Energy integration of multiple effect evaporators in sugar process production

Heat demand in sugar plants occurs in juice heating, evaporation and crystallization operations. Although all the operations mentioned are necessary for the production process, evaporation is emphasized in the energetic integration aspect, not only due to the largest energy consumption, but also, due to the possibility of using the vapor generated in that operation, as heating source to the remaining of the process. The way for solving the energy integration problem, simultaneously designing the configuration of the multiple effect evaporator (MEE), must be through the decomposition of the thermal system, assuming the existence of two interactive subsystems: MEE and the remaining of the process. To reduce the energy consumption, the evaporator subsystem and the process heating subsystem should be retrofitted to make improved heat recovery possible. Process integration can help to choose the best configuration of MEE in order to achieve a more efficient process in the sense of energy use. In this study the multiple effect evaporation stage in an actual sugar plant was simulated in ASPENPLUS. The problem can be solved iteratively by combining pinch analysis algorithms using ASPENPINCH and simulation of the evaporation step. Since there are several effects, heat flows must be classified as utility, and equipment configuration should be defined according to the thermal demand of the process. The study focuses on a typical sugar cane factory, processing 150 t of cane/h. The properties of the feed steam flows were given by the outlet conditions of streamlines located between the boilers and the preflash unit. The individual thermal loads of the streams were calculated, by using temperature and flow rate data for the juice streams. For MEE configuration analyzed, the simulations were accomplished and compared with the actual process in order to validate de adequacy of models choose. Energy curves were plotted for determining minimum energy consumption of the global process. MEE simulations were accomplished, to make the thermal analyses easier. This approach allows the elaboration of an algorithm that systematizes the use of pinch analysis in sugar plants through process modelling and simulation.