Pros and cons of using CO2

Pros and cons of using CO2 http://www.vinknl.com/

Dutch company Vink is no stranger to refrigeration for the food business, but is a newcomer to fishing and brings some new thinking to producing ice at sea.

The icemaker the company showcased recently, designed for use on fishing vessels as well as in land-based installations, uses CO2 as its refrigerant and combines a Geneglace icemaker, a Boch compressor and an Alfa Laval condensor.

According to the Vink’s Simon Slob, CO2 has its advantages – as well as presenting some challenges.

“There are environmental advantages. EU regulations state that we will have to stop using chemical refrigerants that have the potential to contribute to global warming. So we need to reduce the reliance on chemical refrigerants and while natural refrigerants are best, they also come with drawbacks,” he said.

“Some chemical refrigerants are better than others but still aren’t as good as natural ones – but these have side effects. Fifty or sixty years ago there was a search for chemical refrigerants that were easier to work with, but now we are back where we started working with natural refrigerants again.”

He said that as well as the environment as a whole, the microclimate around the equipment itself has to be secured to ensure the safety of people working around it.

“For years the most common refrigerant has been R404A,” he said, explaining that in environmental terms, CO2 is the baseline, and R404A is rated as being 4000 times worse that CO2.

“The challenges using CO2 are that pressure are higher. R404A works with a maximum pressure rating of 27 bars, but a system with CO2 calls for 120 bars, and that demands a different design of piping and everything has to be more robust. Another problem with CO2 is that it does not condense fully at temperatures over 30°C, but we have come up with a solution for that buy introducing a second heat exchanger. Air is fine as a heat exchange medium up to 25°C, but for higher ambient temperatures we have a water interface that helps with condensation,” he explained.

“We can still use air – but for up to 40% of the condensation we use tap water alongside the air condensation. It’s a system that is fine for countries such as Holland and Denmark where 30°C ambient temperatures are not all that frequent and the additional condensation is only needed for a few weeks each year,” he said.

Simon Slob said that most of Vink’s activity to date has been with land-based installations, supplying fish processing and trading companies, but the new icemaker is ready to be fitted to fishing vessels.

“It uses fresh water to produce flake ice, or if sea water is used, it produces ice of a different texture, slurry ice that can be pumped and stored.”

“This is a new market for us, although this is far from being new for Geneglace who have been supplying icemakers to fishing vessels for years,” he said, commenting that the icemakers with their stationary drum and a knife that revolves around it are highly suitable for fishing vessels as the fixed drum means there are no problems with seals – but the downside is that the installation requires height.

“We produce icemakers that produce 3000kg per 24 hours, and smaller machines down to 500kg. We also supply larger 10 and 20 tonnes capacity machines, but with the kind of installation we are looking at using ammonia as a refrigerant, which has its own advantages as a highly energy efficient medium. But as it is highly corrosive, it requires high-grade stainless steel pipes and fittings. So it’s a good choice for a 10 tonne machine, but not for smaller ones.”

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