Abstract
A gas turbine combustor was modified for addition of Low Heating Value (LHV) gas operation while retaining the original diesel option. New fuel inlets were designed and tested through numerical simulations.
CFD calculations have been made in order to investigate the new design combustion abilities. A commercial 3D finite-volume Navier-Stokes solver was used. The Eddy Dissipation model was used to simulate the combustion phenomena and the flow fields were given by using k-ε model, Algebraic Stress Models and Reynolds Stress Model.
The comparison between predictions using different turbulence models and grids showed some differences. The required grid for having grid independent results was found too CPU expensive. However, comparisons were done to investigate the influence of the turbulence description on the result. This influence was found significant. It was deduced that the mixing controlled the combustion process. The numerical description of quenching of the flame was found to have more influence on the emission predictions than the description of the reacting zone (swirl).
Simulations validated the modified design. Successful combustion operating conditions have been predicted in terms of CO emission. Ammonia conversion to NO was also investigated. The conversion rate was found to be between 65 and 73 %. NO emissions have been predicted, as the maximum temperatures in the combustor were over-predicted, ammonia conversion to NO was also over valued. However, the results show that the combustion process of LHV gas within a small combustor volume is achievable. The swirl was found to be an efficient way to promote the combustion process by improving the mixing. High NO emissions have been predicted. It came from the high conversion rate of fuel ammonia into NO.
