Bergesen - pioneers in liquid petroleum condensing

Why, despite its volatile cargo, are liquid petroleum gas (LPG) carriers so safe? One reason is that the technical requirements are very strict, explains Signar Nils Dahlberg, superintendent, Technical Operation at Bergesen.

Maintaining such a high level of safety with a dangerous cargo requires sophisticated technical systems and constant vigilance by a well-trained and experienced crew. As long as the cargo is treated correctly, and never comes into contact with air, it is fairly stable, explains Dahlberg. “But it is very combustible and can ignite if it mixes with air,” he adds.

The important reliquefaction plant

Basically, the gas cargo – such as propane or butane – is constantly boiling, creating vapor. But this vapor is not vented into the atmosphere. Big compressors suck vapor from the tanks and compress it under high pressure and then return the liquid back to the tank. This process is accomplished in the eliquefaction plant, one of the most important modules on an LPG ship.

“Typically, an LPG carrier will have three or four reliquefaction plants,” says Dahlberg. “Only one or two are needed to treat the cargo while the ship is at sea, while the others are back-ups, in case anything goes wrong with the working plants.” This is part of what accounts for the vessels’ excellent safety record.

“During all operations, no oxygen is involved,” adds Per Arve
Stokke, Sales and Project Engineer at Hamworthy KSE, supplier of the complete reliquefaction plants. “It is an enclosed system and we have therefore eliminated all causes of emissions.”

In addition, the crew members are required to have special training and retain certificates specific to LPG carriers.

Breakthrough

Reliquefaction plants are large and complex and contain many different elements. One of the most important and traditionally bulkiest elements is the cargo condenser. When Bergesen experienced trouble with a heat exchanger on one of its older ships, Alfa Laval saw an opportunity to break into a new market with a revolutionary new product – the AlfaRex.

Heat exchangers in reliquefaction plants have traditionally been of the shell-and-tube type. These takes up a lot of space and are prone to corrosion. The AlfaRex heat exchanger was designed to eliminate these problems. It is a compact unit made of lightweight, corrosion resistant titanium. But it wasn’t without a little persuasion that Alfa Laval managed to convince the shipping industry of its advantages.

Gunnar Selvaag, regional marketing manager at Alfa Laval started by going directly to the biggest gas-carrier operator in the world. He persuaded Oslo-based Bergesen to put one of the new types of heat exchangers on the older ship that was experiencing problems with corrosion in its traditional tube-and-shell condensers. Since the AlfaRex can be installed as a stand-alone unit or incorporated into a reliquefaction plant, it was not difficult to simply “plug and play”.

Good AlfaRex test results

Viggo Bjørnsgaard, a director in Bergesen’s Newbuilding and Project Management Division, says after the first ‘test’ AlfaRex heat exchanger had been sailing for four and a half years that “all expectations had been met.” Says Bjornsgaard: “They take less space on ships, they are more efficient, they can be cleaned with environmental friendly chemicals and they are easier to maintain than the shell-and-tube condensers. It’s a nice piece of equipment.”

Bergesen had made up its mind. The AlfaRex heat exchanger had proven itself and now Bergesen wanted it incorporated as part of the reliquefaction plants it would buy from Hamworthy for its new ships being built in Poland. Hamworthy acknowledged the advantages of the new system and forged a mutually beneficial cooperation with Alfa Laval and Bergesen that has now lasted for almost 10 years and continues to grow.

Today the AlfaRex plate type heat exchanger is being incorporated on some 50 LPG newbuildings at shipyards and has “pretty much become the new standard in the industry,” according to Bjørnsgaard. The AlfaRex has also been mounted on several older ships in operation since it is to efficient and easy to install.

Expanding business

Bergesen is a leading operator in its field and its decision to go with the AlfaRex on all of its newbuildings opened the door to a market that is difficult to penetrate, says Selvaag. But the cooperation with Hamworthy didn’t stop there. It is also resulting in the delivery of other products in other markets.“Thanks to this AlfaRex business, we have become involved in the volatile organic compound (VOC) solution for crude oil carriers,” says Selvaag.

“The VOC product is a completely different market,” explains Hamworthy’s Stokke. “These plants are meant for tankers loading oil, primarily in the North Sea. We are talking about mainly shuttle tankers, which would involve different kinds of shipping companies than Bergesen,” he says. “Two plants have already been installed and are working well,” he adds.

Basically, the VOC concept is a recovery system for gas emissions that occur while tankers are loading oil. When hot crude oil is loaded onto tankers, some of it evaporates and enters the air. “When you fill gas into your car, you can smell that some of it is going into the air. It’s the same concept,” explains Stokke.

The amount of emissions differs from field to field, with some of the fields in the North Sea having high levels of VOC emissions. Now the Norwegian government has put new, very strict air pollution regulations into place, and it is expected that the market for VOC’s will expand substantially.

More new buildings

Bergesen has already taken delivery of its first two newbuildings with the Hamworthy–Alfa Laval reliquefaction plants on them and Bjornsgaard says “they are working perfectly.”

Another vessel from Kawasaki shipyard in Japan has also been delivered with the system onboard and four more are to follow from the same yard. In addition, Bergesen, along with partners, just recently signed a contract at Daewoo shipbuilding in Korea for five more newbuildings, specifying the AlfaRex heat exchanger to be used in the reliquefaction plants along with other AL equipment onboard.