Thermodynamic analysis for the closed solar biomass drying system with a bottom ORC heat recovery

Growing attentions have been given to the investigation on energy saving of farm products air drying systems recently. A solar drying system, including a top solar air heating cycle and a bottom Organic Rankine cycle (ORC), was proposed. In the proposed solar air drying system, the latent and sensible heats of the wet air out of the drying cabin were recovered through the bottom ORC, and the power generated by turbine of the bottom cycle is not only enough to drive the air compressor in the top cycle, and some extra net power output was obtained from the solar air drying system. Thermal performance of the proposed system was analysed to obtain its energy saving characteristics under different operation conditions. The results showed besides the dried products, the positive net power output is achieved with the moisture content in the air out the drying cabin over 50%, and drying cabin outlet temperature over 350 K. Under the given drying cabin outlet temperature and moisture fraction conditions, the different optimal values of the evaporating pressure are obtained to reach the maximal net power output, total thermal efficiency and dimensionless moisture extraction ratio.