The submerged combustion of a gas, such as natural gas, has been used for the
concentration of very corrosive liquors, including spent pickle liquors, weak phosphoric
and sulphuric acids. A suitable burner for direct immersion in the liquor, as developed by
SWINDIN(25)
, is shown in Figure 14.16. The depth of immersion of the burner is determined
by the time of heat absorption and, for example, a 50 mm burner may be immersed by
250 mm and a 175 mm burner by about 450 mm. The efficiency of heat absorption is
measured by the difference between the temperature of the liquid and that of the gases
leaving the surface, values of 2–5 deg K being obtained in practice. The great attraction
of this technique, apart from the ability to handle corrosive liquors, is the very great
heat release obtained and the almost instantaneous transmission of the heat to the liquid,
typically 70 MW/m3.