Lactose – the carbohydrate originating from milk – is usually produced from pre-crystallized whey or permeate concentrates. The lactose crystals are separated from the concentrate in decanters followed by a final separation in a basket centrifuge to obtain a free moisture content in the lactose slurry as low as possible.
The lactose dryer from GEA Niro
The lactose dryer is a fluid bed dryer. The fluid bed is divided into three sections. The first section is a stationary back-mix bed, into which the wet crystals with 6-8 % moisture are fed by a rotating disc. To avoid lump formations this section is equipped with a rotating rake. From the back-mix section the powder enters the plug-flow fluid bed section for the final drying.
All flowsheet animations are available in the GEA Niro download area.
Hot air of about 100 C is used for the drying. In some cases a final drying/sterilizing section is used with higher temperature to reduce the content of mould in the final product. The average crystal size (200-250µ) is of importance for the fluidization velocity that can be used, and it therefore influences the performance of the fluid bed, as smaller crystals would require lower fluidization velocity (= bigger fluid bed area), or too big carry-over of product to the bag filter would be the result.
From the last drying section the powder enters the cooling section which like the last drying section is designed as a plug-flow fluid bed. The air used for cooling should be dehumidified. All the exhaust air is passed through a bag filter for separation of fines, which are returned to the back-mix section.
Lactose powder is very often classified with different crystal sizes. Milling of the powder after the fluid bed and final sifting is therefore used.