Stationary gas turbines and primary energies:: A review of fuel influence on energy and combustion performances

The gas turbine is a continuous-flow engine which develops steady aerodynamics and flame kinetics during stationary operation. These favourable features limit the constraints placed on fuel properties as to the performance of combustion and provide a considerable margin for devising clean combustion designs. This is why gas turbines have by essence access to a broad range of primary energies. However, due to the high specialisation of aero- and aeroderivative engines, this advantage is essentially exploitable by the Heavy Duty branch which, thanks to moderate compression ratios, robust mechanical designs and versatile combustion systems, can utilise a wide series of commercial and process by-products fuels: natural gas, petroleum distillates, gasified coal or biomass, gas condensates, alcohols, ash-forming fuels etc. In this context, a thorough knowledge of the multiple fuel/machine interdependences, which seem insufficiently covered by the existing literature on gas turbines, is of prime interest. This paper offers a consistent approach to three selected aspects of importance for gas turbine designers and users, which are: energy conversion performances; combustion and emissions. This approach includes: (i) a review of main primary energies accessible to stationary gas turbines, (ii) a new, differential method for assessing the influence of fuel on machine thermodynamics, with original equations accounting for performance changes versus fuel, (iii) a comprehensive discussion of how fuel properties impact on NOx emission and combustion design. Finally, the main trends and prospects of gas turbine technology evolution, in terms of efficiency enhancement and low NOx achievement, are tentatively outlined. (C) 2000 Editions scientifiques et medicales Elsevier SAS.