Ways of TPP Power Units Modernization During Their Conversion to Ultra-Supercritical Steam Parameters

The approach to solving the applied problem of modernization of the 300 MW series power units produced by JSC "Ukrainian Energy Machines" by converting them from supercritical to ultra-supercritical steam parameters, provided that regenerative feed water heating system is preserved as much as possible, which will lead to an increase in the energy efficiency of the TPP with minimal conversion, is analyzed in the paper. The conversion of the K-300-240-2 power unit to the parameters of fresh steam 650 °C/30 MPa and intermediate superheated steam 650 °C/7 MPa, determined as optimal as a result of previous studies, can be carried out by completely replacing the high-pressure cylinder of the existing unit for a new high-pressure cylinder with ultra-supercritical steam parameters and superstructure with an additional intermediate-pressure cylinder while fully preserving the parameters and designs of the intermediate- and low-pressure output parts. Two options for modernization of the 300 MW series power unit thermal circuit structure were considered, and the scale of conversion of the regenerative feed water heating system was evaluated. In the first option of the thermal scheme, the 1st steam selection is organized from the cold threads of the modernized high-pressure cylinder with ultra-supercritical steam parameters, and the 2nd one – from the cold threads of the additional intermediate-pressure cylinder. In this case, two high-pressure heaters and a turbo drive of the feed pump are subject to replacement. The disadvantage of this option is that due to a significant increase in steam parameters, it is impossible to choose high-pressure heaters from the existing model range, and a new design must be developed. The electrical efficiency for this modernization option increases from 36.5% (the initial thermal circuit of the K-300-240-2 turbine) to 42.5%. In the second option, it is proposed to install an additional turbine with a capacity of 3 MW, to the input of which a steam from cold threads of the high-pressure cylinder with ultra-supercritical steam parameters is supplied with a loss equal to the sum of the 1st and 2nd selections of the original version of the turbine, on the same shaft with a turbo drive of the feed pump for the sake of preserving the existing high-pressure heater. The steam from the additional turbine selections goes to high-pressure heaters HPH9 and HPH8 with parameters corresponding to the output data of the existing turbine. Taking this into account, high-pressure heaters will not be replaceable. In addition, the power of the additional turbine is sufficient to ensure the operation of the feed pump together with the turbo drive of the feed pump to obtain a water pressure of 34 MPa. In view of this, the turbo drive of the feed pump also remains unchanged, except for the additional turbine installation. The electrical efficiency for the second option of the modernization scheme of the K-300-240-2 power unit is 42.4%. It was determined that the payback period of the modernization according to the first option is 5 years, taking into account the modernization of the boiler unit, and according to the second one – 4.5 years. It is proposed to choose the option of the thermal scheme with an additional turbine, since in this case it is possible to modernize the K-300-240-2 power unit with the maximum possible preservation of the regenerative feed water heating system while increasing its energy efficiency by almost 14%

Investigation of the Oxide Phase Convective Homogenization While Vacuum-arc with Hollow Cathode Remelting of Steel

Discussion of the requirements for the placement of ZrO2 powder in the cathode, which must be taken into account in the production of ODS steel by vacuum-arc remelting in order to provide the high level of homogenization of the oxide particle is presented. The description of the experimental setup and the cathode structure for vacuum-arc remelting of steel, alloyed with oxide nano-powder is given. The role of convective processes in the homogenization of nano-particles in the production of ODS steel is highlighted. The convective flow of liquid metal captures ZrO2 powder particles and carries them throughout its volume.The use of the elementary cylindrical convective cell with mixed boundary conditions is proposed for the description of homogenization of the oxide particles. The structure and spatial distribution of the convective mass transfer in the cylindrical convective cell with the cosinusoidal bottom profile are provided.Spatial distribution of convective flow in the cell is described by the Stokes lines, which are concentrically arranged smooth closed lines, which indicates the formation of convective flow in the form of a single vortex in the cell with mixed boundary conditions. Near the bottom, the Stokes lines reflect the curved cosine bottom profile. Criteria of vacuum-arc melting and convective mixing of ZrO2 nano-particles are formulated.Drops of the liquid material of the cathode with ZrO2 nano-particles penetrate to the central vertical flow of the convective cell. Then, near the wall of the crystallizer, the particles are subjected to vertical forces: Archimedes force (always directed in vertical direction, i.e. upwards); gravity force (always directed downwards); friction force (Stokes force) (directed along the liquid velocity vector) on these particles.The Archimedes force depends on the volume, i.e. size, of the particle. Thus, the less the nano-particle size, the lower the buoyancy force. The criterion of overcoming the Archimedes force allows determining the sizes of the particle at which their uniform distribution in the cell volume is possible.Criteria of convective homogenization ZrO2 nanoparticles are the following:– droplets of cathode material penetrate into the cylindrical convective cell on a circular line which corresponds to the inner circumference of the hollow cathode;– drops of the cathode material penetrate to a depth of convective cells, consistent with its half-height;– ZrO2 particles with sizes less than 90 nm will be stored for a long time in the melt, and homogenized in volume of the melt as a result of convective mass transport

Development of the Engineering Procedure for the Thermotechnical Calculation of a Building Envelope with Air Chambers and a Heat­reflecting Coating

The study has addressed the development of the engineering procedure for the thermotechnical calculation of a building envelope with thermal insulation in which air chambers with a heat-reflecting coating are formed.The engineering procedure implied determining the average RSI-value of the building envelope based on the calculation of a temperature field in it. To find the temperature field, a one-dimensional heat conduction problem in a multilayer building envelope was considered. The thermotechnical heterogeneities caused by the presence of alternating air chambers and dividers of insulation material were taken into account in the mathematical model using the effective thermal conductivity of a corresponding layer. This coefficient takes into consideration the convective and radiant components of heat transfer through air chambers. An expression was obtained for determining its value depending on the temperature at the junction of corresponding layers with adjacent building envelope layers. The iterative procedure was proposed that makes it possible to use this expression for determining the temperature fields in the building envelope under consideration. The geometric and thermophysical characteristics of building envelope elements, as well as the values of indoor and outdoor temperature and heat transfer coefficients of the corresponding surfaces, were used as initial data.The engineering procedure was verified by comparison with the results of three-dimensional CFD simulation, which takes into detailed account the free-convective motion in air chambers and the radiation heat exchange between thermally inhomogeneous walls of the air chamber. It was shown that the use of a one-dimensional mathematical model instead of a detailed three-dimensional one leads to errors not exceeding 2.5 %.As a result of our comparative analysis, the effectiveness of the proposed thermal insulation material having air chambers with a heat-reflecting coating was shown in comparison with the conventional approaches to building envelope thermal insulation. Calculations were performed for the case of the coldest five-day period in the climatic zone of Shymkent (Republic of Kazakhstan

Analysis of the Efficiency of a Power Generating Plant Operating on the Basis of the Brayton Thermodynamic Cycle and Energy Recuperation

The thermal scheme of a power generating plant with a remote heat exchanger operating according to the Brayton cycle with energy recuperation is considered. It is assumed that the plant will work on non-certified (cheap) biofuel. It is shown that, in contrast to the usual Brayton cycle, in the cycle with energy recuperation, the greatest influence on the thermal efficiency is the heating temperature of the working medium and the internal efficiency of the main components of the plant, such as the compressor and the turbine. Also, in contrast to the usual Brayton cycle, a higher efficiency of the plant is achieved with smaller degrees of pressure reduction (increase) in the turbine (compressor). It was established that even at a relatively low temperature of the working medium heating (500 ºC), with high efficiency of the compressor and turbine, it is possible to achieve good characteristics of the power plant as a whole. At a temperature of up to 850 ºC, a thermal efficiency of 40% is achieved, but in this case the cost of materials and production increases. For a final conclusion about the possibility of using the proposed plant and its efficiency, it is necessary to conduct additional studies, in particular, of its main elements, such as a compressor, turbine, heat exchanger and others