Improving Filter Life on Whisky Char Removal

Product

SupaPleat HFC Customised Special

Client

Major Whisky Distillery

Location

Scotland

Sector

Food & Beverage

Introduction

Charred oak barrels have long been used to impart complex flavour profiles to distilled whisky. The hemicellulose, lignin and tannins of the base oak would not react efficiently with the whisky if the charring did not take place. Hemicellulose sugars caramelise during the charring, producing flavours such as walnuts, hazelnuts and almonds while the lignin adds floral elements of cinnamon and clove.

Tannins influence colour and impart oaky flavours as well as spice. The origin of the wood and the degree of charring all influence how various flavours are infused into the whisky. The charring process can also help in the purification of the whiskey in terms of the removal of sulphur compounds by the charcoal. It’s a process which is an inherent part of whisky production and is here to stay.

The Problem

Charred barrels are good for the whisky flavour; however, small particles of charred wood are released into the whisky during maturation and these need to be removed prior to bottling.
At this distillery the customer was finding premature blockage of the large format pleated polypropylene filters leading to additional time spent on filter change outs as well as increased operational cost due to higher filter usage. The blockage issues were variable depending on the whisky type and the barrels used. Amazon Filers were asked to prevent to propose a filter that prevented this premature blockage.

The solution

When using pleated depth filters the aim is to have the particulate loading evenly spread throughout the depth of the filtration media. This ensures maximum dirt holding capacity while maintaining flowrates. The filtration efficiency throughout the depth is varied to try and achieve an optimal balance of filtrate quality and on-stream lifetime. The efficiency required on each of the filtration layers is dependent on the particle size distribution in the fluid being filtered. In this case, whisky.

The most practical way of understanding where the blockage is occurring is by dissecting the used filter and analysing the individual layers. The complete filtration depth is made from multiple layers of melt-blown and spunbonded filtration media with different efficiency rating. As the particulate being removed is highly visible it is relatively easy to see where preferential blocking is occurring and customise the structure to provide optimum performance. The following images show the blockage of three different constructions.

The image below is the dissected original competitive 10 micron filter showing the preferential removal in the second layer. The upstream layer is too open and not capturing much particulate, while the second layer has too high an efficiency for the suspended particulate. This resulted in premature blockage of the filter.

(Upstream layer on the left, downstream layer on the right)

Our standard 10 micron SupaPleat HFC showed preferential removal on the first upstream layer.

From analysis of the two filters a more open and thicker upstream meltblown layer was used with the resulting filter showing equal removal across the layers and a resulting increase in throughput of between 20 and 30% while maintaining flowrate.

Conclusion

The customised Amazon SupaPleat HFC filter utilised 3 filtration layers rather than the 4 on the competitive filter. Even though a much thicker upstream layer was used on the customised Amazon SupaPleat HFC filter the overall thickness was less. This allowed the same filtration area as the competitive cartridge while ensuring better pleat separation. Pleat separation is important. Too close together and bridging of particulate across the pleats can occur. If this happens the full surface area of the filtration media is not used, and premature blockage occurs.

Some key takeaways from this case study are:

Physical dissection of the filter is a powerful way of understanding blocking profiles
The filtration efficiency of the individual layers is critical in ensuring the maximum dirt holding and subsequent on-stream life is achieved
The ability to modify standard filters to improve the processing efficiency on whiskies; or in fact any liquid with varying particle distribution, is a real strength of a filter manufacturer. Large multinational corporations are often not willing to produce special products leading to missed opportunities for process improvements.