Drying is an energy-intensive step in walnut production, accounting for 19% of processing costs and contributing to greenhouse gas emissions. This study surveyed 19 California walnut drying facilities to update energy consumption estimates and identify factors influencing energy use. The variables analyzed included production volume, implementation of energy conservation strategies, the type of fuel used for drying, and ambient air conditions (temperature and relative humidity). The results show that the average energy consumption for walnut drying in California was 1.156 million British thermal units per short ton of in-shell dried walnuts, 11.1% lower than 2009 estimates. Natural gas facilities used 41.5% less energy than those using propane. The type of fuel used for drying was the only factor that significantly affected energy consumption; energy conservation strategies, including in-bin moisture meters and air recirculation, did not have a significant impact. This suggests the need for improved application of energy conservation strategies through better automation and operator training.
Dien et al. (Wed,) studied this question.