The LNG industry is edging closer to putting the final piece of its supply chain jigsaw into place. Floating LNG storage and regasification units (FSRUs) are now a mature technology while three floating LNG (FLNG) production vessels have been completed. What is needed to complete the picture is a floating LNG power plant.
Shipbuilders, conversion yards, electrical engineering firms and offshore contractors developing floating LNG power plant technologies enjoyed a particularly busy year in 2017. Several new concepts were introduced while other, more established designs gained class society approvals in principle (AIPs). The growing commitment to this new type of floater comes after rigorous assessments of market potential by the principals.
The same advantages advocated for FSRUs and FLNG vessels apply to floating LNG power plants. Such floaters will enable the direct supply of electricity to remote communities much more quickly and at lower cost than would be possible with a shore-based power plant. This option could also allow the use of a cleaner-burning fuel to repower existing, older generation oil-burning plants.
The use of natural gas rather than heavy fuel oil to generate electricity will help governments meet their pollution reduction targets. Also, as countries step up their commitments to renewables, floating LNG plants can provide a flexible substitute source of power to cover situations when renewables are unable to meet demand.
In addition, if electric utilities lease the required power plant vessels, there is no longer an obligation to make a long-term financial commitment to gain the other benefits on offer.
The capacity of the shipboard processing plant envisaged for such vessels can be graded to accommodate specific needs, from relatively small outputs of 50 MW up to medium-scale power generation levels of 500-600 MW. Using modular construction helps meet the challenge of providing the required processing capacity.
Various designs have been put forward to meet particular needs. Some of the floaters are effectively upgraded FSRUs, with the ability to generate electricity added to the intrinsic capabilities of LNG storage and regasification. Such Ďall-roundersí can be either newbuild units or existing LNG carriers converted for their new role.
Alternative approaches to floating LNG plant design provide what is essentially an electricity generating station that relies on separate, adjacent units for LNG regasification and, possibly, storage.
Most newbuild units are designed to the barge-mounted power plant (BMPP) configuration. Constructed as an industrial installation on a marine-classed deck barge, the vessels are either self-propelled or delivered to the selected site by ocean tow or heavy-lift ship.
BMPPs are relatively low-draught vessels designed for mooring in sheltered coastal areas and on rivers, while robust hull coatings are advocated to enable underwater inspections to substitute for drydockings. The power generated on board is supplied to the onshore electricity grid by high-voltage subsea power cables.
Samsung all-in-one solution
Engineers from Samsung Heavy Industries (SHI) described their all-in-one solution for a 500 MW-class floating LNG power plant at Gastech 2017 in Tokyo in April. The basic vessel, which SHI calls its SEP-T500GC design, integrates a combined cycle power plant, an LNG cargo containment system based on GTT Mark III membrane tanks, a regasification unit and associated mooring arrangements.
SHIís power plant barge would be provided with a basic propulsion system to facilitate both moving between sites and onsite manoeuvrability. The vesselís four underdeck cargo tanks can accommodate 174,000 m3 of LNG.
The SEP-T500GC vesselís two power generation blocks, the compressor and machinery room, the regas plant, the electrics and instrument building and the accommodation block are positioned on the main deck. Each power block is comprised of four gas turbines, four once-through steam generators and one steam turbine. A gas combustion unit, which is used in lieu of a flare tower, is also located topsides.
LNG from the delivery tanker would be transferred to the power plant vessel using cryogenic hoses while moored in the side-by-side mode. The power plant vessel itself would be moored either to an offshore jetty structure or a submerged turret, depending on project suitability.
Like all floating LNG plant designs, the SEP-T500GC concept is scalable, to cater for a range of power output requirements.
Cavalcade of designs
The 2017 cavalcade of floating LNG plant developments commenced in January when Wison Offshore & Marine, the Shanghai-based shipbuilder, announced it had developed a range of floating LNG power plants ranging in capacity from 10 to 800 MW. Like the SHI design, Wisonís W-FSRP series of barge designs integrates LNG loading, storage, regasification and power generation in a single vessel.
Later in the year, in November, Wison signed a memorandum of understanding with Shanghai Electric Power Generation under which the two parties will work to advance FSRP projects at the higher end of the series scale.
In April Lloydís Register and Hyundai Heavy Industries embarked on an assessment programme aimed at securing an AIP for the Korean yardís barge-mounted, dual-fuel power plant concept. The HHI unit would use 13 HiMSEN dual-fuel engines to generate up to 221 MW, upgradeable up to 400 MW through the addition of extra engines. The vessel is not able to store or regasify LNG.
In June ABS granted an AIP to Japanís Chiyoda Corporation for its conceptual design based on the conversion of an existing LNG carrier to a floating plant capable of providing anything from 72 MW to 400 MW in power output. The advantage of vessel conversions is further reductions in project times and costs.
Chiyoda is not the only Japanese company exploring the potential for floating LNG power plants. IHI Corporation, Mitsubishi Heavy Industries, Modec and Mitsui OSK Lines are all engaged in the development of BMPP concepts.
In December ABS issued another floating LNG power plant AIP, this time to GEís Marine Solutions and the Hudong-Zhonghua yard in China for their design for a 100 MW vessel that utilises GEís combined gas turbine, electric and steam (COGES) technology.
Each power plant vessel would be provided with three COGES systems and each COGES power train would comprise one GE LM2500+ gas turbine generator, one heat recovery steam generator and one steam turbine generator. The vessel is equipped with two azimuth thrusters to enable it to be moved independently without tug assistance.
Building on a prototype
There are currently more than 75 floating power plants worldwide. Most burn heavy fuel oil but there are some with gas turbines that run on local sources of natural gas. As yet, there are no floating LNG-powered plants, although there has been a prototype vessel of sorts.
In 2015 the Schramm Group put the LNG hybrid barge Hummel into service in Hamburg, providing electricity to the cruise ship AIDAsol while the vessel is in the port. On each outing from its berth the 77 m barge makes use of two replenished 40-foot cryogenic tank containers as the LNG fuel supply source.
Hummel is also outfitted with equipment to supply heat and electricity to other ships visiting Hamburg during the winter months. The bargeís five Caterpillar marine gas engines can generate 7.5 MW of power.
The march towards the first order for a floating LNG power plant has gained pace over the past year. Irrespective of the design chosen for the inaugural contract, the necessary technology is available and market demand has been ascertained. The pioneering project developer can base his decision to proceed on solid foundations.