Words/ Ian Wisniewski
Cooling towers and cooling ponds play a vital role during the production process, but are rarely mentioned. We look at what they do
Water is a vital consideration for every distillery, not only in terms of the quantities needed but also the temperature. A constant supply of cold (ie. ambient temperature) water is required to pass through the condensers, in order to cool the alcohol vapours and condense them back into liquid. However, in the process of cooling the vapours, the water becomes much warmer. Consequently, when leaving the condensers, this warmer water needs to be cooled to an appropriate temperature, so that it can either be returned to the source from which it was abstracted, such as a river, or to be ‘recycled’ and re-used to cool the condensers. Two methods of achieving this are cooling towers and cooling ponds, though each operates in a very different way.
An essential distinction is that cooling towers use propellor-style fans (housed within a metal ‘tower’) that create cold air to cool the water. Cooling ponds are essentially a “no-tech” feature that can be integrated into the landscape, being literally a pond in which water cools naturally.
So, what are the criteria for using one or the other? “A cooling pond looks nicer and is cheaper to run than a cooling tower and once the pond is there, it’s there forever,” says Hamish Fraser, distillery manager, Torabhaig (operational since 2017).
However, a cooling pond must have a sufficiently large surface area to lose heat from the water quickly enough; how quickly depends on the weather and production schedules, among other factors. This means far more space is required for a cooling pond than a cooling tower, which is remarkably compact, and at Isle of Arran, for example the cooling tower is 12 feet tall and eight feet wide.
‘We had plenty of space for a cooling pond being on a seven acre site. We dug out thousands of tons of earth, creating a circular space with a diameter of 60 metres, which is three to four metres at the deepest point. ‘The resulting pond has a surface area of around 3,000 square metres containing 1.8 million litres of water,’ says Hamish Fraser.
Water from Torabhaig’s condensers, at a temperature of 20-25 degrees centigrade, is conducted through an underground pipe. This emerges by the edge of the pond and directs water onto the surface.
‘Hotter water initially sits on the surface of the pond, because it has a lower density than cold water. As the hot water cools it sinks into the depths of the pond, from where it drains through a central point, and is piped back into the river from where it was extracted,’ says Fraser.
Regulations stipulate that water returned by Torabhaig cannot raise the river temperature by more than three degrees centigrade. In winter the river water is around 4-5 degrees centigrade, and peaks at 12-15 degrees centigrade in summer.
‘We have a temperature monitor in the river at the point where we extract water, and another monitor by the outlet of the pond into the river. The temperatures are displayed on a computer screen as part of a management system, which ensures we comply with the regulations,’ says Fraser.
The time scale at Torabhaig for water to cool sufficiently and be returned to the river is around three days. This compares to a matter of minutes when using a cooling tower, as at Isle of Arran, for example.
“Water from the condensers, currently at a temperature of 24.7 degrees centigrade, takes two minutes to pass through the cooling tower, and results in water leaving the tower at 13.9 degrees centigrade,” says James MacTaggart, distillery manager, Isle of Arran Distillery.
Exactly how this is achieved depends on the design of a cooling tower, with different options available to the distiller (the technology involved is continually evolving). Glasgow Distillery Company, established in 2012, provides one example.
‘Water from the condensers is pumped to the top of our cooling tower and channeled through a drift eliminator,’ says Lachlan McIntyre, head distiller, Glasgow Distillery Company ‘This is effectively a large plastic tray with numerous perforations, ensuring that water falls from it in the form of small droplets.
‘As the droplets fall to the base of the tower, which is three metres tall, a propellor-style fan run by electricity creates cold air that cools the droplets. Once cooled the water can be re- circulated and used again to cool the condensers, which is a very economical use of water.’