A Review and Update of Bubble Column Evaporator Processes

Abstract

This paper gives an updated review of the bubble column evaporator (BCE) and its various new processes. These include recent work on helium gas desalination and high temperature inlet gas decomposition. The BCE process offers a continuously produced source of high gas-water interface and consequently provides high overall heat and mass transfer coefficients. Very different results have been obtained using nitrogen, oxygen, carbon dioxide and helium inlet gases. Although the bubbling process itself is both simple to use and apply, our understanding of the fundamental physical and chemical principles involved is surprisingly limited and there are many issues yet to be explained.  Recently the process has been used to develop new methods for the precise determination of enthalpies of vaporisation of concentrated salt solutions, as an evaporative cooling system, a sub-boiling thermal desalination unit, for sub-boiling thermal sterilization, for low temperature thermal decomposition of different solutes in aqueous solution and for the inhibition of particle precipitation in supersaturated solutions. These novel applications can be very useful in many industrial practices, such as desalination, water/wastewater treatment, thermolysis of ammonium bicarbonate (NH₄HCO₃) for the regeneration in forward osmosis and refrigeration related industries. The background theories and models use to explain the BCE process are also reviewed and this fundamental knowledge is applied to the design of BCE systems and to explain recently explored applications, as well as potential improvements.  Many other prospective applications of the BCE process are also reported in this paper.