A New Energy-saving Hybrid System Consisting of Latent Thermal Energy Storage and Flash Evaporation

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An energy-saving hybrid system which consists of a latent thermal energy storage unit and a flash evaporation unit has been developed in order to generate the process steam by utilizing various sources of intermittent waste heat. We adopt form-stable polyethylene as a phase change material, and water as a heat transfer medium. The adaptation of this phase change material, which does not undergo melt flow even above the melting temperature, make it possible to perform the direct heat exchange with the heat transfer medium. The spray flash evaporation technique developed originally in our laboratory is applied to the flash evaporation unit. The heat transfer medium heated in the latent thermal energy storage unit is injected through a circular tube nozzle into the flash evaporation unit, where a portion of it flashes off as vapor.The discharge characteristics of the latent thermal energy storage unit, the evaporation efficiency of the flash evaporation unit, and the over-all thermal efficiency of the hybrid system are experimentally examined. As a result, the system is found to generate the process steam relevant to the heat quantity more than 95% of the stored thermal energy, even in the case of lower superheats, due to the high efficiency of the spray flash evaporation technique. The result suggests that out hybrid system can be applied to energy-saving systems.In addition, semi-empirical equations for predicting the time variation of the temperature and the evaporation rate of the heat transfer medium are deduced as the function of various operating parameters. These results make it possible to simulate the time variation of the amount of steam generated.