Abstract
Nowadays, thermodynamic cycles are actively studied, in which pure oxygen and fuel are fed into a combustion chamber, and a temperature of a working fluid is regulated by the supply of carbon dioxide and/or water vapor. These cycles are called “oxygen-fuel”. They allow easy to separate CO2, resulting from a fuel combustion, from the working fluid and remove it from the cycle in its pure form. In addition, it has already been shown that an efficiency of electric power generation of such cycles is approaching the best known technologies. However, the efficiency of cogeneration of electricity and heat is more important for many energy systems, especially for Russian, in comparison with the efficiency of electricity generation. The main goal of the study was to analyze the thermal efficiency for cogeneration of electricity and heat of one of the options for the implementation of oxygen-fuel cycles - compressorless combined cycle gas turbine (CCGT) units. A mathematical model of the compressorless CCGT units was developed, which allows to study the thermal performance in a wide range of operating modes. It is conventionally accepted that the system requires a maximum power for power supply of 300 MW, and a maximum power for heat supply of 600 MW. It is assumed that 300 MW of electricity is constantly supplied to the network. In addition, the heat load is provided according to the standard schedule depending on the ambient temperature, and at the same time an averaged data on the temperature of atmospheric air for central Russia over a tenyear period is accepted. The comparison is made with a steam turbine CHP plant and a CCGTCHP plant. The results of the comparison showed a significant advantage of the compressorless CCGT unit.
Highlights
The desire to reduce anthropogenic emissions of greenhouse gases, including CO2, initiates the search for new technologies of generating electric and thermal energy
The structure and value of the annual excess fuel flow, shown in Fig. 10, show that the steam turbine CHP plant at all time intervals is inferior to the compressorless cycle gas turbine (CCGT) unit, and the total annual value of the excessive fuel consumption exceeds more than 15%
Researches have shown that the cycle of compressorless CCGT unit permits to achieve very high rates of thermal efficiency
Summary
The desire to reduce anthropogenic emissions of greenhouse gases, including CO2, initiates the search for new technologies of generating electric and thermal energy. The following assumptions are accepted: temperature, required for air separation - 100 K; coefficient, taking into account the production efficiency of liquid oxygen, does not depend on the operating mode of the compressorless CCGT unit. The initial data for comparison are the following results of thermal tests [8]: efficiency in the condensation mode, referred to the lower calorific value, is equal to 59.8% (this value corresponds to 53.7% for the higher calorific value); guaranteed thermal power in the cogeneration mode is 40% of electric power; CFU in the cogeneration mode equals 80% and 72%, respectively, attributed to the lower and higher calorific values Based on these data, as well as for the steam turbine CHP plant, the dependence of the energy losses structure on the heat load is plotted (Fig. 12). The CCGT-CHP plant is inferior in all other time periods and loses a little more than 5% in general for the annual period
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