Parametric analysis on the low temperature wet air waste heat recovery through an organic Rankine cycle

Removing moisture in the wet farm products through the open air ventilation is a traditional postharvest treatment method. However, its overall energy consumption is high and the drying time is long. Here, a combined system is proposed through integrating a bottom organic Rankine cycle (ORC) to a top closed farm products air drying cycle to save energy and decreasing the drying time. Based on a steady state thermodynamic model without any losses, a theoretical work on thermal performance the proposed system has been conducted. The key operation parameters and suitable operation conditions for both the prominent energy saving ratio and high moisture extraction characteristics have been analyzed. The calculation results showed both the prominent energy saving and high moisture extraction performances can be achieved at the low ORC evaporating pressure condition, but the optimal energy saving performance and the moisture extraction performance could not be achieved simultaneously. Increasing dew point temperature of the humid air leaving the drying chamber improves both the energy saving and moisture extraction performances of the drying system significantly. Under the working conditions in this research, with the dew point temperature value of the humid air leaving the drying chamber over 323 K, the optimal energy saving performance is achieved at a fixed low ORC evaporation pressure. But, the prominent energy saving and high moisture extraction performances could not be accomplished simultaneously, with the dew point temperature value of the humid air leaving the drying chamber lower than 323 K.