2.2 Commercial Market
Within the marine commercial market a number of developments have occurred making gas turbines an attractive option for propulsion/electrical power generation. The E-business revolution now offers worldwide shopping to every household with a resultant necessity for fast and economical freight transport. Fast freight transport is normally associated with air freight but is considerably more expensive than sea shipment. High speed ships incorporating specialised cargo handling facilities, with set schedules throughout the year and operating from dedicated ports are under development. One such project is Fastship Inc. whose target market is the transportation of high value or time sensitive (perishable) cargo. These ventures require propulsion systems with performance, reliability and low levels of maintenance such that schedules can be maintained. To maintain these schedules the propulsion equipment must be easy to operate, maintain and inherently reliable:-
a) The repairable on board failures require a mean time to repair of less than 4 hours
b) All maintenance must be on condition
c) Engine replacement must be achieved within 12 hours.
Latest aero gas turbine technology incorporated in systems such as the Trent 800 fulfil these arduous requirements and offer the additional benefits of high cycle efficiency.
The last decade has also seen an increase in the cruise market offering an alternative source of holiday transportation enabling relaxation during transit to and from different destinations. The use of gas turbines and in particular advance cycle gas turbines provides the ship architect with greater flexibility. The cruise ship no longer has to be designed around the propulsion plant. The high power/low weight benefits of gas turbine allow the adoption of the All Down Aft Machinery allowing generator set and the podded propulsion motors to be located adjacent. This lowers the service corridor and increases revenue space, passenger space for cabins, entertainment or recreation areas. Additionally the passenger cabin areas amidships are not infiltrated by spacious inlet and exhaust ducting leading to the main deck. As with the cargo ship, reliability and availability are of paramount importance to ensure that the ship has the speed and manoeuvrability to arrive on schedule at its destination. Additionally the passengers wish to travel in comfort, free of noise and vibration. Diesel engines emit low frequency noise which is difficult to dampen out. Whereas gas turbines emit high frequency noise that is readily dampened to ensure passenger comfort even in close vicinity to the engine room. Gas turbines emit no soot or visible smoke in the exhaust and hence provide a cleaner environment on the sun decks for the passengers. Finally gas turbine ships in comparison to diesel powered ships provide significant environmental benefits. Nowadays more attention is paid to environmental issues such as global warming and air pollution. Emission regulations shall become more restrictive. The main concerns regarding pollution are for NOx, SOx and CO2. Both NOx and SOx are significantly lower on gas turbines compared to diesels. CO2 levels in gas turbines are generally higher than diesels as the levels of emissions have a direct relationship with the amount of fuel consumed. However the more efficient advanced cycle gas turbine significantly reduces the levels of CO2 output towards levels emitted by the diesel engine.
3. ADVANCEMENTS IN GAS TURBINE TECHNOLOGY
Rolls-Royce gas turbine developments over the past decade offer the latest technology for the emerging marine naval and commercial markets. Two prominent products born from these developments are the advanced cycle WR-21 and the Marine Trent. These products are described in the following sections.
3.1. WR-21
The WR-21 engine system is an advanced cycle gas turbine incorporating intercooler and recuperator heat exchangers to provide significant fuel savings across the entire power range. The WR-21 concept was primarily developed for naval propulsion and the validation programme has been jointly funded by the United States Navy, the British Royal Navy and the French Navy. Work began in December 1991 following a contract award to Northrop Grumman Marine Systems (NGMS) for the design and development of an intercooled recuperated gas turbine engine system. The project team included NGMS as the system integrator, Rolls-Royce as the gas turbine provider, Honeywell as the provider of heat exchangers and CAE as provider of the control system.
The programme objectives were to design, develop and qualify a new generation of gas turbine with significant through life cycle cost benefits for future ship applications. The main contributors to the improvements in through life cycle costs are fuel efficiency, reliability and maintainability.
The WR-21 offers significant fuel savings over the entire power range which is particularly beneficial for Naval applications where the majority of operation is part power.
The WR-21 achieves its high cycle efficiency compared to simple cycle engines through the incorporation of heat exchangers into the engine system. Figure 2 diagramatically illustrates the engine cycle for the WR-21 .
