Energy Consumption Requirements of Agricultural Dryers: An Overview

Abstract

Artificial dryers promote high-quality dried food products in spite of their considerable energy consumption. This paper presents a review of energy consumption of agricultural dryers in order to ensure optimal dryer design and cost effective dryer operation which yield better quality dried products. From the review, dryer design, type, crop characteristics, and ambient environmental conditions are seen as major factors affecting dryer energy consumption. Energy consumption of different dryers with different products was reported using different empirical expressions and graphical approaches. Results obtained show that microwave dryers have about 70% energy savings when compared to other artificial dryers due to their low energy consumption at higher power densities, but are cost-intensive when operated at the recommended 500W power density for thin-layer or slice products. For other types of dryers, energy consumption generally increases with increase in air velocity and drying time, and decreases with temperature. It also decreases exponentially with drying time and moisture content for different sample geometries; while for microwave dryers, it varies inversely with temperature at constant air velocity. Vacuum-infrared dryer reveals that the total energy consumption varies inversely with the microwave power and slice thickness of crop sample and increases with increased absolute pressure. Other field test results for different drying systems and products were also presented. Suggestions were made towards improving reviewed dryers for efficiency in drying at optimal operating conditions.