Comparison between two quadruple-effect evaporator sets operating in co-current and mixed-flow arrangements

摘要

To explore the possibility of reducing exhaust-steam requirement for multiple-effect evaporators, this study investigates the mixed-flow mode of evaporator operation. In the mixed-flow mode, sugar juice and steam are moved in the same direction in the 1st effect, but the concentrated juice leaving the first effect is flashed to the fourth effect. Sugar juice and steam then flow in opposite directions from the fourth effect to the second effect. This arrangement is designed to increase the heat transfer between the steam and juice compared with the conventional co-current flow arrangement, and to prevent the exposure of syrup to high steam temperatures in the first effect that would occur in a fully counter-current flow arrangement. Simulation results indicate that the quadruple-effect evaporator in the mixed-flow arrangement consumes 4% less exhaust steam than the quadruple-effect evaporator in the co-current flow arrangement that operates under the same conditions and has the same total heating surface areas.