Sterilization /
Heat Treatment

Paddle Dryer

Multifaceted thermal processes The GMF-Gouda Paddle Dryer is a machine that is used for a wide variety of applications. Applications for which stringent demands are set on uniform product quality (accurate retention time control and/or strict temperature control), a careful treatment of the product in order not to damage it or cause it to generate dust, or precisely the robustness of the machine. And not unimportant: its compact construction in comparison with other machines. The hollow shape of the paddle shafts ensures that the total surface area of the interior functions as a heat exchanger. Many square metres of heat-exchanging surface on only a limited amount of required floor space.

How does the GMF-Gouda Paddle Dryer work? The product is fed into the front of machine through the top cover. Because the machine is placed on a small slope, the product moves evenly through the machine under the force of gravity. Consequently, the paddles do not have a transport function. The paddles provide good heat transfer to the product and mixing of the product. At the end of the machine, the end-product moves over the overflow unit and leaves the machine via the underside. The product comes into intensive contact with the walls of the trough, the shafts and the paddles. These are all heated.

The product level reaches slightly above the paddles. Above the product level there is a collection area for vapours. The vapours that collect there are removed from the machine. The working principle of the GMF-Gouda Paddle Dryer, with low rotation speed of the paddle shafts and indirect drying principle, contributes to a negligible or even zero substance emission. When it is nevertheless decided to use a gas cleaner, such as a gas scrubber or gas filter, its size can remain small due to the low gas flow rates. The table below shows how the GMF-Gouda Paddle Dryer relates to a stirred heated tank (CSTR). The parameters listed are relative to one another.

	Heated surfaces	Volume process area	Heat transfer	Product flow
GMF-Gouda Paddle Dryer	many	low	high	plug-flow
Stirred heated tank (CSTR)	few	high	low	arbitrary

Direct drying versus indirect drying The GMF-Gouda Paddle Dryer works on the basis of the indirect drying principle. Indirect drying has various advantages in comparison with direct drying. Direct drying In direct drying, the heat of gasses is transferred immediately to the product. The hot gasses come in direct contact with the product. That has a number of consequences, including:
	The product may often not come into contact with gasses (e.g. due to product contamination, hygroscopic products, etc.); Intensive product contact with gasses generates dust; Relatively large volumes of hot gasses must be cleaned, which requires gas cleaning equipment; The recovery of solvents is more difficult; Much unused heat leaves the dryer again.

Indirect drying with the GMF-Gouda Paddle Dryer In indirect drying, the heat is transported to the product via a metal wall. The heating medium (steam, oil or water) remains separated from the product.
	That has a number of advantages, including: The product never comes into contact with the heating medium; Little or no dust formation due to slowly-rotating paddles shafts; Intensive product contact through special paddle shape with relatively much heat-exchanging surface; No need to use sweep gas. The result is low or even no flow waste gasses that have to be cleaned. Furthermore, toxic, odorous and flammable products can be processed safely; The recovery of solvents is simpler.

Higher heat transfers coefficients The GMF-Gouda Paddle Dryer produces an intensive contact with the product during the rotation of the shafts. The heat transfer coefficients are high as a result of the specific paddle design.

The wedge-shaped paddle ensures for excellent contact on both sides of the paddle and mixes the product in radial direction. In addition, the wedge-shaped paddle ensures for shear forces on the paddle surface and this keeps the paddle clean and contributes to improved heat transfer. The paddle shafts turn in opposite directions. Paddle plates are attached to the paddle. The paddle plates keep the walls of the trough clean and also provide for extra mixing. The paddles are attached to the shafts in such a way that during turning they "grip" between the other paddles. This configuration reinforces the mixing effect and the heat transfer due to the increased shear forces.

View of a half-filled GMF-Gouda Paddle Dryer.     The paddle shafts use a staggered grip.     Optimal mixing and heat transfer.

The efficiency of the GMF-Gouda Paddle Dryer The compact construction As mentioned earlier, the GMF-Gouda Paddle Dryer is a compact machine. That is because it has many square metres of heat-exchanging surface relative to the content. Two hollow shafts with hollow paddles turn in opposite directions in the horizontal trough. The trough has an ω-(omega) shape that follows the contour of the paddles.

The paddle shape Moving parts are crucial for the system. They have been expertly designed. Excellent heat transfer is ensured when the product is refreshed regularly and remains in good contact with the heat-exchanging surface. The paddles of the GMF-Gouda Paddle Dryer play a large role in creating these optimal conditions.

Specific paddle shape for maximum heat transfer     and self-cleaning capacity.

Pasty products in the Paddle Dryer.

The fragile product is not damaged because the smooth paddle shape does not force it to flow; The uniquely-shaped paddle has a self-cleaning capacity. The wedge-shaped paddle produces shear forces on the paddle surface and this keeps the paddle clean and contributes to a higher heat transfer; Even pasty and/or sticky products that do not flow freely can be processed perfectly; An even flow (plug flow) through the machine gives each product particle an identical retention time and ensures a high uniform product quality; The front and back of the paddle transfer heat to both sides because they are not placed in slanted position. It therefore has a propelling force on both sides. This is in contrast with transport screws or other paddle dryers that only transfer heat on the propelling side.

Transport screw: product contact = heat flow in only a single direction.

Paddle: product contact = heat flow in both directions.

As the product moves through the machine, the paddles ensure that the product is well mixed and that it flows easily through the machine. The paddles gives excellent mixing in radial direction. The product is mixed poorly in axial direction. As it moves further into the machine, the product increasingly meets the end specifications with preservation of the plug flow.

The shafts are accurately aligned. The paddles turn alongside one another and this creates a good ratio between product / heat-exchanging surface and product flow. The dustproof cover of the GMF-Gouda Paddle Dryer can also be adjusted for a process under vacuum or overpressure. Condensation that may result during the process can be prevented by completely heating the cover or by a light air flow (if necessary with an inert gas) to the central discharge outlet on the cover. Additional process techniques Heating / cooling combination The GMF-Gouda Paddle Dryer offers the possibility to process products with different temperature zones in the machine. In this way, the product can undergo two or even three temperature treatments. For example, the product can first be heated quickly. The product can then be given a certain retention time at a lower temperature in order to meet the end specifications. And when the product meets the specifications, it can be cooled. All in a single machine. Removal of solvents Special attention is given to the sealants in order to prevent the escape of solvents. The collection of solvents occurs by keeping their concentration in the exhaust vapours as high as possible. The pressure is monitored by a small gas de-aerator. The solvents are condensed and the waste gasses / non-condensables are drawn off. Recirculation Some products become very viscous when they have a certain moisture content. In most cases this "sticky phase" or pasty phase can be well processed using standard paddle shafts. For, the paddles have a self-cleaning capacity. Where other systems have to recirculate a dried product in order to avoid the stick phase, the Paddle Dryer can usually dry the product in one step without recirculation. Well-coordinated quality check Thanks to a well-dosed product flow, the product temperature at the product outlet can serve as a measure for the moisture content and as a check of the supply of heating medium. In this way, a constant product quality can be achieved, even when the amount of the supply and the moisture content vary. Applicability The GMF-Gouda Paddle Dryer is a machine used for a wide variety of applications. The applications for which this machine can be used include:

Industry-oriented Chemical Environment Pharmaceutical Foodstuff Process-based Drying Heating Cooling Roasting Melting Cooking / braising Calcination Crystallisation Sterilisation Removal of solvents

Half-filled Paddle Dryer with polished paddle shafts.

Pilot plant ensures process data GMF-Gouda has an extended database containing knowledge and experience of a large number of products. The pilot plant can be used for products that have not been tested before or for existing processes that need further improvement. All processes can be simulated in our laboratory. The reliability of the simulations is proven by the success of hundreds of installations worldwide. In certain cases, tests can be done at the customer's site. Mobile test machines can be leased for that purpose.

Test facilities Manual test To perform a manual test, we need about 5 kg of product in order to determine the behaviour of the product. Guarantee test To perform a guarantee test, we need between 500 and 1000 kg of product in order to determine the capacity and the process parameters. On that basis, process guarantees are granted and a comprehensive report is made.

Mobile test machine