The report discloses thermodynamic studies of the semi-closed oxy-fuel combustion combined cycle. The computer simulation and parametric optimization approaches are described in details. The oxy-fuel cycle net efficiency in relationship to the carbon dioxide turbine exhaust pressure and the steam turbine inlet pressure is shown. The power production efficiency reduction is related to the turbine cooling losses is described. It is shown that the semi-closed oxy-fuel combustion cycle maximal net efficiency of 52.5% occurs at the initial temperature and pressure 1400°C and 60 bar at the carbon dioxide turbine exhaust pressure 0.5 bar and the steam turbine inlet pressure 90 bar. The cooling losses consideration leads to the net efficiency of 47.76% that is reached at the carbon dioxide turbine exhaust pressure 1 bar and the steam turbine inlet pressure 90 bar.

The fuel price increase and severe environmental regulations determine energy-saving importance. Useful utilization of low-potential heat sources with 300–400 °С temperature becomes topical. The application of low-temperature power production facilities operating low-boiling heat carriers could be a solution to this problem. A comparative parametric study of a number of heat carriers resulted in a choice of the most promising fluids that are not expensive, have low toxicity and flammability, low ozone depletion and low global warming potential. These heat carriers are considered for application in simple power production cycles with and without regeneration. The main parameters were optimized at the initial temperatures of 323.15–623.15 K. The cycle without regeneration has a maximal net efficiency of 29.34% using the water at an initial temperature of 623.15 K. The regenerative cycle at a temperature below 490 K has its maximal efficiency using a water heat carrier, and at a higher temperature above 490 K with R236ea. The cycle with R236ea at 623.15 K has an electrical net efficiency of 33.30%. Using a water heat carrier, the maximal efficiency can be reached at pressures below 5 MPa for both cycles. Among the organic heat carriers, the minimal optimal initial pressure of a simple cycle is reached with the R236ea heat carrier below 45 MPa without regeneration and below 15 MPa with regeneration. Therefore when utilizing the latent heat with temperatures above 500 K R134a, R236ea and R124 are the most promising organic fluids. Such conditions could be obtained using different industrial sources with water condensation at elevated pressures.

Fossil fuel thermal power plants account for almost 60% of Russian electricity and heat. Steam turbine units make almost 80% of this amount. The main method for steam turbine unit efficiency improvement is the increase in the initial steam parameters’ temperature and pressure. This reduces fossil fuel consumption and harmful emissions but requires the application of heat-resistant steel. The improvement in steel’s heat resistance leads to a non-linear price increase, and the larger the temperature increase, the more the steel costs. One of the methods of improving efficiency without a significant increase in the capital cost of equipment is an external combustion chamber. These allow an increase in the steam temperature outside the boiler without the need to use heat-resistant alloys for boiler superheaters and steam pipelines between the boiler and the steam turbine. The most promising is hydrogen–oxygen combustion chambers, which produce steam with high purity and parameters. To reduce the cost of high-temperature steam turbines, it is possible to use a cooling system with the supply of a steam coolant to the most thermally stressed elements. According to the calculations, the efficiency reduction of a power unit due to the turbine cooling is 0.6–1.27%. The steam superheating up to 720 °C in external combustion chambers instead of a boiler unit improves the unit efficiency by 0.27%. At the initial steam temperatures of 800 °C, 850 °C, and 900 °C, the unit efficiency reduction caused by cooling is 4.09–5.68%, 7.47–9.73%, and 8.28–10.04%, respectively.

The co-generation facilities have maximal thermal efficiency. In the case of the Russian Federation, for the power production industry, the development of the co-generation combined cycle facilities (CCGT-CHP) is especially urgent. The CCGT-CHP daily load schedule requires the demand of both electricity and heat, and the heat demand depends only upon the ambient air temperature. The gas turbine power reduction and the subsequent steam turbine power reduction during the electric load drop down are limited by the necessity to maintain the steam flow to district water heater to supply heat power. Methane steam reforming allows the recovery of the excess steam heat in the form of synthetic gas together with the CCGT-CHP electric power reduction. This paper considers three versions of the CCGT-CHP steam use in the Methane reforming: Bleeding steam supply, throttling of the heat recovery steam generator exit steam and the supply of this steam to the steam production in a steam transformer. Steam Methane reforming allows a reduction in the steam turbine supply power of 25% during the electric system power drop down. In the daytime, during the maximal system load, the produced synthetic gas is used and it is necessary to use the peak load gas turbine, which allows a 23% electric power increase. Energy storage by steam Methane reforming increases the contribution margin by 2.9%.

Combined cycle gas turbine cogeneration power plants provide maximal thermal efficiency. The facility thermal load depends upon ambient conditions and it may limit its unloading degree, or control range. Energy accumulation extends the control range by the energy storing during the power excess period and the energy discharge during the high consumption period. This paper considers two accumulation technologies, with the steam methane reforming and with hydrogen storage by using electrolyzer and fuel cell. In steam methane reforming technology a part of heat recovery steam generator steam passes to the synthetic gas production and reduces the electric power production during the low load periods. During the peak load periods, the synthetic gas is burned in combined cycle gas turbine and peak load gas turbine combustors. In hydrogen accumulation technology the excessive power produces hydrogen in an electrolyzer, which is stored and used during the peak load periods in fuel cells for additional electricity production. The simulation was carried out in the Aspen Plus software, the thermo-physical fluid properties were determined using the Peng-Robinson state equation. Application of the steam methane reforming accumulation technology increases the facility contribution margin by 2.6%, the hydrogen accumulation technology reduces this margin by 0.1%.