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26
International Journal of
Science and Engineering Investigations vol. 3, issue 26, March 2014
ISSN: 2251-8843
Design of a Combined Groundnut Roaster and Oil Expeller
Machine
Olawale J. Okegbile1, Abdulkadir B. Hassan2, Abubakar Mohammed3, Osigbodi Obajulu4
1,2,3,4Department of Mechanical Engineering, Federal University of Technology, Minna, Nigeria
(3a.mohammed@futminna.edu.ng)
Abstract- This paper presents the design of a combined
groundnut roaster and oil expeller machine. The designs
consist of two distinct units: the roasting and expelling units.
The components design includes the hopper, machine
capacity, casing, conveyor trays, vibrator motor, heating
filament, shaft diameter, auger, belt length and velocity of
electric motor. The various units were combined so as to
remove the drudgery and constraints associated with having to
do the roasting and expelling processes separately. This
combination makes it portable and reduces space.
Keywords-Design, Groundnut, Groundnut Roaster, Oil
Expeller,
I. INTRODUCTION
Groundnut (Arachis hypogea) is a member of the
Papilionaceae and is the largest and most important member of
the Leguminosae [1, 2]. It originated from Latin America and
was introduced into West Africa by Portuguese traders in the
16th century. The origin of this crop dates back to 350BC [3].
The first probable domestication of groundnut took place in the
valley of the Panama and Paraguay River systems in the grain
Chiaco area of South America and then moved to the North
America through slave trade. Major groundnut zones are the
Sudan and Northern Guinea Savanna where the soil and agro
climatological conditions are favorable. Groundnut requires
500 to 1600mm of rainfall, which may last for 70 to 200 days
of rainy season in the Sudan Savanna. It also requires well-
drained light colored, loosed friable sandy loam soil, optimum
moisture in pod zone and mean daily temperature of about 300
[3]. The rainfall should be well distributed during the flowering
and pegging of the crop.
The production of oil from groundnut involves a post
processing of groundnut which includes shelling, roasting and
pressing. Several groundnuts shelling machines has been
fabricated [4, 5]. Roasting reduces moisture content and
develops a pleasant flavor which makes the products more
acceptable for consumption [6]. Roasting also enhances better
extraction as it reduces the oil’s viscosity, releases oil from
intact cells and reduces the moisture content. The amount of oil
produced will be much if it is properly roasted. However,
excess heating during roasting results in low nutritional quality
of protein. It also reduces the quantity of oil as well as it makes
the colour of the oil extracted to be dark [7].
In many part of the world, groundnut oil has proved to be a
very valuable product with universal demand. The possible
income from groundnut oil extraction is therefore often enough
to justify the relatively high cost of setting up and running a
small scale oil businesses. However, interest in small to
intermediate scale oil seed processing on the part of farmers
grew dramatically in the last decade. Various small scale
techniques are available to ensure people in rural areas to
process their own oil seeds locally. Careful consideration is
needed to select the systems that will best suit the local
circumstances. These circumstances include the scale of
operation required, the availability of power sources and a
number of other factors [6].
Some of the roasting machines in used include a manually
operated rotating drum that is heated externally. The drum is
housed in a brick and clay construction, similar to a scale
bakery oven. For uniform roasting, the drum is rotated
continuously throughout the process. The drum roaster consists
of two drums. The outer drum is fitted to the brick work. The
inner drum is made in form a drawer that is detachable for
loading and unloading the groundnut [8]. A high intensity pulse
infrared radiation for roasting groundnut was also reported [9].
Due to the radiation, it has optimum product quality in terms of
colour, texture and free acid content. This method of roasting
yields increased oil compared to previous methods as well as
better oil quality. However, the cost of setting up a pulsed
infrared roaster is exorbitant [2]. Batch roasters offers the
advantage of adjusting for different moisture contents of
groundnut lost from storage. Batch roasters are typically
natural gas-fired revolving oven (drum-shaped). Continuous
dry roasters vary considerably in type. Continuous roasting
labour, ensures a steady flow of groundnut for other processes
and decreases spillage. The continuous roaster move groundnut
through oven on a conveyor tray by gravity feed. In this
system, the groundnut is agitated to ensure that air passes
around the individual kernels to promote an even roast [2].
Some groundnut oil expelling machine has been produced [10-
12].
Roasting of this crop and extraction of oil from this crop
has however been a serious issue to its processing. Machines
which could combine roasting of the nut and expelling of the
oil from the nut are not commonly available. In some rural
International Journal of Science and Engineering Investigations, Volume 3, Issue 26, March 2014
27
www.IJSEI.com Paper ID: 32614-06
ISSN: 2251-8843
parts of the country, roasting and extraction of the oil is
achieved by traditional method. This process is very slow,
tedious and time consuming considering the present level of
production. In order to sustain the increase in oil production
from groundnut, there is the need to improve on the technology
especially at the rural level. There is usually a problem when
several units of the oil processing operations are separated. The
time taken to move the raw materials from one unit to another
is sometimes enormous. Apart from that, the labour required to
man these separate unit also add to the cost of production.
However, if some of these units can be integrated it can
generally enhance the efficiency of the entire process. It is in
view of these that the present study is to carry out a combine
roasting and expelling units of a groundnut oil processing into
a single unit.
II. COMPONENTS DESIGN
The design of the machine consists of a roasting and
expelling units. Figure 1 below shows the combined groundnut
roaster and oil expeller machine.
Figure 1. Combined groundnut roaster and oil expeller machine
A. Roasting Unit
The roasting unit consists of the hopper, conveyor trays,
vibrator motor, cabinet (casing) and lagging materials,
bearings, heating filament, frame and exhaust.
1) Determination of Hopper and machine capacity
The volume of the hopper is derived from the expression
(1)
The machines capacity in volume per hour is given as
(2)
Where, is the machine capacity ( ; is the
roasting time of groundnut (hr); is density of groundnut
(kg/m3) and is the mass of the groundnut (Kg).
Using equations (1) and (2), the volume of hopper
is , the density of groundnut was determined
experimentally as 983.5kg/m3, and the roasted time of 3kg of
groundnut to be 30 mins, the machines capacity obtained using
equation (1) and (2) is .
2) Determination of Power Required To Roast Groundnut
The power of the heating element that is required to roast
the groundnut must be sufficient to withstand heating process.
The power required to roast groundnut is given as
(3)
The quantity of heat required to roast the groundnut is
giving as
(4)
Where, P is the power required; Q is the quantity of heat
required to heat the groundnut (KJ); t is the time it takes to
roast the groundnut (t); M is the mass the groundnut (Kg); c is
the specific heat capacity (KJ/kg/K); T1 is initial temperature
and T2 is the final temperature.
For 30kg mass of groundnut and a temperature range of
300C to 900C, the power required calculated from equation (3)
and (4) is 1.5KW and resulted in the selection of a heating
filament of 1.8KW to account for factor of safety of 20%.
3) Determination of Heat Loss
The amount of heat loss through the inner wall of the tank
and the insulators to the environment is given as:
(5)
The thermal resistance of the material used is given as
(6)
The area of the mild steel is given as:
(7)
The area of the insulating material is given as:
(8)
Where, q is the heat transfer rate (W); is the change in
temperature (0C); is the total thermal
resistance (ohms); is the thickness of the materials (m); Ai is
the areas (m), Ki is the thermal conductivity of the materials
International Journal of Science and Engineering Investigations, Volume 3, Issue 26, March 2014
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www.IJSEI.com Paper ID: 32614-06
ISSN: 2251-8843
(W/m), is the area of mild steel (m2), is the area of
insulator (m2), is the breadth of mild steel material (m), is
length of mild steel (m), is the breadth of insulating material
(m) and is length of insulator material (m).
Given that the thermal conductivities of mild steel and
insulator are respectively 42.9W/m and 0.04W/, the total
thermal resistance obtained from equation (6) is 3.29.
With a temperature difference of 600C and thickness of
insulating material and mild steel are 25mm and 2mm, the
values obtained for the heat transfer rate from calculation using
equations (5) to (8) above is 18.24W.
4) Determination of Power Required to Vibrate Trays
The power required to vibrate the trays is given as
(9)
And
(10)
Where, is the power required to vibrate trays (W); M is
the vibrator Mass (Kg); r is the radius of mass (m); is the
angular velocity (rad/sec) and is the revolution per minute
(rpm).
Given that N is 3000 rpm, radius of mass is 0.05m and the
vibrator mass is 1.4kg, the power required to vibrate the trays
using equation (9) and (10) is 22W.
5) Determination of Angle of Inclination of Conveyor
Trays
The angle of inclination of conveyor trays is given as
(Douglas, 2001):
=
(11)
Where, is angle of inclination and the angle of repose.
Given that the angle of repose is 30, the angle of
inclination calculated from equation (11) is 5.
B. Oil Expelling Unit
1) Determination of shaft diameter
The diameter of the shaft is calculated from the relationship:
(12)
a) Torsional moment
The torsional moment is given as:
(13)
The angular velocity of the shaft is given as:
(14)
(15)
b) Bending moment
The bending moment of the shaft is determine by
considering the forces acting on the shaft. The total loads on
shaft are the load due to the hopper, groundnut collector and
the gear.
The load due to the hopper and groundnut collector is given
as:
(16)
Where,
(17)
And
(18)
The load due to the gear is defined as
(19)
Where,
(20)
Where, d is the shaft diameter (m), P is the power of motor
(kw), is angular velocity (rad/s), is the Maximum
torsional moment (Nm), is the Maximum bending moment
(Nm), N is the speed of shaft (rpm), Ss is the allowable stress
(, is the combined shock and fatique applied to
bending moment (1.5), is the combined shock and fatique
factor applied to torsional moment (1.0), Wh is the total weight
of groundnut collector (N), Wv is the vertical load of gear (N),
ρ is the density of roasted groundnut (kg/m3), m is the mass of
metal sheet (kg), DG is the diameter of gear (m), is the total
volume (m3).
c) Shaft diameter
Given that P=0.746kw, N= 60 rpm, DG=250mm, ρ
=983.4kg/m3, m=1.802kg, . The diameter
of the shaft is calculated using equations (12) to (20) as 29mm.
2) Determination of Auger Capacity
The surface area of the Auger where pressure is exerted
most is given as;
(21)
The force required for extraction is given as;
F (22)
International Journal of Science and Engineering Investigations, Volume 3, Issue 26, March 2014
29
www.IJSEI.com Paper ID: 32614-06
ISSN: 2251-8843
Tangential Force
(23)
Where,
(24)
and
(25)
Pressure developed at the expelling end by the auger ,
(26)
The pressure generated equals the maximum pressure that
is required to expell oil in a continuous expeller. Hence the
auger will expell oil.
The Torque required is given as;
(27)
The capacity of the auger is given as;
(28)
The mass is given as:
(29)
The minimum power requirement of auger is given as;
(30)
Where; Px is the mean Pitch of shaft (m), μ is the
coefficient of friction (0.2), L is the length of shaft (m), Q is
the Capacity of Auger (), W is the bulk weight of groundnut
(N/m3), F is the material factor = 0.3, minimum power
requirement (), ρ is the density of material (kg/m3), T is the
torque required, dmean is the mean diameter of the auger (m), D
is the diameter at the auger’s feeding end (m), d is the diameter
of the auger’s expelling end (m), Ft is the tangential Force (N),
N is the speed (rpm), A is the cross sectional area of the auger
(m2), m is the mass of the auger (kg), V is the volume of the
auger (m3), F is the force required for extraction, and P is the
maximum pressure to expell oil ().
Given that P = 13.6 , d=40mm, D = 50mm,
dmean=45mm, N=60rpm, ρ=983.4kg/m3, L=0.45m and
Px=30mm, using equations (21) to (30), the minimum power
requirement of auger is 374.7Watts (with factor of safety 1hp
motor rating is used) and the Capacity of the auger is 0.288
m3/hr.
3) Casing Design
The surface area of the casing is given as:
(32)
The Volume of the casing is given as:
(33)
a) Thickness of the casing;
The casing was constructed considering its thickness to
withstand the increase in pressure with depth due to increase in
area.
(34)
Where P is the Maximum pressure on the casing (Mpa), d
is the internal diameter of casing where pressure is highest
(m), Sh is the tensile strenght of the material (Mpa), is the
thickness of the casing (m), is the surface area of the casing
(m2), is the Volume of the casing (m3), is the length of
casing (m), is the radius of larger end (m) and r is the radius
of smaller end (m).
Given that Sh =450Mpa, d= 60mm and P=23.6Mpa, the
volume and thickness of the casing are and
mm.
4) Design for Belt Drive
a) Length of Belt
The Length of Motor-Gear box Belt is given as:
(35)
The centre distance between the motor pulley and the gear
box shaft pulley is given as:
(36)
Where, L is the length of Belt (m), C is the centre distance
between the motor pulley and the gear box shaft pulley (m), D1
is the diameter of gear box pulley (mm) and D2 is the Diameter
of motor pulley (m).
Given that D1 =30mm and D2 =60mm, the length of Motor-
Gear box Belt is 294.3mm. A belt of 300mm was selected.
b) Determination of the Velocity of Motor – Gear Box
Belt
The velocity of the belt can be determined by using the
expression
V
(37)
International Journal of Science and Engineering Investigations, Volume 3, Issue 26, March 2014
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www.IJSEI.com Paper ID: 32614-06
ISSN: 2251-8843
Where, V is the velocity of the belt (m/s), is the speed of
the motor pulley (1500rpm), and is the diameter of the
motor pulley (60mm).
Given that =1500rpm, and = 60mm, the velocity of
the belt is
c) Determination of the Angle of Contact of Belt
between the Motor and Gear Box Pulleys
The angle of lap of the belt between the two pulleys can be
calculated from the expression below
(38)
Such that
(39)
Where, is the angle of contact of the belt between the two
pulleys (rad), is the radius of the Gear Box pulley (m), is
the radius of the motor pulley (m) and is the centre difference
between the two pulleys (m).
Given that =15mm, =30mm and =75mm, the angle of
contact of belt between the motor pulley and the gear box
pulley is .
d) Weight of Pulley
The weight of gear box pulley is expressed as:
(40)
Where, W is the weight of the drum pulley (N), m is the
mass of pulley () and g is the acceleration due to gravity
(2). The weight of the gear box pulley is N
III. CONCLUSION
The design of a combined groundnut roaster and oil
expeller machine has been presented. The components design
includes the hopper, machine capacity, casing, conveyor trays,
vibrator motor, heating filament, shaft diameter, auger, belt
length and velocity of electric motor. The machine was
designed for a capacity of for a 3kg of
groundnut.
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