Steam Generators In Power Plants Research Articles

Physical and Numerical Modelling of Internal Aerodynamics of the Vortex Furnace with Distributed Tangential Input of Burner Streams

The work is devoted to experimental and numerical modelling of internal aerodynamics of a new type furnace for the thermal power plant steam generator with technology of pulverized-coal combustion in vortex flow. Measurements of aerodynamic features of the flow in the laboratory air isothermal model of the furnace have been performed with twocomponent laser Doppler velocimeter. Numerical simulation of three-dimensional turbulent isothermal flow in the laboratory model has been carried out with the use of CFD package FLUENT. Detailed 3-D flow structure in the studied model has been obtained. The agreement between numerical predictions and measurements on mean flow velocity distributions has been shown

Prime Energy Challenges for Operating Power Plants in the GCC

There is a false notion of existing available, abundant, and long lasting fuel energy in the Gulf Cooperation Council (GCC) Countries; with continual income return from its exports. This is not true as the sustainability of this income is questionable. Energy problems started to appear, and can be intensified in coming years due to continuous growth of energy demands and consumptions. The demands already consume all produced Natural Gas (NG) in all GCC, except Qatar; and the NG is the needed fuel for Electric Power (EP) production. These countries have to import NG to run their EP plants. Fuel oil production can be locally consumed within two to three decades if the current rate of consumed energy prevails. The returns from selling the oil and natural gas are the main income to most of the GCC. While NG and oil can be used in EP plants, NG is cheaper, cleaner, and has less negative effects on the environment than fuel oil. Moreover, oil has much better usage than being burned in steam generators of steam power plants or combustion chambers of gas turbines. Introducing renewable energy or nuclear energy may be a necessity for the GCC to keep the flow of their main income from exporting oil. This paper reviews the GCC productions and consumptions of the prime energy (fuel oil and NG) and their role in electric power production. The paper shows that, NG should be the only fossil fuel used to run the power plants in the GCC. It also shows that the all GCC except Qatar, have to import NG. They should diversify the prime energy used in power plants; and consider alternative energy such as nuclear and renewable energy, (solar and wind) energy.

Fluidelastic Instability Modeling of Loosely Supported Multispan U-Tubes in Nuclear Steam Generators

Steam generators in nuclear power plants have experienced tube failures caused by flow-induced vibrations. Two excitation mechanisms are responsible for such failures; random turbulence excitation and fluidelastic instability. The random turbulence excitation mechanism results in long-term failures due to fretting-wear damage at the tube supports, while fluidelastic instability results in short-term failures due to excessive vibration of the tubes. Such failures may require shutdowns, which result in production losses, and pose potential threats to human safety and the environment. Therefore, it is imperative to predict the nonlinear tube response and the associated fretting-wear damage to tubes due to fluid excitation. In this paper, a numerical model is developed to predict the nonlinear dynamic response of a steam generator with multispan U-tubes and anti-vibration bar supports, and the associated fretting wear due to fluid excitation. Both the crossflow turbulence and fluidelastic instability forces are considered in this model. The finite element method is utilized to model the vibrations and impact dynamics. The tube bundle geometry is similar to the geometry used in CANDU steam generators. Eight sets of flat-bar supports are considered. Moreover, the effect of clearances between the tubes and their supports, and axial offset between the supports are investigated. The results are presented and comparisons are made for the parameters influencing the fretting-wear damage, such as contact ratio, impact forces, and normal work rate. It is clear that tubes in loose flat-bar supports have complex dynamics due to a combination of geometry, tube-to-support clearance, offset, and misalignment. However, the results of the numerical simulation along with the developed model provide new insight into the flow-induced vibration mechanism and fretting wear of multispan U-tubes that can be incorporated into future design guidelines for steam generators and large heat exchangers.

Assessment of Remaining Useful Life of Power Plant Steam Generators – a Standardized Industrial Application

The Web based condition monitoring and diagnostic system “Boiler Fatigue Monitoring” enables on-line assessment of cumulative boiler creep and low cycle fatigue according to the European standard EN 12952-3/4 issued in 2001.The application is employed as autonomous module as well as fully integrated into the Siemens process control system SPPA-T3000 and is becoming more and more a standard part of the power plant instrumentation and control (I&C).The Fatigue Monitoring System (FMS) is a standard industrial application for both, new built power plants and retrofits of existing units of any kind. The system is not limited to Siemens I&C systems, it is possible to integrate FMS also into power plants with I&C systems of other suppliers. FMS is also capable for calculating the remaining lifetime for boilers designed according to the American standard ASME VIII-2.

고온, 고압 알칼리 수용액에서의 Alloy 600 산화막 특성에 미치는 납 농도 영향

0.1 M NaOH 용액에 PbO첨가양이 증가함에 따라 Alloy 600에 형성되는 산화막의 부동태 피막 특성이 열화되었다. 또한 뚜렷한 2중층 구조의 산화막이 점차 사라지고, 산화막내 존재하는 납의 양이 증가하였다. 산화막 내부 납의 양이 증가함에 따라 산화막 내부 니켈의 결핍이 점차 커졌다. 납에 의해 산화막의 부동태 특성이 약화됨에 따라, 응력부식균열 저항성 또한 급감하였을 것으로 판단된다. Outer diameter stress corrosion cracking (ODSCC) has occurred for Alloy 600 (Ni 75 wt%, Cr 15 wt%, Fe 10 wt%) as a heat exchanger tube of the steam generator (SG) in nuclear power plants (NPP) during long term operation. Among many causes for SCC, lead (Pb) is known to be one of the most deleterious species in the secondary system. In the present work, the oxide formed on Alloy 600 was characterized as a function of the PbO content in 0.1 M NaOH at <TEX>$315^{\circ}C$</TEX> by using an electrochemical impedance spectroscopy (EIS), a transmission electron microscopy (TEM), equipped with an energy dispersive x-ray spectroscopy (EDS). The oxide property was analyzed in view of SCC susceptibility.

고온 고압 환경에서 인코넬 690 재료의 프레팅 마모 특성에 관한 실험적 연구

증기 발생기 내부의 U-tube와 지지 구조간의 충격에 의하여 발생하는 프레팅 마모는 원자력 발전소 안전성에 영향을 미치게 된다. 증기발생기의 신뢰성을 향상시키기 위하여 이러한 프레팅 마모 현상을 평가하는 것이 필요하며, 본 연구는 프레팅 마모현상을 정성적, 정량적으로 규명하기 위하여 증기발생기의 실제 상황과 같은 조건의 온도와 압력하에서 실험을 수행하였다. 다양한 실험조건에 대하여 기본적인 실험을 수행하였으며 일률과 마모량의 관계를 온도에 따라 구하였다. 90℃, 200℃, 340℃ 각각의 온도에서의 마모상수는 9.051x10<SUB>-16</SUB> Pa<SUB>-1</SUB>, 3.009x10<SUP>-15</SUP> Pa<SUP>-1</SUP>, 2.235x10-15 Pa-1 로 구해졌으며 특히 저온 수중상태의 마모상수는 물의 점도의 영향으로 상온 공기중의 값보다 작은 것으로 나타났다.

In situ X-ray absorption spectroscopy for identification of lead species adsorbed on a nickel surface in acidic perchlorate solution

In situ X-ray absorption spectroscopy (XAS) using a synchrotron radiation was applied to identify the Pb species adsorbed on Ni surface in acidic perchlorate solution containing 10−4MPb2+ with relation to the Pb-induced stress corrosion cracking (Pb-SCC) of Ni-base alloys used as tubing materials of steam generators in nuclear power plants. The periodical emersion method under potentiostatic polarization, using the Ni plate with large specific surface area (surface roughness, Sr=78.3) as a working electrode, was developed to detect sensitively the sub-monolayer coverage of Pb on Ni. The Pb LIII absorption spectra in a scanning XAS mode were measured by monitoring the Pb Lα fluorescence line. The Pb LIII absorption near-edge structure (XANES) at the potential more positive than −0.245V (SHE) corresponding to the equilibrium potential of Pb-electrodeposition in 10−4MPb2+ solution has revealed that the Pb species adsorbed on the Ni surface are metallic, providing the clear evidence of underpotential deposition (UPD) of Pb on the Ni surface. Moreover, the extended X-ray absorption fine structure (EXAFS) analysis was performed with a two-shell fit involving Pb–Ni and Pb–Pb interactions assuming that the Ni (111) plane is mainly exposed to the solution. The EXAFS results were convincingly explained in terms of the Pb-UPD model which represents the coexistence of the surface alloy phase and the adlayer with the same p(2×2) structure in the narrow potential range of −0.185V (SHE) to −0.245V (SHE).

A robust method for coupling detection among process variables

Investigating complex interaction patterns among multiple process variables (PVs) is an important task. This paper demonstrates a robust method to estimate direction and strength of interactions among process variables. The method captures rapid changes in process variables through wavelet analysis. It uses single degree of freedom (SDOF) modelling to approximate a non-linear system in terms of linear damped forced oscillators. Phase interaction theory then extracts coupling direction and strength among process variables. The robustness of the proposed technique is verified on simulated Van der Pol oscillators with known directionality and coupling strength with varying signal to noise ratio (SNR). The effectiveness and feasibility of the proposed method have also been demonstrated on simulated data emanating from Canada Deuterium Uranium (CANDU) nuclear power plant steam generator level control mechanism. The extracted patterns of interaction structure among PVs aid to uncover the polishing mechanisms and provide more insights to investigate fault propagation scenarios.

An Inverse Control-Based Set-Point Function for Steam Generator Level Control in Nuclear Power Plants

In this paper, the water level control problem of U-Tube Steam Generators (UTSG) of Nuclear Power Plants (NPP) is addressed through the design of an innovative set-point function; hence, the original architecture of the controller is retained for easy industry acceptance. The set-point function is synthesized based on the inverse-control theory, which is able to improve the transient performance of the UTSG level subject to power adjustments. Based on the lead time between the power adjustment decision and the actual initiation of the adjustment, the proposed set-point function can apply appropriate control on the feed-water flow rate preemptively. This preemptive control action allows the steam generator to prepare itself for the upcoming power change, i.e., steam flow-rate change, to minimize the transient effects. Detailed design and simulation processes are described based on Irving UTSG model under the entire operating power range. The simulation studies have shown that the proposed scheme is capable of keeping the water level within the admissible range effectively. When compared with a swell-based set-point function, the proposed scheme can reduce the percentage overshoot and undershoot by as much as 35.4% and 69.7%, respectively.

Effect of Electrode Coatings on Diffusible Hydrogen Content, Hardness and Microstructures of the Ferritic Heat Affected Zones in Bimetallic Welds

Bimetallic welds (BMWs) have been a necessity within the steam generators of nuclear power plants, where the heavy section low alloy steel components are usually connected to stainless steel primary piping systems. These welds represent zones with metallurgical discontinuities, which tend to localize the strains and cause failures. The other critical issues which must be taken care of while welding of bimetallic joints include solidification cracking, thermal fatigue and residual stresses in welds. The occurrence and severity of all these problems associated with bimetallic welds depend upon the type of welding process used along with the other variables like welding consumables, heat input etc. In shielded metal arc welding (SMAW), welding electrode consumables/coatings play an important role in deciding the weld metal quality. The development of welding electrode coatings is quite difficult due to very rapid complex reactions taking place during welding and the involvement of many controlled process variables. The present paper is an effort to highlight the general issues and challenges for the systematic and scientific development of welding electrode coatings for bimetallic welds. The experimental procedure contains three sets of coated electrodes having varying ferro-alloys, silica and carbon content. In the first set of electrodes, non-ferrous elements are also introduced into the weld metal through flux addition. Further, the welded joints are subjected to various tests and then evaluated to ascertain their mechanical as well as metallurgical behaviour.

ABRASIVE BLASTING TECHNOLOGY FOR DECONTAMINATION OF THE INNER SURFACE OF STEAM GENERATOR TUBES

The inner surfaces of bundled inconel tubes from steam generators in South Korean nuclear power plants are contaminated with cobalt and abrasive blasting equipment has been developed to efficiently remove the cobalt. The principal parameters related to the efficient removal using this equipment are the type of abrasive, the distance from the nozzle, and the blasting time. Preliminary tests were performed using oxidized inconel samples which enabled the simulation of cobalt removal from the radioactive inconel samples. The oxygen in the oxidized samples and the cobalt in the radioactive inconel were removed more effectively using the blasting distance, blasting time, and a silicon carbide abrasive. Using the developed abrasive blasting equipment, the optimum decontamination conditions for radioactive inconel samples were blasting for more than 6 minutes using silicon carbides under 5 atmospheric pressures.

Failure Analysis of Low Pressure Evaporator Tubes in a Typical Combined Cycle Power Plant

Flow-induced corrosion is one of the most prevalent tube damage mechanisms in steam generators of power plants. In this study, tube failure of a steam generator in Fars Combined Cycle Power Plant is evaluated. In addition to analysis of the measured tube thicknesses and the failure statistics data, computational fluid dynamic (CFD) methods are used to simulate flow distribution inside and outside of the tubes in one header of the low pressure circuit of the plant steam generator. The results show that regarding the created two-phase flow pattern inside the tubes, the droplet impingement erosion is the main source of tube failures in the bending areas where the extrados surface of the tubes are partially prone to the droplets. The results are useful for modifying the design of the steam generator from different viewpoints such as, optimal design for appropriate configuration of downcomer, header and footer and tube bending. Also, selecting suitable material for the steam generator tubes and implementation of protective coating in risky areas would benefit from the present results.

An experimental study on fretting wear behavior of cross-contacting Inconel 690 tubes

A fretting wear test rig employing a piezoelectric actuator has been developed, which is equipped with a heating and water circulation system. The fretting wear tests of cross-contacting Inconel 690 tubes, which is widely used for power plant steam generator, have been carried out in room temperature ambient and 80 °C in-water conditions. Maximum normal load was 55 N, and the sliding amplitude was below 50 μm. Scars of the mixed-slip and the gross-slip fretting wear have been measured in terms of scar diameter and wear volume. From the relationship between the work rate and the wear rate, a threshold of work rate has been defined, and this is found to be closely related with fretting wear regimes. The wear coefficients have been evaluated in the gross-slip regime. Distinct fretting wear mechanisms have been observed for the two different test conditions from SEM microphotographs. The crack formation, large particle separation and resulting third body effect were significant in room temperature ambient condition. The protective nature of the tribologically transformed layers coupled with non-uniform contact results in the lower wear coefficient while smooth wear scar and extensive abrasion produces higher wear volume in the other condition.

증기발생기 전열관 재료의 2차측 응력부식균열 민감성

Alloy 600 (Ni 75 wt%, Cr 15 wt%, Fe 10 wt%) as a heat exchanger tube of the steam generator (SG) in nuclear power plants (NPP) has been degraded by various corrosion mechanism during the long-term operation. Especially lead (Pb) is known to be one of the most deleterious species in the secondary system causing outer diameter stress corrosion cracking (ODSCC). Oxide formation and breakdown is requisite for SCC initiation and propagation. Therefore it is expected that a property change of the oxide formed on SG tubing materials by lead addition into a solution is closely related to PbSCC. In the present work, the SCC susceptibility was assessed by using a slow strain rate test (SSRT) in caustic solutions with and without lead for Alloy 600 and Alloy 690 (Ni 60 wt%, Cr 30 wt%, Fe 10 wt%) used as an alternative of Alloy 600 because of outstanding superiority to SCC. The results were discussed in view of the oxide property formed on Alloy 600 and Alloy 690. The oxides formed on Alloy 600 and Alloy 690 in aqueous solutions with and without lead were examined by using a transmission electron microscopy (TEM), equipped with an energy dispersive x-ray spectroscopy (EDXS).

New technology for purging the steam generators of nuclear power plants

A technology for removal of undissolved impurities from a horizontal steam generator using purge water is developed on the basis of a theoretical analysis. A purge with a maximal flow rate is drawn off from the zone with the highest accumulation of sludge in the lower part of the steam generator after the main circulation pump of the corresponding loop is shut off and the temperatures of the heat transfer medium at the inlet and outlet of the steam generator have equilibrated. An improved purge configuration is used for this technology; it employs shutoff and regulator valves, periodic purge lines separated by a cutoff fixture, and a D{sub y} 100 drain union as a connector for the periodic purge. Field tests show that the efficiency of this technology for sludge removal by purge water is several times that for the standard method.

Selection of Steam Drum Level Control Method for Multiple Drum Interacting Loops Pressure Tube-Type BWR

Three element Steam Drum (SD) Level Controller has been conventionally used for most of the boilers, Nuclear power plant steam generator & Boiling Water Reactor (BWRs). Based on the process dynamic studies it was found that this scheme does not work properly for an interacting, interconnected multiple loop boiling water system i.e., Advanced Heavy Water Reactor (AHWR). It is a pressure tube type light water cooled heavy water moderated Boiling Water Reactor (BWR). It has 4-inter-connected parallel loops with 113 × 4 = 452 boiling channels in the Main Heat Transport (MHT) system. These multiple (four) interconnected loops influences the Steam Drum (SD) level control adversely. Such a behavior has not been reported in the open literature. The open loop response is stable, non-oscillatory and non-diverging for a step change in the feed flow rates. Also it is not possible to maintain a steady level in all the SDs even without any external disturbance/perturbation with 4 conventional 3-element individual SD level controllers. To overcome these interactions it is proposed to interconnect all the four steam drums in the liquid & vapor regions respectively. This makes the 4 SDs behave like a single entity. The influence of the interconnect configuration & the level controller are studied in detail to find a robust solution. The response obtained for unsymmetrical core power, symmetrical power maneuvering and reactor trip transients shows that the SD levels do not diverge and quickly settle very near to the set points assigned with SD interconnect schemes.

Thermoeconomic optimisation of heat recovery steam generators of combined cycle gas turbine power plants considering off-design operation

One of the practical uses of the thermoeconomic models is to find a trade-off between efficiency and cost in the design of a power plant. Usually, the thermoeconomic analyses involve a thermodynamic model of the power plant and an economic model dedicated to assess the costs. In combined cycle gas turbine (CCGT) power plants, the thermodynamic model usually calculates the performance and the energy balances of the power plant at the design conditions. However, nowadays, after several years of CCGTs operation experience, data of annual operation may be found, which differ to some extent from the design conditions. This paper shows a methodology to achieve thermoeconomic optimisations of CCGT power plants taking into account the frequent off-design operation of the plant. Therefore, the aim of the work is to improve the thermoeconomic design of the power plant by means of considering a more realistic annual operation scenario. In addition, the methodology is applied to optimise several CCGT configurations operating under different scenarios of energy production. The results of the optimisations are compared to those obtained with usual thermoeconomic models based on design conditions performance.

Magnetic testing of creep deterioration

In this work a new magnetometer setup and a novel model based data evaluation technique was used to determine the creep damage in ferritic power plant steel. The tested material was lCr-0.5Mo-0.25V ferritic steel which is commonly used as pipeline base material of steam generators in power plants. It is commonly accepted that a combined form of fatigue and the creep processes cause the deterioration of this structural parts due to long time elevated temperature service. Nowadays, there is increasing need for remaining lifetime estimation of these engineering structures. In this paper, the variation of magnetization curves of Cr-Mo-V ferritic steel due to creep measured and the relation between creep damage and the magnetic property changes is discussed. A new data evaluation technique is presented which is based on the hyperbolic model of magnetization. A magnetic descriptor was derived from the hyperbolic model which can be determined from the initial part of the normal magnetization curve. The introduced parameter and evaluation technique seems to be especially useful for magnetic nondestuctive remanent lifetime evaluation.

A study on fretting fatigue characteristics of Inconel 690 at high temperature

Inconel 690 alloy is used in nuclear power plant steam generator tubes. Fretting fatigue experiments were performed on Inconel 690 specimens at room temperature and at the nuclear power plant operating temperature of 320 °C. By comparing the fretting fatigue test data at room temperature and 320 °C, this study analyzed the change in characteristics related to the fatigue limit at 10 7 cycles. In addition, this study attempted to measure changes in the friction force for repetitive cycles in fretting fatigue tests, and analyzed the mechanism of fretting fatigue by observing the fracture surfaces and performing spectrum analysis.

Numerical model for estimation of corrosion location in nuclear power plant steam generators

Deposition of dissolved impurities and corrosion in steam generators is a significant problem in the operation of nuclear power plants. Impurities and corrosion products usually accumulate in the secondary sides of steam generators (SG) and form deposits on the SG surfaces. A high level of impurity concentration close to the SG heating surface causes the corrosion process to occur with more intensity. The aim of this study is to estimate the most probable locations of impurity concentration and deposition in a SG. Equations representing the convection and diffusion in the liquid phase close to the heated surface (the viscous sub layer) are derived. Based on the mass balance of impurities in the viscous sub layer as the boundary condition, the derived differential equations are solved by the finite volume (upwind) methods. The distribution of impurities, sediment formation rate and the location of the depositions in the viscous sub layer at different heat flux values are studied in steady and unsteady states.