Performance analysis of solar-biomass hybrid heat pump batch-type horizontal fluidized bed dryer using multi-stage heat exchanger for paddy drying

Abstract

The paddy drying performance of a solar-biomass hybrid heat pump batch-type horizontal fluidized bed dryer (FBD) using a multi-stage heat exchanger was investigated. Drying experiments were performed under two different operating modes: the drying system with heat recovery (FBD-WHR mode) and the drying system without heat recovery (FBD-NHR mode). The FBD-NHR and FBD-WHR reduced the paddy moisture content from 28.52% dry basis (db) to 16.28% db with a mass flow rate of 0.10328 kg/s in 26.76 and 23.68 min, at average temperatures of 69.8 and 70.3 °C, respectively. The average specific energy consumption, specific thermal energy consumption, and specific electrical energy consumption were 8.85, 5.81, and 3.04 kWh/kg, respectively, for FBD-NHR and 7.43, 4.22, and 3.21 kWh/kg, respectively, for FBD-WHR. The average specific moisture extraction rates were 0.19 and 0.24 kg/kWh for FBD-NHR and FBD-WHR, respectively. The average pick-up and exergy efficiencies were 41.3% and 51.0%, respectively, for FBD-NHR and 40.4% and 57.7%, respectively, for FBD-WHR. The improvement potential ranged from 199.5 to 628.7 W for FBD-NHR and from 113.1 to 669.1 W for FBD-WHR, with average values of 295.6 and 247.7 W, respectively. The thermal dryer efficiencies varied from 3.5% to 29.6% and from 3.7% to 40.8% for FBD-NHR and FBD-WHR, respectively, with average values of 16.5% and 21.8%, respectively. Thermal energy savings of approximately 46.7% were achieved by using the FBD-WHR mode.