ABSTRACT
This work is predicated upon the design and construction of a simple cassava pelleting equipment that produces both at low cost, minimal gelatinization and low temperature. It involves the pouring of mildly moistened dry cassava flour, made by grinding dried broken cassava roots or chips, through a hopper into a compacting cylindrical chamber. The extrusion is effected by means of a screw conveyor shaft which turns to impact some pressure on the cassava mass pushing it against a die plate with multiple perforated openings of diameter about 6mm at the end of the cylindrical casing through which the pellets pass under pressure from the compacting chamber and is cut by a wire knife behind the die plate. The machine has been designed, produced and tested. The machine is powered by a 2.23hp, 3- phase geared electric motor with its speed reduced from 1420 to 17 rpm to suit the design. The production rate of the machine was found to be about 180 – 200 Kg/hr. It was found that when mixed with about 1.5 – 2.5 litres of hot water, a 5kg mass of feed (dry fermented cassava, non – fermented cassava and yam flour) gave a high quality pellet of the three products with high resistance to abrasion, impact and compression as well as an average pellet length of 10 – 12mm though the non fermented type was tougher. For instance, when compressed in a hollow cylinder of diameter 28mm, filled up to 86mm under a tensiometer the compressive strengths for dried the three dried pellet samples were 71mPa, 130mPa and 64mPa respectively, resulting from their starch contents and by extension their level of gelatinization without needing any extra gelatinization.
TABLE OF CONTENTS
COVER PAGE……………………………………………..……… (i)
TITLE PAGE……………………………………………………… (ii)
CERTIFICATION…………………………………………………. (iii)
DEDICATION……………………………………………………… (iv)
ACKNOWLEDGEMENT………………………………………….. (v)
ABSTRACT………………………………………………………….(vi)
TABLE OF CONTENTS…………………………………………… (vii)
LIST OF FIGURES……………………………………………….. (xiv)
LIST OF TABLES………………………………………………… (xvi)
LIST OF SYMBOLS……………………………………………… (xvii)
CHAPTER ONE
INTRODUCTION ——————————————————————1
- Brief history of base material (cassava) ————————–1
- What is cassava pellet———————————————–1
- Processing method (A) from dried cassava chips or broken roots———————————————————————————–4
- Cassava chips—————————————————–5
- Broken Roots—————————————————–5
- Processing of the chips——————————————5
- Drying of the chips———————————————-6
- The ground cassava flour—————————————6
- Processing method (B) from crushed wet cassava tubers———7
- Design Criteria————————————————————–7
- Description of the machine————————————7
- Principle of Operation—————————————–9
- Drying the pellets———————————————————10
- Additives/Binders——————————————————–10
- Raw materials, storage and selection——————————-10
- Aims and objectives—————————————————–11
- Scope ———————————————————————11
- Relevance of Research————————————————–12
- Application (Beneficiaries) ——————————————–13
- Methodology/Work plan————————————————13
- Product Specification/Result of Project——————————-14
CHAPTER TWO
- LITERATURE REVIEW————————————————-15
- Pellet Quality——————————————————–16
- Pellet Binders——————————————————–16
- Types of Pelleting Equipment Presently in Use—————-16
- Ring and Plate Pelleter——————————————16
- The Pelleting Section of California Pelleting Mill (CPM)–18
- Cold Pelleters—————————————————–19
- Conditioner Pelleters——————————————–20
- Extrusion Cooling ———————————————-20
- Advantages of Extrusion————————————–22
- Classification of Extruders———————————–22
- Comparison between the single and twin-screw extruder Mechanism———————————————————–24
- Single Screw Design————————————————25
- Twin Screw Extruder————————————————26
2.8.(i) Process Stability———————————————-26
2.8.(ii) Design———————————————————27
2.9 Pressure—————————————————————27
2.10 Other features——————————————————-29
2.11 Moisture————————————————————–29
2.12 Cost——————————————————————-30
2.13 Conclusion——————————————————-31
CHAPTER 3
- THEORETICAL CONSIDERATIONS ———————–32
- Mechanism of Operation of Cassava Pelleting Machine————32
- 1 Circular Motion and Centrifugal Force (Fc)—————32
- Rotational Torque———————————————32
3.1.2. (i) Work done by Torque————————————33
3.1.2. (ii) Power Developed by Torque—————————–33
3.1.3 Pulleys and Belt Drive—————————————33
3.1.4 Power Transmitted Using Tension Terms—————–34
3.1.5 Horsepower Transmitted Using Tension Terms———-34
3.1.6 Belt Length—————————————————-35
3.1.7 Force analysis on the shaft of the pelleting machine—–35
3.1.8 Shaft Diameter————————————————-36
3.1.9 Bearing selection——————————————–37
3.1.10 Screw Conveyor Output (Throughput) ——————37
3.2 Conclusion —————————————————————-37
CHAPTER FOUR
- DESIGN CALCULATION OF CASSAVA PELLETING MACHINE–38
4.1 Power Transmission using Pulleys——————————38
4.2 Pulley arrangement———————————————–38
4.3 Angular Velocity of turning for the Screw Conveyor —39
4.4 Torque (T) developed due to speed————————-39
4.5 The Output Torque (To) ————————————-40
4.6 Theoretical Power Requirement—————————-40
4.7 Horsepower Needed—————————————–40
4.8 Belt Tensions T1 and T2————————————-40
4.9 Length of Belt (L) ——————————————-42
4.10 Throughput of Screw Conveyor—————————42
4.11 Mass of Material Conveyed/Minute———————–43
4.12 Pressure developed in the extrusion Barrel (Pr) ——————–43 4.12(i) Area of Cylindrical Section (Ac) ————————–44
4.12(ii) Area of Conical Section (Ak) ——————————44 4.12(iii) Effective Area of Extrusion (VE) ————————-44 4.12(iv) Pressure Developed (Pr) ———————————–44
4.12(v) Volume of Extrusion Area (AE) ————————–45
- Forces on Screw Conveyor Shaft (Design of shaft) —————45
- Calculation of Bearing Reactions R1 and R2————————-46
- Calculation of Maximum Bending Moment (Mmax) —————-47
- Calculation of Shaft Diameter—————————————–49
- Bearing Selection———————————————————50
4.17(i) Total Load Acting on Bearing (Pb) ————————-50 4.17(ii) Bearing Life in Hours—————————————-50
4.17(iii) Bearing Life in Million Revolution (L10) —————-50
4.17(iv) Bearing number for point c on the shaft——————51
CHAPTER FIVE
5.0 MANUFACTURING PROCESS, PERFORMANCE EVALUATION AND COST ANALYSIS———————————-53
5.1 Machine Components—————————————-53
5.1 The selected parts——————————————————–53
5.1.1 The selected Parts—————————————————–53
5.1.2 The Fabricated Parts————————————————–53
5.2 Manufacturing Process—————————————53
5.2.1.Fabrication of Structural Stand————————————–53
5.2.2 Electrical Motor Seating——————————————–54
5.2.3. Bearing Housing—————————————————–57
5.2.4. Pelleting Barrel Cover———————————————–57
5.2.5. Wire Cutter————————————————————57
5.2.6. Inlet Hopper———————————————————-58
5.2.7 Screw Conveyor—————————————————–58
5.2.8 Transmission Shaft————————————————–58
5.2.9 Driver and Driven Pulleys——————————————58
5.2.10 Bearing—————————————————————-59
5.2.11 Electric Motor——————————————————–59
5.2.12 V-Belt —————————————————————-59
5.2.13 Bolts and nuts——————————————————–59
5.2.14 The three fingered Scooper Blade———————————59
5.3 Assembly Process—————————————————-60
5.4 Test Running———————————————————-62
5.4.1Test Running Without Load———————————-62
5.4.2 Preparation of the Chips, Broken Roots and Flour——-62
5.4.2(a) Flour Preparation——————————————62
5.4.2(b) Pre – pelleting Treatment of Powder——————-62
5.4.3 Loading and Test – running——————————–62
5.5 Observation——————————————————–63
5.6 Performance Evaluation——————————————63
5.6.1 Measurement of Production Rate of Different Feed Materials
Using Varying Volumes of Hot and Warm Water————–64
5.6.2 Measurement of % Quality, Rpm and Length of Pellets———-65
5.6.3 Tests to Determine Ability of Pellets to withstand Stress———66
5.6.3(a) Test 1: Impact Test————————————————66
5.6.3(b) Test 2: Compression Test—————————————-67
5.6.3b (i) Calculation of stress ——————————————67
5.6.3b (ii) Average compressive strength ——————————68
5.6.3b (iii) Determination of compression of pellets per unit volume –68
5.6.3b (iv) Calculation of strain on all the pellet types —————–69
5.7 Cost Analysis———————————————————-75
5.7.1 Material Cost—————————————————–75
5.7.2 Labour Cost——————————————————76
5.7.3 Overhead/Miscellaneous Cost———————————77
5.7.4 Total Cost——————————————————–77
CHAPTER SIX
DISCUSSION, SUMMARY, CONCLUSION AND RECOMMENDATION——————————————————78
- Discussion—————————————————————78
6.1.1 Mass Flow Rate of Pellets————————————–79
6.1.2 Percentage Quality of Pellets———————————-79
6.1.3 Speed of rotation and Length of Pellets———————80
6.2 Summary—————————————————-82
6.3 Conclusion————————————————-83
6.4 Recommendation—————————————–83
References———————————————————–84
APPENDIX I—————————————————————-86
APPENDIX II—————————————————————86
APPENDIX III ————————————————————-89
APPENDIX IV————————————————————–92
APPENDIX V—————————————————————92
APPENDIX VI ————————————————————-92
APPENDIX VII———————————————————–93
CHAPTER ONE
- INTRODUCTION
1.1 Brief History of Base Material (Cassava)
There is archeological evidence of two major centers of origin for cassava, one in Mexico and Central America and the other in Northeastern Brazil. The first Portuguese settlers found the native Indians in Brazil growing the crop, and Pierre Martyr wrote in 1494 that the ‘poisonous roots’ of a yucca were used in the preparation of Bread. It was believed that cassava was introduced to the western coast of Africa in about the sixteenth century by slave merchants (1).
The Cassava plant, botanically called “manihot utilissima pohl” is of the family “euphorbiaceae.” It is grown for its edible tubers and is about the most abundant tropical food substance, essential for the quantity of edible starch content of its roots. It continued to spread to different parts of the world. The ease of its expansion might be attributed to its ability to grow on different types of soil and climate. It is grown for its edible tubers; it serves as a staple food in many tropical countries and is also the source of an important starch. It is propagated by its stem, which grows, projected up above the ground while the edible tubers are in the ground. Usually, when the tubers are uprooted, the shoot (stem) can be preserved for a long time before it is cut and laid into the ground to germinate at its node. It is grown all through the rainy season and performs best when grown during the early and late rains especially in Nigeria. It is grown predominantly in all communities of the nation. Depending on variety and available nutrients, it matures between six months and two years.
0
1.2 What is Cassava Pellet
Cassava pellets are obtained from dried and broken roots or chips of cassava by grinding and hardening into cylindrical shapes. The cylinders are about 2-3 cm long and about 0.4-0.8cm diameter and are uniform in appearance and texture. The production of pelleted chips has recently been increasing as they meet a ready demand on the European markets. They have the following advantages over chips, their closest rival.
- Quality is more uniform.
- They occupy 25-30% less space than chips of equal weight, thus reducing the cost of transport and storage.
- Handling charges for loading and unloading are cheaper.
- They usually reach their destination sound and undamaged; while a great part of a cargo of sliced chips is damaged on long distance shipment because of sweating and heating.
- They can be put to further use by being reprocessed into other products for human and animal consumption(1)
According to available statistical report from Raw Material Research and Development. Council (RMRDC), cassava production experienced a quantum jump from 15.5 million tons in 1988 to 29.18 million tons in 1992, then a slight increase to 31.27 million tons in 1995 (2)(RMRDC Compilation on Cassava, 2004). House of Representatives Committee on Agriculture reported in April 2009 that annualcassava production rate has risen up to 49 million tons (3). Based on this, it is clear that Nigeria can sustain a large export market of cassava products.
Presently, Thailand derives much income from the export of cassava pellets, though their method of production is roller press pelleting mill. But this mill is a very complex machine that is very complicated and expensive. A simpler and cheaper machine is the extrusion-pelleting machine proposed here.
In a letter to the Vice Chancellor, U.N.N., dated April 5, 2005 from the Director General (D.G.), Raw Materials Research and Development Council (RMRDC), Abuja captioned: Design of Cassava Pelleting Equipment, roller press pelleting method was being preferred to extrusion method of cassava pellet production. Among other reasons for this preference were the high cost of extrusion and the adverse effect of much gelatinization on the durability and further reprocessing of the product. Since then, no specific work has been reported to address these said shortcomings of extrusion pelleting equipment.
Cassava has over the years found use as one of the most easily available and cheap staple foods in Nigeria. It is being used as a base material in the processing of different food and non-food products. Some of the food products include, cassava flour, garri, slices (salad or abacha), chips, tapioca, broken roots, pellets among others. It is also used for producing starch, tablets, etc (1).
Large-scale livestock production requires a lot of input from cassava tubers in terms of feed. Industrial manufacture of these feeds requires mechanized processing plants for increased productivity. Naturally occurring materials and their extracts when used in feed production give high nutrient and of course better health for the livestock. Hence the growing demands for cassava products e.g. cassava chips, pellets and floor. Also cassava pellets have continued to find usage in the pharmaceutical industry in the production of tablets (4).
In view of the numerous demands for cassava products both nationally and internationally, it is very necessary that all the various unit operations involved in the processing of cassava into these various products be mechanized in order to achieve increased productivity, which will enable the sustenance of both internal and external market. Fig 1.1 below shows the general sequence of unit operations for processing of cassava roots into various products.
Harvested
Cassava Roots
|
Fresh Root Market
Or
Storage
Fig. 1.1 Flow Diagram For General Sequence Of Unit Operations For Processing Cassava Roots Into Various Products (5).
Before Pelleting, the cassava has to be in flour form. There are two methods for preparing the cassava flour dry and wet methods.
1.3 Processing Method (A) (from dried chips/broken roots) (see fig1.2).
1.3.1 Cassava Chips: This is the most common form in which dried cassava roots are marketed and most exporting countries produce it. The chips are dried irregular slices of cassava roots, which vary in size but should not exceed 5 cm in length so that they can be stored in silos (1). They are produced extensively in Thailand, Malaysia, Indonesia and some parts of Africa, especially in Nigeria.
Fig1.2 Process Flow Chart For Method (A) (Dry Pelleting Method)
1.3.2 Broken Roots
Broken roots are similar to chips in appearance but generally thicker and longer. They are often 12-15cm long and can jam the mechanism of handling equipment. They are produced mainly in Africa where local processors prefer to produce longer roots because of the domestic demand mainly for products suitable for human consumption, as cassava is part of the staple diet.
However, it is important to note that the process of preparing chips is the same as that of broken roots. The only difference is that the size of pieces of chips is smaller than those of broken roots.
1.3.3 Processing of the Chip
This is the same process for producing the broken roots, which form the major base material for the pellets. The cassava roots are peeled and washed and then chipped by cassava chipping machine or cut into the desired sizes with knife and then spread under the sun to dry.
1.3.4 Drying of the Chips
Sun drying is mostly used. The sliced roots are spread out on drying areas or concrete floors. Large mats of different sizes and makes are usually used to spread the chips especially in areas or seasons of intermittent rains and sunshine. With the mats collection is easy when the rains threatened. Experiments showed however, that the concentration of chips during drying should not exceed 10 – 15kg/m2, the required drying area being about 250m2 for each ton per day of dried roots produced. (1)
To produce good quality chips, the roots must be sliced and dried as quickly as possible after harvest. The chips are usually turned periodically in the drying period, usually two to four sunny days until the moisture content reaches 10-15%. The chips are considered dry when they are easily broken but too hard to be crumbled by hand. The thickness of the slices also has an effect on the quality of chips. Thick slices may appear dry on the surface when their internal moisture content is still high.
When the rain threatens during the drying process, the chips are collected by hand or by a tractor into piles under a roof. However, interrupted sun drying affects the quality of the finished chips and pellets. When the semi-dried chips are wet again by rain, they become soggy and upon completion of drying, lose their firm texture. In rainy regions and seasons where and when continuous sun drying is difficult, some form of artificial heat drying is required.
1.3.5 The Ground Cassava Flour
When the broken roots and chips have been fully dried, they are crushed into flour by the popular grinding machines on every street of Africa. If the broken roots or chips are too dry they may require a little water or at best a little palpy starch to gelatinize it and make it possible to coagulate the powdery flour and then properly mixed. Alternatively, the grinding might be carried out before the chips and broken roots become too dry.
- Processing Method (B): (from crushed wet tubers.)
Various unit operations are involved in the production of cassava pellets from tubers. The most commonly identifiable ones include the following: Peeling and washing, Grating (milling), Dewatering (Pressing), Depulping,Pelletizing, Drying, and Packaging.
The cassava is peeled and washed. It is then grated in a grating machine which is a popular machine in all the streets of Nigeria. After grating the cassava paste is then packed into a bag and dewatered by a dewatering process such as manual press or hydraulic press. It is then depulped by breaking the lumped cassava into tiny particles using sieve. It is then poured into the pelleting maching which brings it out in pelleted form. The pellets are however wetter than those produced from dry chips and takes longer time to dry. After drying it is then packaged and stored or exported. See attached process flow chart diagram for wet method of pellet production below (4).
Fig 1.3 Process Flow Chart For Wet Pelleting Method
It is with the view of mechanizing the unit operations involved in cassava processing that necessitated the idea of designing, constructing and testing a motorized cassava-pelleting machine.
1.5 DESIGN CRITERIA
The drawing of the conceived machine is shown below.
1.5.1 DESCRIPTION
The machine consists of the following components namely: Electric motor, V-belt, Driver pulley, Driven pulley, Bearing housing, Bearings, Extrusion Barrel, Extrusion die, Feed hopper, Screw conveyor, Shaft, Structural stand, Structural reinforcements, Bolts and nuts, Cutting wire, and Rolling tyres
Fig.1.4 The Concieved Pelleting Machine
The extrusion barrel houses the screw conveyor and shaft. The bearing housing is coupled to the extrusion barrel through flanges. The extrusion die is also coupled to the frontal end of the barrel with bolts and nuts. The screw conveyor inside the barrel is tapered towards its terminal end. Just beside the end of the screw conveyor, scupper blade is mounted. A wire-cutting device is mounted in front of the extrusion die.
An inlet hopper is fixed at the leading end of the extrusion barrel. The transmission shaft runs through both the extrusion barrel and the bearing housing with an external extension to accommodate the driven pulley. A large driven pulley (in relation to the driver pulley) is used in order to achieve speed reduction. The driver pulley is keyed to the electric motor. The pulleys are all linked to one another using V-belt. The arrangement of all the components of the machine is carried on a structural stand.
1.5.2 Principle of Operation
The electric motor provides the primary motion required to power the machine. This motion is transmitted to the shaft and screw conveyor via the belt, pulleys and bearings. The cassava flour, mildly moistened with hot water and/or additives is gradually introduced into the extrusion barrel through the hopper.
The screw conveyor transports the mixture to the extrusion die.
Pressure is generated by continuous transportation of the mixture towards the inner section of the extrusion barrel. The mixture now under pressure begins to surge through the several tiny cylindrical holes on the die plate. A wire-cutting device tensioned and adjusted to the required distance helps to cut the pellets to the required length. The pellets then drop into a receiver. They are then dried either in sunlight or in a dryer and packaged as required.
1.6 Drying the Pellets
The term drying refers to the transfer of liquid from wet solid into an unsaturated gas phase. Moisture could also be removed from gases. This process through drying in a way is known as dehumidification and adsorption.
Drying is applied to food products for preservative purposes. Different kinds of dryers are used for different kinds of materials.
Electrically heated tray dryer could be used for drying of cassava chips and pellets. Other types of dryers that could be used for drying of chips and pellets and grated semi – wet cassava are cabinet dryer, tunnel dryer, flash dryer, rotary dryer, solar dryer, spray dryer, vacuum dryer etc. the chips and pellets after drying, are cooled and bagged for export purposes. They could be further processed into cassava flour or processed further for poultry and animal feeds.
1.7 ADDITIVES/BINDERS
Additives such as molasses at 2 – 5% or gelatinized starch can be mixed moderately with the flour pelleting to enable the products to remain hard and durable especially for feeds that are used in the feeding of fishe. Other binders include bentonite clays and lignosulphonates at about 1 –2%. Some other additives such as sweetening and nutritious agents can be added to the floor before pelleting so as to increase its nutritional value.
1.8 Raw Material Storage and Selection
As we had earlier said, the basic raw materials for these cassava pellets are dried broken cassava roots and chips, so carefully prepared that there should be no pebbles, sand, pieces of metal, rubbishes and chemical or physical contaminants. These raw materials must be very dry to prevent attack by micro-organisms, pests and insects. When these raw materials are not well dried before storage, they may be disposed to mould formation, which will subsequently spoil the taste of the end product.
Storage areas must be waterproof and well ventilated, and as well provide protection against infestation by insects and vermin, which cause serious damage to the stock. These materials, stored in bags should be kept in a building having a concrete floor. The roof and walls need only to be lightly constructed provided that they are pest and waterproof. The bags should be stacked a few centimeters above the floor level, for example on a wooden pallet or in bins formed with partitions in conventional stores. It is from these stores that the raw materials are taken, weighed and ground into powder ready to be made into pellets.
1.9 Aims and Objectives
The research objectives are to:
- Design a multi-hole cassava – pelleting machine that has a low cost of energy utilization and also useful for mass production of other pelleted products.
- Fabricate and test the designed cassava machine.
- Produce cassava pellets without gelatinization and/or much moisturization.
- Show that the increased extrusion area caused by the conical end of the screw conveyor cylinder facilitates the increase in extrusion product flow rate.
- Show cassava pelleting machine as a means of mechanizing the process of converting the easily perishable cassava tubers into storable and valuable cassava product. In this manner the shelf life of cassava is highly increased and then serve as a raw material for other industries such as poultry feed production and food for animal husbandry.
- To show that with a short extruder barrel, very hard and durable pellets can be produced.
1.10 Scope:
In this work we are expected to Design, Construct and carry out Performance evaluation of the cassava pelleting machine. The prpduction rate of the machine is expected to reach about 200 – 400 kg/hr of pellets under a continuous feed condition.
1.11 Relevance of Research
- The first ever UNIDO regional consultation meeting on agricultural machinery industry in Africa, co-sponsored by F.A.O., E.C.A. and O.A.U. was held in Addis Ababa, Ethiopia from the 5th to 9th April 1982. The participants from Europe, America, Asia and Africa condemned in one voice, the near total dependence of African agriculture on agricultural machinery designed and manufactured by the industrialized countries for their advanced farmers and mostly temperate crops (5).
- The Seven Point Agenda of President Umaru Musa Yar’ Adua, has land and agriculture as focal points for the sole reason of making food available for Nigerians and non-Nigerians alike. Without good preservation process such as pelleting of cassava to keep it in a durable form, we may not be able to maximize the economic value of high yield of cassava from our farms.
- Presently, there is global food insecurity and preservation of cassava in pelleted form makes it highly durable and portable, so it can be sold to countries that need it for both animal and human consumption.
- The need for farmers to be able to formulate their own animal feed by mixing desired feed components before pelleting cannot be overemphasized. This advantage is not possible in the roller mill-pelleting machine.
- Poor quality of pellets if noticed can be corrected or recycled immediately with our new machine.
- Prolonged exposure of the extrudate to excessive pressure, mechanical shear and high temperature as experienced in the present extrusion process negatively affects the pellets especially when the extrudate is cassava (4). It may be over cooked and make further reprocessing of the pellets difficult. This makes our new pelleting equipment relevant, as its short length will reduce the residence time of the extrudate in the extrusion barrel to a minimum amount.
- At present in Nigeria pellets are being processed by means of roller mill, which is a complex array of machines. The two pelleting mills in Nigeria at Ajaokuta and Ewu (Edo state) are making use of this costly equipment, set up be California Pellet Mills (CPM). The two companies stay out of business, waiting to get expatriates to maintain the equipments in the event of machine failure. But our machine is simple and cheap.
- The greatest problem facing Africa is the development of local products to suit export demand. Hence, the development of new products from cassava, which is the most abundant food crop in Nigeria, is a matter of necessity, especially if the product has found relevance on the world market. Cassava pellet is one such product. It has an increasing demand for both animal feeds and human consumption.
1.12 Application (Beneficiaries):
The major benefactors of this project are namely.
- Small/medium agro processing industries involved in export trade.
- Feed mill production industry
- Pharmaceutical industry
- Animal husbandry industry including aquatic life breeders.
1.13 METHODOLOGY/WORK PLAN
The process of carrying out this project is sequential in nature. The different steps are categorized below.
- Information gathering:
The collation of information from the Internet, the liberaries and companies such as those producing pellets with other antiquated, costly and imported technologies. This process lasts from the beginning of the project to the last day of defence.
- Material Selection:
Cassava, which is the raw material for the pellet has some acidic contents such as butyric acid and some other organic acids which are produced as a result of fermentation caused by some micro organism as the flour lasts. Of particular interest is hydrocyanic acid, a normal component of cassava, which is fixed as dark coloured compound by iron ions whenever the two come in steady contact for some hours. This tends to destroy pure ferrous metal used in this process. For this reason stainless steel is usually prefered because of its resistance to chemical attack and its ability of remaining smooth and slippery for the sliding movement of the extrudate. But since it is too costly we may opt for the use of galvanized steel.
However, in the event that stainless steel is inaccessible we may be left with no option than to use galvanized steel.
- Material Collation:
Having selected the make of the materials to be used especially those that will come in contact with cassava flour; we now gather the parts of the equipment.
1.14 Product Specification/Results of Project
We expect to get cassava pellets of size between 0.4cm to 0.8cm diameter and 2 – 3cm long. The product will be fairly dry after production. It is expected to have 15% to 20% of water content. This can then be further dried under the sun up to the desired water content of about 5% – 10% before storage and exportation. We expect a production rate of between 200 and 400 kg per hour.
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