1 CATHLEAN: Catalytic, Hybrid, Lean Premixed Burner for Gas Turbines Richard Carroni 1* , Timothy Griffin 1 , Greg Kelsall 2 1 Alstom Power Technology, CH-5405 Baden-Dättwil, Switzerland. 2 Alstom Power Technology Centre, Whetstone, LE8 6LH, United Kingdom. Abstract CATHLEAN (an EU FP5 project) addresses the research and development of an advanced, ultra-low NOx, hybrid burner for gas turbines (present and future), that combines catalytic and lean-premix combustion components. Such a hybrid design enables this new technology to be introduced in a lower-risk manner. The catalytic elements serve to pre-treat the fuel in order to enhance performance in terms of emissions (<3ppmv NOx and <10ppmv CO @ 15% O 2 at 50-100% load, for natural gas fuel), part-load stability (reducing the lean blowout temperature by over 100°C) and thermoacoustic phenomena (pulsations << 0.3% of pressure). The principle scientific objective is to quantify the advantages of the hybrid burner in terms of the above-mentioned criteria, relative to traditional, lean-premixed combustors. The present paper describes the technical and organisational aspects of the project, including an outline of state-of-the-art catalytic combustion technology, technical specification of the advanced burner and a description of the methods used to attain project goals. Key words: Catalytic combustion, advanced hybrid burner. INTRODUCTION Extensive effort has been placed on reducing thermal NOx emissions from gas turbines over the past decade. The market introduction of lean-premixed combustion was accompanied by a drastic reduction of these emissions. Today, the leading producers of modern, heavy-duty gas turbines (running on natural gas) achieve NOx emissions of 25ppm (15% O 2 ) and below. However, legislation concerning such emissions has, or is likely to, become more stringent, particularly for gas turbine power plants located in or near urban areas [1], where the lowest achievable emissions rate (LAER) standards may be required. An alternative approach to the reduction of NOx emissions is catalytically stabilised combustion (first demonstrated in 1974 [2]), in which the fuel/air mixture, or a portion thereof, is converted heterogeneously over a catalyst. Detailed descriptions of the fundamentals of catalytic combustion can be found in the literature [3,4,5]. This technology is now commercially available in several guises, and has been demonstrated to consistently achieve <3ppmv NOx for several small machines [6,7]. The principle is also compatible with the trend of increasing gas turbine firing temperatures, which contribute to higher machine efficiencies and hence reduced CO 2 emissions. Traditional catalytic combustion is mainly seen as an alternative vehicle for NOx emissions abatement. Unlike tail-end systems such as SCR and SCONOX, catalytic combustion actively reduces the formation of pollutants, rather than cleaning up the flue gases. It enables essentially all applications and sizes of gas turbines to approach zero NOx emissions, thus broadening their applicability. In contrast to the tail-end, cleanup systems, catalytic combustion also has the potential to positively influence the following: • reduce pulsations [8], • enhance lean blowout limits, * corresponding author, email: richard.carroni@power.alstom.com, fax: +41 (0)56 486 73 59.