The paddle dryer processes powders, granules and also pasty products. The “one step through process” requires no back-mixing. The indirect heating concept results in high energy efficiencies.
Product enters the unit through the cover on the feed side. The entire machine is slightly inclined so gravity transports the product to the opposite discharge end. The paddles have a specially designed wedge shape. It makes the heat transfer from the heating medium to the particle very high. Heating media can be either steam, thermal oil or hot water. Not only has the machine a heated trough, the shafts and the paddles are heated also.
The paddles efficiently exchange energy with the product. This results in an excellent product temperature control and enables a uniform product quality. At the outlet side, the product moves out of the machine via an adjustable weir. The weir controls not only the residence time of the product, it also allows emptying of the unit.
The dryer its accurate plug flow characteristic ensures an even distribution of the particle’s residence time in the unit. This results in an excellent control of the product temperature as well as a uniform product quality.
The flow of exhaust gas is relatively low and concentrated due to the absence of drying air. This makes scrubbers or bag house filters compact. The process control of the paddle dryer is simple so plant integration is easy.
The wedge shaped paddle is the crux of the design. The hollow paddles interweave with the opposite counter rotating paddle shaft. This creates a high shear force on the particles. It makes the heat transfer from the heating medium to the particle very high. As the paddles do not transport the product, their primary function is to transfer heat to the product. The paddles mix well in radial direction. There is no mixing in axial direction, towards the product outlet side.
The most commonly used process steps are heating, drying, baking, roasting, pasteurization and sterilisation. Vacuum solutions are available to process temperature sensitive products. Gas tight designs permit the safe processing of toxic or of very sensitive products.
Other drying technologies to consider
≡ The Plate Dryer is likely the better choice for brittle products. The product is moved gently across a heated plate without any exposure to shear forces.
≡ For high throughput applications and when plug flow is slightly less important, the Rotary Tube Dryer may be a good alternative. This technology can easily process 20 tph in a single unit.
≡ When the product temperature needs to be lower, you may consider vacuum technology or convective (air drying) technology. Typical air dryers are the Spiral Flash Dryer, the Fluidised Bed Dryer or the conventional Flash Dryer. In these technologies, product temperatures are commonly around 45-50°C for the majority of applications.
Contact us if you like to know how we can assist you selecting the best dryer for your application.