Date of Graduation

7-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Biological and Agricultural Engineering

Advisor/Mentor

Sadaka, Sammy S.

Committee Member

Atungulu, Griffiths G.

Second Committee Member

Bautista, Rusty

Third Committee Member

Costello, Thomas A.

Fourth Committee Member

Hestekin, Christa N.

Keywords

Dehumidification; Fluidized bed drying; Modeling; Rice drying; Rice quality

Abstract

For more than half of the world's population, rice (Oryza sativa L.) is a staple meal. However, rice growers encounter difficulties supplying this demand, particularly in developing nations, where rice is susceptible to spoilage if the moisture content is not lowered to a safe level soon after harvest. As a result, traditional drying methods, such as sun drying and natural air drying, are commonly used by rice growers, particularly in underdeveloped nations. However, these procedures are time-consuming and can lead to rice spoilage. On the other hand, fluidized bed drying is a well-established technology that might give rice growers a rapid, practical, economical, and portable drying procedure. According to past research, the primary benefit of fluidized bed drying is the increased drying rate.

On the other hand, other research has expressed concerns about inferior rice quality, which is considered a significant weakness in fluidized bed drying. In the United States of America, the farmers and processors lack consensus and thus there is a mistrust to utilize fluidized bed drying for rice. As a result of the lack of agreement, an extensive study to understand the fluidized bed drying of rice is needed.

In the Mid-South region of the United States, high humidity ambient air is typical, resulting in stoppage of the in-bin rice drying process to avoid rewetting of rice. Ambient air dehumidification may be able to solve this problem and allow for a continual drying process. However, no study utilized desiccant for ambient air dehumidification for drying rice; through this study, an attempt was made to bridge the research gap and determine the benefits and practicalities of ambient air dehumidification to achieve continuous rice drying.

A lab-scale mobile batch fluidized bed dryer was constructed and used in this study. Several tests were done to improve the system that included designs, additions, and replacements of parts.

In a fluidized bed and fixed bed drying system, the effects of ambient air dehumidification, air temperature, and drying duration on rough rice quality were investigated. Energy and exergy analyses were done to determine the thermal efficiency of the drying system. Mathematical modeling was done to optimize the drying of rough rice.

Overall, it was found that fluidized bed drying technology can be utilized for drying rough rice without compromising the quality compared to the fixed bed drying. The air temperature used was between 40 to 50°C, and rice was dried for no more than 60 min. In addition, the ambient air dehumidification reduced the relative humidity of drying air and did not affect rice quality but increased the rice moisture removal, ultimately increasing the drying rate.

The study recommends using air temperatures below 50°C and a drying duration of less than 60 min to achieve effective rough rice drying with fluidized bed drying technique. In addition, ambient air dehumidification can be employed for reducing ambient air relative humidity by few points. However, more research must be done at the farm and industrial scale to check the accuracy of these findings at a large scale.

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