The local refrigeration industry has proven just how innovative it can be completing a high efficiency makeover of one of the most demanding and toughest freezer systems currently being used by fishing vessels operating in Australian tropical waters.
The installation of a new pre-chilling refrigeration and hydraulic snap freezer system had to be completed in time for the Northern Prawn Fishery season which began on April 1, 2015.
Cairns-based company, Tropic Ocean Prawns Pty Ltd, had the new system installed in its prawn trawler ‘Gulf Bounty’ before it left for the Gulf of Carpentaria.
Fishing vessels operating in tropical waters have industrial scale refrigeration requirements to keep their catch in perfect condition.
Typically, a prawn trawler might catch several tonnes of prawns in sea water warmer than thirty degrees centigrade, and these prawns need to be packed and frozen to minus thirty degrees as quickly as possible.
This extremely demanding refrigeration task is generally achieved using refrigerant HCFC-22, which is being phased out under the Montreal Protocol to reduce the use of ozone depleting gases. As the phase out of the gas has progressed, the cost of HCFC-22 has risen strongly, to the point where, the Gulf Bounty for instance needed over $30,000 worth of the gas for a full charge.
As a result, the Australian prawn industry needed a new and effective approach and quickly. The Australian Seafood Cooperative Research Centre (CRC) and Tropic Ocean Prawns provided the $675,000 needed to design and install the new system which was designed by the Expert Group in association with ISECO Engineering Services.
It was installed by Cairns based Casco Engineering. Expert Group managing director, Peter Brodribb said the application is one of the toughest and most demanding refrigeration tasks in the economy.
He said the average vessel is only 22 metres long with a common plant room for the main engine, auxiliary power generation, refrigeration plant and other services.
“The lack of space for a separate refrigeration plant room, with sea water available at up to 32oC for condensing, high vibration, corrosion, limited refrigeration skills on-board and the huge task of snapping up to six tonnes of banana prawns per day, led us to the conclusion that we only had one refrigerant choice, HFC-404A,” Brodribb said.
“In order to devise a more economic and environmentally beneficial solution, we had to think about the problem differently rather than simply focusing on the refrigerant GWP.
“The result is a system that is both cost-effective and more environmentally friendly as it uses less refrigerant due to the improved containment design.
“The system is more energy efficient and has greater snap freezing capacity. All of this equates to lower emissions per kilogram of prawns caught and processed as the main engine produces more than 65 per cent of the emissions when trawling.”
Brodribb said the system includes the latest options in automatic controls, variable speed drives and economisers on all compressors, computer monitoring and remote fault diagnosis for vessels at sea. Other features include:
Pre-chilling of prawns down to 15oC to improve the equipment operating efficiencies and enhance product quality.
A hydraulic deck snap freezer capable of freezing 1 tonne of prawns in six hours (versus traditional times of 11 to 16 hours), and a fixed plate snap in the hold with capacity of snap freezing 4.5 tonnes in around 10 hours.
“The new system was developed and designed with a focus on refrigerant containment to mimimise the risk of refrigerant leaks,” Brodribb said.
“This is achieved by eliminating high-risk connections, using stainless steel welded piping and incorporates a five point sample draw refrigerant leak detection system.”
The Expert Group is finalising the system performance results, design standards and manuals for the CRC who will make them available for other vessel operators through its member bodies, the Australian Council of Prawn Fisheries, the WA Fishing Industry Council and the Fisheries R&D Corporation.