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Drying Technology An International JournalPublication details including instructions for authors and subscription informationhttpwwwtandfonlinecomloildrt20

INDUSTRIAL-SCALE PROTOTYPE OF CONTINUOUSSPOUTED BED PADDY DRYERThanid Madhiyanon a Somchart Soponronnarit a amp Warunee Tia ba School of Energy and Materials King Mongkuts University of Technology ThonburiSuksawat 48 Road Bangkok 10140 Thailandb School of Energy and Materials King Mongkuts University of Technology ThonburiSuksawat 48 Road Bangkok 10140 ThailandPublished online 06 Feb 2007

To cite this article Thanid Madhiyanon Somchart Soponronnarit amp Warunee Tia (2001) INDUSTRIAL-SCALE PROTOTYPEOF CONTINUOUS SPOUTED BED PADDY DRYER Drying Technology An International Journal 191 207-216 DOI 101081DRT-100001362

To link to this article httpdxdoiorg101081DRT-100001362

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DRYING TECHNOLOGY 19(1) 207ndash216 (2001)

TECHNICAL NOTE

INDUSTRIAL-SCALE PROTOTYPEOF CONTINUOUS SPOUTED

BED PADDY DRYER

Thanid Madhiyanon Somchart Soponronnaritand Warunee Tialowast

School of Energy and Materials King MongkutrsquosUniversity of Technology Thonburi Suksawat 48 Road

Bangkok 10140 Thailand

ABSTRACT

An industrial-scale prototype of spouted bed dryer with acapacity of around 3500 kgh was constructed and tested The pro-totype is shown to have a desirable feature of a spouted bed as wellas the capability of continuous drying and offering consistent re-sults throughout the testing period Experimental results show thatthe prototype performs well in reducing the moisture content ofthe paddy and yields high product quality in terms of the millingquality The high temperatures up to 130ndash160C were applied todry paddy from various initial moisture contents to the range of14ndash25 dry basis without significant change in quality Thermalenergy consumption in the range of 31ndash38 MJkg water is com-parable with other commercial dryers

Key Words Continuous spouting Drying Grain

lowastCorresponding author E-mail waruneetiakmuttacth

207

Copyright Ccopy 2001 by Marcel Dekker Inc wwwdekkercom

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208 MADHIYANON SOPONRONNARIT AND TIA

INTRODUCTION

The combination of two distinct hydrodynamic features viz the pneumatictransport of particles in the spout which allows intensive heating and moistureevaporation and a falling bed in the downcomer in which tempering of particlestakes place are the main features of the spouted bed To overcome some of thelimitations of the conventional cylindricalndashconical spouted bed Mujumdar (1)proposed the two-dimensional spouted bed in which scaling up can be easilyperformed Kalwar et al (2) Kalwar and Raghavan (34) studied drying of grainsin two-dimensional spouted beds with draft plates using soybeans wheat cornand shelled corn as test materials It was found that thin-layer drying behavior asthat predicted by Pagersquos equation is in very good agreement with experimental dataThe circulation of particles strongly depends on the entrance height spout widthand slant angle It is also shown that the drying rate is significantly influenced bygrain circulation rate In another experiment conducted by Wetchacama et al (5) alinear equation was found to be suitable to describe the drying rate of paddy whichdepends on hold-up and drying temperature The milling quality of paddy in termsof head rice yield as well as the drying characteristics of paddy was investigated byNguyen et al (67) A triangular spouted bed was proposed in their experimentsThe result of head rice yield is satisfactory as long as the moisture content is keptabove 176 dry basis regardless of the high inlet air temperature up to 160C

Although extensive research has already been performed on the spoutedbed grain drying the focus was only on batch drying operation For drying on acommercial scale continuous operation is always preferable It is thus the objectiveof this project to design and test an industrial-scale prototype of a continuousspouted bed dryer for use in a rice mill In addition to the fluidized bed dryer whichhas been commercialized the spouted bed dryer is an alternative for continuousdrying of grain with high initial moisture content Moreover the expectation is thatgrain quality is preserved though it is continuously dried to a moisture contentsafe for storage

MATERIALS AND METHODS

Drying studies were conducted in an industrial-scale prototype spouted beddryer with a capacity of 3500 kgh as shown in Figures 1 and 2 using paddy as atest material The dryer consists of a vertical rectangular chamber 06 m in width145 m in height and 21 m in length The front wall and both of the sidewallsjust above the slanting base of the drying chamber are fitted with glass windowsto permit visualization of the grain flow pattern The slanting base is inclined at60 The air entrance and spout widths are 004 and 006 m respectively Thedraft plates with 062 and 082 m in height were centrally installed in the first and

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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

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210 MADHIYANON SOPONRONNARIT AND TIA

second phase of experiments respectively The entrance heights of 010 0125and 015 m were varied from one experiment to the other to match the feed rate ofpaddy Heat derived from burning diesel fuel was supplied to heat the air beforeit was drawn through the blower The inlet air temperature was controlled by aPID temperature controller to be within plusmn2C of the set values The heated airwas then forced through the ductwork connected to the drying chamber The hotand humid air leaving the drying chamber was discharged into a cyclone withsome portion of it exhausted to the ambient The rest (approximately 60ndash70 oftotal circulation air) was recirculated and mixed with ambient air at the combustionchamber Paddy was continuously fed into the drying chamber The paddy traveledupward through the draft channel before raining back onto the downcomers andmoved vertically downward The paddy movement alternated between spout anddowncomer until paddy came out of the outlet port at the bottom of drying chamberAir and paddy temperatures were measured using k-type thermocouples connectedto a data logger with an accuracy of plusmn1C The pressure drop across the bed wasmeasured using a U-tube manometer A hot air anemometer with an accuracyof plusmn4 was used to measure the air velocity Paddy samples were taken fromthe outlet port of the drying chamber for measuring moisture content head riceyield and whiteness at 10-min intervals for a period of 80 min Moisture contentswere determined using a hot air oven set at 103C for 72 h Head rice yieldwas determined according to the method of the Rice Research Institute and thewhiteness 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 theentire length of the dryer due to the proper functioning of ductwork connected to theinlet of the drying chamber In the first phase of experiments the spouting did notoccur continuously This could be attributed to the improper blower performancewhich resulted in a low pressure drop across the bed and low inlet air velocity atthe entrance of the drying chamber To solve this problem an existing blower wasreplaced with a high-pressure blower during the second phase of the experimentsFigure 3 presents the variation of the bed height along the length of dryer at afeed rate of 3550 kgh and hold-up of approximately 310 kg The shape of bothdowncomer sides is not quite symmetrical This is because the draft plates maynot be positioned exactly at the center of the drying chamber The effect of the bedheight difference between each side on the moisture distribution in the bed cannotbe identified since the moisture distribution was not measured in this study

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INDUSTRIAL-SCALE CONTINUOUS SPOUTED BED DRYER 211

Figure 3 Variation of bed height with length of dryer feed rate 3550 kgh hold-up310 kg

Drying Efficiency and Milling Quality

Fifteen experiments were carried out in phases 1 and 2 The results of thefirst and second phase experiments are summarized in Tables 1 and 2 respectivelyTo study dryer performance in terms of moisture content reduction milling qualityand energy consumption feed rate of paddy and the inlet air temperature werevaried from one experiment to the other

Moisture Content

Cycle time strongly affects the moisture distribution inside the paddy kernelin the downcomer as well as the number of turns of paddy flowing through thedraft channel Partial tempering occurs in the downcomer while intense heatingand moisture removal take place in the draft channel However it is impracticalto record cycle time in these experiments because of the continuous operationInstead the mean residence time in the dryer (tm) is defined by the followingequation

tm = hold-up

feed rate(1)

The moisture reduction result of test No 1 (Table 1) was not satisfactoryThis is probably due to nonmatching between the airflow rate and the high feedrate which led to residence times that were too short Therefore feed rates inall subsequent experiments were limited to 1000 kgh which consequently ledto good results in terms of moisture reduction The results in Table 1 show thatpaddy was dried from a moisture range of 200ndash303 to 144ndash215 dry basis

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212 MADHIYANON SOPONRONNARIT AND TIA

Table 1 Summary of the First Phase Experimental Results

Test No

Description 1 2 3 4 5 6 7

Feed rate (kgh) 3140 1000 900 844 664 939 816Hold-up (kg) 180 210 135 125 190 190 190Residence time (min) 40 126 90 89 172 121 140Average inlet air temp (C) 185 144 144 146 146 133 126Exit grain temp (C) 67 71 69 67 72 72 71Average moisture content

BFD ( dry basis) 319 200 232 250 303 262 266AFD ( dry basis) 285 144 178 204 213 215 199

Head rice yieldBFD () 629 342 456 371 482 395 435AFD () 648 334 427 392 480 368 455

WhitenessBFD 419 476 502 510 459 496 446AFD 392 475 511 511 467 503 450

Drying rate (kg waterh) 83 49 41 33 49 39 46Energy consumption(MJkg water evaporated)

Heat 71 67 70 77 56 77 NAElectricity 050 076 091 112 074 100 080

AFD after drying BFD before drying NA not available temp temperature entranceheight 10 cm (for all experiments)

and that the mean residence time lay between 9 to 17 min At the second phase ofthe experiments (Table 2) the old blower was replaced by a high-pressure blowerThe prototype was then able to handle a maximum capacity of around 3500 kghwith moisture reduction in the range of 217ndash294 to 171ndash250 dry basisHowever the main difficulty was that high moisture reduction was required ata feed rate over 3000 kgh Since the mean residence time was relatively shortthat is in the range of 5ndash6 min grains were less frequently drawn through thedraft channel The final moisture content appeared to be consistent throughout thetesting period as shown in Figure 4 (test No 13) Similar trends were found for all15 experiments

The question of how to reach high moisture reduction that is from 30down to 16ndash18 dry basis is of practical interest It was to be expected fromthe near-to-linear trend in the moisture content with time (5) that high moisturereduction could be achieved by extending the drying chamber length which wouldresult in a longer mean residence time

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INDUSTRIAL-SCALE CONTINUOUS SPOUTED BED DRYER 213

Table 2 Summary of the Second Phase Experimental Results

Test No

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

Feed rate (kgh) 2470 2440 1990 2370 2400 3160 3280 3550Hold-up (kg) 60 360 340 240 210 335 290 310Residence time (min) 15 89 102 60 53 64 53 52Average inlet air temp (C) 154 149 141 152 159 154 156 160Exit grain temp (C) 68 71 66 71 68 67 67 68Average moisture content

BFD ( dry basis) 261 217 285 221 250 294 282 228AFD ( dry basis) 227 175 236 171 197 250 233 190

Head rice yieldBFD () 561 459 533 490 496 501 543 412AFD () 589 457 542 474 484 524 550 408

WhitenessBFD 419 457 442 476 476 478 464 467AFD 416 454 450 468 467 475 463 459

Drying rate (kg waterh) 68 87 79 101 106 111 130 101Energy consumption(MJkg water evaporated)

Heat 65 70 NA 44 52 35 38 31Electricity 060 060 060 050 050 046 040 046

AFD after drying BFD before drying NA not available temp temperatureaDraft channel blade angle 85 entrance height 10 cmbDraft channel blade angle 89 entrance height 10 cmcDraft channel blade angle 89 entrance height 125 cmd Draft channel blade angle 89 entrance height 15 cm

Figure 4 Comparison of moisture content between before and after drying inlet air temp154C feed rate 3160 kgh hold-up 335 kg tm 64 min

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214 MADHIYANON SOPONRONNARIT AND TIA

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 successor failure of a grain-drying system As seen in Tables 1 and 2 it is clear that thepresent drying process does not have much effect on milling quality No significantquality change was observed when paddy was dried down to 14ndash25 dry basisregardless of the high inlet air temperature of up to 130ndash160C For the head riceyield this was due to the fact that the moisture gradient inside the grain kernelwas somewhat redistributed and equalized while passing through the downcomerwhich resulted in relaxation of the stress developed within the grain kernel andthus 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 airin the spouting region within a very short time In addition the alternative methodfor preservation of milling quality is to apply a zoning concept that is using ahigh temperature in the first zone for fast drying and a lower temperature in thesubsequent zone of the dryer for gentle drying This is analogous to employingthe different temperature level concept as described by Nguyen et al (67) Thehead rice yield and whiteness results of test No 13 are presented in Figure 5A 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 56ndash77 MJkg water removed This

Figure 5 Comparison of head rice yield and whiteness between drying with ambient airand drying with spouted bed dryer (inlet air temp 154C feed rate 3160 kgh hold-up335 kg tm 64 min)

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INDUSTRIAL-SCALE CONTINUOUS SPOUTED BED DRYER 215

be attributed to noncontinuation of the spouting which would result in poor paddycirculation However in the second phase of the experiments thermal energyconsumption was reduced to the range of 31ndash38 MJkg water according to afeed rate of 3100ndash3500 kgh (test Nos 13ndash15 in Table 2) The decrease of thermalenergy consumption in the second phase especially for test Nos 13ndash15 is probablyattributed to a much higher circulation rate than that achieved in the first phase ofthe study

CONCLUSIONS

An industrial-scale continuous spouted bed dryer with a capacity of 3500kgh was developed and tested No serious loss in quality was observed duringthe experiments while the high drying air temperature was used Final moisturecontent and milling quality results appear to be consistent throughout the testingperiods However with the limitation of the existing drying chamber length ahigh percentage of moisture reduction corresponding to the high paddy feed ratecould not be achieved The energy consumption is comparable to those of othercommercial 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 acknowledgedfor its cooperation during this study

REFERENCES

1 Mujumdar AS In Spouted Bed Technology A Brief Review Dryingrsquo84Hemisphere Washington 1984 151ndash157

2 Kalwar MI Kudra T Raghavan GSV Mujumdar AS Drying of Grainsin a Drafted Two-Dimensional Spouted Bed J Food Proc Eng 1991 13321ndash332

3 Kalwar MI Raghavan GSV Batch Drying of Shelled Corn in Two-Dimensional Spouted Beds with Draft Plates Drying Technol 1993 11 (2)339ndash354

4 Kalwar MI Raghavan GSV Circulation of Particles in Two-DimensionalSpouted Beds with Draft Plates Powder Tech 1993 77 233ndash242

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216 MADHIYANON SOPONRONNARIT AND TIA

5 Wetchacama S Soponronnarit S Swasdisevi T Panich-ing-orn JSuthicharoenpanich S In Drying of High Moisture Paddy by Two-Dimensional Spouted Bed Technique Proceedings of the First Asian-Australian Drying Conference (ADC rsquo99) Bali Indonesia Oct 24ndash27 1999300ndash307

6 Nguyen LH Driscoll RH Srzednicki GS In Drying Characteristics ofPaddy in a Triangular Spouted-Bed Proceedings of the 11th InternationalDrying Symposium (IDS rsquo98) Halkidiki Greece Aug 19ndash22 1998 1397ndash1404

7 Nguyen LH Driscoll RH Srzednicki GS In Flowing Performance andDrying Characteristics of Paddy in a Triangular Spouted-Bed 7th Interna-tional Working Conference on Stored-Product Protection Beijing China Oct14ndash20 1998

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208 MADHIYANON SOPONRONNARIT AND TIA

INTRODUCTION

The combination of two distinct hydrodynamic features viz the pneumatictransport of particles in the spout which allows intensive heating and moistureevaporation and a falling bed in the downcomer in which tempering of particlestakes place are the main features of the spouted bed To overcome some of thelimitations of the conventional cylindricalndashconical spouted bed Mujumdar (1)proposed the two-dimensional spouted bed in which scaling up can be easilyperformed Kalwar et al (2) Kalwar and Raghavan (34) studied drying of grainsin two-dimensional spouted beds with draft plates using soybeans wheat cornand shelled corn as test materials It was found that thin-layer drying behavior asthat predicted by Pagersquos equation is in very good agreement with experimental dataThe circulation of particles strongly depends on the entrance height spout widthand slant angle It is also shown that the drying rate is significantly influenced bygrain circulation rate In another experiment conducted by Wetchacama et al (5) alinear equation was found to be suitable to describe the drying rate of paddy whichdepends on hold-up and drying temperature The milling quality of paddy in termsof head rice yield as well as the drying characteristics of paddy was investigated byNguyen et al (67) A triangular spouted bed was proposed in their experimentsThe result of head rice yield is satisfactory as long as the moisture content is keptabove 176 dry basis regardless of the high inlet air temperature up to 160C

Although extensive research has already been performed on the spoutedbed grain drying the focus was only on batch drying operation For drying on acommercial scale continuous operation is always preferable It is thus the objectiveof this project to design and test an industrial-scale prototype of a continuousspouted bed dryer for use in a rice mill In addition to the fluidized bed dryer whichhas been commercialized the spouted bed dryer is an alternative for continuousdrying of grain with high initial moisture content Moreover the expectation is thatgrain quality is preserved though it is continuously dried to a moisture contentsafe for storage

MATERIALS AND METHODS

Drying studies were conducted in an industrial-scale prototype spouted beddryer with a capacity of 3500 kgh as shown in Figures 1 and 2 using paddy as atest material The dryer consists of a vertical rectangular chamber 06 m in width145 m in height and 21 m in length The front wall and both of the sidewallsjust above the slanting base of the drying chamber are fitted with glass windowsto permit visualization of the grain flow pattern The slanting base is inclined at60 The air entrance and spout widths are 004 and 006 m respectively Thedraft plates with 062 and 082 m in height were centrally installed in the first and

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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

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210 MADHIYANON SOPONRONNARIT AND TIA

second phase of experiments respectively The entrance heights of 010 0125and 015 m were varied from one experiment to the other to match the feed rate ofpaddy Heat derived from burning diesel fuel was supplied to heat the air beforeit was drawn through the blower The inlet air temperature was controlled by aPID temperature controller to be within plusmn2C of the set values The heated airwas then forced through the ductwork connected to the drying chamber The hotand humid air leaving the drying chamber was discharged into a cyclone withsome portion of it exhausted to the ambient The rest (approximately 60ndash70 oftotal circulation air) was recirculated and mixed with ambient air at the combustionchamber Paddy was continuously fed into the drying chamber The paddy traveledupward through the draft channel before raining back onto the downcomers andmoved vertically downward The paddy movement alternated between spout anddowncomer until paddy came out of the outlet port at the bottom of drying chamberAir and paddy temperatures were measured using k-type thermocouples connectedto a data logger with an accuracy of plusmn1C The pressure drop across the bed wasmeasured using a U-tube manometer A hot air anemometer with an accuracyof plusmn4 was used to measure the air velocity Paddy samples were taken fromthe outlet port of the drying chamber for measuring moisture content head riceyield and whiteness at 10-min intervals for a period of 80 min Moisture contentswere determined using a hot air oven set at 103C for 72 h Head rice yieldwas determined according to the method of the Rice Research Institute and thewhiteness 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 theentire length of the dryer due to the proper functioning of ductwork connected to theinlet of the drying chamber In the first phase of experiments the spouting did notoccur continuously This could be attributed to the improper blower performancewhich resulted in a low pressure drop across the bed and low inlet air velocity atthe entrance of the drying chamber To solve this problem an existing blower wasreplaced with a high-pressure blower during the second phase of the experimentsFigure 3 presents the variation of the bed height along the length of dryer at afeed rate of 3550 kgh and hold-up of approximately 310 kg The shape of bothdowncomer sides is not quite symmetrical This is because the draft plates maynot be positioned exactly at the center of the drying chamber The effect of the bedheight difference between each side on the moisture distribution in the bed cannotbe identified since the moisture distribution was not measured in this study

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INDUSTRIAL-SCALE CONTINUOUS SPOUTED BED DRYER 211

Figure 3 Variation of bed height with length of dryer feed rate 3550 kgh hold-up310 kg

Drying Efficiency and Milling Quality

Fifteen experiments were carried out in phases 1 and 2 The results of thefirst and second phase experiments are summarized in Tables 1 and 2 respectivelyTo study dryer performance in terms of moisture content reduction milling qualityand energy consumption feed rate of paddy and the inlet air temperature werevaried from one experiment to the other

Moisture Content

Cycle time strongly affects the moisture distribution inside the paddy kernelin the downcomer as well as the number of turns of paddy flowing through thedraft channel Partial tempering occurs in the downcomer while intense heatingand moisture removal take place in the draft channel However it is impracticalto record cycle time in these experiments because of the continuous operationInstead the mean residence time in the dryer (tm) is defined by the followingequation

tm = hold-up

feed rate(1)

The moisture reduction result of test No 1 (Table 1) was not satisfactoryThis is probably due to nonmatching between the airflow rate and the high feedrate which led to residence times that were too short Therefore feed rates inall subsequent experiments were limited to 1000 kgh which consequently ledto good results in terms of moisture reduction The results in Table 1 show thatpaddy was dried from a moisture range of 200ndash303 to 144ndash215 dry basis

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212 MADHIYANON SOPONRONNARIT AND TIA

Table 1 Summary of the First Phase Experimental Results

Test No

Description 1 2 3 4 5 6 7

Feed rate (kgh) 3140 1000 900 844 664 939 816Hold-up (kg) 180 210 135 125 190 190 190Residence time (min) 40 126 90 89 172 121 140Average inlet air temp (C) 185 144 144 146 146 133 126Exit grain temp (C) 67 71 69 67 72 72 71Average moisture content

BFD ( dry basis) 319 200 232 250 303 262 266AFD ( dry basis) 285 144 178 204 213 215 199

Head rice yieldBFD () 629 342 456 371 482 395 435AFD () 648 334 427 392 480 368 455

WhitenessBFD 419 476 502 510 459 496 446AFD 392 475 511 511 467 503 450

Drying rate (kg waterh) 83 49 41 33 49 39 46Energy consumption(MJkg water evaporated)

Heat 71 67 70 77 56 77 NAElectricity 050 076 091 112 074 100 080

AFD after drying BFD before drying NA not available temp temperature entranceheight 10 cm (for all experiments)

and that the mean residence time lay between 9 to 17 min At the second phase ofthe experiments (Table 2) the old blower was replaced by a high-pressure blowerThe prototype was then able to handle a maximum capacity of around 3500 kghwith moisture reduction in the range of 217ndash294 to 171ndash250 dry basisHowever the main difficulty was that high moisture reduction was required ata feed rate over 3000 kgh Since the mean residence time was relatively shortthat is in the range of 5ndash6 min grains were less frequently drawn through thedraft channel The final moisture content appeared to be consistent throughout thetesting period as shown in Figure 4 (test No 13) Similar trends were found for all15 experiments

The question of how to reach high moisture reduction that is from 30down to 16ndash18 dry basis is of practical interest It was to be expected fromthe near-to-linear trend in the moisture content with time (5) that high moisturereduction could be achieved by extending the drying chamber length which wouldresult in a longer mean residence time

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INDUSTRIAL-SCALE CONTINUOUS SPOUTED BED DRYER 213

Table 2 Summary of the Second Phase Experimental Results

Test No

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

Feed rate (kgh) 2470 2440 1990 2370 2400 3160 3280 3550Hold-up (kg) 60 360 340 240 210 335 290 310Residence time (min) 15 89 102 60 53 64 53 52Average inlet air temp (C) 154 149 141 152 159 154 156 160Exit grain temp (C) 68 71 66 71 68 67 67 68Average moisture content

BFD ( dry basis) 261 217 285 221 250 294 282 228AFD ( dry basis) 227 175 236 171 197 250 233 190

Head rice yieldBFD () 561 459 533 490 496 501 543 412AFD () 589 457 542 474 484 524 550 408

WhitenessBFD 419 457 442 476 476 478 464 467AFD 416 454 450 468 467 475 463 459

Drying rate (kg waterh) 68 87 79 101 106 111 130 101Energy consumption(MJkg water evaporated)

Heat 65 70 NA 44 52 35 38 31Electricity 060 060 060 050 050 046 040 046

AFD after drying BFD before drying NA not available temp temperatureaDraft channel blade angle 85 entrance height 10 cmbDraft channel blade angle 89 entrance height 10 cmcDraft channel blade angle 89 entrance height 125 cmd Draft channel blade angle 89 entrance height 15 cm

Figure 4 Comparison of moisture content between before and after drying inlet air temp154C feed rate 3160 kgh hold-up 335 kg tm 64 min

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214 MADHIYANON SOPONRONNARIT AND TIA

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 successor failure of a grain-drying system As seen in Tables 1 and 2 it is clear that thepresent drying process does not have much effect on milling quality No significantquality change was observed when paddy was dried down to 14ndash25 dry basisregardless of the high inlet air temperature of up to 130ndash160C For the head riceyield this was due to the fact that the moisture gradient inside the grain kernelwas somewhat redistributed and equalized while passing through the downcomerwhich resulted in relaxation of the stress developed within the grain kernel andthus 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 airin the spouting region within a very short time In addition the alternative methodfor preservation of milling quality is to apply a zoning concept that is using ahigh temperature in the first zone for fast drying and a lower temperature in thesubsequent zone of the dryer for gentle drying This is analogous to employingthe different temperature level concept as described by Nguyen et al (67) Thehead rice yield and whiteness results of test No 13 are presented in Figure 5A 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 56ndash77 MJkg water removed This

Figure 5 Comparison of head rice yield and whiteness between drying with ambient airand drying with spouted bed dryer (inlet air temp 154C feed rate 3160 kgh hold-up335 kg tm 64 min)

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INDUSTRIAL-SCALE CONTINUOUS SPOUTED BED DRYER 215

be attributed to noncontinuation of the spouting which would result in poor paddycirculation However in the second phase of the experiments thermal energyconsumption was reduced to the range of 31ndash38 MJkg water according to afeed rate of 3100ndash3500 kgh (test Nos 13ndash15 in Table 2) The decrease of thermalenergy consumption in the second phase especially for test Nos 13ndash15 is probablyattributed to a much higher circulation rate than that achieved in the first phase ofthe study

CONCLUSIONS

An industrial-scale continuous spouted bed dryer with a capacity of 3500kgh was developed and tested No serious loss in quality was observed duringthe experiments while the high drying air temperature was used Final moisturecontent and milling quality results appear to be consistent throughout the testingperiods However with the limitation of the existing drying chamber length ahigh percentage of moisture reduction corresponding to the high paddy feed ratecould not be achieved The energy consumption is comparable to those of othercommercial 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 acknowledgedfor its cooperation during this study

REFERENCES

1 Mujumdar AS In Spouted Bed Technology A Brief Review Dryingrsquo84Hemisphere Washington 1984 151ndash157

2 Kalwar MI Kudra T Raghavan GSV Mujumdar AS Drying of Grainsin a Drafted Two-Dimensional Spouted Bed J Food Proc Eng 1991 13321ndash332

3 Kalwar MI Raghavan GSV Batch Drying of Shelled Corn in Two-Dimensional Spouted Beds with Draft Plates Drying Technol 1993 11 (2)339ndash354

4 Kalwar MI Raghavan GSV Circulation of Particles in Two-DimensionalSpouted Beds with Draft Plates Powder Tech 1993 77 233ndash242

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216 MADHIYANON SOPONRONNARIT AND TIA

5 Wetchacama S Soponronnarit S Swasdisevi T Panich-ing-orn JSuthicharoenpanich S In Drying of High Moisture Paddy by Two-Dimensional Spouted Bed Technique Proceedings of the First Asian-Australian Drying Conference (ADC rsquo99) Bali Indonesia Oct 24ndash27 1999300ndash307

6 Nguyen LH Driscoll RH Srzednicki GS In Drying Characteristics ofPaddy in a Triangular Spouted-Bed Proceedings of the 11th InternationalDrying Symposium (IDS rsquo98) Halkidiki Greece Aug 19ndash22 1998 1397ndash1404

7 Nguyen LH Driscoll RH Srzednicki GS In Flowing Performance andDrying Characteristics of Paddy in a Triangular Spouted-Bed 7th Interna-tional Working Conference on Stored-Product Protection Beijing China Oct14ndash20 1998

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Order now

Reprints of this article can also be ordered at

httpwwwdekkercomservletproductDOI101081DRT100001362

Request Permission or Order Reprints Instantly

Interested in copying and sharing this article In most cases US Copyright Law requires that you get permission from the articlersquos 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 PermissionReprints Here link below and follow the instructions Visit the US Copyright Office for information on Fair Use limitations of US copyright law Please refer to The Association of American Publishersrsquo (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 or personal 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 Agreement for more details

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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

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210 MADHIYANON SOPONRONNARIT AND TIA

second phase of experiments respectively The entrance heights of 010 0125and 015 m were varied from one experiment to the other to match the feed rate ofpaddy Heat derived from burning diesel fuel was supplied to heat the air beforeit was drawn through the blower The inlet air temperature was controlled by aPID temperature controller to be within plusmn2C of the set values The heated airwas then forced through the ductwork connected to the drying chamber The hotand humid air leaving the drying chamber was discharged into a cyclone withsome portion of it exhausted to the ambient The rest (approximately 60ndash70 oftotal circulation air) was recirculated and mixed with ambient air at the combustionchamber Paddy was continuously fed into the drying chamber The paddy traveledupward through the draft channel before raining back onto the downcomers andmoved vertically downward The paddy movement alternated between spout anddowncomer until paddy came out of the outlet port at the bottom of drying chamberAir and paddy temperatures were measured using k-type thermocouples connectedto a data logger with an accuracy of plusmn1C The pressure drop across the bed wasmeasured using a U-tube manometer A hot air anemometer with an accuracyof plusmn4 was used to measure the air velocity Paddy samples were taken fromthe outlet port of the drying chamber for measuring moisture content head riceyield and whiteness at 10-min intervals for a period of 80 min Moisture contentswere determined using a hot air oven set at 103C for 72 h Head rice yieldwas determined according to the method of the Rice Research Institute and thewhiteness 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 theentire length of the dryer due to the proper functioning of ductwork connected to theinlet of the drying chamber In the first phase of experiments the spouting did notoccur continuously This could be attributed to the improper blower performancewhich resulted in a low pressure drop across the bed and low inlet air velocity atthe entrance of the drying chamber To solve this problem an existing blower wasreplaced with a high-pressure blower during the second phase of the experimentsFigure 3 presents the variation of the bed height along the length of dryer at afeed rate of 3550 kgh and hold-up of approximately 310 kg The shape of bothdowncomer sides is not quite symmetrical This is because the draft plates maynot be positioned exactly at the center of the drying chamber The effect of the bedheight difference between each side on the moisture distribution in the bed cannotbe identified since the moisture distribution was not measured in this study

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INDUSTRIAL-SCALE CONTINUOUS SPOUTED BED DRYER 211

Figure 3 Variation of bed height with length of dryer feed rate 3550 kgh hold-up310 kg

Drying Efficiency and Milling Quality

Fifteen experiments were carried out in phases 1 and 2 The results of thefirst and second phase experiments are summarized in Tables 1 and 2 respectivelyTo study dryer performance in terms of moisture content reduction milling qualityand energy consumption feed rate of paddy and the inlet air temperature werevaried from one experiment to the other

Moisture Content

Cycle time strongly affects the moisture distribution inside the paddy kernelin the downcomer as well as the number of turns of paddy flowing through thedraft channel Partial tempering occurs in the downcomer while intense heatingand moisture removal take place in the draft channel However it is impracticalto record cycle time in these experiments because of the continuous operationInstead the mean residence time in the dryer (tm) is defined by the followingequation

tm = hold-up

feed rate(1)

The moisture reduction result of test No 1 (Table 1) was not satisfactoryThis is probably due to nonmatching between the airflow rate and the high feedrate which led to residence times that were too short Therefore feed rates inall subsequent experiments were limited to 1000 kgh which consequently ledto good results in terms of moisture reduction The results in Table 1 show thatpaddy was dried from a moisture range of 200ndash303 to 144ndash215 dry basis

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212 MADHIYANON SOPONRONNARIT AND TIA

Table 1 Summary of the First Phase Experimental Results

Test No

Description 1 2 3 4 5 6 7

Feed rate (kgh) 3140 1000 900 844 664 939 816Hold-up (kg) 180 210 135 125 190 190 190Residence time (min) 40 126 90 89 172 121 140Average inlet air temp (C) 185 144 144 146 146 133 126Exit grain temp (C) 67 71 69 67 72 72 71Average moisture content

BFD ( dry basis) 319 200 232 250 303 262 266AFD ( dry basis) 285 144 178 204 213 215 199

Head rice yieldBFD () 629 342 456 371 482 395 435AFD () 648 334 427 392 480 368 455

WhitenessBFD 419 476 502 510 459 496 446AFD 392 475 511 511 467 503 450

Drying rate (kg waterh) 83 49 41 33 49 39 46Energy consumption(MJkg water evaporated)

Heat 71 67 70 77 56 77 NAElectricity 050 076 091 112 074 100 080

AFD after drying BFD before drying NA not available temp temperature entranceheight 10 cm (for all experiments)

and that the mean residence time lay between 9 to 17 min At the second phase ofthe experiments (Table 2) the old blower was replaced by a high-pressure blowerThe prototype was then able to handle a maximum capacity of around 3500 kghwith moisture reduction in the range of 217ndash294 to 171ndash250 dry basisHowever the main difficulty was that high moisture reduction was required ata feed rate over 3000 kgh Since the mean residence time was relatively shortthat is in the range of 5ndash6 min grains were less frequently drawn through thedraft channel The final moisture content appeared to be consistent throughout thetesting period as shown in Figure 4 (test No 13) Similar trends were found for all15 experiments

The question of how to reach high moisture reduction that is from 30down to 16ndash18 dry basis is of practical interest It was to be expected fromthe near-to-linear trend in the moisture content with time (5) that high moisturereduction could be achieved by extending the drying chamber length which wouldresult in a longer mean residence time

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INDUSTRIAL-SCALE CONTINUOUS SPOUTED BED DRYER 213

Table 2 Summary of the Second Phase Experimental Results

Test No

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

Feed rate (kgh) 2470 2440 1990 2370 2400 3160 3280 3550Hold-up (kg) 60 360 340 240 210 335 290 310Residence time (min) 15 89 102 60 53 64 53 52Average inlet air temp (C) 154 149 141 152 159 154 156 160Exit grain temp (C) 68 71 66 71 68 67 67 68Average moisture content

BFD ( dry basis) 261 217 285 221 250 294 282 228AFD ( dry basis) 227 175 236 171 197 250 233 190

Head rice yieldBFD () 561 459 533 490 496 501 543 412AFD () 589 457 542 474 484 524 550 408

WhitenessBFD 419 457 442 476 476 478 464 467AFD 416 454 450 468 467 475 463 459

Drying rate (kg waterh) 68 87 79 101 106 111 130 101Energy consumption(MJkg water evaporated)

Heat 65 70 NA 44 52 35 38 31Electricity 060 060 060 050 050 046 040 046

AFD after drying BFD before drying NA not available temp temperatureaDraft channel blade angle 85 entrance height 10 cmbDraft channel blade angle 89 entrance height 10 cmcDraft channel blade angle 89 entrance height 125 cmd Draft channel blade angle 89 entrance height 15 cm

Figure 4 Comparison of moisture content between before and after drying inlet air temp154C feed rate 3160 kgh hold-up 335 kg tm 64 min

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214 MADHIYANON SOPONRONNARIT AND TIA

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 successor failure of a grain-drying system As seen in Tables 1 and 2 it is clear that thepresent drying process does not have much effect on milling quality No significantquality change was observed when paddy was dried down to 14ndash25 dry basisregardless of the high inlet air temperature of up to 130ndash160C For the head riceyield this was due to the fact that the moisture gradient inside the grain kernelwas somewhat redistributed and equalized while passing through the downcomerwhich resulted in relaxation of the stress developed within the grain kernel andthus 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 airin the spouting region within a very short time In addition the alternative methodfor preservation of milling quality is to apply a zoning concept that is using ahigh temperature in the first zone for fast drying and a lower temperature in thesubsequent zone of the dryer for gentle drying This is analogous to employingthe different temperature level concept as described by Nguyen et al (67) Thehead rice yield and whiteness results of test No 13 are presented in Figure 5A 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 56ndash77 MJkg water removed This

Figure 5 Comparison of head rice yield and whiteness between drying with ambient airand drying with spouted bed dryer (inlet air temp 154C feed rate 3160 kgh hold-up335 kg tm 64 min)

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INDUSTRIAL-SCALE CONTINUOUS SPOUTED BED DRYER 215

be attributed to noncontinuation of the spouting which would result in poor paddycirculation However in the second phase of the experiments thermal energyconsumption was reduced to the range of 31ndash38 MJkg water according to afeed rate of 3100ndash3500 kgh (test Nos 13ndash15 in Table 2) The decrease of thermalenergy consumption in the second phase especially for test Nos 13ndash15 is probablyattributed to a much higher circulation rate than that achieved in the first phase ofthe study

CONCLUSIONS

An industrial-scale continuous spouted bed dryer with a capacity of 3500kgh was developed and tested No serious loss in quality was observed duringthe experiments while the high drying air temperature was used Final moisturecontent and milling quality results appear to be consistent throughout the testingperiods However with the limitation of the existing drying chamber length ahigh percentage of moisture reduction corresponding to the high paddy feed ratecould not be achieved The energy consumption is comparable to those of othercommercial 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 acknowledgedfor its cooperation during this study

REFERENCES

1 Mujumdar AS In Spouted Bed Technology A Brief Review Dryingrsquo84Hemisphere Washington 1984 151ndash157

2 Kalwar MI Kudra T Raghavan GSV Mujumdar AS Drying of Grainsin a Drafted Two-Dimensional Spouted Bed J Food Proc Eng 1991 13321ndash332

3 Kalwar MI Raghavan GSV Batch Drying of Shelled Corn in Two-Dimensional Spouted Beds with Draft Plates Drying Technol 1993 11 (2)339ndash354

4 Kalwar MI Raghavan GSV Circulation of Particles in Two-DimensionalSpouted Beds with Draft Plates Powder Tech 1993 77 233ndash242

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216 MADHIYANON SOPONRONNARIT AND TIA

5 Wetchacama S Soponronnarit S Swasdisevi T Panich-ing-orn JSuthicharoenpanich S In Drying of High Moisture Paddy by Two-Dimensional Spouted Bed Technique Proceedings of the First Asian-Australian Drying Conference (ADC rsquo99) Bali Indonesia Oct 24ndash27 1999300ndash307

6 Nguyen LH Driscoll RH Srzednicki GS In Drying Characteristics ofPaddy in a Triangular Spouted-Bed Proceedings of the 11th InternationalDrying Symposium (IDS rsquo98) Halkidiki Greece Aug 19ndash22 1998 1397ndash1404

7 Nguyen LH Driscoll RH Srzednicki GS In Flowing Performance andDrying Characteristics of Paddy in a Triangular Spouted-Bed 7th Interna-tional Working Conference on Stored-Product Protection Beijing China Oct14ndash20 1998

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ovem

ber

2014

Order now

Reprints of this article can also be ordered at

httpwwwdekkercomservletproductDOI101081DRT100001362

Request Permission or Order Reprints Instantly

Interested in copying and sharing this article In most cases US Copyright Law requires that you get permission from the articlersquos 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 PermissionReprints Here link below and follow the instructions Visit the US Copyright Office for information on Fair Use limitations of US copyright law Please refer to The Association of American Publishersrsquo (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 or personal 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 Agreement for more details

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] at

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ovem

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2014

ORDER REPRINTS

210 MADHIYANON SOPONRONNARIT AND TIA

second phase of experiments respectively The entrance heights of 010 0125and 015 m were varied from one experiment to the other to match the feed rate ofpaddy Heat derived from burning diesel fuel was supplied to heat the air beforeit was drawn through the blower The inlet air temperature was controlled by aPID temperature controller to be within plusmn2C of the set values The heated airwas then forced through the ductwork connected to the drying chamber The hotand humid air leaving the drying chamber was discharged into a cyclone withsome portion of it exhausted to the ambient The rest (approximately 60ndash70 oftotal circulation air) was recirculated and mixed with ambient air at the combustionchamber Paddy was continuously fed into the drying chamber The paddy traveledupward through the draft channel before raining back onto the downcomers andmoved vertically downward The paddy movement alternated between spout anddowncomer until paddy came out of the outlet port at the bottom of drying chamberAir and paddy temperatures were measured using k-type thermocouples connectedto a data logger with an accuracy of plusmn1C The pressure drop across the bed wasmeasured using a U-tube manometer A hot air anemometer with an accuracyof plusmn4 was used to measure the air velocity Paddy samples were taken fromthe outlet port of the drying chamber for measuring moisture content head riceyield and whiteness at 10-min intervals for a period of 80 min Moisture contentswere determined using a hot air oven set at 103C for 72 h Head rice yieldwas determined according to the method of the Rice Research Institute and thewhiteness 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 theentire length of the dryer due to the proper functioning of ductwork connected to theinlet of the drying chamber In the first phase of experiments the spouting did notoccur continuously This could be attributed to the improper blower performancewhich resulted in a low pressure drop across the bed and low inlet air velocity atthe entrance of the drying chamber To solve this problem an existing blower wasreplaced with a high-pressure blower during the second phase of the experimentsFigure 3 presents the variation of the bed height along the length of dryer at afeed rate of 3550 kgh and hold-up of approximately 310 kg The shape of bothdowncomer sides is not quite symmetrical This is because the draft plates maynot be positioned exactly at the center of the drying chamber The effect of the bedheight difference between each side on the moisture distribution in the bed cannotbe identified since the moisture distribution was not measured in this study

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INDUSTRIAL-SCALE CONTINUOUS SPOUTED BED DRYER 211

Figure 3 Variation of bed height with length of dryer feed rate 3550 kgh hold-up310 kg

Drying Efficiency and Milling Quality

Fifteen experiments were carried out in phases 1 and 2 The results of thefirst and second phase experiments are summarized in Tables 1 and 2 respectivelyTo study dryer performance in terms of moisture content reduction milling qualityand energy consumption feed rate of paddy and the inlet air temperature werevaried from one experiment to the other

Moisture Content

Cycle time strongly affects the moisture distribution inside the paddy kernelin the downcomer as well as the number of turns of paddy flowing through thedraft channel Partial tempering occurs in the downcomer while intense heatingand moisture removal take place in the draft channel However it is impracticalto record cycle time in these experiments because of the continuous operationInstead the mean residence time in the dryer (tm) is defined by the followingequation

tm = hold-up

feed rate(1)

The moisture reduction result of test No 1 (Table 1) was not satisfactoryThis is probably due to nonmatching between the airflow rate and the high feedrate which led to residence times that were too short Therefore feed rates inall subsequent experiments were limited to 1000 kgh which consequently ledto good results in terms of moisture reduction The results in Table 1 show thatpaddy was dried from a moisture range of 200ndash303 to 144ndash215 dry basis

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212 MADHIYANON SOPONRONNARIT AND TIA

Table 1 Summary of the First Phase Experimental Results

Test No

Description 1 2 3 4 5 6 7

Feed rate (kgh) 3140 1000 900 844 664 939 816Hold-up (kg) 180 210 135 125 190 190 190Residence time (min) 40 126 90 89 172 121 140Average inlet air temp (C) 185 144 144 146 146 133 126Exit grain temp (C) 67 71 69 67 72 72 71Average moisture content

BFD ( dry basis) 319 200 232 250 303 262 266AFD ( dry basis) 285 144 178 204 213 215 199

Head rice yieldBFD () 629 342 456 371 482 395 435AFD () 648 334 427 392 480 368 455

WhitenessBFD 419 476 502 510 459 496 446AFD 392 475 511 511 467 503 450

Drying rate (kg waterh) 83 49 41 33 49 39 46Energy consumption(MJkg water evaporated)

Heat 71 67 70 77 56 77 NAElectricity 050 076 091 112 074 100 080

AFD after drying BFD before drying NA not available temp temperature entranceheight 10 cm (for all experiments)

and that the mean residence time lay between 9 to 17 min At the second phase ofthe experiments (Table 2) the old blower was replaced by a high-pressure blowerThe prototype was then able to handle a maximum capacity of around 3500 kghwith moisture reduction in the range of 217ndash294 to 171ndash250 dry basisHowever the main difficulty was that high moisture reduction was required ata feed rate over 3000 kgh Since the mean residence time was relatively shortthat is in the range of 5ndash6 min grains were less frequently drawn through thedraft channel The final moisture content appeared to be consistent throughout thetesting period as shown in Figure 4 (test No 13) Similar trends were found for all15 experiments

The question of how to reach high moisture reduction that is from 30down to 16ndash18 dry basis is of practical interest It was to be expected fromthe near-to-linear trend in the moisture content with time (5) that high moisturereduction could be achieved by extending the drying chamber length which wouldresult in a longer mean residence time

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INDUSTRIAL-SCALE CONTINUOUS SPOUTED BED DRYER 213

Table 2 Summary of the Second Phase Experimental Results

Test No

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

Feed rate (kgh) 2470 2440 1990 2370 2400 3160 3280 3550Hold-up (kg) 60 360 340 240 210 335 290 310Residence time (min) 15 89 102 60 53 64 53 52Average inlet air temp (C) 154 149 141 152 159 154 156 160Exit grain temp (C) 68 71 66 71 68 67 67 68Average moisture content

BFD ( dry basis) 261 217 285 221 250 294 282 228AFD ( dry basis) 227 175 236 171 197 250 233 190

Head rice yieldBFD () 561 459 533 490 496 501 543 412AFD () 589 457 542 474 484 524 550 408

WhitenessBFD 419 457 442 476 476 478 464 467AFD 416 454 450 468 467 475 463 459

Drying rate (kg waterh) 68 87 79 101 106 111 130 101Energy consumption(MJkg water evaporated)

Heat 65 70 NA 44 52 35 38 31Electricity 060 060 060 050 050 046 040 046

AFD after drying BFD before drying NA not available temp temperatureaDraft channel blade angle 85 entrance height 10 cmbDraft channel blade angle 89 entrance height 10 cmcDraft channel blade angle 89 entrance height 125 cmd Draft channel blade angle 89 entrance height 15 cm

Figure 4 Comparison of moisture content between before and after drying inlet air temp154C feed rate 3160 kgh hold-up 335 kg tm 64 min

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214 MADHIYANON SOPONRONNARIT AND TIA

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 successor failure of a grain-drying system As seen in Tables 1 and 2 it is clear that thepresent drying process does not have much effect on milling quality No significantquality change was observed when paddy was dried down to 14ndash25 dry basisregardless of the high inlet air temperature of up to 130ndash160C For the head riceyield this was due to the fact that the moisture gradient inside the grain kernelwas somewhat redistributed and equalized while passing through the downcomerwhich resulted in relaxation of the stress developed within the grain kernel andthus 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 airin the spouting region within a very short time In addition the alternative methodfor preservation of milling quality is to apply a zoning concept that is using ahigh temperature in the first zone for fast drying and a lower temperature in thesubsequent zone of the dryer for gentle drying This is analogous to employingthe different temperature level concept as described by Nguyen et al (67) Thehead rice yield and whiteness results of test No 13 are presented in Figure 5A 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 56ndash77 MJkg water removed This

Figure 5 Comparison of head rice yield and whiteness between drying with ambient airand drying with spouted bed dryer (inlet air temp 154C feed rate 3160 kgh hold-up335 kg tm 64 min)

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ORDER REPRINTS

INDUSTRIAL-SCALE CONTINUOUS SPOUTED BED DRYER 215

be attributed to noncontinuation of the spouting which would result in poor paddycirculation However in the second phase of the experiments thermal energyconsumption was reduced to the range of 31ndash38 MJkg water according to afeed rate of 3100ndash3500 kgh (test Nos 13ndash15 in Table 2) The decrease of thermalenergy consumption in the second phase especially for test Nos 13ndash15 is probablyattributed to a much higher circulation rate than that achieved in the first phase ofthe study

CONCLUSIONS

An industrial-scale continuous spouted bed dryer with a capacity of 3500kgh was developed and tested No serious loss in quality was observed duringthe experiments while the high drying air temperature was used Final moisturecontent and milling quality results appear to be consistent throughout the testingperiods However with the limitation of the existing drying chamber length ahigh percentage of moisture reduction corresponding to the high paddy feed ratecould not be achieved The energy consumption is comparable to those of othercommercial 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 acknowledgedfor its cooperation during this study

REFERENCES

1 Mujumdar AS In Spouted Bed Technology A Brief Review Dryingrsquo84Hemisphere Washington 1984 151ndash157

2 Kalwar MI Kudra T Raghavan GSV Mujumdar AS Drying of Grainsin a Drafted Two-Dimensional Spouted Bed J Food Proc Eng 1991 13321ndash332

3 Kalwar MI Raghavan GSV Batch Drying of Shelled Corn in Two-Dimensional Spouted Beds with Draft Plates Drying Technol 1993 11 (2)339ndash354

4 Kalwar MI Raghavan GSV Circulation of Particles in Two-DimensionalSpouted Beds with Draft Plates Powder Tech 1993 77 233ndash242

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] at

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06 2

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ber

2014

ORDER REPRINTS

216 MADHIYANON SOPONRONNARIT AND TIA

5 Wetchacama S Soponronnarit S Swasdisevi T Panich-ing-orn JSuthicharoenpanich S In Drying of High Moisture Paddy by Two-Dimensional Spouted Bed Technique Proceedings of the First Asian-Australian Drying Conference (ADC rsquo99) Bali Indonesia Oct 24ndash27 1999300ndash307

6 Nguyen LH Driscoll RH Srzednicki GS In Drying Characteristics ofPaddy in a Triangular Spouted-Bed Proceedings of the 11th InternationalDrying Symposium (IDS rsquo98) Halkidiki Greece Aug 19ndash22 1998 1397ndash1404

7 Nguyen LH Driscoll RH Srzednicki GS In Flowing Performance andDrying Characteristics of Paddy in a Triangular Spouted-Bed 7th Interna-tional Working Conference on Stored-Product Protection Beijing China Oct14ndash20 1998

Dow

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] at

22

06 2

1 N

ovem

ber

2014

Order now

Reprints of this article can also be ordered at

httpwwwdekkercomservletproductDOI101081DRT100001362

Request Permission or Order Reprints Instantly

Interested in copying and sharing this article In most cases US Copyright Law requires that you get permission from the articlersquos 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 PermissionReprints Here link below and follow the instructions Visit the US Copyright Office for information on Fair Use limitations of US copyright law Please refer to The Association of American Publishersrsquo (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 or personal 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 Agreement for more details

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2014

ORDER REPRINTS

INDUSTRIAL-SCALE CONTINUOUS SPOUTED BED DRYER 211

Figure 3 Variation of bed height with length of dryer feed rate 3550 kgh hold-up310 kg

Drying Efficiency and Milling Quality

Fifteen experiments were carried out in phases 1 and 2 The results of thefirst and second phase experiments are summarized in Tables 1 and 2 respectivelyTo study dryer performance in terms of moisture content reduction milling qualityand energy consumption feed rate of paddy and the inlet air temperature werevaried from one experiment to the other

Moisture Content

Cycle time strongly affects the moisture distribution inside the paddy kernelin the downcomer as well as the number of turns of paddy flowing through thedraft channel Partial tempering occurs in the downcomer while intense heatingand moisture removal take place in the draft channel However it is impracticalto record cycle time in these experiments because of the continuous operationInstead the mean residence time in the dryer (tm) is defined by the followingequation

tm = hold-up

feed rate(1)

The moisture reduction result of test No 1 (Table 1) was not satisfactoryThis is probably due to nonmatching between the airflow rate and the high feedrate which led to residence times that were too short Therefore feed rates inall subsequent experiments were limited to 1000 kgh which consequently ledto good results in terms of moisture reduction The results in Table 1 show thatpaddy was dried from a moisture range of 200ndash303 to 144ndash215 dry basis

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212 MADHIYANON SOPONRONNARIT AND TIA

Table 1 Summary of the First Phase Experimental Results

Test No

Description 1 2 3 4 5 6 7

Feed rate (kgh) 3140 1000 900 844 664 939 816Hold-up (kg) 180 210 135 125 190 190 190Residence time (min) 40 126 90 89 172 121 140Average inlet air temp (C) 185 144 144 146 146 133 126Exit grain temp (C) 67 71 69 67 72 72 71Average moisture content

BFD ( dry basis) 319 200 232 250 303 262 266AFD ( dry basis) 285 144 178 204 213 215 199

Head rice yieldBFD () 629 342 456 371 482 395 435AFD () 648 334 427 392 480 368 455

WhitenessBFD 419 476 502 510 459 496 446AFD 392 475 511 511 467 503 450

Drying rate (kg waterh) 83 49 41 33 49 39 46Energy consumption(MJkg water evaporated)

Heat 71 67 70 77 56 77 NAElectricity 050 076 091 112 074 100 080

AFD after drying BFD before drying NA not available temp temperature entranceheight 10 cm (for all experiments)

and that the mean residence time lay between 9 to 17 min At the second phase ofthe experiments (Table 2) the old blower was replaced by a high-pressure blowerThe prototype was then able to handle a maximum capacity of around 3500 kghwith moisture reduction in the range of 217ndash294 to 171ndash250 dry basisHowever the main difficulty was that high moisture reduction was required ata feed rate over 3000 kgh Since the mean residence time was relatively shortthat is in the range of 5ndash6 min grains were less frequently drawn through thedraft channel The final moisture content appeared to be consistent throughout thetesting period as shown in Figure 4 (test No 13) Similar trends were found for all15 experiments

The question of how to reach high moisture reduction that is from 30down to 16ndash18 dry basis is of practical interest It was to be expected fromthe near-to-linear trend in the moisture content with time (5) that high moisturereduction could be achieved by extending the drying chamber length which wouldresult in a longer mean residence time

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2014

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INDUSTRIAL-SCALE CONTINUOUS SPOUTED BED DRYER 213

Table 2 Summary of the Second Phase Experimental Results

Test No

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

Feed rate (kgh) 2470 2440 1990 2370 2400 3160 3280 3550Hold-up (kg) 60 360 340 240 210 335 290 310Residence time (min) 15 89 102 60 53 64 53 52Average inlet air temp (C) 154 149 141 152 159 154 156 160Exit grain temp (C) 68 71 66 71 68 67 67 68Average moisture content

BFD ( dry basis) 261 217 285 221 250 294 282 228AFD ( dry basis) 227 175 236 171 197 250 233 190

Head rice yieldBFD () 561 459 533 490 496 501 543 412AFD () 589 457 542 474 484 524 550 408

WhitenessBFD 419 457 442 476 476 478 464 467AFD 416 454 450 468 467 475 463 459

Drying rate (kg waterh) 68 87 79 101 106 111 130 101Energy consumption(MJkg water evaporated)

Heat 65 70 NA 44 52 35 38 31Electricity 060 060 060 050 050 046 040 046

AFD after drying BFD before drying NA not available temp temperatureaDraft channel blade angle 85 entrance height 10 cmbDraft channel blade angle 89 entrance height 10 cmcDraft channel blade angle 89 entrance height 125 cmd Draft channel blade angle 89 entrance height 15 cm

Figure 4 Comparison of moisture content between before and after drying inlet air temp154C feed rate 3160 kgh hold-up 335 kg tm 64 min

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214 MADHIYANON SOPONRONNARIT AND TIA

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 successor failure of a grain-drying system As seen in Tables 1 and 2 it is clear that thepresent drying process does not have much effect on milling quality No significantquality change was observed when paddy was dried down to 14ndash25 dry basisregardless of the high inlet air temperature of up to 130ndash160C For the head riceyield this was due to the fact that the moisture gradient inside the grain kernelwas somewhat redistributed and equalized while passing through the downcomerwhich resulted in relaxation of the stress developed within the grain kernel andthus 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 airin the spouting region within a very short time In addition the alternative methodfor preservation of milling quality is to apply a zoning concept that is using ahigh temperature in the first zone for fast drying and a lower temperature in thesubsequent zone of the dryer for gentle drying This is analogous to employingthe different temperature level concept as described by Nguyen et al (67) Thehead rice yield and whiteness results of test No 13 are presented in Figure 5A 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 56ndash77 MJkg water removed This

Figure 5 Comparison of head rice yield and whiteness between drying with ambient airand drying with spouted bed dryer (inlet air temp 154C feed rate 3160 kgh hold-up335 kg tm 64 min)

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INDUSTRIAL-SCALE CONTINUOUS SPOUTED BED DRYER 215

be attributed to noncontinuation of the spouting which would result in poor paddycirculation However in the second phase of the experiments thermal energyconsumption was reduced to the range of 31ndash38 MJkg water according to afeed rate of 3100ndash3500 kgh (test Nos 13ndash15 in Table 2) The decrease of thermalenergy consumption in the second phase especially for test Nos 13ndash15 is probablyattributed to a much higher circulation rate than that achieved in the first phase ofthe study

CONCLUSIONS

An industrial-scale continuous spouted bed dryer with a capacity of 3500kgh was developed and tested No serious loss in quality was observed duringthe experiments while the high drying air temperature was used Final moisturecontent and milling quality results appear to be consistent throughout the testingperiods However with the limitation of the existing drying chamber length ahigh percentage of moisture reduction corresponding to the high paddy feed ratecould not be achieved The energy consumption is comparable to those of othercommercial 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 acknowledgedfor its cooperation during this study

REFERENCES

1 Mujumdar AS In Spouted Bed Technology A Brief Review Dryingrsquo84Hemisphere Washington 1984 151ndash157

2 Kalwar MI Kudra T Raghavan GSV Mujumdar AS Drying of Grainsin a Drafted Two-Dimensional Spouted Bed J Food Proc Eng 1991 13321ndash332

3 Kalwar MI Raghavan GSV Batch Drying of Shelled Corn in Two-Dimensional Spouted Beds with Draft Plates Drying Technol 1993 11 (2)339ndash354

4 Kalwar MI Raghavan GSV Circulation of Particles in Two-DimensionalSpouted Beds with Draft Plates Powder Tech 1993 77 233ndash242

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ded

by [

Col

umbi

a U

nive

rsity

] at

22

06 2

1 N

ovem

ber

2014

ORDER REPRINTS

216 MADHIYANON SOPONRONNARIT AND TIA

5 Wetchacama S Soponronnarit S Swasdisevi T Panich-ing-orn JSuthicharoenpanich S In Drying of High Moisture Paddy by Two-Dimensional Spouted Bed Technique Proceedings of the First Asian-Australian Drying Conference (ADC rsquo99) Bali Indonesia Oct 24ndash27 1999300ndash307

6 Nguyen LH Driscoll RH Srzednicki GS In Drying Characteristics ofPaddy in a Triangular Spouted-Bed Proceedings of the 11th InternationalDrying Symposium (IDS rsquo98) Halkidiki Greece Aug 19ndash22 1998 1397ndash1404

7 Nguyen LH Driscoll RH Srzednicki GS In Flowing Performance andDrying Characteristics of Paddy in a Triangular Spouted-Bed 7th Interna-tional Working Conference on Stored-Product Protection Beijing China Oct14ndash20 1998

Dow

nloa

ded

by [

Col

umbi

a U

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rsity

] at

22

06 2

1 N

ovem

ber

2014

Order now

Reprints of this article can also be ordered at

httpwwwdekkercomservletproductDOI101081DRT100001362

Request Permission or Order Reprints Instantly

Interested in copying and sharing this article In most cases US Copyright Law requires that you get permission from the articlersquos 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 PermissionReprints Here link below and follow the instructions Visit the US Copyright Office for information on Fair Use limitations of US copyright law Please refer to The Association of American Publishersrsquo (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 or personal 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 Agreement for more details

Dow

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] at

22

06 2

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ovem

ber

2014

ORDER REPRINTS

212 MADHIYANON SOPONRONNARIT AND TIA

Table 1 Summary of the First Phase Experimental Results

Test No

Description 1 2 3 4 5 6 7

Feed rate (kgh) 3140 1000 900 844 664 939 816Hold-up (kg) 180 210 135 125 190 190 190Residence time (min) 40 126 90 89 172 121 140Average inlet air temp (C) 185 144 144 146 146 133 126Exit grain temp (C) 67 71 69 67 72 72 71Average moisture content

BFD ( dry basis) 319 200 232 250 303 262 266AFD ( dry basis) 285 144 178 204 213 215 199

Head rice yieldBFD () 629 342 456 371 482 395 435AFD () 648 334 427 392 480 368 455

WhitenessBFD 419 476 502 510 459 496 446AFD 392 475 511 511 467 503 450

Drying rate (kg waterh) 83 49 41 33 49 39 46Energy consumption(MJkg water evaporated)

Heat 71 67 70 77 56 77 NAElectricity 050 076 091 112 074 100 080

AFD after drying BFD before drying NA not available temp temperature entranceheight 10 cm (for all experiments)

and that the mean residence time lay between 9 to 17 min At the second phase ofthe experiments (Table 2) the old blower was replaced by a high-pressure blowerThe prototype was then able to handle a maximum capacity of around 3500 kghwith moisture reduction in the range of 217ndash294 to 171ndash250 dry basisHowever the main difficulty was that high moisture reduction was required ata feed rate over 3000 kgh Since the mean residence time was relatively shortthat is in the range of 5ndash6 min grains were less frequently drawn through thedraft channel The final moisture content appeared to be consistent throughout thetesting period as shown in Figure 4 (test No 13) Similar trends were found for all15 experiments

The question of how to reach high moisture reduction that is from 30down to 16ndash18 dry basis is of practical interest It was to be expected fromthe near-to-linear trend in the moisture content with time (5) that high moisturereduction could be achieved by extending the drying chamber length which wouldresult in a longer mean residence time

Dow

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] at

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ber

2014

ORDER REPRINTS

INDUSTRIAL-SCALE CONTINUOUS SPOUTED BED DRYER 213

Table 2 Summary of the Second Phase Experimental Results

Test No

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

Feed rate (kgh) 2470 2440 1990 2370 2400 3160 3280 3550Hold-up (kg) 60 360 340 240 210 335 290 310Residence time (min) 15 89 102 60 53 64 53 52Average inlet air temp (C) 154 149 141 152 159 154 156 160Exit grain temp (C) 68 71 66 71 68 67 67 68Average moisture content

BFD ( dry basis) 261 217 285 221 250 294 282 228AFD ( dry basis) 227 175 236 171 197 250 233 190

Head rice yieldBFD () 561 459 533 490 496 501 543 412AFD () 589 457 542 474 484 524 550 408

WhitenessBFD 419 457 442 476 476 478 464 467AFD 416 454 450 468 467 475 463 459

Drying rate (kg waterh) 68 87 79 101 106 111 130 101Energy consumption(MJkg water evaporated)

Heat 65 70 NA 44 52 35 38 31Electricity 060 060 060 050 050 046 040 046

AFD after drying BFD before drying NA not available temp temperatureaDraft channel blade angle 85 entrance height 10 cmbDraft channel blade angle 89 entrance height 10 cmcDraft channel blade angle 89 entrance height 125 cmd Draft channel blade angle 89 entrance height 15 cm

Figure 4 Comparison of moisture content between before and after drying inlet air temp154C feed rate 3160 kgh hold-up 335 kg tm 64 min

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2014

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214 MADHIYANON SOPONRONNARIT AND TIA

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 successor failure of a grain-drying system As seen in Tables 1 and 2 it is clear that thepresent drying process does not have much effect on milling quality No significantquality change was observed when paddy was dried down to 14ndash25 dry basisregardless of the high inlet air temperature of up to 130ndash160C For the head riceyield this was due to the fact that the moisture gradient inside the grain kernelwas somewhat redistributed and equalized while passing through the downcomerwhich resulted in relaxation of the stress developed within the grain kernel andthus 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 airin the spouting region within a very short time In addition the alternative methodfor preservation of milling quality is to apply a zoning concept that is using ahigh temperature in the first zone for fast drying and a lower temperature in thesubsequent zone of the dryer for gentle drying This is analogous to employingthe different temperature level concept as described by Nguyen et al (67) Thehead rice yield and whiteness results of test No 13 are presented in Figure 5A 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 56ndash77 MJkg water removed This

Figure 5 Comparison of head rice yield and whiteness between drying with ambient airand drying with spouted bed dryer (inlet air temp 154C feed rate 3160 kgh hold-up335 kg tm 64 min)

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INDUSTRIAL-SCALE CONTINUOUS SPOUTED BED DRYER 215

be attributed to noncontinuation of the spouting which would result in poor paddycirculation However in the second phase of the experiments thermal energyconsumption was reduced to the range of 31ndash38 MJkg water according to afeed rate of 3100ndash3500 kgh (test Nos 13ndash15 in Table 2) The decrease of thermalenergy consumption in the second phase especially for test Nos 13ndash15 is probablyattributed to a much higher circulation rate than that achieved in the first phase ofthe study

CONCLUSIONS

An industrial-scale continuous spouted bed dryer with a capacity of 3500kgh was developed and tested No serious loss in quality was observed duringthe experiments while the high drying air temperature was used Final moisturecontent and milling quality results appear to be consistent throughout the testingperiods However with the limitation of the existing drying chamber length ahigh percentage of moisture reduction corresponding to the high paddy feed ratecould not be achieved The energy consumption is comparable to those of othercommercial 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 acknowledgedfor its cooperation during this study

REFERENCES

1 Mujumdar AS In Spouted Bed Technology A Brief Review Dryingrsquo84Hemisphere Washington 1984 151ndash157

2 Kalwar MI Kudra T Raghavan GSV Mujumdar AS Drying of Grainsin a Drafted Two-Dimensional Spouted Bed J Food Proc Eng 1991 13321ndash332

3 Kalwar MI Raghavan GSV Batch Drying of Shelled Corn in Two-Dimensional Spouted Beds with Draft Plates Drying Technol 1993 11 (2)339ndash354

4 Kalwar MI Raghavan GSV Circulation of Particles in Two-DimensionalSpouted Beds with Draft Plates Powder Tech 1993 77 233ndash242

Dow

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Col

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rsity

] at

22

06 2

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ovem

ber

2014

ORDER REPRINTS

216 MADHIYANON SOPONRONNARIT AND TIA

5 Wetchacama S Soponronnarit S Swasdisevi T Panich-ing-orn JSuthicharoenpanich S In Drying of High Moisture Paddy by Two-Dimensional Spouted Bed Technique Proceedings of the First Asian-Australian Drying Conference (ADC rsquo99) Bali Indonesia Oct 24ndash27 1999300ndash307

6 Nguyen LH Driscoll RH Srzednicki GS In Drying Characteristics ofPaddy in a Triangular Spouted-Bed Proceedings of the 11th InternationalDrying Symposium (IDS rsquo98) Halkidiki Greece Aug 19ndash22 1998 1397ndash1404

7 Nguyen LH Driscoll RH Srzednicki GS In Flowing Performance andDrying Characteristics of Paddy in a Triangular Spouted-Bed 7th Interna-tional Working Conference on Stored-Product Protection Beijing China Oct14ndash20 1998

Dow

nloa

ded

by [

Col

umbi

a U

nive

rsity

] at

22

06 2

1 N

ovem

ber

2014

Order now

Reprints of this article can also be ordered at

httpwwwdekkercomservletproductDOI101081DRT100001362

Request Permission or Order Reprints Instantly

Interested in copying and sharing this article In most cases US Copyright Law requires that you get permission from the articlersquos 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 PermissionReprints Here link below and follow the instructions Visit the US Copyright Office for information on Fair Use limitations of US copyright law Please refer to The Association of American Publishersrsquo (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 or personal 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 Agreement for more details

Dow

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ovem

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2014

ORDER REPRINTS

INDUSTRIAL-SCALE CONTINUOUS SPOUTED BED DRYER 213

Table 2 Summary of the Second Phase Experimental Results

Test No

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

Feed rate (kgh) 2470 2440 1990 2370 2400 3160 3280 3550Hold-up (kg) 60 360 340 240 210 335 290 310Residence time (min) 15 89 102 60 53 64 53 52Average inlet air temp (C) 154 149 141 152 159 154 156 160Exit grain temp (C) 68 71 66 71 68 67 67 68Average moisture content

BFD ( dry basis) 261 217 285 221 250 294 282 228AFD ( dry basis) 227 175 236 171 197 250 233 190

Head rice yieldBFD () 561 459 533 490 496 501 543 412AFD () 589 457 542 474 484 524 550 408

WhitenessBFD 419 457 442 476 476 478 464 467AFD 416 454 450 468 467 475 463 459

Drying rate (kg waterh) 68 87 79 101 106 111 130 101Energy consumption(MJkg water evaporated)

Heat 65 70 NA 44 52 35 38 31Electricity 060 060 060 050 050 046 040 046

AFD after drying BFD before drying NA not available temp temperatureaDraft channel blade angle 85 entrance height 10 cmbDraft channel blade angle 89 entrance height 10 cmcDraft channel blade angle 89 entrance height 125 cmd Draft channel blade angle 89 entrance height 15 cm

Figure 4 Comparison of moisture content between before and after drying inlet air temp154C feed rate 3160 kgh hold-up 335 kg tm 64 min

Dow

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2014

ORDER REPRINTS

214 MADHIYANON SOPONRONNARIT AND TIA

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 successor failure of a grain-drying system As seen in Tables 1 and 2 it is clear that thepresent drying process does not have much effect on milling quality No significantquality change was observed when paddy was dried down to 14ndash25 dry basisregardless of the high inlet air temperature of up to 130ndash160C For the head riceyield this was due to the fact that the moisture gradient inside the grain kernelwas somewhat redistributed and equalized while passing through the downcomerwhich resulted in relaxation of the stress developed within the grain kernel andthus 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 airin the spouting region within a very short time In addition the alternative methodfor preservation of milling quality is to apply a zoning concept that is using ahigh temperature in the first zone for fast drying and a lower temperature in thesubsequent zone of the dryer for gentle drying This is analogous to employingthe different temperature level concept as described by Nguyen et al (67) Thehead rice yield and whiteness results of test No 13 are presented in Figure 5A 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 56ndash77 MJkg water removed This

Figure 5 Comparison of head rice yield and whiteness between drying with ambient airand drying with spouted bed dryer (inlet air temp 154C feed rate 3160 kgh hold-up335 kg tm 64 min)

Dow

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2014

ORDER REPRINTS

INDUSTRIAL-SCALE CONTINUOUS SPOUTED BED DRYER 215

be attributed to noncontinuation of the spouting which would result in poor paddycirculation However in the second phase of the experiments thermal energyconsumption was reduced to the range of 31ndash38 MJkg water according to afeed rate of 3100ndash3500 kgh (test Nos 13ndash15 in Table 2) The decrease of thermalenergy consumption in the second phase especially for test Nos 13ndash15 is probablyattributed to a much higher circulation rate than that achieved in the first phase ofthe study

CONCLUSIONS

An industrial-scale continuous spouted bed dryer with a capacity of 3500kgh was developed and tested No serious loss in quality was observed duringthe experiments while the high drying air temperature was used Final moisturecontent and milling quality results appear to be consistent throughout the testingperiods However with the limitation of the existing drying chamber length ahigh percentage of moisture reduction corresponding to the high paddy feed ratecould not be achieved The energy consumption is comparable to those of othercommercial 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 acknowledgedfor its cooperation during this study

REFERENCES

1 Mujumdar AS In Spouted Bed Technology A Brief Review Dryingrsquo84Hemisphere Washington 1984 151ndash157

2 Kalwar MI Kudra T Raghavan GSV Mujumdar AS Drying of Grainsin a Drafted Two-Dimensional Spouted Bed J Food Proc Eng 1991 13321ndash332

3 Kalwar MI Raghavan GSV Batch Drying of Shelled Corn in Two-Dimensional Spouted Beds with Draft Plates Drying Technol 1993 11 (2)339ndash354

4 Kalwar MI Raghavan GSV Circulation of Particles in Two-DimensionalSpouted Beds with Draft Plates Powder Tech 1993 77 233ndash242

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2014

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216 MADHIYANON SOPONRONNARIT AND TIA

5 Wetchacama S Soponronnarit S Swasdisevi T Panich-ing-orn JSuthicharoenpanich S In Drying of High Moisture Paddy by Two-Dimensional Spouted Bed Technique Proceedings of the First Asian-Australian Drying Conference (ADC rsquo99) Bali Indonesia Oct 24ndash27 1999300ndash307

6 Nguyen LH Driscoll RH Srzednicki GS In Drying Characteristics ofPaddy in a Triangular Spouted-Bed Proceedings of the 11th InternationalDrying Symposium (IDS rsquo98) Halkidiki Greece Aug 19ndash22 1998 1397ndash1404

7 Nguyen LH Driscoll RH Srzednicki GS In Flowing Performance andDrying Characteristics of Paddy in a Triangular Spouted-Bed 7th Interna-tional Working Conference on Stored-Product Protection Beijing China Oct14ndash20 1998

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2014

Order now

Reprints of this article can also be ordered at

httpwwwdekkercomservletproductDOI101081DRT100001362

Request Permission or Order Reprints Instantly

Interested in copying and sharing this article In most cases US Copyright Law requires that you get permission from the articlersquos 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 PermissionReprints Here link below and follow the instructions Visit the US Copyright Office for information on Fair Use limitations of US copyright law Please refer to The Association of American Publishersrsquo (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 or personal 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 Agreement for more details

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2014

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214 MADHIYANON SOPONRONNARIT AND TIA

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 successor failure of a grain-drying system As seen in Tables 1 and 2 it is clear that thepresent drying process does not have much effect on milling quality No significantquality change was observed when paddy was dried down to 14ndash25 dry basisregardless of the high inlet air temperature of up to 130ndash160C For the head riceyield this was due to the fact that the moisture gradient inside the grain kernelwas somewhat redistributed and equalized while passing through the downcomerwhich resulted in relaxation of the stress developed within the grain kernel andthus 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 airin the spouting region within a very short time In addition the alternative methodfor preservation of milling quality is to apply a zoning concept that is using ahigh temperature in the first zone for fast drying and a lower temperature in thesubsequent zone of the dryer for gentle drying This is analogous to employingthe different temperature level concept as described by Nguyen et al (67) Thehead rice yield and whiteness results of test No 13 are presented in Figure 5A 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 56ndash77 MJkg water removed This

Figure 5 Comparison of head rice yield and whiteness between drying with ambient airand drying with spouted bed dryer (inlet air temp 154C feed rate 3160 kgh hold-up335 kg tm 64 min)

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INDUSTRIAL-SCALE CONTINUOUS SPOUTED BED DRYER 215

be attributed to noncontinuation of the spouting which would result in poor paddycirculation However in the second phase of the experiments thermal energyconsumption was reduced to the range of 31ndash38 MJkg water according to afeed rate of 3100ndash3500 kgh (test Nos 13ndash15 in Table 2) The decrease of thermalenergy consumption in the second phase especially for test Nos 13ndash15 is probablyattributed to a much higher circulation rate than that achieved in the first phase ofthe study

CONCLUSIONS

An industrial-scale continuous spouted bed dryer with a capacity of 3500kgh was developed and tested No serious loss in quality was observed duringthe experiments while the high drying air temperature was used Final moisturecontent and milling quality results appear to be consistent throughout the testingperiods However with the limitation of the existing drying chamber length ahigh percentage of moisture reduction corresponding to the high paddy feed ratecould not be achieved The energy consumption is comparable to those of othercommercial 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 acknowledgedfor its cooperation during this study

REFERENCES

1 Mujumdar AS In Spouted Bed Technology A Brief Review Dryingrsquo84Hemisphere Washington 1984 151ndash157

2 Kalwar MI Kudra T Raghavan GSV Mujumdar AS Drying of Grainsin a Drafted Two-Dimensional Spouted Bed J Food Proc Eng 1991 13321ndash332

3 Kalwar MI Raghavan GSV Batch Drying of Shelled Corn in Two-Dimensional Spouted Beds with Draft Plates Drying Technol 1993 11 (2)339ndash354

4 Kalwar MI Raghavan GSV Circulation of Particles in Two-DimensionalSpouted Beds with Draft Plates Powder Tech 1993 77 233ndash242

Dow

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by [

Col

umbi

a U

nive

rsity

] at

22

06 2

1 N

ovem

ber

2014

ORDER REPRINTS

216 MADHIYANON SOPONRONNARIT AND TIA

5 Wetchacama S Soponronnarit S Swasdisevi T Panich-ing-orn JSuthicharoenpanich S In Drying of High Moisture Paddy by Two-Dimensional Spouted Bed Technique Proceedings of the First Asian-Australian Drying Conference (ADC rsquo99) Bali Indonesia Oct 24ndash27 1999300ndash307

6 Nguyen LH Driscoll RH Srzednicki GS In Drying Characteristics ofPaddy in a Triangular Spouted-Bed Proceedings of the 11th InternationalDrying Symposium (IDS rsquo98) Halkidiki Greece Aug 19ndash22 1998 1397ndash1404

7 Nguyen LH Driscoll RH Srzednicki GS In Flowing Performance andDrying Characteristics of Paddy in a Triangular Spouted-Bed 7th Interna-tional Working Conference on Stored-Product Protection Beijing China Oct14ndash20 1998

Dow

nloa

ded

by [

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umbi

a U

nive

rsity

] at

22

06 2

1 N

ovem

ber

2014

Order now

Reprints of this article can also be ordered at

httpwwwdekkercomservletproductDOI101081DRT100001362

Request Permission or Order Reprints Instantly

Interested in copying and sharing this article In most cases US Copyright Law requires that you get permission from the articlersquos 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 PermissionReprints Here link below and follow the instructions Visit the US Copyright Office for information on Fair Use limitations of US copyright law Please refer to The Association of American Publishersrsquo (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 or personal 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 Agreement for more details

Dow

nloa

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Col

umbi

a U

nive

rsity

] at

22

06 2

1 N

ovem

ber

2014

ORDER REPRINTS

INDUSTRIAL-SCALE CONTINUOUS SPOUTED BED DRYER 215

be attributed to noncontinuation of the spouting which would result in poor paddycirculation However in the second phase of the experiments thermal energyconsumption was reduced to the range of 31ndash38 MJkg water according to afeed rate of 3100ndash3500 kgh (test Nos 13ndash15 in Table 2) The decrease of thermalenergy consumption in the second phase especially for test Nos 13ndash15 is probablyattributed to a much higher circulation rate than that achieved in the first phase ofthe study

CONCLUSIONS

An industrial-scale continuous spouted bed dryer with a capacity of 3500kgh was developed and tested No serious loss in quality was observed duringthe experiments while the high drying air temperature was used Final moisturecontent and milling quality results appear to be consistent throughout the testingperiods However with the limitation of the existing drying chamber length ahigh percentage of moisture reduction corresponding to the high paddy feed ratecould not be achieved The energy consumption is comparable to those of othercommercial 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 acknowledgedfor its cooperation during this study

REFERENCES

1 Mujumdar AS In Spouted Bed Technology A Brief Review Dryingrsquo84Hemisphere Washington 1984 151ndash157

2 Kalwar MI Kudra T Raghavan GSV Mujumdar AS Drying of Grainsin a Drafted Two-Dimensional Spouted Bed J Food Proc Eng 1991 13321ndash332

3 Kalwar MI Raghavan GSV Batch Drying of Shelled Corn in Two-Dimensional Spouted Beds with Draft Plates Drying Technol 1993 11 (2)339ndash354

4 Kalwar MI Raghavan GSV Circulation of Particles in Two-DimensionalSpouted Beds with Draft Plates Powder Tech 1993 77 233ndash242

Dow

nloa

ded

by [

Col

umbi

a U

nive

rsity

] at

22

06 2

1 N

ovem

ber

2014

ORDER REPRINTS

216 MADHIYANON SOPONRONNARIT AND TIA

5 Wetchacama S Soponronnarit S Swasdisevi T Panich-ing-orn JSuthicharoenpanich S In Drying of High Moisture Paddy by Two-Dimensional Spouted Bed Technique Proceedings of the First Asian-Australian Drying Conference (ADC rsquo99) Bali Indonesia Oct 24ndash27 1999300ndash307

6 Nguyen LH Driscoll RH Srzednicki GS In Drying Characteristics ofPaddy in a Triangular Spouted-Bed Proceedings of the 11th InternationalDrying Symposium (IDS rsquo98) Halkidiki Greece Aug 19ndash22 1998 1397ndash1404

7 Nguyen LH Driscoll RH Srzednicki GS In Flowing Performance andDrying Characteristics of Paddy in a Triangular Spouted-Bed 7th Interna-tional Working Conference on Stored-Product Protection Beijing China Oct14ndash20 1998

Dow

nloa

ded

by [

Col

umbi

a U

nive

rsity

] at

22

06 2

1 N

ovem

ber

2014

Order now

Reprints of this article can also be ordered at

httpwwwdekkercomservletproductDOI101081DRT100001362

Request Permission or Order Reprints Instantly

Interested in copying and sharing this article In most cases US Copyright Law requires that you get permission from the articlersquos 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 PermissionReprints Here link below and follow the instructions Visit the US Copyright Office for information on Fair Use limitations of US copyright law Please refer to The Association of American Publishersrsquo (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 or personal 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 Agreement for more details

Dow

nloa

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umbi

a U

nive

rsity

] at

22

06 2

1 N

ovem

ber

2014

ORDER REPRINTS

216 MADHIYANON SOPONRONNARIT AND TIA

5 Wetchacama S Soponronnarit S Swasdisevi T Panich-ing-orn JSuthicharoenpanich S In Drying of High Moisture Paddy by Two-Dimensional Spouted Bed Technique Proceedings of the First Asian-Australian Drying Conference (ADC rsquo99) Bali Indonesia Oct 24ndash27 1999300ndash307

6 Nguyen LH Driscoll RH Srzednicki GS In Drying Characteristics ofPaddy in a Triangular Spouted-Bed Proceedings of the 11th InternationalDrying Symposium (IDS rsquo98) Halkidiki Greece Aug 19ndash22 1998 1397ndash1404

7 Nguyen LH Driscoll RH Srzednicki GS In Flowing Performance andDrying Characteristics of Paddy in a Triangular Spouted-Bed 7th Interna-tional Working Conference on Stored-Product Protection Beijing China Oct14ndash20 1998

Dow

nloa

ded

by [

Col

umbi

a U

nive

rsity

] at

22

06 2

1 N

ovem

ber

2014

Order now

Reprints of this article can also be ordered at

httpwwwdekkercomservletproductDOI101081DRT100001362

Request Permission or Order Reprints Instantly

Interested in copying and sharing this article In most cases US Copyright Law requires that you get permission from the articlersquos 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 PermissionReprints Here link below and follow the instructions Visit the US Copyright Office for information on Fair Use limitations of US copyright law Please refer to The Association of American Publishersrsquo (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 or personal 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 Agreement for more details

Dow

nloa

ded

by [

Col

umbi

a U

nive

rsity

] at

22

06 2

1 N

ovem

ber

2014

Order now

Reprints of this article can also be ordered at

httpwwwdekkercomservletproductDOI101081DRT100001362

Request Permission or Order Reprints Instantly

Interested in copying and sharing this article In most cases US Copyright Law requires that you get permission from the articlersquos 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 PermissionReprints Here link below and follow the instructions Visit the US Copyright Office for information on Fair Use limitations of US copyright law Please refer to The Association of American Publishersrsquo (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 or personal 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 Agreement for more details

Dow

nloa

ded

by [

Col

umbi

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nive

rsity

] at

22

06 2

1 N

ovem

ber

2014