J. A. Sharwoods, leading manufacturers of mango chutney, Indian and oriental foods, use bulk sugar in the manufacture of their foods. Granulated sugar is stored, conveyed and weighed into mixers and a new system was required to replace the existing bunker and vacuum conveying system which was troublesome. High factory and atmospheric humidity conditions had resulted in the sugar picking up moisture whilst being stored and conveyed leading to blockages, down time and jeopardised production.

A new system was required to ensure that the granulated sugar would be stored, conveyed & weighed in a dry, free flowing condition.

After hearing about the Aptech Closed Loop Conveying System, Sharwoods invited us to draw up a design to overcome the problem.

The closed loop conveying system consists of an enclosed loop of pipework. A drier is used to purge the system with dried air which is then re-circulated. Product is fed in through a rotary valve and a blower conveys the product from a silo to a cyclone/receiver. Here the product and conveying air are separated and the air is returned via the circuit of pipework back to the blower inlet. The same air is continually circulated thus avoiding the introduction of moisture into the line. As a result the sugar is kept dry, free flowing and hygienically clean. The sealed system also prevents product loss and dust emissions. The drier is very small as it only needs to be sized to accommodate the air lost from leakage through the system’s rotary valves, so running costs are low.

The project comprised a 35 tonne sugar silo, 6 tonne per hour pneumatic conveying system feeding 6 pan mixers and a PLC control system working with a Promtek weigh controller. A single conveying line is used to feed all six mixers and one air return line is used to return the air and any dust back to a filter receiver positioned adjacent to the blower. The cleaned air is piped off the dust filter to the blower inlet to re-cycle back around the system.

Any fines collected in the filter receiver are returned straight back into the conveying line via a rotary valve.

A regenerative desiccant dehumidifier is used to provide the source of dried air. The drier is positioned by the silo and used to initially purge the system and then top up any air losses. The drier has sufficient capacity to provide conditioned air to the conveying line and silo, preventing condensation in the silo.

Sugar dust is explosive and under current legislation vessels containing sugar require explosion protection. Normally this would be carried out by installing bursting panels which must be vented out to atmosphere or a safe area. Unfortunately the process mixing area is situated in the middle of the factory building making venting to a safe area impossible.

The closed loop conveying system has the advantage of being a sealed circuit of pipework and designing the system to 10 bar pressure rating (max explosion pressure of sugar dust is 9 bar) means that the system satisfies the explosion risk by way of containment and eliminates any need for explosion panels and venting or suppression systems in the process area.