Using an Eighth-scale Grain Drying Bin to Compare the Effects of Drying with Ambient Air versus Heated Air

Authors: Lewis, Micah; Trabelsi, Samir; NELSON, S.O. - US Department Of Agriculture (USDA)

Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 6/4/2019
Publication Date: 7/10/2019
Citation: Lewis, M.A., Trabelsi, S., Nelson, S. 2019. Using an Eighth-scale Grain Drying Bin to Compare the Effects of Drying with Ambient Air versus Heated Air. ASABE Annual International Meeting. ASABE Paper No. 1901892,ASABE Annual International Meeting, Boston, MA, July 7-10, 2019.

Interpretive Summary: Cereal grain, such as wheat and corn, and oilseed, such as soybeans are stored in large cylindrical grain bins after harvest. Such bins can have grain heights as great as 28.7 m and diameters as great as 18.3 m. Grain and oilseed in the storage bins must be dried for safe storage to avoid product degradation. They are dried by aeration, a process in which heated or unheated ambient air is forced up through the bed of grain or oilseed. However, the choice of whether to use heated or ambient air is often not known, and it can have an important effect on the overall quality of the product. A significant problem when drying with heated air is overdrying the bottom layer in an attempt to dry the top layer. However, while the bottom layer is less likely to be overdried when using ambient air, there is a risk that the upper layers could be subject to mold and degradation if moisture is not removed quickly enough. Knowing moisture content in real-time would aid in choosing whether to use heated air or ambient air or even when to alternate between them. By using a microwave moisture sensor operating at 5.8 GHz, developed within USDA, ARS, the moisture content of grain or oilseed can be measured continuously, providing real-time moisture content during drying. The microwave moisture sensor was implemented within an eighth-scale grain drying system equipped with eight temperature sensors and four relative humidity sensors to observe drying parameters and moisture migration in the bin as grain or oilseed dried. Trials were run in which only ambient air was used and in which only heated air was used. A 30% and 72% increase in required drying time were observed when ambient/unheated air was used to dry wheat and soybeans, respectively. Depending on weather conditions during drying, such increases could lead to spoilage in the upper layers. Further research with this experimental system will provide better guidelines for the use of heated or unheated air under given environmental conditions and provide for better management of grain drying operations to conserve energy and preserve quality of grain and oilseed products.

Technical Abstract: Cereal grain and oilseed such as wheat, corn and soybeans are stored in large cylindrical grain bins after harvest. Such bins can have height as high as 28.7 m and a diameter as much as 18.3 m. Grain or oilseed within the storage bins must be dried for safe storage and to avoid product degradation. They are dried by aeration, a process in which heated or ambient air is forced up through the bed of grain or oilseed. However, the choice of whether to use heated or ambient air is often complex, and it has a great effect on the overall quality of the product. A significant problem when drying with heated air is overdrying the bottom layer in attempting to dry the top layer. This is possible because grain or oilseed within a grain bin can be more than 15.2 m deep. However, while the bottom layer is less likely to be overdried when using ambient air, there is a risk that the upper layers could be subject to mold and degradation if moisture is not removed quickly enough. Knowing moisture content in real-time would aid in choosing whether to use heated air or ambient air or even when to alternate. By using a microwave moisture sensor operating at 5.8 GHz, developed within USDA ARS, the moisture content of grain or oilseed can be measured continuously, providing real-time moisture content during drying. The microwave moisture sensor was implemented within an eighth-scale grain drying system equipped with eight temperature sensors and four relative humidity sensors to observe drying parameters and moisture migration throughout as grain or oilseed dried. Trials were run where only ambient air was used and only heated air was used. A 30% and 72% increase in drying time were observed when ambient/unheated air was used to dry wheat and soybeans, respectively. Depending on climate, such increases could lead to spoilage.