Towards improved VLGC reliquefaction

Two important new pieces of equipment from Wärtsilä Hamworthy are being fitted on board a fully refrigerated 84,000m³ LPG carrier being built at Hyundai Heavy Industries for operation in the Solvang fleet. The ship is due for delivery in 2013.

They are a reliquefaction plant which incorporates a newly patented technology and the company’s Krystallon marine scrubbing system for treating engine exhaust. The Krystallon package for the very large gas carrier (VLGC) represents the world’s first full-vessel scrubber system and the first scrubber to be installed on an LPG carrier.

“The new reliquefaction technology confers a number of operational and cost benefits for shipowners,” states Knut Erik Heggem, Wärtsilä Hamworthy business development manager, LPG. “The system has been developed for larger LPG carriers, typically ships above 60,000m3, with the aim of reducing installation, operation and maintenance costs. In contrast to the traditional approach of four reliquefaction units for such vessels, the new design features two units of increased size.

“The concept has been developed to provide increased reliquefaction capacity and improved loading rates at terminals. At the same time, the new system comes with fewer components, lower power consumption and reduced manpower compared with existing technologies yet still maintains the required level of redundancy. In addition the variable-frequency speed control of the compressors will result in reduced wear and tear and better adaptation to available generator capacity.”

The new technology embraces explosion-proof compressor rooms and, as such, is in compliance with the provisions of the newly revised International Gas Carrier (IGC) Code. This arrangement eliminates the need for a separate motor room, thus reducing quotas for equipment such as ventilation fans.

Two cargoes can be handled simultaneously with the new VLGC reliquefaction technology. The reliquefaction units handle the main cargo and provide the required redundancy while the provision of a condenser unit enables carriage of the second grade of cargo.

The Krystallon scrubbers for the new Solvang VLGC will comprise one for the main engine and one combined scrubber for three auxiliary engines. The scrubbers and washwater treatment system will be built to a modular design and positioned in the funnel of the vessel.

Wärtsilä Hamworthy points out that the Krystallon scrubber concept, which enables the ship to continue burning heavy fuel oil after the new emission restrictions enter into force later in the decade, can readily be applied to a range of vessel types. The design of the new Solvang VLGC has been developed to take into account all aspects of ship energy efficiency and environmental performance, using the extensive experience of both Solvang and HHI.

Initiatives specific to the exhaust gas cleaning systems will include varying the washwater amounts, depending on the load and sulphur content of the fuel oil, as well as installing an additional particulate matter (PM) capture system which will reduce PM emissions by in excess of 90 per cent. LPG