Sasha Savic

Techno-Economic Evaluation of Commercially Available High Fogging Systems

High fogging (wet compression, spray inter-cooling) is a technology used for gas turbine (GT) power augmentation. By evaporative spray inter-cooling of the air during compression, which is the main physical effect associated with the HF, a 5–7% power boost of the GT (for each percent of injected water per mass of air) is achieved. HF of a gas turbine can be accomplished using different spray technologies. In this study three different, commercially available spray technologies — pressure-swirl, hot water injection and air-assisted atomization — are compared regarding both technical and economical benefits and risks. The comparison is based on droplet sizing results, system complexity, the feasibility of system integration into the GT’s control and plant operation concept, GT performance and operational and additional O&M costs. It is also known that high fogging carries certain risks to the safe operation of a GT, such as compressor blades erosion, reduction in compressor surge margin and cooling airflows. To minimize the negative impact of high fogging, it is therefore important to select the most appropriate high fogging system as well as to provide for its full engine integration.Copyright

Redesign of a Multistage Axial Compressor for a Heavy Duty Industrial Gas Turbine (GT11NMC)

Different approaches to compressor design exist in industrial practice. This paper describes two design philosophies that can be followed with compressor development (re-staggering and new airfoil design), and reports on field experience gained with an advanced compressor design using CDA (Controlled Diffusion Airfoils) profiles. The first philosophy described is based on incremental changes of compressor design, consisting of keeping the same blade profiles and re-staggering a number of rotor blades and/or stator vanes. The second philosophy described is to utilize advanced CDA profiles in compressor design, optimized for increased mass-flow and backpressure. The second philosophy was followed in the development of a compressor upgrade for ALSTOM’s GT11NM gas turbines, where a significant increase in GT power output (exceeding 10%) and improved overall engine efficiency (+0.4% additive) at unchanged surge margin were achieved. Power output and improved efficiency resulted solely from the advanced blade design, requiring no additional power augmentation techniques. These figures were measured on a natural gas-fired GT operating in an open-cycle power plant.Copyright

Automated Blade Optimization and 3D CFD Analysis for an Axial Multistage GT Compressor Redesign

This paper focuses on (1) the basic compressor layout based on meridional through flow analysis and (2) the re-design of blades and vanes using sophisticated automated design optimization methods. All tools and processes are integrated into a consistent Compressor Design System, which runs on a powerful Linux cluster. This design system allows designing, analyzing and documenting blade design in mostly automated way. This frees the engineer from repetitive tasks and allows him to concentrate on a physical understanding and improvement of the compressor. The tools and methods are illustrated on the basis of an actual ALSTOM compressor. The main objectives of this upgrade are a modest increase in mass flow and an efficiency improvement. The latter is to be achieved through the replacement of NACA blades by modern Controlled Diffusion Airfoils (CDA). Results are presented including a CFD analysis of the front stages of the baseline and upgrade compressor.Copyright