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MULTIPLE EFFECT DISTILLATION (MED) OF WATER AS A RURAL MICROENTERPRISE

BY

ANURAG MUDGAL Department of Applied Mechanics

Submitted

in fulfilment of the requirements of the degree of

Doctor of Philosophy to the

Indian Institute of Technology, Delhi

October 2009

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© Indian Institute of Technology, New Delhi, 2009

All Rights Reserved

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Dedicated to my

Parents and Teachers

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CERTIFICATE

This is to certify that the thesis entitled "Multiple Effect Distillation (MED) of Water as a Rural Microenterprise" being submitted by Anurag Mudgal (2006AMZ8181) for the award of the degree of Doctor of Philosophy, to the Indian Institute of Technology, Delhi is a record of the original bonafide research work carried out by him under our guidance and supervision and that the material embodied in this thesis has not been submitted in part or full to any other University or Institute for the award of any other Degree or Diploma.

We further certify that such help and source of information, as has been availed of during the course of investigation have been duly acknowledged by him.

(P. K. Sen) Professor

Department of Applied Mechanics Indian Institute of Technology, Delhi Hauz Khas, New Delhi 110 016, India

(S. N. Singh) Professor

Department of Applied Mechanics Indian Institute of Technology, Delhi Hauz Khas, New Delhi 110 016, India

(Padma Vasudevan Sen) Professor

Centre for Rural Development & Technology Indian Institute of Technology, Delhi Hauz Khas, New Delhi 110 016, India

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ACKNOWLEDGMENT

I express my deep sense of gratitude and regards to Prof. P. K. Sen, Prof. Padma Vasudevan Sen and Prof. S. N. Singh for their inspiring guidance, encouragement, caring attitude, and help extended throughout the study period. They took keen interest in guiding and shaping my ideas towards the work presented in this thesis. I am lucky to have them as my thesis supervisors. Their availability at any time for discussions was greatly beneficial to me. I shall remain indebted to them throughout my life.

I wish to express my hearty thanks to the Faculty of the Department of Applied Mechanics, IIT, Delhi. I specially acknowledge the keen interest shown by Prof. V.

Seshadri, Prof. Y. Nath, Prof. S. V. Veeravalli and Dr. Sriram Hegde of the Department of Applied Mechanics; Prof. Sunil Kale and Prof. P. M. V. Subbarao, of the Department of Mechanical Engineering, IIT Delhi, and Prof. Phillip Davies, of Aston University, U.K., in this study. I am grateful to them all.

I express my deep regards and gratitude to Dr. R. M. Dubey, Managing Director, Institute of Foreign Trade and Management (IFTM), Moradabad, in which I am a faculty in the College of Engineering and Technology (CET). Dr. Dubey provided me all facilities, including leave to go to IIT, Delhi from time to time, and inspired me to undertake the research work and complete the work. He ensured that there be no interruptions during the course of my work. I express my gratitude to all my colleagues at CET and IFTM who were a constant source of inspiration and encouragement during this investigation.

I also express my sincere thanks to the technical and support staff of the Gas Dynamics Laboratory (GD Lab), Fluid Mechanics Laboratory (FM Lab), and the Departmental Workshop in the Department of Applied Mechanics, IIT, Delhi.

Without their wholehearted support, the fabrication of the MED unit would have been difficult. Mr. Sita Ram, retired Senior Technician has been an asset in the

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development of the unit at my work place in Moradabad and I acknowledge his help and devotion in carrying out the fabrication and commissioning of the MED unit with utmost gratitude.

I extend my sincere thanks to my friends, Mr. S. Chandrahas and Mr. S. Chandel, for providing me moral support and encouragement during the course of my investigations.

It is indeed a great pleasure to express my gratitude to my late grandparents (late) Mrs. Moorti Devi and (late) Mr. Harkesh Sharma, and my parents Mrs. Nirmala Sharma and Dr. R. S. Sharma who brought me up, and despite all odds, made sure that I study and become independent. They have always been a major source of inspiration and strength during the course of my studies.

My wife Dr. Varsha, son Aditya and daughter Megha deserve all praise for their wholehearted co-operation in every possible way. They tolerated my delayed homecoming and staying away from home in the Institute campus, and outside Moradabad at IIT, Delhi, even for months during the course of my investigations.

They were always with me to share my joys and sorrows and provide me emotional support.

Study leave granted by CET, IFTM, and the project support by the Rajiv Gandhi National Drinking Water Mission, Department of Drinking Water Supply, Government of India, Department of Science and Technology, Government of India, and Aston University, U.K, are gratefully acknowledged.

Finally, I would like to thank all those who helped me directly or indirectly in the completion of this study, and above all, Almighty God who is always there with me.

Dated: October 13, 2009 (Anurag Mudgal)

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ABSTRACT

Increased water pollution due to industrial activities, growth of population and increasing requirement of water for the agricultural sector have led to a situation wherein access to safe drinking water in many parts of the country has become a problem. There are several areas in India where water is contaminated by toxic chemicals such as arsenic and fluoride. Removal of dissolved salts and toxic chemicals especially at part per million (ppm) levels is one of the most difficult problems. There are several methods used for water purification. The choice of the method depends mainly on the level of feed water salinity, source of energy and type of contaminants present. Distillation is an age old method which can get rid of all types of impurities including dissolved impurities but the challenge lies in designing for small scale operations and optimizing it. Multiple effect distillation (MED) is a method in which latent heat of once produced steam is recycled several times, which economizes the operation, and, produces many units of distilled water with one unit of primary steam input.

This technology is already in use for large scale production of distilled water especially in the Middle East, even from sea water (with — 30,000 ppm salts). These methods are already being used to treat water on a large scale (3000 — 30, 000 m3 per day). Efficient small scale distillation systems for distilled water production for rural communities have not been developed and commercialized as known till date except for a triple effect unit that was fabricated at IIT, Delhi in 2003. This unit showed the

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feasibility of operation at small scales but was not optimized in terms of design aspects and operational issues.

In the present work a MED unit with extendable number of effects has been designed and operationalised for optimum yield of product water in terms of total distillate produced. The unit can be operated with any number of effects varying from two to ten effects. The unit comprises a baby boiler integrated with pressurised feed water pre-heater (PFPH) and economizer, vertical tube evaporators (VTE-s), condenser, mist eliminators or feed entrainment separators, distillate withdrawal capillaries, parallel feed and brine transferring capillaries, pump and other peripherals. The unit is insulated to minimise heat loss to the surroundings. The baby boiler selected is capable of producing 30 kg/h steam continuously.

The present work is aimed at improving the performance and ease of handling of the system for varying number of effects (from three to nine), optimizing various design parameters, selecting appropriate feed water supply configuration and improved efficiency of heat input from the boiler. In depth performance studies have been conducted and aspects leading to improved design, operation, maintenance and better economic returns, were looked into.

Parametric studies were undertaken on the improved MED system so designed for optimising operational parameters. The unit was tested for 9 effects + condenser (9+C), 6+C and 3+C units. The optimum yield of total distillate produced was found to be 167± 1, 121± 1 and 91± 1 litres per hour respectively at 95% confidence level

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for an input of 30 kg/h steam. The PFPH was integrated with the boiler assembly to give high top brine temperature. Controlled flow rate of feed water using calibrated capillaries, optimization of annular clearance for better feed water film formation over evaporator tubes, and mixed feed arrangements have been amongst the major contributions of the present work. Maximum overall heat transfer coefficient (OHTC) found in the first effect was around 20000 W/m2 °C. Such a high value of OHTC is the secret of success of the unit.

Long term maintenance, contingencies and economic issues were considered in terms of scaling and corrosion. Strategies to minimize these were also considered. In the Indian scenario economic feasibility of the unit has been looked into in the context of a rural micro enterprise.

The unit is capable of fulfilling the drinking water needs of forty families with 5-6 members in a family, by operating for 8-9 hours per day. If requirement is more, the unit may be run for a longer period. It can also be taken up as a self employment option and the product water may be sold directly to the battery markets, laboratories and other industries using distilled water for electroplating, pharmaceuticals and so forth.

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Contents

Listof Figures ... i

Listof Tables ... v

List of abbreviations ... viii

Listof symbols ...x

Chapter 1 INTRODUCTION... 1

1.1 Dynamics of water supply and demand :... 2

1.1.1 Water quality standards ... 4

1.1.2 Drinking water and health issues ...5

1.2 Removal of dissolved chemicals ...7

1.2.1 Reverse osmosis (RO) ...10

1.2.2 Distillation ...11

1.2.3 Motivation for the present study ...13

Chapter 2 LITERATURE REVIEW ...16

2.1 Introduction ...16

2.2 Multi Stage Flash (MSF) ...17

2.3 Vapour compression (VC) ...21

2.4 Multiple effect distillation (MED) ...28

2.4.1 Horizontal tube evaporator (HTE) ...30

2.4.2 Vertical tube evaporator (VTE) ...33

2.4.3 Feed water arrangements ...36

2.4.4 Significance of number of effects ...37

2.4.5 Significance of the overall heat transfer coefficient ...38

2.5 Scope of the present study ...39

2.5.1 Objectives of study ...40

Chapter 3 DESIGN, FABRICATION AND COMPONENT OPERATION OF THE PRESENT MULTI-EFFECT DISTILLATION (MED) SYSTEM ... 41

3.1 Introduction ... 41

3.2 Overall working of the system ...42

3.3 Crucial design considerations for improved performance ...47

3.4 Steam generation ...47

3.5 Boiler assembly ...48

3.5.1 Pressurised feed water pre-heater (PFPH) ...52

3.5.2 Economizer ...52

3.5.3 Water feeding to the boiler and PFPH ...53

3.6 Vertical Tube Evaporator (VTE) ...54

3.6.1 Heat transfer area ...56

3.6.2 Design of VTE units ...57

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3.7 Optimizing feed water plate annular clearance, for film formation over the

tubes...61

3.7.1 Experimental results for different annular clearances ...67

3.8 Use of Capillary for brine transfer and distillate withdrawal ...73

3.9 Optimising number of effects ...80

3.10 Safety measures in operation ...82

Chapter 4 OPERATION AND PERFORMANCE OF THE MED SYSTEM AND PARAMETRIC STUDIES ...86

4.1 Introduction ... 87

4.2 Operation of the MED system ...87

4.3 Selection of parameters for parametric studies ...92

4.4 Measuring devices and range of parameters ...96

4.4.1 Uncertainty analysis ... 98

4.5 Experimental results ... 99

4.5.1 Performance of the 9+C unit ...102

4.5.2 Performance of the 6+C unit ...117

4.5.3 Performance of the 3+C unit ...127

4.6 Comparison of the three systems ...137

4.6.1 Analysis and explanation of high OHTC ...140

4.7 Energy balance at different stages ... 148

4.7.1 Energy balance of Boiler unit ...148

4.7.2 Energy balance for a particular effect of the MED unit ...149

4.8 Concluding remarks ...157

4.9 Maintenance, Contingencies and Economics ...159

4.9.1 Salt balance ... 160

4.9.2 Scaling ...161

4.9.3 Corrosion ...164

4.10 Economic feasibility ...165

4.10.1 Daily fixed cost and operating cost ...166

4.11 Remineralisation cost ...168

4.12 Conclusions ...168

Chapter 5 CONCLUSIONS AND SCOPE FOR FUTURE WORK ...170

5.1 Salient findings ...171

5.2 Scope for future work ...173

REFERENCES AND BIBILIOGRAPHY ...174

AppendixA ...180

AppendixB ...185

Brief Bio-data of the Author ...191

References

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