Thermal Engineering最新文献

The article considers the use of supercritical carbon dioxide (sCO₂) as working fluid in the turbine stage consisting of a vane row and a mixed-flow blade row. The operation of the existing turbine on natural gas combustion products and on supercritical carbon dioxide is analyzed by way of comparison. The numerical simulation results show that the use of supercritical carbon dioxide makes it possible to increase the turbine power output to 14.3 MW. This is more than a factor of 30 higher than the power output of the same turbine operating on natural gas combustion products. Such a significant increase of power output is achieved without changing the turbine stage design, which points to the possibility of modernizing the existing units without the need to make essential changes of the design. The turbine stage efficiency during its operation on supercritical carbon dioxide was estimated at 0.87, and that during operation on natural gas combustion products was 0.88. Despite an insignificant drop of the efficiency, the total increase of the power output results in that the use of sCO₂ is economically feasible. Based on the data obtained, a conclusion has been drawn that it is advisable to use the existing turbine stages for operation on supercritical carbon dioxide. This opens the prospects in achieving more efficient operation of power systems without the need to develop new types of turbines, decreasing capital outlays, and more rapidly introducing new technologies. The transition for using supercritical carbon dioxide as working fluid can result in obtaining a significantly higher output of turbine units while retaining high efficiency indicators and making minor changes in the equipment design.

A comparative performance analysis of a Kalina Cycle System 11 (KCS11) without and with solar energy is done based on 4E-analysis (energy, exergy, environment, and economic) for generating additional electricity from fluegas waste energy of a 660 MWe Supercritical (SupC) coal-fired power plant. The result shows that the integration of solar assisted KCS11 with main steam power plant increases the net plant energy and exergy efficiencies by about 0.04 and 0.03% points, respectively due to additional electricity generation of 647.43 kW at 40 K of superheat. Condenser and evaporator are the maximum contributor of energy and exergy losses, respectively in the proposed systems. Energetic performance of solar assisted Kalina cycle is higher than the standalone KCS11 due to decrease in turbine exhaust pressure and additional poor exergetic performance of solar heater causes less exergy efficient of solar assisted KCS11 compared to standalone KCS11. Use of solar integrated KCS11 reduces the annual ({text{C}}{{{text{O}}}_{{text{2}}}}) emission by about 1089.58 t at full load which is nearly 1.25 times higher than the standalone KCS11. The Levelized Cost of Electricity (LCoE) for producing additional electricity by solar energy at 40 K of super-heat is about 0.13 $/kW h which is 8.5% lower value compared to the solar thermal power plant.

The volume-of-fluid (VOF) method, supplemented by models of interfacial heat and mass transfer, is a universal and very effective tool for simulation and detailed analysis of intricate processes occurring in systems with phase transitions. The key feature of this method is that it can quite accurately and in detail describe the physical pattern of running processes in the presence of a sharp phase boundary and provide quantitative data on the distribution of local heat-transfer characteristics and the dynamics of the interphase boundary and associated phenomena, thereby making the VOF method advantageous in researches and engineering practice. Development and improvement of heat and mass transfer models and efficient numerical VOF algorithms, as well as preparation of recommendations for the application of these approaches, are an urgent problem. This paper proposes an approach to the prediction of interfacial heat and mass transfer rate, which is based on the analysis of phase transitions in single-component systems using the linear theory of nonequilibrium processes. The results are presented of verification calculations performed for several standard problems. The classical problems of one-dimensional boiling and condensation (the Stefan problem) are examined as are such problems as vapor condensation in tubes of different orientations, condensation from stagnant or moving vapor on the surface of smooth horizontal tubes, and film boiling on the surface of horizontal cylinders. The predictions are verified against classical solutions and available experimental data. Calculations were carried out for fluids with different thermophysical properties, including water, pentane, propane, R-113, R-21, and R-142b. The maximum ratio of the densities of liquid and vapor phases was as high as 1600 (water at atmospheric pressure). The simulation results demonstrate the versatility of the proposed approach, which allows us to recommend it for solving a variety of engineering problems.

The results obtained from experimental investigations of the dynamic characteristics of a condenser and new ejector are presented. The investigations were carried out at a thermal power plant under the turbine commercial operation conditions using an extended arrangement for measuring the ejector operation parameters and an automated data-acquisition system. The dependences of the ejector’s first stage suction pressure on the dry (atmospheric) air flowrate and the pressure in the condenser and in the ejector’s first stage receiving chamber on the steam–air mixture flowrate during their joint operation are obtained. It is proposed to determine the maximal volumetric throughput of the ejector operating on dry air with using the minimal slope factor as a function of the air flowrate. With an increase of air inleakages into the steam turbine unit vacuum chamber, the pressure difference at the initial and total air inleakages at the ejector suction varies according to a linear law and that in the condenser according to an exponential law. By using the measurement system, the condenser’s and ejector’s dynamic characteristics were determined. It has been found that the pressure growth rate at the ejector suction increases with increasing the amount of air admitted into the condenser. The time taken for the pressure to become stable remains approximately the same. However, the pressure growth rate in the condenser does not depend on the amount of air admitted, and the time taken for the pressure to become stable increases exponentially with increasing the amount of air admitted. For diagnosing the vacuum system malfunctions in controlling the steam turbine unit’s operation mode, it is recommended to provide indication of the ejector suction pressure on the turbine control board. As regards the pressure sensor, it is proposed to install it on the common pipeline supplying steam–air mixture to the ejectors. The investigation of the condenser–ejector system dynamic characteristics will make it possible to improve the turbine vacuum protection, which is one of the turbine protection system components.

The work is devoted to simulation of the bulk condensation in a supersonic flow of a vapor-gas mixture through the Laval nozzle considering the finite rate of the interphase heat transfer. Numerical methods are examined for predicting the temperature of droplets using the improved VOF (Volume of Fluid) and Eulerian multiphase models. It has been demonstrated that, compared to the Eulerian model, the VOF model more accurately predicts the known experimental data and provides the numerical solution whose stability is less susceptible to the effect of high intensity source terms. Comparison of the predictions with the experimental data of other authors has revealed that the two-temperature model more accurately describes the flow with bulk condensation than the single-temperature model does. The application of a single-temperature approximation is justified when the impurity content in the mixture does not exceed 2% (by weight) since the zone of the active condensation onset is relocated considerably compared to its relocation in the case of the two-temperature approximation. However, the single-temperature approximation is recommended only for calculating the overall heat release level that could be beneficial, for example, for quick assessment of the effect of bulk condensation on turbine stage performance. The previously obtained estimates confirmed the applicability of the single-temperature formulation at an impurity content as high as 5 wt %, but solving this problem in 3D formulation improved the accuracy of these estimates. It has been revealed that the assumption about the flow homogeneity along the channel height (as one of the assumptions employed in one-dimensional calculations) during bulk condensation in a slot-type Laval nozzle is not valid on changing-over to a three-dimensional two-temperature formulation: supersaturation persists at the phase boundary, as a result of which the droplet growth process continues at the circumference of the flow.

The thermal power plant recognized as the most pollutants emitted power plant in the world. The use of the solar systems is essential for reducing carbon emissions from thermal power plants. Such hybrid systems need a skillful energy management technology as well as incorporation of carbon conversion technology that will help to run the system expertly to maintain the power generation-demand balance and make the thermal plant more cleaner than before respectively. This work describes a fuzzy logic-based energy management system for a thermal-solar hybrid system and a carbon conversion technology to convert the captured carbon into the chemical products after calculating the environmental impact of a stand-alone thermal power plant through life cycle assessment (LCA) tool. The results of a case study demonstrate that the suggested schemes are feasible, effective and environmentally acceptable. Thermal-solar-based hybrid power plant can work environmentally harmlessly if the carbon produced from the plant is converted into the chemical product.

Rapid development of energy technologies results, in particular, in that photovoltaic modules often become obsolete even before the end of their assigned service life. It is sufficient to say that, for the period from 2014 to nowadays, the average efficiency of photovoltaic modules has increased from 14–15 to 21%. The prices for photovoltaic products also continue to decrease. In this connection, the possibility of substituting the equipment of existing solar power plants with more advanced components is of interest. Photovoltaic module replacement versions, as well as technical and economic aspects of this process, are discussed taking Russia’s first grid-tied photovoltaic plant Kosh-Agach-1 as an example. The modern types of photovoltaic modules and the options of using them for solar plant renovation purposes are analyzed. The prime cost of the electricity generated is estimated with taking into account the replacements of modules and inverters. Special attention is paid to the compatibility of new modules with the old support structures and inverter equipment. The decrease of electricity prime cost after installing the new modules serves as the main renovation feasibility criterion. It is shown that the refurbishment of plants equipped with thin-film silicon modules by replacing them with domestically produced or Chinese modules consisting of silicon photovoltaic plates 166 × 166 mm in size looks to be the most promising option. The minimal prime cost of generated electricity is achieved in the case of using heterojunction modules and modules on the basis of photovoltaic converters with a rear contact.

It is possible at present to reduce the emission of harmful substances into the environment during the operation of industrial enterprises by cleaning emissions and modernizing existing technological equipment. A survey of purification plants showed that sorption technologies are more accessible and simpler. Adsorption is an effective physical and chemical process for capturing carbon dioxide. The modern market offers a wide range of adsorbents that can be used to capture harmful substances, but, as a rule, for reasons of economic efficiency, it is more profitable to use secondary resources: production waste. At energy sector enterprises, various wastes are generated during the generation of thermal and electrical energy. Thus, when preparing a heat carrier at water-treatment plants, wastewater after clarifiers and ion exchange filters can be utilized to create a sorption material capable of capturing carbon dioxide, one of the main greenhouse gases. Obtaining adsorbents from waste from water-treatment plants will reduce the volume of sludge-storage facilities or eliminate their use altogether. Industrial waste is a secondary raw material and, as a rule, is inferior in its original form to traditional industrial adsorbents in terms of the activity indicator, which characterizes the ability to capture carbon dioxide. Therefore, to obtain high absorption capacity, waste is combined and activated. An adsorbent obtained from waste from water-treatment plants of thermal power plants is presented. The waste used was sludge water discharges and spent regeneration solutions after the softening filter. The component composition of the adsorbent and the method of its preparation by activation and preparation of waste are described. The efficiency of the developed adsorbent was tested on a laboratory setup. Comparative results of laboratory studies with the most frequently used adsorbents are presented. The results of determining the strength, porosity, permeability coefficient, and specific surface area of the studied adsorbents are presented.

Steam boilers of various arrangements (or profiles) exist in the world. The most widely used ones include, for example, semitower boilers (or L-paso boilers). In Russia, there is not sufficient experience in designing such boilers, especially in their practical application. The paper analyzes advantages and disadvantages of semitower boilers. As with tower boilers, their main advantage is a small footprint. However, compared to tower boilers, the L-paso boilers have a lower height. According to the performed analysis, the semitower configuration is best suited to boilers fired with gaseous or liquid fuel. In Russia, due to its climatic conditions, semitower boilers can be used for replacements of obsolete (type E) natural circulation gas-and-fuel oil-fired boilers with a steam output of 210–420 t/h. As an example, the paper presents a brief description of the L‑paso (type Ep) natural circulation reheat boiler manufactured by the well-known Babcock–Wilcox Co. This boiler, which is a part of a 158-MW power unit, has been successfully fired with sulfur fuel oil for many years. A customized numerical model of the boiler was developed in the Boiler Designer software package. Multivariant calculations of the boiler were performed on the basis of this model. An analysis of the predictions has confirmed that the boiler can operate in a wide range of loads while maintaining the design steam conditions. The furnace heat release rate q_F, the furnace cross-section heat release rate q_V, and the flue gas temperature at the furnace outlet (vartheta _{{text{f}}}^{{''}}) have been demonstrated to considerably exceed the values allowed by the applicable Russian regulations for similar boilers. This fact is explained. The gas velocities in the boiler gas ducts are noticeably higher, and the gas and air velocities in the air heater are approximately the same as in the Russian-made boilers. The steam enthalpy increments Δh and the mass velocity ρw in the superheater stages basically correspond to the concepts of Russian specialists.

Due to the advanced capabilities of modern computational fluid dynamics (CFD) codes and developed models and algorithms, numerical simulation has become an efficient tool for studying two-phase flows, analyzing the entire totality of the processes occurring in them, and obtaining the data on flow local characteristics, which are difficult to measure directly. Active efforts taken for incorporating new models into various CFD codes should be accompanied by their cross-verification, the results of which can serve as a basis for selecting the most accurate, efficient, and universal models and algorithms. In this article, the results obtained from the solution of the problem about the condensation of R-142b refrigerant saturated vapor in a horizontal tube in the wall conjugate statement using two CFD codes, ANES and ANSYS Fluent, are analyzed. The copper tube’s inner diameter is 28 mm, its length is 2.75 m, wall thickness is 2 mm, and the total mass flux is 47 kg/(m² s). The studies are of relevance for heat recovery installations based on the organic Rankine cycle. The calculations were carried out using the modified Lee model that we suggested previously, and which has been implemented in the ANES CFD code developed at the Department of Engineering Thermophysics, NRU MPEI. The cross verification of the VOF algorithms implemented in the ANES and ANSYS Fluent codes has shown that the results of modeling the saturated vapor condensation in a horizontal tube obtained using the above-mentioned codes are in good agreement with each other and are close to the empirical dependences recommended in the literature sources (M. Shah) for calculating the condensation in a horizontal channel. Data on the distribution of local heat-transfer characteristics over the tube’s inner wall are presented, which demonstrate that the heat-transfer coefficient features an essential nonuniformity over both the tube length and perimeter.