直接接触式膜蒸馏热效率的优化及其与热泵的耦合研究
发布时间：2018-08-19 06:15
【摘要】：膜蒸馏是以多孔疏水膜为介质,膜两侧蒸汽压差为传质推动力的一种新型膜分离技术,广泛应用在非挥发性水溶液浓缩和挥发性有机物溶质脱除领域。跨膜导热、环境热损失以及挥发性溶剂相变能耗大等因素导致膜蒸馏过程热效率低,至今未工业化。因此,除研制性能优良、低热导率分离膜的同时,选择恰当的操作条件、封装分率以及组件的进料方式,能有效提高膜蒸馏过程的膜通量和热效率。为了回收膜冷侧的热量,外部热能回收主要采用多效膜蒸馏和热泵耦合两种方式。实验比较了两种组件串联形式的膜通量和热效率,为多效膜蒸馏奠定研究基础。在热泵-膜蒸馏耦合实验中,采用不同膜面积的组件与热泵进行耦合,研究了不同热侧进口温度下膜蒸馏热效率、热泵制热系数COP和造水比GOR的变化关系。论文主要从以下四个方面展开研究:(1)操作条件的影响用实验探讨了操作条件(热侧进料温度、热侧流量、冷侧流量)对膜通量和热效率的影响,结合中空纤维膜在直接接触式膜蒸馏(DCMD)过程中的传递模型,分析影响机理。结果表明,热侧进料液温度升高和冷、热侧流量增大均能提高膜通量,它们对传质系数影响较小,主要是提高了膜两侧的温度差,导致膜两侧水蒸汽压差增大,进而提高传质推动力。热侧进料温度升高、热侧流量增大和冷侧流量减小均能提高过程的热效率,因为它们均有利于提高平均膜面温度。(2)组件封装分率及进料方式的影响组件内膜丝的不均匀分布造成大量低效或无效区域。随着封装分率上升,膜通量先增大后减小,热效率一直呈上升趋势。在冷、热侧流量恒定的情况下,随着封装分率的增加,膜通量先增加后下降,热效率持续上升。因为随着封装分率的上升,沟流效应减弱,膜通量上升;继续提高封装分率对冷侧传热过程影响不大,但对热侧的不利影响加剧,膜通量反而降低。随着封装分率的上升,膜两侧温差减小,跨膜热传导的热量减少。水蒸汽汽化能耗的先升后降,导热量的持续降低,两者共同作用,使得热效率随封装分率的提高而升高。比较了四种组件放置和进料方式,组件水平放置且冷侧出口朝上时的膜通量和热效率均较高,是最理想的放置方式。(3)组件串联形式的影响实验比较了两种串联形式的膜通量和热效率,两种串联方式的共同点是两个组件的热侧串联,不同点是冷侧串联(串联组件(1))或各自独立冷却(串联组件(2))。组件串联后产水量明显升高,但膜通量和热效率降低。串联组件(1)第一段膜通量小于单根组件,但热效率高于单根组件。串联组件(1)中两段组件互相影响,第一段导致第二段热侧进口温度降低,第二段导致第一段冷侧进口温度降低。串联组件(2)中两段的相互影响较小,仅第一段导致第二段热侧进口温度降低。不同的组件串联形式影响的是各段组件的冷、热侧进出口温度差和平均膜温,从而引起膜通量和热效率变化。膜通量由大到小依次为:串联组件(2)第一段、串联组件(1)第一段、串联组件(1)第二段、串联组件(2)第二段;热效率由大到小依次为:串联组件(1)第一段、串联组件(2)第一段、串联组件(2)第二段、串联组件(1)第二段。(4)DCMD过程与热泵耦合性能的初步研究采用压缩式热泵回收DCMD冷侧的余热,并用于加热热侧的进料液。实验分别考察了不同膜面积下热侧进料温度以及冷、热侧流量对热泵-DCMD耦合系统的影响。进料温度和冷、热侧流量的变化均会影响热泵蒸发器的进口温度,从而改变热泵温升及COP。膜热侧进口温度维持在35℃至60℃时,COP大于3.0,膜热效率60%,GOR达到2.0。采用大膜组件与热泵耦合,COP始终维持在4.0以上,GOR可达1.14~1.21。
[Abstract]:Membrane distillation (MD) is a new membrane separation technology with porous hydrophobic membrane as the medium and vapor pressure difference on both sides of the membrane as the driving force. It is widely used in the concentration of non-volatile aqueous solutions and the removal of volatile organic compounds. In order to recover the heat from the cold side of the membrane, two kinds of heat recovery methods, namely multi-effect membrane distillation and heat pump coupling, have been adopted. In the heat pump-membrane distillation coupling experiment, the heat efficiency of membrane distillation, the COP of heat pump and the GOR of water-making ratio were studied at different inlet temperatures. The main contents of this paper are as follows: (1) The effects of operating conditions (hot-side feed temperature, hot-side flow rate and cold-side flow rate) on membrane flux and thermal efficiency were investigated experimentally. The mechanism of the effects was analyzed by combining the transfer model of hollow fiber membrane in direct contact membrane distillation (DCMD). Increasing the temperature of the side feed liquid and cooling the flow rate at the hot side can increase the membrane flux, which has little effect on the mass transfer coefficient. The main reason is that the temperature difference between the two sides of the membrane is increased, which leads to the increase of the water vapor pressure difference on both sides of the membrane, and then increases the mass transfer impetus. (2) The uneven distribution of the filaments in the package leads to a large number of inefficient or invalid areas. With the increase of the package fraction, the membrane flux first increases and then decreases, and the thermal efficiency always increases. In the case of constant flow rate on the cold and hot sides, with the seal. With the increase of packing fraction, the membrane flux first increases, then decreases, and the thermal efficiency continues to increase. The energy consumption of steam vaporization rises first and then decreases, and the heat conduction decreases continuously. The heat efficiency increases with the increase of package fraction. The film flux and heat efficiency of four kinds of modules are compared when the modules are placed horizontally and the cold side outlet is upward. (3) The influence of the series configuration of the modules on the membrane flux and thermal efficiency was compared. The common point of the two series configuration was that the hot side of the two modules was in series, the cold side was in series (1) or the cold side was in series (2). The water yield of the modules increased significantly, but the membrane flux and thermal efficiency were in series. The first stage of the series module (1) has a smaller membrane flux than the single module, but a higher thermal efficiency than the single module. The difference of temperature between the inlet and outlet of each module and the average membrane temperature on the hot side will result in the change of membrane flux and thermal efficiency. The order of membrane flux is: series module (2) first stage, series module (1) first stage, series module (1) second stage, series module (2). The thermal efficiency is in the following order: the first stage of the series module (1), the first stage of the series module (2), the second stage of the series module (2), and the second stage of the series module (1). (4) The coupling performance of the DCMD process and the heat pump is studied preliminarily. The inlet temperature of the heat pump evaporator will be affected by the change of the feed temperature and the flow rate of the cold and the hot side, so the temperature rise of the heat pump and the inlet temperature of the COP will be changed. When the inlet temperature of the hot side of the membrane is maintained between 35 and 60 degrees Celsius, the COP is greater than 3.0, the thermal efficiency of the membrane is 60%, and the GOR is 2.0. The coupling of membrane module and heat pump, COP always stays above 4, and GOR can reach 1.14~1.21..
【学位授予单位】：北京工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ028.8
本文编号：2190894
[Abstract]:Membrane distillation (MD) is a new membrane separation technology with porous hydrophobic membrane as the medium and vapor pressure difference on both sides of the membrane as the driving force. It is widely used in the concentration of non-volatile aqueous solutions and the removal of volatile organic compounds. In order to recover the heat from the cold side of the membrane, two kinds of heat recovery methods, namely multi-effect membrane distillation and heat pump coupling, have been adopted. In the heat pump-membrane distillation coupling experiment, the heat efficiency of membrane distillation, the COP of heat pump and the GOR of water-making ratio were studied at different inlet temperatures. The main contents of this paper are as follows: (1) The effects of operating conditions (hot-side feed temperature, hot-side flow rate and cold-side flow rate) on membrane flux and thermal efficiency were investigated experimentally. The mechanism of the effects was analyzed by combining the transfer model of hollow fiber membrane in direct contact membrane distillation (DCMD). Increasing the temperature of the side feed liquid and cooling the flow rate at the hot side can increase the membrane flux, which has little effect on the mass transfer coefficient. The main reason is that the temperature difference between the two sides of the membrane is increased, which leads to the increase of the water vapor pressure difference on both sides of the membrane, and then increases the mass transfer impetus. (2) The uneven distribution of the filaments in the package leads to a large number of inefficient or invalid areas. With the increase of the package fraction, the membrane flux first increases and then decreases, and the thermal efficiency always increases. In the case of constant flow rate on the cold and hot sides, with the seal. With the increase of packing fraction, the membrane flux first increases, then decreases, and the thermal efficiency continues to increase. The energy consumption of steam vaporization rises first and then decreases, and the heat conduction decreases continuously. The heat efficiency increases with the increase of package fraction. The film flux and heat efficiency of four kinds of modules are compared when the modules are placed horizontally and the cold side outlet is upward. (3) The influence of the series configuration of the modules on the membrane flux and thermal efficiency was compared. The common point of the two series configuration was that the hot side of the two modules was in series, the cold side was in series (1) or the cold side was in series (2). The water yield of the modules increased significantly, but the membrane flux and thermal efficiency were in series. The first stage of the series module (1) has a smaller membrane flux than the single module, but a higher thermal efficiency than the single module. The difference of temperature between the inlet and outlet of each module and the average membrane temperature on the hot side will result in the change of membrane flux and thermal efficiency. The order of membrane flux is: series module (2) first stage, series module (1) first stage, series module (1) second stage, series module (2). The thermal efficiency is in the following order: the first stage of the series module (1), the first stage of the series module (2), the second stage of the series module (2), and the second stage of the series module (1). (4) The coupling performance of the DCMD process and the heat pump is studied preliminarily. The inlet temperature of the heat pump evaporator will be affected by the change of the feed temperature and the flow rate of the cold and the hot side, so the temperature rise of the heat pump and the inlet temperature of the COP will be changed. When the inlet temperature of the hot side of the membrane is maintained between 35 and 60 degrees Celsius, the COP is greater than 3.0, the thermal efficiency of the membrane is 60%, and the GOR is 2.0. The coupling of membrane module and heat pump, COP always stays above 4, and GOR can reach 1.14~1.21..
【学位授予单位】：北京工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ028.8
【参考文献】
相关期刊论文 前1条
1 于福荣;陈东;彭长章;谢继红;郝维维;刘荣辉;;热泵膜蒸馏系统及其特性分析[J];化工装备技术;2013年06期
，本文编号：2190894
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