ULTRA LOW NOX COMBUSTION TECHNOLOGY: Power-Gen International 2008—Orlando, Florida Clifford Johnson, Barton Pepperman, Michael Koenig, Khalil Abou-Jaoude, Anil Gulati, Ali Moradian, Siemens Power Generation Inc., 4400 Alafaya Trail, Orlando, FL 32826-239 9 Greg Hall Idaho Power, Boise, Idaho


Siemens Power Generation combustion technology has under gone 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 relativelyhigher levels of emissions output of some constituents, SiemensPower 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 fo urstage premixed combustion process is designed to produce r eliable 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 em is sions. In addition to stable combustion, the Ultra Low NOx system is characterized by a five stage prem ixed 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, a s recently demonstrated at Idaho Power’s Evander Andrews site.


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. In response to market requirements for even lower NOx emissio ns, Siemens has leveraged this DLN design and operating experience into the deve lopment of the next-generation ULN combustion system technology, which has dem onstrated sub-9ppm NOx emissions for F-class engines. In addition to the lo w NOx emissions, the ULN comb ustor 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.

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 C-stage 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 enabl es 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
Figure 1: Ultra-Low NOx combustor cross-section

Since the original engine test of this system in 2004 [3], the support hou sing 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 t he 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 d esign, the main fuel nozzles were designed to minimize CO production during loading. T he pilot nozzle (Figure 4) and com bustor 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
Figure 2: Original Gas Only Support Housing

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