直接接觸式膜蒸餾熱效率的優(yōu)化及其與熱泵的耦合研究
發(fā)布時間：2018-08-19 06:15
【摘要】：膜蒸餾是以多孔疏水膜為介質(zhì),膜兩側(cè)蒸汽壓差為傳質(zhì)推動力的一種新型膜分離技術(shù),廣泛應(yīng)用在非揮發(fā)性水溶液濃縮和揮發(fā)性有機(jī)物溶質(zhì)脫除領(lǐng)域�？缒�(dǎo)熱、環(huán)境熱損失以及揮發(fā)性溶劑相變能耗大等因素導(dǎo)致膜蒸餾過程熱效率低,至今未工業(yè)化。因此,除研制性能優(yōu)良、低熱導(dǎo)率分離膜的同時,選擇恰當(dāng)?shù)牟僮鳁l件、封裝分率以及組件的進(jìn)料方式,能有效提高膜蒸餾過程的膜通量和熱效率。為了回收膜冷側(cè)的熱量,外部熱能回收主要采用多效膜蒸餾和熱泵耦合兩種方式。實驗比較了兩種組件串聯(lián)形式的膜通量和熱效率,為多效膜蒸餾奠定研究基礎(chǔ)。在熱泵-膜蒸餾耦合實驗中,采用不同膜面積的組件與熱泵進(jìn)行耦合,研究了不同熱側(cè)進(jìn)口溫度下膜蒸餾熱效率、熱泵制熱系數(shù)COP和造水比GOR的變化關(guān)系。論文主要從以下四個方面展開研究:(1)操作條件的影響用實驗探討了操作條件(熱側(cè)進(jìn)料溫度、熱側(cè)流量、冷側(cè)流量)對膜通量和熱效率的影響,結(jié)合中空纖維膜在直接接觸式膜蒸餾(DCMD)過程中的傳遞模型,分析影響機(jī)理。結(jié)果表明,熱側(cè)進(jìn)料液溫度升高和冷、熱側(cè)流量增大均能提高膜通量,它們對傳質(zhì)系數(shù)影響較小,主要是提高了膜兩側(cè)的溫度差,導(dǎo)致膜兩側(cè)水蒸汽壓差增大,進(jìn)而提高傳質(zhì)推動力。熱側(cè)進(jìn)料溫度升高、熱側(cè)流量增大和冷側(cè)流量減小均能提高過程的熱效率,因為它們均有利于提高平均膜面溫度。(2)組件封裝分率及進(jìn)料方式的影響組件內(nèi)膜絲的不均勻分布造成大量低效或無效區(qū)域。隨著封裝分率上升,膜通量先增大后減小,熱效率一直呈上升趨勢。在冷、熱側(cè)流量恒定的情況下,隨著封裝分率的增加,膜通量先增加后下降,熱效率持續(xù)上升。因為隨著封裝分率的上升,溝流效應(yīng)減弱,膜通量上升;繼續(xù)提高封裝分率對冷側(cè)傳熱過程影響不大,但對熱側(cè)的不利影響加劇,膜通量反而降低。隨著封裝分率的上升,膜兩側(cè)溫差減小,跨膜熱傳導(dǎo)的熱量減少。水蒸汽汽化能耗的先升后降,導(dǎo)熱量的持續(xù)降低,兩者共同作用,使得熱效率隨封裝分率的提高而升高。比較了四種組件放置和進(jìn)料方式,組件水平放置且冷側(cè)出口朝上時的膜通量和熱效率均較高,是最理想的放置方式。(3)組件串聯(lián)形式的影響實驗比較了兩種串聯(lián)形式的膜通量和熱效率,兩種串聯(lián)方式的共同點是兩個組件的熱側(cè)串聯(lián),不同點是冷側(cè)串聯(lián)(串聯(lián)組件(1))或各自獨立冷卻(串聯(lián)組件(2))。組件串聯(lián)后產(chǎn)水量明顯升高,但膜通量和熱效率降低。串聯(lián)組件(1)第一段膜通量小于單根組件,但熱效率高于單根組件。串聯(lián)組件(1)中兩段組件互相影響,第一段導(dǎo)致第二段熱側(cè)進(jìn)口溫度降低,第二段導(dǎo)致第一段冷側(cè)進(jìn)口溫度降低。串聯(lián)組件(2)中兩段的相互影響較小,僅第一段導(dǎo)致第二段熱側(cè)進(jìn)口溫度降低。不同的組件串聯(lián)形式影響的是各段組件的冷、熱側(cè)進(jìn)出口溫度差和平均膜溫,從而引起膜通量和熱效率變化。膜通量由大到小依次為:串聯(lián)組件(2)第一段、串聯(lián)組件(1)第一段、串聯(lián)組件(1)第二段、串聯(lián)組件(2)第二段;熱效率由大到小依次為:串聯(lián)組件(1)第一段、串聯(lián)組件(2)第一段、串聯(lián)組件(2)第二段、串聯(lián)組件(1)第二段。(4)DCMD過程與熱泵耦合性能的初步研究采用壓縮式熱泵回收DCMD冷側(cè)的余熱,并用于加熱熱側(cè)的進(jìn)料液。實驗分別考察了不同膜面積下熱側(cè)進(jìn)料溫度以及冷、熱側(cè)流量對熱泵-DCMD耦合系統(tǒng)的影響。進(jìn)料溫度和冷、熱側(cè)流量的變化均會影響熱泵蒸發(fā)器的進(jìn)口溫度,從而改變熱泵溫升及COP。膜熱側(cè)進(jìn)口溫度維持在35℃至60℃時,COP大于3.0,膜熱效率60%,GOR達(dá)到2.0。采用大膜組件與熱泵耦合,COP始終維持在4.0以上,GOR可達(dá)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..
【學(xué)位授予單位】：北京工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TQ028.8
本文編號：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..
【學(xué)位授予單位】：北京工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TQ028.8
【參考文獻(xiàn)】
相關(guān)期刊論文 前1條
1 于福榮;陳東;彭長章;謝繼紅;郝維維;劉榮輝;;熱泵膜蒸餾系統(tǒng)及其特性分析[J];化工裝備技術(shù);2013年06期
，本文編號：2190894
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