Conditioning is one of the processing steps in pelleting, it is a process to carry out water heating treatment to the powder raw material before feed pelleting. According to the domestic research, conditioning is one of the most important elements that affect the feed pellet quality, account for 20% of the total quality of feed pellet.

I. Functions of Conditioner in the Feed Pellet Processing

1. Aging the powder materials.

Most of the animals are poor at digesting the starch, but better at digesting the aging starch. Conditioner increases the starch degree of gelatinization by water heating, and promote the denaturation of protein in the materials, denatured proteins are easily digested, thus increase the digestibility of feed pellet.

2. Sterilize the powder materials.

Most of the pathogenic bacteria such as Escherichia coli and Salmonella are not heat-resistant. Conditioner can kill these bacteria content in the materials under a certain temperature, ensuring the hygienic quality of feed. Comparing with medicine disease prevention, this method has advantages of low cost, no pollution, no drug residue and side-effect.

3. Conditioner can improve the water resistance of feed pellet obviously. In the process of water heating treatment, stickiness component such as gelatinized starch, denatured protein can play the role of binder, effectively bind other components around. Under the pressure of die and roller, particles become closer, the pellets become compact and smooth at surface, not easy to be eroded by water, increase the stability in water.  

4. Conditioner can improve the granulation of materials, increase the yield, save pelleting energy consumption, lengthen the service life of pellet machine dies and rollers. By conditioning, materials are soften and with more plasticity, friction in the process of pressing through die holes, inner wall of die and roller surface reduced, preventing the plenty of mechanical energy translated into heat energy while pelleting, and slow down the wear of die and roller.

II. Types and Working Principles of Conditioner

1. Single shaft blade-type conditioner

This is the earliest and most widely used conditioners in domestic and overseas feed industry, the structure is simple, it is a cylinder shell with a mixing shaft in the center, the shaft is equipped with several adjustable and replaceable blades. When the conditioner working, materials move around the shaft and toward the shaft direction under the stir of blade, movement locus is similar to helix. Generally the rotation speed of conditioner is 150-450r/min, advance speed of material related to the shaft rotate speed and blade picking angle, in a certain rotation speed condition, operator can adjust the picking angle of the blade to control the material conditioning time, if the angle of the blade is reduced to the intermediate position, that is, an angle of 750 to 850 with the blade shaft, in this way, the pushing effect of each blade on the material can be weakened and the residence time of the material in the conditioning room can be prolonged. General single shaft blade-type conditioner length is 2-3 meters, powder can stay in the conditioning room for 20-30 seconds, aging degree reach to about 20%, basically meet the general requirements of some grain feed conditioning.

2. Steam jacket conditioner

This kind of conditioner structure is similar to the single shaft blade-type conditioner, the difference is the shell adopts double layer jacket, steam gets into the jacket for the function of thermal insulation. This kind of steam jacket conditioner has limited heating effect on the powder material, because the heat is transmitted to the material from the conditioner surface only. But the ratio of surface area to capacity is usually low, coupled with the usual poor heat-conducting property of the mixed powder, there is not so much heat to be transmitted to the material. However, steam jacket stop the direct heat exchange between condition room and outdoor temperature, effectively reduced the heat loss, so that the internal conditioning able to maintain a higher temperature. This kind of conditioner effect is more significant in the cold winter and areas with low temperatures.

3. Two-way, three-way conditioner

In order to lengthen and control the residence time for the powder materials to stay in the conditioner, sometimes we overlay 2-3 standard single shaft blade-type conditioner at the top of the pellet machine, this is two-way/three-way multi-layer conditioner we called. This kind of conditioner installed in series with each other, has several steam inject ports, powder materials get through every conditioners in turn, lengthen the tempering time, materials can be mixed with steam more sufficiently, increasing the aging degree of powder to about 40%. 

4. Double shaft different diameter different rotation speed blade-type conditioner

Double shaft different diameter different rotation speed blade-type conditioner is also called DDC pre-conditioner, it is developed from the single shaft blade-type conditioner, the shell is welded by two different radius semicircle, in the shell there are two mixing shafts with different rotation speed, and many independent steam volume adjustable steam ports and liquid adding ports. While the conditioner is working, since the shafts are different in rotation speed, opposite rotate direction, blades move at different speed, making the powder material and adding liquid threw up by the two shafts and become convection current, cut and mixed fully under the function of blade, part movement locus is “8” shape and pushed by pivoting, the movement route being lengthen, the axial movement speed of powder has a greater adjustable range. For 2m length conditioners general adjustable tempering time is from dozens of seconds to 240 seconds, which can satisfy the requirements for high aging rate and high sterilizing rate of special feed pellet, aging rate can reach to 50-60%, at the same time, blades with higher rotate speed and brush each other, making this type of conditioner has a high self-cleaning ability, powder residue in the conditioning room is also been improved.

5. Extender

Extender is also called expander, domestic name is annulus space extruding machine, the working principle of expander is same to extruder, using mechanical energy to increase the heat of materials before pelleting. Powder materials pass through the narrow space between screw and die under the pressure, being pressed and cut, having intense friction with screw and cylinder, producing plenty of heat, aging and sterilize the materials, improve the pelleting quality. Gap of dies is adjustable for expander, controlling the strength of compression, friction and cutting, to control the heat spread into the material. General expander can generate 40Pa pressure with the temperature of 120-130℃，materials physical changes quickly under this condition for just 3-5 seconds. The degree of starch gelatinization and the solubility of the protein were significantly improved. However, the heat-sensitive nutrients in the material will be a greater loss in the process of high temperature.

6. Universal pellet aging machine

Universal pellet aging machine is Universal Pellet Cooker, referred to as UPC. It is a new type of conditioning pelleting equipment first proposed by the Wenger factory in the United States. The system is basically made up of efficient conditioner and a set of improved short residence time extruding equipment. In the working process, conditioner supply residence and duration of exposure to improve the feed quality, while the improved extruding equipment forces the powder material gets through the proper size holes of the die and shaped to feed pellet. The degree of starch gelatinization of such equipment is quite high, typically greater than 70%, feed pellet is of good quality and water resistance. Even the powder material is added by more than 10% fat, the quality of pellet is still receivable. Another feature of this system is the replacement of the die is very simple and convenient. At present, this kind of conditioning pelleting equipment has a wide application prospect in aquatic feed, young animal feed and pet feed.

In addition to the above-mentioned conditioner, there is pressure conditioner, the basic concept is to improve the working pressure of the conditioning chamber, thus the temperature rise. High pressure can force the moisture and heat faster and more thoroughly get into the powder pellet inside, thereby improving the conditioning effect.