Electricity consumption by people is increasing every year, followed by an increase in harmful emissions of carbon dioxide into the atmosphere during its generation. A promising solution to the problem of global pollution can be an oxy-fuel technology for energy production. It has been proven that the Allam cycle at an initial temperature of 1100 C is the most efficient oxy-fuel cycle. With a further increase in the initial temperature, the efficiency of this cycle decreases due to an increase in the relative coolant flow rate. This paper discusses the effect of the changeover from carbon dioxide to nitrogen coolant on thermal and hydraulic characteristics of cooling channels for the first-stage blade of a carbon dioxide turbine. We have found that, upon changeover from carbon dioxide to nitrogen cooling, the heat transfer coefficient decreases for a channel with pin intensifiers 1.3 to 1.65 times, for a channel with pin-and-dimple intensifiers, 1.65 to 1.77 times. We have also found that, upon changeover from pin intensifiers to pin-dimple ones, the heat transfer coefficient is increased for a cooling system using carbon dioxide coolant 2.2 to 2.5 times, whereas when using nitrogen coolant, the heat transfer coefficient remains unchanged. It has been also found that, to maintain a constant heat transfer coefficient upon changeover from carbon dioxide to nitrogen coolant, we should provide a 23.6% higher nitrogen flow rates compared to dioxide.
Today, most of the electrical energy in the world is generated by fossil fuel incineration. This causes significant emissions of harmful substances into the atmosphere. The noted problem can be solved by switching to power plants with zero emissions, operating in semi-closed cycles, and producing electricity through oxygen combustion of fuel. A significant drawback of most of the known oxygen–fuel cycles is the lack of useful utilization of various sources of low-grade heat, which is especially typical for power plants operating on gasified coal fuel; as a result of the gasification process, a significant amount of excess heat is released into the atmosphere. This paper presents the results of the development and study of oxygen–fuel cycle thermal schemes of increased efficiency with coal gasification. It was determined that the modernization of the scheme using the carbon dioxide Rankine cycle for the utilization of low-grade heat makes it possible to achieve an increase in the net electrical efficiency equal to 1.2%.
To reduce carbon dioxide emissions into the environment, the energy sector develops oxygen-fuel energy cycles. One of the most promising cycles is the Allam cycle that features the highest efficiency of electricity generation among all others. One of the main elements of an oxy-fuel energy cycle is a high-temperature carbon dioxide turbine. The turbine’s working fluid and coolant consist predominantly of carbon dioxide at a supercritical pressure. Currently, there are no recommendations in the literature for the design of carbon dioxide turbines for an oxy-fuel energy system (OFES) operating according to the Allam cycle; therefore, there is a need to study the influence of parameters of the flow path of carbon dioxide turbines on its efficiency and overall performance. In this paper, we have presented the results of one-dimensional calculations of a flow path of the carbon dioxide turbine for the Allam cycle with a capacity of 300 MW, with an initial temperature and pressure of 1100 °C and 30 MPa, and an outlet pressure of 3 MPa. The study was carried out by varying the rotor speed, the reactivity level and the average diameter. Based on the results of one-dimensional calculations, we have found that the highest efficiency of the turbine flow path is achieved at a speed of 471 rad/s, a reactivity of 0.5, and an average diameter of 1.1 m for the first stage.
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