Innovative Air Bypass System for Low-Emission Multi-Can Combustors

Abstract

Gas turbines that are used as compressor drives are often operated in the part load regime because compressor stations are usually designed for operation with full power at extreme weather conditions. Consequently, these gas turbines must comply with strict emission regulations at unfavorably low turbine inlet temperatures. To extend the low emissions operation range of the premixed combustion systems, many gas turbines bypass a part of the compressed air upstream of the combustor and either blow it off into the exhaust stack or re-inject it into the secondary combustion zone. This study presents a new approach that overcomes shortcomings by injecting the compressed air in the burner head in the vicinity of the primary combustion zone. This is particularly attractive for multi can combustors. Atmospheric combustion tests are conducted for two different air injection designs. The first design features lower air injection velocity and the second features higher injection velocities. Both injection strategies are tested with the industrial MGT gas turbine can combustor. The full size burner is tested at atmospheric conditions in a burner test rig with a quartz flame tube and natural gas as fuel. The performance of the air bypass system is assessed by means of CO and NOx emission measurements for different air bypass ratios. Additionally, OH* chemiluminescence camera pictures are presented and compared to CFD calculations. It is found that the air injection in the annular vicinity of the swirl flame does not cause increased CO emissions by quenching or other effects.