Dry low emission (DLE) systems employing lean, premixed combustion have been successfully used with natural gas in combustion turbines to meet stringent emission standards. However, the burning of liquid fuels in DLE systems is still a challenging task due to the complexities of fuel vaporization and air premixing. Lean, premixed, and prevaporized (LPP) combustion has always provided the promise of obtaining low pollutant emissions while burning liquid fuels, such as kerosene and fuel oil. Because of the short ignition delay times of these fuels at elevated temperatures, the autoignition of vaporized higher hydrocarbons typical of most practical liquid fuels has been proven difficult to overcome when burning in a lean, premixed mode. To avoid this autoignition problem, developers of LPP combustion systems have focused mainly on designing premixers and combustors that permit rapid mixing and combustion of fuels before spontaneous ignition of the fuel can occur. However, none of the reported works in the literature has looked at altering fuel combustion characteristics in order to delay the onset of ignition in lean, premixed combustion systems. The work presented in this paper describes the development of a patented low NOx LPP system for combustion of liquid fuels, which modifies the fuel rather than the combustion hardware in order to achieve LPP combustion. In the initial phase of the development, laboratory-scale experiments were performed to study the combustion characteristics, such as ignition delay time and NOx formation, of the liquid fuels that were vaporized into gaseous form in the presence of nitrogen diluent. In the second phase, a LPP combustion system was commissioned to perform pilot-scale tests on commercial turbine combustor hardware. These pilot-scale tests were conducted at typical compressor discharge temperatures and at both atmospheric and high pressures. In this study, vaporization of the liquid fuel in an inert environment has been shown to be a viable method for delaying autoignition and for generating a gaseous fuel stream with characteristics similar to natural gas. Tests conducted in both atmospheric and high pressure combustor rigs utilizing swirl-stabilized burners designed for natural gas demonstrated an operation similar to that obtained when burning natural gas. Emission levels were similar for both the LPP fuels (fuel oils 1 and 2) and natural gas, with any differences ascribed to the fuel-bound nitrogen present in the liquid fuels. An extended lean operation was observed for the liquid fuels as a result of the wider lean flammability range for these fuels compared to natural gas.

Nearly all states now have renewable portfolio standards (RPS) requiring electricity suppliers to produce a certain fraction of their electricity using renewable sources. Many renewable energy technologies have been developed to contribute to RPS requirements, but these technologies lack the advantage of being a dispatchable source which would give a grid operator the ability to quickly augment power output on demand. Gas turbines burning biofuels can meet the need of being dispatchable while using renewable fuels. However, traditional combustion of liquid fuels would not meet the pollution levels of modern dry, low emission (DLE) gas turbines burning natural gas without extensive back-end clean-up. A Lean, Premixed, Prevaporized (LPP) combustion technology has been developed to vaporize liquid ethanol and blend it with natural gas creating a mixture which can be burned in practically any combustion device in place of ordinary natural gas. The LPP technology delivers a clean-burning gas which is able to fuel a gas turbine engine with no alterations made to the combustor hardware. Further, the fraction of ethanol blended in the LPP gas can be quickly modulated to maintain the supplier’s overall renewable quotient to balance fluctuations in power output of less reliable renewable power sources such as wind and solar. The LPP technology has successfully demonstrated over 1,000 hours of dispatchable power generation on a 30 kW Capstone C30 microturbine using vaporized liquid fuels. The full range of fuel mixtures ranging from 100% methane with no ethanol addition to 100% ethanol with no methane addition have been burned in the demonstration engine. Emissions from ethanol/natural gas mixtures have been comparable to baseline natural gas emissions of 3 ppm NOx and 30 ppm CO. Waste heat from the combustor exhaust is recovered in an indirect heat exchanger and is used to vaporize the ethanol as it is blended with natural gas. This design allows for startup on natural gas and blending of vaporized ethanol once the heat exchanger has reached its operating temperature.

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A Lean, Premixed, Prevaporized (LPP) combustion technology has been developed that converts liquid fuels into a substitute for natural gas. This fuel can then be burned with low emissions in virtually any combustion device in place of natural gas. This technology offers the possibility of using unprocessed oil-field Natural Gas Condensate (NGC) for local or export power generation using a DLN-equipped gas turbine rather than flaring, as is common practice in some regions. The ability to run a turbine on natural gas condensate with NOx and CO emissions comparable to those of natural gas has been demonstrated using a surrogate fuel made up from a mixture of naphtha (representing C4 and greater) and methane (representing <C4). The naphtha was vaporized using an LPP system, mixed with methane, and used to generate power in a 30kW Capstone C30 microturbine. The LPP Gas™ was tailored to match the modified Wobbe Index (MWI) of methane. NOx emissions in pre-mix mode on the surrogate NGC fuel were sub 5 ppm, indistinguishable from those when running on methane. CO emissions were sub 20 ppm, comparable to those on methane. At lower loads (in diffusion mode), NOx and CO emissions on surrogate NGC-based LPP Gas™ remain comparable to those on methane. No changes were required to the DLN gas turbine combustor hardware.