applied to both develop and test the model. The experimental work and test runs required for model development are described in detail and the resulting model is verified against experimental data.     

喷气增焓型单级MVR蒸发结晶系统性能分析

针对工业废水蒸发结晶过程中含盐浓度增大、从而导致沸点升和增压比偏高等问题,提出了喷气增焓型单级机械式蒸汽再压缩（MVR）蒸发结晶系统。基于EES软件建立了喷气增焓型单级MVR蒸发结晶系统数值模型,并研究了闪蒸压力P_flash、物料入口浓度c₀、物料循环倍率CR、换热温差△T_preh和△T_mhex以及补气压比指数n和补气率β_v对系统热效率COP、单位闪蒸量的压缩机耗功w_comp、压缩机出口蒸汽过热度△t_suph和换热器UA值等参数的影响。结论如下：喷气增焓型MVR系统相比无喷气过程的单级MVR蒸发结晶系统具有更高的COP、更低的w_comp以及更小的△t_suph;随CR增大,压缩机增压比降低了32.8%,COP提高了54.8%;随P_flash增大,COP呈先降后升趋势,在30~35kPa时存在最低值;换热系统中,主换热器温差△T_mhex对MVR系统性能影响更为显著,△T_mhex每增大1K,COP平均降低4.0%、w_comp平均升高4.9%、UA_mhex平均增加8.9%。     

基于蒸汽压缩技术的热泵蒸汽系统热力性能分析

热泵蒸汽技术相比电锅炉及燃煤、燃气锅炉制取蒸汽,具有更高的一次能源利用效率,并且不产生CO₂和NO_x,符合我国节能环保发展战略。本文提出一种基于蒸汽压缩技术的热泵蒸汽系统,采用两级冷凝直接制取低压蒸汽,再通过蒸汽压缩升压至0.7MPa。并基于EES软件建立数值模型,分析冷凝温度T_cond、蒸发温度T_evap、经济器温度T_econ、喷气率β_g对冷媒压缩机功耗W_refri、蒸汽压缩机功耗W_vapor和系统能效系数COP的影响。结果如下：基于蒸汽压缩的热泵蒸汽系统,制取165℃的饱和蒸汽,在T_evap为50℃、T_cond为93℃时,系统COP为2.996,制取1t蒸汽消耗功率仅为247kW·h;系统COP随T_evap的升高逐渐增大,但是T_evap的升高需要更高的热源温度;蒸发温度不变时,系统存在最佳的T_cond、中间冷却温度T_econ和喷气率β_g,当蒸发温度T_evap为50℃,最佳冷凝温度T_cond为93℃时,最佳经济器温度T_econ为65℃,最佳喷气率β_g为0.13。     

Influence of Solution Composition on the Formation of Crystalline Scales

Scale formation is a difficulty encountered with water containing ions of sparingly soluble salts that can readily precipitate on heat transfer surfaces in evaporative concentration operations. Scale formation, hindering the heat transfer process, increases specific energy consumption and operating costs and causes frequent shut down of the evaporator for cleaning. The effects of changes in composition of the solution due to evaporation and CO₂ release on the formation of crystalline scales in seawater evaporators are studied. A model that predicts the CO₂ release is presented. The carbonate system in the salt solution on its whole flow path through the evaporator and the scaling (crystallization) tendency are described. Simulation results for different process configurations are shown and the differences are discussed, particularly with regard to the incrustation tendency.     

基于机械蒸汽再压缩的蒸发结晶单元改进设计

为了解决常规蒸发过程能耗高的问题,采用机械蒸汽再压缩(MVR)技术设计了一种维生素的蒸发浓缩、结晶方案。从能量和成本的角度分析了常规过程与MVR过程。相较于常规过程,MVR过程所需的热功率减少了90.1%,折合成标煤减少了72.5%。从成本的角度来看,MVR过程在年运行7200 h的条件下,年度化投资偿还成本减少了54.8%。定义了单位产出在蒸发结晶单元的投入成本,并研究了在不同运行时间下的变化。单位产出在蒸发结晶单元的投入成本随运行时间的增大而减小。在相同运行时间下,MVR系统的单位产出在蒸发结晶单元的投入成本要小于常规过程。     

机械蒸汽再压缩(MVR)技术在全卤制碱工艺中的应用

探讨了离子膜法制碱工艺实行全卤制碱的一些方法,并结合重庆市映天辉氯碱化工有限公司资源能源情况,对MVR技术在全卤制碱工艺中的应用作了全方位分析。     

罗茨压缩机驱动MVR热泵系统的实验研究

机械蒸汽再压缩(MVR)蒸发系统是一种高效节能的蒸发体系。本文采用降膜蒸发器为蒸发主体、罗茨压缩机为蒸汽压缩机, 并以水为实验原料研究了一套MVR蒸发装置。实验中以总蒸发水量和单位能耗蒸发水量(SMER)作为MVR蒸发系统的性能指标, 分别研究了进料温度、蒸发压强、压缩机频率对其影响。结果表明:最佳进料温度是蒸发压强下的饱和液体温度;最适蒸发压强与具体系统的蒸发能力和压缩机效率密切有关, 在压缩机效率保持较高水平的前提下, 适当降低蒸发压强有利于系统的节能;压缩机的频率直接影响系统的蒸发量和压缩机的功耗, 在压缩机允许的范围内增大压缩机频率, 单位能耗蒸发量是增加的。     

基于热力蒸汽压缩蒸发的油田污水淡化系统及分析

针对油田污水污染物成分复杂、污染性强不适合膜法脱盐的特点和淡水消耗与余热资源共存的实际,提出用热力蒸汽压缩（TVC）蒸发技术对油田污水进行集中脱盐处理的技术方案。建立了基于TVC的油田污水脱盐系统的工艺流程设计计算模型,系统分析了蒸发温度等主要运行参数的影响。结果表明：系统性能系数随蒸发温度的降低而增大,降低蒸发温度有助于减少主蒸汽消耗,但所付出的代价是总传热面积和污水泵流量的增大;TVC系统的热力学完善度相对较低,与多效蒸发系统联合使用是改善系统性能的基本途径之一。尽管如此,对于油田生产来说,当存在合适的余热资源时,简单的单效TVC系统仍不失为合理的技术方案。