Siàƒ¢n Green, Managing Editor
GE has unveiled its latest gas turbine offering, the LMS100. Based on a unique blend of aeroderivative and heavy duty frame technology, the engine is the result of extensive industry collaboration and will be the world’s most efficient simple cycle gas turbine.
In 2000, engineers at GE Energy (formerly GE Power Systems) pitched the idea of developing a 100 MW-class, flexible and highly efficient gas turbine unit to the company’s senior management. Just three years later, and following extensive collaboration with other GE units as well as several external partners, GE Energy was ready to unveil its latest product to the power generation industry ” the LMS100.
In unveiling the LMS100 at Power-Gen International in December 2003, GE hailed it as the world’s most efficient simple cycle gas turbine. Through the use of off-engine intercooling technology within the compressor section of the gas turbine, the LMS100 reaches a simple cycle efficiency of 46 per cent ” ten per cent greater than GE’s highest efficiency gas turbine on the market today, the LM6000.
The LMS100 is the first modern production gas turbine to employ intercooling technology in the power generation industry. Its design is the result of the most extensive collaboration of design and manufacturing in GE’s history, with four GE business units and three other companies participating in its development. The unit represents the first time that GE has combined actual components from GE Energy’s heavy duty frame gas turbines and GE Aircraft Engines’ aeroderivative gas turbines.
The intercooled LMS100 consists of a low pressure compressor, aeroderivative “supercore” and power turbine
The main driver for the development of the LMS100 was market research conducted by GE that indicated that its customers wanted a gas turbine with the flexibility to operate economically over a wide range of dispatch scenarios. Specific desired characteristics were high efficiency, cyclic capability, fast starts, dispatch reliability, turndown capability, fuel flexibility, load following capability and low emissions. The research indicated that a 100 MW machine would be an ideal power block size.
GE chose the intercooled cycle and the union of technology from its Aircraft Engines and Energy divisions to meet these needs. “The LMS100 represents a significant change in power generation technology. The marriage of frame technology and aircraft engine technology has produced unparalleled simple cycle efficiency and power generation flexibility,” said John Rice, president and CEO of GE Energy. “GE is the only company with the technology base and product experience to bring this innovative product to the power generation industry.”
LMS100: competitive strength in a range of applications
The result of the development programme is a gas turbine that can be used in simple cycle, combined heat and power and combined cycle applications. According to GE, the LMS100 offers characteristics that are not available in other 80-160 MW gas turbines, including high part-power efficiency, cycling capability without increased maintenance cost, and a low lapse rate for hot day power.
At 50 per cent downturn, the part-power efficiency of the LMS100 is 40 per cent ” greater than most gas turbines on the market today. It can start and achieve full power in ten minutes and has load following capabilities. With a low hot day lapse rate, no inlet conditioning is required, helping to keep installed cost low.
The cycle design of the LMS100 was based on matching the existing compressor of GE Aero Engines’ CF6-80C2 (CF6) aircraft engine with available GE Energy compressor designs. The firing temperature was increased to the point allowed by the cooled high pressure air to maintain the same maximum metal temperatures as the LM6000 gas turbine. The result is a design compression ratio of 42:1 and a firing temperature class of 1380à‚°C.
The LMS100 consists of a three-spool gas turbine that uses an intercooler between the low pressure compressor (LPC) and the high pressure compressor (HPC). The LPC is derived from GE Energy’s MS6001FA (6FA) gas turbine compressor, and provides the high airflow capacity required by the LMS100 cycle. Compressed air passes from the LPC to the intercooler, and on to an aeroderivative “supercore”. The supercore consists of:
- A high pressure compressor (HPC) based on the CF6 aircraft engine compressor, strengthened for a high pressure ratio
- A combustor
- A high pressure turbine (HPT), also derived from the CF6 aircraft engine
- A two-stage intermediate pressure turbine (IPT).
The third element of the gas turbine is a five-stage aircraft design power turbine (PT) that has been specifically designed for the LMS100. It is connected to a robust power turbine aft shaft based on frame gas turbine design practices.
Low pressure compressor: The LPC comprises the first six stages of the 6FA and has a mass airflow of 209 kg/s. The compressor discharges through an exit guide vane and diffuser into an aerodynamically designed scroll case. Air leaving the scroll case is delivered to the intercooler through stainless steel piping.
High pressure compressor: Air exiting the intercooler is directed to the HPC scroll case. The HPC discharges into the combustor at 160à‚°C lower than the LM6000 aeroderivative gas turbine. This combination of low inlet temperature and less work per unit of mass flow results in the high pressure ratio and low discharge temperature, providing significant margin for existing material limits.
Combustor: The combustor will be made available in two configurations: a single annular combustor (SAC), which is an aircraft-style single dome system with water or steam injection for NOx control; or a Dry Low Emissions-2 (DLE2) configuration, which is a multi-dome lean premixed design operating dry to 25 ppm NOx and CO.
High pressure turbine: The HPT module contains the latest airfoil, rotor, cooling design and materials from the CF6 engine.
Intermediate pressure turbine: The IPT drives the LPC through a mid-shaft and flexible coupling.
Power turbine: the PT is based on the CF6 and LM6000 designs.
The intercooler system consists of a heat exchanger, piping, bellows expansion joints, moisture separator and variable bleed valve system. Two configurations will be available: an air-to-air intercooler for use in locations where water is scarce or expensive; and an air-to-water intercooler for use where water is more abundant.
Intercooling brings unique attributes and benefits to the cycle. It benefits the Brayton cycle by reducing the work of compression for the HPC, allowing a high pressure ratio. The reduced inlet temperature for the HPC allows increased mass flow, resulting in higher specific power, while the lower compressor discharge temperature provides colder cooling air to the turbines, allowing increased firing temperatures. The intercooler also allows for a constant HPC inlet temperature regardless of the ambient temperature.
The LMS100 control system is based on a collaboration between GE Aircraft Engines, GE Energy and GE Industrial Systems’ Turbine Controls division. It employs dual redundant control, instrumentation and sensors, and has been designed to enhance reliability.
Other aspects of the LMS100 have also been designed with reliability and maintainability in mind. The engine supercore can be removed and replaced in the field within 24 hours. Lease pool supercores will be available to allow continued operation during overhaul periods or unscheduled events.
A large part of the success of the LMS100 development programme is down to the ability of GE’s business units to work closely with each other as well as with other business partners. External partners involved in the development of the LMS100 include Avio S.p.A of Torino, Italy, which is responsible for the design, development, manufacturing and assembly of the IPT rotor/stator module and for the design of the PT as well as for the manufacturing of a large portion of the PT module components. Japan’s Sumitomo Corporation is responsible for the supply of a significant share of production generators.
Volvo Aero Corporation of Sweden is designing and manufacturing the PT case and compressor rear frame and is also manufacturing the IPT frame. Volvo Aero has been a partner with GE since the 1980s in the CF6 engine, and the two have also cooperated in the aeroderivative segment, including the LM6000 gas turbine.
The use of an intercooled compressor system raises the specific work of the LMS100 cycle
GE businesses involved in the development and production of the LMS100 include:
- GE Aircraft Engines’ Industrial Aeroderivative group is leading the programme and designing the core engine, intermediate turbine frame, PT module, core engine control and leading the system engineering and integration efforts.
- GE Energy’s Gas Turbine Technology group is designing the LPC, exit and inlet scrolls, power turbine aft shaft system and exhaust diffuser/collector.
- GE Aero Energy is designing the engine mounting system, package enclosure, control software and auxiliary support systems.
- GE Industrial Systems is designing and supplying the control system using its new Mark VIe control system.
- GE Global Research Center is providing technical expertise and conducting rig testing for the DLE2 combustor.
Road to production
The LMS100 core engine will be tested in a high altitude test cell in May 2004. The compressor and turbine rotor and airfoils will be fully instrumented, and testing will be done on both gas and liquid fuel. The test will validate HPC and HPT aeromechanics, combustor characteristics, starting and part load characteristics, rotor mechanical design and aero thermal conditions.
A full load test will be carried out in the first half of 2005. This will validate the performance of the intercooler system with the production engine configuration and air-cooled generator. All mechanical systems and component designs will be validated together with the control system.
After testing, the supercore and PT rotor/stator assemblies will be replaced with uninstrumented production hardware. The unit will be shipped to a demonstration customer’s site for endurance testing. This site will be the fleet leader, providing early evaluation of product reliability. The first LMS100 gas turbine generator will be shipped in the second half of 2005.