Amandus Kahl GmbH & Co. KG (Germany) - Press Release: For liquid addition in feed production, spraying at the end of the production line (PPA - post-pelleting application) has become established in recent years. In case a liquid quantity of > 7-8% has to be added to pellets, a vacuum application after pelleting or extrusion is inevitable. Compared to spraying pellets under normal atmosphere, 30 to 75% more liquid can be introduced into a product without it showing liquid on the surface. In the vacuum application, the liquid medium is not only bound to the surface, but penetrates the core of the pellets at the porous fracture surfaces and pores. Thus, fat additions of up to 30-40% are possible with extruded feed and 8-10% with pelleted feed. Enzymes and other active ingredients can also be added in small quantities, either directly or in a liquid mixture (blend).
The vacuum coating process was developed in the 1990s for the salmon feed industry in Norway and is now, 30 years later, also used for the production of pet food, poultry feed and in the food industry. The most common types of vacuum coater to date are twin-shaft paddle mixers and conical screw mixers. Long-known points of criticism with these mixer designs are high fines formation due to aggressive mixer tools, insufficient hygiene (caking, dead spots) and high specific mechanical energy consumption. Due to these points and the resulting market requirements, the machine manufacturer AMANDUS KAHL has reconsidered this process and developed a new technology for vacuum coating.
The new Gentle Vacuum Coater GVC consists of a rotating mixing drum that is swivelled around its own axis into different positions during the respective work cycles. The interior of the machine is equipped without separately rotating mechanical mixing tools, which offers maximum product protection and minimum breakage and abrasion. This is a crucial aspect, as resulting fines can lead to caking and, due to the higher surface area, would also bind more liquid and thus tend to over-concentrate. The mixer cover of the GVC contains both the spray nozzles for up to ten liquids and a special rubber lip seal for sealing during vacuum generation. After a sufficient vacuum of up to 50 mbar abs. has been generated in the machine, the liquid is sprayed onto the product kidney that forms during the mixing process. This then mixes gently according to the free-fall principle. The mixing drum is emptied by a vertical swivelling movement. Such a process with the machine type GVC 1000 was recently put into operation at the world's largest feed producer, among others. At the production site in Thailand, the machine is used to refine extruded fish feed.
Continuous operation on site has confirmed that, in direct comparison to a twin-shaft paddle mixer, the Gentle Vacuum Coater GVC can achieve consistent product quality with the production of less pellet breakage and fines. An analysis of the operating data shows that this machine can achieve enormous potential savings in production costs.
Cost Savings through the Reduction of Pellet Breakage and Fines:
From the perspective of plant operators, fines are a cost factor that should not be neglected. In the production of fish feed and pet food, the rule of thumb in Central Europe is 25 €/t of recycled fines. The reason is that in so-called dry recycling, the fines have to be added again proportionally before grinding and thus have to pass through the entire process again. This means that the entire mechanical and thermal process energy is used again. On top of this, there are the wear, maintenance and personnel costs, as well as the loss of production capacity due to precisely these fines.
Calculated on the basis of an example of a medium-sized fish feed company, an annual production of 80,000 t/a results in about 1-3% fines that are screened out of finished pellets. The causes of the fines are, apart from the stress on the pellets caused by mechanical conveying, mainly the mechanical stress during vacuum coating (e.g. with the twin-shaft paddle mixer). These 1-3% fines result in a total quantity of 800 - 2,400 t/a in the aforementioned operating example. Calculated with the above-mentioned rule of thumb of 25 €/t of fines, recycling costs of 20,000 - 60,000 €/a accrue for this production plant.
It has shown that by using the Gentle-Vacuum-Coater compared to a twin-shaft paddle mixer, the production of fines during vacuum coating can be reduced to less than 0.1% on average. Thus, the annual savings potential for a production plant is obvious.
Another problem is the fines that are produced both during transport of the feed to the fish farm and during fish farming due to the use of automated feeding systems. Particularly in the case of pneumatic pressure conveying from the transport ship to the floating net cages, as is frequently used in Scandinavia, for example, the stress on the pellets is especially high. Excessive pre-stressing of the pellets in the vacuum coater can lead to "micro-cracks" in the pellet structure of the finished feed. These cracks then lead to further break-up of the pellet structure after delivery to the fish farmer due to pneumatic pressure conveying (air speeds > 30 m/s). This results in pellet breakage and renewed fines formation. This fraction cannot be eaten by the fish and reduces the feed conversion rate (FCR). In RAS systems (recirculating aquaculture systems), this additionally leads to excessive contamination of the filter systems in the water treatment. This loss of feed and the resulting loss costs for the farm are usually significantly higher than the example calculated above, depending on the size of the fish farm.
Using the example of a medium-sized Scandinavian salmon farm consisting of 6 to 10 floating net cages, up to 40 t of pellets worth approx. 60,000 € are fed per day, depending on the water temperature. These feed costs give an idea of the dimensions in which savings can be achieved for the fish farmer by avoiding micro-cracks and the resulting fines.
Cost Savings through the Reduction of Energy Consumption:
Furthermore, the design of the new Gentle Vacuum Coater GVC provides potential savings in energy consumption. Compared to other vacuum coater designs of the same size, the GVC, operated by a 4 kW drive motor, requires up to 80% less drive power. In addition, in the standard version all drive motors in the entire system are operated with frequency converters (vacuum coater, vacuum pump, liquid pumps), which can save a further < 40% energy per drive motor.
Cost Savings through Automatic Cleaning (CIP):
As vacuum coating takes place at the end of the production line, there are high requirements in terms of hygiene and cleanability to prevent contamination. Compared to the twin-shaft paddle and conical screw mixer designs, the GVC has a high degree of self-cleaning, as the entire mixing drum is permanently in contact with the product. This means that there are no dead spots. In the event that cleaning with a rinsing liquid is nevertheless necessary, for example after the use of medical additives or other critical additives, the system of the GVC offers a fully automatic cleaning programme according to CIP (cleaning in place). The special feature is that this cleaning process does not require any personnel to carry out the disassembly and cleaning work on the machine. A water-based cleaning liquid is added to the GVC completely automatically, and after a short washing process, it is automatically drained into a separate outlet and disposed of. This results in significant savings for maintenance personnel as well as a reduction in downtimes.
Depending on the application example and the plant size, vacuum coating offers potential savings in operating costs in many respects. These can be easily calculated for each application.