【作者】 邓润亚；

【导师】 金红光；

【作者基本信息】 中国科学院研究生院（工程热物理研究所） ， 工程热物理， 2009， 博士

【摘要】 目前，随着人们对水资源需求的不断扩大，淡水资源缺乏问题逐渐显现出来，因此寻求节能高效的造水方法途径势在必行。多效蒸发是化工过程蒸发系统常用的工艺，也是最早采用的海水淡化方式之一。低温多效海水淡化系统(LT-MED系统)是目前商业运行的海水淡化系统的主要形式之一，其中热压缩多效蒸馏系统(MED-TVC系统)由于附加设备蒸汽压缩器(TVC)结构简单、投资少、易于维护且能较大提高系统造水能力而被广泛应用。在海水淡化解决淡水资源短缺的同时，大量的浓海水排放也带来了环境问题，因此海水淡化零排放成为研究的热点。本文在常规热力性能评价指标和经济性能评价单目标评价准则的基础上，建立和推导了综合系统热力和经济性能的多目标统一量化的评价准则COP的公式；着重研究高浓缩倍数下顺流进料多效蒸发海水淡化MED-TVC工艺的能量利用状况，进一步研究了效数、顶温、进料海水的盐度和温度等对海水淡化系统造水比和(火用)耗的影响规律，分别对逆流进料和顺流进料海水淡化系统进行全面经济分析比较研究；深入研究多效蒸发真空制盐工艺处理浓海水的能量利用状况，进一步研究了浓海水的盐度和温度对真空制盐系统(火用)耗的影响规律；利用多联产的基本原则和集成理论，研究了动力发电系统、海水淡化和真空制盐的多联产集成系统，构建了新型串联型系统的流程结构，分析研究比较系统深度集成的优势，从而实现海水全面的综合利用。通过对高浓缩顺流进料的MED-TVC系统进行模拟，利用EUD分析方法对该MED-TVC系统的能量利用状况进行了分析，结果表明：(1)对于高浓缩倍数下的顺流MED-TVC系统，喷射器损失为31．2%，15效损失共30．26%，两者是系统能量损失的主要部分。动力蒸汽品位与抽气品位差较大，由于加入TVC抽气后蒸汽量减少，导致抽气后(火用)损失有所减少。(2)高浓缩倍数下的顺流MED-TVC系统的造水比随着顶温升高而降低，(火用)耗随之升高；升高入料海水温度可以提高造水比，降低(火用)耗。随着入料海水盐度升高，造水比逐渐下降，(火用)耗增加；在效数增加时，可以提高造水比，降低(火用)耗。(3)对MED和MED-TVC进行经济性分析，TVC的引入可以使热消耗费用明显减少，降低MED海水淡化的制水成本。(4)由DEEP分析结果可知，随着系统效数增多，设备的生产强度降低，而加热蒸汽经济性提高，制水成本下降。但效数增加，各效的传热温差损失的总和也将增加，致使有效的传热温差减少，同时设备投资也相应增加，15效是较为适宜的方案。通过对五效多效蒸发真空制盐系统进行物料和能量平衡计算，利用EUD分析方法对整个系统进行了(火用)流分析，得出了以下结论：(1)多效蒸发真空制盐系统(火用)总效率为14．19%，即系统(火用)的损失量占85．81%。(2)第五效的二次蒸汽直接大气式混合冷凝器引起的(火用)损失不可小视，约占总输入的11．71%。末效的二次蒸汽直接进入大气式混合冷凝器，二次蒸汽和循环水两者品位差较大，导致(火用)损失较大，若将末效二次蒸汽的(火用)加以利用，将大大提高整个系统的用能水平。(3)系统各效的冷凝水被闪蒸后作为下效的动力蒸汽，因而末效闪蒸后的冷凝水温度和压力较低，用闪蒸后的冷凝水来预热海水淡化后的浓缩盐水，两者的温差较小引起的(火用)损失较小，约占总输入的4．23%。系统的冷凝水和循环下水虽然量大，但其品位太低，可利用程度小。(4)系统单位析盐的(火用)损随进料盐度、温度和效数的增大而减小，但效数和进料盐度对系统单位析盐的(火用)损影响较大，进料温度对其影响较小。通过采用多联产集成的基本理论和原则，提出了新颖的串联型海水淡化一制盐多联产系统，对其进行了模拟和分析，结果表明：(1)较直排方案循环水温度下降了1．88℃，机组煤耗下降3．07g/kw·h。(2)海水冷却塔无需向大海排出部分浓缩海水，完全杜绝了给海洋造成的热污染和生态影响。(3)随着入料海水温度的提高，海水淡化系统的造水比在效数不同的情况下均提高了3%以上，而(火用)耗却降低了3%以上；随着入料海水盐度的提高，海水淡化系统的造水比在效数不同的情况下降低了3%左右，而(火用)耗却增加了3%以上；但在相同的效数情况下，温度提高引起造水比提高的幅度要比盐度提高引起的造水比降低的幅度要大，而温度提高引起(火用)耗降低的幅度要比盐度提高引起的(火用)耗增加的幅度要大，综合来看，直流方式较之于直排方式能提高了海水淡化系统的性能。(4)随着入料浓海水温度的提高，真空制盐系统的(火用)耗降低了4%以上，效数越多，(火用)耗降低的幅度越大；随着入料浓海水盐度的提高，真空制盐系统的(火用)耗降低了4%以上，效数越多，(火用)耗降低的幅度减小。入料浓海水温度和盐度的提高均能降低真空制盐系统的(火用)耗，提高系统的性能。更多还原

【Abstract】 Presently, the growing demand for water resources, the scarcity of water resources gradually is coming out, therefore it is imperative to search for an energy-saving and efficient way to make fresh water. The low-temperature multiple-effect evaporation for seewater desalination (LT-MED) system is one of main forms of commercial desalination systems, in which multiple-effect distiller with thermal vapor compression ( MED-TVC ) system is used widely because the additional equipment TVC have some advantages such as simple structure, low investment cost, easy maintenance and improving ability to water production. Seawater desalination solves the lack of fresh water resources, at the same time, the vast thick seawater emissions has brought the impact on the surrounding environment. Hence, the research on zero emission of seawater has been paid attention.This study builds multi-objective and unified scale evaluation criterion that integrates thermodynamic performance and economic performance, mainly researches on energy utilization of forward feed MED-TVC under the high cycle of concentration, and reveals gain operation ratio (GOR) and exergy consumption variety rules with the number of the evaporator’s effects, the top brine temperature and sea water salinity, and also compares economic performances between countercurrent feed and forward feed seawater desalination systems. Furthermore, energy utilization status of the process of multi-effect vacuum evaporation salt production from dense seawater is studied, and exergy consumption variety rules with sea water salinity and temperature of this system are revealed. Based on the theory and principle of system integration, a novel polygeneration system producing fresh water, salt and power is proposed. Through analysis and comparison with conventional system, result shows the new system realizes synthetically effective utilization of seawater.Forward feed MED-TVC system with high cycle of concentration is simulated, also exergy destruction of the system is analyzed by the use of EUD method. The results indicate: (1) the exergy destruction of ejector and 15 effects are 31.2% and 30.26%, respectively. They are main contributors to total exergy destruction of the system. The application of TVC causes the reduction on steam supply which consequently reduces exergy destruction. (2) GOR reduces as top temperature increase, while exergy consumption increases. Increasing the temperature of feed seawater can raise up GOR and reduce exergy consumption. As the salinity of feed water is up, GOR will reduce accordingly. Increasing the effect numbers of MED and MED-TVC can raise up GOR and reduce energy consumption. (3) The economic analysis on MED and MED-TVC shows that TVC application makes an energy cost lower obviously and also reduces water product cost. (4) Through the analysis of DEEP, the results show that: with the increase of the number of effects, the motive steam efficiency would be enhanced, and the equipment’s productivity and the total water cost would decrease. But the sum of temperature differences loss would increase, so that the effective heat transfer temperature differences, and at the same time, it will increase the equipment investment. Thus it was appropriate to apply MED-TVC with 15 evaporator effects.The material and energy balance of the five effects multiple-effect vacuum evaporation salt production system are carried out. Then exergy distribution of the system was analyzed by the use of EUD method. Results show that: (1) exergy efficiency the system of is about 14.19%, which means that exergy destruction accounts for 85.81%. (2) The exergy destruction in the atmospheric type mix condenser shouldn’t be neglected, which accountes for 11.71%. The energy level difference between motive steam and cooling water is big, which is the main reason for exergy destruction. Making use of steam from the last effect would improve exergy efficiency of the system. (3) After flash process, the temperature and pressure of condensate would become lower. The temperature difference between condensate and brine is small in the preheated section, so that the exergy destruction is small, about 4.23%. The amount of circulating water and condensed water is in a large quantity, but their energy level is too low to take a potential utilization. (4) With the increasing of the number of effect, the temprature and salinity of feed, the exergy destruction will decrease. The number of effect and the salinity of feed influence exergy destruction more, while the temperature of feed influences less.Based on the fundamental theory and principle of system integration, a novel seawater desalination polygeneration system producing fresh water and salt is proposed. The results of simulation and calculation show; (1) Compared with a direct discharge alternative, the temperature of cooling water is 1.88℃down and coal consumption is reduced 3.07g/kWh. (2) As there is no need to discharge the brine to sea from cooling tower, the ecological impact on ocean is eliminated. (3) As the temperature of feed water is increased, the GOR of desalination is 3% up on average with different numbers of desalination effects, while exergy consumption is 3% down. With the increase of feed salinity, the GOR is 3% down while exergy consumption is 3% up. In consideration of the same numbers of desalination effects, the increase of temperature contributes greatly to a lager GOR compared with salinity increase. Generally speaking, the direct flow configuration can give a better performance on desalination system than the direct discharge. (4) With the increase of feed temperature, exergy consumption of vacuum salt-making system reduces over 4%. Consequently, more desalination effects will make exergy consumption decrease rapidly. With the increase of feed salinity, exergy consumption of vacuum salt-making system will decrease over 4%. It results in a decrease of exergy consumption by adopting more desalination . The increase both feed temperature and salinity will contribute to reduction on exergy consumption which is impetus to vacuum salty production.更多还原