The loss of performance of a gas turbine at off-design is primarily due to the rapid drop of the major cycle performance variables with decrease in output, and this may be aggravated by poor component performance. Postulated propulsion demands require that future engines attain performances much more advanced than those of the present day. The specific nature of the improvement in performance will depend on engine duty, but it is expected that the improvement will include higher power loadings and better response, in addition to better fuel burn characteristics. Innovative design and advanced materials and structures will play key roles in bringing about a revolution in gas turbine technology, but these will have to be accompanied by novel control methods which can influence the position of the engine operating point. The latter may require the use of variable geometry in one or more gas path components to improve the internal matching of a component or to re-match the engine cycle such that the component operating point and/or the primary cycle performance variables are re-optimized or controlled with changing operating conditions. This paper examines how variable geometry could be used to improve the off-design performance of gas turbines.

BRAKINE is a component-matching thermodynamic analysis computer program designed to simulate both the design point and off-design steady state performance of arbitrary BRAyton or RanKINE cycle plants, or of combined cycles and cogeneration processes. Plant performance can be appraised by simulating either all fluid streams or only those streams that completely describe the working cycle. A power plant is assumed to be constructed in modular form with each component handling a specific thermodynamic process. As a result, flexibility of operation is provided by the use of ‘codewords’, which allow the user to simulate any plant type by stacking in the appropriate sequence the various modules that describe the performances of the components that make up the plant. This paper describes the mechanics of operation of BRAKINE and concludes that the program is a useful tool for power plant performance simulation.

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Industrial concerns, the world over, are embracing gas/steam turbine combined cycles and combined heat and power as means of meeting energy needs. The main reason is that the potential for energy savings is huge, due to the utilisation of waste heat as useful energy — the key to the excellent thermodynamic performance exhibited by combined energy systems. Excellent thermodynamic performance may not be matched by excellent economic performance, and in certain cases it may not be economical to choose a combined energy system over a mix of supply from conventional plants. The factors governing the economics of combined energy are numerous, though a few are decisive. In choosing a plant for a given duty, an economic assessment of life-cycle costs should be carried out for candidate plants, to arrive at the most economically viable investment proposal, among alternatives. With this in mind, a computer program PEACES was developed to aid the appraisal of energy investment proposals based on combined energy systems. The economic model on which the program was structured is described in this paper. A case study is carried out, where the software was used at arriving at the most economically viable solution for meeting the energy needs at an industrial site.

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