Multi-belt dryer-cooler combinations by stela Laxhuber, Massing
Today, extruded products are integral to the product range of almost every well-known manufacturer in the food, pet food and animal feed sectors.
In food production, the focus is mainly on snacks and breakfast cereals in a variety of shapes, colours and flavours, as well as filled co-extrudates, both sweet and salty. Similar products made from fish, meat and cereals can also be found in the pet food sector. The basic ingredients are usually grains such as maize, rice, wheat, barley and rye, while potato flour, soya and milk protein are also increasingly being used.
In both production areas, the focus is now on customer-specific products with a focus on a limited number of features specifically designed for customer groups. Muesli, for example, should be vegan or gluten-free, and dry food should be specially formulated for the older, long-haired domestic cat that moves very little.
This leads increasingly to production plants that accommodate this and can process small and medium batch sizes flexibly and efficiently.
The stela Laxhuber multi-belt dryer-cooler combination is a cost-effective and easy-to-maintain drying solution for this purpose.
For almost 100 years, the long-established Bavarian company has been solving drying challenges in a wide range of industries and can therefore, with its expertise that crosses the boundaries of individual sectors, offer attractive detailed solutions for customer-specific problems.
For example, after a first drying stage, the semi-finished product can be coated. The coating can be used to apply flavourings or to enhance the surface structure. This opens up a wide range of possibilities and raw materials such as vegetable oils, nuts, chocolate, honey, herbs and spices, milk powder, honey or cheese, in the food sector or flavourings, and fats and oils in animal feed production. A downstream, integrated cooling section then stabilises the products for the following packaging lines and feeds the heat released from the product back into the drying process.
With around 200 highly qualified employees currently working in development, planning, design, manufacturing and servicing of drying systems and a very high level of vertical integration, stela Laxhuber Trocknungstechnik GmbH, now in its third generation of family management, is a competent and reliable partner for all matters relating to drying and cooling, and not just in the food sector.
To date, around 4,000 agricultural and industrial drying systems have been delivered and commissioned in over 60 countries worldwide. While originally developed for the agricultural sector, the latest stela drying technology is now used in a wide range of food and non-food industries.
Almost all products leaving the extruder first need to have surface moisture, which is required for the mouldability of the product, reduced and removed. Only this way can the products achieve their desired consistency, dimensional stability and shelf life. There are a wide range of basic methods and designs for this drying process.
For products that require a high degree of uniformity and drying quality, belt dryers are the ideal solution. The drying process is continuous here, and the extrudates are also turned during drying and ventilated on all sides with multi-stage devices.
Coating (coat or spray) generally takes place outside of the drying process. This involves the use of flavourings, spices in fat-based suspensions or water-based sugar solutions for cereals. The extra moisture film that has been applied must be dried off in an additional step – drying, cooling or drying with cooling.
The suspensions applied in the process tend to cause the products to clump together quickly, and the solution that drips off clogs up the dryer. Dryers used at this point in the production process must therefore meet high cleaning requirements and also enable rapid and uniform drying without clumping of the products. This is the only way to ensure fault-free and uninterrupted production with constant product quality. Belt technology and geometry are key factors here. As a rule of thumb, the lower the pouring height and the higher the number of turning steps, the lower the risk of product clumping. Stela meets this cleaning requirement with large doors for good accessibility to the interior of the dryer, as well as a proven CIP (Cleaning-In-Progress) system, which partly even enables continuous cleaning during the drying. For belts, stela Laxhuber uses self-guiding stainless steel belts in various geometries and, depending on the application, also thermoset, cost-effective plastic belts.
After drying the product to the required final moisture content, an additional cooling process is usually required before the product can be further processed or packaged. This can be implemented actively using an external cooling circuit or passively with ambient air. The latter is an energy-efficient way of minimising production operating costs and ensuring long-term economic operation, alongside a sophisticated air circulation system in the drying area of the system.
Stela Laxhuber’s current flagship drying technology project in the pet food sector is a multi-belt dryer-cooler combination for Mera Petfood, Kevelaer.
This is another third-generation family business, which develops high-quality nutritional concepts adapted to the needs of the pet. The combination of high-quality ingredients, the highest quality controls and the regional production of the products in Germany are all part of the company’s tradition. Their long-standing partnership with stela Laxhuber has brought together two companies cut from the same cloth.
In response to the special requirements of the Mera specialists, stela designed a combined system with three independently operating drying and cooling belts. The new combination dryer/cooler performs both drying steps – before and after coating – as well as the cooling.
As well as cost-effective operation and low maintenance requirements, the design of the belt dryer stands out for its small footprint and ingenious air ducting. All process steps can be carried out with a single supply and exhaust air system; a gas surface burner provides the required heat in a space-saving “rucksack element” on the side of the dryer. The integrated zone partitioning with the corresponding multi-thermal stages allows the drying process to be adapted to the respective process step or product. The exhaust air from the cooling zone is automatically fed into the drying process. During the engineering phase, particular attention was paid to the interaction between product variance and belt geometry, as well as user-friendly cleaning of the belt to optimise the productivity of the system. After 12 months of dryer operation, stela Laxhuber’s concept proved to be completely successful.
Source: Der Lebensmittelbrief Ausgabe January/February 2021