OEM PROFILE: Aero engine portfolio highlights three options for electric generation

The LM2500 engine started out in the 1960s as a TF39 aircraft derivative—a nominal 17.9-MW “twin-shank” machine. The next major upgrade came in 1983 with the infusion of CF6 commercial engine technology into the LM2500; it became a higher-power “single-shank” machine. Note that single shank and twin shank refer to the high-pressure (HP) turbine configurations. 

GE gained considerable field experience with the 1983 uprate of the LM2500 and was able to gradually increase the engine’s power over time (Fig 1). By the early 1990s, output had been bumped up to 22.8 MW ISO (gas/dry) without any sacrifice in component life or reliability. Today, this standard single-shank LM2500 engine is more commonly referred to as the LM2500 “base” engine.

For many years, the LM2500 base-engine combustion system was a single annular combustor (SAC). It required water or steam injection to operate with low NOx emissions. So the next evolutionary step was to introduce the Dry Low Emissions (DLE) combustor to the LM2500 base engine, which made it possible to achieve 25 ppm NOx on gas fuel, but without the need for water or steam injection.

Later, a 15-ppm-NOx DLE combustion system was introduced for the LM2500 base engine to meet more stringent emissions requirements for certain customers.

GE LM series 1, 2

The mid-1990s saw the next significant jump in output with the introduction of the LM2500+ (Fig 2). The “plus” engine retains a great deal of commonality with the base engine, but it has an additional stage of HP compression. It also has a more modern compressor, variable stator vane system (VSV), single-crystal metallurgy in the HP turbine section, and changes in the six-stage power turbine to accommodate the higher mass flow.

All these changes enabled the plus engine to operate at a higher firing temperature and produce a significantly higher output of 42,000 shp nominal. The plus engine also is offered with a SAC or DLE combustion system. A dual-fuel DLE combustion system was introduced in 2000.

The LM2500+ G4 engine was introduced in the mid-2000s. It has the same footprint as an LM2500+, but produces about 3 MW (10%) more power at ISO conditions, and about 20% more on hot days, compared to its predecessor. It also has about 17% more exhaust energy than the plus engine, which makes it well suited for cogeneration and combined-cycle service.

The main changes that enable the G4 engine to achieve all this are a redesigned stage-zero blisk (bladed disk) with increased air flow, more rugged inlet guide vanes, changes in VSV schedules, improvements in the SAC combustor, technology improvements in the DLE combustor version, material and cooling-scheme changes in the HP turbine section, and some minor changes to the power turbine section.

Today, there are well over 2400 engines from the versatile LM2500 family operating worldwide. Service applications include propulsion of naval, ferry, and cruise ships; power generation; oil and gas platforms; and pipeline and LNG compression units—all with high reliability, availability and performance.

LM6000. In the late 1980s, GE began to look at using the newly certified CF6-80C2 aircraft engine as the basis for a small simple-cycle product that would set new standards of thermal efficiency at more than 40%.  The original concept was dubbed the “40 × 40” (40% simple-cycle efficiency and 40 MW ISO). The new product was to be called the LM6000 engine, denoting a product approaching 60,000 hp, and was a near-perfect match for 60-Hz power generation, because the low-pressure (LP) spool was well suited to operation at 3600 rpm.

That was the basis for the launch of the LM6000PA, which went into service in 1991. NOx abatement was still with water or steam, and a combination of water scarcity and tighter regulations led to the development of the DLE version of the PA model, called the PB, in 1994.

It soon became apparent that the market would demand more powerful machines, and the PC (SAC) and PD (DLE) models followed in 1997. The PC and PD essentially had the same footprint as the PA and PB, but the LP turbine was improved, allowing these machines to generate more power, more efficiently, in simple-cycle service. The PA is upgradable to a PA-uprate, which basically behaves like a PC engine. Many PCs were pressed into service in the North American “peaker” segment in the early 2000s (Fig 3).

It was not long before the need for increased hot-day power became evident. GE responded with the Sprint™ (Spray Intercooled Turbine) upgrade which uses water injection at the engine inlet to improve hot-day power output. Much of the North American LM6000 fleet is now Sprint-equipped. The mid 2000s also saw the introduction of the LM6000PF, which has newer DLE technology, enabling it to meet a more stringent 15-ppm NOx standard. The LM6000PF was the first gas turbine capable of 15 ppm or lower NOx emissions with a simple-cycle efficiency above 40%.

GE LM series 3, 4

The need for higher power output and combined-cycle operation encouraged further development of the LM6000 engine, beginning in the mid-2000s. It resulted in the LM6000PG (SAC) and PH (DLE) models (Fig 4), both of which have the same turbine footprint as their respective predecessors; all changes are internal to the turbomachinery.

Increased air flow is achieved by operating the basic LM6000 LP compressor at a higher speed (~3930 rpm). The hot section is derived from the CF6-80E1 aircraft engine, and there are changes to the combustor and LP turbine as well. Combined, these changes enable the PG engine to produce a nominal 54 MW (ISO/25-ppm NOx, water injection) and the PH engine about 48 MW nominal (ISO). Today there are more than 850 LM6000 units in worldwide service, operating in a wide variety of applications (Fig 5).

The LMS100 engine was developed in the early 2000s. GE took a bold new approach to the 100-MW-class “hybrid” intercooled aeroderivative. It used some parts and technology from its bigger cousins—GE’s heavy-duty frame gas turbines. For example, GE’s 6FA compressor technology is used in the LMS100’s LPC; HP compressor and turbines are derived from GE’s CF6-80E1 aircraft engine.

GE LM series 5, 6

The LMS100 also has an all-new lightweight two-stage intermediate-pressure turbine and a five-stage free power turbine for flexibility (Fig 6). Additionally, LPC discharge air is cooled before it enters the HPC. This integrated arrangement allows fast starts, has very good load-following characteristics, and high part-load efficiencies.

The first LMS100 PA (SAC) engine, rated 103 MW nominal at ISO conditions, entered commercial service in the US in mid-2006. It can be water-injected to achieve 25-ppm NOx. The PA was followed by a DLE version, the PB engine, rated at 100 MW nominal/25 ppm NOx. The first pair of PBs was installed in Russia in 2013. Initially, the 50- and 60-Hz power turbines were slightly different, but today there is one single power turbine specific to each model that is optimized for all applications.

LM engines have enjoyed continued worldwide success and acceptance, in part because of the millions of hours of operational experience with the basic design features that were accumulated on their parent flight engines from GE Aviation. In addition, GE has continually strived to improve its LM engines to meet customer expectations.

Madhu Madhavan, GE Power & Water/Distributed Power,
with Gil Badeer, Tayo Montgomery, and Rick Hook

Posted in WTUI |

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