EQUIPMENT DESIGN FOR PREKESE FUNCTIONAL FRUIT DRINK PROCESSING
1 Department of Energy and Environmental Engineering, University of Energy and Natural Resources, Sunyani, Ghana; Department of Chemical Engineering, Faculty of Engineering and Technology, Kumasi Technical University, Kumasi, Ghana
2,3,4,5Department of Chemical Engineering, Faculty of Engineering and Technology, Kumasi Technical University, Kumasi, Ghana
ABSTRACT
The need to design process equipment to produce Tetrapleura tetraptera (prekese) functional fruit drink is necessary in order to meet the needs expressed by customers. These equipment were carefully selected and designed to suit the task each is expected to perform at their various stage functions. The major areas of a process plant needed to produce prekese functional fruit drink have been identified along the production line as fruit preparation, milling, extraction, filtration, evaporation and mixing. The extraction and evaporation unit operations are crucial for obtaining the prekese extract with retained active ingredients needed in the functional fruit drink. This study successfully designed the various equipment needed for the production of prekese functional fruit drink. The equipment design was based on laboratory scale results of producing Prekese functional fruit drink which was operated in a batch mode. The equipment comprised a washer, a cutter, a miller, an extractor, a filter, an evaporator, and a mixer. The equipment were sized and engineering drawings were prepared. Electricity has been identified as the major source of energy to the various unit operations except the evaporator and extractor which are also powered by heat energy. With prekese feed flow rate of 1000 kg/h, the total electrical power requirement was determined to be 88.06 kW and steam power requirement was 55.19 kW. The capacity of the washer, miller, extractor, filter, evaporator and mixer were respectively 56.5 m3, 1020 kg/h, 7.1 m3/h, 5.97 m3/h, 14.13 m3/h and 10 m3/h.
Keywords:Equipment, Prekese, Design, Drawings, Material balance, Power requirement.
ARTICLE HISTORY: Received: 16 November 2017, Revised: 8 February 2018, Accepted: 12 February 2018, Published: 15 February 2018
Contribution/ Originality: This study documents the design of various equipment needed for the production of Tetrapleura tetraptera functional fruit drink. The designed equipment make it possible to process the prekese fruits in order to maintain its antioxidant properties and other health-benefit properties which makes it suitable as a functional fruit drink.
1. INTRODUCTION
Manufacturing equipment usually are large vessels or sections called units or lines that are interconnected by piping or other material or moving equipment which can carry streams of material. Such material streams can include fluids (gas or liquid carried in piping) or sometimes solids or mixtures such as slurries. A chemical plant is an industrial process plant that comprises of various unit operations or equipment that manufactures (or otherwise processes) chemicals, usually on a large scale Ellison-Taylor [1]. Lutz [2] has posited that inherent safety alternatives have become a requirement in companies that understand that, inherently safer equipment have lower lifetime costs and therefore are more profitable.
Industrial equipment for solid–liquid extraction is designed for batch wise, semi continuous or continuous processing [3]. The method of contacting solids with solvent is either by percolation of solvent through a bed of solids or by immersion of the solid in the solvent followed by agitation of the mixture. When immersion is used, counter current, multistage operation is common. With percolation, either a stage wise or a differential contacting device is appropriate. An extractor must be efficient to minimize the need for solvent because of the high cost of solvent recovery [4]. The extraction process may have energy saving possibilities, when solvent recovery is easy as the process can be operated in moderate temperatures and the solvent reused [5]. Some important aspects of extractor selection are costs, availability, chemical stability and nontoxicity of the solvent [6].
In filtration, suspended solid particles in a liquid or gas are removed by passing the mixture through a porous medium that retains particles and passes the clear filtrate [7]. Filtration is performed on screens by gravity or on filters by vacuum, pressure or centrifugation [8]. In cake filtration, the filter medium can be a cloth of natural or artificial fibres or metal [9]. After filtering, the washing of the cake takes place by displacement of the filtrate and by diffusion [7]. Batch filters can be coupled to continuous plant by using several units in parallel, or by providing buffer storage capacity for the feed and product [10]. A guide to filter selection by slurry characteristics is given by Towler and Sinnott [10]. To release the solid particles captured within the bed, the flow is periodically reversed [9].
Evaporators are normally used to produce a concentrated liquid, but a dry solid product can be obtained with some specialized designs [10]. The type of evaporator also affects the overall heat transfer coefficient, being higher with forced circulation than with natural circulation [11]. In long-tube evaporators the liquid flows as a thin film on the walls of long, vertical heated tubes. Both falling film and rising film types are used and are suitable for high capacities and low viscosity solutions [10]. Single-effect evaporators are only used when the capacity needed is small. Multi-effect systems recover and reuse the latent heat of the vaporized material which is lost in a single effect evaporation. In multi-effect evaporator, each effect in itself acts as a single effect evaporator [7]. Multi-effect evaporators may be forward-feed operated, backward-feed operated or parallel-feed operated [9].
The general objective of equipment design is to manufacture the various unit operations needed along the production line of a product to perform their respective stage functions in the production process [12] at a minimum cost, being environmentally benign and user friendly. With the use of rules of thumb and the various design equations as guide, in this study, the various equipment used in the production of the prekese functional food drinks were selected and designed. The major process equipment needed for the production of prekese functional fruit drink have been identified along the production line as washing unit (fruit preparation), milling unit, extraction unit, filtration unit, evaporation and mixing unit. These equipment were carefully selected and designed to suit the task each is expected to perform at their various stage functions.
2. MATERIAL AND METHODS
The equipment design was based on laboratory scale results of producing Prekese functional fruit drink which was operated in a batch mode. The equipment comprised a washer, a cutter, a miller, an extractor, a filter, an evaporator, and a mixer. Material balances and energy requirements were calculated around each unit. The equipment were sized and engineering drawings were prepared.
In the production of the prekese functional food drink, the raw material (prekese fruit) is washed to get rid of dirt. The pulp of the fruit is shredded and sent to the hammer mill for milling. The milled pulp is then mixed with water and a slurry obtained by boiling in an extractor. The slurry is filtered to obtain an extract, which is sent to an evaporator for concentrating into a syrup. The syrup is then diluted in a stirred tank and sugar added to taste. The extraction and evaporation unit operations are crucial for obtaining the prekese extract with retained active ingredients, antioxidants, needed in the functional fruit drink. The block diagram of the processing of prekese functional fruit drink is shown in Figure 1.
Figure-1. Process block diagram for the processing of prekese fruit drink
3. THEORY AND CALCULATIONS
3.1. Mass Balance Calculations around the Various Units
Figure 2 depicts the mass balance calculations around the milling unit, whilst a summary of mass balances around all the unit equipment is presented in the results (Table 1).
Figure-2. Mass balance around milling unit
Calculation around the miller
Assumption: 1% loss of water and pulp
Pulp component balance
Amount of solids= 0.923(527.75) = 487.11 kg
Amount of solids retained in mill = 0.01(487.11) = 4.87 kg
Water component balance
Amount of water in pulp= 0.077(527.75) = 40.64 kg
Amount of water in feed= 40.64 kg + 10 kg = 50.64 kg/h
Amount of water retained in mill = 0.01(50.64 kg) = 0.51kg
Amount of feed retained in mill= amount of solids retained + amount of water retained
= 4.87 kg + 0.51 kg
= 5.38 kg
Compositions of components in retained feed in mill
3.2. Energy Requirements by the Various Units
3.2.1. Washer
A turbine agitator is proposed to be employed in the washer to create a turbulent region to aid in the removal of dirt. The specification includes an Impeller speed (N) of 180rpm (3rps) and Agitator diameter (D) of 1m with density of water being 1000 kgm-3. The power number (Np) for a pitch blade turbine impeller is 1.27 (www.fusionfluid.com/fusionfluid equipment LLC/html/impellers-pb turbine.html).
Power, P is calculated using definition of power number:
Power (P) = Np×ρ×N3×D5
Where P is the turbine power, Np is the Power Number, ρ is the density of water, kg/m3,
N is the agitator speed measured in rps, and D is the impeller diameter.
Thus, P = 1.27×1000 kgm-3 × (3rps) 3 ×(1m)5= 34290 W = 34.29 kW
Hence agitator power required to effect some turbulence needed for the washing of the prekese fruit is 34.29 kW.
3.2.2. Miller
A hammer mill is used to shred or crush aggregate material into smaller pieces by repeated blows of little hammers. The basic principle is straight forward: it contains a horizontal or vertical rotating shaft on which hammers are mounted. The hammers are free to swing on the ends of the cross, or fixed to the central rotor. The rotor is spun at a high speed inside the drum while material is fed into the feed hopper. The material is impacted by the hammer and is thereby shredded and expelled through screens in the drum of a selected size. The hammer mill uses air flow to separate small particles from larger ones. Calculating the horsepower of the motor;
3.2.3. Extractor
In the extractor, the feed consists of the solute to be extracted and solvent. The principle for the solid-liquid extraction is that the soluble compounds of a solid matter, are extracted by a solvent. The solute diffuses from inside the solid into the surrounding solvent. Either the extracted solid fraction or the insoluble solids, or both, may be valuable products. Leaching is widely used in the metallurgical, natural product, and food industries [4]. In this study, the solvent of choice was saturated steam. Saturated steam (from Steam Table) has a temperature of 150 oC, specific heat capacity of 1.9857 kJkg-1K-1, and a pressure of 1bar. In this study, mass of prekese to extractor is 531.9687 kg/h, at an inlet temperature of 37oC and outlet temperature of 100oC. It is assumed that the specific heat capacity of prekese slurry is the same as that of orange juice which is 3.8 kJkg-1K-1.
3.2.4. Filter
The rotary vacuum drum filter is used to filter the slurry. To obtain a formula for sizing a rotary-drum filter, the mechanism of liquid flow through a porous medium is considered. As the filter drum rotates through the slurry tank, a porous solid deposits on the surface of the drum, increasing the resistance to liquid flow. The surface of the filter cake is at atmospheric pressure. If it is assumed that the pressure downstream of the filter medium is constant (created by a vacuum pump), then the pressure drop across the filter cake and medium is constant. As the filter cake thickens, the liquid flow rate decreases because of the increasing resistance to flow. The starting point for deriving a formula to calculate the filtration area is the Kozeny-Carmen equation for flow through porous media [13]. The flow, which is laminar, follows a path through the cake. The Kozeny-Carmen equation, for a differential cake thickness, is
-(dP/dx) = [4.17s2μvs(1-ε)2] / ε2 (i)
where P is the pressure at any point in the cake, x is cake thickness, ε is the specific surface (surface area per unit volume of particle), μ is the liquid viscosity, vs, is the superficial liquid velocity, and s, is the porosity of the cake [13] . The differential mass of dry cake, dm, is given by
dm = (1-ε) ρs AF dx (ii)
where dm is the differential amount of dry cake in a layer of thickness dx and the volume fraction of solids in the wet cake is (1 - ε).
From equations i and ii,
-dP/dm = ks2μvs(1-ε) / ρs ε2 AF (iii)
Specific resistance, α is defined as
α = ks2(1-ε) / ρs ε2 (iv)
The rotary-drum filter is to filter 20 m3/h of a prekese extract at 20 °C. The pressure drop across the cake is 9.541 psi. The slurry contains 0.15 mass fraction of prekese fruit, and the filter cake contains 0.40 mass fraction of water. Water density is 998.3 kg/m3 and its viscosity (20 °C) is 0.001 Pa-s (1 cp). Prekese density is 2709 kg/m3, thus, average density of the slurry,
ρ = 0.85 (998.3) + 0.15 (2709) = 1255 kg/m3
Mass Balance Equations:
y1,1 ρ1 V1 = yc,1 mc + ρ2 V2 ………………………………………….. (1)
y1,2 ρ1 V1 = yc,2 mc ………………………………………….. (2)
y1,1 + y1,2 = 1 ………………………………………….. (3)
yc,1 + yc,2 = 1 ………………………………………….. (4)
For the first subscript, 1 represents entering stream and 2 represents the leaving stream. For the second subscript, 1 represents liquid, and 2 represents solid, and c represents wet cake.
Rate Equation:
AF2 = [(1 – n)αμ(c1,2) (VF2)] / [2tF(Po – PV)] …………………………… (5)
AF = fAT …………………………… (6)
Where α is the specific resistance, μ is the liquid viscosity and Po – Pv is pressure drop.
System Properties:
ρ1 = y1,1 ρ1,1 + y1,2 ρ1,2 ……………………………… (7)
c1.2 = y1,2 ρ1 ……………………………… .. (8)
α = αo(Po – Pv)n ………………………………... (9)
n, usually varies from 0.2 to 0.8. If n = 0, the cake is incompressible.
From Equation 3, y1,1 = 0.85, and from Equation 7 the average density of the slurry,
ρ = 0.85 (998.3) + 0.15 (2709) = 1255 kg/m3
Equation 4 gives yc,2 = 0.60. The formation rate of wet cake, mc, can now be calculated from Equation 2. Thus, mc = (0.15/0.6) x 1255 kg/m3 x 20m3/h = 6.275 x 103 kg/h
From (1) volumetric flow rate of filtrate V2 = (21340 – 2510) / 998.3 = 18.86 m3/h
Assume αo = 1.604x1010 and n = 0.2664
The pressure at the interface of the filter cake and filter medium, Pj, is assumed to be equal to the pressure downstream of the filter medium, Pv. Therefore, P0 - Pv = 0.658 bar or 6.58xl04 Pa for filtering a prekese slurry. Therefore, α = 1.604xl010 (0.658)0.2664 = 1.435xl010 m/kg
The cycle time for filtering prekese slurry is erstimated to be 5 min. Since the drum is only partially submerged (37.5%), the filtering time, tf = 0.375 x 5 x 60 = 112.5 s.
The volume of filtrate collected, VF = V2 tf = 0.5894 m3
From (8) concentration of solids in entering stream c1,2 = 0.15(1255) = 188.3 kg/m3
Finally, the filter area AF = (1-0.2664)/2(115.5) s x 1.435x1010 m/kg x 0.001/6.58x104 Pa-s/Pa x 188.3kg/m3 x 0.58942 m6 = 6.731 m2
Now, from (6) the drum area, AT = 6.731/0.375 = 17.95 m2
With a safety factor of 29.5%, a surface area of approximately 23.22 m2 is obtained for the filter. From rule of thumb, a sized filter of 23.22 m2 surface area will require 11.18 kW and 22.37 kW to power the drum drive and agitator drive respectively [13]. This filter with a roll discharge, has a size diameter of 3.05m and a nominal length of 2.44m as also shown by Silla [13].
3.2.5. Evaporator
Agitated thin film evaporators (ATFE) which have short residence times and relatively high heat transfer coefficients, are best used for concentrating foods that are heat sensitive and cannot tolerate high temperatures [14].
3.2.6. Mixer
In estimating the energy requirements of the mixer the focus is mainly on the power consumption of the agitator. The shaft power required to drive an agitator can therefore be estimated using the following generalised dimensionless equation:
4. RESULTS AND DISCUSSIONS
A summary of the overall mass balance and power requirement around the various unit equipment are shown in Table 1 and Table 2 respectively
Table-1. Summary of material balance
Table-2. Summary of power requirement
| Equipment | Power required (kW |
|
Electricity |
Saturated steam |
|
| Washer | 34.29 |
|
| Miller | 5.56 |
|
| Extractor | 35.38 |
|
| Filter | 33.55 |
|
| Evaporator agitator | 14.43 |
|
| Evaporator steam | 19.81 |
|
| Mixer | 0.23 |
|
| Total power required | 88.06 |
55.19 |
4.1. Design Specifications of Washer
Vertical agitation combines the natural cleaning power of water with the hydrokinetic energy developed when parts are agitated. The agitation produces a natural hydraulic purging action that forces solution between parts and in and out of cavities providing the highest degree of fluid exchange for the fastest cleaning. This makes the agitating parts washer ideal for cleaning parts with complex shaped geometries like prekese fruits. The specifications for agitated immersion washer is depicted in Table 3.
Table-3. Agitated immersion washer specifications
| Parameters | Specifications |
| Vessel capacity (m3) | 56.5 |
| Agitator speed (rpm) | 180 |
| Agitator diameter (m) | 1 |
| Vessel diameter (m) | 4 |
| Height (m) | 4.5 |
| Agitator power requirement(kw) | 34.29 |
4.2. Design Specifications of Hammer Mill
Table 4 depicts a summary of the mill characteristics derived from calculations. The engineering drawing of a hammer mill is shown in figure18. In the milling unit the power of the motor was arrived at from calculation as 2.62 hp and the diameter of the grinding chamber also arrived at as 90 mm whiles the energy need to crush a kilogram of feed obtain as 13.18 kJ/kg and the volume and height of the hopper were obtained as 5.816and 2.4m respectively. The engineering drawing of a hammer mill is shown in Figure 3.
Table-4. Hammer Mill specification
| Parameters | Specifications |
| Power of motor (hp) | 2.62 |
| Rotor speed (rpm) | 1300 |
| Number of blades | 8 |
| Dimension of blade (mm) | 910 × 240×460 |
| Capacity (kg/h) | 1020 |
| Diameter of grinding chamber (mm) | 254 |
| Energy input (kJ/kg) | 13.18 |
| Shaft speed (rpm) | 1500 |
a) Cross sectional view
b) Top view
Figure-3. Hammer mill
4.3. Design Specifications of Extractor
Various extractors are available for solid-liquid extraction. Selection of equipment is affected by various factors including flow rate, residence time, number of stages, cost, and viscosity. The kettle brew extractor was selected in this study and the design specifications were based on various design equations. Table 5 shows the specifications of the kettle brew extractor.
Table-5. Kettle Brew Extractor specifications
| Parameter | Specifications |
| Rate of heat transfer (kW) | 35.38 |
| Capacity (m3) | 7.1 |
| Height | 1 |
| Steam pressure (bar) | 1 |
| Steam temperature (0 C) | 150 |
| Diameter (m) | 3 |
| Area (m) | 23.6 |
4.4. Design Specifications of Filter
For the design of filters, it is necessary to establish a filtration time (the time between filling the filter to the time at which it proceeds to download the cakes). In this work, a filtration time of 5 minutes was proposed. At this time, the rotary-drum filter is to filter 20 m3/h of prekese extract at 20 °C. Accordingly, from the calculations, the designed capacity is 5.9 m3 with a height of 1.32 m and area of 19 m3 (Table 6). Engineering drawing of the rotary drum vacuum filter is shown in Fig 4.
Table-6. Rotary vacuum drum filter specification
| Parameter | Specification |
| Drum drive (kW) | 11.18 |
| Agitator drive (kW) | 22.37 |
| Height (m) | 1.32 |
| Capacity (m3) | 5.97 |
| Drum diameter (m) | 2.4 |
| Area (m3) | 19 |
a. Front view
b. Side view
Figure-4. Engineering drawing of filter drum (dimensions in mm).
4.5. Design Specifications of Evaporator
Due to the intensive mixing action within the bow wave, temperature sensitive products are prevented from over-heating and fouling on the heat transfer surface can be reduced or eliminated. Agitated Thin Film Evaporators are designed with a cylindrical shape and with an internal rotor that is used to spread a thin layer of liquid film on the inner side of a metallic wall, while a utility stream (e.g. steam or hot oil) provides heat flowing in the external jacket [16-18]. The mixing in the liquid phase is assured by the blades that during their rotation produce a thin-film and a bow wave in front of the blade where the excess liquid is directed and mixed. ATFE are widely used in the food [19, 20] pharmaceutical and bio-based industry as concentrators and separators [14] due to their short residence times and relatively high heat transfer coefficients. From the calculations in this study, the volume of the evaporating vessel was obtained as 14.13m3 (Table 7). From calculation the power needed to power the agitator was obtained as 19.35 horse power, hence the agitated thin-film evaporator should have a diameter of 2 m and it should have a volume of 14.13m3 to be able to process 939.14 kgh-1 of the prekese extract into a syrup of viscosity 330-2400 cP. The engineering drawing of the evaporator is shown in Figure 5.
Table-7. Evaporator Specification
| Agitated thin-film evaporator | Specifications |
| Rotor speed (rpm) | 1200 |
| Vessel capacity (m3) | 14.13 |
| Evaporator diameter (m) | 2 |
| Agitator height (m) | 4.5 |
| Impeller diameter (m) | 1 |
| Agitator power (kW) | 14.43 |
Figure-5. Cross sectional view vertical agitated thin-film evaporator
4.6. Design Specifications of Mixer
Mixing is generally helpful for intensification of mass and heat transfer [18]. From the design calculations the volume of the mixing tank was obtained as 10m3 and the diameter of the mixing tank 2m and height 3.2m and the agitator power was obtained as 0.231 kW (Table 8). The Engineering drawing of mixer is shown in Figure 6.
Table-8. Design specifications of a mixer
| 4-Picthed blade mixer | Specifications |
| Rotor speed (rpm) | 300 |
| Number of blades | 4 |
| Vessel capacity (m3/hr) | 10 |
| Tank diameter (m) | 2.0 |
| Tank height (m) | 3.2 |
| Impeller diameter (m) | 0.96 |
| Baffle width (m) | 0.167 |
| Baffle clearance (m) | 0.027 |
| Agitator power (kW) | 0.231 |
Figure-6. Engineering drawing of mixer
5. CONCLUSION
This study proposes the various designed equipment, needed for the production of prekese functional fruit drink. The designed unit equipment makes it possible to process the prekese fruits in order to maintain its antioxidant properties and other health-benefit properties which makes it suitable as a functional fruit drink. The equipment comprised a washer, a cutter, a miller, an extractor, a filter, an evaporator, and a mixer. The equipment had been sized and engineering drawings prepared. Electricity had been identified as the major source of energy to the various unit operations except the evaporator and extractor which are also powered by heat energy. With prekese feed flow rate of 1000 kg/h, the total electrical power requirement was determined to be 88.06 kW and steam power requirement was 55.19 kW. The capacity of the washer, miller, extractor, filter, evaporator and mixer were respectively 56.5 m3, 1020 kg/h, 7.1 m3/h, 5.97 m3/h, 14.13 m3/h and 10 m3/h.
6. RECOMMENDATION
Validation of the designed equipment could be carried out and where necessary, modifications made. The designed equipment provide useful means for value addition to Tetrapleura tetraptera (Prekese) fruit and up-scaling of the functional fruit drink processing, which is encouraged to be pursued.
| Funding: This study received no specific financial support. |
| Competing Interests: The authors declare that they have no competing interests. |
| Contributors/Acknowledgement: All authors contributed equally to the conception and design of the study. |
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