Speyside distillery concentrates on heat issues
26 Jan 2010
Speyside, Scotland – Glenfarclas Distillery on Speyside was established in 1836 and is still owned and run by the Grant family who originally acquired the business in 1865. The distillery uses traditional processes and skills to produce its single-malt whiskies, but it also invests heavily in the latest technology to maintain efficiency and quality, for example in its pot ale area.
Pot ale – or spent wash - is a by-product from the first distillation stage in malt whisky production. Concentrated into a syrup and rich in proteins, carbohydrates and yeast residues, it makes a nutritious livestock feed; either on its own or mixed with draff - spent malted barley grains - to produce what are known as dark grains. Glenfarclas produces around four tonnes of pot ale syrup a day for sale to UK feed producers.
At Glenfarclas, Pot Ale is concentrated to around 45% solids using evaporation. Glenfarclas had employed a conventional falling film, shell & tube evaporator for this duty, but as Shane Fraser, the distillery’s production manager explains, it was very inefficient and extremely difficult to maintain.
“The old evaporator gave us a lot of problems simply because it fouled so easily,” Fraser said. “It was extremely difficult to clean and maintain because it was over six metres high and impossible to access. Towards the end, we were probably operating at 50% efficiency because the evaporator was fouling so badly.”
In the autumn of 2007, Shane contacted Alfa Laval to discuss the installation of a new Pot Ale evaporation system. The brief was for the equipment to offer high levels of thermal efficiency yet to be low fouling and easy to access for maintenance and cleaning. Alfa Laval’s plate heat exchanger technology suited this description and provided the added advantage of compact size and low weight which kept the space needed for the total installation to a minimum.
Since Alfa Laval also supplies sanitary flow equipment, it was able to design a plant which incorporated all of the sanitary pumps, valves and ancillary controls in addition to the core heat transfer technology. The complete system was assembled and readied for installation in the Alfa Laval workshops before delivery to Glenfarclas in mid-2008.
At the heart of the system are two Alfa Flash evaporators, providing two effects; an M6 plate heat exchanger which is used as a pre-heater and an AlfaCond condenser. The Alfa Flash’s high wall shear keeps viscosity low and the risk of fouling to a minimum, which, in turn, extends cleaning intervals, while the true counter-current flow of all three heat exchangers ensures optimal heat transfer efficiency between the media and enhances the efficiency of the CIP system.
As a first step in the concentration process, pot ale, at around 4%, enters the second Effect evaporator and is part concentrated using vapour from the first Effect as the heat source. From the second Effect, it then travels to an M6 PHE, where it is further heated using heat recovered from the condensate from the second Effect. Finally, it is pumped to the first Effect evaporator where it is concentrated to the desired thickness of 45%.
The AlfaCond semi-welded plate condenser is used to condense the vapour from the second Effect AlfaVap. Its cooling water channels induce high turbulence while the welded vapour channels feature a wide gap with extremely low pressure drop.
Glenfarclas uses steam or hot water recovered from firing the pot stills to power other processes, and the new evaporator system has taken this energy recovery to a higher level. The energy required for evaporation is recovered from the distillation process, but the distillery now also collects exhaust flue gases from two of the principal pot stills to pre-heat boiler water.
The new evaporator system started operating in August 2008. Initially, there were teething problems, with one of the evaporators losing efficiency due to fouling. However, according to Fraser, this was where the decision to go with plate evaporators was vindicated. “We were able to open up the unit very easily and quickly clear the accumulated product . It was apparent we had over-concentrated the wash and so it was simply a question of adjusting the concentration to the optimum level.
“With regular CIP, there has been no repetition. Apart from a scheduled summer close-down, the system has run without interruption, producing the quality and consistency of Pot Ale we want. In fact, when we inspected the heat transfer surfaces during the summer shut-down, they were clean as a whistle.”
