负压-气隙式和多级膜蒸馏装置及其于含盐水蒸发过程的研究

摘要

膜蒸馏(MD)是正在发展中的一种新型膜技术，在浓海水的淡化、含盐水的浓缩、高盐水的资源化处理等方面具有潜在应用前景。本研究使用具有高孔隙率、高疏水特性PTFE中空纤维膜，设计并研制出渗透侧负压气隙式膜蒸馏(V-AGMD)装置。通过考察在负压条件下的气隙式膜蒸馏性能、在不同进料温度、流速、盐浓度及冷凝液温度条件下，V-AGMD和AGMD的运行性能比较，以及通过正交试验，进行V-AGMD和AGMD的最优运行条件的考察等，所得结论如下:
　　1.研究使用具有高孔隙率、高疏水性的PTFE中空纤维膜，并设计出新型的膜元件，此膜元件以多孔的中空纤维膜内腔为待蒸发含盐溶液的流道，用无孔的中空纤维内腔为冷凝水的流道，用于构建气隙式膜蒸馏(AGMD)装置，该装置最大程度避免了膜的亲水化现象发生，提高了膜元件使用寿命，为膜蒸馏过程的稳定运行、过程放大应用奠定基础。
　　2.通过在渗透侧辅加真空泵，所设计的负压-气隙式膜蒸馏装置，用于膜蒸馏的蒸发实验。在迸料液温度为80℃，盐浓度为0.0253％，冷凝液温度为20℃时，随进料液流速由2增加到4 L/min，PR和η分别提高了15.25％和11.99％;在进料液流速4 L/min，温度50℃下，PF和GOR分别增加了24.96％和14.29％。该结果说明有效地提升了AGMD的运行性能。该试验结果表明，负压-气隙式膜蒸馏装置能有效提高膜蒸馏过程的蒸发通量(PF)、热效率(η)，增益膜蒸馏的输出比率(GOR)和性能比(PR)。
　　3.通过正交实验，获得了不同操作条件下的最优值。在进料液温度80℃，流速4 L/min，盐浓度0.0253％。在此条件下，获得了最高的PF和η。在进料液温度为70℃，流速2 L/min，盐浓度1.6335％的条件下，获得了AGMD过程最高的PR和GOR值。对于V-MEMD过程，在80℃、4 L/min、0.0253％的条件下获得了最优的PF、η和PR的值，而最优的GOR则在80℃、2 L/min、4.4825％的条件下获得。
　　进一步设计出的具有多级能量回收功能的多效膜蒸馏(MEMD)装置，用于对含盐水溶液的膜蒸馏试验研究。试验结果表明:在高能耗的V-MEMD过程中辅加一级能量回收单元，能有效地提高V-MEMD的渗透流量并降低能耗;同时设计了具有三级能量回收单元的V-MEMD装置，并进行二种装置运行性能的比较，所得结论如下:
　　1.所设计的具有一级能量回收单元的V-MEMD膜蒸馏过程，试验结果表明: PF，PR和GOR均有所提升，能耗(EC)/m3有所下降。与一级的V-MEMD过程相比，三级的V-MEMD过程，具有更高的运行性能并降低能耗，有效地提高了V-MEMD过程的效率。
　　2.对于具有三级能量回收单元的V-MEMD膜蒸馏过程，当进料流速400L/hr，渗透侧真空度0.085 MPa，进料温度80℃和盐浓度为5.71％时，其V-MEMD过程的PF，PR和GOR均有明显提高。
　　3.对于具有三级能量回收单元的V-MEMD膜蒸馏过程，当进料盐浓度由5.71％上升到19.60％时，V-MEMD过程对潜热明显提高，热能回收率在17.32％与34.92％之间，电能回收率则提高到86.85％到91.50％之间。
　　4.实验结果表明，与一级的V-MEMD过程相比，三级的V-MEMD过程有更高性能和更低的能耗，且引入能量回收过程有效地提高了V-MEMD过程的效率。

目录

声明

Acknowledgements

Table of Contents

List of Tables

List of Figures

Abstract

摘要

Chapter 1 Introduction

1．1 Issues，reasons and challenges

1．2 Research background

1．2．1 Membrane distillation(MD)technology

1．3 Objectives

1．3．1 Membrane distillation(MD)technology

Chapter 2 Literature review

2．1 Global water situation

2．2 Membrane distillafion(MD)technology

2．3 The Principle of MD technology

2．4 Different kinds of the MD technology and its applications

2．5 Advantages and disadvantages of different MD configurations

2．6 Membrane characteristics of the MD technique

2．6．1 Liquid entry pressure(LEP)

2．6．2 Membrane thickness

2．6．3 Thermal conductivity

2．6．4 Membrane pore size and pore size distribution

2．6．5 Membrane porosity and tortuosity

2．7 Different factors affecting MD process performance

2．7．1 Effect of feed inlet temperature

2．7．2 Effeet of feed flow rate

2．7．3 Effect of feed salt concentration

2．7．4 Effect of coolant(condensing)temperature

2．7．5 Effect of vacuum(downstream)pressure

2．7．6 Effect of air gap thickness

2．7．7 Effect of operation time

2．8 AGMD mechanism model

2．8．1 Heat transfer

2．8．2 Mass transfer

2．9 VMD mechanism model

2．9．1 Heat transfer

2．9．2 Mass translfer

Chapter 3 Effect of different operation conditions on AGMD process performance

3．1 Introduction

3．2 Experimental equipment and procedures

3．2．1 AGMD set-up and materials

3．2．2 AGMD experiments

3．2．3 Measurements and calculations of various heat energy fluxes during AGMD process

3．3 Results and discussion

3．3．1 Effect of feed inlet temperature and feed flow rate

3．3．2 Effect of feed flow rate and cooling water temperature

3．3．3 Effect of feed flow rate and feed salt concentration

Chapter 4 Effect of different operation conditions on V-AGMD performance process

4．1 Introduction

4．2 Experimental equipment and procedures

4．2．1 V-AGMD set-up and materials

4．3 Results and discussion

4．3．1 Effect of feed inlet temperature and feed flow rate

4．3．2 Effect of feed flow rate and feed salt concentration

Chapter 5 Comparison between AGMD and V-AGMD processes

5．1 Introduction

5．2 Experimental equipment and procedures

5．3 Results and discussion

5．3．1 The performance of the V-AGMD process at different feed temperatures (TF)

5．3．2 The performance of the V-AGMD process at different feed flow rates(MF)

5．3．3 The performance of the V-AGMD process at different feed salt concentrations(CF)

5．4 Orthogonal experiment

Chapter 6 Effect of different operation conditions on three-stage vacuum multi-effect membrane distillation(three-stage V-MEMD)system

6．1 Introduction

6．2 Experimental equipment and procedures

6．2．1 Three-stage V-MEMD set-up and materials

6．2．2 Three-stage V-MEMD experiments

6．3 Measurements and calculations of various energy fluxes during three-stage V-MEMD system

6．4 Results and discussion

6．4．1 Effect of feed inlet temperature and feed flow rate

6．4．2 Effect of feed flow rate and feed salt concentration

6．4．3 Effect of feed inlet temperature and vacuum pressure

Chapter 7 Effect of different operation conditions on one-stage vacuum multi-effect membrane distillation(one-stage V-MEMD)system

7．1 Introduction

7．2 Experimental equipment and procedures

7．2．1 One-stage V-MEMD set-up and materials

7．2．2 One-stage V-MEMD experiments

7．3 Measurements and calculations of various energy fluxes during one-stage V-MEMD system

7．4 Results and discussion

7．4．1 Effect of feed inlet temperature and feed flow rate

7．4．2 Effect of feed flow rate and feed salt concentration

7．4．3 Effect of feed inlet temperature andvacuum pressure

Chapter 8 Comparison between three-stage and one-stage V-MEMD systems

8．1 Introduction

8．2 Experimental equipment and procedures

8．3 Results and discussion

8．3．1 The performance of three-stage V-MEMD system at different feed inlet temperatures(TF)

8．3．2 The performance of three-stage V-MEMD process at different feed flow rates(MF)

8．3．3 The performance of three-stage V-MEMD process at different feed salt concentrations(CF)

8．3．4 The performance of three-stage V-MEMD process at different vacuumpressure(FV)

Chapter 9 Conclusions，Innovations and Future works need to be done

9．1 Conclusions

9．2 Innovations(Creation points)

9．3 Future works need to be done

References

List of Publications