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An analysis was carried out for different thermodynamic cycles of power plants with air turbines. Variants with regeneration and different cogeneration systems were considered. In the paper, we propose a new modification of a gas turbine cycle with the combustion chamber at the turbine outlet. A special air by-pass system of the combustor was applied and, in this way, the efficiency of the turbine cycle was increased by a few points. The proposed cycle equipped with a regenerator can provide higher efficiency than a classical gas turbine cycle with a regenerator. The best arrangements of combined air–steam cycles achieved very high values for overall cycle efficiency—that is, higher than 60%. An increase in efficiency to such degree would decrease fuel consumption, contribute to the mitigation of carbon dioxide emissions, and strengthen the sustainability of the region served by the power plant. This increase in efficiency might also contribute to the economic resilience of the area.

An analysis was carried out for different thermodynamic cycles of power plants with air turbines. A new modification of a gas turbine cycle with the combustion chamber at the turbine outlet has been described in the paper. A special air by-pass system of the combustor was applied, and in this way, the efficiency of the turbine cycle was increased by a few points. The proposed cycle equipped with an effective heat exchanger could have an efficiency higher than a classical gas turbine cycle with a regenerator. Appropriate cycle and turbine calculations were performed for micro power plants with turbine output in the range of 10–50 kW. The best arrangements achieved very high values of overall cycle efficiency, 35%–39%. Such turbines could also work in cogeneration and trigeneration arrangements, using various fuels such as liquids, gaseous fuels, wastes, coal, or biogas. Innovative technology in connection with ecology and the failure-free operation of the power plant strongly suggests the application of such devices at relatively small generating units (e.g., “prosumers” such as home farms and individual enterprises), assuring their independence from the main energy providers. Such solutions are in agreement with the politics of sustainable development.

The co-generative micro-power plant with the HFE7100 as a working medium was designed and built for experimental investigations. The heat output of the plant was assumed equal to 20 kW, while the electric output amounted to about 3kW. In the paper a multi-stage micro-turbine with partial admission of all the stages is described in detail and the results of the particular experimental investigations and numerical calculations are shown, followed by an appropriate discussion and conclusions. The flow calculations were performed using ANSYS package and finally the axial multistage turbine was chosen. This allowed to apply typical nozzle and blade profiles. The turbine consists of 5 similar (almost identical) stages with constant section blades, the only difference being the increase of the admission arc (number of nozzles) in the successive stages. The rotor speed was assumed equal to 8000 rpm, mean rotor diameter −100 mm and blade height −10 mm. The stream lines, pressure and temperature distribution in the nominal and off-design conditions are presented and discussed in the paper. The micro-turbine was built and tested experimentally. The turbine performance was calculated for HFE7100 but also for air and nitrogen as a working medium for testing purposes. In the first stage of experiments the turbine behaviour was checked using these gases and the results were compared with the calculation data. The results of the experiments correspond very well with the appropriate CFD calculation data.

The use of various biofuels, usually of relatively small Lower Heating Value (LHV), affects the gas turbine efficiency. The present paper shows that applying the proposed air by-pass system of the combustor at the turbine exit causes tan increase of efficiency of the turbine cycle increased by a few points. This solution appears very promising also in combined gas/steam turbine power plants. The comparison of a turbine set operating according to an open cycle with partial bypassing of external combustion chamber at the turbine exit (a new solution) and, for comparison, a turbine set operating according to an open cycle with a regenerator. The calculations were carried out for different fuels: gas from biomass gasification (LHV = 4.4 MJ/kg), biogas (LHV = 17.5 MJ/kg) and methane (LHV = 50 MJ/kg). It is demonstrated that analyzed solution enables construction of several kW power microturbines that might be used on a local scale. Such turbines, operated by prosumer’s type of organizations may change the efficiency of electricity generation on a country-wide scale evidently contributing to the sustainability of power generation, as well as the economy as a whole.

The efficiency of a gas turbine can be affected by the use of different biofuels usually with a relatively Lower Heating Value (LHV). The paper evaluates the impact of calorific value of fuel on turbine performance and analyzes the possibilities of optimizing turbine construction from the point of view of maximum efficiency for a particular fuel. The several variants of design of small power microturbines dedicated to various biofuels are analyzed. The calculations were carried out for: gas from biomass gasification (LHV = 4.4 MJ/kg), biogas (LHV = 17.5 MJ/kg) and methane (LHV = 50 MJ/kg). It is demonstrated that analyzed solution enables construction of several kW power microturbines that might be used on a local scale. Careful design of such devices allows for achieving high efficiency with appropriate choice of the turbine construction for specific fuel locally available. Such individually created generation systems might be applied in distributed generation systems assuring environmental profits.

Problems faced by designers of such turbines are associated with very small volumetric flow rate of working medium. It leads to small values of height of flow-part blades (hence to increased loss of flow rate) and high values of rotor speed, namely from a few dozen to over a hundred thousand rpm, usually.In all the considered variants the power plants operated on the Solkatherm ® SES36 working medium. Calulations were performed in compliance with the power plant schematic diagram shown in Fig. 1, for four values of the cycle's thermal power: 25 kW, 50 kW, 75 kW and 100 kW. Particular variants, depending on a heat power value, differred from each other only by value of working medium flow rate, and its parameters at turbine inlet, as well as pressure behind the turbine were the same for all the considered cases:-the pressure at turbine inlet, p 0 = 1464 kPa,-the temperature at turbine inlet, t 0 = 140 0 C, -the pressure behind the turbine, p 2 = 189 kPa.Within the frame of performed design analyses the following types of microturbines were taken into account:

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