Ice-cold chemistry far more sustainable
Occasionally, the application of chemistry leads to fantastic results with respect to energy saving and CO2 reduction. An excellent example of this is a new technology for cold storage that saves large quantities of energy and consequently reduces CO2 emissions too. These benefits are the result of quite a technical story.
Industry makes considerable use of cold storage facilities to keep a wide range of products fresh, such as fruit imported via harbours. The refrigerants are chemical substances, such as liquid ammonia and CO2, that are pumped through the cooling systems. While in transit, these substances lose some of their cooling, which leads to the formation of gas with droplets. Droplets make the cooling less efficient and cause damage, such as moisture damage, which increases the maintenance costs.
To prevent this as much as possible, industry has long made use of components that separate the droplets from the gas, the so-called “separator”. The droplets are returned to the system, and the gas is compressed into droplets that also return to the system. In the case of ammonia, 98 percent of the droplets are separated from the gas, and for CO2, that figure is 95 percent. Although these seem to be impressive results, every droplet is a droplet too much. Because the drier the gas, the better the compression, the more efficient the cooling and the lower the energy consumption and maintenance costs.
A relatively new technique called “Uniflow”, marketed by Prevesco in Amsterdam, demonstrates that this droplet separation can be realised far more efficiently. Prevesco was originally a family company, and the former owner Johan Dijkstra started working on a new method in 2009 in collaboration with Titus Bartholomeus, owner of Thermass Innovations in Sittard. In 2011, they realised a prototype of Uniflow, which was introduced to the Dutch market for cooling technology in 2012. The sales market has since been expanded to France, Germany, the UK and the US and is currently worth 100 units per year, each of which costs between 10,000 and 20,000 euros.
‘The core of our technology’, explains Prevesco director Anouk Dijkstra, ‘is making the gas flow more uniformly. This means that at every location, the gas flows at the same speed and in the same direction. Hence the name Uniflow, a short way of saying uniform flow.’ In conventional droplet separators, the droplets are only separated from the gases if the weight of the droplet is more dominant than the speed of the gas. Furthermore, the calculations for the fall speed of the droplets is based on assumptions, averages and the idea that the droplets will fall earlier at lower speeds.
Anouk: ‘However, Uniflow works with speeds that are slightly lower than the drag velocity of the droplets, which can be compared to the speed at which the wind carries splashing water from a wave. That yields 99.99 percent dry gas. With this approach, we get around the concept that we need to know the size of the component to make the weight of a droplet more dominant than the speed of the gas flow.’ In the case of ammonia, the Uniflow technology yields a saving of 2 percent on the total installed electric power, and for CO2, that figure is 5 percent. Saving on the electrical power reduces the CO2 emission, which is considerable bearing in mind that the systems can be in use 24/7 for up to 30 years.
Anouk: ‘If all the industrial cold stores in the Netherlands, France and United Kingdom switched to Uniflow, then on an annual basis, that would save the amount of energy produced by an entire nuclear power station.’