Vol 66, No 9 (2019)

Nowadays, dedicated computer programs developed on the basis of finite element analysis and using modern mathematical models of physicochemical processes are widely applied in designing new or optimizing existing devices and installations firing organic fuels. Such multiparametric tasks, which encompass a wide range of physical problems, are predominantly solved by means of CFD modeling based on the finite volume method. This numerical method for integrating systems of differential equations with partial derivatives features versatility and numerical stability. Particular problems that are dealt with by applying computer programs that use CFD modeling are solved in a few sequential stages: preparing the problem for solving, verifying the mathematical model, visualizing the calculated results and preprocessing them, and analyzing the obtained results. The article discusses the experience gained with modeling and suggests the main recommendations on using this software product in engineering practice for solving particular problems concerned with ignition and burnout of gaseous and liquid fuel and emission of harmful combustion products in power installations for developing new or optimizing existing designs of various furnace and burner devices.

Among the characteristics of the power-generating steam turbines, the specific metal intensity ranks very high. Low-pressure cylinders (LPCs) that use a two-tier Baumann stage have the lowest value of this parameter. The Baumann stage allows a 50% increase in the limit steam passage rate to the condenser without increasing the last-stage blade length and the weight of the turbine. In Russia, such a solution was implemented in the most widely used K-200-12.8 (K-200-130) turbine manufactured by LMZ. However, the experience from operating the turbine and results of investigations into the economic efficiency of the K-200-12.8 turbine have shown that these turbines equipped with the Baumann stage have lower efficiency than similar turbines without the Baumann stage. In the course of subsequent modernization of the K-200-12.8 turbine, the Baumann stage was replaced by a new last stage with longer rotor blades. The design solutions employed by different turbine manufacturers to modernize the K-200-12.8 turbine have been analyzed. It is pointed out that the LPC of this turbine was modernized without analyzing the causes of the low economic efficiency of the basic LPC. An investigation into the real causes of the reduced efficiency of the K-200-12.8 turbine has shown that the LPCs modernized by different companies preserved the drawbacks intrinsic to the basic design. In view of this, a simple variant for modernization of the LPC preserving the Baumann stage is proposed. Its efficiency should not be inferior to the efficiency of modern LPCs whose last stage is equipped with longer blades; a conclusion that is supported by the results of mathematical modeling of the flows in the penultimate- and last-stage nozzle diaphragms of the new LPC.

The use of production waste, primarily various kinds of biomass, for generating heat and electricity is an important trend in solving the energy saving problem. By applying the fluidized bed technology, it is possible to incinerate biomass, including waste from agricultural and some industrial production facilities, in boilers. It is shown that bed agglomeration, a phenomenon that may cause the bed material to become sintered, the temperature inside the bed to become nonuniform, and fluidization to become degraded and even to stop, is one of essential problems associated with biomass combustion in a fluidized bed with conventional bed material (sand). Foreign investigations aimed at clarifying the main agglomeration mechanisms are analyzed. It is shown that the Ca/(K + Na), (Na + K)/(Ca + Mg), and Ca/P ratios, the presence of chlorine in the fuel, and the combustion temperature are the key factors facilitating the fluidized bed material to become agglomerated during biomass combustion. The results from investigations of agglomeration processes carried out in the industry-grade boiler installed at the combined heat and power plant (CHPP) no. 3 of the Arkhangelsk Pulp and Paper Mill (PPM) are presented. The effect that the alkali metals contained in biomass ash have on the bed agglomeration processes and on the agglomeration initiation temperature is considered. It is shown that the bed agglomeration also depends on the phosphorus, sulfur, and chlorine compounds in ash. Certain heavy metals may also participate in the bed agglomeration processes during the combustion of phosphorus-containing biomasses and their mixtures. The basic methods for predicting the onset of agglomeration and for controlling its occurrence are outlined. Significant prospects of preventing agglomeration are associated with using alternative bed materials. The results obtained from investigations into the microstructure and chemical composition of cake particles produced in the course of fragmentation during rapid wood pyrolysis that have been carried out at the All-Russia Thermal Engineering Institute are presented.

The effect of heat conduction in the wall on temperature distribution along a heat exchanger with parallel flow of heat carriers and on heat exchanger effectiveness has been investigated. The problem was solved based on a system of one-dimensional (cross-section averaged) energy equations for two heat carriers and the heat conduction equation for the wall. The wall ends were assumed to be heat insulated. The system was solved using the finite-difference technique. For the special cases, the system was solved analytically. The parameter determining the effect of the wall axial conduction on the heat exchanger effectiveness and the value of this parameter at which this effect can be neglected have been found. This dimensionless parameter is proportional to the heat transfer coefficient, thermal resistance of the wall, and square of the heat-exchanger length to the tube wall thickness ratio. Besides the parameter describing the effect of axial heat conduction, the solution depends on the number of heat transfer units and the ratios of thermal equivalents of the heat carriers and heat transfer coefficients on the hot and cold sides. For a cocurrent flow of the heat carriers, the best result is attained when the value of these two ratios is 1. In this case, the effectiveness of the heat exchanger does not change as compared to that with no effect of the axial heat conduction of the wall. For a countercurrent heat exchanger, the effect of axial heat conduction on the heat exchanger effectiveness is at a minimum when the ratios of thermal equivalents of the heat carriers and heat transfer coefficients on the cold and hot sides are equal. The estimations based on the results of calculations demonstrate that, in case of microchannel heat removal, the effect of axial heat conduction in the heat exchanger wall can considerably reduce the heat exchanger effectiveness.

The article considers the specific features related to operation of the power valve and orifice lines within turbine plant piping systems whose inlets receive water medium with saturation parameters (separated moisture or condensate). It is shown that transportation of working medium in these piping systems is accompanied by pressure drop, boiling, and formation of various two-phase flow patterns from bubble in the initial segment to dispersed-annual in the end segment. Under certain conditions, a slug flow pattern can occur, which behaves as a source of piping vibration. Practical experience has shown that the use of homogenizing inserts for suppressing vibration load in the heating steam condensate (HSC) discharge lines downstream of the moisture separator reheaters (MSRs) of nuclear power plant (NPP) turbines often leads to intensified local flow-accelerated corrosion and pipeline failures. The article considers examples illustrating failures of piping segments downstream of homogenizing inserts and presents statistical data on damageability of heating steam and separated moisture piping of NPP turbines. The steam–water flow patterns in the MSR HSC transportation line of an NPP turbine are determined. The results from hydrodynamic modeling of working medium flow under the conditions of an abrupt expansion at the outlet from the homogenizing insert channel are presented. It is shown that the location of zones characterized by the maximum wear of piping downstream of homogenizing inserts in the MSR HSC discharge lines is determined by the flow pattern and specific features of the working medium flow hydrodynamics. It has been established that droplet impingement erosion is the dominating mechanism causing destruction of stainless-steel piping segments downstream of the homogenizing inserts in the MSR HSC lines of NPP turbines. It is important to note that, if the pipeline is made of carbon or low alloy steel, its metal experiences a combined effect of droplet impingement erosion and flow-accelerated corrosion. The obtained study results can be used in elaborating measures aimed to prevent wear of piping components in the heating steam condensate and separated moisture discharge lines of NPP turbines.

The article considers the methods for a hierarchical description of complex systems’ engineering, which is the foundation for aggregation and decomposition technology of structurally complicated electrical systems’ computer-aided design. The issues of technology application in the design of the automated process control system, the improvement of these methods, and the expansion of the class of designed systems are discussed. The technology development issue and its application in the automated design of secondary wiring systems in general and TPP essential auxiliaries in particular is considered. The process of introducing the automated design technology at АО Zarubezhenergoproekt, realized in the Elektrika TsVK CAD system, is described. The CAD-based technology was tested in the design of the 0.4 kV alarm and essential auxiliaries' control systems at the Pregolskaya TPP with 4 × 110 MW of electric power. The features of the design process’s organization at the Pregolskaya TPP are provided: the degree of the design institute’s equipment availability with technologies and design automation facilities at the beginning of the project, the assimilation degree of these technologies by the personnel, and the possibility of integrating existing technologies with the new developments. The issues of mutual adaptation of the new technology’s components and routine design procedures and operations existing in the design institute, information flows between the technology components and design groups, and structural units (departments) of the design institute are considered. The quantitative indicators of the information volume transmitted in the design process between the structural units of the design institute, as well as the volumes of design documentation developed in the CAD system, are given. The expected timetable to obtain a result using the new technology is indicated.

A mathematical model of mass transfer in an atmospheric bubbling deaerator storage tank at thermal power stations (TPS) to calculate the removal efficiency of dissolved gases from water is considered. For mathematical simulation and calculation of the deaerator efficiency, a system of differential equations of mass and heat transfer is written in a local form for the liquid phase of the layer with volume interphase sources of mass and heat. Mass transfer of the dissolved gases from water to the vapor phase is taken into account using volume interphase sources and the balance equations. Parameters of the interphase sources and correlations for calculating the eddy viscosity of the liquid phase depending on bubbling conditions are given. Results from the system of equations' numerical solution are presented and compared with the available experimental data on the final concentration of dissolved oxygen at the deaerator outlet. Curves of the efficiency of dissolved oxygen removal depending on the operating conditions and design characteristics of the bubbling process are presented, and scientific-and-engineering solutions have been developed to upgrade the bubbling storage tank. It has been found that an increase in gas velocity sharply raises the deaeration efficiency to a certain value (depending on the specified initial parameters), and the efficiency growth is then retarded. Similarly, increasing the length of a bubbling device improves the efficiency in removal of dissolved oxygen from water. One of the causes of a decrease in the water deaeration efficiency is likely to be back mixing of the flow. Upgrading of the deaerator tank is in the installation of perforated baffles across the flow to considerably reduce back mixing of the liquid phase. This increases the driving force of mass transfer, and its efficiency improves by five to 20% depending on the steam velocity. The presented mathematical model can be generalized to a wide range of bubbling apparatuses with a high two-phase layer.