Vol 66, No 8 (2019)

The article presents the results from analyzing the application conditions of the thermophysical processes similarity theory as applied to modeling the hydrodynamics and heat transfer in liquid-metal cooled nuclear power facilities, namely, in channels, in the reactor core rod systems, and in the reactor pressure vessel under different operating conditions. It is shown that direct modeling can be used without limitations only for processes whose determined similarity numbers (criteria) are functions of only the system’s geometrical simplexes and one determining criterion. The availability of two determining criteria in the heat transfer description, e.g., the Reynolds and Prandtl numbers, noticeably complicates the modeling. With three determining criteria, direct modeling is impracticable as a rule. In such cases, systematic multivariate experiments must be set up. The aim of such experiments is to reveal the effects that are allowed by the general mathematical model but which cannot be simulated—either analytically or numerically—using state-of-the-art mathematical technologies. It has been shown from numerical and theoretical investigations and from generalization of experiments, including data on temperature distribution patterns in a liquid-metal flow, that the thermal resistance at the coolant–heat-transfer surface interface boundary is essentially zero if the concentration of impurities in the coolant does not exceed their solubility at the circulating metal temperature. In the case of using liquid metals and alloys (Pb, Pb–Bi, Hg, Na, Na–K, Li, etc.), the heat transfer is described under such conditions by a unified dimensionless dependence on the Peclet number. The transfer of heat in fuel assemblies takes place mainly by convective heat transfer, and the temperature field is governed by the increase in liquid-metal temperature. The temperature distribution depends on the classical similarity criteria, including the Reynolds, Peclet (Prandtl), and Grashof criteria, and on the design and thermophysical characteristics of fuel elements and fuel assemblies (the latter serve as the fuel element approximate similarity criterion). Forced circulation in the reactor vessel is simulated in small-scale water models using the Froude and Peclet numbers, and natural circulation is simulated using the Euler number. The similarity of currents in stably stratified coolant zones is determined by the Froude and Peclet numbers and by the local-gradient Richardson number.

The article discusses matters concerned with improving the performance of automatic closed-loop control systems of thermal plants with a time delay in responding to a change in the setpoint. The improvement is achieved by applying the fastest response algorithm (FRA) according to the Pontryagin maximum principle and using linear prediction of the controlled variable. It is shown that, during operation with switching the maximum control outputs applied to a plant with a time delay, linear prediction is inefficient, and self-oscillations may occur in the system. The technical solution proposed for eliminating self-oscillations implies the use of a hybrid closed-loop control system comprising an FRA, a PID controller, and an automatic controller tuning (ACT) unit, which performs the function of determining the plant model parameters and optimizing the controller parameters. The actuator is considered as a proportional section that is used as part of the plant. The control limitations are related to the level of the control output applied to the plant. The ACT unit comprises accelerated controller tuning algorithms that use active plant identification methods based on analyzing the response to an impulse input and two cycles of the excited self-oscillations. These algorithms make it possible to determine four parameters of the second-order plant model with a time delay. The self-oscillations occurring in systems with the FRA and plants with a time delay are eliminated at the end of the transient by making a switchover to PID control. Four embodiment versions of a system with the FRA are analyzed, specifically, those with and without control output reversal and also with using the plant simulation model without a time delay that is obtained from the ACT operating in parallel with the plant. For practical embodiment of the MSRA as part of a hybrid system, it is recommended to use its version without control output reversal. Relations for calculating the controlled variable prediction coefficient in terms of the plant model parameters in a wide range are obtained. Two examples of using the hybrid system equipped with industry-grade controllers for a temperature control system are given: one with the electric heater power controlled using a pulse-width modulator and the other with a constant speed actuator.

By means of airflow aerodynamic classification, high-calcium fly ash (with a bulk density of 1.14 g/cm³ and size distribution parameters of d_av = 5 µm and d₉₀ = 14 µm) produced from the combustion of Irsha-Borodinsky coal and sampled from the fourth field of the electrostatic precipitator at the Krasnoyarsk TPP-2 has been separated. The obtained morphologically homogeneous fractions of spherical particles with a narrow distribution are characterized by d_av = 1, 2, 3, 4, and 10 μm and d₉₀ = 3, 4, 5, 9, and 16 μm. It has been established that the main chemical component of the obtained narrow fractions is represented by CaO with a content of 34–43 wt %; the content of the other components is as follows: 15–34 wt % of SiO₂, 13–16 wt % of Fe₂O₃, 9–10 wt % of MgO, 8–10 wt % of Al₂O₃, 2–10 wt % of SO₃. The phase composition has 35–49 wt % of crystalline calcium-containing compounds, including 11–15 wt % of aluminum substituted calcium ferrite and 8–11 wt % of tricalcium aluminate, which are the main phases of Portland cement. The content of crystalline quartz amounts to 2–7 wt %, and that of the amorphous glass phase is 41–51 wt %. It has been established that, as the average fraction size d_av obtained after the aerodynamic separation of ash increases from 1 to 10 μm, the bulk ash density exhibits an increase from 0.89 to 1.50 g/cm³ and the content of the magnetic component also increases, amounting up to 4 wt %. At the same time, the chemical composition of the fractions exhibits an increase in the content of SiO₂ as well as a decrease in the content of Al₂O₃ and SO₃. The content of СаО and Fe₂O₃ in the fractions having d_av = 1–3 μm increases, then it exhibits an abrupt decrease with increasing particle size. As far as the phase composition is concerned, an increase in the content of crystalline quartz is observed, and the total fraction of calcium-containing phases gradually decreases. At the same time, the percentage of calcium sulfate decreases and the percentage of free calcium oxide exhibits a considerable increase. The content of calcium hydroxide increases in the fractions having d_av = 1–2 μm and then decreases with increasing particle size.

The principles of implementing a scalable microprocessor system for automation of auxiliary and d.c. power supply switchgear at power plants and substations are described taking as an example the demonstration model of the cabinet with self-contained switchgears for shutoff and control valves (of the KRUZA P type). The computerized subsystem constructed on the basis of a communication programmable logic controller is described. The controller serves for supporting digital data exchange according to the standard protocols used in the electric power industry (Modbus, IEC 61850, and IEC 60870-101/104). The field-level digital networks transmit data exchanged with distributed signal input/output modules and panel-mounted instruments. The upper-level network transmits these data to the process instrumentation and control system (process I&C). Approaches to elaborating application software that allows scalable automation system configurations to be developed are considered. Embodiment versions in the form of a self-contained automation system, process I&C subsystem, or a remote-control subsystem are given. The use of standard modules in cabinet designs and in control algorithms helps enhance the reliability in designing production process control systems.

The expressions derived previously from the three-layer Owen model of a turbulent boundary layer and the Deissler and the van Driest models are demonstrated to be valid for predicting heat transfer coefficients in the entrance region of channels. The basic parameters in these expressions are the dynamic velocity, dimensionless viscous sublayer thickness, and dimensionless turbulent boundary layer thickness. Correlations are presented for predicting these parameters in the entrance region of a plate or circular pipe. The predicted heat transfer coefficients agree with the available data. With consideration of the fact that the friction and the heat transfer laws established by S.S. Kutateladze and A.I. Leont’ev are conservative with respect to disturbances in the turbulent boundary layer, parameters of the expressions for average heat transfer coefficients in channels with heat transfer intensifiers (such as roughness, transverse ring protrusions, and annular groves in pipe walls) were determined. In calculating friction and heat transfer, the main characteristics are the dynamic velocity and the ratio of the friction coefficient on a smooth surface to that on a surface with heat transfer intensifiers. The expression was derived for calculating the Nusselt number as a function of the Reynolds number and the friction factor. The predicted average heat transfer coefficients agree well with the experimental data and the predictions by empirical correlations. Calculations were performed in a wide range of Reynolds number (from 10⁴ to 10⁶) and smooth-to-intensified surface friction factor ratio (from 1.92 to 9.2). The proposed correlations can be used for predicting local heat transfer coefficients in the entrance region on a body in a flow and average heat transfer coefficients in intensified channels.

An integrated approach is presented on wastewater treatment for power plants and the disposal of carbonate sludge—the waste forming at the make-up water pretreatment stage at power facilities. Usually, carbonate sludge accumulates on sludge waste sites located on the territory of power plants, which leads to an adverse impact on the environment. In addition to solid waste, the station also produces a large quantity of wastewater, which must be cleaned before being discharged into a waterbody. Concentrated wastewater is traditionally subjected to local treatment, which is associated with economic costs, while domestic and storm sewage is treated at general production wastewater treatment plants. The article proposes a wastewater biosorption technology at the Karmanovskaya GRES in which conditioned carbonate sludge is used as a sorption material. The sorption ability of carbonate sludge is confirmed by sorption isotherms of petroleum products and ammonium nitrogen. The kinetic curves obtained as a result of research confirm that biosorption wastewater treatment with carbonate sludge has a higher efficiency than conventional biological treatment. With the introduction of carbonate sludge into the aerotank for biosorption, the efficiency of wastewater treatment at the Karmanovskaya GRES increases significantly in terms of 5-day BOD, phosphate ion, chemical oxygen consumption (COD), ammonium nitrogen, and petroleum products. The use of carbonate sludge as a sorption material will improve the quality of treatment of all types of wastewater without their local treatment, which is equivalent to the wastewater’s final biofiltration. When implementing the technology of biosorption cleaning with water treatment sludge, the prevented environmental damage to the Karmanovsky reservoir will amount to 1 463 000 rubles per year in the event of oil- and salt-containing wastewater discharge from the GRES into the inlet chamber. The economic calculation of the presented technology is performed: the payback period will be 3 years and 10 months and the economic effect will be 563 000 rubles per year.

Implementation of automatic water chemistry control at power units of thermal power stations (TPS) is hindered by the unavailability of analyzers required for monitoring certain standardized characteristics of the coolant. Important characteristics include salt content and ammonia concentration in the feedwater and salt content and phosphate concentration in the boiler water. If automatic analyzers are not available, phosphate concentration in the boiler water of drum boilers with an operating pressure above 10 MPa can be determined using conductivity measurements. In this case, the concentration of phosphates is calculated using the regression equation correlating phosphate concentration with electric conductivity of a cooled boiler water sample from the salt compartment or the equation derived by transformation of the system of equations describing the ionic equilibrium in the feedwater and the boiler water. The procedure was developed based on the results of a full-scale experiment performed at the TETs-26 cogeneration power station of PAO Mosenergo. It has been demonstrated that the correlation coefficient is 1.0 and the phosphate concentration is a function of the specific electric conductivity of a direct sample and an H-cation-treated cooled sample of water taken in the salt compartment of a drum boiler. However, for practice, the results of measurement of the specific electrical conductivity of an H-cation-treated sample are the only correct ones that enables the effect of a change in the quality of the working solution of sodium phosphate or feed water to be eliminated. Additional measurements of boiler water pH make it possible to calculate the concentration of salt components and improve the reliability of chemical control if fast upsets of the water chemistry occur. The developed calculation method for determining phosphate concentrations in boiler water using conductivity measurements was verified in a TP-87 boiler with a drum pressure of 13.8 MPa at the Ivanovo TETs-3.