Performance Evaluation Of A Locally Fabricated Mini Cassava Flash Dryer

Researcher, 1(3), 2009, http://www.sciencepub.net, sciencepub@gmail.com

Performance Evaluation Of A Locally Fabricated Mini Cassava Flash Dryer

K.R. AJAO (Ph.D.)
Department of Mechanical Engineering, University of Ilorin, Ilorin, Nigeria
e-mail: ajaomech@unilorin.edu.ng
I.K. ADEGUN (Ph.D.)
Department of Mechanical Engineering, University of Ilorin, Ilorin, Nigeria
e-mail: kadegun2000@yahoo.com

Abstract: A mini cassava flash dryer was parameterized, developed and tested. The flash dryer is a
mechanized way of drying cassava mash for mass production of cassava flour for flour mills, confectionery
and pharmaceutical industries. The traditional method of producing cassava flour cannot give product of
high quality and quantity for industrial usage because its mode of drying is dependent on climatic
conditions and susceptible to contamination. After three passes of cassava mash through the flash dryer, the
percentage of dryness achieved was 57.1%. [Researcher. 2009;1(3):54-60]. (ISSN: 1553-9865).

Keywords: Flash dryer, parameterized, mechanized, industrial uses, percentage of dryness.

1.
Introduction
With an estimated population of 120 million people, a land mass of approximately 93,700 square
kilometers and vast mineral and agricultural resources, Nigeria has substantial economic potential in its
agricultural sector. However, despite the importance of agriculture in terms of employment creation, its
potential for contributing to economic growth is far from being fully exploited. The sector’s importance has
fluctuated with the rise and fall in oil revenue. Over the past 10 years, Nigerian agricultural sector has
remained stagnant while the contribution of the manufacturing sector to the GDP has declined over the
same period.
Although efforts at the political level have been intensified to increase the agricultural sector’s
contribution to economic growth, there has been no significant impact on employment creation, or
improvement in rural incomes. This is because growth in agriculture has been incapacitated by lack of
adequate agro industries to spur demand for agricultural raw materials. While various programs have been
designed to achieve sustainable agricultural growth, they have mainly focused largely on increasing farm
productivity through the maximization of agronomic efficiency. Through the efforts by various agricultural
research institutes, technologies for transforming smallholder agriculture have been developed for
production through postharvest, but adoption of these remains low. Also, efforts to promote
commercialization and agro enterprise development have not received adequate attention [1].
Nigeria is the largest producer of cassava in the world as shown in table 1 below. Its production is
currently put at about 33.8 million tonnes a year [2]. Total area harvested of the crop in 2001 was 3.1
million ha with an average yield of about 11 t/ha. Cassava plays a vital role in the food security of the rural
economy because of its capacity to yield under marginal soil conditions and its tolerance to drought. It is
the most widely cultivated crop in the country; it is predominantly grown by smallholder farmers and
dependent on seasonal rainfall. Rural and urban communities use cassava mainly as food in both fresh and
processed forms. The meals most frequently eaten in the rural areas are cassava-based.
Cassava production is still carried out by manual labour using local simple farm implements such as
hoes and knives in most parts of the country. There is a general absence of mechanized production to the
local farmers who constitute the majority of the producers. Cassava roots are processed at household and
cottage levels in the rural areas of the major cassava producing states by traditional methods handed down
through time as cassava was adopted as food by the people. Processing at these levels involve mainly the
production of garri, fermented and unfermented flour, as well as fufu(local delicacy) for both domestic
consumption.
The processing of cassava roots into garri, flour and fufu are done involve peeling – grating
(mashing) – dewatering/fermentation –sieving – frying – packaging. The process for production of flour
involve peeling – cutting into pieces – sun drying – milling – sieving – packaging (for unfermented flour);
peeling – cutting – steeping (soaking in water) and fermentation – (mashing) – sun drying –milling –
sieving – packaging (for fermented flour). The process for fufu production is similar to fermented flour
production except that the sun drying is omitted and the mash dewatered after sieving.

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There was no indication of processing cassava root into chips and pellets for animal feeds in the
country. Likewise, processing of cassava to value added products like alcohol, dextrins, glue, sweeteners,
monosodium glutamate (MSG), modified starch etc are very low in the country and as at present, no bakery
uses cassava flour for bread or biscuits [3].

Table 1: Production Levels of Cassava in Nigeria and other major Cassava Producing
Countries (Reproduced from [3] )



2.
Cassava processing and utilization
Cassava is a very versatile commodity with numerous uses and by-products. Each component of the
plant can be valuable to its cultivator. The leaves may be consumed as a vegetable, or cooked as a soup
ingredient or dried and fed to livestock as a protein feed supplement. The stem is used for plant propagation
and grafting. The roots are typically processed for human and industrial consumption.
In Nigeria, the consumption pattern varies according to ecological zones. Garri, a roasted granule is
the dominant product and is widely accepted in both rural and urban areas. It can be consumed without any
additives, or consumed with a variety of additives such as sugar, groundnut, fish, meat and stew. Fufu and
Akpu, a fermented wet paste from cassava is also widely consumed throughout the country especially in the
southern zones.
Estimates of industrial use of cassava suggest that approximately sixteen percent of cassava root
production was utilized as an industrial raw material in 2001 in Nigeria. Ten percent was used as chips in
animal feed, five percent was processed into a syrup concentrate for soft drinks and less than one percent
was processed into high quality cassava flour used in biscuits and confectionary, dextrin pre-gelled starch
for adhesives, starch and hydrolysates for pharmaceuticals, and seasonings [4].
Cassava processing operations in Nigeria can be described at 5 levels of capacity. The common terms
used to describe these capacity levels are household (or cottage), micro, small, medium and large.
Household level processing typically does not employ any outside labour. The household consumes
virtually all of the processed products and sells a small amount to raise income for additional household
needs. At present, most Nigerian processors fall within this category.
At the micro processing capacity the employment of one or two units of labour may take place while
processing a variety of cassava products. This enterprise typically uses batch processing. Batch processing
may take four hours per day and this would be sufficient for the owner/operator.
Nigeria has a few cassava processors in this category of operation. The small and medium processing
operations typically employ three to ten workers and are very sparse at present.

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Large scale cassava processing is virtually non-existent in Nigeria. Large-scale operations are
enterprises employing 10-30 or more labourers. Large-scale operations would also have the capacity for
large tonnage processing with wider marketing opportunities.
Medium to large scale cassava processing equipment and fabricators of this equipment are few and far
between in Nigeria. Garri is the only product that is currently able to push the industry from a traditional to
a semi-mechanized process. Table 2 below shows daily cassava processing capacity by product and scale of
operation in Nigeria.


Table 2. Daily processing capacity by scale of operation and product (Reproduced from [4])

The need for innovative cassava processing technologies is enormous. Traditional cassava
processing has a number of undesirable attributes. It is time consuming, provides low yields and lacks
storage capacities. Time is spent peeling roots, washing, soaking, wet sieving and copiously adding water
before pressing.

3.
Cassava utilization in food industries
Most industrial processing of cassava is to produce starch and its by-products. Adhesives are made
from cassava starch using simple technologies. These include gums made by gelatinizing starch by heat
treatment without any additives and those made by adding different materials.
Starch is a polymer of glucose and hence it is the raw material for glucose. The hydrolysis of starch
to glucose can be carried out by acid hydrolysis or enzyme hydrolysis. Starch is suspended in water
approximately 25-30% solids, and sufficient HCL is added to bring it to a normality level of 0.01 – 0.02
HCL. It is heated in a converter under a pressure of 0.35kg/cm2 for 15minutes and temperature range of
140-1600C [5]. Glucose syrup is used widely in the confectionery and pharmaceutical industries.
Fructose syrup has gained importance in view of the harmful effects of synthetic sweeteners.
Fructose is four times sweeter than glucose and the conversion of glucose to fructose can be achieved by
alkali or by the enzyme glucoisomerase. Maltose is a disaccharide formed from two glucose units and is a
reducing sugar. It can be obtained commercially from starch by enzyme treatment.
The process of producing starch-based plastics involve mixing and blending starch with suitable
synthetic polymers as stabilizing agents and suitable amount of appropriate coupling, gelatinizing and
plasticizing agents.
The Federal Government of Nigeria put in place a policy of ten percent inclusion of High Quality
Cassava Flour (HQCF) into wheat flour for Bakery and Confectionery. This policy created a huge demand
for HQCF by flour millers. However the government could not properly enforce the compliance of this
policy as a result of inadequate supply of HQCF. So also there was a glut of cassava root tubers as a result
of insufficient cassava processing facilities.

4.
Production of cassava flour using flash dryer

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Drying is an energy-intensive process. A pneumatic dryer is used in various branches such as: in
the chemical, ceramic, mining, and food industries for drying grains, tubers and their flours. Pneumatic
drying can be classified as a gas-solid transport system which provides a continuous convective heat and
mass transfer.
A typical example of a pneumatic dryer is the cassava flash dryer. It major components are the
heating chamber, flash duct, cyclone and exhaust fan as shown in Figure 1 below. The lumps of wet
cassava flour are fed into the flash dyer through the feeder. It enters the drying chamber having a 1000
Watts rated heater and an agitator operated by a 3kW electric motor breaks the lumps of cassava mash into
smaller particles. For the drying of cassava residues the transport and heating media is hot air, which is
available through direct heating. The large surface for heat and mass transfer, as well as the high turbulence
and relative velocities lead to high drying rates.
The mixture of the cassava flour passes through the inlet line and then to the flash duct. In the flash
duct, drying take place due to reduction in pressure and the larger space for the air and cassava flour to mix
together. From the flash duct through the inlet line, the mixture of cassava flour and hot air enters the
cyclone.
Due to large pressure drop in the cyclone, cassava flour drops by gravity and the dried product is
then collected at the exit port while hot air proceeds through the exhaust line. Furthermore the dryer needs
only a small installation area and impresses with low capital costs in comparison with other types of dryers.



Flash Duct
Cyclone
Product out
Drying
chamber
Electric motor
Blower


Figure 1: Locally fabricated mini cassava flash dryer




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5.
Experimental results and discussion
Pneumatic drying is generally described by the equations of convective heat transfer. The total
energy input is necessary for: water evaporation, heating up the dry material and heat losses by radiation.
The energy balance shows appropriate relations between the total provided energy, utilized energy, and
heat losses in the drying process. The simplified drying system model is composed of four flows i.e. input
and output of the drying mediums and the input and output flow of the drying material.
The calculation of the drying processes of a given flow rate of drying material leads to the necessary heat
consumption. Therefore the calculation equation energetic balance for a drying process is given by [6]:



'
'
'
'
Q
= Q
+ Q
+Q
)
1
(
Total
Evap.
Mater.
Loss
'
Where, Q
= Total heat supplied (kJ/s)
Total
'

Q
= Heat for water evaporation
Evap.
'

Q
= Heat for heating of drying material
Mater.
'

Q
= Heat loss
Loss
'
Q
= . '
c m . ? ??
Mater.
( 2 1)
(2)

Where, c = specific heat capacity of the material (kJ/Kg0K)
'
m = quantity of moist material before drying (kg/s)
? ,? = temperature of the material before and after drying (0C)
1
2
The quantity of drying air m3/s is given by
'
Q
'
V
Total
=
( )
3
c (t ? t )
p
1
2
c = specific heat capacity of air (kJ/Kg0K)
p
t = Air temperature at the inlet of the dryer (0C)
1
t = Air temperature at the out of the dryer (0C)
2
Specific heat consumption in kJ/kg is given by:
'
Q
q
Total
=
(4)
'
W
'
Where, W = quantity of evaporated water (kg/s).

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During testing of the flash dryer, at the drying chamber temperature of 900C, a sample of 125.6g
of cassava mash is fed into the chamber through the feeder. Three passes of the sample was carried out and
the percentage drying per pass is calculated:
Initial mass of cassava mash before drying M = 125.6g
i
Mass of cassava flour after 1st pass M = 58.7g
1
(M ? M )
Percentage dryness after 1st pass
i
1
D =
%

1
(5)
M i
D = 53.2%
1
Mass of cassava flour after 2nd pass M = 55.3g
2
Therefore percentage dryness after 2nd pass D = 2.7%
2
Mass of cassava flour after 3rd pass M = 53.3g
3
Percentage dryness after 3rd pass D = 1.2%
3
Hence, 57.1% dryness was achieved after three passes of operation. The mass of cassava flour after the 3rd
pass was then oven dried to remove the remaining moisture content of the flour.
Mass of cassava flour after oven drying M = 41.2g
4
Percentage dryness after oven drying D = 10.03%
4
The dryness curve for the drying operation in the flash dryer is shown in Figure 2 below.

Figure 2. Dryness curve for cassava flour in the flash dryer



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6.
Conclusion
The parameterization, development and testing were carried out for a mini cassava flash dryer.
The percentage of dryness achieved after three passes of cassava mash through the flash dryer was 57.1%.
There is a greater need for improvement in component designing, assembly and testing over a period of
time.
If cassava is processed and sold only at the primary level, the prospects for cassava as a source of
income are limited. Nigeria has demonstrated the importance of cassava as more than a mere subsistence
crop, and that a large volume industrial processing system can be developed around this crop. Value
addition to cassava is a gradual process and long term survival will necessitate that higher value cassava
flour be developed to meet local and international demands.


7.
References
[1]
IITA (International Institute of Tropical Agriculture). “Preemptive management of the virulent
cassava mosaic disease through an integrated cassava development approach for enhanced rural
sector economy in the south-south and south-east zones of Nigeria”. IITA, Ibadan, Nigeria, July,
2003.
[2]
FAO. “Integrated cassava project”. Food and Agricultural Organization (FAO), December, 2006.
Available at www.fao.org . Accessed on 12th December, 2008.
[3]
Raw Materials Research and Development Council (RMRDC), Abuja. “Report On Survey Of
Selected Agricultural Raw Materials In Nigeria”. October, 2004.
[4]
T. P. Phillips, D. S. Taylor, L. Sanni & M.O. Akoroda. “A cassava industrial revolution in
Nigeria: The potential for a new industrial crop”. FAO, 2004.
[5]
C. Balagopalan. “Cassava Utilization in Food, Feed and Industry”. Journal of Scientific and
Industrial Research. 1996.
[6]
N. D. Tung & D. Steinbrecht. “Modeling a Combined Heat and Power Cogeneration system in
Vietnam with a Fluidized Bed Combustor Burning Biomass”. Agricultural Engineering
International: the CIGR Ejournal. Vol. X. December, 2008.

3/10/2009

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