Tilapia Fingerlings Feed Pellet Processing
I. The Fish Feed Formula Design
1.Clear TargetMinimize the cost and maximize economic benefit
2. Nutritional Requirements of Tilapia Fingerlings: Water≤ %12.5, Crude protein≥ %40, Crude fat %6-9, Crude fibre≤ %3, Crude Ash≤ %14, Lysine≥ %2.5, Sulfur-containing amino acid≥ %1.5, Total phosphorus≥ %10, Total Energy(MJ/Kg)≥ %16.0
3.Physiological Digestion Characteristic of Tilapia Fingerlings in Growth StageAnimal food accounts for larger proportion in tilapia fingerlings diet. When tilapia fingerlings grow to 5 cm, they need higher content of protein.
II. Principle of Feed Formula DesignScientificity, practicality, economy and security
III. Feed Formula of Tilapia Fingerlings
IV. Basic Demands for Feed Pellet Processing
1. Receiving Different Types of Raw Materials
♦ Bulk raw materials: for bulk materials transported by truck or train, unload the material into discharging pit by the truck after materials are weighed by the weighbridge.
♦ Packaged materials: unload by manual handling or mechanical handling.
♦ Liquid materials: bottled liquid materials or barrelled liquid materials can be directly carried into the warehouse by manual power.
2. Storing Raw Materials
Due to various forms of raw materials, different types of stock bins should be applied depending on the characteristics of raw ingredients.There are two types of stock bins: silo and house-type warehouse. The major ingredients, cereal materials like corn and sorghum, are characterized by good fluidity and less susceptible to agglomeration, which can be stored by the silo. However, the minor ingredients, like wheat bran and soybean meal, are featured with powdery and poor flow movement, which are easily caked after a period of storage resulting in further difficult discharging. Therefore it is better to use house-type warehouse to store these materials.
3. Cleaning Raw Ingredients
There will be dust or other impurities in the raw ingredients, which not only directly affects pellet quality but also concerns feed processing equipment;quality and operation security. It may be worse that impurities badly damage the equipment to result in the shutdown of machines. So to protect the processing machines and ensure the pellet quality, impurities should be eliminated in time. There are impurity cleaning equipment in application including screening equipment and magnetic separation equipment. The former is for removing big and long sundries in the ingredients like blocks, clods and etc.. The latter is used to remove the iron impurities.
4. Grinding Raw Materials
The grinding process by fish feed hammer mill depend on particle size required, material variety and so on. According to the grinding frequency, there are one-off grinding or regrinding(cycle grinding). According to the working sequence of material proportioning and grinding, there are pre-proportioning & post-grinding and pre-grinding & post proportioning.
a. One-off grinding
It is the simplest and the most common grinding way. Whether the single material or mixed materials, the one-off grinding can be applied. Depend on the number of grinders, there are single machine grinding and coordinate machines grinding. For small scale feed processing factory, single machine grinding is commonly adopted. In medium scale factory, two grinders or more are used for grinding process. The weaknesses are nonuniform particle size distribution and higher power consumption.
♦ Regrinding in single cycleAny material that enters the grinding chamber must be reduced to a size below the diameter of the screen holes to pass through the screen that covers the mill’s discharge opening. Crushed by the grinder, materials are sieved by the siever. Through sieving, larger size particles will return to the original grinder for regrinding.
♦ Regrinding in stagesTwo grinders with different screens are respectively equipped with a two-layer grading siever.Through the first siever, eligible particle sizes on the below layer can directly go into the blender, but particle sizes on the upper layer will enter the first grinder for regrinding, then they will be sieved by the second grading siever. Qualified particle sizes will enter the blender, and particle sizes not meeting the demand will go into the second grinder for pulverizing and then go into the blender.
♦ Regrinding by pulverizing combinationTwo types of grinders are utilized. Double-shaft grinder for the first grinding and the hammer mill for second grinding. These two grinders are connected by the two-layer grading siever.
c. Pre-proportioning & post-grindingProportioning ingredients based on the certain ratio in formula, then pulverize mixed ingredients in the grinder.
d. Pre-grinding & post proportioningFirstly crush raw materials, and then proportioning crushed materials according to the formula.
5. Feed Material Proportioning
a. Proportioning ingredients by manpowerThe process is that feed materials for proportioning are weighed by manpower and then are poured into the mixer. This type of material proportioning by manpower is widely employed in small scale feed processing plant. The advantages are simple process, low equipment cost, low product cost and flexible weighing. The disadvantages are high labor intensity, low labor productivity and more prone to make mistakes under long-term working.
b. Volume-type batcher for the stock binc. One weighing machine for one stock bind. One weighing machine for several stock binse. Several weighing machines for several stock bins
6. Feed Mixing
♦ Batch mixing: based on the proportion of formula, different ingredients are mixed in batches in “the batch blender” which operates periodically. It is convenient to adjust the formula to mix in batch type, and there is less mingling in each batch. The design and the method of operation of the batch mixing provide for a high degree of mixing precision. This kind of blending is widely applied in the feed processing industry. Due to frequent opening & closing operation, batch mixing is usually controlled by the auto-programming system.
♦ Continuous in-line mixing: the mixer can continuously blend ingredients to form homogenous flow of materials. The merits are: continuous blending, convenient to connect the crushing and pelleting and not frequent operation. The shortcomings are: difficult to control material flow and materials mingling seriously in each batch.
7. Feed Pellet Making Process
♦ ConditioningConditioning is the most significant part in pelleting, which directly affects the quality of feed pellets. By conditioning mixed dry ingredients has become the powdery feed with certain moisture content and humidity, which is beneficial to pelleting. Generally, good conditioning can be achieved by adding steam.
♦ Extrusion by fish feed extruderThe fish feed extruder is a long barrel with a screw auger inside which is specially designed to subject feed mixtures to high heat and steam pressure. When feed exits the die at the end of the barrel, trapped steam blows off rapidly, the soft warm pellets expand, and a low density floating pellet is produced. After that a cutting device will cut the formed pellets into different length as required.
♦ CoolingDue to steam in pellet making with high temperature and moisture content and quantity of heat generated by material compression, pellets come out of the pellet machine are with high moisture content of 16-18% and temperature of 75-85℃. In this situation, pellets can easily stick to each other, lose their shape or even have chance of combustion and mildewing. So the cooler is indispensable to lower moisture content to below 14% and temperature to 8℃ higher or less than ambient temperature .
♦ Sieving and packingThere will be parts of materials not meeting the production demand, like powders. So to sieve pellets for getting uniform sized final products.