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Better solids handling improves plant hygiene

15 March 2021

Find out how the adoption of a material handling solution has helped a confectionery company to improve plant hygiene. 

Each week Scottish confectionery company, Hannah’s Sweets, processes between 50 to 60 tonnes of sugar, milk powder, whey powder, wheat flour and other dry ingredients received in 25kg bags. This equates to about 300 bags per day emptied at the rate of 1,675kg/hr. 

To reduce manual bag handling and dust, and prevent pallets from entering the hygienic mixing room, the company has installed a Flexicon bag dump station and pneumatic conveying system, integrated with an outsourced roller conveyor and vacuum sack lifter. 

The delivery system needed to capable of handling material with bulk densities from 208kg/m3 for milk powder to 705kg/m3 for granulated sugar. 

Tom Munro, Hannah’s Managing Director, said: “Flexicon offered a turnkey system to handle all ingredients, whereas others could only supply parts of what we were looking for.” 

Using a vacuum lifter, operators move the sacks from pallets onto the roller conveyor, which transports them through a wall into the mixing room where the bag dump station is located. Equipped with a high velocity vacuum fan, the unit draws airborne dust generated by the manual dumping process away from the operator onto two cartridge filters having a combined surface area of 9m3. Dust accumulation on outer filter surfaces is dislodged on a timed cycle by alternating blasts of air from nozzles located within each filter, maintaining dust collection efficiency. Dislodged dust falls into the unit’s 140l capacity hopper, eliminating waste.

Material is then fed through a pickup adapter mounted below the base of the hopper, into a Flexicon pneumatic conveying system. Powered by a 7. kW blower, this transports ingredients through a 12m long, 75mm diameter line with three pneumatically-actuated diverter valves that sequentially feed three 450mm diameter filter receivers, each feeding a separate mixing tank. Once separated from the airstream, material is metered through the filter receiver’s rotary valve into a 28l surge hopper that discharges into a mixing tank, where dry ingredients are blended with vegetable fats. The resulting liquid chocolate compound is formed into various shapes using automatic moulding equipment.

PLC controlled
The system is controlled by a PLC that opens and closes each diverter valve, starts and stops each rotary valve as signals are received from each hopper’s high level sensors, and stops the conveying system’s blower when a signal is received from the bag dump station’s low level sensor. The mixing tanks are filled to a combined batch weight of 2 to 3 tonnes of liquid chocolate.

The enclosed system precludes contamination of the product and plant environment, while the pneumatic blower evacuates the conveying line. This eliminates the need to flush the system during material changeovers, and ensures all batch ingredients reach the mixing tanks, eliminating waste.  “We have a clean-as-you-go policy but the new delivery system requires only a wipe down by the operators each day,” said Munro. Since installation, the system has been highly reliable, delivering consistent performance. “The lines have been running a year and we haven’t had to do any maintenance,” concluded Munro. 


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