Desalination, 2nd Edition

Chapter 9Humidification-Dehumidification Desalination

John H. Lienhard V

Rohsenow Kendall Heat Transfer Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139-4307 USA.

Abstract

Humidification-dehumidification (HDH) desalination involves vaporizing water from a saline liquid stream into a carrier gas stream and then condensing the vapor to form purified water. This chapter describes various forms of the HDH cycle, with analysis of the energy consumption of various realizations of the process. The use of mass extraction/injection to improve performance is discussed. Analyses using both fixed component effectiveness and fixed component size are considered. Bubble column dehumidifiers are described, and the effect of very high feed salinity on energy and efficiency is discussed.

Keywords: Humidification-dehumidification desalination, Carrier gas extraction, Bubble column dehumidifier, Thermodynamic balancing, Mass injection and extraction, Effectiveness, Gained-output-ratio, Enthalpy pinch, Modified heat capacity rate ratio, High salinity

9.1 Introduction

Nature uses air as a carrier gas to desalinate seawater by means of the rain cycle. In the rain cycle, seawater gets heated (by solar irradiation) and evaporates into the air above to humidify it. Then the humidified air rises and forms clouds. Eventually, the clouds ‘dehumidify’ as rain, and that which falls over land can be collected for human consumption. The engineered version of this cycle is called the humidification-dehumidification ...