Development Of DLN Technology – GE DLN1 :Over the past 20 years, manufacturers of gas turbine combustors have been striving to keep pace with a changing regulatory landscape. One of the prominent pollutants that needed to be dealt with was NOx. Early gas turbine combustors employed a diffusion flame that inherently had good stability but poor emission characteristics. When emissions needed to be controlled, water or steam was used as a diluent and NOx was brought down to less than 50 ppm at the expense of reliability and performance.

About 15 years ago, gas turbine manufacturers were challenged to meet lower emission requirements without diluent injection. DLN technology was GE’s response to that challenge. The DLN1 combustor was GE’s first commercially available premixed combustor DLN1-style combustors have been used in a variety of E class combustors. Overall, DLN combustors have compiled more than 27 million hours of operation on more than 787 GE Frame B and E gas turbines worldwide.

In addition to helping power plant operators comply with local emission regulations, DLN combustion technology offers extended combustion intervals, which may lead to reduced maintenance costs. Converting to a dry system eliminates water usage and associated costs.

Fuel flexibility allows the burning of cheaper and alternative fuels. DLN technology provides the capability to reduce load to 60% full power or lower while maintaining emission levels, thus providing additional operability. It also has the capability to add OpFlex software software enhancements. OpFlex technology offers the capability to operate continuously across a range of gas-derived fuels of varying compositions while maintaining performance, reliability and operating flexibility, said GE.

The GE DLN systems integrate a staged, premixed combustor, the gas turbine’s Speedtronic controls and the fuel and associated systems. There are two principal measures of performance. The first is meeting the emission levels required at baseload on both gas and oil fuel and controlling the variation of these levels across the load range of the gas turbine.

The second measure is system operability, with emphasis placed on the smoothness and reliability of combustor mode changes, ability to load and unload the machine without restrictions, capability to switch from one fuel to another and back again, and system response to rapid transients (such as generator breaker open events or rapid swings in load). GE’s goal is to make the DLN system operate so transparently that the gas turbine operator does not know whether a DLN or a conventional combustion system has been installed.

A significant portion of the DLN design and development effort focused on system operability. As operational experience has increased, design and development efforts have moved toward hardware durability and extending combustor inspection intervals. Design of a successful DLN combustor for a heavy-duty gas turbine also requires the designer to develop hardware features and operational methods that simultaneously allow the equivalence ratio and residence time in the flame zone to be low enough to achieve low NOx, but with acceptable levels of combustion noise (dynamics), stability at partload operation and sufficient residence time for CO burning.

The GE DLN1 and latest design DLN1+ combustors are two-stage premixed combustors designed for use with natural gas fuel and capable of operation on liquid fuel. The combustion system includes four major components: fuel injection system, liner, venturi and cap/center body assembly. These components form two stages in the combustor. In the premixed mode, the first stage thoroughly mixes the fuel and air and delivers a uniform, lean, unburned fuel-air mixture to the second stage. This premixing of fuel and air reduces flame temperature and NOx emissions.

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