EFFECT OF SECONDARY AIR CONFIGURATION IN GAS TURBINE COMBUSTOR FIRING NATURAL GAS

The effect of secondary air inlet conditions on natural gas combustor is investigated numerically. Secondary air inlet conditions include its amount, position, total number of inlet ports and its arrangement along the combustor. The secondary air is introduced normally through inlet ports at different levels along the combustor. Each level includes a number of ports distributed around the combustor periphery. The number of ports levels varied from four up to sixteen and the number of ports in each level varied from four up to sixteen ports. Thus, the total number of ports varied from 16 up to 256. The combustor used has an air swirler at its upstream. Primary air, secondary air and fuel lines are also included. The sheer-stress transport (SST) k-omega model was used to simulate the turbulent isothermal flow and the non-premixed combustion model was used to simulate the turbulent reacting flow. For validating the model, a comparison between the measured and the calculated axial temperature distribution is made which show a reasonable agreement. Primary air swirl number of 0.87 and air to fuel ratio of 30 are used in this study. Secondary air leads to a decrease in flame size. For secondary to primary air ratio (SPAR) greater than 0.3, the flame became narrower in diameter and shorter in length. For certain secondary air configuration, NO, CO, CO2 are decreased with secondary air and are further decreased when increasing the value of SPAR.