industrial-scale prototype of continuous

8/10/2019 Industrial-scale Prototype of Continuous

1/12

This article was downloaded by: [Iran University of Science &]On: 19 November 2012, At: 05:02Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: MortimerHouse, 37-41 Mortimer Street, London W1T 3JH, UK

Drying Technology: An International JournalPublication details, including instructions for authors and subscription information:

http://www.tandfonline.com/loi/ldrt20

INDUSTRIAL-SCALE PROTOTYPE OF CONTINUOUS

SPOUTED BED PADDY DRYERThanid Madhiyanon

a, Somchart Soponronnarit

a& Warunee Tia

b

aSchool of Energy and Materials, King Mongkut's University of Technology, Thonburi,

Suksawat 48 Road, Bangkok, 10140, ThailandbSchool of Energy and Materials, King Mongkut's University of Technology, Thonburi,

Suksawat 48 Road, Bangkok, 10140, Thailand

Version of record first published: 06 Feb 2007.

To cite this article:Thanid Madhiyanon, Somchart Soponronnarit & Warunee Tia (2001): INDUSTRIAL-SCALE PROTOTYPECONTINUOUS SPOUTED BED PADDY DRYER, Drying Technology: An International Journal, 19:1, 207-216

To link to this article: http://dx.doi.org/10.1081/DRT-100001362

PLEASE SCROLL DOWN FOR ARTICLE

Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to

anyone is expressly forbidden.

The publisher does not give any warranty express or implied or make any representation that the contentswill be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug dosesshould be independently verified with primary sources. The publisher shall not be liable for any loss, actionclaims, proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly orindirectly in connection with or arising out of the use of this material.
http://dx.doi.org/10.1081/DRT-100001362http://www.tandfonline.com/page/terms-and-conditionshttp://dx.doi.org/10.1081/DRT-100001362http://www.tandfonline.com/loi/ldrt20


2/12

DRYING TECHNOLOGY, 19(1), 207216 (2001)

TECHNICAL NOTE

INDUSTRIAL-SCALE PROTOTYPE

OF CONTINUOUS SPOUTED

BED PADDY DRYER

Thanid Madhiyanon, Somchart Soponronnarit,

and Warunee Tia

School of Energy and Materials, King Mongkuts

University of Technology, Thonburi, Suksawat 48 Road,

Bangkok 10140, Thailand

ABSTRACT

An industrial-scale prototype of spouted bed dryer with a

capacity of around 3500 kg/h was constructed and tested. The pro-

totype is shown to have a desirable feature of a spouted bed as well

as the capability of continuous drying and offering consistent re-

sults throughout the testing period. Experimental results show that

the prototype performs well in reducing the moisture content of

the paddy and yields high product quality in terms of the milling

quality. The high temperatures up to 130160C were applied to

dry paddy from various initial moisture contents to the range of

1425%, dry basis without significant change in quality. Thermal

energy consumption, in the range of 3.13.8 MJ/kg water, is com-

parable with other commercial dryers.

Key Words: Continuous spouting; Drying; Grain.

Corresponding author. E-mail: [email protected]

207

Copyright C2001 by Marcel Dekker, Inc. www.dekker.com


3/12

ORDER REPRINTS

208 MADHIYANON, SOPONRONNARIT, AND TIA

INTRODUCTION

The combination of two distinct hydrodynamic features, viz., the pneumatic

transport of particles in the spout which allows intensive heating and moisture

evaporation and a falling bed in the downcomer in which tempering of particles

takes place are the main features of the spouted bed. To overcome some of the

limitations of the conventional cylindricalconical spouted bed, Mujumdar (1)

proposed the two-dimensional spouted bed in which scaling up can be easily

performed. Kalwar et al. (2), Kalwar and Raghavan (3,4) studied drying of grains

in two-dimensional spouted beds with draft plates, using soybeans, wheat, corn,

and shelled corn as test materials. It was found that thin-layer drying behavior as

that predicted by Pages equation is in very good agreementwith experimental data.The circulation of particles strongly depends on the entrance height, spout width

and slant angle. It is also shown that the drying rate is signi ficantly influenced by

grain circulation rate. In another experiment conducted by Wetchacama et al. (5), a

linear equation was found to be suitable to describe the drying rate of paddy which

depends on hold-up and drying temperature. The milling quality of paddy in terms

of head rice yield as well as the drying characteristics of paddy was investigated by

Nguyen et al. (6,7). A triangular spouted bed was proposed in their experiments.

The result of head rice yield is satisfactory as long as the moisture content is kept

above 17.6% dry basis regardless of the high inlet air temperature up to 160C.

Although extensive research has already been performed on the spouted

bed grain drying, the focus was only on batch drying operation. For drying on a

commercial scale, continuousoperation is always preferable. It is thus the objective

of this project to design and test an industrial-scale prototype of a continuous

spouted bed dryer for use in a rice mill. In addition to the fluidized bed dryer, which

has been commercialized, the spouted bed dryer is an alternative for continuous

drying of grain with high initial moisture content. Moreover, the expectation is that

grain quality is preserved, though it is continuously dried to a moisture content

safe for storage.

MATERIALS AND METHODS

Drying studies were conducted in an industrial-scale, prototype spouted bed

dryer with a capacity of 3500 kg/h as shown in Figures 1 and 2, using paddy as a

test material. The dryer consists of a vertical rectangular chamber, 0.6 m in width,1.45 m in height, and 2.1 m in length. The front wall and both of the sidewalls

just above the slanting base of the drying chamber arefitted with glass windows

to permit visualization of the grain flow pattern. The slanting base is inclined at

60. The air entrance and spout widths are 0.04 and 0.06 m, respectively. The

draft plates with 0.62 and 0.82 m in height were centrally installed in the first and
http://lastpage/


4/12

ORDER REPRINTS

INDUSTRIAL-SCALE CONTINUOUS SPOUTED BED DRYER 209

Figure 1. Schematic diagram of the overall experimental set-up.

Figure 2. Dimensions of the continuous spouted bed dryer.
http://lastpage/


5/12

ORDER REPRINTS


second phase of experiments, respectively. The entrance heights of 0.10, 0.125,

and 0.15 m were varied from one experiment to the other to match the feed rate of

paddy. Heat derived from burning diesel fuel was supplied to heat the air before

it was drawn through the blower. The inlet air temperature was controlled by a

P.I.D. temperature controller to be within 2C of the set values. The heated air

was then forced through the ductwork connected to the drying chamber. The hot

and humid air leaving the drying chamber was discharged into a cyclone with

some portion of it exhausted to the ambient. The rest (approximately 60 70% of

total circulation air) wasrecirculated and mixed with ambient airat the combustion

chamber. Paddy was continuously fed into the drying chamber. The paddy traveled

upward through the draft channel before raining back onto the downcomers and

moved vertically downward. The paddy movement alternated between spout anddowncomer until paddy came outof theoutlet port at thebottom of dryingchamber.

Air and paddy temperatures were measured using k-type thermocouples connected

to a data logger with an accuracy of1C. The pressure drop across the bed was

measured using a U-tube manometer. A hot air anemometer with an accuracy

of4% was used to measure the air velocity. Paddy samples were taken from

the outlet port of the drying chamber for measuring moisture content, head rice

yield, and whiteness at 10-min intervals for a period of 80 min. Moisture contents

were determined using a hot air oven set at 103C for 72 h. Head rice yield

was determined according to the method of the Rice Research Institute, and the

whiteness was measured using the Kett meter.

RESULTS AND DISCUSSION

Paddy Motion in the Spout and Bed Shape

It was observed that the flow of paddy was relatively uniform through the

entirelength of thedryer dueto theproper functioning of ductwork connectedto the

inlet of the drying chamber. In the first phase of experiments, the spouting did not

occur continuously. This could be attributed to the improper blower performance,

which resulted in a low pressure drop across the bed and low inlet air velocity at

the entrance of the drying chamber. To solve this problem, an existing blower was

replaced with a high-pressure blower during the second phase of the experiments.

Figure 3 presents the variation of the bed height along the length of dryer at afeed rate of 3550 kg/h and hold-up of approximately 310 kg. The shape of both

downcomer sides is not quite symmetrical. This is because the draft plates may

not be positioned exactly at the center of the drying chamber. The effect of the bed

height difference between each side on the moisture distribution in the bed cannot

be identified since the moisture distribution was not measured in this study.
http://lastpage/


6/12

ORDER REPRINTS


Figure 3. Variation of bed height with length of dryer: feed rate, 3550 kg/h; hold-up,

310 kg.

Drying Efficiency and Milling Quality

Fifteen experiments were carried out in phases 1 and 2. The results of the

first and second phase experiments are summarized in Tables 1 and 2, respectively.

To study dryer performance in terms of moisture content reduction, milling quality

and energy consumption, feed rate of paddy, and the inlet air temperature were

varied from one experiment to the other.

Moisture Content

Cycle time strongly affects the moisture distribution inside the paddy kernel

in the downcomer as well as the number of turns of paddy flowing through the

draft channel. Partial tempering occurs in the downcomer while intense heating

and moisture removal take place in the draft channel. However, it is impractical

to record cycle time in these experiments because of the continuous operation.

Instead, the mean residence time in the dryer (tm) is defined by the following

equation:

tm =hold-up

feed rate(1)

The moisture reduction result of test No. 1 (Table 1) was not satisfactory.This is probably due to nonmatching between the airflow rate and the high feed

rate, which led to residence times that were too short. Therefore, feed rates in

all subsequent experiments were limited to 1000 kg/h, which consequently led

to good results in terms of moisture reduction. The results in Table 1 show that

paddy was dried from a moisture range of 20.030.3% to 14.421.5%, dry basis
http://lastpage/


7/12


8/12

ORDER REPRINTS


Table 2. Summary of the Second Phase Experimental Results

Test No.

Description 8a 9b 10b 11c 12c 13c 14c 15d

Feed rate (kg/h) 2470 2440 1990 2370 2400 3160 3280 3550

Hold-up (kg) 60 360 340 240 210 335 290 310

Residence time (min) 1.5 8.9 10.2 6.0 5.3 6.4 5.3 5.2

Average inlet air temp. (C) 154 149 141 152 159 154 156 160

Exit grain temp. (C) 68 71 66 71 68 67 67 68

Average moisture content

BFD (% dry basis) 26.1 21.7 28.5 22.1 25.0 29.4 28.2 22.8

AFD (% dry basis) 22.7 17.5 23.6 17.1 19.7 25.0 23.3 19.0

Head rice yield

BFD (%) 56.1 45.9 53.3 49.0 49.6 50.1 54.3 41.2

AFD (%) 58.9 45.7 54.2 47.4 48.4 52.4 55.0 40.8

Whiteness

BFD 41.9 45.7 44.2 47.6 47.6 47.8 46.4 46.7

AFD 41.6 45.4 45.0 46.8 46.7 47.5 46.3 45.9

Drying rate (kg water/h) 68 87 79 101 106 111 130 101

Energy consumption

(MJ/kg water evaporated)

Heat 6.5 7.0 N/A 4.4 5.2 3.5 3.8 3.1

Electricity 0.60 0.60 0.60 0.50 0.50 0.46 0.40 0.46

AFD, after drying; BFD, before drying; N/A, not available; temp., temperature.a Draft channel blade angle 85; entrance height, 10 cm.b

Draft channel blade angle 89

; entrance height, 10 cm.cDraft channel blade angle 89; entrance height, 12.5 cm.dDraft channel blade angle 89; entrance height, 15 cm.

Figure 4. Comparisonof moisture contentbetween before andafter drying:inlet airtemp.,

154C; feed rate, 3160 kg/h; hold-up, 335 kg; tm, 6.4 min.
http://lastpage/


9/12

ORDER REPRINTS


Milling Quality

The milling quality, in terms of head rice yield and whiteness, is very sen-

sitive to the drying method and is usually employed in appraising the success

or failure of a grain-drying system. As seen in Tables 1 and 2, it is clear that the

present drying process does not have much effect on milling quality. No significant

quality change was observed when paddy was dried down to 1425% dry basis,

regardless of the high inlet air temperature of up to 130160C. For the head rice

yield, this was due to the fact that the moisture gradient inside the grain kernel

was somewhat redistributed and equalized while passing through the downcomer,

which resulted in relaxation of the stress developed within the grain kernel and

thus gave a satisfactory result in the head rice yield. The high inlet air temperaturemakes no significant change in the whiteness, since grain is exposed to the hot air

in the spouting region within a very short time. In addition, the alternative method

for preservation of milling quality is to apply a zoning concept, that is, using a

high temperature in the first zone for fast drying and a lower temperature in the

subsequent zone of the dryer for gentle drying. This is analogous to employing

the different temperature level concept as described by Nguyen et al. (6,7). The

head rice yield and whiteness results of test No. 13 are presented in Figure 5.

A similar trend of consistency was observed in all experiments.

Energy Consumption

Thermal energy consumption in the first phase of experiments (Table 1)

was relatively high, that is, in the range of 5.67.7 MJ/kg water removed. This

Figure 5. Comparison of head rice yield and whiteness between drying with ambient air

and drying with spouted bed dryer (inlet air temp., 154 C; feed rate, 3160 kg/h; hold-up,

335 kg;tm, 6.4 min).
http://lastpage/


10/12

ORDER REPRINTS


be attributed to noncontinuation of the spouting, which would result in poor paddy

circulation. However, in the second phase of the experiments, thermal energy

consumption was reduced to the range of 3.13.8 MJ/kg water according to a

feed rate of 31003500 kg/h (test Nos. 1315 in Table 2). The decrease of thermal

energy consumption in thesecond phase, especially fortest Nos. 1315 is probably

attributed to a much higher circulation rate than that achieved in thefirst phase of

the study.

CONCLUSIONS

An industrial-scale continuous spouted bed dryer with a capacity of 3500

kg/h was developed and tested. No serious loss in quality was observed during

the experiments while the high drying air temperature was used. Final moisture

content and milling quality results appear to be consistent throughout the testing

periods. However, with the limitation of the existing drying chamber length, a

high percentage of moisture reduction corresponding to the high paddy feed rate

could not be achieved. The energy consumption is comparable to those of other

commercial dryers.

ACKNOWLEDGMENTS

The authors would like to thank the Thailand Research Fund for financialsupport and Rice Engineering Supply Co. Ltd. for supplying facilities for the con-

struction of the prototype dryer. The Kungleechan Rice Mill is also acknowledged

for its cooperation during this study.

REFERENCES

1. Mujumdar, A.S. In Spouted Bed Technology: A Brief Review, Drying84;

Hemisphere: Washington, 1984; 151157.

2. Kalwar, M.I.; Kudra, T.; Raghavan, G.S.V.; Mujumdar, A.S. Drying of Grains

in a Drafted Two-Dimensional Spouted Bed. J. Food Proc. Eng. 1991, 13,

321332.3. Kalwar, M.I.; Raghavan, G.S.V. Batch Drying of Shelled Corn in Two-

Dimensional Spouted Beds with Draft Plates. Drying Technol. 1993,11 (2),

339354.

4. Kalwar, M.I.; Raghavan, G.S.V. Circulation of Particles in Two-Dimensional

Spouted Beds with Draft Plates. Powder Tech. 1993,77, 233242.
http://lastpage/


11/12

ORDER REPRINTS


5. Wetchacama, S.; Soponronnarit, S.; Swasdisevi, T.; Panich-ing-orn, J.;

Suthicharoenpanich, S. In Drying of High Moisture Paddy by Two-

Dimensional Spouted Bed Technique, Proceedings of the First Asian-

Australian Drying Conference (ADC99), Bali, Indonesia, Oct. 2427, 1999;

300307.

6. Nguyen, L.H.; Driscoll, R.H.; Srzednicki, G.S. In Drying Characteristics of

Paddy in a Triangular Spouted-Bed, Proceedings of the 11th International

Drying Symposium (IDS98), Halkidiki, Greece, Aug. 1922, 1998; 1397

1404.

7. Nguyen, L.H.; Driscoll, R.H.; Srzednicki, G.S. InFlowing Performance and

Drying Characteristics of Paddy in a Triangular Spouted-Bed, 7th Interna-

tional Working Conference on Stored-Product Protection, Beijing, China, Oct.1420, 1998.
http://lastpage/


12/12

Order now!

Reprints of this article can also be ordered at

http://www.dekker.com/servlet/product/DOI/101081DRT100001362

Request Permission or Order Reprints Instantly!

Interested in copying and sharing this article? In most cases, U.S. Copyright

Law requires that you get permission from the articles rightsholder before

using copyrighted content.

All information and materials found in this article, including but not limited

to text, trademarks, patents, logos, graphics and images (the "Materials"), are

the copyrighted works and other forms of intellectual property of Marcel

Dekker, Inc., or its licensors. All rights not expressly granted are reserved.

Get permission to lawfully reproduce and distribute the Materials or order

reprints quickly and painlessly. Simply click on the "Request

Permission/Reprints Here" link below and follow the instructions. Visit the

U.S. Copyright Officefor information on Fair Use limitations of U.S.

copyright law. Please refer to The Association of American Publishers

(AAP) website for guidelines on Fair Use in the Classroom.

The Materials are for your personal use only and cannot be reformatted,

reposted, resold or distributed by electronic means or otherwise without

permission from Marcel Dekker, Inc. Marcel Dekker, Inc. grants you the

limited right to display the Materials only on your personal computer orpersonal wireless device, and to copy and download single copies of such

Materials provided that any copyright, trademark or other notice appearing

on such Materials is also retained by, displayed, copied or downloaded as

part of the Materials and is not removed or obscured, and provided you do

not edit, modify, alter or enhance the Materials. Please refer to our Website

User Agreementfor more details.
http://s100.copyright.com/AppDispatchServlet?authorPreorderIndicator=N&pdfSource=Dekker&publication=DRT&title=INDUSTRIAL-SCALE+PROTOTYPE+OF+CONTINUOUS+SPOUTED+BED+PADDY+DRYER&offerIDValue=18&volumeNum=19&startPage=207&isn=0737-3937&chapterNum=&publicationDate=01%2F31%2F2001&endPage=216&contentID=10.1081%2FDRT-100001362&issueNum=1&colorPagesNum=0&pdfStampDate=07%2F28%2F2003+10%3A21%3A46&publisherName=dekker&orderBeanReset=true&author=Thanid+Madhiyanon%2C+Somchart+Soponronnarit%2C+Warunee+Tia&mac=sXPluCe5la$swnX6f%n%MA--http://www.copyright.gov/fls/fl102.htmlhttp://www.publishers.org/conference/copyguide.cfmhttp://www.dekker.com/misc/useragreement.jsphttp://www.dekker.com/misc/useragreement.jsphttp://s100.copyright.com/AppDispatchServlet?authorPreorderIndicator=N&pdfSource=Dekker&publication=DRT&title=INDUSTRIAL-SCALE+PROTOTYPE+OF+CONTINUOUS+SPOUTED+BED+PADDY+DRYER&offerIDValue=18&volumeNum=19&startPage=207&isn=0737-3937&chapterNum=&publicationDate=01%2F31%2F2001&endPage=216&contentID=10.1081%2FDRT-100001362&issueNum=1&colorPagesNum=0&pdfStampDate=07%2F28%2F2003+10%3A21%3A46&publisherName=dekker&orderBeanReset=true&author=Thanid+Madhiyanon%2C+Somchart+Soponronnarit%2C+Warunee+Tia&mac=sXPluCe5la$swnX6f%n%MA--http://www.dekker.com/misc/useragreement.jsphttp://www.dekker.com/misc/useragreement.jsphttp://www.publishers.org/conference/copyguide.cfmhttp://www.copyright.gov/fls/fl102.html

industrial-scale prototype of continuous

Documents