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Optimum heat uniformity for enhanced drying

30th May 2014

Posted By Paul Boughton


CakeStand vacuum tray dryer
Temperature mapping testing results

Camille Flores reveals the latest in drying technology for use in the lab.

A vacuum drying oven remains a necessary technology during drug development and lab scale studies. With the development of the agitated filter dryer for lab scale production, process experts predicted the end of tray drying technology.

However, static drying happens to be a more suitable process for certain types of powder that are too sensitive for dynamic drying. But traditional tray dryers can cause problems with proper cleaning and - most of all - homogeneous drying across the shelves. In a bid to overcome such difficulties, a new technology has been developed: the CakeStand tray dryer (Fig. 1).

The novel name explains what sets this tray dryer apart from its competitors. The CakeStand has floating shelves hanging from the roof of the cabinet, thus creating a convection heat circulating around the shelves.

Each shelf leaves a space between the cabinet wall and the heated plate, even at the back. This feature also makes cleaning easier by avoiding the hidden pockets or non-accessible gaps that can make the cleaning procedure problematic. The entire cabinet can be cleaned-in-place (CIP) and then wiped. The whole shelving structure can be removed when necessary.

This design enables the technology to achieve an almost-perfect heating homogeneity across the shelves. The trays are put on heating plates hanging from the roof. The combination of direct heat and convection heat circulating in the vacuum oven results in a similar temperature recorded from the top to the bottom trays.

CakeStand tray dryer has been tested using thermocouple probes

The heating uniformity across the shelves of the CakeStand tray dryer has been tested using thermocouple probes secured on the same six locations on each of the four shelves of a small-scale production oven.

The temperature of the thermocouples was recorded with PicoLog software after 15 minutes of heating fluid circulation through the shelves once the temperature reached 60°C. The findings are shown in Fig. 2. The highest recorded temperature was 59.7°C (on shelf No. 3). The lowest recorded temperature was 57.7°C (on shelf No. 4). Therefore the maximum recorded temperature variation was ±1.0°C.

With regard to supply temperature fluctuation, the water circulating temperature controller supply temperature fluctuation was recorded to be ±0.25°C.

This vacuum drying oven allows for capacities from kilograms up to large-scale production. It also results in better drying times due to a uniform direct heating system. The CakeStand's design features enhanced ergonomics through optimum tray size, pivot door design and front and back access.

The dryer can operate in down-flow booths, clean rooms or in conjunction with Powder Systems Limited (PSL) containment isolators, providing high containment when handling highly potent active pharmaceutical ingredients (HPAPIs) and other highly active or cytotoxic compounds. It can also meet sterile process requirements when necessary for drying toxic or sensitive products.

For more information at www.scientistlive.com/eurolab

Camille Flores is business development manager, Powder Systems Limited (PSL), Liverpool, UK.





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