Fuel Flexible Rich Catalytic Lean Burn System for Low BTU Fuels

Abstract

Limited fuel resources, increasing energy demand, and stringent emission regulations are drivers to evaluate process off-gases or process waste streams as fuels for power generation. Often these process waste streams have low energy content and their operability in gas turbines leads to issues such as unstable or incomplete combustion and changes in acoustic response. Due to above reasons, these fuels cannot be used directly without modifications or efficiency penalties in gas turbine engines. To enable the use of the wide variety of ultra-low and low Btu fuels in gas turbine engines, a rich catalytic lean burn (RCL®) combustion system was developed and tested in a subscale high pressure (10 atm.) rig. Previous work has shown promise with fuels such as blast furnace gas (BFG) with Lower Heating Value (LHV) of 3.1 MJ/Nm3 (85 Btu/scf). The current testing extends the limits of RCL® operability to other weak fuels by further modifying and improving the injector to achieve enhanced flame stability. Fuels containing low methane content such as weak natural gas with an LHV of 6.5 MJ/Nm3 (180 Btu/scf) to fuels containing higher methane content such as landfill gas with an LHV of 21.1 MJ/Nm3 (580 Btu/scf) were tested. These fuels demonstrated improved combustion stability with an extended turndown (defined as the difference between catalytic and non-catalytic lean blow out) of 140°C–170°C (280°F–340°F) with CO and NOx emissions lower than 5 ppm corrected to 15% O2.