The conversion of heat into mechanical shaft power or electrical energy is still the worldwide most used electric and propulsion energy source. Whether coal, liquid hydrocarbons, natural gas, nuclear or solar heat are used as primary energy source such cycles are continuously improved aiming at better efficiency, at flexible operating conditions or at reducing manufacturing or maintenance cost. The classic thermal power cycle design uses detailed simulation of the cycle fluid’s changes of state (typically represented by averaged pressure and temperature or specific enthalpy) along the flow paths. Components of such a cycle may be ducts, filters, mixers, compressors, combustors, heat exchangers, nozzles, turbine stages etc. The notations of exergy and anergy were invented in the nineteen-fifties but they still play an astonishingly silent role in education. Knowing already the Carnot factor a student can understand the second law of thermodynamics by the simple fact that the exergy part of energy can be converted into any other form of energy while the anergy part cannot be converted into any exergy form of energy. The most used approach via the saying “that the state variable entropy can only grow” is for most students a mental detour because they do not understand the tie of energy conversion and entropy. The exergy loss breakdown of a cycle gives an instructive view to opportunities and challenges. This paper explains methods to calculate a breakdown of the exergy losses with the example of a typical but notional turbofan using commercially confirmed component performance data. The considerations cover exergy losses by heat exchange, by combustion, by heat loss to ambient, by mixing different fluids, by internal pressure losses, by friction and dissipation in turbomachinery and by the bottoming heat discharge as well as in the propulsive process. Quantified exergy losses for such effects make the limitations of technical improvements visible without going into detailed design work. The purpose of this paper is to motivate for teaching and using exergy-based considerations especially in the basic performance simulation. Additionally the context is occasion for an extra plea on replacing the colloquial expression “energy consumption” by “exergy consumption”. The reader of this paper should have basic knowledge of thermodynamic cycle performance simulation methods and of turbomachinery.

Gas turbine combined cycles (GTCC) using a steam bottoming cycle are a widely used technology for electric power generation. From [1] it is known that the best current large GTCC’s loose around 25% of the fuel exergy just by combusting the fuel while all other exergy losses sum up to around 15%. For the net efficiency of such plants 60% is remaining. This paper shows thermodynamic calculation results of GTCC’s with variable pressure ratio and turbine inlet temperature (TIT) aimed at understanding the efficiency potential associated with further increases of the TIT thus reducing the exergy loss by combustion. The assumptions of these calculations correspond to published industrial experience and standard assumptions in two different scenarios. The results are curves showing net efficiency and specific power as functions of TIT. Other data like the related pressure ratio and compressor exit temperature are shown too. The conclusion shows that a net efficiency of 63…65% is feasible with a hot gas temperature of around 1750°C based on the two scenarios. The winning cycle arrangement uses an adiabatic compressor. A GTCC with GT-compressor having one intercooling stage is clearly less favorable in several respects.

On 07.07.1939 the Neuchatel gas turbine passed its performance test under the supervision of Aurel Stodola [1]. This was the world’s first open gas turbine for electric power generation in commercial operation. It launched the past eighty year period of further development and corresponding market growth. The Baden area played an important role. The aim of this paper is to complete the already published comprehensive historical information with two additional aspects especially regarding the second 40 years, in which the author was an involved contemporary witness: The first is how the predominance of something like a local spirit integrated both a considerable share of foreign engineering staff and also the changes of the ownership of the technology from Brown Boveri to ABB and then to Alstom and recently to GE and Ansaldo. The second aspect is the inside view of the author, who has both shaped and suffered these gas turbine developments in several job positions allowing direct contact to both top management and shop floor workers. These two aspects will be integrated in the historical sequence. As a rule the roles of the persons acting after the seventies are given but not their names. The history of the involved companies has caught much attention of media and writers. After the formation of ABB it was used for both celebrating outstanding management performance and despicable management mistake. I will add as an engineer my insider view to this and mention the corresponding book references. This paper is limited to the mainstream open GT development for space reasons and therefore omits other interesting side developments of BBC such as closed Helium cycles, IGCC applications and compressed air energy storage as well as the other products of BBC, which all played a role in equalizing the business cycles.

Polytropic change of state calculations are used within many thermodynamic cycle analysis tasks for turbomachinery like gas turbines or compressors. The typical approach is using formulas, which are theoretically valid for ideal gas conditions only. But often gases are used, which do certainly not behave like ideal gases. This is motivation to check how and which polytropic change of state algorithms can be used for real gases or corresponding mixtures. There is a vast experience on polytropic efficiencies achievable with existing turbomachinery. Manufacturers calibrate their performance analysis with real test results for compensating potential deviations from their analysis approach. But they normally do not disclose their approaches for the thermodynamic calculation and the corrections made based on their test results. But for investigations of new thermodynamic cycles before the stage of development with an available demonstrator a best possible prediction of the performance is desired. In this paper the assumptions and formulas for calculating polytropic changes of state and polytropic efficiencies are gathered from literature. The most fundamental assumption is based on a constant dissipation rate during the polytropic change of state. It could be tracked back to Zeuner, Stodola and Dzung. A numerically convenient approximation is the “polytropic exponent approach”. It fulfills the first assumption for an ideal gas but it is only an approximation for real gases. The temperature after a polytropic change of state is defined by its initial condition, the pressure ratio and the polytropic efficiency. Three different calculation algorithms are compared here: The recursive “constant dissipation rate algorithm” suggested by the author, the most used “ideal gas formula” and the “polytropic exponent formula” as the most used approximation for real gases. Numeric results for compression from 1bar to up to 100bar are shown for dry air, Argon, Neon, Nitrogen, Oxygen and CO2. The deviations of the different calculation approaches are considerable.

The gas turbine combined cycle (GTCC) is the best currently available choice, if gaps in the renewable electric power supply need being filled with power from fossil fuels. The GTCC manufacturers are in a fierce competition responding to these needs, especially for the best part load efficiency, the fastest load ramp capability and for the lowest low load power parking at an acceptable NOx and CO emission level. But there is an option outperforming the GTCC technology for the above mentioned requirements, which is theoretically known since years but it has not yet been practically developed. It is the semiclosed recuperated cycle (SCRC). Wettstein (2013) has described this recently in “The Air Breathing Semiclosed Recuperated Cycle and Its Super Chargeable Predecessors,” Gas Turbine World 2013, March/April Issue, Vol. 42, No. 2). The SCRC does not require any component technology, which is not yet proven in operating large commercial GTCC or GT plants. But of course the cycle integration is a different one, requiring a specific design of the components. An inherent side feature of the SCRC is the exhaust gas composition, which corresponds to a near-stoichiometric combustion gas. This allows comparing the SCRC with a (CO2−) capture ready GTCC having exhaust gas recirculation. The above mentioned article, the thermodynamic performance analysis of a SCRC with an adiabatic compressor is described. But the cycle becomes even more attractive with an intercooling stage in each of the two compressors. Here, this is quantified with another detailed thermodynamic analysis. Additionally, also an ideal case with isothermal compression is analyzed. The latter is of course unrealistic for a practical realization. But it indicates the potential of using more than one intercooling stage per compressor. The aim of this paper is to quantitatively compare the three variants with adiabatic, intercooled and isothermal compressors. In all three cases the same turbine and recuperator temperature limitations are used while some other cycle data assumptions are adapted to the compressor technology in order to achieve an optimal performance level for each variant. The thermodynamic results have been cross-checked with a breakdown of the exergy losses in the three variants. The final results for base load operation indicate that the intercooled variant could become the best choice.