A Simple Paddy Dryer – Innovation in Practice

by Eng. ParakramaJayasinghe

The Mechanical Engineering Sectional Committee had adopted the three themes of Energy Transport and Innovation as the most topical issues currently facing Sri Lanka in the recent times. In addition the MESC was also desirous of lending a helping hand to the segments of society who are generally not in the focus of either the state or other agencies, but who deserve our consideration.

Accordingly after much discussion on the target groups and possible activities that would have the greatest impact and could be considered as a much touted Corporate Social Responsibility activity, the decision was made that the rural paddy farmers could do with some help. It is well recognized that, the paddy farmers who feed the nation are facing many difficulties but are forever kept at subsistence level by successive governments. While there are many areas where the farmers do deserve greater consideration and assistance, the MESC had to select a task that could be both achievable in a reasonable time frame as well as in an area where our own knowledge and expertise could be made us of, to ensure the success of the task selected. It is also considered desirable if the activity would have a significant impact on as large a group as possible. Based on some newspaper articles by concerned people such as Late Mr. RanjithMuleriyawa, a rural farmer himself and therefore could be considered as a reliable source, it was agreed that a critical point at which the rural paddy farmer is at greatest risk is at the time of converting the hard won harvest to hard cash.

Even though the government declares guaranteed prices for the purchase of paddy, the amount purchased is limited to 2 tons per farmer, creating much hardships to the farmers. This is further compounded by the stipulation of moisture content, based on which the paddy brought to the purchasing center by the farmers, having spent for the transport and waiting in a queue, may be rejected. This problem is most acute if there is a cloudy spell which would prevent the farmers using the traditional sun drying.

To alleviate at least this problem, it was proposed to design a simple dryer for paddy, which can be manufactured at an affordable cost, preferably by a village workshop, as a CSR project by the Mechanical Engineering Sectional Committee.

Once the decision was made the challenge was put to the members to come out with their proposals and designs. Not many of our members are familiar with the issues involved in the cultivation and harvesting and processing of paddy except perhaps at a cursory level. Therefore in order to give them an initial kick start and a base line for their design efforts, a number of meetings were held, to which well-known experts were invited to attend or to provide their inputs by mail.

Arising from these meetings a set of preliminary design parameters were developed as a guideline as out lined below.

The Concept and Preliminary Considerations

Dryer Size- In order to keep the size of the dryer and cost within acceptable limits, the size of the dryer will be limited by the capacity to dry the output from 1 ha of paddy, within three to four days.

Source of Energy – Other than the motive force for any moving parts in the final design, operated by electricity preferably single phase domestic level of supply, the thermal energy required shall be from biomass.

Being a paddy dryer, the obvious choice is paddy husk. An alternative of Gliricidia or other Short Rotation Coppicing tree crops or even readily available agricultural waste, such as corn cobs or sillage, can also be considered. This will be crucial in case paddy husk is not available at the beginning of the harvesting season.

Solar energy is not considered as the present designs developed by various parties have not found wide acceptance. This may be due to the uncertainty of the sunny days or the size of the dryer and the capacity to handle the harvest during the short time desired. A hybrid solution remains on the drawing board.

Dryer Design Parameters

The tentative design parameters used for the development of the prototype arrived at after preliminary discussions are listed below. The valuable inputs from Dr.SanathAmaratunga and Dr.GaminiKulatunga are gratefully acknowledged .

It is necessary to bring down the moisture content to below 14%, with the optimum value being + or -2 %. As per the acceptance specifications of the Paddy Marketing Board

  1. The inlet moisture content of paddy as harvested ranges from 20% to 25%
  2. The estimated period of drying per batch – 10 h
  3. The operating Temperature – Inlet air 65°C maximum ( if air stream is used)
  4. Feeding mechanism – Manual
  5. Collection of dried paddy – directly into sacks
  6. Rate of Drying
  7. Harvest from 1 ha - 5000 kg @ 20-25% MC ( 100 bushels x ( 21 kg x 100 = 2100 kg / per acre x 2.5 ))
  8. Total Drying Time - 10 h x 3 days
  9. Rate per day - 500 (or 1000 kg if two batches are handled)
  10. Rate per hour to optimize quality - to be determined (may not arise if batch drying is done)
  11. Maximum temperature rise in the paddy -45 °C
  12. Targeted price range Rs. 25,000 – Rs. 50,000

Some aspects considered for the design illustrating the wide ranging discussions held.

Dryer Type / Advantages / Disadvantages
1 / Horizontal mesh conveyer with upward movement of hot air / Better control
A stack may be adequate / Need power to drive conveyer.
High cost due to gears etc
2 / Fixed trays with mesh through which the hot air would travel / Simple and cost effective. / More labour
Stack may not be adequate
3 / A cross flow dryer with vertical downward movement of paddy. / Continuous flow
Flow control can regulate the drying rate
Furnace can be mounted on a side / PD required may not be possible with Stack alone
Height may be high

Several Members took up the challenge and spent considerable time in developing the designs. In particular Eng. KushanMeepawala, Eng LoshanPalayangoda and Eng KumudHerath provided preliminary design concepts. Eng ParakramaJayasinghe provided some inputs in respect of the aspects to be considered in arriving at a conceptual design. However, while, no design could be ignored until tested, the time constraints and the added challenge of having a unit ready to be exhibited at the Techno 2016, prompted the fabrication of the simplest design in a convenient size.Useful discussions at the MESC meetings with the guidance and encouragement of the Chairman Eng. ArjunaManaperi ensured that the team had its nose closely to the grind stone to ensure timely delivery.

As it turned out the design conceptualized by Eng. LoshanPalayangoda with his closer association with the paddy milling industry. Proved to be most innovative and the simplest without any moving parts, which also facilitated expeditious fabrication. The MESC is most grateful to the Dockyard General Engineering Services (Pvt.) Ltd, General Manager Eng. T. G.Weerasingheand Eng. ThimiraGodakumbura and Eng. Mahesh Dharmasena for a most professional fabrication free of charge as a gesture of good will. The transport of the dryer to Anuradhapura was also done by Dockyard General Engineering Services (Pvt.) Ltd, also free of charge.


Dryer is ready for testing at Post Harvest Research Institute, Anuradhapura

Some of the features incorporated in the design deserve special mention.

  • No moving parts
  • The water tank serves dual purpose of even drying and limiting the drying temperature
  • Easily adapted for any type of available fuel
  • Convenient loading and unloading
  • Expandable to meet batch size
  • Simple design capable of manufacture at village level

(Many additional features and modifications have been discussed for further development discussed later)

As they say the proof of the pudding is in the eating. So true to the spirit of teamwork, exhibited throughout the project, the team members used their networking skills and called on personal contacts, to make arrangements to perform the testing of the prototype at the Post Harvest Research Institute at Anuradhapura, the most logical place which could be trusted to undertake the testing,diligently and bring in their own experience and knowledge to the task. As further measure of widening the interest group which no doubt will stand in good stead in the future, Eng. Kushan used his initiative to rope in a few undergraduate students from the Faculty of Agriculture at Rajarata University to Assist Eng.Rathnayake at the Post Harvest Institute during the testing.


The team – Eng. ParakramaJayasinghe, Eng. LoshanPalayangoda, Eng. D.D.M.P. Bandara, Eng. Mahesh Dissanayakeand Dr. GaminiKulathunga. (Eng. H.M.A.P.Rathnayake is not in the picture)

As it turned out, the testing proved the unit to perform splendidly with a batch of 25 kg of raw paddy being dried down to the required 13% within one hour.

Batch No / Batch Size(kg) / Ambient Temp.
(Average) °C / Relative Humidity (%) / Initial Moisture Content (Average %) / Final Moisture Content (Average %) / Type of Biomass / Time Duration
(min)
01 / 09 / 34.4 / 69.56 / 17.7 / 13 / Wood / 30
02 / 19 / 33.5 / 69.20 / 17.45 / 12.9 / Wood / 75
03 / 20 / 34.3 / 68.80 / 16.20 / 12.5 / Wood / 80
04 / 20 / 30.7 / 59.4 / 17.1 / 13.1 / Wood / 60

The dryer was exhibited at the Techno 2016 and attracted many interested visitors from different segments of society. Many useful comments were made which has been recorded for future reference.


Paddy Dryer – at MESC stall, Techno 2016

The way forward

The unqualified success of the prototype in meeting the desired performance characteristics, exceeding what the team dared to expect, has thrown open fresh challenges. It is with a sense of Serendipity that we realized that we have hit upon a unit which could have a much greater impact than as a mere dryer of paddy at harvest time to help the rural farmer.

During the discussions with the Director and Staff at PHRI, it transpired that even the current size of the unit could serve as companion dryer for the 35 kg parboiling unit developed by the PHRI, which has received ready acceptance with more than 50,000 units sold already. This option immediately solved a problem that was nagging us through out. As the dryer was designed to dry the raw paddy at harvest time it would have usage only twice a year, with no productive usage and possible deterioration in the interim period. The above match solve this problem splendidly and the necessary modifications required are already being discussed.

Many other possible usages such as drying other agricultural products such as pepper chilies, vegetables were suggested both that the PHRI as well as by visitors to our stall at Techno 2016. One visitor even suggested that it could be used for drying Papadam during the manufacturing process.

The team takes all these suggestions as challenges to be addressed and many simple but effective modifications are under consideration such as

  • Closer temperature control
  • Simple means of temperature measurement
  • Ease of unloading the dried product
  • Expansion of capacity to suit
  • Ensuring longevity of the dryer
  • Simplification of construction to reduce costs of manufacture

  • Different size modules for different applications

Guidance from experts to the students did the testing

H.P.B.G. Senarathna, V.P. Ranasinghe, D.S.M.D. Silva

Some of the graduate students who participated in the testing have expressed their willingness to undertake further testing and modifications on the above lines as a graduate project. The Dean Faculty of Agriculture also considered this a positive move and it is proposed to take this matter further. The sharing of the engineering knowledge of our members with the essential inputs from the agriculture experts will augur well for the development of a successful and versatile dryer

The Paddy Dryer CRS team invites further comments and recommendations for further development of the unit. Our gratitude is due to all the experts and other participants for their valuable inputs to date and their continued support is solicited. In particular the support of the President and IESL both financially and in other ways was invaluable and is solicited for further improvement as proposed.

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