Annex 3.5 T

TABLES ON DRYING

Table 3.5.1. Methods of drying paddy or rough rice.

Method	Description	Process	Additional information	Comments	References
Field drying	Cut panicles are spread in the field to dry for few hours or days. Sometimes cut panicles are bundled and let standing in the field to dry. Allowing paddy to dry before cutting.	Sun or solar drying of unthreshed or uncut panicles in the field.	Usually practiced during the rain season harvesting after rain.	Subject the grain to more losses due to rats, birds and grain shattering. Quality deterioration due to heating when left longer in the field.	35, 45, 63
Shade drying	Bundled cut panicles are placed under the shade to dry. Threshed paddy are spread on mat, floor or any other materials or surfaces inside the house or shaded place to dry.	Shade or air drying.	Used for seeds during rains; long drying time; Sometimes bundled panicles for seeds are hang above cooking place in the kitchen.	Subject to grain loss due to pests and spillage.	45
Sun drying	Spreading threshed paddy in drying floors (Mats, pavement, roadside and others) to dry under the sun. An improved unit where air heated by solar heat absorber is passed through a thin layer of wet paddy on perforated flooring by convective current.	Sun or solar drying. Frequent stirring by hand, feet, rake or others.	Cheapest and most common method used by all sectors involved in paddy production or processing.	Losses occur due to spillage, animals feeding, checking of grain if soaked by rain and others. Laborious, usually done by women or children in the farm.	31, 35, 45

Table 3.5.1. Methods of drying paddy or rough rice (continued).

Method	Description	Process	Additional information	Comments	References
Shallow bed batch type	Grain placed on perforated flooring of up to 40 cm thickness is dried by forcing heated air through the grain.	Continuous heated air batch drying until grain is safe for storage or milling.	Air heated to 43 C, no stirring, higher air temperature cause uneven layer drying.	Easy to operate, commonly used by small paddy processors.
Deep bed batch drying	Deep bin with perforated floor where dry or slightly heated air is forced through the grain layer.	Drying and cooling of grain in storage.	Sometimes perforated pipes are inserted on the bin to force and exhaust the air through the grain.	Method used to prevent grain deterioration while waiting for dryer availability. Used in big paddy processing plants.	34, 42, 45
Continuous flow non-mixing dryer	A column of grain about 30 cm thick supported by perforated sheet walls with feeding hopper on top and discharge mechanism at the bottom.	Heated air of up to 70 C is forced through the column of grain to effect drying as it flows downward. Exposure time is about l0-l5 minutes.	Grain is transferred to an aerated tempering bin to remove evaporating moisture and moisture in the grain to equilibrate.	Used in big commercial installations; total exposure time to heated air is decreased compared with continuous drying; Uneven drying due to one side exposure of grain.	42, 45

Table 3.5.1. Methods of drying paddy or rough rice (continued).

Method	Description	Process	Additional information	Comments	References
Continuous flow mixing dryer	A column of grain with perforated sheet walls with baffles, loading hopper on top and discharge mechanism at the bottom. The LSU (US) design has inverted Vs alternately arranged inside the bin. Heated air is forced in one layer of inverted Vs and discharged to the adjoining inverted Vs as the wet grain flows downward.	Baffle with grain flow zigzagging downward as heated air forced across to dry the grain mass.	Grain is transferred to an aerated tempering bin to remove evaporating moisture and in the grain to equilibrate.	Used in big commercial installations, total exposure time to heated air is decreased compared with continuous drying. More even grain drying due to mixing process.	42, 45

Notes:
For each mechanical heated air drying method power is provided to drive the blower to move the air, a heater to heat the drying air, ducting and associated elevators, conveyors and others as needed. Power can be petrol or diesel engine or electric motors and the heat source could be electricity, kerosene, LPG, rice husk and others depending on the cost and availability in the area.

2. Other methods of drying as the fluidized bed, flame, heated sand and other materials as steel balls, use of infra red lamps in flowing grain layer, rotary dryers, tray dryers and other dryers are also used in drying paddy. These methods however are seldom used because of availability of equipment, technical requirements, critical operations and high risk of losing the grain if not operated properly.

Table 3.5.2. Methods of drying, their suitability and losses.

Method of drying	Features	Comments
Sundrying		Labour-intensive, high losses uncontrolled quality of dried paddy, unreliable during the rainy season, environment friendly, suitable for household level drying, most popular method among developing countries.
Aeration in storage	Can be a very low cost drying and storing system for home stocks of paddy ranging from 1 to 2 tons per family; however, needs heating element such as electric heating coils mostly during times when drying need is critical, i.e., wet paddy during the rainy season.	Long duration; ineffective/damage risk under high humidity; ties up storage structure; prototype design of low-cost in-store dryer is available from the University of Agriculture and Forestry, Vietnam.
Heated air or mechanical		High capital and operational cost; Polluting and GHG emitting due to fuel burning; seasonal and low utilization except by commercial mills.
Batch		Small capacity; uneven drying; high cost
Continuous flow		High energy; controlled and uniform drying; suitable for commercial mills
Recirculating		High energy; suitable for commercial-scale mills

Table 3.5.3 Types, capacities, sources of supply, and prices of commercial grain dryers available in the Philippines as of October 1995..

Type of dryer	Capacity	Manufacturer supplier/dealera	Price, Philippine pesosb as of October 1995
Batch Type
Flat bed	2 t/6-8 hours	14 local accredited manufacturers	65,000
Twin bed	3 t/6-8 hours	Marinas Industries, Pila, Laguna	130,000
Reversible flat bed	2 t/4-6 hours	Kuizon, Tacloban, Leyte	130,000
Columnar (Kongskilde)	10 t/8-12 hours	Scancon (imported), Manila	2.6 million
Columnar	5 t/8 hours	Marinas, Oila, Laguna	300,000c
In-store	60 t/6 days	NAPHIRE, Munoz, Nueva Ecija	250,000
Continuous recirculating
LSU	1-4 t/hour	Padiscor (local), Pasig City	1-2 million
Cimbria	10-15 t/hour	Padiscor (imported, Denmark), Pasig City	~ 5-10 million
Shanzer	10-15 t/hour	Leverson (imported, USA), Pasig City	~ 10-15 million
Satake	5-10 t/hour	Mechaphil (imported, Japan), Pasig City	~ 3-5 million
Suncue	1.2-6 t/10-12 hours	H.E. Enterprises Inc. (imported, Taiwan), Tondo, Manila	400,000
Columnar	500-600 kg/hour	14 local accredited manufacturers (all over the country)	1000,000
Rotary	600-80 kg/hour	Jamandre, Iloilo City	100,000
Fluidised bed	500 kg/hour	ASIS, Cagayan de Oro City	85,000
Flash	1 t/hour to 18% m.c.	BUPHRE d, Munoz, Nueva Ecija	80,000 c

^a Not an endorsement of any manufacturer, dealer or product.

^b During October 1995, about 25 Philippine pesos (PHP) = US$1, subject to changes.

^c As of January 1998, about 41 PHP=US$1, subject to change.

^c Bureau of Postharvest Research and Extension, formerly NAPHIRE

Source: Andales, 1996.