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Development of a Recirculatory Cross-flow Paddy Dryer

M.N. lslam
Associate Professor
Dept. of Farm Power and Machinery, Bangladesh Agric. Univ., Mymensingh, Bangladesh

M. Ali
Dept. of Farm Power and Machinery, Bangladesh Agric. Univ., Mymensingh, Bangladesh

S.M. Rezaul lslam
Program Organizer
PROSHIKHA, Dhaka, Bangladesh

Abstract/ Executive Summary:

A batch-type recirculatorY cross-flow paddy dryer was designed, constructed and installed in the laboratory. A husk furnace was constructed by converting an oil drum to supply heated air to the dryer. An oil drum was converted to ash separator by dividing its inner space with baffles of wire netting covered with a layer of lubricating oil. A centrifugal blower was used for delivering heated air to the dryer. Drying tests were performed by feeding the grain into the dryer from top. Paddy was recirculated with the help of a bucket type elevator. Hot air circulated to the dryer was made to flow perpendicular to the direction of the grain flow, thereby eliminating the possibility of redeposition of moisture in the grain. Use of easily accessible low cost materials and simple technology for construction along with cross-flow air supply system made this dryer well suited to and advantageous for paddy drying under Bangladesh conditions.

Keywords: Smoke, Ash and Oily Substances, Delivery Pipes, Heat Exchanger

Location: Department of Farm Power and Machinery

Start Date:

End Date:

Program Area: Farm Mechanization

Commodity: Product development

Objectives:

To design and construct a cross-flow paddy dryer and a rice husk furnace with an ash separator using locally available lowcost materials and simple technology with a view to making this drying system easily available to farmers.

Methodology:

A cross-flow dryer was designed for paddy drying consisting of a dryer unit, a bucket elevator, a husk furnace, an ash separator and a blower. Flat bars, G.I. sheet and wirenet covering were used as the principal materials of construction for the cylindrical shaped experimental dryer. The dryer was designed for drying 140 kg paddy per batch. A small cylinder made of wire net and having conical shaped ends was placed inside the dryer unit through which heated air was supplied. Grain was discharged from the dryer into a hopper for recirculation using a bucket-type elevator. Through this arrangement, a continuous recirculation of grain was maintained in the dryer. An oil drum was converted into husk furnace. An inclined gate was constructed at the lower end of the drum by fitting inclined baffles to facilitate air flow required for burning the husk. One end of a perforated G.I. pipe (7.0 cm diameter) was placed at the center of the husk furnace and rice husk was packed around this pipe. The other end of the pipe was connected with the suction end of the blower through an ash separator. Another oil drum was converted into ash separator by fixing a baffle into the drum @ig. 1). The baffle was made of wire net and was soaked with lubricating oil for better cleaning of air. The dryer was installed on a steel frame for convenient use. Hot air was supplied to the dryer by a blower which was installed between the dryer unit and ash separator. The ash separator and the husk furnace were installed parallel to the dryer. They were connected by a U-shaped steel pipe. The top of the dryer unit was connected with a bucket elevator for continuous feeding and recirculation of grain. The bottom of the dryer dropped into the hopper through a hose pipe. Due to unavailability of freshly harvested paddy, dried paddy was remoistened by spraying water and mixing it thoroughly and keeping over 24 h for uniform diffusion of moisture. The moisture content of the remoistened paddy was determined by oven method and was found to be 25s/o (d.b.) which was considered as the initial moisture content to paddy for the test. The remoistened paddy was fed into the dryer from the top by the elevator. Dry and wet bulb temperatures of drying air both at inlet and outlet of dryer were measured. Heated air temperature was adjusted to and made constant at 40'C before starting drying test. Grain temperature within the dryer was measured at five different places. Grain samples were collected periodically to determine grain moisture content and drying rate. Drying test was continued for 3 h.

Source of Information: AGRICULTURAL MECHANIZATION IN ASIA, AFRICA AND LATIN AMERICA 1993 VOL.24 NO.l, PP:42-44

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The developed dryer was very useful for the farmers and small rice processors as it would improve the quality of marketed rice. The dryer was advantageous because of its simplicity in construction and operation. The paddy dryer required minor modification for successful operation. A suitable heat exchanger should be developed for husk furnace so that smoke, ash and oily substances could be removed. The blower could be placed before the heat exchanger to reduce heat loss. Delivery pipes and heat exchanger should be insulated to reduce heat loss.

Knowledge Management: Journal