Moisture Separator Research Articles

Heat transfer characteristics in super-low finned-tube bundles of moisture separator reheaters

Abstract Experimental investigation on the heat transfer characteristics of superheat vapor through a new designed moisture separator reheater with “super-low” finned-tube bundles for Generation III+ nuclear power plant, was carried out based on a 5*30 tube bundle test section. Impacts of the vapor mass flow rates are analyzed on the heat transfer characteristics of superheat vapor through the finned-tube bundle. A group of experiments are reviewed on single-phase fluid flowing across the triangular super-low finned-tube bundles whose fin heights are less than 2.75 mm and ratios of fin height to fin diameter are from 0.05 to 0.15. Combining the presented experimental data with the other open published data for single-phase turbulent gases flowing across triangular super-low finned-tube, a new heat transfer correlation is proposed for the MSRs super-low finned-tube bundles, which shows better accuracy and has wider Reynolds number range in application.

Numerical investigation of the performance of moisture separators based on two-way coupling model by Lagrangian-Eulerian methodology

Moisture separator is one of the crucial equipment of the pressurized water reactor (PWR) nuclear power plant. In the separators, droplets could be regarded as the dispersed phase in terms of the gas–liquid two-phase flow. In order to predict the pressure drop of the droplet-laden flows in a more reasonable way, a fully two-way momentum coupling model based on the Lagrangian-Eulerian methodology is established. Then, a skilled self-programming code is implemented into the commercial CFD software FLUENT by the interface called User Defined Function (UDF) to solve this two-way coupling model. In the model application part, we first perform the numerical investigation of three different kinds of wave-type separators. The magnitude of the modeling separation efficiency and the changing trend of the pressure drop are in good agreement with the experimental data. Second, the gas–liquid flow in a swirl-vane separator is simulated under different operation conditions. The maximum relative error of the pressure drop by the two-way coupling model is over two times less than the simulation results by the one-way coupling model. Hence, the results show that the two-way coupling model, as well as the UDF solving program, performs a more comprehensive approach for the modeling of the gas–liquid two-phase flows in the moisture separators.

Numerical simulation of drainage performance in a drain device of steam generator

As the last stage of a moisture separator, the drain device is an important part of the secondary separator which can affect the separation efficiency. The emphasis of this paper is placed on studying the flow structure and predicting the free liquid surface height in the drain device. Four different turbulence models including k-ε, k-ω, Shear Stress Transport (SST) and Scale-Adaptive Simulation (SAS-SST) were used to simulate the drainage process with air-water mixture (cold state) under ambient temperature and atmosphere pressure. These models were validated by the experimental data obtained in our previous study. Simulation results showed that the free liquid surface height predicted by the SAS-SST model is in best agreement with the experimental results under cold state. Therefore it was further used to perform the simulation for steam-water mixture (hot state) under the standard working condition (138.1 m3/h, 7 MPa and 285.8 °C). The maximum free liquid surface height is simulated to be 269.3 mm for the hot state by the SAS-SST model which is 4.5% higher than that of the cold state. However, it could also meet the design object.

Study on separation abilities of moisture separators based on droplet collision models

Moisture separators are widely used for eliminating the droplets from the gas–water/steam mixture flows. The volume fraction of droplets is often not small in most separators, so the collision behavior of droplets is crucial in changing their velocity, size and number distributions to affect the separation abilities of these separators. In this paper, the collision models of droplets are established to simulate the droplet-laden flows in the moisture separators. First, a stochastic searching algorithm to find the collision droplet pairs is performed by utilizing the collision kernels and defining the mean free path of a droplet. Second, the criteria to distinguish the different regimes of binary droplet collision are carried out. The regime map drawn by these criteria is highly consistent with that from previous experiments. Third, a set of formulas to predict the velocity, size and number distributions of droplets after bouncing, coalescence, reflexive and stretching separation are proposed based on the conservation law and some empirical relations. Finally, the separation abilities of the cyclone and swirl-vane separators are investigated by simulating the droplet-laden flows coupled with the droplet collision models. As for the cyclone, the simulation separation efficiencies are in good agreement with the experimental data. It is further shown that the separation efficiency curve begins to climb up very quickly in the region with small droplet diameters, and then keep constant as the droplet diameter increasing. As for the swirl-vane separators, the simulated separation efficiencies are little larger than those of the experiment within 5% difference, which is mainly due to the fact that coalescence dominates the collision behaviors from the simulation results. The theoretical and simulation results show that these collision models present a new view to study the flowing behaviors of the droplets in the moisture separators.

Nondestructive testing of moisture separator reheater tubing system using Hall sensor array

This paper presents a nondestructive testing system for inspecting the moisture separator reheater (MSR) tubing system in a nuclear power plant. The technique is based on partial saturation eddy current testing in which a Hall sensor array is used to measure the radial component of the electromagnetic field distributed in the tubes. A finned MRS tube of ferritic stainless steel (SS439) with artificial, flat–bottom hole-type defects was used in the experiments. The results show that the proposed system has potential applications in the MSR system or ferromagnetic material tubes in general, which could detect the artificial defects of about 20% of the wall thickness (0.24 mm). Furthermore, the defect volume could be quantitatively evaluated.

Numerical Investigation of Moisture Separators with Corrugated Plates

Abstract The moisture separator is widely used in nuclear power plants to remove entrained water droplets from two phase flow. The present work presents a comparative analysis of the performance of three types of separators with corrugated plates. The effects of inlet velocity and plate spacing on the pressure drop and separation efficiency have been numerically investigated by applying the realizable k - ɛ model and discrete phase model. The results show that the pressure drop and separation efficiency of the separator with hooks is the highest of the three types of separators at the same inlet velocity and plate spacing. The predicted pressure drop and separation efficiency for the three types of separators are enhanced with the increase of inlet velocity. And the reduction in plate spacing increases the pressure drop and separation efficiency. Besides, the separation efficiency of the large-scale droplets is higher than that of the small-scale droplets for the same inlet velocity.

Laboratory model study of newly deposited dredger fills using improved multiple-vacuum preloading technique

Problems continue to be encountered concerning the traditional vacuum preloading method in field during the treatment of newly deposited dredger fills. In this paper, an improved multiple-vacuum preloading method was developed to consolidate newly dredger fills that are hydraulically placed in seawater for land reclamation in Lingang Industrial Zone of Tianjin City, China. With this multiple-vacuum preloading method, the newly deposited dredger fills could be treated effectively by adopting a novel moisture separator and a rapid improvement technique without sand cushion. A series of model tests was conducted in the laboratory for comparing the results from the multiple-vacuum preloading method and the traditional one. Ten piezometers and settlement plates were installed to measure the variations in excess pore water pressures and moisture content, and vane shear strength was measured at different positions. The testing results indicate that water discharge–time curves obtained by the traditional vacuum preloading method can be divided into three phases: rapid growth phase, slow growth phase, and steady phase. According to the process of fluid flow concentrated along tiny ripples and building of larger channels inside soils during the whole vacuum loading process, the fluctuations of pore water pressure during each loading step are divided into three phases: steady phase, rapid dissipation phase, and slow dissipation phase. An optimal loading pattern which could have a best treatment effect was proposed for calculating the water discharge and pore water pressure of soil using the improved multiple-vacuum preloading method. For the newly deposited dredger fills at Lingang Industrial Zone of Tianjin City, the best loading step was 20 kPa and the loading of 40–50 kPa produced the highest drainage consolidation. The measured moisture content and vane shear strength were discussed in terms of the effect of reinforcement, both of which indicate that the multiple-vacuum preloading method has a better treatment effect not only in decreasing the moisture content and increasing the bearing capacity, but also in increasing the process uniformity at different depths of foundation.

Improvement of very soft ground by a high-efficiency vacuum preloading method: A case study

ABSTRACTThis paper describes a full-scale test on a very soft clay ground around 70,000 m2, which is conducted in Huizhou of Guangdong Province, China, to present a new method of vacuum preloading method. A novel moisture separator was developed, which can automatically regulate the vacuum pressure variation by changing the volume of the gas inside it. A large quantity of water drained by the proposed moisture separators can be directly used as a surcharge loading, which would shorten the ground improvement time and save costs as well. Three levels of silt-prevention prefabricated vertical drains were used in the treating process to accelerate the consolidation. In addition, the vacuum preloading method also included an effective radial drainage device which would strengthen the dredged soft clay fill in a deep layer. In the in situ test, tens of piezometers and settlement plates were installed to measure the variations of excess pore water pressures and settlement of two stages of observation points at different positions in the ground. The results show that the largest average consolidation settlement was 314.1 cm and made a saving of more than 66% in power consumption compared with traditional method. It demonstrates that this adopted method is an efficient, cost-effective, and environmentally friendly method for improving sites with low bearing capacity and high compressibility soils.

Study on working mechanism of AP1000 moisture separator by numerical modeling

AP1000 (Advanced Passive 1000) moisture separator that consists of primary, gravity and secondary separators is a crucial device to eliminate droplets from steam and supply dry-saturated steam to turbines. In order to understand the working mechanism of AP1000 moisture separator, droplet-laden flows are simulated in moisture separators based on the Lagrangian–Eulerian approach. In terms of details, the actual droplets are represented by parcels whose equations of motion are cast in a set of ordinary differential equations (ODEs), and the steam phase is described by Reynolds-Averaged Navier–Stokes (RANS) equations. Particularly, the numerical stability of solving the ODEs by using a fourth-order Runge–Kutta scheme is analyzed by a theoretical method in order to increase the time step size to save the computational time. Further, a distinct algorithm is introduced to rise the execution speed of locating a droplet in the grid by about 6000 times. The results show that, firstly, the separation efficiency of primary separator is beyond 90%. According to the moisture distribution on the x–z plane, the swirl-vanes placed in the inner barrel indeed play an important role to eliminate droplets. Secondly, the gravity space has no separation function, but it can make droplets follow the steam without speed disparity. Thirdly, the separation efficiency of the secondary separator is about 25%. This low value is attributed to the fact that only the hooks at the first and third stages can trap droplets.

Root cause analysis of the folding deformation for the expansion joint in the nuclear power station

In the nuclear power station, the expansion joint of moisture separator re-heater (MSR for short) was founded locally folding deformation under the outage condition. Folding deformation increasing will lead expansion joint leak, it would cause emergency stop when leaking seriously. To solve these problems, this paper analysis mainly on three aspects: the material organization performance, the expansion joint installation and the stress characteristic of expansion joint. Both the verticality deviation in the process of installation and the material hardness value exceed standard are the root cause of these problems. At the end of the paper, the improvements have been put forward for this problem.

Structure modification and numerical study of the moisture-separation performance of special crossunder pipe separators for nuclear power steam turbines

The present paper investigated the enhancement of moisture-separation efficiency for ordinary special crossunder pipe separators (SCRUPSs) and proposed three structure-modified separators (combined separator, Z-shaped SCRUPSs, and spiral-type SCRUPSs). Deposition mechanisms for droplets with different sizes were considered using commercial CFD flow solver. Results show that three-structure modified separators can increase droplet deposition rate to varying degrees. Regarding flow losses, spiral-type SCRUPSs cause the highest increase, with a total pressure loss coefficient of 231%, although it has the best deposition rate improvement. Among the three structure-modified separators, "Z" shape separator has the best separation performance because of its higher moisture-separation efficiency and lower total pressure loss efficiency. Results could provide theoretical basis for research on and development of this new type of moisture separator.

Simulating particle collision process based on Monte Carlo method

Particle collision is non-trivial in many processes occurring in nuclear power system. A new particle collision algorithm has been carried out based on Monte Carlo approach under Lagrangian methodology. According to different collision kernel, the traveling time that a particle experiences between two neighborhood collision events is obtained in a more physical way than that in the current standard algorithm of O'Rourke. Besides, the outcomes of particle collision are acquired by proper collision models in choosing collision pairs, which are picked up by calculating the colliding times between two particles in each pair. To evaluate the performance of this new algorithm, first, a simulation for the total number changing with time of Brownian aerosols is compared with analytical solution. And the modeling result and the analytical formulation are in excellent agreement. Second, two mutual-impingement sprays are simulated by the new collision algorithm against that of O'Rourke. Then the modeling results are compared with experimental data, and it is found that the shapes of the mutual-impingement sprays obtained by the new algorithm are much better than that got by O'Rourke algorithm. Moreover, in order to investigate the working mechanism of the secondary moisture separator of AP1000, this new collision algorithm is applied to model the distribution of droplets moving in it. These modeling cases above show that the new collision algorithm is useful for numerical analysis, some kinds of particle-laden flows within particle collision process, such as sprays and droplet-steam flows, etc.

F214 湿分分離性能向上のための液滴径粗大化機構に関する研究(OS9 熱・流動(4))

The moisture separator reheater (MSR) is a facility which is used to improve the thermal efficiency for the nuclear power plant. We have been developing the technique to improve moisture separation efficiency of MSR using wire-mesh combined with wave-shaped vanes. The goal of this study is to clarify the wire-mesh configurations which can minimize the exit moisture by droplet diameter measurement under a dispersed flow condition which was made by air and water from a spray nozzle. The results showed that droplet diameters were increased as the number of layer was increased. Within our experiment range, the wire-mesh configuration which has more than three layers yields the increase of the droplet diameter. Besides, although the increasing flow velocity caused generation of small droplets, it was indicated that the velocity range which keeps droplets coarse, can expand using means of increasing layer of the mesh.

Modeling droplet-laden flows in moisture separators using k-d trees

Moisture separators, such as cyclone and swirl-vane separators, are crucial devices that are used for eliminating droplets in flows, and supply dry-saturation steam for turbines. In this paper, droplet-laden flows were simulated in cyclone and swirl-vane separators based on Lagranian–Eulerian approach. With respect to details, the actual droplets are represented by some characteristic droplets, and the carrier phase is described by Reynolds-Averaged Navier–Stokes (RANS) equations. Our solving routine of the model was coupled with the commercial CFD (computational fluid dynamic) softwares, which were used to calculate the fluid properties of the carrier phase and store them on the mesh grids. However, the CFD softwares could hardly export the grids in an explicit data structure. Therefore, we carried out a data structure called k-d trees to rearrange the grids. Firstly, the results show that the executing speed of our new solver using k-d trees is thousands times larger than the old approach. Secondly, we computed the separation efficiencies of cyclone and swirl-vane separators. Thirdly, our modeling outcomes are verified against experimental data. Finally, the moisture distributions of the separators were analyzed.

Optimization of a moisture separator reheater

The optimization of component size aimed to minimize the weight and volume is an important issue to a nuclear power plant design. The optimization algorithm is applied to determine the optimum structural and operation parameters of components in order to reduce the difficulty of manufacture and transport of large components in those nuclear power plants with high powers. A preliminary optimal design is performed on the moisture separator reheater of Qinshan I nuclear power plant in this paper. A self-adapting multi-complex-shape algorithm has been developed and coupled with the thermal mathematical model of the moisture separator reheater, written in C#. The steady-state thermal mathematical model of moisture separator reheater is used to estimate the weight of moisture separator reheater according to the variation of a given number of structural and operation parameters. Then, the thermal mathematical model coupled with the self-adapting multi-complex-shape algorithm permits a set of best structural and operation parameters of the moisture separator reheater to be determined. The results clearly show that there is plenty of potential to improve the design of moisture separator reheater, while satisfying the structural and performance constraints. The results can also help both designers and operators to make a more convenient selection of the structural and operation parameters of moisture separator reheater.

EVALUATION OF PH CONTROL AGENTS INFLUENCING ON CORROSION OF CARBON STEEL IN SECONDARY WATER CHEMISTRY CONDITION OF PRESSURIZED WATER REACTOR

The effect of various pH agents on the corrosion behavior of carbon steel was investigated under a simulated secondary water chemistry condition of a pressurized water reactor (PWR) in a laboratory, and the steel’s corrosion performance was compared with the field data obtained from Uljin NPP unit 2 reactor. All tests were carried out at temperatures of 50oC ? 250oC and pH of 8.5 ? 10. The pH at a given temperature was controlled by adding different agents. Laboratory data indicate that the corrosion rate of carbon steel decreased as the pH increased under the test conditions and the highest corrosion rate was measured at 150oC. This high corrosion rate may be related to high dissolution and instability of Fe oxide (Fe3O4) at 150oC. It was also found that an addition of ethanolamine (ETA) to ammonia was more effectivefor anticorrosion than ammonia alone, and that mixed treatment reduced 50% of iron or more at pHs of 9.5 or higher, especially in the steam generator (SG) and the moisture separator & re-heater (MSR).

1028 ワイヤメッシュ積層構造による微小液滴除去手法の開発

The moisture separator reheater (MSR) is a facility which is used to improve the thermal efficiency for the nuclear power plant. We have been developing the technique to improve moisture separation efficiency of MSR using wire-mesh combined with wave-shaped vanes. The objective of this study is to clarify the wire-mesh configurations which can minimize the exit moisture by droplet diameter measurement. We confirmed that droplet diameters were increased and the exit moisture was reduced as the number of layer was increased. Within our experiment range, six layered wire-mesh with 0.65 mm diameter can minimize the moisture, which is reduced from 0.45% without wire-mesh to 0.08%.

Development of wall thinning screening system and its application to a commercial nuclear power plant

A new non-destructive evaluation (NDE) method has been developed for metal pipes for the detection wall thinning. The method has been showed to be suitable for applications to electric power generation plants where flow accelerated corrosion (FAC) of carbon steel piping is a significant cause of increased maintenance and plant personnel casualty. The wall thinning screening system (WalSS) was developed in two major phases. In the first phase, the equipotential switching direct current potential drop (ES-DCPD) method was developed for piping wall (Ryu et al., 2008a, 2010). In the second phase, in this paper, a quantitative detection criteria was developed. The relative ES-DCPD change of 3.8% has been defined as the screening criteria for wall thinning schematization. This criteria means that the component with measured ES-DCPD change greater than 3.8% is called for a more comprehensive examination. In the criteria development, all variables were taken into consideration based on commercial plant piping inspection data such as initial thickness distributions, wall thinning shape and nominal thickness. The developed WalSS based on ES-DCPD was applied to a moisture separator reheater (MSR) drain line of a commercial nuclear power plant (NPP) during a scheduled overhaul. The measured ES-DCPD change was 2.16%, which is lower than the ES-DCPD criteria, identifying the pipe having adequate wall thickness. This is confirmed by site thickness inspection using ultrasonic technique (UT).

Influence of harvesting conditions on grain losses after separator

Mathematical and multivariable graphic models for the index «grain losses after separator» depending on straw rate, crop moisture content and separator characteristics are developed.

Dynamic Simulation on Secondary System of Nuclear Power Plant

The secondary system of Qinshan phase I nuclear power plant is simulated in this study. According to the characteristics of the JTopmeret model, the system is divided into six parts for modeling, which are the deaerator, the high pressure (HP) turbine, the low pressure (LP) turbine, the moisture separator reheater (MSR), the condensate system, and the feedwater system. All parts are built as the graphic automatic models in JTopmeret and debugged on the large-scale simulation platform GSE to complete the steady-state and dynamic simulation of the models. The results show that the steady-state and dynamic processes of the models are consistent with the characteristics of the actual system. It verifies the correctness of the simulation models. Thus, this research is able to provide guidance for the operation analysis and the equipment debugging of the secondary system of the nuclear power plant.