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CORN QUALITY AFTER DELYING BY FLUIDIZATIONTECHNIQUE AT HIGH TEMPERATURESomchart Soponronnarit a , Anan Pongtornkulpanich b & Somkiat Prachayawarakorn ca School of Energy and Materials , King Mongkut's Institute of Technlogy Thonburi , Suksawad48 Rd, Bangkok, 10140, Thailandb Former graduate student , King Mongkut's Institute of Technlogy Thonburi , Suksawad 48 Rd,Bangkok, 10140, Thailandc Faculty of Engineering , King Mongkut's Institute of Technlogy Thonburi , Suksawad 48 Rd,Bangkok, 10140, ThailandPublished online: 03 May 2007.

To cite this article: Somchart Soponronnarit , Anan Pongtornkulpanich & Somkiat Prachayawarakorn (1997) CORN QUALITYAFTER DELYING BY FLUIDIZATION TECHNIQUE AT HIGH TEMPERATURE, Drying Technology: An International Journal, 15:10,2577-2586, DOI: 10.1080/07373939708917378

To link to this article: http://dx.doi.org/10.1080/07373939708917378

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DRYING TECHNOLOGY, 15(10), 2577-2586 1(:1997)

CORN Q-UALITY AFTER DRXLNG BY FLUIDIZATION TIECHNIQUE AT HIGrH TEMPERATURE

Sonnchart Soponronnaritl, Anan E'ongtornkuipanichz and Somkiat Praehayawarakorn3

1 School of Energy and Materialls, 2 Former graduate student 3 Faculty of Engineering

King Mongkut's Institute taf Technlogy Thonburi Sutksawad 48 Rd., Bangkok 10140, Thailand

Key words : Breakage; Stress crack; Fluidized bed drying; Grain; Quality

ABSTRACT

Corn quality, in terms of stress crack, breakage and colour, after drying by fluidization technique was investigated. Drying air temperatures for this study were 150, 170 and 200°C. Experimental results showed that drying corn of 43% (d.b.) initial moisture content to 16% (d.b.) final moisture content (approximate 9 minutes) with drying air temperature up to 170°C (inlet air relative humidity less than 5%) could be done without significant loss of quality , ie . no breakage of corn kernel, stress crack less than 12% and just small change of'colour of grain surface. Empirical equations describing evolution of multiple stress crack and grain surFgce colour were developed. Results obtained. from the equations are in good agreement with experimental ones.

INTRODUCTION

Although drying corn a.t high temperature can enhance drying rate, quality of

dried product, i.e., stress crack and breakage, is normally affected. Surface colour may

2577

Copyright O 1997 by Marcel Dekker, Inc.

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2578 SOPONRONNARIT. PONGTORNKULPANICH. AND PRACHAYAWARAKORN

be too dark and not be accepted in market. Drying corn at temperature higher than

150•‹C is not very common in conventional continuous flow dryers. However, it is

quite possible with fluidization technique due to uniform and better heat and mass

transfers compared to those in conventional dryers. In Thailand, fluidized bed paddy

dryer is now very popular. Moreover. application of fluidized bed for corn drying is

now practiced, Information on corn quality after drying at high temperature will be

therefore useful for grain industry.

Gustafson et all" investigated thin layer corn drying at drying ternperature in

the range of 70-12O0C, final moisture content of 13-19% wet-basis and at different

tempering time. It was concluded that breakage susceptibility depended on final

moisture content and tempering time Gunasekaran and ~aulsen"' investigated corn

quality such as breakage susceptibility and stress crack after fixed bed drying with

different temperatures (20, 35. 50 and 60•‹C). I t was found that breakage

susceptibility depended linearly with drying ternperature or drying rate. Beke and

~ u j u m d d " investigated the effect of drying conditions such as final moisture content.

drying temperature (20-140•‹C) and sphericity (0.40-0.95) on corn quality after drying

(ratio of weight of damage grains such as kernels with stress crack and breakage to

total weight). It was reponed that grain damage increased with drying temperature

and sphericity but decreased with final moisture content. Rodwiboonchai and

Soponronnarit "I conducted an experiment on convective rotary corn drying at 100-

130•‹C and found that kernel breakage based on weight-basis was lower than 2%.

Effect of drying air humidity on drying rate . multiple stress crack and breakage

susceptibility was investigated by Estrada and Litchfield I" who dried corn in tray at air

humidity from 0.8 to 80% and temperature of 71-104•‹C. The results showed that

drying rate, stress crack and breakage susceptibility decreased when air humidity

increased.

As already mentioned, drying corn at high temperature yields advantage

especially in terms of drying rate Soponronnarit et al.'61 has already studied corn

drying with fluidization technique at temperature ranging from 120 to 200•‹C. The

objective of this paper was to investigate the effect of drying air temperature on corn

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CORN QUALITY AFTER DRYING BY FLUIDIZATION 2579

quality after drying by fluidization technique at high temperature. Stress crack,

breakage and surface colour of grain are concentrated.

MATERIALS AND METHODS

Corn kernel, yellow dent, a local variety for feed grain industry, was dried in a

batch fluidized bed dryer made of stainless steel sheets as shown in Figure I. The

system comprises of a cylinder-shaped vessel. 20 cm diameter and 140 cm high, four

separately controlled 3 kW electric heaters and a backward-curved blade centrihgal

fan driven by a 1.5 kW motor. Air flow rate could be adjusted by mean of a

mechanical variable speed controller at the fan, The whole system was insulated with

glass wool in order to minimize heat loss. Some pans of exhaust air were recycled,

mixed with the fresh air and reheated to a desired temperature. which was controlled

by PID controller with an accuracy of i I OC.

Dry corn was rewetted by spraying pre-calculated amount of water, mixed and

kept in a temperature controlled room at temperature of 4 4 • ‹ C for 5-7 days. Before

starting the experiments, it was taken out from the controlled room and let to attain

thermal equilibrium with ambient air. The experiments were carried out to dry corn of

43% ( d b ) initial moisture content to about 5% (db. ) moisture content using inlet hot

air temperatures of 150, 170 and 200•‹C. superficial air velocity of 3 d s and bed depth

of 8 cm. During experiments, temperatures at various positions such as inlet air

temperature, wet-bulb and dry-bulb temperatures of exhaust air and fresh air were

measured with K-type thermocouple from which signal was transferred to a data

logger with an accuracy of +I0C. Air velocity was measured with a hot-wire

anenometer. The samples were collected from the dryer at 2. 4, 6, 8 10. 15 and 20

minutes of drying time. The moisture content of corn was determined at temperature

of 1 0 3 T for 72 hours according to ASAE standard.

Multiple stress crack of corn kernel was determined by investigating 200 g

sample by visual inspection under light. Percentage was based on weight.

Breakagibility was determined from the ratio of weight of broken corn kernel to total

weight of corn (200 g) using the same method. Grain surface colour was determined

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:2580 SOPONRONNARIT, PONGTORNKUILPANICH, AND PRACHAYAWARAKORN

1 3. Air velocity 100 cm 4 4. Wet bulb temperature

LT' Distributor 3.

Figure I Experimental batch fluidized bed dryer

by a colour meter, Juki JP 7100 p. a and b values in Hunter system which related to

red and yellow colsurs were read.

RESULTS AND DISCUSSION

Stress Crack

Corn was dried from 43% (d.b.1 moisture content to about 5% (d.b.) moisture

content. Experimental results showed that th,ere was no breakage of grain kernel at the

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CORN QUALITY AFTER DRYING BY FLUI:I>XZA?'IOM 2581

drying air temperatures of 150 and 1 70° C (inkt air relative humidity less than 5%) but

multiple stress crack specified by visual illspection occurred, varying linearly with

drying time according to Figure 2, or increasing with decreasing final moisture content

as shown in Figure 3. It was also observed that stress cracking increased with drying

air temperature . At drying air temperature of 200 OC , stress crack started very

quickly, 2-4 minutes after drying. In addition, breakage of grain kernel developed.

An equation describing the relationship among multiple stress crack, drying air

temperature and final moisture content was developed empirically from experimental

data as shown bellow.

MSG = exp (8.366025-0 07322 Mf- 0.00014 T- 0.63217 In (MfT))

R' = 0.99

Std Err of y Est = 0.09

where MSC = multiple stress crack, %

Mf = final moisture colntent, % dry-basis

T = drying air temperature, O C

Figure 3 shows very good agreement between experimental results and

calculated ones.

So far, there is no market's standard concerning stress crack in Thailand.

However, this is very important in some countries such as USA. According to Figure

3, maximum stress crack at 16.3% (d.b.) final moisture content (safe for storage) is

only 9 and 12% for 150 C and 170 O C drying air temperature respectively.

Breakagibility

At drying air temperatures of 150 and 170" C (inlet air relative humidity less

than 5%), there was no breakage of corn Ikernel. With drying air temperature of

200°C , breakage started to develop within 2-4 minutes after drying as shown in

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2582 SOPONRONNARIT. PONGTORNKULPANICH. AND PRACHAYAWARAKORN

4 0 5 10 15 20 25 30

Drying time, min

Figure 2 Relationship between multiple stress crack and drying time at different temperature I initial moisture content =43 Ydb. suwrficial air 'velocity = 3.0 m/s and bed depth = 8.6 cm]

I 0-r-r 0 0.077 0.106 0.141 0.163 0.187 0.223 0

Final moisture content , (db)

Figure 3 Relationship between multiple stress crack and final moisture content at different tempemhue [ initial moisture content = 43 W b , superficial air velocity = 3.0 m/s and bed depth = 8.0 cm]

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CORN QUALITY AFTER DRYING BY FLUIDIZATION 2583

Figure 4. ARer 4 minutes, breakage became similar to pop corn and was almost fully

broken after 15 minutes In this study, breakage was verified by visual inspection.

Colour of Dried Corn

Evolution of grain surface colour (a and b values in Hunter system) was shown

in Figures 5 and 6. At drying air temperatures 150 and 170•‹C (inlet air relative

humidity less than 5%) , a and b values changed slowly, a increased but b decreased

with time. On the contrary, they varied rapidly with time at drying air temperature of

200•‹C . Rate of colour change was found to be zero order with rate constant

expressed in Arrehnius's form as follows :

dddt = 19.20761 exp (-77228.9lRT)

R' = 0.81

Std Err of y Est = 0. I9

and -dbldt = 12.64136 exp (-S1864.O/RT)

R' = 0.87

Std Err of y Est = 0.13

where R = gas constant (8.3 14 Jlmole-K)

T = temperature (K)

t = time (min)

According to experimental results, it is recommended that drying air

temperature for drying corn with fluidization technique should be lower than 200•‹C.

recommending at 170 'C, to attain acceptable quality in terms of stress crack.

breakage and colour. With 17O0C drying air temperature, stress crack developed

slowly until final moisture content reached 16% dry-basis (safe for storage). At this

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25&l SOPONRONNARIT. PONGTORNKULPANICH. AND PRACHAYAWARAKORN

0.4

0

-0.3 2 8

-0.25

4 0 - -0.1

20 '-.._ - 0.05

0 7 -- - - . o

0 5 10 15 20 25 30

Drying time, min

Figure 4 Relationship between breakagibility, final moisture content and drying time [ initial moisture content = 43 %db, superficial air velocitv = 3.0 d s . bed deoth = 8.0 cm and inlet air temperature = 200 C ]

35 7

Drying time , min

Figure 5 Relationship between "a" value and drying time at different temperature

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CORN QUALITY AFTER DRYING BY FLUIDIZATION 2585

I I 0 - A 0 5 10 15 20 25

Drying time, min

Figure 6 Relationship between " b value and drying time at different temperature

moisture content, stress crack is 12% while there are no breakage and little change o f

colour o f kernel surface.

CONCLUSION

Corn with 43% (d.b.) initial moisture content can be dried down to 16% (d.b.)

moisture content by fluidization technique with dlying air temperature up to 170•‹C

without significant loss of quality in terms of stress crack, breakage and grain surface

colour. At this final moisture content, there are 12% stress crack, no breakage and

little change o f colour. Empirical equations describing evolution o f multiple stress

crack and colour were developed. There are very good agreement between

experimental results and calculated ones.

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2586 SOPONRONNARIT. PONGTORNKULPANICH. AND PRACHAYAWARAKORN

ACKNOWLEDGEMENT

The authors gratefully acknowledge the Thailand Research Fund and Australian

Centre for International Agricultural Research for financial support.

REFERENCES

[I ] Gustafson. R.J., Mahmoud. A.Y. and Hall. G.E., 1983. Breakage Susceptibility

Reduction by Short-Tern Tempering of Corn. Trans. ASAE. 26. 918-922.

[2] Gunasekaran, S. and Paulsen. MR.. 1985. Breakage Resistance of Corn as a

Function of Drying Rates, Trans. ASAE, 28(6). 2071-2076.

[3] Beke. J, and Mujumdar. A.S.. 1993, Influence of Drying Conditions on the

Fragility of Corn Kernels. Drying Technology, I 1 (3). 603-614.

[4] Rodwiboonchai, P. and Soponronnarit. S.. 1992. Drying Corn by Rotary Dryer :

Mathematical Model and Drying Strategies. Kasetsan Journal (Natural Science)

26. 50-59 (in Thai).

[5] Estrada. J.A. and Litchfield, J.B.. 1993. High Humidity Drying of Corn : Effect on

Drying Rate and Product Quality, Drying Technology. l l (I), 65-84.

[6] Soponronnarit. S., Pongtornkulpanich. A. and Prachayawarakorn, S., (in press),

Drying Characteristics of Corn in Fluidized Bed Dryer. Drying Technology,

15 (5). 1997.

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