1 The Future of Gas Turbine Technology 7 th International Gas Turbine Conference 14-15 October 2014, Brussels, Belgium Paper ID Number (To be filled out by ETN) THE ULTRA-WET CYLCE FOR HIGH EFFICIENCY, LOW EMISSION GAS TURBINES Panagiotis Stathopoulos, Steffen Terhaar, Sebastian Schimek, Christian Oliver Paschereit Chair of Fluid Dynamics, TU Berlin Müller-Breslau-Straße 8 D-10623 Berlin stathopoulos@tu-berlin.de ABSTRACT The ultra-wet gas turbine cycle offers a significant increase in efficiency and power density compared to its dry alternative. Steam injection effectively inhibits NO x formation and makes gas turbine operation on hydrogen- rich fuels and almost stoichiometric mixtures feasible. In the present paper, the potential of ultra-wet gas turbine cycles is assessed in terms of efficiency increase and emission reduction. The first part of the paper presents a comparison of wet cycles to their dry alternatives for typical, industrial gas turbines. The ability of wet cycles to facilitate operation on almost stoichiometric mixtures is underlined and the effects of this operation on the efficiency and the power density of the cycles are analyzed. In the second part of the paper, the influence of steam- dilution on the emissions formation under atmospheric and elevated pressures is experimentally investigated. The results show that the addition of 20% (related to the inlet air mass flow rate) of steam ensured NO x levels below 10 ppm up to near stoichiometric conditions without detrimental effects on the CO burnout. The reduction in NOx emissions, even at a constant flame temperature, is mainly caused by lower concentrations of atomic oxygen at steam-diluted conditions, constraining the thermal pathway. This is also identified as the reason why the emissions reduction due to steam dilution is even stronger at higher pressures. NOMENCLATURE Abbreviations HRSG: Heat Recovery Steam Generator STIG: STeam Injected Gas turbine Latin Characters k: Turbine constant at chocked conditions [-] m air : Mass flow rate of air [kg/s] m airmax : Maximum mass flow rate of air delivered from a compressor [kg/s] m TO : Mass flow rate entering the turbine [kg/s] P: Power [W] P Crel : Compressor power relative to the power extracted by the turbine from the exhaust gases. [-] p T : Turbine inlet pressure [bar] p r : Pressure ratio [-] p map : Pressure ratio calculated from the compressor map[ -] p iter : Pressure ratio calculated during an iteration[-] TIT: Turbine Inlet Temperature [°C] TOT: Turbine Outlet Temperature [°C] Greek Characters η: Electrical efficiency [%] η Cnom : Compressor nominal isentropic efficiency η T : Turbine isentropic efficiency η Tm : Turbine mechanical efficiency φ: Equivalence ratio of the combustion reaction [-] Ω: Steam/air mass flow ratio [-] INTRODUCTION - MOTIVATION The continuous expansion of decentralized electricity production and wind power exploitation has a major impact on centralized electricity production facilities, leading to low operating hours of the costly combined cycle plants. The fact that these plants must also cover the fluctuating electricity production of the renewables led to considerable efforts to increase their flexibility. Although a further improvement of the operational flexibility of these plants is expected in the foreseeable future, alternatives should be sought if higher penetration of renewable sources is to be implemented. Such alternatives are the so called wet gas turbine cycles, the simplest of which is the STIG cycle (Steam Injection Gas turbine cycle). This cycle is based on the use of the exhaust heat of a turbine to produce steam, which is then injected at various points in the turbine cycle. This cycle offers relatively high efficiency with minor impact on the operational flexibility. Although it has already been the topic of numerous theoretical investigations, it only found