Eastman Chemical Company declared its FlameSheetTM combustion system conversion project a “remarkable technical success”, during its presentation at the annual 7F Users Group conference, held in Orlando in May 2016. Chuck Goodson, Eastman Chemical Company’s utilities maintenance area manager, described to the conference why the company selected PSM’s FlameSheetTM technology, which was implemented in 2015 on the two 7F gas turbines at their Longview (Texas) cogeneration facility and the collaboration between PSM and Eastman Chemical Company that enabled all project operational-flexibility goals to be fully realised.
“Prior to installing FlameSheetTM, the plant could operate both gas turbines to maximise output, but was exposed to low demand and low market pricing. When operating just one gas turbine, the plant could meet the host electrical demands, but was unable to ramp to capture high market pricing,” said Jim Stark, Eastman Chemical Company’s area manager of utilities- cogeneration operations. “FlameSheetTM’s extended turndown capability allows us to increase market participation with the full capability of the plant available while minimising exposure to unfavorable market conditions.”
Dr Alex Hoffs, PSM president, said: “Power generation market dynamics require gas turbine power plants to operate in increasingly flexible operating windows. FlameSheetTM was developed with this in mind. With its extended turndown capability, as well as lower maintenance costs, reduced emissions, and significantly increased fuel flexibility, implementing FlameSheetTM technology, like Eastman Chemical Company did, can enable customers to implement strategic operational changes to increase profitability in their respective markets.”
FlameSheetTM is an innovative retrofittable combustion system with inherent operational flexibility characteristics that are “aligned to dynamic & challenging power generation market needs”, says PSM Power Systems Mfg, formerly owned by Alstom (and before that Calpine), but acquired by Ansaldo Energia Group as a way of meeting conditions imposed by the European Commission on GE when it purchased Alstom’s power businesses in 2015.
The FlameSheetTM combustor employs a 2-in-1 can-annular concept. Leveraging patented fuel/ air mixing concepts, FlameSheetTM provides up to a 30% gas turbine operating load range increase while maintaining single digit NOx & CO emissions. Designed to operate up to 32 000 factored hours between inspections, FlameSheetTM is ideally suited for shale gas, liquefied natural gas (LNG), or alternate fuel operation on such fuels as ethane, propane, and hydrogen, “to name a few”, says PSM, “all with up to a 3x increase in Modified Wobbe Index (MWI) operational range compared to the current 7F combustion technology.”
The name FlameSheetTM derives from the way the fuel–air mixture is injected as a continuous uninterrupted sheet into the reaction zone of the combustor, with an aerodynamically generated trapped vortex employed to anchor and stabilise the flame. FlameSheetTM employs what has been described as a “combustor-within-a-combustor concept”, allowing the staged operation of each at various load conditions. At high loads both combustors are used, with the outer combustor flame structure looking like an annular “sheet of flame” around the inner combustor. At low loads, the outer combustor is mainly used.
The diagram illustrates the overall structure of the FlameSheetTM system. The pilot and main stages are fed from the compressor discharge plenum. Pilot air passes through the radially outermost circuit to the head end of the combustor where it enters a radial inflow swirler. Fuel is mixed into the air stream through a row of vanes. The fuel–air mixture then enters the combustor and a flame is swirl stabilised behind a bluff body on the centreline of the combustor. The main stage air flows along the back part of the combustion liner and then through a main fuel injector. The fuel-air mixture is then turned 180 degrees and flows into the combustor.
As the flow enters the combustor it separates off the combustion liner and forms a strong recirculation region, or aerodynamically trapped vortex, which stabilises the flame.