Assessment of heat exchangers for the integration of concentrated solar energy into the catalytic hydrothermal gasification of biomass

Abstract

Using concentrated solar energy to power a hydrothermal gasification (HTG) of biomass requires thermal energy storage (TES) to compensate for the inherent intermittence of solar irradiation. The energy transfer from the TES to the HTG process is accomplished through a heat-transfer fluid (HTF) passing through a heat exchanger (HX) incorporated into the salt-separation step of the HTG process. The HX performance determines the temperature profile inside the salt separator, thereby influencing the removal of the salts from the feedstock. In this work, we compare the performances of three HX types based on exploiting fluidized beds, porous media, and axially finned tubes. The effect of the HX configuration on the temperature profile inside the salt separator is assessed through CFD simulations considering pure water as the model feed to the separator. We find that all considered HX types could provide the desired temperature profile within the separator. However, the estimate for the power required to pump the HTF through the fluidized-bed HX is roughly two orders of magnitude higher than those for the axially finned tubular and porous-media HXs.