Constantly increasing demands on quality and economic efficiency call for innovative solutions in the manufacture of end and intermediate products in the chemical, fine chemical, pharmaceutical and food industries. Especially where products for the building material, adhesives and sealants sectors are concerned, functional additives such as chalk, carbon black or calcium carbonate are essential. Their moisture content should be as close as possible to zero, preventing unintended reactions with other product components from impacting on quality. This is where conventional drying systems reach their limits. Bolz fulfils these demanding requirements with its cylindro conical dryer CCD. The gentle yet intensive mixing ensures short drying times without significant product debris. Drying is effected at a very low pressure of less than 30 mbar absolute and the final moisture content is no more than a few ppm, depending on the application.
The efficient cylindro conical dryer is often used after mechanical solid-liquid separation, but can also be operated without a preceding mechanical separation stage. It is an all-purpose dryer which meets various process requirements due to the different agitator designs including helix, double helix, paddle or segmented helix. Different application-specific materials are available for the product contacted parts, from stainless steel to (super) duplex, Hastelloy or titanium. Thanks to its flexibility, the Bolz cylindro conical dryer can be used for vacuum contact drying as well as for evaporation, sterilisation and alkalisation or as a reactor handling slurries, pastes, filter cakes, granules and powders.
Sophisticated functionality
The central mixing helix is the core technology of the Bolz cylindro conical dryer with its central shaft agitator. Precisely adapted to the vessel design and running close to the wall, the helix guarantees optimum mixing of the product. The mixing helix feeds the product upwards along the heated vessel wall, while in the centre of the vessel vertical mixing is ensured by gravity. Rotation results in a horizontal flow component. The three-dimensional mixing principle means new material is continuously fed to the heated vessel wall, leading to a homogeneous temperature in the dryer. In combination with a heated mixing helix, the optimised agitator achieves perfect mixing results and reduced drying times.
The vessel including the dished cover is heated by a jacket, half-pipe coils or pillow plates using heat carriers such as hot water, (saturated) steam or thermal oil, which can be heated to temperatures of up to 400 °C. By heating the complete dryer, the formation of cold spots is prevented. In addition, an insulating jacket keeps the heat inside the dryer and at the same time offers operator protection against injury.
A ball segment valve with an inflatable, sanitary lip seal is normally used as an emptying device at the cone’s central outlet, guaranteeing maximum tightness in vacuum or pressure operation. It allows the lowest helix segment to be adapted exactly to the ball segment’s geometry, thus minimising unmixed zones and product residues.
The cylindro conical dryer is often used as a vacuum contact dryer for increased throughput as well as gentle product drying at low temperatures. A vacuum pump provides the required vacuum, producing an operating vacuum in the dryer in the range from 5 to 100 mbar absolute. As a result, moisture evaporates at lower temperatures, throughput is higher and energy losses are reduced. The lower process temperatures have a positive effect on the quality of the end and intermediate products, particularly when handling temperature-sensitive substances such as enzymes.
For easy and hygienic cleaning, the Bolz cylindro conical dryer features WIP or CIP nozzles. At the end of the drying process and before the next drying batch starts, cleaning liquid can be sprayed into the interior of the dryer under (high) pressure while the agitator is rotating. After the cleaning liquid has been completely discharged, the dryer is heated and the remaining moisture evaporates.
Vapour filter
Like every Bolz dryer, the cylindro conical dryer CCD also has a vapour filter to prevent product particles from escaping into the environment or the connected vacuum pipeline during charging or discharging. The filter surface, filtration efficiency and material are always adjusted to the dryer size, the operating parameters and the product. To avoid condensation of the vapours and thus sticking and blocking of the filter elements, the vapour filter is heated and insulated. The vapour filter is jet-cleaned to rule out product deposits on the filter elements.
Wide range of applications
The Bolz cylindro conical dryer is not only used as a vacuum contact dryer. It demonstrates its flexibility and versatility in the production of cocoa, for example. First, the fermented cocoa beans, broken into cocoa nibs, are heated in the central shaft dryer by the addition of steam. An alkaline solution is then also added by means of overpressure and temperature, reducing the bitter flavouring components, raising the pH to approximately 7, washing out unwanted bitter substances and adjusting the cocoa’s colour. This process includes operation under vacuum, use as an overpressure reactor, homogeneous mixing and sterilisation of the broken cocoa nibs. The Bolz cylindro conical dryer is moreover ideal for sterilising spices by adding superheated steam as well as for evaporating liquid or pasty products, which are difficult or impossible to filter due to their low solids content, meaning that no mechanical solid-liquid separation can be installed upstream.
Bolz Process Technology GmbH, Wangen
Author: Frank Bessner
Product Manager,
Bolz Process Technology
