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Top five technologies for drying in chemical applications

| By Chemical Engineering

ANDRITZ Separation has been serving industries ranging from petrochemicals and soda ash to agrochemicals for more than a century. What all these chemical applications have in common is the importance of highly efficient thermal separation with either continuous or discontinuous drying equipment.















At ANDRITZ Separation we are proud to offer the broadest portfolio of mechanical and thermal separation technologies and services available, guaranteeing you the resources you need to ensure decades of profitable performance. Thanks to our large product portfolio, we can recommend you the ideal solution for your process and project requirements rather than pushing one specific technology. This is why we would like to provide you with an overview of the top five most reliable drying technologies in chemical processes, all of which can be installed in a line with our ANDRITZ dewatering equipment, consisting of centrifuges (peeler, pusher and decanter centrifuges) or filters (drum, disc and cross flow filters or filter presses).

The table below provides a brief overview of the continuous drying technologies and how to select the correct dryer type. We will introduce these technologies in more detail as we move along:

If a hygienic design is very important and a batch process is requested, we recommend the helix dryer, which dries gently at low temperatures under vacuum.

Technology no. 1 – Fluid bed dryers, coolers and granulators: Safe and efficient drying and cooling





Fluid bed processing is basically simple and reliable. It was first used for industrial purposes in the 1920s. Almost one hundred years later, the technology is well established in all areas of bulk material processing industries. The key unit is a metal housing with a gas distribution plate that holds the product up. Fluidizing gas that is blown upwards from the bottom chamber via the gas distribution plate to the product chamber reduces the product to a fluid-like state. As fluidization is possible in a wide range of gas velocities, the technology provides stable processing and is quite resistant to fluctuations in feed rate, moisture and other changes in process conditions. The wet product is fed directly to the fluidized layer, where it is immediately mixed with warm and dry material. Mixing, heat and mass transfer as well as product transport through the product chamber is provided by the hydraulic characteristics of the fluidized layer itself. The final product is discharged from the fluid bed through an overflow opening. The mechanical impact on the particles is negligible so the fluidization process does not lead to substantial particle attrition. The exhaust gas containing evaporated moisture and dust leaves the dryer through its suction hood leading to the exhaust gas nozzle.

Fluid bed drying systems are tailor-made and come in all different shapes and sizes, so choosing the right one might be a challenge – but experience makes the difference! As ANDRITZ was among the first to introduce fluid bed technology for use in industrial drying (in the early 1960s), we are able to use our experience and target-oriented development of process solutions to provide you with the optimum solution for your process. No matter whether the best type of fluid bed is static (convective fluid bed DDC), vibrating (vibrating fluid bed VDC), high-temperature or a unit with built-in heat exchangers (heat exchanger fluid bed HDC), feeding or processing devices: ANDRITZ has them all and will find the best set-up for your particular requirements. A wide variety of design features, such as air distribution plates and different types of heat exchangers, enables ANDRITZ to put together the ideal fluid bed for your application.

Benefits of fluid bed dryers:

• Gentle and efficient processing
• Flexible when facing fluctuations
• Combined drying and cooling
• Easy to maintain

Technology No. 2 – The plate dryer: Exact temperature control for optimum thermal treatment

The ANDRITZ plate dryer is a vertically designed, continuous contact dryer/cooler available in atmospheric, gas-tight or vacuum configuration. Hazardous products can be processed in this closed system under vacuum or with inert gas blanketing. The plate dryer treats products very gently and without any impact on the environment. In addition, it can safely handle toxic or solvent-containing products. Stationary, horizontal plates in the dryer are heated while rotating arms with plows transport the product in a spiral pattern across the heated surface of the plates. As such, the product is repeatedly turned over and each particle comes into frequent contact with the drying surface. The thin product layer on the surface of the plates in combination with frequent turning over of the product results in a short retention time and uniform drying. This mode of operation protects the product against thermal degradation.

The fixed plates have a jacket on the underside and can be heated or cooled with a liquid heating medium or steam. Plates can be grouped together to form multiple heating/temperature zones, allowing exact temperature control for optimum thermal treatment. This is a unique ANDRITZ feature for continuous contact dryers. The number and the size of the plates are determined by the heat transfer surface required by the process and the number of temperature zones needed. The maximum heating temperature is 300 °C, and the typical heating medium is hot water, steam or thermal oil. Different arm and plow arrangements are possible on each plate: between two and eight arms, plow lengths between 90 and 160 mm and a forward or backward plow orientation. The plate dryer can also be adapted to specific operating conditions by adding optional features or extra equipment. These features have made the plate dryer a proven choice for various applications in the chemical industry, mainly for detergent additives, fungicides, herbicides, insecticides, salts, aluminum hydroxide and lithium, among others.

Benefits of the plate dryer:
• The drying process is optimized by adapting the product layer, the speed of the product conveying system, the number of conveying arms, and the type and size of the plows
• Suitable for a wide range of particle sizes
• No product back-mixing, ensuring consistent and highly reproducible product quality
• Precise adjustment of retention time
• Exact temperature control with separately heated/cooled plates
• Low mechanical stress on the product
• Unrestricted vertical product flow

Technology No. 3 – The contact drum dryer – Environmentally friendly drying with highest hygienic standards

In a drum dryer, products are dried by spreading them in a thin and uniform layer onto the heated surface. Due to the kneading effect of the applicator system and the scraped heat exchange surface, the dryer is unique for drying of viscous, pasty and sticky materials. Due to the short retention time of the product at high temperature, virtually no heat damage will occur. Contrary to the direct drying method, which uses hot air for evaporation, the drum dryer does not need any dust separation.

The thermal efficiency is favorable, whilst no heat is wasted in the largest volumes of exhaust air. A very thin layer of the product to be dried is applied to the outside of a rotating cylinder (drum). This drum is heated on the inside by means of steam. When in contact with the heated surface, the liquid will evaporate from the thin layer very quickly. After almost complete rotation of the drum, the remaining dried product is scraped off the drum surface in the form of a film or as a powder. A special composition of cast iron gives the drum a combination of favorable properties: very accurate shape retention even at high steam pressure and temperature as well as excellent “scraping properties” for the scraping knife. Steam heating ensures uniform temperature distribution over the drum surface, which results in a consistent product quality. The steam condenses on the inside of the drying drum. The condensate is removed continuously from the drum to make the largest possible surface area available on the inside of the drum for condensation of the steam. The steam system is fully enclosed, which means that the product cannot come into contact with the steam or condensate.






The drum dryer is well-known for its use in baby food production but has also seen success in several chemical applications like glue, pesticides, sodium benzoate, polymers, pigments, detergents and enzymes. Especially heat-sensitive products benefit highly from the gentle drying on a vacuum drum dryer with a double drum configuration.

Benefits of the drum dryer:
• Highest hygienic standard
• Low energy consumption
• High thermal efficiency
• Long, continuous life cycle
• Short residence time
• Atmospheric and vacuum design available

Technology No. 4 – Paddle dryers – Versatile thermal processing

This dryer has a heated trough containing rotating, heated paddle shafts. The specially shaped paddles do not have a transport function but are designed for maximum heat transfer. This results in excellent control of the temperature of the product and enables uniform product quality. At the outlet side, the product moves out of the dryer via an adjustable overflow. ANDRITZ Gouda’s paddle dryers/coolers are well-known for their robust construction with accurate and constant tolerances. Whatever its type, every paddle dryer unit is manufactured in a modular design – one which allows for many alternatives and can always be adapted to the extraordinary requirements of individual products and processes. This has made it a great choice for different chemical applications like polymers (PET, SAP, PA), gypsum, minerals or metal powders, among others.

Benefits of the paddle dryer:

  • Good plug flow
  • Large heat transfer area
  • Closed process chamber
  • Atmospheric and vacuum design available

Technology No. 5 –Batch helix dryer: Flexible mixing and drying

The ANDRITZ helix dryer achieves efficient mixing of friable bulk goods but also of sticky pastes by using the helical mixer, a top-driven, central agitator. By heating the vessel wall, and optionally the mixer as well, the helix dryer becomes a high-performance contact dryer for thermal solid/liquid separation at low temperatures and under vacuum. The steep vessel wall in combination with central product discharge at the bottom provides fast, easy emptying with minimum product retention. High thermal transfer, maximum product discharge and fully automated cleaning have been improved in the latest ANDRITZ helix dryer generation, type ANDRITZ Gouda helix dryer. Proven features and patents of the former Krauss-Maffei dryers have been implemented as well.


A variety of different peripheral units, such as dust filters, isolation valves without dead spots for filling, discharge and sampling, CIP spraying devices as well as purge gas systems are available to meet the most demanding requirements. ANDRITZ helix dryers are mainly operated as vacuum contact dryers, but sometimes also as reactors.

With this wide product range, we accommodate individual demands and can offer tailor-made solutions. This has made the helix dryer a great choice for applications like APIs, fine chemicals, pharmaceutical intermediates, agrochemicals and pigments or dyes.

Benefits of the helix dryer:

• Flexible operation
• Product handling without contamination and losses
• Gentle drying at low temperatures under a vacuum
• Efficient mixing of both friable bulk goods and sticky pastes
• Highly hygienic designs

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