Gas turbine powers into marine market
Siemens Power Generation (PG) has been awarded a contract from the Norwegian shipping company FPSOcean AS for supply of two SGT-500 gas turbine gensets to be installed on an oil tanker which FPSOcean is currently converting into a Floating Production, Storage and Off-loading vessel (FPSO), to be called Deep Producer 2.
The two gas turbine sets are scheduled for delivery in May and August 2008.
This was a follow-up to the order for two SGT-500 gas turbines for Deep Producer 1. These turbines will be used to produce power for the vessel's dynamic positioning installation, the facility which eliminates the need for the vessel to be connected to the ocean bed, its position being maintained instead by means of electrically driven propulsion pods.
These orders mark the beginning of a new era for the SGT-500, which has recently passed type tests for heavy fuel oil (HFO) IF180, increasing its competitive¬ness on the marine market by offering consider¬able fuel cost savings. The 17-MW SGT-500 gas turbine (23,290bhp in mechanical drive) not only offers operators very low maintenance costs due to its low firing temperature, but also meets high demands for flexibility and availability using a variety of fuels, e.g. gas, diesel oil and IF180.
Although gas turbines have been providing clean and cost-effective power in land-based industrial applications worldwide for many years, until now their use in the marine industry has been restricted to aero-derivative engines designed to burn expensive light diesel oil. Diesel engines and steam turbines fuelled on heavy bunker oil have been the prime choice for marine power generation and propulsion. Now that the Siemens SGT-500 industrial gas turbine has proved its ability for HFO operation, the barrier to the use of industrial gas turbines has fallen.
The tripling of price for distillates in recent years and increasing price difference between distillates and HFO has increased the incentive to use SGT-500 for marine applications.
The SGT-500, originally designed for operation with HFO, has broad experience of operation with a variety of fuels, including intermediate fuel oils. SGT-500 turbines are already successfully operating in two FPSO's , in the Leadon and Banff fields of the North Sea UK Sector. Two dual-fuel units are installed on each FPSO. SGT-500 are also operating in high speed passenger ferries in Scandinavia and Argentina, the Scandinavian ferry having operated with HFO since 2003.
After reviewing the results of HFO operation with SGT-500, DNV (Det Norske Veritas) signed a statement of preliminary approval, rendering the SGT-500 the only industrial gas turbine to be available for marine application with Heavy Fuel Oils. (The following marine ISO (8217) fuels can be used for the SGT-500 gas turbine: DMX, DMA, DMB, DMC, RMA 30, RMB 30, RMD 80, RMG 180, RMF 180 and RMG 380.) The trial operation was problem-free, combustion efficiency was high, and the result indicates no significant effect on turbine maintenance. Most importantly, no visible smoke is given off with this fuel.
Already in use as a cost-effective alternative to existing mature ship propulsion technology, the Siemens SGT-500 can now operate on heavier fuel oils better than ever before, reducing fuel costs dramatically. The SGT-500 provides a seamless transfer between gas and liquid fuels, and can run on practically any combin¬ation of liquid and gas.
The key to the exceptional fuel flexibility of the Siemens SGT-500 is its combustion system. The combustor chambers are significantly larger than those used in aero-derivative gas turbines. This means that the larger sized heavy fuel oil droplets have sufficient time to burn completely, before passing into the power turbine section at a considerable lower temperature than the aero-derivative equivalent. The reduced turbine inlet temperature also provides a secondary advantage, as no cooling is required for either the turbine vanes or blades, leading to reduced component wear and improved overall performance.
Gas turbine-based installations are considerably smaller and lighter than diesel engines of comparable power. As many types of ship, such as fast ferries, need engines with high power output and low weight, the gas turbine provides the optimal solution. Capable of operating for very long periods between routine maintenance intervals, the engines require almost no attention from the crew, and virtually none at all while at sea. Ideally, major maintenance activities should coincide with the ship's docking schedule, typically for the SGT-500 once every two to five years depending on operation profile.
The lighter weight and smaller size of such a system provides significant potential for higher revenues. Cruise ships can install more cabins, container ships can carry more containers, tankers and general cargo ships can have more cargo space. Conventional two-stroke and four-stroke marine diesel engines normally require special structural supports to minimize the vibration transmitted throughout the ship. In contrast, gas turbines produce substantially less vibration and noise than reciprocating cylinder engines leading to increased comfort and easy installation.
In addition, the relatively small size makes it easy to house the gas turbine in an insulated, sound-attenuating acoustic enclosure, reducing the noise level to less than 85dB(A), compared to 102-108dB(A)for comparably-sized diesel engines, and reducing radiated heat to a minimum.
DNV approval for SGT-500 propulsion using HFO opens up the potential for full use of the general strengths of the SGT-500, namely:
* Fuel flexibility: HFO, gas and mixed firing.
* Emissions: low NOX, no smoke.
* High reliability.
* Long maintenance intervals and low maintenance cost.
This translates to specific advantages in particular applications:
Today's standard for propulsion is optimized for diesel engines. When concepts, installations and operation are optimized for propulsion with gas turbine based systems, potential for further improvements will be apparent.
Although forced by current regulatory and environmental pressures to clean up their act, marine diesel engine manufacturers still have a long way to go before they reach the emissions levels routinely achieved today by gas turbine-based power systems. NOx emission regulations announced for implementation in a couple of years from now can easily be achieved with good margin for SGT-500 with today's proven systems. For reduction of SOx emissions, low-sulfur HFO can already be used without restriction in the SGT-500. The recent SGT-500 orders indicate that the eyes of the FPSO market are opening to this fact, giving the SGT-500 the signal to forge ahead at full speed.
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