Nothing fishy about this discharger

It used to take the people at Skretting in Lancashire 25 to 30 minutes to discharge each of the 11 ingredients used in the production of fish feed for industrial fish farming. Now 1-tonne bulk bags (FIBC’s) are discharged in around 5 minutes. Over eight years ago a specialist contractor had installed the materials handling system at Skretting with a simple bulk bag unloading arrangement, which fed ingredients into a ‘Spiroflow’ Aero-Mechanical Conveyor. The Aero-Mechanical Conveyor lifts product up to a horizontal screw conveyor on the floor above. The screw conveyor has 11 outlets, each of which delivers ingredients to their appropriate storage bunkers. From here, weighed measures of the required ingredients are loaded into a mixer and, finally, the mixture is pelleted and packed ready for despatch.

Bottleneck in discharge
It was the ‘simple bulk bag unloading arrangement’ that proved to be the bottleneck in the production process and the cause of constant frustration to the operatives. Comprising just a lidded hopper with a spigot to which the neck of the bulk bag was attached, the ‘simple bulk bag unloading arrangement’ required the presence of a forklift truck for the duration of discharge as there was no other means to support the bag. In addition, an operative had to be on standby to aid the flow of poor flowing or compacted products.

As production manager Bill Edmondson comments, “There is just no comparison with the previous system. Our new Spiroflow discharger has enabled us to increase productivity and we can use the forklift truck for other duties whilst the bulk bags are being emptied – not that that takes long”.

Limited space
The bulk bag discharger supplied to Skretting is specifically designed for applications with restricted headroom. At Skretting there is a mezzanine floor area directly above the location of the bulk bag discharger, which makes it almost impossible to lift full bags into the discharger safely.

Spiroflow’s model T5 discharger has two sections. The upper section, which holds the bags, is lifted off at its base and lowered to ground level. Here, by way of a lifting frame, full bags can be loaded by forklift truck whose forks only have to be raised a little higher than the height of the bag and its extended lifting loops. Once the bag is safely in place, the top section is lifted via the fork channels at its base back on to the business section of the discharger – and locked into place.

There is a dust-tight docking seal between the upper and lower sections. An access door in the discharger hopper allows the bag to be untied without emissions or spillage. Once the bag is untied, flow begins and this door is closed. Pneumatically operated bag base massagers have been fitted to the lower half of the discharger at Skretting. They are there to deal with any products that are poor flowing or which have become compacted during transit. It is these base massagers that make it essential that the two sections of the discharger are locked together.

The model T5 discharger boasts the same spring-loaded side tension arms as all other models in the range. These raise the bulk bag as it empties helping to ensure complete discharge on one hand and preventing the neck of the bag sagging into the conveyor below on the other.

About Skretting
Skretting is the UK’s and Ireland’s largest aquaculture feeds producer and leads the market with innovative feeds and feeding expertise. It is part of the Nutreco group of companies that collectively operate in 22 countries, employ 12,000 people and have a global turnover of €3.8 million.

At their Longridge, Preston site, Skretting mainly produces varieties of feed for industrial trout farming but also some for salmon too. Between them, the 30 employees produce an annual output of 24,000 tonnes. That’s around 100 tonnes per working day – which makes it clear why they needed a more efficient bulk bag discharger. Spiroflow was chosen because they already had good experience with the Aero-Mechanical Conveyor that was installed in 1997.