Performance and energy consumption of liquid desiccant dehumidification grain in-bin drying system via layered model

Abstract: Wet grain drying is a significant processing step in grain production. Grain in-bin drying is one of the most widely-used and effective drying ways to integrate with drying and storage in grain drying areas. Therefore, this study aims to clarify the performance and energy consumption of liquid desiccant dehumidification grain in-bin drying using a layered model. A system of grain in-bin drying was also designed using liquid desiccant dehumidification driven by a heat pump. New technology was finally developed to achieve safe, efficient, and energy-saving grain drying and storage process for grain in-bin drying. The mathematical models were established to verify, including heat pump, dehumidifier/regenerator, and grain in-bin drying. A specific process was simulated, where the top layer of rice with a grain pile height of 3 m and initial moisture content of 0.2 (wet basis) was dried to reach the safe moisture content of 0.135 (wet basis) by the air flow rate of 120 m3/(h·t) under different outdoor weather parameters with the air temperature of 20-32 ℃ and relative humidity of 55%-80%. Some parameters were determined, including the drying time, the unit and total energy consumption, the dry matter loss (DML), and the whiteness of the top rice after drying. After that, a comparison was made on the performance of the system with various drying. The results showed that the range of drying completion time was 194-358 h. Taking the grain temperature of 20 ℃ and 25 ℃ as examples, the drying completion time was within 21 and 14 d of the safe drying period, respectively. Both met the requirements of a safe drying period, indicating the feasibility of drying time specification. Moreover, the DML top layer of rice after drying was 0.33%-0.52%, where most of the weather parameters met the specification requirement of DML < 0.5%. The initial whiteness value of the top layer of rice was 51.5, while the whiteness value after drying was 51.331-51.452 acceptable in the market (>45), indicating that the overall whiteness value decreased slightly after drying. The suitability of the heat balance model and thin-layer drying equation were verified, where the air entered the grain bin in a state close to the outdoor air temperature and low humidity after dehumidification and heat exchange. Furthermore, the unit energy consumption range was 2.09-3.25 kW·h/ (1% moisture·t), and the total energy consumption was 6 930-9 530 kW·h. It was more conducive to reduce the unit and total energy consumption of the system for high drying efficiency when the outdoor air temperature was higher than before. Nevertheless, the high temperature may lead to more DML of the top layer of rice, even to lower quality. It was found that each thin layer of rice met the dual specification requirements of DML (<0.5%), and the unit energy consumption of the system (<2.5 kW·h/(1%·t)) at the air temperature of 30 ℃. The drying rate and energy consumption under the summer parameters were better than those under the autumn, whereas, the DML and color of rice were inferior to the autumn parameters. The improved system presented a fast speed, less energy consumption, and better rice-related quality, compared with heat-pump drying. Consequently, the system performed well in terms of drying time, energy consumption, and rice-related quality indicators under specific weather conditions, indicating the appropriate and accurate model. The finding can provide a preferred choice for safe, efficient, and energy-saving grain in-bin drying.