Aeroderivative Gas Turbines
®
LM2500 to LM2500+DLE Gas Turbine Combined Cycle Plant Repowering
Authors: Michael T. McCarrick GE Energy Kenneth MacKenzie P.Eng. City of Medicine Hat
LM2500 to LM2500+DLE Gas Turbine Combined Cycle Plant Repowering Michael T. McCarrick
Kenneth MacKenzie P.Eng.
GE Energy
City of Medicine Hat
Abstract The province of Alberta, Canada developed annual emission
engine driving a generator. Over the intervening years, the plant
intensity limits for the power generation sector in order to
grew into a strictly Rankine-cycle steam plant and finally into
preserve air quality by reducing emissions of sulfur dioxide (SOx),
today’s configuration, a fully combined cycle plant.
nitrogen dioxide (NOx), and primary particulate matter. Effective January 1, 2006, all new gas-fired power plants were required to
The present configuration of the plant is shown in Figure 1. Units
meet Annual Emission Intensity Limits for NOx. In the Spring of
10 and 11, the subject of this paper, were originally installed in
2006, the City of Medicine Hat (COMH) LM2500 gas turbine units
1990 as refurbished General Electric (GE) Frame 5M gas turbines
were due for their 50,000-hour major overhaul cycle, and COMH
operating in simple cycle with a heat rate of 13,900 BTU/kWe-Hr
was faced with this new NOx emission requirement, along with
(LHV). A summary of past and present unit configurations is
an increasing power load demand for the city. Working closely
shown in Table 1.
with GE Energy’s Aero Services group, COMH decided to upgrade the two LM2500 gas turbines to two LM2500+DLE gas turbines to meet the new emissions requirements and boost power output to support the growing needs of the city.
In 1993, single-pressure HRSGs were constructed for both units to improve plant efficiency and increase plant capacity, achieving a combined cycle heat rate of 8,880 BTU/kWe-Hr (LHV) with a corresponding steam turbine power production of 10.1 MWe.
This paper will describe the engineering design challenges to modify the existing LM2500 gas turbine package to accept the longer and more powerful LM2500+DLE gas turbine, and the results of the evaluations of the additional mass flow impact on steam production and combined cycle plant performance. This paper will also detail the upgrade execution outages and commissioning experience of the LM2500+DLE gas turbines at the COMH plant. The actual operational performance results will
Figure 2 shows the heat balance for the 1993 configuration. In 1998 the Frame 5M units were replaced with GE’s LM2500-PE model aeroderivative gas turbines in an attempt to improve reliability and further improve efficiency. The LM2500 is derived from the CF6 family of aircraft engines used on a variety of commercial aircraft and is a hot-end drive, two-shaft gas generator with a free power turbine. The LM2500-PE features a Single Annular Combustor (SAC) and a 6-stage power turbine.
be outlined to show the approximately 30% increase in gas turbine power output, 5% decrease in gas turbine heat rate, and
The ISO exhaust flow of the LM2500-PE engines, at 499,000 lb/hr
the annual reduction in NOx emissions of up to 900 tons per year.
was significantly lower than the previous Frame 5 ISO engine exhaust rate of 716,000 lbs/hr. Thus, the steam production from
Background and Description of Original Plant Configuration
the respective Unit 10 and 11 HRSGs decreased to 6.1 MWe as measured in steam turbine electric power output. However, the
The City of Medicine Hat (COMH) Electric Utility is a municipally owned utility in Alberta, Canada that operates a natural gas-fired combined cycle power plant with a 209 MW ISO capacity.
combined cycle heat rate improved to 7,500 BTU/kWe-Hr (LHV) as a result of the turbine replacements. Figure 3 shows the heat balance for the 1998 configuration with the LM2500-PE.
The plant began in 1910 with a single-cylinder natural gas-fired
Simple Cycle Heat Rate LHV BTU/MWe-Hr)
Gas Turbine Generator Power (MWe)
HRSG HP Steam (lb/hr)
Steam Turbine (MWe)
Combined Power Combined Cycle (MWe) Heat Rate LHV BTU/MWe-Hr)
Frame 5M
13.90
17.9
91,000
10.1
28.0
8.9
LM2500PE
9.74
20.4
55,000
6.1
26.5
7.50
LM2500PR
8.88
27.0
62,000
6.9
33.9
7.08
Table 1 – Units 10 and 11 Performance Summaries (at 15C 60%RH 666m el.) 2
Figure 1
Figure 2
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Figure 3
LM2500 Gas Turbine History and Evolution to the LM2500+/+G4 In the early 1970s, the LM2500 gas turbine was derived from the CF6-6 flight engine, which to date has accumulated over 300,000,000 flight hours on a variety of commercial aircraft. The LM2500 utilized a 16-stage compressor section with inlet guide vanes and 6-stages of variable stator vanes with a 2-stage high-pressure turbine (HPT) section exhausting into a 6-stage free power turbine. The original design had twin-shank HPT blades and an ISO power rating of 17.9 MW with 35.8% simple cycle thermal efficiency. In 1992 a single-shank HPT blade was introduced that allowed for a higher firing temperature while maintaining the expected 25,000-hour hot section life on natural gas. The ISO power rating was correspondingly increased to 23.8 MW with a 37.5% simple cycle thermal efficiency.
In 1997, the LM2500 was upgraded to the LM2500+ when a zero stage blisk was added to the front end of the compressor section to provide a total of 17 stages of compression and boost the compression ratio from 20:1 to 23:1. Some material changes in the HP turbine section and enlarging of the free power turbine flow function raised the ISO power rating to 31.3 MW with 39.5% simple cycle efficiency. The major differences between the LM2500 and the LM2500+ gas turbines are shown in Figure 4. The LM2500+G4 gas turbine, the most recent uprate to the LM2500 family, was introduced in 2005. The LM2500+G4 provides approximately a 10% power increase over the LM2500+ model and was considered for this use in this project, however, the electric generator could not handle the LM2500+G4 output across the full range of ambient conditions, and the LM2500+ was selected for the COMH Repowering Project. As of this writing, the LM2500/+/+G4 models have over 51,000,000 operating hours in power generation, marine, cogeneration, and mechanical drive applications.
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Figure 4 – LM2500 vs. LM2500+ Cross-Sectional View (SAC Versions Shown)
Standard Annular Combustor (SAC) vs. Dry Low Emissions (DLE) Technology
was introduced to achieve 25 ppmvd NOx emissions without
The original LM2500 gas turbines operated with a standard
comprised of 75 staged injectors and a 4-passage compressor
annular combustor that utilized a single compressor diffuser pas-
diffuser. The LM2500+DLE gas turbine has over 2,400,000
sage and a single row of 30 fuel nozzles, and NOx emissions
operating hours, and can achieve 25 ppmvd NOx and 25 ppmvd
abatement was accomplished with water or steam injection to
CO from 75% to 100% load. The SAC and DLE Combustors are
suppress the firing temperature and reduce the formation of
compared in Figure 5 below.
water or steam injection. The DLE combustor uses 30 premixers
NOx. In 1995, a Dry Low Emissions (DLE) combustion technology
Dry Low Emissions
Single Annular Combustor
Figure 5 – DLE (Triple Annular Combustor) vs. Single Annular Combustor (SAC)
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Repowering Drivers and Benefits
2. Increased Power Output
The original LM2500-PE gas turbines were scheduled to achieve
The COMH electrical load in the 21st century has been growing
their 50,000-hour major overhaul cycle in 2006, and the COMH
at an average of 2% per year, with corresponding increases in
was faced with four options:
air-conditioning load peaks during the summer months.
1. Rebuild the existing LM2500 SAC engines at the depot to achieve Zero Time.
Replacing the LM2500-PE with a similar engine would obviously do nothing to increase plant capacity to meet this increasing
2. Replace existing LM2500 SAC engines with identical new LM2500 SAC units.
load. On the other hand, the LM2500-PR offered a modest 7.4 MWe increase in combined cycle capacity per unit,
3. Replace the LM2500 SAC engines with new LM2500 DLE
well within the regulatory limits set on the amount of electrical generation the City may hold.
engines. 4. Increase the capacity and reduce emissions by replacing the LM2500 SAC engines with LM2500+ DLE engines. To comply with emissions reductions commitments made to regulatory agencies, and to increase plant capacity with a marginally improved heat rate, it was decided to pursue Option 4, replacement of the engines with the LM2500+ DLE engines, known formally as the LM2500-PR model.
3. Improved Heat Rate The LM2500-PR features a higher compression ratio (23:1) than the LM2500-PE (20:1), and consequentially is a more efficient turbine. The guaranteed simple cycle heat rate for the LM2500-PR was 9,238 Btu/kWe·Hr LHV versus the guarantee rate for the LM2500-PE at 9,743 Btu/kWe·Hr LHV, a 5% improvement.
1. Emissions Reductions
Technical Challengers Encountered in LM2500 to LM2500+DLE Repowering
In prior years, the COMH had made commitments to the
1. Accommodation of Longer Engine
regulator, Alberta Environment (AENV) that would see NOx
By far the biggest challenge in the project was altering the
abatement technologies implemented on Units 10 and 11 prior
turbine compartments to fit the longer engines. As shown in
to renewal of the environmental permit in 2009.
Figures 6 and 7, the plenum wall was moved 13-13/16” and the main structural base was extended a proportionate amount.
The LM2500-PE units had historically and consistently produced
The front engine mounts were changed from the top-hung
NOx emissions of approximately 170 ppmvd, equivalent to a
"horseshoe" frame to a link style system supported from the
mass emission of 125 pounds per hour of NOx.
subbase, which also required extension.
Under the AENV’s 2006 Emission Intensity Limits for NOx, new
The original turbine compartment crane was removed and
units in the 20 to 60 MW range (that range covers the LM2500
replaced with a higher capacity unit due to the increased weight
models) would be required to achieve an intensity of less than 0.4
of the PR engine. The engine-lifting beam required extensive
kg/MW-Hr.
modifications as a result of reduced headroom from the modifications.
As shown in Table 2, the original LM2500-PE units produced NOx emission intensities well in excess of the 2006 Limits. NOx
2. Capacity of Generator
abatement equipment such as Selective Catalytic Reduction
The generator supplied in 1998 with the original LM2500-SAC
(SCR) or water/steam injection would have been necessary to
package is a Brush Electric Machines Ltd. Type BDAX-7-167ESS
achieve the 2006 limits using the LM2500 SAC engine.
rated at 35,412 KVA at a 0.85 Power Factor.
The LM2500-PR was predicted, and has proven capable in
On cold winter days, the LM2500-PR turbine is capable of
meeting the 2006 limits.
producing 30.1 MW with a corresponding turbine inlet temperature
NOx conc. (ppvmd) (ref.15% O2)
NOx mass emission (kg/Hr)
Combined HP Steam (lb/hr)
Steam Turbine (MWe)
LM2500-PE
170.00
57.0
91,000
10.1
LM2500-PR
21.60
10.0
55,000
6.1
of 32 degrees Fahrenheit. This power output matches exactly the Brush generator capability at the 0.85 Power Factor and thus no changes to the generator were required. The mechanical
Table 2 – NOx Intensities Comparison at Site Conditions
coupling connecting the turbine to generator was found to be inadequate for the higher mechanical power transmission duty of the PR turbine and was replaced. 6
3. Fuel System
4. Control System
The original LM2500-PE engines required a natural gas fuel
The existing Woodward Netcon control system was removed and
supply delivered at 385 psig and 100 Degrees F at the skid base.
replaced with a MicroNet Plus digital controller. This required new
The new LM2500-PR engines require a significantly higher inlet
control cubicles to be built and installed next to the existing
pressure of 520 psig.
Turbine Control Panels (TCP). The field wiring between the MTTB and the TCP was installed prior to the outage, and then
A review of the entire gas system was conducted to ensure that
terminated once the outage began.
the gas delivery system piping and vessels were capable of the increased operating pressure. This review revealed that the ANSI
5. Inlet Air Filtration
Class 300 flanges and piping were indeed capable of the
As a result of the Stage 0 Blisk incorporated in the LM2500-PR,
increased pressure, but that the stainless steel filter vessels
the airflow through the filter house to the engine increased from
would need alteration of nozzle reinforcement before being
499,000 lb/hr to 612,000 lb/hr. Consideration was given to
recertified for the higher design pressure. A local pressure vessel
increasing the size of the filter house, but the penalty in power
shop performed this alteration during the package conversion
output created by the additional inlet pressure drop was
activities.
predicted to be only a few hundred kilowatts.
Figure 6 – LM2500 vs. LM2500+ Turbine Compartment – Plan
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Figure 7 – LM2500 vs. LM2500+ Turbine Compartment – Elevation
Outage Summary
Corrected Heat Rate LHV (BTU/ MWe-Hr)
Gas Turbine Corrected Power (MWe)
Corrected Power Margin %
Corrected Heat Rate Margin %
Average LHV, Btu/lb
Unit 10
8.865
27.1
0.75
4.1
19,998
Unit 11
8.904
27.0
0.25
3.7
20,049
Average
8.885
27.0
0.5
3.9
20,024
The upgrades of Units 10 and 11 were planned as back-to-back outages of 30 days each. Unit 11 was the first outage executed, and took 14 days longer than expected due to fit-up, alignment, and clearance issues. However, the lessons learned on the first conversion expedited the second, as its duration was 30 days per the plan.
Table 3 – Performance Test Summary
Performance Testing Both new gas turbines were tested in general accordance with ASME PTC-22, "Gas Turbine Power Plants."
The actual combined cycle unit heat balance for Units 10 and 11 is shown in Figure 8. The combined cycle heat rates for Units 10 and 11 improved from 7.5 to 7.1 BTU/MWe-Hr, an improvement
Table 3 summarizes corrected power output and heat rate of the two LM2500+DLE 6-Stage (PR) units. The guaranteed power output is 26,903 kW. The guaranteed heat rate is 9,248 Btu/kW-
of 5.6%. Figure 9 is compiled from plant data and contrasts the respective combined cycle heat rates with those of the sister unit, an LM6000-PD.
hr (9,757 kJ/kW-hr). The tested units yielded corrected power output and heat rate better than guaranteed values.
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Figure 8
Conclusion In general, the two units have been performing very well and have delivered a 30% increase in power output, and over a 5% reduction in combined cycle heat rate. A few issues remain outstanding at time of writing: • Turbine compartment temperatures have been high during the hot summer months, and ventilation air modifications are planned for the fall of 2007. • The power turbine thrust balance pressure is in alarm on both units, and both the cause and solution are under investigation by GE. Unit availability and reliability for the first two quarters of 2007 have been very high at 98.7% and 99.9% respectively.
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Figure 9 – Comparison of Heat Rates and Load
References 1. Alberta Regulation No. 33/2006, Environmental Protection and Enhancement Act, Emissions Trading Regulation. 2. Figures 6 and 7 provided courtesy of Fern Engineering of Pocasset, Massachusetts. Fern provided engineering design services for the package modifications, and have provided similar services on other Gas Turbine projects. 3. GER 4250 “The LM2500+G4 Aeroderivative Gas Turbine for Marine and Industrial Applications” by Gilbert H. Badeer, GE Energy September 2005.
www.ge-aero.com LM2500 is a trademark of General Electric Company. Copyright © 2012, General Electric Company. All rights reserved. GEA18640A (10/2012)
