Structural-&-Phase Condition and the Damageability of the Welded Joints of Steam Pipelines at Thermal Power Plants

The authors studied the interrelation between the type of structure and the damage rate of the welded joints of steam pipelines made of the heat-resistant pearlitic steels that were operated for a long time, i.e. more than 270 thousand hours in the conditions of creepage and low-cycle fatigue. The purpose of this research was to establish the interrelation between the structural-&-phase condition of the metal used for welded joints of the elements of steam systems and their damageability rate for the service life of welded joints exceeding 270 thousand hours. During the studies, the methods of optical and electron microscopy were used according to the requirements of the guideline documentation and also the methods that are used for the determination of mechanical properties. The level of their reliability has been substantiated and the residual life has been determined. To impart functional performances to welded joints we used well-known methods that were appropriately emended according to the structural changes of above joints. Such changes condition the conversion of the original structure of welded joints into the ferrite-carbide mixture. The availability of the conversion process of the initial structure on the thermal action zone sections (TAZ) of welded joints has essential distinctions due to a different disposition of metal to its own damageability. On the whole, the welded joints are damaged more intensively in comparison to the basic metal of steam pipelines. The analysis of the structural state of welded joints in the steam pipelines of thermal power plants as for the extension of their service life results in a considerable economic effect. Understanding the fact that the metal deterioration in welded joints adheres mainly to the fragile mechanism we managed to establish the level of their damageability that demands the renewal of damaged welded joints. We believe that the damageability level of welded joints that tots up to 0.25 or 0.35 of the volume of their TAZ section should be considered as critical for the service life exceeding 270 thousand hours. The damaged welded joints should be renewed throughout the time period of 15 to 20 thousand hours as soon as the specified damageability level is attained.

Selection of the Design of a Contact Condenser of a Gas-Steam Plant with Steam Injection into the Combustion Chamber

Due to the importance of the problems of implementing energy-saving technologies in modern conditions, one of the promising areas is the use of gas turbines for combined heat and power generation. One of the areas of effective development and technical re-equipment is the widespread use of highly economical combined steam and gas plants and gas turbines. The operation of the gas turbine unit “Aquarius” SE NPCG “Zorya-Mashproekt” with the injection of steam into the combustion chamber, which operates on the advanced cycle A-STIG and has in its circuit equipment for water regeneration, condensed from a vapor-gas mixture is considered. For condensation of steam from the vapor-gas mixture, a contact condenser-gas cooler is used, which is a mixing heat exchanger of complex design. The efficiency of heat transfer is determined by the design of the nozzle, namely, the developed heat transfer surface, small hydraulic supports, high heat transfer coefficients. An important aspect is the overall dimensions, which must be within certain limits. In the work it is offered to execute a design of the condenser in the form of a packed column. Different types of nozzles are considered to choose the best option. As a result of thermal design calculation of the contact capacitor, it is proposed to use Rashiga rings (15152) as a nozzle, which provide the lowest height of the nozzle at the required diameter of the device.

CFD Design of Waste Heat Boiler Burner in the Education System of Masters Heat Engineering Specialties

Modern CFD methods for calculating combustion processes make it possible to take into account changes in temperatures, heat loads, rates of coolants, as well as further changes in fuel quality. To develop the skills of CFD design and understanding of combustion processes among future specialists in thermophysical specialties, work was carried out to simulate the burner device of a waste heat boiler. For the study, the design of the gas burner of the waste heat boiler RB-70-4.0-440, which operates as a part of the power unit at the LLC “Rubezhansky Cardboard and Container Plant” in the city of Rubezhnoe, was selected. When constructing a geometric model, the hydraulic resistance to the flow of the supply and distribution manifolds was taken into account. To simplify the calculations, the problem was carried out in a two-dimensional, axisymmetric formulation. Analyzing the computational combustion models, the Non-Premixe Combustion model was chosen, which made it possible to take into account the entry of fuel and oxidizer into the reaction zone by two different flows, as well as turbulent diffusion flame propagation. Six variants of models were investigated: the first three variants with a flame tube with a solid disc with diameters of 32, 48, 56 mm, the next three variants, had a burner with a discontinuous disk 32 mm in diameter at a distance of 6, 16, 32 mm from the flame tube. As a result of the research, the optimal shape of the burner was chosen, which corresponds to model 4, and provides a high-quality combustion process, as evidenced by the high temperature of the torch and the lowest temperature at the disk. The conducted research gives future masters the skills of modeling combustion processes in power equipment.

Decreasing NOx Emissions by Way of the Staged Fuel Combustion

The purpose of this scientific paper was to analyze the mathematical model built for the staged arrangement of the fuel combustion system and calculate the formation of nitrogen oxides throughout the boiler furnace height for the different distributions of thermal loadings along the full vertical extent of the combustion chamber. The obtained results enable the determination of the overall amount of nitrogen oxides formed in the boiler and it allows us to provide appropriate ecological indices for the boiler when regulating the air concentration in the burner rows. In practice, to suppress the formation of nitrogen oxides we often use such basic methods as low-toxic burners, staged fuel combustion, flue gas recirculation, etc. The analysis of the computations done allows us to draw a conclusion that the operation of the boiler with ecological indices that satisfy standard values of the European Directive 2010/75/EU is only possible for the load below 40 %. After reconstruction of the burner system and adjustment of the air supply system with the observation of above ecological norms the boiler power can be increased up to 80 % using the staged fuel burning with the ensurance of environmental performances during its operation. Computational and experimental data errors varied in the range of 8 % to 12 %. With the increase in the overall chemical incomplete combustion by 40 % to 60 % (q3) these losses are compensated by a decrease in absolute losses due to the boiler aggregate load and the losses through external walls (q5) due to an increase in the boiler power.

Specific Features of the Replacement of the Available Flow Path by the Optimal Flow Path when Upgrading the Steam Turbine High-Pressure Cylinder

This scientific paper gives the main research data obtained during the solution of the search problem to define optimal parameter values for the thermal circuit of the К-540-23.5 turbine unit that would provide the most efficient operation both for the optimal version of the high pressure cylinder (HPC) as part of the turbine unit and the turbine unit on the whole. The effect of the distribution of heat differences in the stages of the optimal flow part of the high pressure cylinder used by the К-540-23.5 turbine on the integral quality factors of the turbine unit has been assessed. The calculation studies of the thermal circuit of the turbine unit with the optimal flow section of the high-pressure cylinder showed that the temperature of the underheated feed water in the high pressure heater (HPH) arranged near the steam generator has the most critical effect on the power and economical efficiency of the high pressure cylinder and entire turbine unit. The two-criterion Pareto problem for the upgrading of the turbine unit was formulated and solved to define optimal underheating temperature values. Consideration was given to the two variants of the solution of the optimization problem for the feed water underheating temperature in the high pressure heater. Comparison and analysis of the two variants of solution for the two-criterion optimization problem showed the identity of the obtained data and it confirms the correctness of the problem formulation and the algorithms used for its solution.

Flutter of Fan Blades in the Aircraft Engine in the Three-Dimensional Subsonic Gas Flow

Aeroelasticity problems arise in the different fields of technology. The accident-free operation of the airborne machines is one of the most important factors that should be taken into account during their designing and upgrading. The solution of this problem involves the implementation of many measures to provide the system reliability on the whole, including its individual elements, in particular aircraft engine, its fan whose wide-chord blades can be exposed to the wreckage due to different reasons including the aeroelastic effects, i.e. self-excited vibrations. As a result, the origination of the aeroelastic phenomenon (flutter) in design and off-design modes should be eliminated at the stage of the design and operational development of the rotor wheel that would result in a considerable increase of the level of reliability of the aircraft engine. Based on the analysis of the available methods used for the flutter prediction we can draw a conclusion that the most promising approach to the analysis of the aeroelastic behavior of the blade ring of fan is the use of the method based on the three-dimensional model of the aerodynamics and dynamics (the method used for the solution of the coupled aeroelastic problem). By solving the coupled aeroelastic problem of the nonstationary aerodynamics and elastic vibrations of the blades we can get the amplitude –frequency blade vibration spectrum for the three-dimensional gas flow, including forced vibrations and self-excided vibrations in order to increase the reliability of the blade row of turbine machines. The developed numerical method was used for the analysis of the aeroelastic behavior of the blade ring of the fan mounted in the airborne engine for the operation mode of 3520 rmp with appropriate boundary conditions at the inlet and outlet behind the ring. The computation data confirmed the origination of self-vibrations for the given fan operation mode.

Particularity of Heat Exchange of Twisted Heat Exchangers in External Flow

Perfecting the existing technologies and developing new ones require to rethink the processes in order to obtain qualitatively new results. Widespread use of cryogenic engineering in the chemical industry and medicine calls for a thorough analysis of both the efficiency of thermodynamic cycles and the hardware design of appropriate equipment. The power necessary to obtain low working medium temperatures is distributed between the cooling of the object and the losses in the various elements of the cryogenic setup. One of the best ways to increase the efficiency of the setup is to use the cold energy recovery. This is done by using various designs of recuperative heat exchangers, such as twisted heat exchangers. Existing methods of calculating the parameters of power equipment are based on empirical dependencies, which require some justification and clarification in order to be used for calculating cryogenic equipment parameters. The article describes the experimental setup, presents the research methods applied and analyses the results of the study on convective heat transfer in external flow past the tubular surface of the twisted heat exchanger. The obtained results for the laminar gas flow mode at Re < 2300 allowed determining the length of the initial heat section depending on the regime parameters of the contact phases and the geometric specifications of the twisted heat exchanger. The obtained dependence will make it possible to refine the method of calculating the parameters of the twisted heat exchanger in the annular channel.

Heat Exchange of the Cylindrical Liquid Body of a Limited Height with the Environment

The experimental investigations of the intensity of the heat exchange between the internal surface of the thin-wall metal cylinder and the studied liquid medium were carried out in conditions of its cooling (heating), i.e. under nonstationary heat exchange conditions. The existence of the regular thermal mode in the liquid medium surrounded by the thin-wall metal cylinder has been established. Local in time heat loss coefficients were derived using appropriate dimensionless equations for the stationary mode conditions of heat-exchange in a large volume. Heat loss coefficients were determined using regular thermal mode methods and computational-&-experimental heat loss coefficients. The changes in the relative values of the heat loss coefficients were analyzed using the method of regular thermal mode and computational-&-experimental heat loss coefficients. The deviations in the values of given coefficients in time are mainly within ± 10 %. Relative values of the heat loss coefficients deviate within ± 40 % using appropriate dimensionless equations for the conditions of the stationary mode of heat exchange in a large volume. This conclusion is natural because the cooling (heating) process is nonstationary.

Modernization of Anaerobic Bioreactor for Waste Water Purification Plant

Analysis of literature sources suggests that the use of anaerobic treatment methods is especially effective for high concentrations of contaminants in wastewater, as well as for large volumes of water supplied for treatment, which is typical for industrial wastewater. In biotechnological production and food industry, waste water has a high level of pollution with organic compounds, it is advisable to use anaerobic treatment methods. Anaerobic wastewater treatment processes are characterized by low energy consumption and the ability to recover energy through the combustion of methane. To ensure the required temperature regime for the operation of the bioreactor, a new design of the heat exchange device of the anaerobic bioreactor with immobilized microorganisms has been developed. This design of the bioreactor can provide the required degree of wastewater purification at significantly lower costs for construction, operation, and material and energy resources. For clarity, the design features were designed bioreactor with a plane load of bundled software SOLIDWORKS and a mathematical model of the processes of anaerobic wastewater treatment.

Flow Characteristics of the Nozzle Blade Cascade in the Mode of the Joint Operation with the Radial Diffuser

The obtained research data are given for the nozzle cascade used by a small-size gas turbine of an average fanning in combination with the radial diffuser. Aerodynamic characteristics of the nozzle blade cascade were determined in a wide range of a change in the Reynolds number varying from 4∙105 to 106 and the reduced velocity varying in the range of 0.4 to 1.13. The flow rate coefficient of the nozzle cascade was derived for all modes using the integral methods and the drainages behind the cascade. The kinetic energy loss coefficient and the flow angles were calculated using the measurement data of flow parameters in three control modes that were obtained due to the use of orientable pneumometric probes. When the expansion degree of the convergent –divergent annular duct behind the cascade is equal to 1.43 the flow in the narrow section of this duct is “enlocked” in the mode when the reduced velocity behind the cascade is equal to 1.127. At such velocity the Reynolds number 106 is self-similar for the flow rate coefficient. At lower values of Reynolds number, the decrease of it is accompanied by an intensive decrease in the flow rate coefficient for all the values of the reduced velocity. For the Reynolds number lower than 7∙105 an increase in the velocity results in a decreased flow rate coefficient. When this number exceeds 8∙105 an increase in the velocity results in an increase of the flow coefficient up to the moment when the flow is “enlocked” in the nozzle cascade.