- Pre – Cleaning & Dust Collection
The first step in pelleting is conveying ingredients from bulk silos or godown to the batching bins. It is essential to remove oversize foreign materials and iron trash etc. which otherwise can affect the functioning of slide gates, gravity /screw feeder in batching or downstream. Pre-cleaning machines generally include rotary sieve, jute remover, magnetic catchers, etc. In automatic plants, it is desired that system is designed to give continuous efficient cleaning at a maximum flow of ingredients.
In modern plants, automatic weighing of different materials as per formulation to make one batch is called batching or proportioning. In this, any no. of silos of suitable capacity as per the total capacity of the plant, are incorporated and are having gravity or screw feeders for controlled discharging of material into weighing bin underneath it. Generally, two sets of bin or silos are installed - one for major ingredients, second for minor ingredients. The discharge of both weighing bin come into common surge for further processing. Bin vibrator or shaking devices are installed on some or all of the bins to make the material flow in case of jamming of the bin.
The weighing is done through an electronic controller working on PLC or microprocessor-based, which can be operated through a computer. The computer control and record all the detail of a batch- over or under weighing of ingredients from setpoint, reporting on each batch, shift, day, weak, monthly basis. The generally desired features of a batching system are:
It should give accurate weighing within the specified time to meet the output of the plant.
Though it should be highly reliable and work automatically, it should have manual control also in case of auto failure.
After batching, the next step is to reduce the material to the required degree of fineness to have maximum surface area for exposure to heat and moisture to accomplish gelatinization in conditioners.
In pelleting process grinding and pelleting are two major energy-consuming operations.
If we can perform fine grinding with a minimum of energy, it will not only cut grinding costs but also save on the energy required in pelleting.
Efficient mixing of micro-ingredients in a whole batch is significant in making quality feed. The designed features of a good mixing system are.
It should perform mixing to achieve a minimum coefficient of variation in minimum time.
The mixer discharging mechanism should aim at no leakage of gates with minimum residue in the drum to avoid carryover to the next batch.
Conditioning is done to add heat and moisture in mixed feed to achieve gelatinization and making the product more pliable for pelleting. An ideal conditioning system should meet the following:
It should raise the temperature and moisture of the product by direct or indirect heating.
It should give desired retention time in conditioners.
After conditioning, the product is passed through a die-in pellet mill with the help of rollers and powdery material is converted into pellets. The quality and output of pellet mill is dependent on so many parameters, like;
Quality of grinding, conditioning, Formulation of feed: - (percentage of oil, protein, fiber, etc.), Die configuration: - Deciding working on the product in pelleting.
Crumbling is a process in which a pellet after cooling is broken into small pieces to make it suitable for small chicks. If not required it can be bye-passed and the product escapes from the side of crumbling rolls. A well-designed crumbler should have the following features:
Should give the uniform size of crumbs at both ends of crumbling rolls.
Should break the material without making many fines.
Should have a mechanism for equal gap adjustment on both sides.
Product coming out of crumbler is either in pellets (if crumbler bye passed) or crumbs form. These are required to be screened to remove fines and overs. Single-deck screeners are used to removing fines only while double deck screeners are used to removing both fines and overs. The unbroken or the overs are returned to crumbler and fines return to the pelleting line for re-pelleting.
After the screener, the finished product is filled into bags. In small to medium plants, bagging can be carried out manually but for higher output, it is better to go for an electronic bagging machine.
An electronic bagging machine can perform bagging with high accuracy and a much faster rate.