By Carlos Elwart Flow chart of the extrusion line, drying and milling Flour loading Volumetric dosimetry Steam Conditioning Water Indirect heating Extrusion Water Cut Drying Warm air Cooling Fresh air Milling Bulking Packing By Carlos Elwart Operation of the extrusion line, drying and milling Flour loading: The loading of raw flours is carried out in a platform opposed to a 300 kg grain feeder. This grain feeder possesses a separating grid of thick particles such us bags, cardboards, threads etc. At the bottom of the grain feeder, there is an elevating screw that carries the flour up to the platform of the volumetric dosimeter. Volumetric dosimeter: The flour, coming from the loading feeder, falls into a stainless steel lung tank. At the bottom of this lung tank, there are two parallel screws which turning speed is related directly to the amount of flour being measured. This equipment has a speed shifter and therefore its load can be varied into the following stage. Conditioning: This operation is carried out by a stainless steel, which possesses inside an axle with transporting pallets. This equipment contains water and steam ingress. The water entering into the equipment is perfectly known since its ingress is performed through a Moyno bomb that defines accurately the coming-in volume of water. The steam entering into the equipment is controlled by a modulating valve that is subject to the temperature set required in a thermocouple which is attached to a side of the outlet of the conditioning unit. The conditioning unit has a cladding mouth and this implies the heating in the outlet and in equipment attached to the conditioning unit. This equipment, that connects the conditioning unit and the extruder, is called diverter. This stretch possesses a small screw conveyor that allows the accurate introduction of conditioned flour within the extruder. Extrusion: Iin this stage the wet and warmed flour is carried into the extruder. The flour fills in the extruder screws, and in this way the screws have the function of mixing, warming, cooking and changing the flour structure. These screws have a speed shifter and therefore, the turning speed is a determining factor in the operation. The whole casing of the extruder has cladding, through which steam circulates and it warms the extruder barrels. It is possible to inject water into the extruder to wet the product, if necessary, since the coming-in volume of water is perfectly known for being injected by a moyno bomb with speed shifter. In the extruder extreme, there is a mould which is a plate with 60 wholes of 3 mm. As the product has high pressure, high temperature and low humidity inside the extruder, when it goes out to the environment, it undergoes and expansion and therefore its density varies. Cut: As the product goes out in a continuous way, it meets four shears turning at a very high speed which allows the cutting of the product in a predetermined size and shape. The size and shape are very important in the following stage of the drying. Once the product has been dried, it is carried pneumatically into the drying machine; this carriage is performed by a high pressure fan, which aspires from a cyclone that is located on top of the drying machine, where the product undergoes a cyclonic effect and falls into a canal which makes the extruded pellet enter within the drying machine. The humidity of the product on the extruder outlet depends on the amount of water and steam that has already entered into the conditioning machine and on the amount of water that has already entered into the extruder. Generally, the humidity is 16-18%. By Carlos Elwart Drying: The product enters the drying machine through a distributor, that consist on a stainless steel oscillating bar, that allows the uniform outlet along the whole extension of the transversal conveyor of the drying machine. The drying machine basically consists of a horizontal stainless steel conveyor that carries the product. The drying is performed by means of warm air that comes from a centripetal fan which takes the air from the environment and drives it through a pipe. The air gets at a natural gas burner that produces warming of the air. The air temperature can be controlled by a thermocouple, which measurement is associated with the admission valve of the natural gas burner. The warm air enters the low part of the conveyor and flows through the product layer; the drying machine possesses two inlets in each side. In the final stretch of the drying machine, there are two lateral injection cones, one in each side of air injection, aiming at cooling the product. The wet and warm gases are removed from the drying machine by a fan that aspires through a cyclonic divider in the following way: it eliminates these gases out and the little carried particles are collected in the mouth of the cyclone. Once the product has been dried, it falls from an elevator of oscilling buckets, that carries the product into the following stage. Milling: Once the product is dried, it falls within a distributor that guides the product into the milling chamber. The size of the product is reduced by the action of shears that turn at a very high speed. The size will depend on the fabric sieve located it the mill, these fabrics are exchangeable. Bear in mind that the turning direction of the mill must be inverted each week as well as the clapped of the product admission into the mill. The sizes of meshes that can be employed in the mill are 0.6mm and 0.9mm. There is a mechanism by which it is possible to make a product by pass so as to avoid its ingress into the mill and to pack a pellet in predetermined shape and size. The carriage into the sleeve filter is performed from a high pressure fan. Once the size of the product has been reduced, the pneumatic carriage takes it into a cyclone that contains a sleeve filter. This filter prevents the product from escaping into the atmosphere. Bulking: The product falls from the sleeve filter through pipes up to the bulking. This can be carried out in bags of 25, 50 or large bags of 500 kg. Packing: This operation is carried out in the fractionation sector, in different formats: 125g, 250g, 350g, 400g, or in the format requested by the customer.
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