Compact heat exchangers provide operators with cost and maintenance gains while improving emissions
As enginerooms become increasingly congested with hard-working and overheated machinery, operators are looking for cooling systems that are more compact, efficient, unobtrusive and lower in emissions.
A largely unsung but vital technology, heat exchangers have long performed sterling work, particularly the plate, shell and tube-type systems that are deployed mainly on cruise ships, LNG carriers, container ships and car carriers, with their giant engines, generators and other heavy-duty forms of power.
Featuring a high-performance corrugated steel plate, their main function is to lower the temperature of the lubricating oil, main generator and auxiliary machinery. They should also start fast and be relatively easy to maintain and disassemble.
Norway’s Hydroniq Coolers has recently booked a string of orders for its most advanced technologies – the titanium-based Pleat seawater cooling system and its more radical cousin, the Rack system, which is installed not in the engineroom but in the hull.
In mid-February Ulstein Verft contracted Hydroniq to deliver a Pleat heat exchanger for Nexans’ submarine cable-laying vessel, Aurora, that will connect offshore windfarms to the grid. The patented Pleat is a module-based cooler for seawater to freshwater, with design pressure of six bars and a design temperature of 0.95°C.
Also in mid-February, Turkey’s Cemre Shipyard went a step further and ordered a hull-integrated Rack technology for an 83 m-long Salt Ship-designed vessel that will service offshore windfarms. The Rack solution will be integrated in the hull below the engineroom in a way that offers a range of operational and cost-saving benefits compared with traditional plate heat exchangers, Hydroniq claims.
One advantage is a simplified and shorter pipeline than usual for processing the seawater. A second is that pressure loss is much lower, the company says, which reduces energy consumption for the seawater pumps and lowers costs.
In another of a rush of orders, Tersan Shipyard contracted Hydroniq to supply three Pleat systems to the sister ship of the Bjorg Pauline, a wellboat launched last December.
And finally, in late January Norwegian shipyard Aas Mekaniske Verksted handed Hydroniq another contract for its Rack technology, this time for an environmentally advanced, diesel-electric wellboat under construction for Nova Sea, one of the largest producers of Atlantic farm salmon. With an energy storage system battery pack used for peak shaving to limit the number of generators in operation, the engineroom on the 77 m-long vessel may not be as congested as otherwise. But the shipyard, which also designed the vessel, still wants the heat exchanger to be located in the hull below the main engineroom. “Here it safely reduces temperatures in the ship’s engines and other auxiliary systems through use of seawater, but without taking up valuable space in the engineroom,” the company says.
Hydroniq must be doing something right because this is the third contract it has won with Aas Mekaniske Verksted. So what is the company’s breakthrough?
“The Pleat seawater cooler is a type of plate cooler, but at the same time [it is] different to a traditional plate heat exchanger,” says Hydroniq head of corporate communications Endre Johansen. “Both are installed in the engineroom and the functionality for both products is the same: to cool down the main engine and auxiliary systems through the use of seawater.”
But it is here that the technology differs in terms of principle and design. “One Pleat cooling element is equal to approximately 15 plates in a traditional plate heat exchanger,” Mr Johansen continues. “A Pleat system is dismantled, cleaned under high pressure and the few robust elements are easily reassembled and made watertight. One person can do the job in an hour.”
The Rack system, Hydroniq’s latest model, represents another step or two up in terms of technology. Not only does it save room by being installed in the hull, it is equipped with frequency-controlled pumps that require low back pressure to push the same amount of seawater through the system.
“This reduces energy consumption significantly versus, for example, traditional plate heat exchangers,” says Mr Johansen. “They require higher and higher water pressure to push seawater through the system when the plates are clogged, for instance by marine growth.”
Hydroniq has not by any means turned its back on more traditional heat exchangers. With more than 200 standard models of shell and tube-type products with a wide range of cooling surfaces, it continues to service the traditional market.
But the Rack system is its top-ranked technology. A highly condensed system, it boasts several features: there is one lifting point, reducing handling problems; a protection shield prevents foreign particles from invading the system; hidden away in the hull, generally between the frames in a double-bottomed structure, it is a space saver; with few service gaskets to replace, it is labour-friendly; and because the system is completely insulated from the hull structure, there is no risk of galvanic corrosion.
Among other advantages, the tubes are designed to minimise marine growth and other unwanted invasions that can rapidly clog up heat exchangers. Unlike box-type coolers, it does not need to be dry-docked. And there is a heat recovery element that captures surplus energy for other uses.
Hydroniq claims substantial savings for its latest technologies. Perhaps most importantly, Hydroniq has learned from clients that cleaning time is reduced by as much as 90%.
When towage group PSA Marine retrofitted the Pleat coolers on its fleet of 12 tugboats at work on Singapore Bay, it kept comparative records of the benefits. Until then, crews had spent a total of 2,500 hours a year maintaining the cooling systems for the fleet, a process that required the pipes to be dismantled and the heat exchangers cleaned just about every week.
“But with the Hydroniq Pleat coolers installed, we were able to extend the cleaning program by 10 months for each vessel,” PSA reports. This has significantly reduced resource costs and downtime for the vessel owner.
Overall cleaning time per unit fell from eight hours to one hour. The corporation estimated it got the original US$15,000 investment back in four months.