Fluid bed dryers give extended residence times

Ventilex fluid-bed dryers and coolers from Orthos include a unique drive system that tightly controls residence times to guarantee processing uniformity for many products

Ventilex fluid-bed dryers and coolers from Orthos include a unique drive system that tightly controls residence times to guarantee processing uniformity for many products.

The availability of a rotary weir is particularly beneficial to the production of food items such as breadcrumbs where coloration by 'toasting' a proportion of the product is desired.

The drive system's use of a high-amplitude, low-frequency agitation, ensures that the product bed is subjected to sub-fluidisation, so that it does not depend fully on air or gas flows for its aerated state.

Benefits of this are lower air/gas circulation rates, which reduce energy consumption, and smaller peripheral equipment as well as the control of residence time within very tight limits.

Processing uniformity is ensured by there being very little if any variance in residence times of individual particles within the bed.

To enhance the drying process further, a rotary weir can be installed to control the rate of discharge of the processed material.

It is an open segmented wheel similar to a rotary air lock and rotates continuously at slow speed moving upwards against the end of the product bed.

This action ensures that product is removed evenly from the bed's entire cross-section rather than preferentially from the top, as is the case with static weirs, and also avoids causing turbulence within the bed.

The rotary weir allows increasing the depth of the bed and therefore the residence time within the dryer.

Plug flow is maintained at all times and closely controllable bed depths in the range 5cm to 60cm and residence times up to two hours are achievable.

Another option being offered is installing a weir across just part of the dryer's width combined with a longitudinal divider plate.

This allows part of the product flow to have an extended residence time and become 'toasted' while the rest flows through more quickly and is simply dried.

In the case of breadcrumbs, the two product streams can then be mixed to produce the required colouration.

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