Desalination (Thermal Desalination): Article Review

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Table of Contents

Abstract
Introduction
Distillation methods
Solar distillation
Refro-distiller-a new method
Conclusion
Reference

Abstract

About 125 countries are converting salt water from the oceans and seas into fresh water through desalination procedures. Many studies have focused on bringing down the cost of desalination methods so that they could be embraced by many countries worldwide. This study will review the different distillation methods for production of fresh water from salt water that have been adopted by various countries worldwide.

Introduction

Rapid population growth and pollution caused by industrial activities have led nations to utilize thermal energy to convert salt water into fresh water for use by domestic, industrial and agricultural applications (Saidur, Elcevvadi, Mekhilef, Safari & Mohammed, 2011). Seawater, fresh water and glaciers take 97%, 0.5% and 2% respectively of total water found on the earth, while other sources take the remaining 0.5%. Approximately 75 million people worldwide use desalinated water for domestic and industrial purposes. There was a rapid increase in the number of units of desalination plants from 10,350 units in 2002 to 17,348 units 2004. The current global desalination plants could handle a total of 40 million m³ of water per day. The top five countries that have succeeded in desalination efforts are Saudi Arabia, USA, United Arab Emirates, Spain, and Kuwait. The Jabal Ali multi-stage flash desalination plant has the highest capacity in the world and could handle a total of 300 million m³of water annually.

Distillation methods

Distillation procedures involve boiling salt water at high temperatures to obtain water and dissolved atmospheric gases as the vapor which is condensed to form clean water (Saidur et al., 2011). Simple traditional distillation is the most elementary and most expensive distillation method of desalination. Single stage distillation method is more complex than the traditional distillation method, and it is more economical in energy consumption. It is generally used in marine environments and chemical laboratories. The multiple effect distillation method attempts to save energy to vaporize a larger amount of salt water using the same amount of energy. Larger plants have more effects and better performance ratios. Multiple stage flash method has high efficiency enhanced by use of increased operating temperatures. Vapor compression distillation uses internal energy derived from the vapor in the plant to heat the salt water (Saidur et al., 2011).

Solar distillation

This is a relatively cheap method that uses solar energy to heat salt water in distillation plants (Saidur et al., 2011). The energy from the sun is trapped by the solar plate which is then transferred to the salt water in the vessel to cause vaporization. The water vapor is cooled to obtain fresh water droplets safe for human and industrial applications.

Refro-distiller-a new method

The main disadvantage of the simple traditional distillation method is the large amount of energy needed to heat and boil the salt water in the distillation plant. The Refro-distillation method is an efficient method of isolating salts from pure water. In addition, the distiller uses typical refrigeration principles to cool and heat distiller components. This helps to save the amount of energy needed to heat and boil the distiller components (Saidur et al., 2011). The following equations are important in this new method of desalination:

Total energy cost = total energy used / mass of water.

Total energy cost = work done by compressor / mass of water.

= 1 / production rate.

Evacuation energy cost = change in pressure x amount of 1kilogram of distilled water.

Conclusion

Thermal desalination methods are used in large-scale and small-scale conversion of salt water into fresh water for both industrial and domestic purposes. Distillation methods involve heating salt water in distillers at high temperature until it vaporizes, leaving salts at the bottom of the vessel. Condensation of the water vapor leads to the formation of water. Most of the research studies that have been done in the recent past have concentrated on developing systems that use a small amount of energy. For example, the Refro-distiller is a relatively new method that uses the heat recovery principle to conserve heat. In addition, it utilizes low pressure-low boiling temperature mechanism to decrease the amount of energy required to boil the salt water in the distillation plant. Research studies in the future need to focus on improving the efficiencies of the various distillation methods.

Reference

Saidur, R., Elcevvadi, E. T., Mekhilef, S., Safari, A., & Mohammed, H. A. (2011). An overview of different distillation methods for small scale applications. Renewable and Sustainable Energy Reviews, 15(9), 4756-4764.

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