Wartsila PP a Id Floating Solutions (1)

[ ENERGY / IN DETAIL ]

[ ENERGY / IN DETAIL ]

Floating solutions A U T H O R S : R o g e r E h n s t r ö m , G e n e r a l M a n a g e r, P r o j e c t P u r c h a s i n g & L o g i s t i c s K a i K e t t u , P r o j e c t M a n a g e r, Po w e r P l a n t s P r o j e c t M a n a g e m e n t , A m e r i c a s A r e a K a r i Tu o m i n e n , S e n i o r C h i e f P r o j e c t E n g i n e e r, E l e c t r i c a l

Wärtsilä has delivered floating power barges to the market for around 25 years, but the latest barge for the Dominican Republic represents a milestone in its history – it will be the company’s first combined cycle power barge. The increased efficiency of combined cycle operation will give the plant an advantage in dispatch priority.

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With power demand growing at about 5 percent a year, blackouts are not uncommon in the Dominican Republic. Despite its best efforts to meet surging demand, the government has long struggled to bring uninterrupted power to the 10 million inhabitants of the Caribbean island. In fact as long as 20 years ago, the island installed its first barge mounted power plant on the river flowing through its capital, Santo Domingo, to supply emergency power to the city.

This approximately 40 MW barge was supplied by Wärtsilä to a company called Seaboard Corporation, an independent power producer with a 90-year history that has its roots in grain and agricultural products. Then, 10 years later, in 2000, Wärtsilä supplied a much larger power barge of 71 MW, again to Seaboard, to further boost power supply to the capital. But with the need for power continuing to grow, Seaboard once again contacted Wärtsilä to build another barge power station that will replace the two older

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barges. This 106 MW barge, known as Estrella Del Mar II, is notably Wärtsilä’s first combined cycle power barge Greater flexibility The decision to opt for another floating power plant makes perfect sense. Seaboard already has permits for the existing two barges, and replacing these is an easier option than attempting to gain a new permit for a land-based project Continuing with a barge concept also has other advantages. A floating power station can be re-located to wherever the power is needed. Seaboard is familiar with the use of combustion engines. In addition to the two power barges, it operates and maintains a number of engines, many of which are Wärtsilä engines, onboard ships. Engine technology was thus the company’s natural choice. The Dominican Republic does not have a domestic gas supply. The country has one LNG terminal with which Seaboard has an existing gas supply agreement. During initial discussions, the company’s original thinking was to use high-pressure gas engines for the new barge. However, this posed the risk of the plant not being able to run in the case of an interruption to the gas supply. Seaboard also has heavy fuel oil (HFO) storage tanks on shore for running its existing barges. The company therefore opted for tri-fuel engines due to their ability to run on either fuel oil or gas. Although the plan is to run the engines on gas as much as possible – due to the higher efficiency and lower emissions – this still offers the option of running on fuel oil if gas is not available. The Wärtsilä 50DF proved to be the ideal choice in terms of power output and footprint. It not only gives flexibility to the operator in terms of fuel, but also has quick start-up and loading time. Furthermore, the Wärtsilä 50DF is designed to give almost the same output whether it is running on natural gas or LFO/HFO. The Wärtsilä 50DF can run on most natural gas qualities. The nominal design point is a Methane number of 80. The engine can be operated on gases with lower Methane Numbers with a different performance. It is also designed for continuous operation on pilot and back-up fuels, without reduction in the rated output. Fig. 1–3 – Estrella del Mar II construction phases.

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[ ENERGY / IN DETAIL ]

[ ENERGY / IN DETAIL ]

Assembly of blocks 1

2

Block Division

3

Fabrication of bottom blocks

4

Installation of center bulkhead

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Joint block B3 to B4

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Install all bulkheads and longitudinal bulkhead.

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Joint block B2 to B3 & B5 to B4

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Joint side block B2P, B2S, B5P & B5S

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10

Install maindeck B2 & B5

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12

Joint block B1 to B2

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Joint block B6 to B5

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The Wärtsilä 50DF operates on the lean burn principle; the mixture of air and gas in the cylinder has more air than is needed for complete combustion. Lean combustion reduces peak temperatures and, therefore, NOX emissions. Efficiency is increased and higher output is reached while knocking is avoided. Combustion of the lean air-fuel mixture is initiated by injecting a small amount of LFO (pilot fuel) into the cylinder. The pilot fuel is ignited in a conventional diesel process, providing a high-energy ignition source for the main charge. To obtain the best efficiency and lowest emissions, every cylinder is individually controlled to ensure operation at the correct airfuel ratio and with the correct amount and timing of pilot fuel injection. The Wärtsilä 50DF is normally started in diesel mode using both main diesel and pilot fuel. Gas admission is activated when combustion is stable in all cylinders. When running the engine in gas mode the pilot fuel, which is always present, amounts to less than 1 percent of fullload fuel consumption. The amount of pilot fuel is controlled by the engine control system. When running the engine in backup fuel mode, the pilot is also in use to ensure nozzle cooling. Combined cycle configuration The decision to use these engines in a combined cycle configuration was driven by the desire for increased plant efficiency. In the Dominican Republic, the plants are ranked according to their efficiency, and power is despatched from the most efficient plants first. Seaboard wanted to boost the plant efficiency and thus be at the top of the despatch order. During the sales phase, Wärtsilä therefore suggested a combined cycle plant. The plant will feature six 18-cylinder Wärtsilä 50DF tri-fuel engines in V-configuration with full heat recovery and a steam turbine generator. Plant output on HFO will be 108 MW, or 106 MW when running on gas. Efficiency will be about 47.8 per cent. Exhaust heat is recovered from the engines and fed to a single pressure heat recovery boiler. Steam generated in the boiler is then fed to a single cylinder, multi-stage, impulse/low reaction condensing type steam turbine. Steam flowing at 12.4 kg/s, with a pressure of 15 bar[a] and a temperature

WÄRTSILÄ TECHNICAL JOURNAL 02.2011

Fig. 4 – Barge 3D design

of 345˚C ±30˚C, leaves the last stage of turbine blades and passes up the exhaust branch to the water-cooled condenser via the condenser ductwork. The geared turbine and auxiliaries are mounted on a composite fabricated steel baseplate unit, part of which also serves as the oil reservoir. The generator is mounted on an extension baseplate, which is aligned and bolted to the main baseplate. The steam turbine generator operates at 60 Hz and has an output of 8.8 MWe. It has a power factor of 0.8 and operates at 13.8 kV. Step-up transformers will allow power to be to provided to the grid at 69 kV. Floating construction Estrella Del Mar II is essentially a landbased combined cycle power station on a barge. Fuel treatment equipment, such as fuel separators, fuel boosters, pilot fuel equipment, and lube oil separators, are all placed on board along with the major power plant equipment. Step-up transformers, high voltage yards and the main fuel storage tanks are located on

shore. A workshop, storage and offices will also be on shore, and a new underground gas pipe will be built to the site. Building a large floating combined cycle plant does not come without its challenges. Fuel day tanks, lubricating oil and fire water tanks have to be located in the hull of the barge. This means there is limited space for the auxiliary equipment that is typically placed below deck. Also, the boilers and associated heat recovery equipment that is placed above deck require a significant amount of space. The powerhouse had to be divided into two sections due to size and space constraint. The exhaust duct from each engine cannot be directed out as in the usual set-up, but instead they have to be turned inward, with the boiler and the stack area located in the centre. There are also physical limitations regarding the barge itself. The barge has to be towed up the river for about one mile from the port, and has to pass under one bridge that has to be opened and another that has a height limitation. This

called for careful design of the barge. The pontoon was designed by Wärtsilä Ship Design in Singapore and classified by the American Bureau of Shipping. The power plant portion of the project was engineered by Wärtsilä and its partner. A key difference between constructing a barge mounted power plant and a land-based project is the limited floor and storage space on the barge. This means project logistics and equipment deliveries have to be carefully planned during project execution. Also, the project team has to work with shipyards and the marine industry – it is involved with classification society issues, naval architects and naval designs etc. Such a project calls for a significant amount of co-ordination between all parties involved, especially during the design phase. The barge is being built in a Thailand shipyard. Over the last 25 years or so, Wärtsilä has built nearly 25 barges – most of them in Asia and a few in the USA. Following extensive research on a number of shipyards, the Thailand shipyard was

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[ ENERGY / IN DETAIL ]

[ ENERGY / IN DETAIL ]

Fig. 5 – The Lihir Gold Limited power upgrade barge Luise ready for sea freight.

found to be the most suitable in terms of cost and delivery time, as well as quality of work. In addition, another barge destined for Lihir Island was being built in the same shipyard, which meant Wärtsilä had developed experience of working with the shipyard. Furthermore, on completion of the first barge, advisors and some of the site people could be immediately transferred to the Seaboard barge project. All of the logistics were also already in place to receive equipment from Europe. Most of the power barges built-to date have been converted from existing barges – i.e. the power station has been added to an existing floating vessel. In contrast, the Seaboard barge is a newly built power barge. At 104.4 m long by 32 m wide vessel, the physical size of the barge is similar to previous barges. However, compared to a traditional barge-mounted HFO plant, there will be much more piping and cabling on board to accommodate the fuel oil tanks and gas fuel equipment, as well as the heat recovery portion of the power station.

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Fig. 6 – The Luise under construction.

would be designed to withstand wind speeds of up to 120 mph for an average of one minute. This is higher than for previous barges. With the new barge replacing two older barges, the moorings are also being reinforced. There will be additional pilings at the bottom of the river, and mooring dolphins will be made larger and cast in concrete. Each of the two mooring dolphins will be connected to a corresponding foundation on shore via a steel pipe structure.

Storm-ready A key impact on the barge construction and design was the need for the power station to be able to withstand hurricanes. Seaboard first contacted Wärtsilä for the project in late 2008. During negotiations, a hurricane passed over the Dominican Republic. With the devastation of New Orleans caused by hurricane Katrina a few years earlier still fresh in everyone’s mind, Seaboard wanted to ensure that the barge met the latest hurricane requirements. Therefore, when the project team became involved in the summer of 2009, it was decided that the barge

Preparing for the journey Although the barge is designed to withstand hurricane force winds, hopefully there will be no hurricanes during its journey from Asia to the Caribbean. During transport, all internal equipment and components will be fastened by temporary lashings. The project is on a very tight schedule – 16 months from contract award (midAugust, 2010) to commercial operation in simple cycle, and 17 months to substantial completion. The barge was launched in the water on June 30, 2011 so that outfitting could be finalised. All engines and generators were lifted

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aboard the barge during one week in July using a mobile 1800 ton crane. The barge will be transported using a semi-submersible vessel and is scheduled to begin its 40-45 day voyage from Thailand at the end of September, 2011. On arrival, about one month has been allocated to complete shore connections and the mooring so that it is up and running in simple cycle by Christmas. Combined cycle operation is scheduled one month later. In order to meet this tight schedule, it is likely that there will be a small commissioning team on board during the voyage to perform some testing prior to the barge’s arrival. Big potential The ability to sell or relocate power barges makes them particularly attractive as ‘temporary plants’, capable of being set up on an island to supply power to a location until an onshore power station is built, or an overhead line is connected to the island. Once this happens, operators can then move the barge to another location that is in need of power.

Even before the Estrella Del Mar II has set sail, Wärtsilä is already seeing interest in this combined cycle concept from other potential customers. It is therefore important that this project goes smoothly and that the barge operates according to its design. The market potential for such projects is huge. In addition to the Caribbean, there have been enquiries from various regions including Africa and Central America. Wärtsilä has received interest from mining companies that may plan to operate for perhaps 10 years – not long enough to warrant investing in a land-based power plant. The barge concept is ideal in this scenario since it can be moved to another location or sold when it is no longer needed. Indeed, another power barge Luise – the first to be built in the same Thailand shipyard as Estrella Del Mar II – is to be used exactly for this purpose. The LGL (Lihir Gold Limited) power upgrade project will see Wärtsilä supply an HFObased simple cycle power barge that will be floated to Lihir Island to supply

power for a gold mining operation. Lihir Island, Papua New Guinea is the home of an old gold mine supplied by two power plants – one geothermal and the other an HFO combustion engine plant. With geothermal steam decreasing from the geothermal plant, the mine is in need of additional power but there is insufficient space to build another power plant. Mounting combustion engines onto a barge offered a good solution. The LGL barge will use eight 20-cylinder Wärtsilä 32 engines, running on HFO with LFO as a backup, to produce 71.3 MW of power. Having left Thailand in July, the barge has arrived in Lihir Island and is awaiting connections to shore. The knowledge and skills being built up from the last 26 projects, including LGL and Estrella Del Mar II, will give Wärtsilä an advantage over other companies in what is becoming a growing business.

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