Wärtsilä Introduces New Engine
The Wärtsilä 18V50SG runs at 500 or 514 r/min for 50 or 60 Hz applications and produces 18 810 and 19 260 kW of mechanical power, respectively by bo svensson

Wärtsilä has introduced its fourstroke, spark-ignited 18V50SG gas engine to meet a market need for larger gas engines that can run power plants with outputs of up to 500 MW. The company said its electrical output of 18 320 kW makes it the world’s largest gas-powered generating set based on reciprocating technology. It will be fit for combinedcycle operation.

The Wärtsilä 18V50SG four-stroke, spark-ignited gas engine takes the power output of the 50SG series up to above 18 MW. It works according to the Otto process and the lean-burn principle, and has the same gas technology as the smaller Wärtsilä 34SG engine.

The first of this new engine type has been sold to Turkish power company Aksa Samsun. The contract comprises engineering and equipment relating to the extension of the Aksa Samsun power plant in Samsun, Turkey. The scope of supply also includes the controls, automation and auxiliary equipment related to the fuel gas, charge air, cooling and exhaust gas systems.

This very first installation of the Wärtsilä 18V50SG unit will feature a power plant efficiency rating of over 50% in combined-cycle mode, said Wärtsilä. In simple-cycle mode the 500 mm bore by 580 mm stroke engine will have an electrical efficiency of 48.6% working in a 50 Hz market. In a 60 Hz market, the electrical output will be 18 759 kW and the corresponding efficiency 48.6%. From a “hot standby” mode, the engine will need 10 minutes from start command to full load.

The Aksa Samsun combined-cycle plant, owned by Aksa Enerji, currently operates using seven Wärtsilä 18V46 engines running on heavy fuel oil (HFO), six of which will be converted to Wärtsilä 18V46GD engines for gas-fired operation. When the Wärtsilä 18V50SG engine is commissioned in 2011, the power plant will have a total electrical output of approximately 130 MW in combinedcycle mode.

“This is an important order and highlights the high level of the company’s engineering expertise,” said Christer Strandvall, regional director, West Europe, Wärtsilä Power Plants. “In converting the Aksa Samsun facility from HFO to gas-fired operation, we are providing added environmental sustainability, while the efficiency level of the new Wärtsilä 50SG engine sets a new benchmark for the industry.”

Wärtsilä already has a strong presence in Turkey’s energy market, and expects to have delivered close to 3 GW of power generating capacity by the end of 2011. Some 85% of these power plants will be running on natural gas. “Our new four-stroke Wärtsilä 18V50SG spark-ignited gas engine has been developed in response to the market need for larger gas engines to run power plants with outputs of up to 500 MW,” said Vesa Riihimäki, group vice president, Wärtsilä Power Plants. “It works according to the Otto process and the lean-burn principle, and has the same proven gas technology as the smaller Wärtsilä 34SG engine. Substantial improvements will maximize the power potential of an engine block.”

Two header pipes per bank provide the gas fuel, one for the main and one for the pre-chamber gas supply. The maximum gas supply pressure required is only 4.5 bar(g). Ignition of the lean air-fuel mixture is initiated with a spark plug located in the prechamber. This provides for a high-energy ignition of the main fuel charge in the cylinder. Maximum temperatures and subsequent NOx formation are low.

The engine uses an exhaust gas wastegate valve to adjust the air-fuel ratio. The valve is located next to the turbocharger turbine to provide optimal charge air pressure and turbine speed. The air-fuel ratio is adjusted to the correct value regardless of varying site conditions under any load. Various parameters such as engine load, speed and cylinder exhaust temperatures are monitored as inputs to the engine control system. With this system each cylinder always works within the operating window for the best efficiency at the lowest emission levels. Individual cylinder combustion control and monitoring provide for even load on all cylinders.

“The Wärtsilä 50SG meets current and future requirements for overall cost of ownership with very high simple- and combined-cycle efficiency,” said Riihimäki. “It is designed for easy maintenance and many hours of maintenance-free operation.” 

Source: www.dieselgasturbine.com

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