Conditioning: Influencing Factor of Feed Pellet Quality
In recent years, with the rocketing development of feed industry, feed pellet has been used widely in livestock and fisheries, and the need of feed pellet has a tendency to grow continuously. Therefore, the feed pellet manufacturers have to improve the feed pellet quality to meet the demand of the market.
There are several factors affecting feed pellet quality, such as feed formulations, steam conditioning, grinding, etc. Steam conditioning is likely to be the most important factor affecting feed pellet quality. Research has shown that it plays about 20% of the role in the influencing factors of overall quality of feed pellets. It improves compressibility and binding properties of feed mixtures. The correct conditioning of the feed mixtures is necessary to obtain the good quality feed pellet and an effective utilization of the pelletizing or extrusion installation. In order to achieve an ideal conditioning result, feed manufacturers must consider the moisture content, steam quality, and modulation time in the conditioner, as well as the dimension of the conditioner in order to optimize pelletizing.
The moisture in the feed serves as the conduit for the transfer of the heat into the feed particles. Studies have shown that moisture addition to the feed has a positive effect on the conditioning process. Moisture is vital for proper agglomeration of the materials and aids in the formation of a durable feed pellet. It also helps ease the passage of the materials through the die by reducing friction. The improvement in gelatinization can also be achieved through proper moisture addition. Besides, the addition of moisture greatly improves the efficiency of the conditioning process by using the fundamentals of heat transfer to move the moisture from the outside of free particles to the interior.
The key to get good quality feed pellets is to target conditioned feed moisture about 16.5-17.0%, and maintain this moisture at all time. If the manufacturers have a good control of moisture content, they will have a better chance to produce high quality pellets consistently.
2. Steam Quality
The steam quality is critical to the correct operation of a pellet mill’s steam harness. It is essential that good steam has the right quantity of heat to optimize the migration of moisture into the interior of the feed particles. Steam conditioning of feed particles requires saturated steam. Wet steam transfers its heat less efficiently than saturated steam and can cause uneven moisture distribution in the mash, resulting in choking or slipping of the pellet die.
The characteristics of the steam affect the conditioning process, saturated steam can increase mash temperature by 60º F (16°C) for every 1% added moisture, while wet steam increases mash temperature by 56º F (13.5°C) for each 1% increase in moisture. The poor quality steam can reduce conditioning temperatures by 43º F to 52º F (6°C to 11°C).
3. Modulation Time
The optimum modulation time for any particular conditioner is the time required for the heat and moisture to reach the centre core of each feed particle. The longer modulation time makes greater degree of gelatinization, which can improve the durability of the feed pellet. Generally, 15-30s is sufficient to meet the need of conditioning. Specific parameters of modulation time depend on the formulation and pellet mill models. Some special types of feed pellets need high degree of gelatinization before pelletizing. So it needs long modulation time. Generally, the aquafeed, livestock and poultry feed need long modulation time.
Some attentions need to be paid to the configuration of the pick angles and the speed of conditioner shaft, which affects the modulation time. By adjusting the picks in the conditioner to the parallel setting, a 5 point increase in feed pellet durability can be achieved. By decreasing the speed of the conditioner shaft, the modulation time would be increased from 5-10 seconds to 20-25 seconds. Also, increasing the modulation time by altering the pick angle is a strategy for increasing feed pellet quality. However, debate exists regarding to the optimum setting. Suggesting pick angle at 45°and discharge of the conditioner at 0° in the center of the conditioner maybe a bit too aggressive. However, the concept remains: altering pick angle can increase modulation time, which will increase feed pellet quality.
A conventional conditioner with a single shaft and a single barrel must be large enough to achieve the proper modulation and mixing time. Generally, the length of sing shaft conditioner is 2-3 meters, the modulation time is 20-30 seconds, and the degree of ripening is about 20%, which could meet the conditioning requirements of some ordinary feeds.
The double-shaft conditioner offers a definite advantage over the single shaft conditioner due to the two conditioner shafts, which are dissimilar in diameter and rotate counter to each other. The counter-rotating shafts are laden with picks set at varying angles, which causes the feed to be mixed evenly in the conditioner barrel. The modulation time can reach up to 240 seconds, and the degree of ripening is 50-60%, which can meet the requirements of special feed pellets. Besides, there are fewer residues in the conditioner.
If you intend to make high quality feed pellets, it is better to take the above influencing factors into consideration when conditioning. I hope you can benefit from it.