Spray-belt system

Vegetable extracts obtained by macera-tion with water or alcohol are a base material for the pharmaceutical industry after further treatment and drying, as well as being aroma and flavour-carriers for food production. Drying using conventional spray-tower technology or vacuum-belt drying without drying aids is sometimes not possible or only very difficult to accomplish, as the extracts tend to develop properties such as thermoplasticity and hygroscopicity when they pass from the liquid into the solid phase. A high resin content impedes drying, and in conventional drying processes leads to severe caking in the tower area as well as problems with the discharge from the system and undesirable structures of the dried product. High thermal loads result in active agents – the actual yardstick of quality – being lost.

In Andernach, this specific drying duty is accomplished by a spray-belt dryer in the SBS-50 series – a combination of a spray dryer and a system-integrated belt conveyor. The extract to be dried is atomised by nozzles in the top section of the spray tower, then drops – with a relatively high residual moisture – onto a belt conveyor installed in the bottom section. Depending on the raw material used, a layer several centimetres thick builds up on the belt, which carries it from the primary drying section to the downstream drying section for secondary drying.

Splitting the actual drying process into several separate sections, and using separate air supply and air conditioning systems, permits the drying parameters to be optimally adapted to the product and individually controlled. In the downstream cooling section, the dried extract is cooled to the required processing temperature. Having passed through the cooling section, the product leaves the belt at the tail end and drops into a screw conveyor system. The screw conveys the dried material from the dryer into a downstream, vortex-type crushing screen, which disintegrates the product to the required grain size.

In the spray-belt system, the entire drying and cooling air is drawn through the product layer and the belt, and is then dissipated from under the belt. The product cake simultaneously acts as a filter, resulting in a dry low-dust agglomerate.

The special geometrical shape of the primary chamber (round extended to square) minimises caking on the walls. This effect is enhanced by the design of the air distributor (divided into two separate air supply systems).

As the first drying phase takes only a few seconds, the maximum cooling temperature of approximately 45 °C allowed for the extract to be dried is not exceeded in spite of the high air inlet temperatures of up to 230 °C and the outlet temperatures of between 70 °C and 110 °C (for salts). On the other hand, secondary drying to residual moistures of in some cases less than 1% is with residence times of up to 30 minutes or more at very low temperatures.

The system technology, which is closely adapted to the drying kinetics, minimises losses of product and active agents.

In addition to several dry-cleaning phases, the integrated belt conveyor can be cleaned wet and then dried during the drying process in the normal cycle. This means there is always a clean and dry belt available for the drying process.

Before the order for this system was placed, drying tests were conducted at a research centre to obtain specific data for the design and process technology, and at the same time demonstrate the suitability of the SBS for this particular drying task. The results which were obtained were then taken into account in the planning and design of the plant. In this case, the dryer has a smaller tower than the standard version, to keep the residence time in the primary drying section as short as possible. This minimises losses of active agents and largely precludes the need to use drying aids. A patented belt guide via laterally integrated V-belts ensures parallel belt travel over the full dryer length.

The plant’s compliance with GMP and FDA directives ensures a high standard of hygiene, allowing the dryer to be used in the pharmaceutical industry. The entire plant is cleaned within a short time by an integrated CIP system (approximately 180 nozzles belonging to different systems).

The scope of supply includes:

• Spray-belt dryer with product supply system, including high-pressure pump and liquid,

• gas dosing system,

• treatment, heating, feeding and conditioning systems for drying air and cooling air,

• complete CIP system,

• exhaust-air cleaning by thermal recombustion,

• complete system for controlling the plant and recording product and plant parameters, including batch data management,

• erection and commissioning.

The spray-belt dryer was test-run with sev-eral different extracts. At a water evaporation rate of more than 200kg/h, the plant is capable of producing dried plant extract quantities which in some cases exceed 300 kg.

Among the other fields of application of the SBS are pumpable and atomisable products with a high fat content (possibly more than 80% fat), sugar, salts in hydrous solution, syrups with a high DE value; highly hygroscopic and thermoplastic products are how-ever also handled excellently by the spray-belt system.

Starcosa Tag

Fax: ++49/531/804235

Further information cpp-206