Effect of Secondary Air Configuration in Gas Turbine Combustor Firing Natural Gas

Abstract

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.

CFD Modeling of Syngas Combustion and Emissions for Marine Gas Turbine Applications

“…The NO values decrease sharply at the end of the combustor due to the reaction with oxygen in air to produce NO 2 and NO 3 . Comparing the results for NO emissions with those published for natural gas in [25], the use of the Schwarzepumpe syngas fuel results in lower NO emission than that produced by natural gas fuel. The maximum values of NO emissions decreased from 0.00045 to 5e-5 mole fractions at the same operating conditions.…”

“…For 62% H 2 , (Schwarzepumpe syngas fuel type) the CO 2 emission is the lowest of the four examined hydrogen percentages in the syngas fuel. Comparing the results of CO 2 emission with that for natural gas in [25], the use of the Schwarzepumpe syngas fuel results in lower CO 2 emissions than that of natural gas fuel.…”

“…Fuel and combustion air lines are used for verifying the numerical analysis. The present model was used in [25] to study the effect of secondary air configurations in a gas turbine combustor firing natural gas. The air entering the gas turbine combustor is divided into two streams, the primary air (combustion air) and the secondary air, the latter used for cooling purposes as shown in Fig.…”

“…The effect of air to fuel ratio on flame size was studied by [25] using the air to fuel ratios from 30 up to 70. It was found that the air to fuel ratio of 40 is appropriate for obtaining a suitable flame size.…”

“…The validation of the CFD model was achieved by comparing the CFD results of temperature distributions with the experimental data recorded for natural gas fuel, published by [25] where the same combustor and the corresponding mesh were used. This was performed by changing the methane fuel concentrations during runs until 100% methane was reached.…”