


卷 65, 编号 8 (2018)
- 年: 2018
- 文章: 10
- URL: https://journal-vniispk.ru/0040-6015/issue/view/10554
Metals and Strength Analysis
Flow-Accelerated Corrosion Wear of Power-Generating Equipment: Investigations, Prediction, and Prevention: 1. Flow-Accelerated Corrosion Processes and Regularities
摘要
The first part of this review considers the prerequisites and scales of damage inflicted to the equipment and pipelines of power plant units as a consequence of flow-accelerated corrosion, and examples of accidents involving lethal outcomes that occurred at nuclear power plants as a result of pipeline ruptures caused by flow-accelerated corrosion are given. It is shown that the scope of items susceptible to flow-accelerated corrosion includes components of condensate–feedwater and wet steam path equipment and pipelines made of carbon and low-alloy steels. The main negative consequences caused by flow-accelerated corrosion are local metal thinning spots that can lead to abrupt failures and depressurization of the process circuit and contamination of working fluid with iron containing products of flow-accelerated corrosion. Sedimentation of these products in a steam generator is one of factors causing damage to and failure of its heat transfer tubes. It is proposed to draw a distinction between general and local flow-accelerated corrosion. General flow-accelerated corrosion causes ingress of iron-containing compounds into the working fluid and is characterized by a moderate metal thinning rate that does not lead to destructions or occurrence of wormholes involving loss of process circuit leak tightness. The effects of local flow-accelerated corrosion manifest themselves in small parts of intricately shaped channels and are characterized by a significant metal thinning rate with possible occurrence of wormholes or abrupt destruction of the pipeline and power-generating equipment components. Typical cases of and statistical data on damages inflicted to nuclear power plant components due to flow-accelerated corrosion are presented. The physicochemical fundamentals and regularities relating to flow-accelerated corrosion of metal occurring in one- and two-phase flows are considered. It is pointed out that the hydrodynamic factor plays the determining role in the occurrence of zones and rate of local thinning caused by flow-accelerated corrosion. The key hydrodynamic characteristics influencing the local flow-accelerated corrosion rate are determined. Fundamental differences between the mechanisms governing flow-accelerated corrosion in two-phase medium and single-phase water flow are shown. These differences stem from the specific features of hydrodynamics pertinent to the motion of liquid film and interphase redistribution of admixtures and gases that gives rise to a change in the pH value of liquid. The results from experiments aimed at studying the effect of temperature on the flow-accelerated corrosion rate of different metals in a two-phase wet steam flow and the effect of steam wetness degree on the liquid film flow mode are presented.



Flow-Accelerated Corrosion Wear of Power-Generating Equipment: Investigations, Prediction, and Prevention: 2. Prediction and Prevention of General and Local Flow-Accelerated Corrosion
摘要
The second part of this review considers physicochemical models and computer codes used for predicting flow-accelerated corrosion wear of power generating equipment. Approaches used to prevent the occurrence of general and local flow-accelerated corrosion that are based on selecting metals resistant to flow-accelerated corrosion and adjusting the water chemistry of power units are also discussed. The existing computer codes use physicochemical models of flow-accelerated corrosion and statistical data on damages inflicted to power units due to flow-accelerated corrosion processes. Advantages and drawbacks of different analytical physicochemical models describing the flow-accelerated corrosion process are pointed out together with the specific features of using them in elaborating flow-accelerated corrosion computing codes. It is shown that the processes lying at the heart of the flow-accelerated corrosion mechanism include, on the one hand, the occurrence of a protective oxide layer on the metal surface and, on the other hand, the dissolution of this layer and carryover of dissolution products in the flow. Differences between the processes through which metal undergoes flow-accelerated corrosion in a single-phase water flow and in a two-phase wet steam flow are analyzed. Thus, the redistribution of admixtures and gases between the phases that takes place in two-phase media may cause a change in the pH values, thereby significantly influencing the flow-accelerated corrosion rate. In addition, the rate with which flow-accelerated corrosion products are carried over into a two-phase stream depends on the liquid film flow mode on the streamlined surface. The flow-accelerated corrosion rate computing codes most widely known around the world, including the COMSY code (Germany), CHECWORKS SFA code (United States), BRT-CICEROTM code (France), and RAMEK code (Russia) are considered. Their specific features and application limits are pointed out. Information on the effect the content of chromium, molybdenum, and copper has on the flow-accelerated corrosion rate is given. It is shown that the choice of metals resistant to flow-accelerated corrosion is a combined technical and economic problem, and the way in which it is solved has an effect on the safety and reliability of power unit operation. It is pointed out that the liquid phase pH value is essentially affected by the steam wetness degree if the latter exceeds 20%.



Topical Problems Associated with Reliability and Safety of Equipment at Thermal Power Stations
摘要
The basic problems important for the industrial safety of equipment at thermal power stations (TPS) are formulated. The issues of determination of the residual service life of equipment experiencing high-temperature creep are examined. The correlation between the actual metal properties and the safety factor, as well as the effect of stressed state on accumulation of microdamages in the metal, are considered. The in-service margins of the high-temperature equipment are analyzed from the standpoint of the equipment fitness for service. The damage mechanism of the equipment operating at temperatures below the creep temperature is analyzed, and the in-service margin of this equipment is evaluated. Low efficiency of the examination of the metal conditions using specimens cut out from the equipment operating at moderate temperatures is stated, while strict requirements are imposed on the scope and quality of diagnostics. The current state of affairs in the field of standardization of the diagnostics and fitness for service assessment of thermal mechanical equipment is considered. It is noted that the procedure for setting up the schedule of technical diagnostics and industrial safety expertise of power equipment and the regulations for performance of these procedures have been revised. The principal provisions and requirements included in the newly introduced regulatory documents having the status of Federal Norms and Rules are examined. It is proposed to extend the terms of reference and enhance the capabilities and responsibility of expert organizations. The issues associated with ensuring the reliability of revamping and greenfield projects are analyzed. The advantages of chromium steels with increased heat-resistance in the manufacture of high-temperature equipment are demonstrated. However, the use of chromium steel in equipment with an operating temperature below 560°С is impractical from both the economic and engineering standpoint. The experience with performance of certification tests is briefly described, and the fact that this procedure enjoys current interest is demonstrated. The need is outlined for a thorough revision of the existing regulations on routine inspection and diagnostics of thermal engineering equipment because of its use in assemblies or elements made from new steels.



Energy Saving, New and Renewable Energy Sources
A Thermodynamic Analysis of a New Cycle for Adsorption Heat Pump “Heat from Cold”: Effect of the Working Pair on Cycle Efficiency
摘要
A thermodynamic analysis was carried out for a new “Heat from Cold” (HeCol) adsorption cycle for transformation of the ambient heat using the following working pairs: activated carbon ASM-35.4–methanol or composite sorbent LiCl/silica gel–methanol. Unlike the conventional cycle of an adsorption thermal engine where the adsorbent is regenerated at a constant pressure by its heating up to 80–150°C, the adsorbent in the HeCol cycle is regenerated by depressurization, which is performed due to a low ambient temperature. The balances of energy and entropy are calculated at each cycle stage and each element of the transformer under conditions of ideal heat transfer. The performance of the cycle for both pairs is compared. The threshold ambient temperature above which useful heat is not produced has been determined. The threshold values depend only on the absorption potential of methanol. It is demonstrated that useful heat with a high temperature potential of approximately 40°C can be obtained from a natural source of low-potential heat (such as a river, lake, or sea) only at a sufficiently low ambient temperature. The cycle with the composite sorbent LiCl/silica gel–methanol yielded much more useful heat than the cycle with the activated carbon ASM-35.4–methanol due to the features of the characteristic curve for methanol vapor adsorption on the composite sorbent. The amount of useful heat increases with decreasing ambient temperature and increasing temperature of the natural low-temperature heat source. The examined cycle can be used for upgrading the ambient heat temperature potential in countries with a cold climate.



A Review of Technologies for Multistage Wood Biomass Gasification
摘要
Currently, small-scale distributed power generation is being intensively developed in Russia and abroad. Given the rise in the rates for the electric and thermal energy, the development of new territories, and the technical infeasible connection to the power supply system, one of the most promising variants of supplying isolated consumers with power is the application of wood biomass gasification technologies. Analysis of the studies in this sphere shows that considerable attention is paid to enhancing the gasification efficiency and ensuring the purity of the gas. These problems are solved using multistage gasification technology. This technology involves the pyrolysis and gasification in separated zones of the gasifier or individual interconnected reactors, which enables achieving the optimal conditions for the conversion of biomass at every separate stage. The major advantage of multistage gasifiers is the production of synthesis gas with a low content of tar. The article represents a review of technologies for multistage wood biomass gasification and comparison of the relevant gasifiers of various types; the basic single-stage and multistage wood biomass gasification technologies are examined and their technical characteristics and examples of their commercial implementation are provided. Analysis of the current situation shows that predominantly foreign multistage wood biomass gasification technologies/plants have found practical application. These technologies allow the produced syngas to be directly used in internal combustion engines and gas turbines without employing expensive auxiliary detarring plants.



Steam Boilers, Power-Generating Fuel, Burners, and Boiler Auxiliary Equipment
Furnaces of the Unified-Family Drum-Type Gas-Fired Boilers
摘要
The article deals with supporting calculations of the furnace dimensions and the method for combustion of natural gas for two types of unified-family drum-type boilers with steam capacities of 75–150 and 200–320 t/h at superheat steam pressures of 3.9, 6.9, 9.8, and 13.8 MPa and temperatures of 440, 510, 540, and 560°C. An approach to unification and the requirements of environmental sustainability, economic efficiency, and flexibility and the basic engineering solutions for each boiler type are set forth. A method was proposed and implemented that allows, using the Boiler Designer software, finding the temperatures of the flue gases, hot air, and recycle gases that are necessary for conducting the thermal analysis of the boiler furnace with a single-stage tubular air preheater and determining the most rational unified design of the latter. The basic concepts and criteria are set forth that underlie the calculations of the furnace size in its plan, the furnace height, and the number and arrangement of swirl burners. With the furnace software for expanded thermal analysis of the furnace, the effect of the superheated steam pressure and the furnace height on the enthalpy increment of 1 kg of the working medium in the evaporating heating surfaces was determined for all boilers of the series in question at the nominal load under conventional fuel combustion conditions without recirculation. For the furnace outlet screen, the increment was calculated using the Boiler Designer software. The correspondence between the obtained enthalpy increments and the recommended values was evaluated. For the case of a significant divergence between the above figures, additional engineering solutions were proposed that facilitate the unification of the boilers. Based on the results of the analysis of the boiler furnaces and the expert estimations of the required convection pass height, a furnace height value was selected for each boiler group. The possibility of reducing the nitrogen oxide concentrations in the combustion products of the unified boilers was studied. The calculation investigations show that it is possible to achieve the required nitrogen oxide concentrations in all boilers at the selected furnace heights by stepwise and staged combustion or by injecting the recycle gasses into the burner box. Specific recommendations for the implementation of the above measures are provided.



Coal Slurry Drying Process Research
摘要
Heavy stocks of high-moisture coal slurries being kept on the territory of Russia should be dried prior to recycling combustion in a TTP’s pulverized coal-fired boilers. The expediency and applicability of coal slurry drying in panel steam dryers (PSD), currently manufactured by JSC Tyazhmash, is shown. The results of laboratory and bench studies of coal slurry drying with a moisture content of 22–28%, ash content of 11%, lower calorific value of 17.8 MJ/kg, and particle sizes of not more than 0.3 mm are presented. The coal slurry drying rate-versus-temperature relationship is determined in a laboratory setting. The influence of PSD drum speed, its filling degree, and water-steam mixture (WSM) (heating medium) temperature on the moisture removal rate (MRR) is examined on a specially designed test bench. It is established that the WSM temperature is insignificant with respect to the MRR, which, however, increases by approximately 1.5–2.0 times with an increase in the drum rotation. The drying rate is equal to 0.127–0.969%/min, which is 2.4–7.8 times lower than the values obtained in a laboratory setting. The MRR is determined at the level of 10 kg/(m2 h), which should be taken into account in the PSD design for coal slurry drying. To ensure the PSD capacity of 75 t/h, the drum filling degree should be 0.20–0.35, the drum angle 1°, the rotation speed 6.3–9.1 min–1, the saturated steam rate 22.5 t/h, and the rate of the drying and aerating agent at a temperature of 100°C should be approximately 12000 m3/h. Basic PSD design characteristics for the capacity of 50 and 75 t/h are given.



Heat and Mass Transfer, Properties of Working Fluids and Materials
Experimental Simulation of Hydrodynamics and Heat Transfer in Bubble and Slug Flow Regimes in a Heavy Liquid Metal
摘要
For the confirmation of the claimed design properties of a reactor plant with a heavy liquid-metal coolant, computational and theoretical studies should be performed in order to justify its safety. As one of the basic scenarios of an accident, the leakage of water into the liquid metal is considered in the case of steam generator tube decompression. The most important in the analysis of such a kind of accidents are questions concerning the motion and heat exchange of steam bubbles in the steam generator and the probability of blocking the flow area owing to freezing coolant, since the temperature of boiling feedwater in the steam generator can become lower than the melting point of lead. In this paper, we present main approaches and relationships used for the simulation of the motion of gas bubbles and heat transfer between bubbles and liquid metal flow. A brief description of the HYDRA-IBRAE/LM computational code that can be used to analyze emergency situations in a liquid metal-cooled reactor facility is also presented. It should be noted that the existing experimental data on the motion and heat transfer of gas bubbles in a heavy liquid metal are insufficient. For this reason, in order to verify the HYDRA-IBRAE/LM code models, experiments have been performed on the cooling of liquid lead by argon and on the motion of gas bubbles in the Rose’s alloy. In particular, a change in the temperature of the coolant over time has been studied, and the void fraction of gas at different flow rates of gas has been measured. A detailed description of the experiments and a comparison of the results of the calculations with the experimental data are presented. The analysis of uncertainties made it possible to reveal the main factors that exert the greatest effect on the results of calculations. The numerical analysis has shown that the models incorporated into the HYDRA-IBRAE/LM code allow one to describe to a sufficient degree of confidence the process of cooling liquid lead melt when argon bubbles pass through it, simulating the flow of water into the liquid metal in the course of steam generator tube rupture.



Steam Turbine, Gas Turbine, and Combined-Cycle Plants and Their Auxiliary Equipment
A Throttle Control Valve for Steam Turbines Operating with Large Volumetric Flowrates of Working Fluids
摘要
A new design of a throttle control valve for steam turbines with throttle steam admission and large volumetric steam flowrates is considered. The difficulty associated with using these valves is that increasing the seat dimensions of spools entails a drastic decrease in the relative valve chest free volume for steam passage. This, in turn, results not only in higher hydraulic losses in the steam admission system but also in a higher nonuniformity of steam flow in the flow paths of such valves. Both these factors facilitate generation of very high pulsations of pressure in the valve’s entire flow path, which gives rise to high levels of acoustic emission and dynamic loads acting on all components of the valve, thus degrading its vibration reliability. Along with the proposed valve design, the article considers the design version of standard balanced control valves installed in large-capacity Russian steam turbines. It is shown that the passage of large volumetric steam flowrates through standard valves entails a significant reduction in the free valve chest volume for passing steam. This results in a growth of local steam velocities inside the chest and in a more pronounced negative influence of the chest shape on the valve flowrate and vibration performance. This situation can be improved by using one of the following two ways: to make the chamber with a significantly larger structural volume (which entails a larger cost of making the chamber) or to radically change the valve design. The article considers the second approach to solving the problem. In the proposed design version, the entire valve balancing system is shifted to the valve chest upper part, and the guide bonnet is made with large lateral ports ensuring free passage of steam to the diffuser seat. To achieve a more uniform circumferential field of velocities in the valve flow path, its cup is made with two perforation belts, the holes of which are connected to a common damping chamber, and the chamber itself is connected via a hollow cylinder with the axial force relief system.



Environment Conservation
A Study of the Absorption of Nitrogen Oxides from the Boiler Flue Gases
摘要
In the past decade, the number of unsolved ecological problems has been steadily increasing. Among the numerous causes of this situation, the exposure of the environment to industrial waste should be mentioned. For example, enterprises of the fuel and energy industry emit a significant amount of hazardous substances into the atmosphere. Flue gases formed in boiler-houses and at thermal power stations get through flue gas stacks into the upper atmosphere and pollute it. In this work, a method is proposed for adsorption treatment of the flue gases from boilers fired with associated petroleum gas. The chemical composition of the associated petroleum gas of Romashkino oil field, the Republic of Tatarstan, is presented and the practicality of its use is demonstrated. Nitrogen oxides contained in the boiler flue gases result from oxidation of molecular air nitrogen during combustion of the fuel. In order to reduce the adverse effect of hazardous substances on the environment, the flue gases are to be compulsorily cleansed of nitrogen oxides. The use of the sludge resulting from coagulation and liming of natural water during the chemical water treatment at Kazan CHPP-1 as a sorption material is proposed. The chemical composition and technical characteristics of the sludge are presented. The properties of the sludge were studied using a laboratory fixed-sorbent-bed setup. The sorption capacity and water-absorption of the sludge were determined and curves of the kinetic and isothermal dependences of the nitrogen oxide adsorption by the sludge were constructed. The change in the nitrogen- oxide sorption capacity of the sludge depending on the sludge particle size was established. The optimal characteristics of a batch-type fixed-bed absorber were calculated. The results of calculating the economic and ecological effects of introducing the adsorption treatment of flue gases to remove nitrogen oxides for the boiler-house of AO Karpov Chemical Plant are provided.


