FLEXIBILITY, FOOTPRINT AND RELIABILITY ADVANCE AERODERIVATIVE TURBINES IN A CHALLENGING MARKET
BY DREW ROBB
A Sulzer technician inspects a GE LM5000 aeroderivative gas turbine
Aeroderivative gas turbines GTs) are a popular choice for energy generation thanks to their reliability, efficiency and flexibility. Based on advanced aircraft engine technologies and materials, they are significantly lighter, respond faster and have a smaller footprint compared with their heavy industrial GT counterparts. With up to 45% efficiency compared to up to 35% for heavier GTs, these turbines are often seen as a good choice in smaller-scale (up to 100 MW) energy generation. The turbines are also popular due to their fuel flexibility — they allow a combination of natural gas and liquid fuel operation.
As such, the global aeroderivative GT market is expected to grow at an annual growth rate of nearly 5% between 2016 and 2020, according to a 2016 study by Technavio. Asia, in particular, deploys many of these machines in power trains for Liquefied Natural Gas (LNG) plants. In the U.S., aeroderivatives are mainly being used in peaker operations, or to compensate for fluctuations in the grid caused by renewables or extreme weather conditions. Just about all the aeroderivatives on the market come from GE, Siemens and Pratt & Whitney Power Systems (PWPS).
There is also a healthy aftermarket served by the OEMs, as well as companies such as Sulzer, EthosEnergy, RWG, and MTU Maintenance.
GE owns the lion’s share of the aeroderivative market. Its LMS100 is a fusion between aero flexibility and heavy-duty power output. The LMS100 uses an intercooler to cool the air between the low- and high-pressure compressor. As a result, the LMS100 can deliver up to 115 MW of power at 44% efficiency. Key features include its CF6 jet engine core derived from the Boeing 747 and the GE LM6000. Its free power turbine can be operated in 50 Hz or 60 Hz without a gearbox. Its 6FA LPC low-pressure compressor comes from the 6FA HD turbine. Clutchless synchronous condensing can restore full power in less than 10 minutes. It is often deployed for renewable peaking power and electrical grid stability. The LMS100 can meet strict emission requirements at 25% power, and use waste heat from the intercooler for desalination. GE’s fleet comprises 62 units operating in 10 countries (all simple cycle except five). Another 14 units are either in the installation or commissioning phase. Overall, the engines have chalked up more than 650,000 hours and 84,000 starts. Run times vary per start from 2 to 4 hours in California to 54 hours in Australia. Fleet reliability is 99.7% with availability at 97.3%.
Pampa Energia in Argentina, owner of the longest running LMS100 in the fleet, just had its second purchase reach commercial operation in August 2017 The LMS100 has been used in several plants as a replacement for the Frame 9E in combined cycle operation due to its low-temperature exhaust. Its exhaust characteristics match up with older 9Es and allow for use in existing plant infrastructures.
The LM9000 is a 66 MW to 75 MW unit that operates at 43% simple cycle efficiency. Derived from the GE90 jet engine used on the Boeing 777, it can be throttled to adjust power output, and started or stopped without impacting maintenance intervals. Power is available in under 10 minutes. Key features include: Dual-fuel capability without water consumption, and maintenance intervals of up to 36,000 hours for the hot section and 72,000 hours for overhaul. It is said to meet 15ppm NOx emission requirements in gas operation, and can switch between different fuels at full load without interruption. Use cases include support to grids with growing renewable sources, power industrial needs, peaking power for hot days or as reliable baseload to an isolated power island. It is also attracting interest for LNG compression and barge applications. The LM9000 configuration can be laid out to minimize its area footprint for maximum power density. Coupled with its aero core, it can survive the changing environments of a barge while providing maximum power in a space-constrained area. GE will begin shipping the first LM9000 gas turbines in 2019.
With 37 million operating hours and an expansive fleet of over 1,200 units shipped, the LM6000 offers +99% operational reliability, +99% start reliability and +98% availability, according to SPS ORAP data. The aviation heritage of the LM6000 originates from GE’s CF6 jet engine found in the B747, B767 and Airbus A330. With more than 5,000+ CF6 engines delivered and 400+ million operating hours, the LM6000 now has more than 1,270 units delivered and 37 million operating hours. Its output ranges from 44 MW to 57 MW in simple cycle and 117 MW to 149 MW in 2×1 combined cycle operation.
Four available models are based on SAC and DLE in lower and higher power versions. The SAC (single annual combustor) uses water for emissions control and has accumulated 26 million operating hours. The DLE (dry low emissions) does not use water and has reached 11 million operating hours. It has been used for peaking power generation, industrial cogeneration, district heating, load following, mechanical drive and combined cycle. The LM6000 features a two-spool optimized design resulting in lower operational maintenance cost in comparison to three-spool designs. Further features: 15 ppm NOx capability; cold start to full power in 5 minutes; gas and liquid dual fuel capabilities; and a compact footprint, highpower density and low-noise capability. The LM6000 DLE 57 is the latest model in the LM6000 family. Production shipments began in May 2017. It features increased core speed, exhaust temperature, simple cycle output, and combined cycle efficiency. Relative to the LM6000 DLE 50, the exhaust temperature of the DLE 57 has increased by 39°C. The simple cycle output has increased by 7 MW, and the 1×1 combined cycle output offers an increase of 0.7% efficiency.
Currently, installation and commissioning of two units is in progress at the customer site in Thailand, with commercial operation beginning in March 2018. Mechanical drive applications will be available in 2018. GE offers a variety of upgrade solutions depending on the operating needs from the unit. These are geared to increasing flexibility, lowering start times, adding up to 5% more power, boosting combustor and hot section life, and battery storage to integrate with renewable power. GE backs up its fleet with a worldwide network of service centers. This includes two Level 4 Service Centers in Houston, TX and Brindisi, Italy and six Level 2 service centers.
The LM6000 was GE’s first GT model to feature a battery energy storage system. This Hybrid EGT enables contingency spinning reserve without fuel-burn between demand events, high-speed regulation, primary frequency response, and voltage support (-8 to +5 MVAR). The Hybrid EGT consists of a lithium ion 10 MW battery, GE Brilliance 1.25 MVA Inverters, and OpFlex Controls upgrades. It incorporates a Mark VIe control system for the hybrid package. Two units are in operation with Southern California Edison Utility in California.
LM2500 and TM2500
The LM2500 is an aeroderivative based on the CF6 aircraft engine. Introduced in 1971, it has three models with multiple configurations and output ranging from 22 MW to 37 MW. Water injected and dry combustor options are available. With more than 90 million operating hours across 2,300 units, the LM2500 is the most widely used aeroderivative GT. It is popular in mechanical drive and offshore power generation applications, as well as CHP and district heating.
GE also offers a mobile version known as the TM2500. It can run on natural gas, LPG and liquid fuels, and is said to ramp from start to full power in under 10 minutes. A three-trailer design enables commissioning in less than 11 days from parking the first trailer. More than 200 units have been sold in 25 countries over the last 10 years.
Siemens acquired several aeroderivatives from Rolls-Royce. These include the 4 to 7 MW SGT-A05 (Industrial 501-K), the 10 to 15 MW SGT-A20 (Industrial Avon 200), the 27 to 38 MW SGT-A30 and SGT-A35 (Industrial RB211), the 41 to 44 MW SGT-A45, and the 53 to 66 MW SGT-A65 (Industrial Trent 60). The overall fleet size is close to 2,500 units installed worldwide.
Aeroderivatives serve market segments that value specific-product attributes. Historically these include lightweight, highpower density, high operational flexibility, such as fast starts and stops, and high simple cycle efficiency. Primary markets include oil & gas for onshore and offshore applications, and power generation in applications ranging from peaking to combined heat and power (CHP).
Siemens has renamed the entire Rolls-Royce aeroderivative turbine line to align with the latest Siemens naming conventions. The Industrial 501-K, for example, is now the Siemens SGT-A05 (p. 81, Turbomachinery 2018 Handbook). More than 1,600 of these GTs have been supplied for industrial use to 40 countries. They have accumulated 110 million operating hours since their introduction in 1963. The SGT A05 was originally based on the T-56 turboprop, used in the Lockheed Martin C-130 Hercules transport, E2C Hawkeye, P-3 Orion and other aircraft. Features include lightweight modular construction, ease of field repair, and use of multiple fuels. With an output between 3.9 and 6.4 MW, the A05 is used in applications, such as co-generation, offshore platforms and emergency power. Single-shaft and two-shaft versions are available. Steam injection can be adjusted to meet varying process steam or electrical requirements, depending on the application.
The Industrial Avon 200 is now the SGT-A20 gas generator. Introduced into service in 1964, it is popular in oil & gas, especially in North America where many units operate on trunk gas lines. Other applications include offshore pumping and compression, stand-by duties at nuclear power stations and combined cycle power generation. Over 1,200 of these units have been sold. The SGT-A35 (Industrial RB211) is also heavily used in offshore oil & gas applications due to its low weight and high power density. It is available in two 34 MW and 38 MW variants.
Siemens has augmented this Rolls-Royce engine with a Dresser-Rand package design optimized for floating applications. It is 30% lighter than its Industrial RB211 predecessors. The variants of this machine have accumulated over 37 million hours in service. The 38 MW variant introduces a gas generator upgrade through a compressor zero-stage, to deliver about 10% more power without any change in the turbine section, and with the same firing temperature. The power increase is achieved through higher core flow and compressor efficiency, rather than over-firing.
The Siemens SGT-A65 is a triple-shaft GT with three independent spools running inside each other. Based on the Industrial Trent 60, it can shift between 3,000 and 3,600 HP without a gear box. All that is required is to change the number of blades in the LP compressor. It has a two-stage LP, seven-stage IP and four-stage HP compressor. Siemens has also derived a mobile unit from the SGT-A65. Known as the SGTA45, it provides 44 MW and has a twoweek installation period. It is delivered in three main trailers with some additional shipped elements. The SGT-A45 can run on gas or liquid fuels, and transition between both fuel types when one becomes unavailable. Low NOx emissions can be achieved by adding water injection capabilities as an optional feature. This option boosts the unit’s power output particularly in warm climates. The GT can generate full power in less than 8 minutes from start without need for auxiliary systems to maintain the unit in an operationally ready standby mode. In the event of a shutdown, the unit can be restarted at any time to restore power quickly, as it has no hot-lockout restrictions.
“The compact design of the SGT-A45 is especially wellsuited for mobile power, for example in Africa or Southeast Asia, allowing us to capture a quickly growing market segment,” said Karim Amin, Head of Sales and Customer Operations at Siemens Power and Gas Division.
PW Power Systems (PWPS) is a group company of Mitsubishi Hitachi Power Systems. The company leverages technology derived from Pratt & Whitney aircraft engines. It has more than 2,000 aeroderivatives installed in over 50 countries worldwide. These can deliver anywhere from 30 MW to 140 MW of power. It also boasts a major gas turbine repair and overhaul business.
The FT4000 SwiftPac GT package is the latest power generation solution offered by PWPS. The engine features a two-spool, axial-flow gas generator based on the Pratt & Whitney PW4000 series of engines that currently powers commercial aircraft applications with thrust ratings that range from 52,000 to over 90,000 pounds. Indust r ial ized and packaged with a new free turbine, the a e r o d e r i v a t i v e FT4000 gas turbine can be configured as either a single- engine unit (one gas turbine driving one 60 to 70 MW electric generator) or a twin-engine unit (two gas turbines driving a common 120 to 140 MW electric generator). The FT4000 SwiftPac has a modular design to maximize the amount of factory assembly and reduce the amount of field assembly leading to lower costs. It features high part-load efficiency, less than 10-minute start-up time, quick engine changeout and greater than 41% simple cycle efficiency.
Key markets include onshore and offshore power generation (peaking, base load, cogeneration, combined-cycle), repowering to replace old gas turbines and mechanical drive. In 2015, after endurance and reliability testing, the FT4000 gas turbine was put into commercial operation. Its two launch customers included a SwiftPac 120 in the United States and a SwiftPac 60 in Argentina. These units have accumulated over 19,200 hours and over 1,575 cycles.
The PWPS FT8 MobilePac GT offers 30 MW of movable power. The package design includes two trailers. The first contains the GT, electric generator, exhaust collector, diffuser, and engine lube oil system. The second trailer carries the 15 kV switchgear, control system, operation panel, protective relays, batteries and charger, motor control center, and the hydraulic start package. A pre-commissioned FT8 MobilePac can be driven to a site and begin generating power in nine days or less. Over 130 of these mobile FT8 units have been sold worldwide. More than 40 have been relocated successfully from one site to another. It can run on liquid, natural gas, or LPG, has optional black start capability and can be operated remotely. With a footprint of 72 feet by 53 feet, little site preparation is required. No foundation or concrete pad is necessary for installation. Its controls are based upon Woodward GAP and HMI software built on the Woodward MicroNet Plus hardware platform. This provides FT8 fleet customers with control in the 5 to 10 millisecond range.
The FT8 SwiftPac can be installed in less than 30 days. This package offers 30 MW or 60 MW. It comes with an assembled enclosure incorporating the gas generator, power turbine, inlet plenum, lube system, and exhaust stack. It is also available in a combined cycle configuration. Features include an integrated lube oil system, quick-disconnect cable, a combined GT and exhaust enclosure, minimal foundation requirements, and a compact layout. It is typically used for distributed generation, peaking applications, and grid support to counterbalance fluctuating wind energy.
The FT8 gas turbine is a derivative of Pratt & Whitney’s JT8D aircraft engine. This is augmented with technologies to generate power with less noise, lower emissions, and higher baseload and part-load efficiency using natural gas fuel. It has been in production since 1991 and over 500 units are in operation worldwide. The fleet has accumulated over 6.5 million hours of operation.
PWPS offers a full range of maintenance, overhaul and repair, as well as field service for aeroderivative GTs. Its Long-term Service Agreement (LTSA) provides scheduled maintenance, unscheduled maintenance, spare parts, annual audits, and site support.
Sulzer maintains and repairs the LM5000 under license from GE. It is a flange-to-flange solution provider for that machine, which GE introduced in 1978 and no longer manufactures or supports. Based on the CF6-50 aircraft engine, over 100 of these 38 MW turbines were produced. The LM5000 has a twin-spool generator driving a free-power turbine. Sulzer also partners with Air New Zealand Gas Turbines (ANZGT) on maintaining and repairing this legacy turbine. ANZGT manages parts supply for some 25 LM5000s that are still in service.
“It appears that the LM5000 fleet will continue running for another five or ten more years based on customer conversations and surveys,” said Michael Andrepont, Manager of Gas Turbine Shop Repairs at Sulzer. As a result, Sulzer has broadened the supplier lists for consumable items for this power turbine to help reduce overhaul cost for end users. The company has also compiled best practices based on the LM5000’s repair history. This enables its technicians to inspect and overhaul these gas turbines in a timely manner. Over the past two years, Sulzer has witnessed the primary driver for emergent inspections and overhauls being bearing failure. The LM5000 uses roller and ball bearings, which have strict inspection criteria. Andrepont noted that dirty lube oil systems often hinder the condition and function of these intricate bearing systems.
MTU Maintenance is also licensed to support the LM5000. Further, its Berlin-Brandenburg facility is a level IV licensed service depot, offering a full range of MRO services for LM 2500, LM 5000 and LM6000 gas turbines. It also boasts a global network of level II service centers, including locations in Australia, Brazil, Norway, Thailand and the U.S. With over 20 years’ experience in working with LM series GTs, MTU Maintenance offers parts supply, test cell facilities, engine exchange and leasing, training and familiarization as well as package services. Its test cell for GTs is one of the largest in the world, using real-load operating conditions to understand vibration patterns. MTU Maintenance recommends regular maintenance, including water washing in the field. It advises users to protect inlets during downtime to avoid corrosion that can lead to removal problems and, ultimately, higher scrap rates of parts, such as compressor vanes. Early recognition and regular checks are recommended for continued operational performance and reduced costs.
“Aeroderivative gas turbines used as peakers will have multiple starts and shutdowns, fewer operational hours and, as a result, maintenance needs are different,” said Gregor Stöcker, Director Sales Industrial Gas Turbines, MTU Maintenance. “We tend to see more thermal distress and material fatigue in such operations.”
RWG Repair & Overhauls Limited is a Siemens and Wood Group Company specializing in the maintenance, repair and overhaul of Siemens aeroderivative gas generators and power turbines. RWG is authorized by Rolls-Royce Naval & Marine to maintain GTs used for marine propulsion. It has its headquarters in Aberdeen, Scotland and regional service centers in Houston and Kuala Lumpur. Between them, they employ 500 people. The company offers a wide range of commercial models, including time and materials, fixed-price and fixed-scope options, and repair rather than replacement service for high technology gas generator components and ancillaries. Its focus is to provide tailored work scopes to operators that optimize performance, mitigate risk of unscheduled maintenance, and lower lifecycle cost.
Due to low commodity prices in both oil & gas and power generation, customer behavior has shifted, said Mick Conway, Business Development Manager at RWG. Operators are less reliant on long-term service agreements, placing a greater focus on cost management of individual maintenance events. Constraints on operator maintenance budgets is extending equipment time between overhauls TBO), he added. Further, lower equipment use in the power generation sector is driving condition-based work scope innovation. “Ultimately the work scope and final maintenance cost is determined by the condition of the gas generator,” said Conway. “By the time the unit reaches our workshop it’s too late to deal with issues that have led to component degradation and failure.”
The workshop, though, can advise on probable cause of wear, corrosion and oxidation. However, adherence to good operations and maintenance practices, added Conway, will avoid many common reasons for rejection and replacement of high-cost gas generator components, including:
• Air inlet filtration condition and integrity of housing structure to minimize airborne contamination and risk from foreign object damage
• Routine maintenance of the fuel skid, conditioning units and oil system to ensure each system will meet OEM specification and does not introduce contamination or degrade critical components
• Regular washing and borescope inspection to monitor and report component degradation and to facilitate consultation with a specialist maintenance provider as necessary
• Timely intervention or rejection of equipment in accordance with the OEM service manual or condition based reports.
In Conway’s experience, most operators maintain their equipment diligently throughout its service life. However, once a decision has been taken to remove the unit for overhaul, there is less focus on good maintenance practice. Any complex machine no longer in use will deteriorate quickly, especially in high humidity environments, he said. ‘Stand still’ corrosion can be a very costly in terms of component rejection. It is critical that an operator applies the same diligence to temporary storage conditions, as they do under a turbine’s normal operating environment. “Prior to storage, routine procedures such as compressor washing, drying, inhibiting of fuel, oil and hydraulic systems will avoid considerable damage from stand still corrosion,” said Conway. “In ideal circumstances, the engine should be installed within a purpose-built container, capable of nitrogen purge.”
RWG recently earned a long-term maintenance support contract with Gulfstream Natural Gas System. It deals with three Siemens SGT-A30 RB (formerly the Industrial RB211 24G) DLE gas turbine generators. The three machines are in operation at Gulfstream’s Compressor Station 410 located at Coden, Alabama. RWG is responsible for the scheduled maintenance, including mid-life and major overhaul. The scope of work encompasses both infield repairs undertaken at Gulfstream’s facilities, supported by Siemens, and gas generator overhauls performed at RWG’s workshops in Aberdeen.
EthosEnergy has a full-service fuel nozzle and accessory service center. It has repair licencing agreements with GE, AA TECH, Parker, Titeflex Smiths, Woodward and Hydra Service. Plants are taking a longer time between removals and maintenance due to lower running hours, said Tom Watson, EthosEnergy’s President of Accessories and Components. This, he added, is being driven by more use of solar and wind. As a result, more units are becoming peakers. Under such circumstances, his advice is to not neglect regular planned maintenance despite lower operating hours. “Just as importantly, schedule regular checks and plan maintenance on rotatable safety stock,” said Watson. “In particular, accessories will suffer from deterioration of seals and other components as they are spending more time on the shelf.” Packaging is also an issue. Badly packaged items sent for maintenance can lead to transit damage, he said. A few hundred dollars of packaging materials could save thousands in unnecessary repairs.