(186b) Hydrodynamic Behaviors of a Fluidized Bed Evaporator in Thermal Desalination Process

Recently, a self-heat recuperation technology, which can save energy consumption in thermal processes drastically, was proposed. Authors applied it to thermal desalination process in order to promote the wider application of the process. Their simulation results showed that the energy consumption of the proposed process was reduced to 1/4 that of conventional counterparts. Furthermore, it was also found that the higher the recovery ratio, defined as the product seawater flow rate divided by feed seawater flow rate, the less the energy consumption in the proposed process. Thus, the self-heat recuperative seawater desalination process with high recovery ratio has a really large energy saving potential. However, when the recovery ratio is high, scale deposits on the heater surface. Scale is a precipitation of salts in seawater and the deposition deteriorates the heat transfer between seawater and heater surface.

Thus, to prevent the scale deposition on the heater surface, we proposed a self-heat recuperative thermal seawater desalination process using fluidized bed. In the process, the fluidized bed is used as an evaporator. The heated particles are fluidized by blown gas. Subsequently they contact seawater fed from the top of the bed. Then, the seawater evaporates on the heated fluidized particles instead of heater surface. Thus, it can be considered that the seawater desalination process using fluidized bed evaporator can prevent the scale deposition on the heater surface. However, it is also known that an excessive amount of liquid feed may cause agglomeration of fluidized particles, which leads to defluidization. When the defluidization occurs, the seawater evaporation does not continue.

So far, we conducted the seawater evaporation experiment and found that the high fluidizing gas velocity can inhibit the agglomeration/defluidization in fluidized bed. However, a blower work increases. In this research, the influence of fluidizing parameters (e.g. fluidizing gas velocity, feed seawater flow rate, particle size) on the fluidization will be investigated. Simultaneously, the optimum conditions under which energy consumption is small and fluidization maintains will be examined.