Film cooling of turbine blades by injecting air through holes or slots affects the main stream flow. A numerical model has been developed to predict the resulting three-dimensional flow and the temperature pattern under steady flow conditions. An elliptic procedure is used in the near injection area to include reverse flow situations, while in the upstream area as well as far downstream a partial-parabolic procedure is applied. As first step an adiabatic wall has been assumed as boundary condition, since for this case experimental data are readily available for comparison. At elevated momentum blowing rates, zones of reverse flow occur downstream of the injection holes resulting in a decrease of cooling efficiency. A variation of the relevant parameters momentum blowing rate m, injection angle α and ratio of hole spacing to diameter s/d revealed the combination of m ≈ 1, α ≈ 30° and s/d ≈ 2 to be the optimum with respect to the averaged cooling efficiency and to the aerodynamic losses. Cooling is more efficient with slots than with a row of holes not considering the related problems of manufacture and service life. The calculated temperature patterns compare well with the experimental data available.

Coal based combined cycles for efficient generation of electricity or cogeneration of thermal and mechanical (electrical) power can be realized making use of Pressurized Fluidized Bed Combustion (PFBC). A draw-back with respect to the efficiency, however, is imposed from the combustion system limiting the temperature to some 850°C. This threshold may be overcome by integrating a high pressure, high temperature gas turbine topping cycle into the process. In a first step, the high pressure, high temperature gas turbine is fired by natural gas, and the exhaust gas of the turbine is fed to the PFB combustor as an oxygen carrier. In a future advanced system, the fuel gas may be provided by an integrated coal gasification process. A basic reference case has been established based on commercially available gas turbine equipment, hot gas filtration systems as actually tested in various pilot installations, and on a conservative steam cycle component technology. With an ISO gas turbine inlet temperature of 1165°C and an overall compression ratio of 16 up to 30, the entire process yields a net efficiency of some 46% (LHV) and an overall power output of some 750 MW with the gaseous fuel making up for some 50% of the overall energy input. Both the efficiency and the power output have been found rather insensitive with respect to a variation of the overall compression ratio. However, for a non-intercooled compression, an increase of the maximum process pressure would allow for the energy input to be shifted towards coal (and to reduce the natural gas input), and in particular for an elevated PFB combustor pressure considered mandatory for compactness as well as for combustion efficiency including emissions. The numerous calculations for the design, the optimization and the prediction of part-load operation of complex systems are efficiently performed with a semi-implicit method, the results of which have been checked carefully against those of a more conventional sequential approach and found in good agreement.

This paper describes a software package designed to optimize the economic and environmental performance of industrial cogeneration plants. The optimization is through a procedure, which optimizes the load allocation between the plant components. The computer procedure is capable of recognizing equipment status and establishes the optimum load allocation between the plant components minimizing an objective function. The objective function is related to the economic and environmental models of the plant components and to the plant boundary conditions. Two prototypes were realized based on two real cogeneration plant. The paper discusses the general modular description of the components and block diagrams of the systems. The model calibrations and load allocations are analyzed and discussed.

Pressurised fluidised bed combustion (PFBC) promises even lower emissions of air pollutant substances than already achieved by atmospheric FBC and allows to burn low rank coal. The elevated heat-transfer rate results in a more compact design. A PFBC-fired steam generator for the heat and power plant of the Technical University of Aachen (RWTH) is under construction. Being part of RWTH’s heat and power supply, a high reliability and a wide range of operation is mandatory. With these two aims in mind a scheme consisting of a turbo-charger’s compressor followed by an electrically driven compressor was chosen for the supply of air. The turbocharger’s turbine is fed by stack-gas previously cleaned by means of a pressure-tube-filter at moderate temperatures. Both machines are serial products. While the turbocharger’s speed is determined by the operating conditions, the electrically driven compressor is controlled by adjustable inlet guide vanes. In the pressurised mode of operation, the load of the steam-generator can be varied between some 30 % and 100 % of maximum output. The turbocharger may be bypassed to operate the system at atmospheric conditions. in this mode, 15 % to some 50 % of the operating range is covered.