Performance characterization and optimization of a ...

Received: 27 July 2016

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Revised: 14 October 2016

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Accepted: 31 October 2016

DOI 10.1111/jfpe.12523

REVIEW ARTICLE

Performance characterization and optimization of a synchronized medium-scale oil palm fruit processing mill T. Afolabi Morakinyo1 | A. Isaac Bamgboye2 1 Department of Food Science and Technology, Obafemi Awolowo University, Ile-Ife, Nigeria 2

Department of Agricultural and Environmental Engineering, University of Ibadan, Ibadan, Nigeria Correspondence Afolabi Tunde Morakinyo, Department of Food Science and Technology, Obafemi Awolowo University, Ile-Ife, Nigeria. Email: [email protected]

Abstract Previous studies revealed that sterilization, digestion, and mechanical oil extraction have not been fully mechanized in Nigeria. A synchronized medium-scale oil palm fruits processing mill consisting of a boiler, sterilizer, inclined screw conveyor, digester and screw-press was developed. Prominent cultivars of Dura and Tenera fruitlets of 20, 30, and 50 years of age were selected for the evaluation of this mill. In this study, the performance evaluation of the unit operations of this mill was characterized. Surface response methodology was employed using STATISTICA Release 7 model: STA862D175437Q to optimize the mill throughput, efficiency and oil yield. The result showed that, the performance efficiency and throughput of boiler, sterilizer, inclined screw conveyor, vertical digester and twin-cam screw-press were 71.3% and 55.0 L/h, 70% and 75.4 kg/h, 72.7% and 70.2 kg/h, 85.4% and 152.4 kg/h, 83.0% and 190.0 kg/h, respectively. The synchronized mediumscale oil palm processing mill had the optimum throughput, efficiency and oil yield of 80.35 kg/h, 84.70% and 29.28%, respectively.

Practical applications About 90% of annual palm oil production in Nigeria is still being processed with traditional and small-scale methods across twenty four oil palm producing states. Over 40 million of rural women and small-scale oil palm processors were grossly burdensome with lack of appropriate indigenous technology. It has been reported that about 140 of indigenous fabricators were involved in producing machines for small-scale processors both in Nigeria and Ghana including palm oil research institutes, without developing a synchronized mill that can enhance productivity, timeliness and oil yield (Elekwachi, Fadare, & Owolarafe, 2012; PIND, 2011). The unit operations of small-scale mills were usually separately installed without instrumentation devices to regulate their processing parameters for optimum oil yield. In this synchronized medium-scale oil palm fruits processing mill, fresh oil palm fruits were fully sterilized using the superheated steam generated from biomass fire-tube vertical boiler which was synchronized with sterilizer. The sterilized fruits were conveyed through inclined screw-conveyor to the steam jacketed digester, which was connected to the twin-cam screw press for the hot extraction processing operation. It is a continuous and full sterilization mill, which has increased oil yield tremendously from 17.8% to 29.3% for Tenera cultivar fruitlets. This study presented technical information in term of mill equipment efficiency and throughput; likewise, the type of cultivar and age of palm fruit that enhances overall optimum mill efficiency and oil yield.

1 | INTRODUCTION

on the manufacturing of indigenous mechanized palm oil processing plant in Nigeria without the advent of a synchronized medium-scale oil

The major challenge confronting oil palm sector in Nigeria includes

palm fruits processing mill (Babatunde, Ajibola, & Ige, 1988; Badmus,

non-availability of appropriate indigenous technology for harvesting

1991; Owolarafe, Faborode, & Ajibola, 2002; Morakinyo & Bamgboye,

and processing (Elekwachi, Fadare, & Owolarafe, 2012; PIND, 2011;

2016). However, optimal design for up-grading small-scale oil palm

Salako, Owolarafe, & Anozie, 2014). Concerted efforts have been made

processing machines to medium-scale level has not being reported.

J. Food Process Eng. 2016; 1–9

wileyonlinelibrary.com/journal/jfpe

C 2016 Wiley Periodicals, Inc. V

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F I G U R E 1 Palm oil extraction methods in Nigeria. (a) Cook of oil palm fruits using metallic drum (traditional method at Agbogbo mill, Osun State). (b) Leg maceration of cooked oil palm fruits using earth dug-pit (traditional method at Agbogbo mill, Osun State). (c) Digestion and cold oil extraction using digester cum mono-screw-press (small-scale method (NIFOR, Edo State).

Hitherto, virtually all operations in traditional and small-scale oil palm

Tenera) of 20, 30, and 50 years of cultivation to justify the capability of

fruit processing methods exist in scattered units which make the oper-

bridging the gap between the small-scale and large-scale methods tech-

ation cumbersome, unhygienic, time consuming and inefficient and

nologically. More importantly, the overall optimum mill efficiency,

more man-power is required for the movement of materials manually

throughput and oil yield will also be established. In this innovation, ster-

(Figure 1). Other challenges associated with these methods are local-

ilization and digestion of the fruits include oil extraction will be fully

ized sterilization, high production and maintenance costs, energy con-

mechanized under controllable processing parameters; hence all unit

sumption, un-friendliness due to heat losses to human and ecosystem

operations will be sterilized to enhance quality and quantity palm oil,

coupled with inconsistent in the qualities such as physico-chemical,

while the whole operations will be continuous, dry and clean

nutritional, textural and organoleptic properties (Amata & Ozuor, 2013;

technology.

Faborode, 2003; Orewa, Adakaren, Ilechi, & Obulechi, 2009; Salako et al., 2014). Unfortunately, about 90% of annual palm oil production in Nigeria is still being processed by about 4 million traditional and smallscale processors, majorly women rural dwellers across twenty four oil

2 | MATERIALS AND METHODS 2.1 | Materials

palm producing states (FAO, 2002; Elekwachi et al., 2012). It is envisaged that a synchronized process mill will be most appropriate in this

The design of aforementioned mill equipment, fabrication techniques,

context considering the dire need for self-reliance and techno-agro-

materials selection for their construction, and the pressure testing of

industrial development in Nigeria. This technological intervention will

kettle, steam chambers, sterilizer tank were done by adopting local

eliminates aforementioned challenges at affordable cost using local

content approach and in accordance with British Standard (BS 3274),

content approach Therefore, there is an urgent need to evaluate the

and standard of American Tubular Heat Exchanger Manufacturers

performance of a newly developed synchronized medium-scale oil

Association (TEMA) specifications (Coulson & Richardsm, 1983;

palm fruit processing mill using two commercial cultivars of palm fruits

Morakinyo 2014, Morakinyo & Bamgboye, 2016). The performance

(Tenera and Dura) to justify the innovation performances an appropriate

evaluation of the newly developed synchronized mill was carried out

indigenous technology. However, this mill comprises of a vertical bio-

using fresh fruit bunches of Dura and Tenera cultivars sourced from

mass fire-tube boiler, sterilizer, inclined screw conveyor and steam

three different oil palm plantations in Nigeria. These plantations were

jacket digester, twin-cam screw press and crude oil tank (Morakinyo &

selected based on the years of their oil palm trees cultivation. The first

Bamgboye, 2016). The machine characteristics were evaluated such as

plantation was Agbongbo village via Obafemi Awolowo University

oil yield, thermal efficiency, throughput and operation efficiency as

Research and Training Farm, Ile-Ife, Osun state, followed by Elere

applicable to each unit operation and the entire mill for the rating.

Adubi Oil Palm Mill, Itori, Ogun State and lastly the University of Iba-

Hence the main objective of this work is to evaluate the machines

dan Teaching and Research Farm, Ibadan, Oyo State. These plantations

characteristics of this newly developed synchronized medium-scale oil

have been cultivated for three different ages: 20, 30, and 50 years,

palm fruits processing mill using two palm fruits cultivars (Dura and

respectively. Fresh fruit bunches (FFB) obtained from these plantations

MORAKINYO

FIGURE 2

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Assembly drawing of a synchronized medium-scale oil palm fruits processing mill

were axed then mulched for 4 days after harvesting, followed by strip-

bution of superheated steam pressure and temperature, which enhan-

ping, screening and washing of fruitlets to remove dirt, stones, and

ces heat penetration during sterilization. But in both traditional and the

other extraneous materials. A sample of fresh oil palm fruits of 40 kg

small-scale mills equipment, there is no boiler, but metallic drum sus-

was taken from each age of cultivations (20, 30, and 50 years) across

pended on stones was usually adopted to cook the palm fruit (Figure

each cultivar to form six samples. The machine evaluation was run in

1a), then after cooling, the fruits will be macerated inside earth dug pit

triplicate for accuracy and effective determination of machine charac-

using legs followed by foaming and descanting of emulsion for separa-

teristics in terms of each unit operation efficiency and throughput.

tion of oil by cooking (Figure 1b). In the small-scale, cooked fruitlets maceration and cold oil extraction were done using the digester cum

2.2 | Machine installation and performance

mono-screw-press (Figure 1c). With the installation of the instrumenta-

evaluation procedures

tion devices, each unit operation of the synchronized medium-scale

The mill equipment consisting of vertical biomass fired fire-in-tube boiler, vertical sterilizer, inclined screw conveyor, steam jacketed digester, twin-cam screw-press and crude oil tank were developed

mill was evaluated using two cultivars of oil palm fruitlets namely: Dura and Tenera of three levels of age of cultivations: 20, 30, and 50 years. The experimental design adopted was 2 3 3 factorial randomized complete block design in three replicates to determine an average value of

(Morakinyo, 2014) and installed at Department of Agriculture and Envi-

each machine characteristics (efficiency and throughput) and likewise

ronmental Engineering, Faculty of Technology, University of Ibadan

optimum mill efficiency, throughput and oil yield were established

was adopted for this study. It is synchronized mill installed in a single

using cultivars and age of the oil palm fruits by employing STATISTICA

line product layout pattern to reduce man power requirement for opti-

Release 7 model: STA862D175437Q.

mum handling, efficiency and timeliness operations. The installation was done by grouting the individually machine on a concrete floor of 3.0 m 3 4.5 m inside a constructed half-wall block shield roofed build-

2.3 | Mode of operation

ing not in scattering pattern unlike traditional and small-scale mills

2.3.1 | Fire-in-tube boiler

equipment. This was done to eliminate drudgery, high production cost,

Prior to the evaluation of the boiler, the calorific values of biomass of

high energy consumption and un-friendliness associated with tradi-

Dura and Tenera cultivars were (Kernel shell and Fiber) measured as

tional and small-scale mills. After seven days of concrete curing, the

heat source for the boiler operation (Table 2). The calorimeter was

instrumentation devices such as thermometers, pressure gauges and

used to establish the cultivar of higher calorific value even at equal

pressure relief valves were installed on machines (Figures 2 and 3) to

weight for the economy reason. Hence the biomass of Dura cultivar

regulate the processing parameters. The localized sterilization associ-

was used for the boiler evaluation. Then the boiler was filled with

ated with small-scale mill was eliminated through the vertical sterilizer,

100 L of cold water at ambient temperature of 28 8C (wet-bulb) during

which is a pressure vessel (Figures 2 and 3). This enables uniform distri-

the each run of the experiment. Then the inlet and outlet gate valves

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FIGURE 3

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A complete synchronized medium -scale oil palm fruits processing mill

were closed, while its furnace was loaded with 20 kg of Dura biomass

The throughput of the boiler was calculated as the average value

composite of a pre-determined calorific value of 504.60 MJ and then

of total superheated steam generated for six experiments. The equa-

ignited (Table 2) likewise on each experimental run. The boiler devel-

tion for the determination of the throughput is depicted below:

oped super-heated steam of properties of 5.5 bar at 155 8C within 60

Throughput 5

min of Dura biomass combustion. The total volume of the superheated steam generated was discharged for sterilization, digestion and hot

Xn i51

Can ni

(2)

where: Ca 5 Throughput

extraction during each experiment. The volume of un-converted water into steam was discharged and measured using graduated plastic

2.3.2 | Vertical sterilizer

pocket of 20 L. According to Rasul & Tappenden (2006), prescribed by

The giant gate valve was closed completely so that the sterilizer could

the ASME Power Test Code, PTC 4.1 and Rasul et al. (2006), the ther-

operate as a close vessel. Then the vertical sterilizer was loaded with

mal efficiency of an insulated boiler using coal can be estimated by

fruitlets Dura and Tenera consecutively of 40 kg through its hopper.

considering that 69.34% to 70.46% of the gross calorific value utilized.

The hopper cover was air-tight with the help of lagging material and

Therefore, the fire-in-tube boiler was evaluated in terms of thermal

fasteners to avoid heat loss. Hence, superheated steam from the fire-

efficiency and throughput using Equation 1 propounded by Rasul et al.

in-tube boiler was discharged into the vertical sterilizer through its

(2006).

inner spraying nozzles. The retention period of 50 mins was observed

Boiler thermal efficiency 5

Qðhg 2 hfÞ 3 100 1 9:65% 0:69 3 q 3 GCV

before discharging the sterilized fruitlets into the digester through (1)

inclined screw conveyor. The throughput was measured by filling the sterilizer tank with water; volume of water discharged at maximum

(Rasul et al., 2006) where: Q 5 quantity of superheated steam generated in an hour (MJ/kg); q 3 GCV 5 energy content of biomass composite burned MJ/ kg;

hg 5 enthalpy

of

superheated

steam

generated

(kJ/kg);

height was multiplied with average bulk density of oil palm, while the efficiency was determined using Equation 3. Performance efficiency 5

hf 5 enthalpy of cold water fed into the Boiler (kJ/kg) at ambient tem-

Output of sterilized fruitlets 3 100% Input of sterilized fruitlets (3)

perature on wet bulb condition. TA BL E 2

Comparison of thermal properties of Dura and Tenera cultivars biomass

Shell

Biomass composite (MJ/kg)

Biomass composite of 20 kg MJ

40

20

25.23 6 1.2

504.60 6 4.3

40

20

24.86 6 2.5

497.28 6 3.8

Biomass composite (%) Sample of biomass composite

Wood

Fiber

Dura biomass 1 N3

40

Tenera biomass 1 N3

40

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2.3.3 | Inclined screw conveyor

Extraction efficiency 5

At the end of each sterilization operation, sterilized fruitlets were discharged into the inclined screw conveyor through giant gate valve orifice into steam jacketed digester on running condition. The inclined

5

Oil yield 3 100% (9) Oil content of palm fruitlets

2.3.6 | The synchronized medium-scale oil palm mill

screw conveyor was driven with 2 hp gear motor and of the speed of

This medium-scale mill has a total length of 3.5 m, breadth of 2.0 m

50 rpm. The characteristics of this machine in terms of throughput and

and height of 2.3 m (Figure 2). The entire mill performance was eval-

efficiency were calculated using Equations 4 and 5.

uated at the end of each consecutive milling operation in terms

Throughput 5

  Quantity of sterilized fruitlets discharged kg (4) Time taken h

Performance efficiency 5

Output of sterilized fruitlets % Input of sterilized fruitlets

(5)

2.3.4 | Steam jacketed vertical digester The performance evaluation of steam jacketed vertical digester was carried out by opening the steam line coming from the boiler directly to the sterilizer through the gate valve, which fed the inner and outer part of the digester tank. The gear motor of this digester was energized for effective maceration within 5 min operation. The macerated fruitlets were discharged gravitational into the twin-cam screw-press. The

throughput, extraction efficiency and oil yield, using Equations 8, 9, and 12. Oil yield 5

Weight of oil extracted 3 100% Weight of oil palm fruitlets sterilized

(10)

2.4 | Description of synchronized medium-scale palm oil fruits processing mill The complete mill consists of a vertical fire-in-tube boiler, vertical sterilizer, inclined screw conveyor, digester, twin-cam screw-press and crude palm oil tank (Figures 2 and 3) (Morakinyo 2014, Morakinyo & Bamgboye, 2016).

undischarge macerated fruitlets were measured to determine through-

2.4.1 | The vertical fire-in-tube boiler

put and efficiency using the Equations 6 and 7.

This is un-lagged biomass fired, fire-in-tube vertical boiler which was

Throughput 5 Weight of pulp macerated fruitlets discharged Time taken Efficiency 5



 kg h

made of low-carbon steel, having outer dimension of Ө 600 mm 3 (6)

1,450 mm (Figures 2 and 3). It has four compartments namely: combustion chamber, kettle, and hot air chamber and steam tank. The total

Output weight of macerated 3 ð%Þ Input weight of sterilized fruitlets 1 weight of steam

(7)

height of this vertical fire-tube boiler is 2,000 mm.

2.4.2 | The vertical sterilizer This machine was made with low-carbon steel of Ө 600 mm 3

2.3.5 | The twin-cam screw-press

768 mm having six components namely: hopper, end disc cover,

The pulp was fed into the modified twin-cam screw-press (Bamgboye

super-heated steam sprayer, cylindrical tank, cone at the base and

& Morakinyo, 2012) through the inclined chute. The feeding rate of

heavy duty giant gate valve for discharging of the sterilized fruitlets

the pulp was regulated to 1.5 kg/min with the help of digester shutter

(Figures 2 and 3).

to eliminate choking of the screw press. Apparently, the screw-press extracted at a constant speed of 90 rpm, while the optimum extraction ratio and oil yield was maintained through the pressurized cone adjustment to linear displacement position of 110 (mm) (Bamgboye & Morakinyo, 2012). The steam gate valve was opened to discharge regulated quantity of superheated steam to sterilize barrel longitudinally to enhance oil yield. The superheated steam flow rate was regulated to 1.5 L/min with steam temperature ranging between 80 and 100 ( 8C) to enhance optimum oil yield. The extracted emulsions were collected through discharge chute into the crude oil tank intermittently for separation, while fiber and kernel were discharged out of screw-press barrel through the gap between pressurized cones and extreme end of the barrel into the cake collector. The throughput and extraction efficiency were measured using Equations 8 and 9. The emulsions collected were clarified by cooking directly, while floated palm oil were decanted and measured. Throughput5 Quantity emulsion 6 kernel nut 6 firbeo discharged ðkg=hÞ Time taken

2.4.3 | The inclined screw conveyor The inclined screw conveyor is a standard pitch auger made of lowcarbon steel, with hollow pipe material of Ө 150 mm 3 1,500 mm length. It has a driven shaft enclosed inside a hollow pipe called barrel of Ө 150 mm, suspended at both ends with the help of two flange bearings fastened to the barrel cover, driven by 2 hp gear motor of the final speed of 50 rpm (Figures 2 and 3).

2.4.4 | The steam jacketed vertical digester The steam jacketed vertical digester was made of low-carbon steel with inner and outer tanks of Ө 450 3 550 3 5 mm and Ө 500 3 550 3 5 mm respectively (Figures 2 and 3). Digester shaft has four macerated arms and two discharged arms of 200 mm 3 35 mm 315 mm propelled by 2 kW gear motor of a final speed of 150 rpm.

2.4.5 | The modified twin-cam screw-press The complete assemble of modified twin-cam screw-press has a total (8)

dimensions of 500 3 750 3 1,560 mm. It consists of these following working components: barrel housing, barrel, two screw-shafts, two

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188.43 6 3.1

159.10 6 2.0 82.50 6 3.0

186.90 6 3.0 82.70 6 1.3

191.37 6 5.5

164.20 6 5.6

181.70 6 4.5

219.30 6 3.6 84.70 6 1.5

The results of the performance evaluation of the newly developed

82.90 6 1.5

3.1 | The vertical fire-in-tube boiler

82.50 6 5.2

3 | RESULTS AND DISCUSSION

82.70 6 4.2

Twin-cam screw-press

body of these following dimensions: 500 3 400 3 350 mm.

228.20 6 3.8

made of mild-steel plate of 6 mm thickness. It has rectangular shape

83.70 6 4.0

pressurize cones; two cone drive shafts gear box and a sprinkler. This is

Thro. (kg/h)

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Eff. (%)

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synchronized medium-scale oil palm fruits processing mill machines 155.53 6 2.1

136.30 6 1.5

156.90 6 1.3

173.40 6 3.2

149.20 6 4.2

of the boiler to evaluate the thermal efficiency and throughput. There-

135.30 6 5.2

justification of utilizing biomass of the Dura cultivar for the operation

149.40 6 1.3

and Tenera) at 3 consecutive years of cultivations. Table 2 showed the

162.90 6 2.8

Thro. (kg/h)

were showed in Table 1 using two cultivars of oil palm fruitlets (Dura

fore, the optimum biomass combination that was used for the evalua85.23 6 2.6

85.30 6 3.2

85.70 6 3.0

84.70 6 2.8

85.50 6 3.2

85.50 6 3.0

85.70 6 2.4

1 showed that during the processing of Dura cultivar fruitlets (20, 30, and 50 years), the average thermal efficiency was 69.49% while that of

85.30 6 2.0

Digester

whole experiments was biomass of the Dura cultivar. However, Table

Eff. (%)

tion of the thermal efficiency of this vertical boiler throughout the

Tenera cultivar fruitlets (20, 30, and 50 years) was 73.24% using opti72.65 6 2.0 71.33 6 2.5 76.03 6 3.0 57.03 6 7.2 73.25 6 3.3 Average

71.33 6 3.3

63.97 6 2.8 54.00 6 5.4 74.00 6 2.1 52.50 6 1.2 77.20 6 2.0 TA50

52.00 6 3.0

68.30 6 3.3 65.00 6 4.3 77.8 6 2.0 60.50 6 3.1 67.80 6 2.7

67.00 6 3.6

85.68 6 3.5 96.00 6 1.6 76.30 6 3.2 95.00 6 2.3

69.67 6 6.3 74.00 6 2.2 74.70 6 5.8 68.17 6 2.6

61.40 6 4.3 58.00 6 3.0 65.30 6 5.0 54.00 6 7.2

66.60 6 3.5 67.00 6 4.2 78.20 6 4.6 65.00 6 2.1

81.00 6 4.0 97.00 6 1.5 80.50 6 3.7

Eff. (%)

TA30

This limitation could be attributed to the diameter of heavy duty gate

58.10 6 4.8

ning this mill with fruitlets of 20 years will increased the throughput.

74.75 6 4.1

mum throughput than any other years (Table 1). This showed that, run-

TA20

that at 20 years of age Dura and Tenera cultivars fruitlets have maxi-

52.97 6 3.0

attributed to differences in their fruitlets masses. It was also observed

69.49 6 5.0

that of Tenera cultivar fruitlets was 76.03 kg/h. This disparity may be

Average

throughput of sterilizer for Dura cultivars fruitlets was 74.70 kg/h while

51.80 6 3.6

respect to the two cultivars was 70.00%. In Table 1, the average

69.75 6 2.3

30 years. Hence, the mean performance efficiency of this sterilizer in

DA50

Bamgboye (2015) reported that the mass of Tenera fruitlets were almost doubled that of Dura fruitlets most especially from age of 20 to

54.30 6 2.5

cultivar fruitlets was 68.17% while that of Tenera cultivar fruitlets was 71.33%. The disparity may be due to mass differences. Morakinyo &

67.33 6 3.1

From Table 1, the average sterilizer performance efficiency for Dura

DA30

3.2 | The vertical sterilizer

85.50 6 3.2

put of this boiler in respect to the two cultivars was 55.00 L/h.

52.80 6 3.0

with superheated steam than Dura fruitlets. Hence, the mean through-

71.34 6 5.2

lets. In summary, Tenera fruitlets have more voids that were occupied

DA20

of superheated steam during the sterilization of Tenera cultivars fruit-

Thro. (kg/h)

that the sphericity of Dura fruitlets tending toward sphere and higher than Tenera fruitlets. These factors justified the need for more volume

Sterilizer

porosity of Tenera fruitlets was higher than that of Dura fruitlets and

Eff. (%)

(2011). More so, Morakinyo & Bamgboye (2015) reported that the

T A B LE 1

their porosity and sphericity values as reported by Hafiz & Shariff

Summary of performance evaluation of synchronized medium-scale mill machines

measured to be 57.03 L/h. The disparity may be due to differences in

Thro. (L/h)

for Dura cultivar fruitlets as: 52.97 L/h while on Tenera cultivar, it was

Eff. (%)

Table 1 showed the average throughput of vertical fire-in-tube boiler

Boiler

efficiency of this boiler in respect to the two cultivars was 71.37%.

Cultivar

sities values (Morakinyo & Bamgboye, 2015). Hence, the mean thermal

Inclined screw conveyor

attributed to differences in their specific heat capacity and bulk den-

Thro. (kg/h)

mum 504.60 MJ of biomass composite (Table 2). This disparity may be

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valve installed which may be increased to accommodate other fruitlets

extraction is relative to palm nut axial dimension to avoid breakage.

of higher sizes of axial dimensions. Hence, the mean throughput of this

Hence, the mean performance efficiency of the twin-cam screw-press

sterilizer in respect to the two cultivars was 75.37 kg/h.

in respect to the two cultivars was 83.0%. In Table 1, the mean throughputs of modified twin-cam screw-press under hot extraction

3.3 | The inclined screw conveyor In Table 1, the average performance efficiency of inclined screw conveyor was 74% for Dura cultivar fruitlets while that of Tenera cultivar fruitlets was 71.33%. The disparity may be due to their physical properties. Previous researchers reported the same trend that the axial dimensions of Dura cultivar fruitlets are usually lower than that of Tenera fruitlets (Hafiz & Shariff, 2011; Morakinyo & Bamgboye, 2015; Owolarafe & Arumughan, 2007). This may attributed to increase in discharge rate of the Dura cultivar fruitlets showed in Table 1. Hence, the mean performance efficiency of the inclined screw conveyor in respect

were 191.37 and 188.43 kg/h for Dura and Tenera cultivars fruitlets respectively. The disparity may be due their physical properties. This same trend was earlier reported that Dura cultivar fruitlets were of lower axial dimensions compared with Tenera cultivar fruitlets (Hafiz & Shariff, 2011; Morakinyo & Bamgboye, 2015). It was observed that, it took lesser time to extract oil from Dura fruitlets than Tenera fruitlets. This was the reason why, in both cultivars fruitlets of 20 years exhibited higher throughput value than any other year. Hence, the average throughput of the twin-cam screw-press in respect to the two cultivars was 190.0 kg/h.

to the two cultivars was 72.7%. However, in Table 1, the average throughput of Dura cultivar fruitlets was 69.67 kg/h, while that of Tenera cultivar fruitlets was 72.65kg/h. This disparity may be attributed to differences in their fruitlets masses (Morakinyo & Bamgboye, 2015). In this work, Tenera cultivar fruitlets were found weightier than Dura cultivar fruitlets across the ages of cultivation and for almost double in value, definitely, the throughput of Tenera cultivar fruitlets must be higher than Dura cultivar fruitlets (Table 1). Hence, the mean throughput of the inclined screw conveyor in respect to the two cultivars was 70.16 kg/h.

3.4 | The steam jacketed vertical digester

3.6 | The synchronized medium-scale oil palm fruits mill The results of six experimental runs were optimized using three dimensional response surface methodology by employing STATISTICA Release 7 model: STA862D175437Q to determine the optimum throughput, extraction efficiency and oil yield of synchronized medium-scale oil palm fruits mill. The quadratic regression Equations 11 to 13 were developed from response surface plotted graphs of Figures 4 to 6 in order to predict optimum throughput, efficiency and oil yield when the two cultivars were processed. Throughput 5 13692:22 1480:99E2649:19C25:44E2

In Table 1, the average performance efficiency of vertical digester was

1 4:14EC 11:45C2

(11)

85.5% for Dura cultivar fruitlets while that of Tenera cultivar fruitlets was 85.23%. There were no much differences in the performance effi-

Efficiency 5 5394:74 2 88:47C 2 20:61T 1 0:37C2 1 0:17CT 1 0:02T 2

ciencies of digester in both cultivars fruitlets due to the high speed and

(12)

power rating of gear motor of the digester. Hence, the mean perform-

Oil yield 5 2283:48 2 56:38 C 1 13:15E 1 0:17C 1 0:28CE20:25E2

ance efficiency of the vertical digester in respect to the two cultivars

(13)

was 85.38%. In Table 1, the average throughput of vertical digester on

where E is performance efficiency (%), C is cultivars, and T is through-

Dura cultivar fruitlets was 149.2 kg/h while that of Tenera cultivar fruitlets was 155.53 kg/h. From these results, it could be observed that, Tenera cultivar fruitlets were of higher throughput values than Dura cultivar fruitlets. This disparity was due to differences in their fruitlets masses and morphological structures of their palm nuts. This observation was earlier reported by Hafiz & Shariff (2011) confirming that Tenera cultivar fruitlets were fleshier than Dura cultivar fruitlets. Therefore, these factors enhanced increase in pulp of Tenera than that of Dura cultivar fruitlets. Hence, the mean throughput of the vertical digester in respect to the two cultivars was 152.4 kg/h.

3.5 | The modified twin-cam screw-press

2

put (kg/h). In Figure 4, the optimum throughput of this mill occurred during the processing of Tenera cultivar fruitlets of 20 years cultivation having the value of 80.35 kg/h followed by Dura cultivar fruitlets of 20 years. In Figure 5, it was shown that the optimum performance efficiency occurred during the processing of Tenera cultivar fruitlets of 20 years cultivations having the value of 84.70%. This could also be validated by considering Figure 3. But the optimum oil yield could be established by considering Figure 6, which occurred at Tenera cultivar fruitlets 50 years of cultivation, having the corresponding value of 29.28%. However, the maximum oil yield when processing Dura cultivar fruitlets occurred at 50-year cultivation, having the value of 24.00%. In this

In Table 1, the mean performance efficiencies of modified twin-cam

work, it has been established that Tenera cultivar fruitlets has higher

screw-press for Dura cultivar fruitlets was 82.9%, while that of Tenera

values than Dura cultivar fruitlets due to their physical properties vari-

cultivar fruitlets was 83.1%. The disparity may be due their nuts physi-

ability. A comparison of this result with cold extraction of NIFOR/

cal properties. Tenera cultivar palm nuts were reported to be lower in

FAO/UNDP (1981) and Bamgboye & Morakinyo (2012), indicates that,

axial dimensions and mass than Dura cultivar palm nuts (Akinoso &

hot extraction enhances oil yield tremendously. In case of mono-screw

Raji, 2011). Since the pitch of the flight of the screw–press for effective

press of NIFOR/FAO/UNDP (1981), Dura cultivar fruitlets oil yield has

8

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F I G U R E 4 Surface response plot of throughput against cultivars and efficiency

MORAKINYO

FIGURE 6

AND

BAMGBOYE

Surface response plot of oil yield against efficiency and

cultivars improved from 14.8 to 24.00% equivalent to about 63%. Hence, Tenera fruitlets oil yield has increased from 16.80 to 29.28% which is equivalent to about 74%. During the evaluation, it was observed that

12.50%; 35 kg/hr and 80%, and 14.80% for throughput, extraction effi-

as the sterilization temperature increased from 80 to 120 8C, Tenera

ciency and oil yield, respectively (Morakinyo, 2014). In summary this

fruitlets oil yield increased from 26.50 to 29.28%. Previous researchers

mill has throughput, efficiency and oil yield percentage of 80.35 kg/h,

reported the same trends that increase in the sterilization temperature

84.70% and 29.28%. However, it takes an average of 2.5 h to complete

and time during oil expeller operation of palm oil increase the oil yield

a circle of oil palm processing operation in this newly developed

percentage when compared with cold extraction (Mohd Fauzi & Sar-

synchronized medium-scale oil palm processing mill, hence for 8 h/day,

midi, 2011). The influence of sterilization on oil yield percentage

three circles will be achieved. Therefore, this synchronized medium-

increase is obviously expected; since sterilization resulted to heat and

scale oil palm mill has an average throughput of 602.63 kg/day of

mass transfer which enhance oil cells expansion which increase mois-

(fresh fruits) in 8 h milling operation/day with efficiency of 84.70% and

ture adsorption process as well as coagulation of protein (Abbas et al.,

oil yield percentage of 29.28%.

2006; Mohd Fauzi & Sarmidi, 2011). Akinoso, Raji, & Igbeka (2009) reported that compressive stress, feeding rate and speed of rotation of screw shaft influenced the oil yield of palm kernel oil. Olayanju (2002)

4 | CONCLUSION

reported that throughput, oil yield, oil and cake qualities of dehulled beniseed were highly affected by worm shaft speed, moisture content and seed accessions. The result of the performance evaluations of traditional and small-scale oil palm processing mills in Nigeria reported by NIFOR/FAO/UNDP (1981) were found to be: 12.5 kg/hr, 60% and

Conclusively, this mill has reduced man power requirement to two to three mill workers. This was observed during the evaluation; unlike the traditional and small-scale mills. It is capable to process 600 kg of fresh palm fruits into palm oil in a single sterilized process line within 8 h. It also conserved energy and enhanced uniform quality and quantity of palm oil production, likewise timeliness in operation. The result of the machine characteristics showed that, the performance efficiency and throughput of boiler, sterilizer, inclined screw conveyor, vertical digester and twin-cam screw-press were 71.3% and 55.0 L/h, 70% and 75.4 kg/h, 72.7% and 70.2 kg/h, 85.4% and 152.4 kg/h, 83.0% and 190.0 kg/h, respectively. Hence, entire the mill has throughput, efficiency and oil yield percentage of 80.35 kg/h, 84.70% and 29.28%, respectively. The optimum throughput, performance efficiency and oil yield of the mill occurred when Tenera cultivar fruitlets 20 years of cultivation was processed. The limitation of this mill is the size of the sterilizer discharge chute and the gain gate valve installed, therefore only palm fruits 20 years of cultivation could discharge maximally, while others years were at disadvantage due increase in their axial dimensions. The regression model equations established the importance of

Surface response plot of efficiency against throughput and cultivars

FIGURE 5

using Tenera fruits cultivar alone for the operation of the mill for maximum efficiency, throughput and oil yield. However, in this work, it has

MORAKINYO

AND

BAMGBOYE

been established that Tenera cultivar fruitlets has higher values in all machine characteristics. With this innovation, the small-scale palm oil process machines have been up-graded to medium-scale palm oil processing plant in a single line machine process layout, with optimum effi-

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Morakinyo, T. A. (2014). Development and evaluation of a synchronized medium-scale oil palm fruits processing mill (pp. 110–136). Ph.D. Thesis. Department of Agricultural and Environmental Engineering, Faculty of Technology, University of Ibadan, Nigeria.

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