A Floating Power Plant : Wärtsilä supplies power plant for floating barge in Dominican Republic
Wärtsilä has been awarded a contract to supply the Dominican Republic with a barge-mounted power plant. The order was made by Seaboard Corp., a U.S.-based company that operates as an independent power producer in the Dominican Republic. According to Sampo Suvisaari, general manager, Power Plants, Central America and the Caribbean, this will be the first floating power plant using the Wärtsilä 18V50DF dual-fuel medium-speed engine and is also the first floating Wärtsilä power plant to operate in combined-cycle mode. In addition, he said it is the first floating power plant from Wärtsilä to reach a heat rate of 6990 Btu/kWh gross.
Six Wärtsilä 18V50DF engines together with a steam turbine generator will produce a total net output of 106 MW, increasing the Dominican Republic’s capacity by over 5%. The 18V50DF is a four-stroke, dualfuel, trunk piston, turbocharged and intercooled engine. The engine has 18 cylinders and operates at 514 r/min for 60 Hz applications with a 500 mm bore and 580 mm stroke. Each 18V50DF engine produces 16 700 kW gross output at site conditions.
The engines are designed to run on either natural gas with light fuel oil as a pilot fuel or on heavy fuel oil only for diesel mode. In gas mode, the engines are started with pilot fuel injection only and when combustion is stabilized in every cylinder, the gas is activated. The engines are designed for continuous operation in gas mode at any load between 15 and 100%. At loads below 15%, the engines automatically switch to diesel mode.
In gas mode, the combustion air and the fuel gas are mixed in the inlet port of the combustion chamber, and the ignition is provided by injecting a small amount of light fuel oil. The injected light fuel oil ignites instantly, which then ignites the air-fuel gas mixture in the combustion chamber. The barge will be located on the Ozama River, a few hundred yards from the sea. Seawater cooling is used for the engines and the steam condenser via heat exchangers. cooling system is equipped with several levels of screening and filtering to remove any trash and plants from the cooling water stream. The filtered cooling water is pumped through the system with six stainless-steel pumps four for continuous operation and two on standby. Each of the six engines drives a synchronous three-phase brushless air-cooled generator. The generator enclosure is IP23.
The plant is designed to operate in combined-cycle mode, reaching a gross efficiency of 48.8% (6990 BTU/kWh) at tropical site conditions. The guaranteed net plant efficiency is 47.8% (7150 BTU/kWh), said Suvisaari. The efficiency gain is achieved by using full power exhaust gas heat recovery boilers on each of the six engines. The steam generating system is designed to deliver superheated steam to one condensing steam turbine rated at 8300 kW. The steam is condensed in a water-cooled steam condenser and the condensate returned to the boiler.
All engines are equipped with separate water tube-type exhaust gas boilers with separate steam drums connected to the exhaust gas boiler evaporator. In order to save barge space and length, Wärtsilä put the two power transformers onshore, next to the HV switchyard and existing transmission line facilities. Suvisaari said the equipment, including all six engines and all six full-size heat recovery boilers, steam turbine and condensing system, will be squeezed in a barge size that would typically be dimensioned for a simple-cycle plant. This is achieved by grouping the heat recovery boilers in the middle. This way, exhaust gas piping is kept as short as possible, and exhaust gas stacks are grouped together for a better plume rise and less environmental impact. The barge is 104 m long and 32 m wide approximately the same size as the 70 MW simple-cycle barge that this new installation replaces. A