ULTRA LOW NOX COMBUSTION
TECHNOLOGY
Power-Gen International 2008—Orlando, Florida
www.siemens.com
PowerGen International | Orlando, Florida | December 2008
ULTRA LOW NOX COMBUSTION TECHNOLOGY
Clifford Johnson, Barton Pepperman, Michael Koenig, Khalil Abou-Jaoude,
Anil Gulati, Ali Moradian
Siemens Power Generation Inc., 4400 Alafaya Trail, Orlando, FL 32826-2399
Greg Hall
Idaho Power, Boise, Idaho
Abstract
Siemens Power Generation combustion technology has undergone a significant transformation over the past 20 years. Evolving from the 1980's diffusion flame combustor technology, which
produces a very stable flame, but is associated with relatively
higher levels of emissions output of some constituents, Siemens
Power Generation incorporated material and technological design
advancements, industry-leading design engineers, and state of
the art design tools to develop a successful Dry Low NOx (DLN)
combustion system in the 1990's. Dry Low NOx technology provides reduced NOx emissions through a staged combustion process and unique temperature and heat release strategy. This fourstage premixed combustion process is designed to produce reliable and stable combustion, with lower level emissions and is
currently installed in over 100 Siemens GT's. Further improving
the environmental compatibility of Siemens Power Generation's
fleet of gas turbines, the Dry Low NOx technology has evolved
into a combustion system, commercially offered as “Ultra Low
NOx “(ULN), which is designed to achieve sub 9 ppm NOx emissions. In addition to stable combustion, the Ultra Low NOx system is characterized by a five stage premixed combustion process that employs a premixed pilot stage.
Demonstration of Siemens Power Generation's combustion technology is typically extensive, following a detailed design, rig and
field test, and then full scale engine testing process, which lead to
commercial introduction. The Ultra Low NOx combustion system
has been introduced into the commercial fleet, and operating experience with it has included high GT efficiency and sub 9ppm
NOx emissions, across a wide operating range, as recently demonstrated at Idaho Power's Evander Andrews site.
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Contents
Introduction ....................................................................................... 4
Combustor Design Features.............................................................. 5
Operation ........................................................................................... 7
Testing and Verification ..................................................................... 8
Field Validation – Idaho Power ..........................................................9
Summary .......................................................................................... 10
Permission for Use ..........................................................................10
References .......................................................................................11
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Introduction
Building upon its history of advanced gas turbine combustion systems, Siemens
has developed a robust Ultra-Low NOx (ULN) combustor design for flexible, reliable power generation is designed to meet the stringent emissions requirements
in the U.S. and abroad. This configuration utilizes a highly premixed combustion
system that was designed for SGT6-5000F and W501F engines. The ULN design is applicable for new units and is also retrofittable to the existing fleet.
The Siemens ULN technology is derived from the well-proven and robust Dry
Low NOx (DLN) combustion system design that has been operating in SGT63000E, SGT6-5000F, and SGT6-6000G (W501D5/D5A, W501F, and W501G)
engines for more than 10 years. Recent enhancements to the DLN combustion
system have contributed to the world-class reliability, performance and operational flexibility of the newest Siemens SGT6-5000F gas turbines. [1]
In response to market requirements for even lower NOx emissions, Siemens has
leveraged this DLN design and operating experience into the development of the
next-generation ULN combustion system technology, which has demonstrated
sub-9ppm NOx emissions for F-class engines. In addition to the low NOx emissions, the ULN combustor design produces lower CO, VOC and particulate
emissions. In combination with the Siemens low load CO system, this combustion system is capable of producing single-digit CO emissions down to 40% load.
Additionally, the ULN design can meet these requirements for a wider range of
fuels, including LNG. [2].
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Combustor Design Features
The ULN combustion system shown in Figure 1 comprises a combustor basket, pilot
nozzle, support housing, C-stage fuel nozzle, and transition. Most of the fuel is injected
through eight main fuel nozzles in the support housing, which is divided into two fuel
stages of four main nozzles each. The remainder of the fuel is divided between the Cstage and the pilot. The pilot nozzle includes a diffusion stage and a premix pilot stage.
The premix pilot (D-stage) and the two main fuel stages (A and B stages) utilize swirler
fuel injection (SFI) technology, which is the key design feature that enables this combustor design to achieve sub-9ppm NOx emissions. By injecting fuel through multiple
injection holes in the swirler vanes, enhanced fuel/air mixing is achieved, thus reducing
the peak temperature of local hot spots that contribute to NOx production. In addition to
improved emissions, this design is capable of handling a wide range of fuel composition
and fuel temperature.
Figure 1: Ultra-Low NOx combustor cross-section
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Since the original engine test of this system in 2004 [3], the support housing was upgraded to add dual fuel capability. The original gas only design that was tested in 2004
is shown in Figure 2. To accommodate the fuel oil tubing and increase the mechanical
robustness of the fuel nozzles, the production support housing main nozzle bodies were
redesigned as shown in Figure 3. As in the initial support housing design, the main fuel
nozzles were designed to minimize CO production during loading. The pilot nozzle
(Figure 4) and combustor basket (Figure 5) are very similar to the design that was
tested in 2004. The ULN combustor basket incorporates design features from the
proven DLN combustion system that has demonstrated the ability to operate at extended service intervals.
Figure 2: Original Gas Only Support Housing
Production
nozzle body
Figure 3: Dual Fuel Support Housing
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Figure 4: Dual Fuel Pilot Nozzle
Figure 5: Combustor Basket
Operation
Table 1 shows the fuel staging used for the ULN combustion system. Similar to DLN,
ignition is performed with fuel split between the diffusion pilot and main A-stage. Fuel is
adjusted between these two stages to maintain stability during acceleration to synch
speed. Near synch speed, the D-stage fuel is added. Below 25% load, the CO emissions are minimized by injecting fuel through only the pilot, A and D-stages. B-stage
fuel is introduced at 25% load to provide more uniform thermal loading and lower NOx
emissions. Above 45% load, C-stage fuel is introduced to provide additional stability in
the high load range. At high loads, 70-90% of the fuel is injected through the main fuel
nozzles, with the remainder of the fuel being divided between the other fuel stages to
provide the optimum tuning for low NOx and CO emissions while maintaining combustion dynamics below limits.
Table 1: Fuel Staging
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Engines with the ULN combustion system are equipped with an active combustion dynamics protection system (CDPS SPPA-D3000) that continually monitors the combustion dynamics levels and the engine emissions. After initial tuning of the engine during
commissioning, the engine controller makes automatic real-time adjustments to the fuel
fractions to maintain low emissions while protecting the engine against combustion dynamics. If the dynamics and NOx readings are within the allowable range, no action is
taken. If NOx emissions exceed the target value (e.g., due to a change in the fuel composition or ambient temperature change), then the controller automatically modulates
the D-stage fraction to reduce NOx, with the balance of the fuel offset by changes to A
and B stages. If the combustion dynamics levels exceed the threshold value, then the
D-stage fraction is adjusted to maintain dynamics levels within limits.
Dual fuel operation with a ULN combustion system is very similar to DLN dual fuel operation. The engine can be started with either gas fuel or oil fuel. Transfers between
gas and oil can be performed up to 70% load.
Testing and Verification
As discussed in [3], the ULN combustion system was developed through a combination
of modeling with computational fluid dynamics, high pressure combustion rig testing and
engine verification. A series of high pressure combustion rig tests were performed
throughout the development of the first engine hardware. This hardware was successfully demonstrated in an engine test on a SGT6-5000F in 2004. As described above,
the production design incorporated dual fuel capability as well as a number of design
enhancements. These design enhancements were tested in a single can high pressure
combustor test rig to assess impacts on emissions and combustion dynamics.
Final engine verification was performed at the Siemens Berlin Test Facility, a highly instrumented full scale SGT6-5000F engine, which operates at full load. The verification
test at Berlin Test Facility included both gas and oil operation. With gas fuel, sub-9ppm
NOx and sub-10ppm CO emissions were demonstrated for part load as well as base
load operation. On oil fuel, sub-42ppm NOx and sub-10ppm CO emissions were demonstrated over the same load range. Fuel transfers between gas and oil were performed over a wide range of part load operation.
More than 500 operating hours of validation and verification were performed between
the first ULN demonstration and the final engine verification at the Siemens Berlin Test
Facility prior to commercial release of the ULN design for production.
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Field Validation – Idaho Power
Following the final engine verification testing at the Berlin Test Facility engine, the first
commercial application of the ULN combustion system was commissioned at the Idaho
Power Evander Andrews project, Mountain Home, Idaho, a simple cycle SGT6-5000F).
First fire of this unit occurred in February, 2008. The unit has performed as expected
based upon Berlin Test Facility results. In particular, the engine has excellent starting
reliability, and base load was achieved without any operational difficulty.
Combustor Dynamics Amplitude
During commissioning, the unit successfully demonstrated base load and part load performance with NOx emissions < 9ppm and meeting all contractual performance requirements. Figure 6 demonstrates that the ULN system meets <9ppm emissions for
base load operation in the acceptable combustor dynamics operating range. Figure 7
shows the turndown from 60% to base load. This performance has been consistently
demonstrated at the Evander Andrews project for a period of over 6 months, totaling
more than 250 EBH and 25 ES. During this time, operation has been validated over a
wide range of ambient operating conditions.
Combustion Dynamics Alarm Limit
Acceptable Combustion Dynamics Operating Range
6
7
8
NOx (ppmvd @ 15% O2)
Figure 6: Combustor Dynamics at Base Load
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PowerGen International | Orlando, Florida | December 2008
10
15
Emissions ppmvd @ 15%O2
NOx
CO
12
9
6
3
0
50
60
70
80
90
100
110
Load %
Figure 7: ULN Emission Results
Summary
The Siemens ULN combustion system has been validated and is now being offered
commercially. The first commissioning effort of this engine at the Idaho Power Evander Andrews project was very successful, meeting all contractual performance guarantees. Emissions levels below 9ppm NOx and 10ppm CO were achieved for part
load and base load operation. The lessons learned and methodology applied in the
development of this combustion system are being used for development of new Siemens gas turbine products.
Permission for Use
The content of this paper is copyrighted by Siemens Power Generation, Inc. and is
licensed only to PennWell for publication and distribution. Any inquiries regarding
permission to use the content of this paper, in whole or in part, for any purpose must
be addressed to Siemens Power Generation, Inc. directly.
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References
1. Kovac, J., Xia, J., “SGT6-5000F Technology Enhancements”, POWER-GEN International 2007.
2. Engel, J., Nag, P., Abou-Jaoude, K., Wu, J., LaGrow, M., “Liquefied Natural Gas
(LNG) Flexibility Solutions for Large-Scale Gas Turbines”, POWER-GEN International 2007.
3. Bland, R., Ryan, W., Abou-Jaoude, K., Bandatu, R., Haris, A., Rising, B., 2004,
“Siemens W501F Gas Turbine : Ultra Low NOx Combustion System Development”,
POWER-GEN International 2004.
© Siemens Power Generation, Inc. 2008. All rights reserved.