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JR Boone, an industrial process and mixing specialist, has designed, installed and commissioned a tea blending and mechanical handling system for a UK tea manufacturer.

The customer set technical specifications for the overall project and the new system replaces a smaller, manually intensive system, which had a limited blending capacity of up to 100 litres.

The scope of supply includes a 1,500-litre-capacity stainless-steel horizontal rotary drum blender, a compact belt and bucket elevator, a vibratory feeder, a bespoke liquid flavour spray coating system, an integrated valve control system and six mobile tote bins for transporting product to and from the blender.

The system is designed to blend batches weighing up to 500kg, made up from a range of black- and green-base leaf teas with average bulk densities ranging from 330kgm-3 to 400kgm-3.

An essential part of the blending process requires the addition of very small quantities of liquid or dry flavourings in powdered, flaked or granular formats.

Once the blend has been completed, the finished product is then discharged into wheeled tote bins for offline QC checking, before being moved on to the packing lines.

A critical parameter for the new installation was the time to blend.

The existing system had long blend times that, coupled with the small batch size, gave a much lower capacity and made it more difficult to achieve blend consistency over time.

The new system produces an optimum blend in one to five minutes, depending on the amount of liquid added, and with a quick and continuous discharge the delicate leaves and granules are protected.

A second important factor in the project related to the mechanical handling of the leaves, both before and after blending.

Again, the delicate handling of the leaves and flavourings is essential to minimise any damage and the customer stipulated that the system should also take up minimum floor space.

To meet the operational requirements, a compact design was generated in close co-operation with the customer’s plant operators and project engineers.

This allows a single elevator to feed tea leaves and a variety of dry flavourings into the blender directly from tote bins and then discharge finished tea blends back into the tote bins without damage.

If the specific recipe calls for liquid flavourings, these can be sprayed from a 30-litre 316 stainless-steel pressurised container (mounted on the side of the blender) via an adjustable lance positioned inside the blender to optimise spray patterns.

The blender design also incorporates a cleaning access door feature to facilitate rapid and hygienic changeover from one flavoured tea to another.

Following in-house trials, JR Boone engineers confirmed that the larger blender could achieve a shorter time to blend, while maintaining tight quality control on the finished product.

The non-shear mixing action within the company’s blenders is produced by a series of blades welded to the inside of the rotating drum.

The rotation lifts and cascades the product off the blades to form a highly fluidised curtain of material, which then folds into the product stream coming from the opposite end.

A short drum length-to-diameter ratio, together with the low-shear fluidised curtain, makes this process suitable for coating and mixing sensitive materials.

Product inlet and outlet can be located at the same end or at opposite ends of the blender to suit the plant layout.

Drum blending is also effective for blending in tiny amounts of additives in ratios as low as 1:150,000 without the need for a pre-mix.

The smallest number of mixing elements ensures minimum product contact area and the ease of total cleaning.

The overall control system, which includes discharge valves and level sensors, has a number of failsafe features.

These enable operator safety and ensure that blending and flavouring processes can only take place in prescribed ways, according to JR Boone.

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