Thermal Solar Desalination

Methods and Systems

Vassilis Belessiotis, Soteris Kalogirou, Emmy Delyannis

• Publisher: Academic Press
• Year: 2016
• Print ISBN: 9780128096567
• eBook ISBN: 9780128097823
• Topic: Technology & Engineering
• Subtopic: Energy Industry
• Index: Technology & Engineering

Thermal Solar Desalination: Methods and Systems presents numerous thermal seawater desalination technologies varying from the very simple, easy to construct and operate solar stills, to the more advance membrane and indirect distillation methods. All types of solar thermal desalination technologies are presented in detail to enable readers to comprehend the subject, from design details to enabling further research to be carried out in this area. The various units used in desalination are outlined, along with diagrams of all detailed working principles of desalination methods and systems. The authors consider the economic aspects of these processes, demonstrating successful implementation of desalination units suitable for areas where supplies of fresh water in natural ways is limited or non-existent. - Includes detailed descriptions and design of all types of solar thermal desalination systems - Lists a comprehensive record of seawater and fresh water thermophysical properties required in the design of desalination systems - Contains equations to calculate and analyze the performance of the processes examined and assesses their practicality and application

Chapter One

Desalination Methods and Technologies—Water and Energy

Abstract

Desalination is increasing tremendously every year in fresh water production capacity as more fresh water is needed for communities, industries, and human population especially in dry regions. Many methods exist to transform sea- and brackish water or even polluted water into fresh water suitable for any use.

This chapter is an introduction and a short overview of all main desalination methods that found major or minor, industrial or community application, in a way that the reader will be accustomed briefly with the desalination concepts. The overview concerns desalination procedures, thermal or nonthermal, powered by conventional fuel, or electricity, as are the large capacity installations, or small capacity units driven by renewable energy, mainly solar. A few procedures that were tested as pilot plants but found no industrial or practical application mainly due to economic reasons or due to their low efficiencies are also included. A brief description of each method gives to the reader a general knowledge of existing desalination methods. This chapter includes also photographs of large desalination installations, especially for nonthermal methods that are not included in the other chapters of this book. Flow sheets are presented of the main desalination systems and for the best combinations of conventional desalination methods with renewable energy sources, including the necessary energy consumption. A special part is dedicated to solar driven desalination analyzing the best combinations of desalination installations to solar energy collectors. At the end of this chapter, a short description of the new methods of desalination which are still under testing and development is given. A selection of interesting relevant book titles on desalination closes this chapter.

Keywords

Desalination methods; conventional methods; renewable energy; solar energy; seawater

1.1 Introduction

Although the main scope of this book is to describe and analyze solar desalination methods and related fields, few words about conventional desalination methods are necessary for students or scientists to refresh their knowledge on what in general desalination is. When we refer to conventional desalination methods, we mean these methods that use as a driving force conventional energy sources, ie, fuels and/or grid electricity. Exactly the same methods may use alternative energy sources like solar, wind, etc., but in this case the desalination system is of smaller capacity and adopted to fit the alternative energy collection system.

Desalination is bounded to the quality of fresh water. Nowadays demographic increase, and tremendous industrial consumption increase, which leads to the rapid water resources exhaustion. Natural fresh water resources and simultaneously natural water streams and wells are polluted by industrial, domestic, or community wastes. The biggest polluting section is agriculture. Of all available water in a region, agriculture consumes about 70% the rest remaining for all other needs. Large amounts of chemical fertilizers, pesticides, and insecticides are drawn away by rain water, polluting water streams, aquifers, natural water aqueducts, thus decreasing available fresh water sources.

World wide there exist regions with no fresh water resources and a minimum of rainfall if at all there is any precipitation. Meanwhile the intensive solar radiation evaporates almost the last drops of existing soil humidity.

Worldwide about 33,000 km of coasts surrounding dry regions are situated mainly in the Indian Ocean, the Arabian Peninsula, the North African coasts and Mediterranean, the Caribbean Islands, and around Australia. In many other places, water is more abundant but quality water resources are rapidly exhausting due to intensive exploitation, and water streams became continuously more polluted. For all these regions, desalination becomes inevitable.

Vigotti and Hoffman (2009) refer that clean fresh water demand has been tripled the last 50 years. About 2000 worldwide, fresh water demand was about 4200 km³, ie, 30% of the available natural fresh water. It is estimated that at about 2025, it will be 70%.

But what do we really mean by desalination methods, described in this chapter?

1.2 What is Desalination?—Where Does it Apply?

Desalination is a physical procedure of separating the excess of dissolved salts from waters, brackish and seawater, or any aqueous salt solution in order to collect low-salt content water for any suitable use, such as drinking, industrial, pharmaceutical, municipal, or household water. Desalination is a pure industrial procedure and an intensive energy system independently of the process, rending energy cost as the major economic problem. Energy consumption of distillation process is higher than any other in the chemical industry and as a consequence desalinated water is still costly despite the dramatic decline in cost during the recent years. Its price is higher than transportation of the same amount of natural water from a short distance. However, transportation or pumping of water from longer distances may be as expensive or more expensive as desalination systems, depending on the distance and the morphology of the site.

Cost of natural water pumping is due mainly to capital cost of the installation. At the beginning of the operation, consumption may be lower than real capacity installed and cost relatively high. Consumption usually increases rapidly and cost decreases until the water source is almost exhausted. Then another source must be found further away from the site to start again. A desalination plant is more flexible to demand fluctuations and capacity may be increased according to demand by installing new units. Furthermore is the only solution for places blessed with abundant brackish water wells or are surrounded by seawater but have no fresh water resources.

1.2.1 The Desalination Processes

The progress in and the development of desalination technology and methods resulted from the activities of Office of Saline Water (OSW) of the US Department of the Interior, from 1952 up to about 1972. During these years, the intensive OSW activities in R&D and the construction of five demonstration plants, of 1 mgd each, developed and promoted desalination to its large industrial application. Since 1972, industry undertook R&D and technical applications.

Many desalination methods have been studied intensively but few of them have found wide industrial application. These methods are divided into two general groups: thermal and nonthermal processes or they may be divided according to the element separation mode, ie, if water or salt is the element that ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Author Biographies
• Preface
• Introduction
• Chapter One. Desalination Methods and Technologies—Water and Energy
• Chapter Two. Water, the Raw Material for Desalination
• Chapter Three. Solar Distillation—Solar Stills
• Chapter Four. Membrane Distillation
• Chapter Five. Humidification–Dehumidification
• Chapter Six. Indirect Solar Desalination (MSF, MED, MVC, TVC)
• Appendix A
• Appendix B
• Appendix C
• Index