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1 THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS 345E 47th St, New York, N.Y:10017,98-GT=41; The Sodety shall not beresponsible for statements cir opinions advanced in papers or &mission. at meetings of the Sodety or oils Dions or ' Secaone, or rend in its publications. Discussion is printed only if the paper is published in an ASME journal. Authorization to Photocopy. for internal or personal use is granted to libraries and other users registered with the Copyright Clearance Center (CCC) provided 53/article or $4/page is paid to CCC: 222 Rosewood Dr., Danvers, MA Requests.tor special permission or - bulitreproduction should be addressed to the ASME.Technical publishing Department. Copyright by ASME All Rights Reserved Extending Use of Marine Gas Turbines through Application of the LM David L. Luck GE Marine and Industrial Engines General Electric Company Evendale, Ohio , Abstract The propulsion configurations of current gas turbine powered military and commercial vessels have been established based upon available power ratings of existing engines, relative to the performance requirements of ship builders and operators. ' Development of the LM2500+ engine has extended power capability with minimal changes to the physical parameters of the current LM2500 marine packages. This paper explores the extended possibilities of gas turbine based propulsion in both military and commercial vessels through application of increased gas turbine power in packages of essentially current size and weight such as the LM Background Gas turbines have become firmly established for marine propulsion applications over the last 20 years, including extensive use in military vessels, and growing application in specific segments of the commercial marine market. The development of aeroclerivative gas turbines, i.e. those derived from flying engines, has made efficient engines with a proven track record of operation available for use in a variety of ship classes. Warship Applications Military ship propulsion systems include a variety of configurations, including the most commonly used combined prime mover combinations, which are referred to as CODOG (COmbined Diesel Or Gas Turbine) and COGAG (COmbined Gas turbine and Gas Turbine). CODOG has been used where the maximum power for high speed is provided by the gas turbines, while the low speed more economical operation has been provided by small diesels engines. For larger ships where the maximum total power requires multiple (usually four) gas turbines, the lower speed operation is provided by using a lesser number' of the installed engines. Smaller vessels (less than 2000 tons displacement) of the corvette or patrol vessel classes have been able to achieve satisfactory performance with a single gas turbine CODOG, combined with multiple small diesels for low speed operation. CODOG propulsion configurations for larger vessels (above 2000 tons displacement) have generally required at least two gas turbines in order to achieve the required speed. The availability of higher power marine gas turbines has the potential to extend use of the simpler and less expensive single gas Presented at the international Gas Turbine & Aeroengine Congress & Exhibition Stockholm, Sweden June 2-June 5, 1998

2 turbine CODOG to frigate and larger size vessels. Figure 1 indicates the approximate distribution of the various configurations in warships. The power requirement fix various ship classes indicated in Figure 1 depends not only on the ship displacement but on the maximum speed required. The total power indicated on the horizontal axis represents the maximum total power available to achieve the maximum speed. For a CODOG configuration, maximum power is generated from the gas turbine(s), because the diesels and gas turbine(s) cannot be Diplom used simultaneously. For a ODGAG configuration, maximum power is generated from the combination of gas turbines. Figure 1 shows no CODAG (COmbined Diesel and Gas Turbine) configurations, although that alternative is now being implemented for the German F124 and is being considered for a number of other projects. For the CODAG configuration the total power available for maximum speed becomes the sum of the gas turbine and diesel power. For the CODAG configuration, use of a larger gas turbine can extend the Single Gas Turbine region well into the region of Two Gas Turbine ship classes. Total rawr Two arrow Gas Tortilla COO AO Two - On Turbin CO Single 0 Turblas. I C0000, TeS11.0wWW.1 Figure 1 Distribution of Gas Turbine Power Plants in Warships Commercial Ship Applications Gas turbines have only recently been put to serious use in commercial ships, as the compact, low weight characteristics of the engines have satisfied an urgent need. The development of the fast ferry market (generally vessels carrying over 50 passengers at over 25 knot speed) created a growing sector of volume sensitive ships carrying low density cargo, such as passengers and cars, which need compact and light weight propulsion systems (1,2). Similarly, cruise ships place a premium on efficient use of internal ship volume, and represent a potential application area (3). Commercial ship propulsion configurations also include CODAG (Combined Diesel And Gas Turbine), where the diesels and gas turbines independently drive waterjets, allowing simultaneous operation of both prime mover types. Multiple gas turbines are also used in the COGAG configuration. Higher rated gas turbines offer extended capability in both commercial configurations. Changes in the Marine Market The range of gas turbine sizes applied in the commercial marine market has been 3 MW to about 23 MW. Low power applications have generally been in very weight sensitive ships such as hydrofoils. The largest commercial ship applications have total power requirements of approximately 68 MW or more resulting in multiple gas turbine COGAG. Commercial vessel configurations have included catamarans and monohull vessels. 2

3 Many catamaran vessels have been built which use two sets of propulsion systems with total power less than 30 MW. The fast ferry trend has moved towards larger vessels with more capacity, operating at speeds over 40 knots. This trend in larger catamarans requires total power over 50 MW, divided into two systems for the two catamaran hulls. A considerable advantage in volume, weight, and cost can be realized if that power can be provided by a single gas turbine in each hull. In the military marine sector, powering requirements are changing for a different reason Instead of continued growth to larger ships with larger power requirements, a down sizing trend seems to be indicated. Instead of the larger frigates, destroyers, and cruisers which have dominated naval shipbuilding in recent years, interest in vessels of the offshore patrol vessel and corvette size is increasing. Ships of these classes normally have displacements around 2500 tans or less, as compared to the larger combatant vessels of 4000 tons and larger common in earlier programs. Smaller ships do not necessarily mean less capable ships. The operational capability requirements for these smaller ships are in some ways more difficult to achieve than with larger ships, since the combat systems payload is extensive. In addition, the speed requirement for these ships must usually match the capability of an existing fleet. larger ships have used multiple gas turbines to achieve the speed required, which is normally 30 knots or greater. Small ships of 1200 ton displacement can achieve this speed with a single gas turbine in a CODOG configuration. Ships with 2000 ton or more displacement have required two gas turbines or have settled for diesel propulsion and lower speed. To maximize the payload of these ships while providing the operational speed needed, a single gas turbine CODOG systems is desirable, because of the weight, space and cost savings. Revival of the previously employed CODAG (Combined Diesel And Gas Turbine) is cccurring in military shipbuilding. This configuration allows the operation of diesel and gas turbine power sources simultaneously. The total power is therefore the sum of that available from all prime movers. The German F124 vessels will employ CODAG with a single gas turbine and two diesels. Use of this same concept with a more powerful gas turbine can allow propulsion of larger ships with a single gas turbine, up to the size that had previously required two gas turbines in a CODOG arrangement. What does the LM2500+ bring? The LM2500 gas turbine has established a long history of operation in military marine applications and is now being used also in commercial marine vessels (1,2). The engine has evolved though a systematic program of component improvements which have increase the available power (4) and the maintenance and reliability (5). The available power rating of the LM2500 for military marine applications is 22 MW for U. S. Navy and up to 23.5 MW for some other international navies depending upon the definition of their rating conditions. In commercial applications with continuous power requirements at maximum output, the LM2500 has been applied at 21 to 22 MW depending upon the condition of operation for the vessel. The LM2500+ development extends the available power while maintaining substantial commonality with the current LM2500. The LM2500+ will be ISO rated at 29 MW after the accumulation of some operating experience with initial installations. The marine rating for continuous operation is slightly over 26 MW for ambient temperature operation at about 20 C. The engine therefore provides approximately 5 MW additional power for most typical marine applications. The marinized technology of the is carried forward in the LM2500+ with a large degree of commonality in components. Long experience in ship operation helps to ensure that LM2500+ is designed for that environment. Design of the LM2500+ The increase in power available with the LM2500+ is realized through increased air flow. An increase in operating efficiency is also achieved through a small increase in firing temperature. Specific improvements in each 3

4 major assembly of the LM2500+ have been previously published (6). For completeness the major upgrades are summarized as follows: Compressor One additional stage of compressor blades has been added forward of the LM2500's first stage blades. The number of compression stages is increased to 17 (from 16) and the air flow is increased by about 20% relative to the LM2500. Compressor airfoils for stages two and three have increased efficiency. Overall the compressor pressure ratio increases from 18.8 for the LM2500 to 23.1 for the LM Hot Section (Combustor and high pressure turbine) Improved materials in the hot section result in a more durable configuration with longer repair intervals. Thermal bather coating is added to the standard combustors resulting in greater temperature margin than in the LM2500, even though the firing temperature is increased. Materials and coating upgrades in the RFT blades and nozzles plus improvements in cooling will result in longer operating intervals between refurbishments for these items, even at the higher ratings of the LM Power turbine Redesigned power turbine blades and increased disk sizing has been incorporated in the LM2500+ to support the higher torque associated with increased power. These improvements have also increased the low cycle fatigue limits of the power turbine. This is especially important for fast ferry applications, which generally have highly cyclic operating profiles. T 1 III II a!vain',... anim ri ---alsidiez _ Allatillibilli t. 0 II" 6 rnorsh.ailllii,., LM2500+ New compressor stage 0, HP turbine material Redesigned PT blades VIGV, now pant mods and cooling upgrades and increased disk sizing LM2500 t.it ttio.,11[ A k rr ri,f. ATi,A rifires. ' ZIMINI Th ""itlirt - 1., Figure 2- Comparison of LM2500+ with LM2500 1' all Installation Parameters for Applications Marine Table 1 compares the specific installation and performance parameters of the LM2500+ to the current LM2500. Increased efficiency and power output are reflected in the table. Of additional interest for ship application are the improvements in power per unit volume and weight which the LM2500+ provides. Because gas turbines are of most interest for ships which are volume limited, i.e. those which carry light density cargo, the improved power density translates directly into additional revenue producing space in commercial vessels. In military vessels the reduction in volume 4

5 occupied by the propulsion prime mover results in greater combat systems payload. A likely reduction in cost per unit power makes LM2500+ more attractive on a first cost basis. Installation costs are very close to the LM2500 because the package is essentially the same. This further reduces first cost per unit power for a ship installation because of the increased power available. Installation and Performance Parameters Parameter Unit LM2500LM2500+ ISO Power Rating MW SFC (at ISO rating) gm/kw-hr Thermal Efficiency Weight * mton Volume * cubic meters Power/unit volume KW/cu meter Power/unit weight KW/KG * Typical commercial marine installation package Table 1 The Military Marine Market The current trend in military warship construction is toward smaller vessels such as corvettes or offshore patrol vessels in the 1000 to 2000 ton class. This trend has been noted for at least the last three years and is driven by two factors: first is the general reduction in defense budgets and the high cost of larger ships; second is the increased attention to the possibility of regional conflicts versus the past concentration on global wars. Smaller vessels satisfy requirements for littoral operations, and provide capability for extended capability as well. For the low end of the surface combatant displacement spectrum (1000 to 1200 tons), the propulsion requirements can be satisfied by multiple diesel CODA]) plants if lower speed (25 knots or less) is adequate for the mission. If greater speed is required, a single gas turbine CODOG plant can provide speeds in excess of 30 knots. Examples are the Korean Dons Hae and Po Hang classes, the Danish Niels Ale] class and the Israeli Eilat class. When additional capability is required, i.e. more combat system capability or the requirement to carry larger helicopters is added, the displacement of the ship approaches 1800 to 2000 tons. At 2000 tons the power requirement to achieve 30 knots is of the order of 27 MW (7). Although current diesels can provide that level of power with 4 x 20 cylinder systems, a considerable weight and volume penalty is paid. Competing requirements are placed upon military ship developments from two categories, operational requirements and life cycle cost limitations. Operational requirements include such capabilities as a) carrying a helicopter, b) supporting vertical launch for anti-air and anti-ship warfare, c) having low detectibility which means low noise, 111, and radar signatures, d) being able to achieve 30 knot top speed, e) maintaining long endurance on station or extended range. Life cycle costs requirements include a) reduced manning, b) low maintenance, and c) reduced fuel expenditure. The combination of operational requirements listed above drive the propulsion configuration to deliver high power with low weight and volume for the system. Previous designs have made use of two gas turbine CODOG configurations for larger vessels to achieve the required power. CODAG combines the smaller cruise diesels with the gas turbine to increase the boost power, but this results in considerable complication in controlling the combination of diesels and gas turbines, and 5

6 requires a multiple speed input gear to use the diesels at a wide range of speeds effectively. Availability of the LM2500+, which can provide the required power for 30 knots in a 2000 tons vessel, has several benefits. First the initial cost, volume and weight of the propulsion system is reduced relative to 4 diesels CODAD or the 2 gas turbine CODOG. Second, the operational benefits of gas turbine operation are realized, including reduced manning for maintenance and operation, much lower acoustic signature for ASW operations, and greater low speed range because of the more efficient cruise diesels combined with the larger fuel load. The Commercial Marine Market The commercial marine market for fast ferries has developed in at least three distinct segments. At the low vessel size and power end (less than 10 MW total power), the market is dominated by the diesel engine, except where weight and volume are so critical that gas turbines are required. Examples of such ships include the Kvaerner Fjellstrand Foilcat and the FBM Tricat. At the high end of the market where total power required is over 60 MW, multiple gas turbines are required because the weight and volume of diesel engines is prohibitive. The middle of the market is characterized by catamarans of the 74 to 90 metes size which have power requirements about 24 to 28 MW. These have been satisfied by four high speed diesel engines, although gas turbines have penetrated this market to a smaller extent. An example of gas turbine propulsion in this size vessels is the Danyard Seajet 250. This has been the fastest growing segment of the market with a large number of vessels sold. Larger vessels are being offered as more operating experience is accumulated. The trend of the medium size catamaran market is toward larger vessels with increasing power requirements. Designs are presently being considered with a power requirement exceeding 50 MW to achieve speed in the 40 knot range. Power requirements of 50 MW are beyond the capacity of a four diesel power plant, but may be achieved with gas turbines capable of continuous ratings at the required operating conditions which may include ambient temperatures at 20 to 25 C. The LM2500+ at a commercial rating of approximately 26 mw may satisfy the requirements of the larger catamaran with one engine in each hull. This simple cycle, low weight propulsion system may extend the size of economically viable catamaran vessels to over 100 meter length. Lower vibration, reduced emissions, and reduced maintenance are likely from this simple propulsion configuration, and will complement the design advantages of lower propulsion weight and volume. The other segment of the high speed commercial market which continues to expand is the fast monohull vessel. Early application of a single LM2500 in combination with MTU diesels in the Rodriquez built Aquastrada class has proven successful in over 5 years of operation. Larger monohulls are now being built, both with multiple diesel CODA]) by BAZAN and with multiple LM2500 gas turbines CODAG by Fuicantieri. Application of the higher power available from the LM2500+ extends the size of monohull vessels which can be powered by a single gas turbine CODAG. A vessels of 120 meter length with 200 car capacity achieving over 40 knots operating speed is possible with this configuration. Summary Propulsion configurations for both military and commercial vessels employing gas turbines have been developed around available size power units. In the military configurations. CODOG plants with one or two gas turbines and COGAG two or four gas turbine plants have become standard. Commercial vessels have fallen into two categories also. Catamarans have two or four gas turbines COGAG, monohuils have one or two gas turbine CODAG. Market evolution in both military and commercial vessels has created a need for a higher power gas turbine unit. Military vessels of the corvette size need a larger gas turbine for a single CODOG or a more powerful CODAG. Demand for vessels of this type is increasing due to changing military requirements and budgets. 6

7 Fast commercial vessels are changing as the market develops. Larger catamarans require increased power to permit applications over 100 meters with two gas turbines. Monohull vessels are increasing in size beyond 120 meters. A higher power engine allows single gas turbine CODAG to provide the required power for these vessels. The availability of the LM2500+ responds to the broader requirements of both the military and commercial vessel designs. Higher power with minimal increase in physical weight and volume for the propulsion system extends the application possibilities in both of these evolving markets. REFERENCES (1) C.O. Brady and D. L. Luck, "The Increased Use of Gas Turbines as Commercial Marine Engines" ASME paper 93-GT-142 (2) D.L. Luck, "Recent Gas Turbine Applications in Large Commercial Vessels" ASME paper 94-GT-120 (3) Carl Brady and David Luck, "Aeroderivative Gas Turbine Cruise Ship Power System Update", proceedings of Cruise and Ferry 97 conference (4) Carl 0. Brady, "LM2500 Marine Gas Turbine Sealift Program Uprate", ASME paper 94-GT-498 (5) Robert E. Reid and John J. Hartranft, "GE LM2500 Marine Gas Turbine Experience Update", ASME paper 91-GT-23 (6) F. G. Haaser, "Developing the LM2500+: Improving the LM2500 for Customer Needs", IGTI-Vol. 9, ASME COGEN- TURBO ASME 1994 (7) P. A. Dupuy, "Combined Diesel and LM2500 Gas Turbine Propulsion Enhances Corvette/Frigate Missions", July 1984 vol Journal of Engineering for Gas Turbines and Power 7