DESIGN OF CONVEYOR, EXTRUDERS AND FERMENTERS [Autosaved].pptx

FOOD PROCESS EQUIPMENT

1. DESIGN OF CONVEYOR, EXTRUDERS AND FERMENTERS

2. Selection of Conveyors The selection of mechanical conveyors depends on the following factors: type and properties of product to be conveyed, (2) capacity, (3) conveying distance, (4) transport direction, (5) packaging of product, (6) energy required, (7) product heating requirements, (8) hygienic (sanitary) and safety requirement, (9) automation, (10) degree of standardization, (11), flexibility, and (12) environmental impact.

3. Uniform Belt conveyor Belt 0.4 -2.5m 100m long Speed-0.4-4.5m/s Synthetic Rubber Combined steel Better hygienic condition Plastic Such as solid woven polyester Rolls or idlers 0.8-2.0m

4. Uniform Belt Conveyors Belt conveyors are used to convey, horizontally or inclined, granular products or larger packed or non-packed pieces. They consist of an endless belt driven by a drum (shaft) at one end of the belt, while a second drum lies at the other end. The drum is driven either directly by a geared electrical motor or indirectly by a transmission belt

5. Advantages of the uniform belt conveyors: Large capacity 2. No damage of transported material 3. Relatively low energy consumption 4. Possibility to remove the product at any place of the belt 5. Low maintenance cost 6. Low noise The disadvantages include: Not suitable for curved paths Inclination restricted Not suitable for dusty products (powders) Increased cost when the conveying distance is reduced

6. Segmented Belt Conveyors Heavy products Speed 1.5 m/s Temp- 100-120

7. Chain Conveyors

8. Advantages of flight conveyors: High capacity 2. No dusting at conveying speeds lower than 0.6 m/s 3. Possibility to convey in air-tight troughs Their disadvantages include: Not suitable for sticky process. 2. They are noisy.

9. Screw Conveyors 40-60 cm Speed 16-140 rpm Advantages of screw conveyors: Effective conveying of even packed products. Good control of conveying capacity. Conveying in all directions is possible. Their disadvantages include: High energy consumption. Products are conveyed without much care. Fire and explosion danger, if dust is packed in the conveyor

10. Pneumatic Conveyors Granular food solids, grains, and powders can be conveyed to long distances through ducts with high velocity air streams. Typical applications include the unloading of granular foods from railroad cars and ships and the transport of such materials within the food processing plant. Food materials handled include wheat, corn, flour, beans, coffee, and granular sugar. The pressure conveying system receives particulate material from one source and delivers it to more than one place (bins), while the vacuum system can receive material from several sources and deliver it to one receiving bin. Vacuum conveying is more expensive than pressure conveying, but it is preferred in transporting dusty products, since it reduces air pollution and explosion hazard.

11. Required data for the design calculations are bulk density, air velocity, and length of the pipeline. The table provides estimated data for the required air saturation of the system (std m3 /kg solids) and the power (kW/t h). The basic equipment of pneumatic conveyors includes the following units: Air blower , usually of the positive displacement rotary type. The blower provides pressure drops up to 0.8 bar . A similar blower is used in vacuum conveying, with a pressure drop of 0.4 bar. 2. A solid feeder, usually of the rotating valve type. 3. A transfer line (duct), diameter 76.2–178 mm (3–7 in.) Schedule 40, or 200–305 mm (8–12 in.) Schedule 30. Length of the line 100 m or higher. 4. Smooth bends of long radius (r), e.g., r ¼ 12 (pipe diameter). 5. Dust collection equipment at the receiving bin (usually filter bags).

12. Hygienic Considerations Perishable foods should be transported fast, avoiding microbial or chemical/biochemical deterioration. Fresh foods, such as fruits and vegetables, should not be bruised or damaged mechanically by the conveying equipment. Belt conveyors are more hygienic than other mechanical transport equipment, e.g., screw conveyors. Smooth belts can be kept more hygienic than segmented, indented, or screen (perforated) belts, which can hold food residues, supporting microbial growth. Plastic and Teflon-coated belts may develop cracks, where food residues may adhere, resulting in undesirable microbial growth. Belts are cleaned and washed with detergents and water, using mechanical scrubbing devices, and installed at the return loop of the belt (Troller 1993). Antimicrobial substances, such as triclosan, could be used to sanitize the belts, provided that they are approved by public health authorities.

13. Extruder

14. Typical components of an extruder An extruder can be divided into four different sections or components. Feeding (delivery) system. 2. Preconditioner. 3. Extruder barrel. 4. Knife cutter

15. Delivery Systems The first basic component of the extruder is a delivery system. The purpose of this section is to deliver, uniformly, the food ingredients/recipe or raw material to the next components. Consistent and uniform feeding of ingredients is necessary for the consistent and uniform operation of an extruder. Preconditioner Material from the delivery system is fed into the next section of the extruder, which is called the preconditioner. It is not necessarily true that every kind of extruder will have a preconditioner. Most of the dry extruders and direct-expanded snack food extruders do not. However, the majority of the food and feed extruders will have a preconditioner. Extruder Barrel The barrel is the heart of the extrusion system. Most of the work is done by this section of the extrusion system. This component consists of screws, sleeves, barrel heads, and dies. This section makes the extruder either a single screw or twin screw extruder. If we have two shafts parallel, then it will be a twin screw extruder, but if we have only one shaft, then it will be a single screw extruder.

16. Knife Assembly This is the fourth and last part of the extrusion system. The main function of this component is to cut the product to the desired length and shape. The knife assembly can be a different design depending on the manufacturer of the extrusion system. There is the option to use two, four, or six knives in the assembly.

17. Types of extruders Single, Segmented Screw Extruders The degree of shear can be modified in two ways: 1. By using shear locks of increasing diameters, requiring increasing pressures to force the product into the adjacent worm section; 2. By selecting between a grooved- and a spiral-walled barrel. More mixing and shearing occurs with the grooved barrel because of greater slippage between the screw flight and barrel walls. Solid screw extruders are still built for special low-pressure cooking and forming applications. But, segmented screw worms and barrel sections offer considerable versatility in customizing screw barrel design and replacing worn parts, and are used in the majority of both single screw and twin screw extruders.

18. Most of the single screw extruder’s processing conditions can be controlled to achieve a variety of effects. For example, cooking temperature within the extruder barrel can range from 80 to 200 C, by configuring with high shear screws and shear locks, injecting direct steam, heating the barrel by circulating steam or heating oil, increasing the speed of the shaft or restricting the die open area. Similarly, residence time in the barrel can be varied from 15 to 300 s by increasing or decreasing the speed of the shaft. In general, single screw extruders have poor mixing ability. Therefore, material should be premixed, or a preconditioner should be used for proper mixing of the ingredients. A typical single screw extruder consists of three different zones: feeding zone, 2. kneading zone, and 3. cooking zone.

19. Dry Extruders All extruders are basically screw pumps through which material is forced, while in the meantime subjected to heat, cooking, and shear forces. The term dry extrusion, as opposed to wet extrusion, refers to the fact that this type of extruder does not require an external source of heat or steam.

20. New Generation Extruders New generation extruders offer several advantages compared to regular extruders. Some of these are ( Rokey , 1998; Strahm , 1999): • 30 -50% increase in capacity. • 5-20% reduction in bulk density. • .25% reduction in energy consumed. • Reduced sensitivity to worn components. • Improved processing of high-carbohydrate diets. • Reduced processing and capital cost.

21. Twin Screw Extruders In twin screw extruders, the screw either rotates in opposing directions (counter-rotating) or in the same direction (co-rotating). Regarding screw position, extruders can have: intermeshing screw in which the flight of one screw engage or penetrates the channels of the other screw, or 2. non-intermeshing screw in which the screws do not engage each other’s threads, allowing one screw to turn without interfering with the other. Non-intermeshing screw extruders function like single screw extruders but have a higher capacity

22. Therefore four types of twin-screw extruders are possible (Miller, 1990): • Non-intermeshed, co-rotating. • Non-intermeshed, counter-rotating. • Intermeshed, co-rotating. • Intermeshed, counter-rotating

23. Fermenter The fermenter or bioreactor are defined as the heart of fermentation process within this fermenter many reactions and activities occur. In fermentation technology whole study is involve, activities like downstream, upstream and midstream studying and controlling them. The fermenter/bioreactor is the vessel that provides biomechanical and biochemical environment which regulate the transfer of oxygen, nutrient to cells and metabolic products from cell. Bioreactor vessels are designed to utilize activity of catalyst to attain desired chemical transformation Fermenter or Bioreactor are cylindrical shape vessel having hemispherical bottom and top and they are mostly made of glass and stainless steel. Difference between classic composting system and the bioreactor is controlling and measurement of the composting process parameters is more in bioreactor Size of Fermenter Vessel and Material The sizes of the bioreactor vary widely from the microbial cell (few mm 3 ) to shake flask (100-1000 ml) to laboratory scale vessel (150L) to pilot level (0.3 10 m 3 ) to industrial scale (2 500 m 3 ) for large volume industrial applications. The width of the manufacturing substance increases with scale. At 3,00,000 4,00,000 dm 3 capacity, 7mm plate are gener al utilized for the side of the vessel and 10mm plate for the upper and lower part, it should be hemispherical to resist pressures.

24. Fermenter Operation There are three different types of operation that are batch, continuous and fed-batch or semicontinuous depending on feed of the fermentation media and the cultures into bioreactor Batch Fermenter Design The impellers in STRs connected to an exterior motor, which runs the stirrer system. The assembly of agitator including seal is a way of contamination so the shaft has to pass from aseptic seals into bioreactor.

25. Construction Material As fermentation required adequate aseptic conditions, for better yield of biomass or product, it is important to select a material for the body of the fermenter, which restricts the chances of contamination. Moreover, it needs to be non-toxic and corrosion free. Glass is a material that provides a smooth surface inside the vessel and also non-toxic in nature. Apart from that, it is corrosion-proof and due to the transparency, it is easy to examine the inside of the vessel. There are mainly two types of glass fermenters A glass vessel with a flat bottom and a top plate with a diameter of 60 cm (approximately). Sterilization of this type of vessel is performed by general autoclaving. Borosilicate battery jars were used as large glass vessels. The second glass vessel contains stainless steel plates at the top and bottom of the glass vessel. In situ sterilization is possible for this type of glass vessel. However, it is more expensive than the glass top vessels due to the use of stainless steel plates.

26. The main disadvantage of glass vessels is that it is difficult to top to design a pilot-scale fermenter with glass. It is difficult to handle glass as a pilot-scale fermenter. Therefore, another non-toxic, corrosion-proof material, stainless steel, was used for pilot scale fermenter. According to America Iron and Steel Institute, steel contains more than 4% chromium is standardized as stainless steel. However, the minimum amount of chromium required to protect the steel from corrosion depends on the corroding agent present in a specific environment. In a pilot-scale fermenter normally the steel contains around 10-13% of chromium. In many cases nickel is also mixed in high concentration with the chromium to make the steel more corrosion resistant and it also provides engineering advantages. In this modern-day, stainless steel fermenters are mostly used for industrial production. However, small scale production requires glass vessels.

27. Temperature Control During the fermentation process heat can be produced mainly in two ways, firstly microbial biochemical reactions and secondly mechanical agitation. In case of fermentation, a temperature control helps to control the temperature at the optimum level by removing or providing heat. In small scale production vessel the amount of produced heat is negligible. Therefore, extra heat is provided by hot bath or internal heat coil or heating jacket with a water circulation system or silicon heating jacket. The silicon heating jacket consists of silicon rubber mats with heating wires and it is wrapped around the fermenter. In the case of pilot-scale fermenters, it is not possible to use silicon jackets due to large size. In such cases, an internal heating coil is used for providing extra heat while cold water circulation helps to remove excess heat.

28. Agitator (Impeller) The objectives of the impeller used in fermenters are bulk fluid and gas mixing, air dispersion, heat transfer, oxygen transfer, suspension of solid particles, maintain the uniform environment inside the vessel, etc. Air bubbles often cause problems inside the fermenter. Impellers involved in breaking the air bubbles produced in a liquid medium. There are mainly three types of agitators used in industrial-scale bioreactors Disc Turbine :  It consists of a disc with a series of rectangular vanes connected in a vertical plane around the disc.

29. Vaned disc :  In this case, the rectangular vanes are attached vertically to the underside of a disc. Variable Pitch open turbine :  This type of agitator lacks disc and the vanes are directly connected to a center shaft.

30. Stirrer glands and bearings The most important factor of designing a fermenter is to maintain aseptic conditions inside the vessel. It is highly challenging in the case of pilot-scale fermenters. Therefore stirrer shafts are required. These stirrer shafts play an important role to seal the openings of a bioreactor. As a result, it restricts the entry of air from outside. The Stuffing Box:   The shafted is sealed by several layers of packing rings of asbestos or cotton yarn which is pressed against the shaft by gland follower. At high stirrer speeds, the packing wears quickly and excessive pressure may need to ensure the tightness of fit. The packing may be difficult to sterilize properly because of unsatisfactory heat penetration and it is necessary to check and replace the packing rings regularly.

31. The Mechanical Seal:  It is used in both small scale and large scale fermenters. The seal is divided into two parts, first is the stationary bearing housing and the second rotates on the shaft. These two parts are pressed together by springs. Steam condensate is used to lubricate and cool the seals during operation and provides protection against the contamination.

32. Magnetic Drives:  This type of seals helps to counter the problem originated by the impeller shaft which is going through the top or bottom of the fermenter plate. The magnetic drive is made up of two magnets one is driving and one driven. The driven magnet held in bearings in housing on the outside of the head plate and connected to a drive shaft. The internal driven magnet is placed on one end of the impeller shaft and held in bearings in a suitable housing on the inner surface of the head plate. When multiple ceramic magnets have been used it has been possible to transmit power across a gap of 16mm. Using this drive water can be stirred in baffled vessels up to 300 dm 3  capacity at speeds of 300 to 2000 rpm.

33. Aeration system Aeration system Aeration supports the growth of the organism by providing appropriate amount of oxygen in the fermenter. The device such as sparger is used to introduce the air in the fermenter. Aerators producing fine bubble should be used. Oxygen is easily transfer through the sparger to greater amount with the large bubbles which has less surface area than the smaller bubbles. In the case of airlift fermenter agitations not necessary, aeration provides enough agitation. But this is feasible with medium or low viscosity or less amount of total solids. Sparger contains air filter to supply sterile air into the fermenter. Three types of the sparger are used widely (a) porous sparger (b) orifice sparger (c) nozzle sparger

34. Baffles There are four baffles that are present inside of an agitated vessel to prevent a vortex and improve aeration efficiency. Baffles are made up of metal strips roughly one-tenth of the vessel diameter and attached to the wall. The agitation effect is slightly increased with wider baffles but drops sharply with narrower baffles. After installation of the baffle there a gap between them and the vessel wall which facilitates scouring action around the baffles and minimizes microbial growth on the baffles and the fermenter wall. Baffles are often attached to cooling coils to increase the cooling capacity of the fermenter. pH control sensors All types of fermenters are attached with a pH control sensor which consists of a pH sensor and a port to maintain the pH inside of the fermenter. pH alteration can lead to death of the organism which leads to product loss. Therefore, it is a crucial instrument for a fermenter and needs to be checked regularly.

35. Fermentation Process It involves the propagation of the microorganism and the production of the desired product. Fermentation process is divided depending on the feeding strategy of the culture and medium as follows. i . Batch Fermentation ii. Continuous Fermentation iii. Fed batch Fermentation

36. i . Batch Fermentation The medium and culture are initially fed into the vessel and it is then closed. After that, no components are added apart from Oxygen. The pH is adjusted during the course of process by adding either acid or alkali. The fermentation is allowed to run for a predetermined period of time and the product is harvested at the end. Foaming is controlled by adding antifoam agents such as palm oil or soybeans oil. Heat generated is regulated by providing water circulation system around the vessel for heat exchange. ii. Continuous fermentation This is an open system. It involves the removal of culture medium continuously and replacement of them with a fresh sterile medium in a bioreactor. reactors which include chemo stat and turbid stat bioreactors are used. Examples: production of antibiotics, organic solvents, beer, ethanol and SCP

37. iii. Fed batch system It is a combination of both batch and continuous systems. In this, additional nutrients are added to the fermentors as the fermentation is in progress. This extends the time of operation, but the products are harvested at the end of the production cycle as in batch fermenter.