Distillery selects plate heat exchanger technology

An evaporation system based on Alfa Laval plate heat exchanger technology has helped Glenfarclas Distillery increase the concentration and quality of its pot ale.

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 highly-nutritious livestock feed; either on its own or mixed with draff - spent malted barley grains - to produce what are known as dark grains.

These days, Glenfarclas produces around 4 tonnes of pot ale syrup per day for sale to feed producers around the UK.

At Glenfarclas, pot ale is concentrated to around 45 per cent solids using evaporation.

Prior to the installation of the Alfa Laval system, Glenfarclas employed a conventional falling film, shell and tube evaporator for this duty.

Shane Fraser, the distillery's production manager, said it was very inefficient and difficult to maintain.

He added: 'The old evaporator gave us a lot of problems simply because it fouled so easily.

'It was extremely difficult to clean and maintain because it was more than 6m high and impossible to access.

'Towards the end, we were probably operating at 50 per cent efficiency because the evaporator was fouling so badly,' he said.

In autumn 2007, Fraser 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 said its 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 is also a supplier of sanitary flow equipment, it was able to design a plant that 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.

The counter-current flow of all three heat exchangers is said to ensure 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 roughly four per cent, 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 plate heat exchanger, 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 per cent.

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 low pressure drop.

The energy required for evaporation is recovered from the distillation process, and the distillery now also collects exhaust flue gases from two of the principal pot stills to pre-heat boiler water.

The new Alfa Laval 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.

He said: 'We were able to open up the unit 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.

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