Heat Exchangers In Power Plants Research Articles

Electromagnetic inspection for defect of ferromagnetic tube using rectangular wave with DC bias

The ferromagnetic steel tubes are used as heat exchangers in power plants or oil plants. When the usual eddy current testing (ECT) of inner type is used for the defect inspection of these steel tubes, it is difficult to detect defects on the opposite side due to the influence of skin effects. In this research, the non-destructive inspection method using rectangular wave excitation current with DC bias is proposed for detecting of the opposite side defect. It is shown that the detecting of the opposite side defect in the steel tube is possible, and the detection sensitivity using the alternating magnetic field of rectangular wave is higher than that with sine wave. The detailed phenomenon of the inspection method is examined using the 3-D nonlinear FEM (finite element method) taking account of minor loop magnetizing properties using the play model method.

Combined Pinch and Exergy Evaluation for Fault Analysis in a Steam Power Plant Heat Exchanger Network

This study demonstrates comparative applications of the standard pinch and exergy analysis and the combined pinch-exergy analysis methodologies to a gas-fired steam power plant’s heat exchanger network. The extent to which each methodology could be used for pin-pointing the location of performance deteriorations in the network and their relative criticality were shown. Using a 12 °C minimum temperature difference, the network minimum hot utility requirement in current operation was determined by a pinch analysis as 539,491 kW, at a supply temperature of 549 °C. This represented a 6% (30,618 kW) increase in the utility requirement when compared with the design minimum requirement (508,873.7 kW). The combined exergy pinch analysis showed the severity of performance deteriorations more clearly, determining a 25% increase in global plant exergy losses with respect to design conditions. With a standard exergy analysis, additional information on the actual network components responsible for the changes was obtained—there were general declines in component performances except for two heaters and the deaerator, whose operation performances improved slightly. Furthermore, avoidable and inevitable exergy losses (Ξ˙d,AVO and Ξ˙d,INE, respectively) were determined for network components. Whereas both were highest for the boiler, the values of the ratio Ξ˙d,AVO/Ξ˙d,INE showed that higher potentials for performance improvement existed in the other network components. This indicates the ratio Ξ˙d,AVO/Ξ˙d,INE as an appropriate measure for deciding equipment in the heat exchanger network that are in need critical attention.

Ceramic-metal composites for heat exchangers in concentrated solar power plants.

The efficiency of generating electricity from heat using concentrated solar power plants (which use mirrors or lenses to concentrate sunlight in order to drive heat engines, usually involving turbines) may be appreciably increased by operating with higher turbine inlet temperatures, but this would require improved heatexchanger materials. By operating turbines with inlet temperatures above 1,023 kelvin using closed-cycle high-pressure supercritical carbon dioxide (sCO2) recompression cycles, instead of using conventional (such as subcritical steam Rankine) cycles with inlet temperatures below 823 kelvin1-3, the relative heat-to-electricity conversion efficiency may be increased by more than 20 per cent. The resulting reduction in the cost of dispatchable electricity from concentrated solar power plants (coupled with thermal energy storage4-6) would be an important step towards direct competition with fossil-fuel-based plants and a large reduction in greenhouse gas emissions7. However, the inlet temperatures of closed-cycle high-pressure sCO2 turbine systems are limited8 by the thermomechanical performance of the compact, metal-alloy-based, printed-circuit-type heat exchangers used to transfer heat to sCO2. Here we present a robust composite of ceramic (zirconium carbide, ZrC) and the refractory metal tungsten (W) for use in printed-circuit-type heat exchangers at temperatures above 1,023 kelvin9. This composite has attractive high-temperature thermal, mechanical and chemical properties and can be processed in a cost-effective manner. We fabricated ZrC/W-based heatexchanger plates with tunable channel patterns by the shape-and-size-preserving chemical conversion of porous tungsten carbide plates. The dense ZrC/W-based composites exhibited failure strengths of over 350 megapascals at 1,073 kelvin, and thermal conductivity values two to three times greater than those of iron- or nickel-based alloys at this temperature. Corrosion resistance to sCO2 at 1,023 kelvin and 20 megapascals was achieved10 by bonding a copper layer to the composite surface and adding 50 parts per million carbon monoxide to sCO2. Techno-economic analyses indicate that ZrC/W-based heat exchangers can strongly outperform nickel-superalloy-based printed-circuit heat exchangers at lower cost.

Data-driven modeling for boiling heat transfer: Using deep neural networks and high-fidelity simulation results

Boiling heat transfer occurs in many situations and can be used for thermal management in various engineered systems with high energy density, from power electronics to heat exchangers in power plants and nuclear reactors. Essentially, boiling is a complex physical process that involves interactions between heating surface, liquid, and vapor. For engineering applications, the boiling heat transfer is usually predicted by empirical correlations or semi-empirical models, which has relatively large uncertainty. In this paper, a data-driven approach based on deep feedforward neural networks is studied. The proposed networks use near wall local features to predict the boiling heat transfer. The inputs of networks include the local momentum and energy convective transport, pressure gradients, turbulent viscosity, and surface information. The outputs of the networks are the quantities of interest of a typical boiling system, including heat transfer components, wall superheat, and near wall void fraction. The networks are trained by the high-fidelity data processed from first principle simulation of pool boiling under varying input heat fluxes. State-of-the-art algorithms are applied to prevent the overfitting issue when training the deep networks. The trained networks are tested in interpolation cases and extrapolation cases which both demonstrate good agreement with the original high-fidelity simulation results.

Effect of fine ash particles on formation mechanism of fouling covering heat exchangers in coal-fired power plants

The 1-D model of thermodynamic iterative calculation is put forward for the prediction of acid condensation considering the complexity of flue gas. The radius of fine ash particles is dominant for condensation rate around fine ash particles at ADP; flue gas components for ADP, critical radius, and condensation rates, especially acid vapor content of flue gas. X-ray fluorescence (XRF) and scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDS) are used to analyze the ash samples collected during the field experiment of a 300 MW sub-critical coal fired boiler unit, i.e. fly ash deposits (>130 °C), dry loose ash deposits (85 °C) and viscous ash deposits (65 °C). The results show that S distribution is connected with the distributions of superfine particles and fine particles, especially superfine particles, which are dissolved in viscous ash samples. According to the experimental results and acid condensation analyses, the presence of fine ash particles (dash < d0) is the primary factor for the acid condensation at ADP and the coupling mechanism of the sticky ash particles. In the waste heat utilization system, the on-line monitoring of the sub-micron ash particles can be added to reflect the low temperature corrosion.

Impacts of Water Flow Rate on Freezing Prevention of Air-Cooled Heat Exchangers in Power Plants

Under cold ambient conditions, the freezing risk of air-cooled heat exchangers, especially the frontal finned tube bundles, has been a critical concern in power plants. Based on the freezing conditions of the cooling deltas under windy conditions, the flow and heat transfer characteristics of natural draft dry cooling system (NDDCS) with 30%, 40% and 50% increased water flow rates are investigated in this work, and the outlet circulating water temperatures of the easily freezing cooling deltas and sectors are obtained. The results show that the deltas in the middle front and rear sectors become free from freezing at all wind speeds when the circulating water flow rate is increased. For the frontal sector with increased water flow rate, the outlet water temperatures of deltas increase conspicuously at 4 m/s and 8 m/s, while as the wind speed rises to 16 m/s, these deltas still face serious freezing risks due to the huge heat rejection to ambient air. Therefore, freezing prevention of air-cooled NDDCS heat exchangers can be achieved by increasing the water flow rates at small wind speeds, while as the wind speed becomes high, the water flow redistribution is suggested for the frontal and middle sectors due to their big performance difference.

Numerical investigation of subcooled flow boiling in an annulus under the influence of eccentricity

The subcooled flow boiling phenomenon usually occurs in a number of industrial applications, such as Pressurized Heavy Water Reactors (PHWR) and heat exchangers in nuclear power plants. The pressure tube deformation, presence of spacer pads, etc., may result in the eccentricity (e) of the rod bundle which causes coolant flow maldistribution and hence influence the heat transfer characteristics. In the present study, the entire rod bundle is modeled as a single inner rod and Eulerian Eulerian Multiphase Flow (EEMF) and Wall Heat Flux Partition (WHFP) model framework is used to simulate the effect of eccentricity (e). This model is validated against the available experimental data in the literature and found to be in reasonably good agreement. This framework is also compared and contrasted against the subchannel analysis predictions to highlight the importance of detailed CFD simulations. Furthermore, in the present study, the thermal hydraulics of narrow and wide gap regions are numerically investigated in an eccentric annulus. Due to eccentricity, early phase change, higher wall temperature and vapour volume fraction were noticed in the narrow gap region, compared to the concentric case (e=0.0), which is undesirable in the PHWR type reactors.

Experimental characterization of an additively manufactured heat exchanger for dry cooling of power plants

Air-cooled heat exchangers for power plant cooling are receiving much attention lately, as they require little or no water for cooling when compared to water-cooled systems. This paper focuses on the design, fabrication, and experimental characterization of a novel additively manufactured air–water heat exchanger for dry cooling of power plants. The heat exchanger consists of manifold-microchannels on the air side and rectangular channels on the water side in a cross-flow configuration. By using additive manufacturing, the manifold-microchannel heat exchanger can be fabricated as a single component, which eliminates the assembly process. Three prototype heat exchangers were fabricated using direct metal laser sintering (DMLS) out of stainless-steel (SS17-4), titanium alloy (Ti64), and aluminum alloy (AlSi10Mg). Air-side heat transfer coefficients in the range of 100–450 W/m2 K at pressure drops of 50–2000 Pa were recorded for the titanium alloy heat exchanger for air flow rate ranging from 1.89 L/s to 18.9 L/s. Based on our analysis and compared to conventional heat exchangers, the performance of this manifold-microchannel heat exchanger was superior. Compared to wavy fin and plain plate fin heat exchangers, up to 30% and 40% improvement, respectively, in gravimetric heat transfer density was recorded for the entire range of experimental data. Compared to state-of-the-art dry cooling, nearly 27% improvement in gravimetric heat transfer density was noted at air-side coefficient of performance (COPair) of 172.

Modelling and Controller Design for Temperature Control of Power Plant Heat Exchanger

Power Plant Heat exchanger is widely used in chemical and petroleum plants because it can sustain wide range of temperature and pressure. Heat exchanger is a high nonlinearity and poor dynamics plant; therefore it is complex to model and difficult to control its dynamics. In this paper two types of heat exchanger model and controller are applied for selecting suitable model and controller. First model is called (Physical model) and derived using real parameter of heat exchanger plant. Second, a Second Order Plus Dead Time (SOPDT model) that is derived from the response of heat exchanger. While the controllers are consisted of fuzzy proportional derivative (FPD) controller and proportional integral derivative (PID) controller and applied to the model and their responses are compared with the existing PID controller. The PID controller response based on Physical model gives similar response of existing PID controller based real heat exchanger plant in comparison with SOPDT model. That means the Physical model is able to represent the heat exchanger plant dynamics more accurately than SOPDT model. For the controller, the FPD control gives a slight enhancement based on SOPDT model. Therefore, FPD controller is more suitable than PID controller.

Determination of plasticity following deformation and welding of austenitic stainless steel

Intergranular strain has been associated with high-temperature cracking of welded pipework in 316H austenitic stainless steel material used in nuclear power plant heat exchangers. In this study, neutron diffraction has been used to study the development of intergranular strains in plastically-deformed and welded 316H stainless steel. Measurements have been made of the intergranular strain evolution with increasing plastic strain in base material, and correlated with further measurements made in samples extracted from welded pipes, where the pipes were welded following plastic deformation to different levels of plastic strain. Strong tensile strain evolution was seen on the compliant 200 grain family. The results were correlated with various proxy measures of plastic strain, including hardness and diffraction peak width, and excellent agreement was obtained.

The Research and Application Status of Inconel 600 Alloy under Extremely Situation

The Inconel 600 alloy relies on high temperature strength and aggressive environment resistance for main pipes and heat exchangers for power plant. Through high energy laser beam surface treatment, upgrade oxidation performance and design based accident prevention, the durable Inconel 600 alloy is realized. At the same time, the chemical diffusion and high energy beam welding are used for wearness enhancement and chemical oxidation. It is suggested that, the laser surface treatment and hydrogen effect are accurately selected for abrasive wear resistance and high temperature oxidation, repectively. As a result, the lifespan of Inconel 600 alloy increases, the pitting concentration and cracks formation are prevented effectively.

Available recovery time prediction in case of an accident scenario for NPP component

In nuclear power plant operations, there is a possibility that a stimulating event can initiate undesired accident. Therefore, prediction of the available recovery time (the time within which restorative measures can be taken without compromising the threshold safety limits) is a serious challenge to avoid any accident scenario. Recent advances in sensor technology has made it possible to continuously monitor the plant component parameters. Fuzzy logic based artificial intelligence data-driven systems compare real time operational parameters with the pre-stored reference failure database to provide an effective estimate of the recovery time available. This paper demonstrates the prediction of available recovery time in case of an accident scenario in U-tubes of Nuclear Power Plant (NPP) heat exchanger. When a failure scenario evolves, its evolution pattern is compared with the reference failure database using fuzzy similarity analysis. A reference failure database consisting of actual accidental history is not feasible. In this research, an effort has been made to generate reference failure database employing Computational Fluid Dynamics (CFD) tool of commercial code ANSYS 16.2. Reference failure database consists of data collected from multiple U-tube temperature based failure scenarios. The validity of this procedure is checked by estimating recovery times for several test patterns. Moreover, the actual and predicted recovery times have been compared for the test patterns. A framework has been presented, in which temperature threshold is detected and a comparison is made between the evolving patterns and the reference database. This study gives a roadmap for the implementation of fuzzy logic prediction to enhance the safety of Nuclear Power Plant (NPP) components.

Reducing water usage with rotary regenerative gas/gas heat exchangers in natural gas-fired power plants with post-combustion carbon capture

It is possible to greatly mitigate the increase of water usage associated with the addition of carbon capture to fossil fuel power generation. This article presents a first-of-a-kind feasibility study of a series of technology options with rotary regenerative gas/gas heat exchangers for the management of the water balance around post-combustion carbon capture process integrated with CCGT (Combined Cycle Gas Turbine) plants with and without EGR (exhaust gas recirculation). Hybrid cooling configurations with a gas/gas heat exchanger upstream of the direct contact cooler reduce cooling and process water demand by 67% and 35% respectively compared to a wet system where the flue gas is primarily cooled prior to the absorber in larger direct contact coolers. The CO2-depleted gas stream is then reheated above 70 °C with enough buoyancy to rise through the stack. Dry air-cooled configurations, relying on ambient air as the cooling medium, eliminate the use of process and cooling water prior to the absorber and the temperature of the flue gas entering the absorber is unchanged. Rotary regenerative heat exchangers do not introduce significant additional pressure drop and gas leakage from a high CO2 concentration stream to a stream with lower concentration can be minimized to acceptable levels with available strategies using a purge and a scavenging slipstream from the higher pressure flow.

Numerical modeling of flow boiling instabilities using TRACE

Dynamic flow instabilities in two-phase systems are a vitally important area of study due to their effects on a great number of industrial applications, including heat exchangers in nuclear power plants. Several next generation nuclear reactor designs incorporate once through steam generators which will exhibit boiling flow instabilities if not properly designed or when operated outside design limits. A number of numerical thermal hydraulic codes attempt to model instabilities for initial design and for use in accident analysis.TRACE, the Nuclear Regulatory Commission’s newest thermal hydraulic code is used in this study to investigate flow instabilities in both single and dual parallel channel configurations. The model parameters are selected as to replicate other investigators’ experimental and numerical work in order to provide easy comparison. Particular attention is paid to the similarities between analysis using TRACE Version 5.0 and RELAP5/MOD3.3. Comparison of results is accomplished via flow stability maps non-dimensionalized via the phase change and subcooling numbers.Results of this study show that TRACE does indeed model two phase flow instabilities, with the transient response closely mimicking that seen in experimental studies. When compared to flow stability maps generated using RELAP, TRACE shows similar results with differences likely due to the somewhat qualitative criteria used by various authors to determine when the flow is truly unstable.

Random Material's Characteristics to Study Fluid‐Structure Interaction

SummaryIn many situations, the vibrating structures are in contact with a fluid (fluid around the hulls of a boat, reservoirs, heat exchangers in power plants, etc.), but the dynamic behavior of the structure can be significantly modified by the presence of the fluid. The sizing must take into account the effects of fluid‐structure interaction. Traditionally, the study of mechanical systems fluid‐structure interaction is based on a deterministic approach where all the parameters used in the model are a fixed value. But it suffices to having conducted a few experimentations to realize that the limitations of such modeling. Hence it needs to take into accounts the uncertainty in the parameters of mechanical systems. This work proposes to take the characteristics of the structure and the fluid as random and shows the efficiency of such approach. The proposed numerical stochastic method of the modal synthesis extended to reliability study, based on FORM (First Order Reliability Method) and SORM (Second Order Reliability Method) approaches, for solving the large vibro‐acoustic problems. The numerical method used takes into account the uncertainties of the input parameters of the two domains. The application of the proposed method is performed on a boat propeller immersed in air and water. To validate the calculation process, the numerical study is compared to an experimental study.

Evolution of precipitated phases during prolonged tempering in a 9%Cr1%MoVNb ferritic–martensitic steel: Influence on creep performance

Ferritic–martensitic steels of the 9%Cr1%Mo type have been extensively used in power plant components, heat exchangers, piping and tubing, etc., due to an excellent combination of properties such as creep resistance, toughness and resistance to oxidation at high temperatures. In these steels the stabilizing role of MX carbonitrides (M = Nb, V; X = C, N) is one of the main factors responsible for the resistance under creep conditions. The control of precipitation and coarsening of MX phases during prolonged, high temperature tempering or post-weld heat treatment is then a key point to obtain the desirable microstructure and hence, to achieve high temperature resistance under service conditions. In the present contribution we report the evolution of the precipitated phases during heat treatment at 780 °C for increasing times in the range 40 min to 7 h for an ASTM A213 T91 steel. The Nb and V contents in solid solution were determined as a function of the time of treatment and maxima were observed for 5 and 5.66 h, respectively. Creep tests to rupture were also conducted at 600 °C – 190 MPa for as-treated specimens. A maximum creep rate was observed to occur in coincidence with the maximum values of Nb and V contents in solid solution. We suggest possible relationships between the observed second phase evolution and the creep resistance behavior.

Electromagnetic Inspection Method of Outer Side Defect on Small and Thick Steel Tube Using Both AC and DC Magnetic Fields

As thick steel tubes of small diameter are used in heat exchangers in various electric power plants and petrochemical plants, the inspection of these steel tubes is very important. The outer side defects are often observed on these small steel tubes. Moreover, since these steel tubes in heat exchangers are stored as a bundle, it is necessary to inspect the outer side defects of these steel tubes from the inside of the tube. In this paper, the electromagnetic inspection method using a direct current (dc) magnetic field and an alternating current (ac) magnetic field is proposed. The behavior of flux in steel is examined using 3-D finite-element method (FEM) taking account of hysteresis (minor loop) and eddy current. It is shown that the detection of outer side defect is possible by the differential permeability of minor loop of which the position on the hysteresis loop is affected by the existence of the defect.

Titanium and super stainless steel welded tubing solutions for sea water cooled heat exchangers

Owing to its outstanding resistance to general and localised corrosion, titanium has become established as the preferred material for sea water cooled heat exchanger tubing, be it for power plant surface condensers or heat exchangers in thermal desalination plant or in the chemical and petrochemical processing industry. Periodic increases in the price of titanium have generated interest in cost effective alternatives using so called 'super alloys': highly alloyed stainless steels showing improved corrosion resistance over conventional compositions. Taking sea water cooled power plant condenser tubes as an example, the mechanical and corrosion/erosion properties of titanium are reviewed together with those of three frequently considered alternatives, UNS S31254 super austenitic alloy, and UNS S44735 and S44660 super ferritic alloys. The results of ASTM G48 pitting and crevice corrosion tests and of electrochemical studies in model sea waters are reported. The effect of heat treatment on the corrosion resistance of S44735 has also been examined. It is concluded that while titanium has a superior balance of corrosion and other properties, super alloys can provide excellent performance in service provided certain precautions are observed.

INHIBITION OF CORROSION OF α-BRASS (Cu-Zn, 67/33) IN HNO3 SOLUTIONS BY SOME ARYLAZO INDOLE DERIVATIVES

ABSTRACT The influence of some arylazo indole derivatives on the corrosion rate of 70/30 α-brass in 2 mol l -1 HNO 3 was investigated using weight loss and galvanostatic polarization techniques. It was found that the investigated compounds behave as inhibitors. The inhibition efficiency increases with increasing the inhibitor concentration, but decreases with increasing the temperature. The adsorption of these compounds on the α-brass surface follows a Frumkin’s adsorption isotherm. The electrochemical results indicated that all the investigated compounds act as mixed-type inhibitors. The influence of the substituent group on the inhibition efficiency of the inhibitor was explained in terms of the density of the electron cloud on arylazo indole moiety. Some thermodynamic parameters for corrosion and adsorption processes were determined and discussed. Keywords: corrosion inhibition; α-brass; synergistic effect; HNO 3 ; arylazo indole derivatives. INTRODUCTION Copper and its alloys, because of their excellent resistance to corrosion in neutral aggressive media and their ease of processing, they are widely used in industries, particularly as condensers and heat exchangers in power plants

Study on Influence of Tube Arrays on Fluid Elastic Instability

The tube bank is used in boilers, heat exchangers in power plants and steam generators in nuclear plants. These tubes sometimes vibrate violently and come to the fatigue failure due to the flow induced vibration which is caused by the cross flow. This phenomenon is that the large vibrations arise at the critical flow velocity and it is called fluid elastic instability. However the relation between the onset velocity of fluid elastic instability and the tube array's geometry has not been clarified sufficiently. There is a few reference related to the relation between the pitch to diameter ratio and the onset velocity even in the lattice arrays. In this paper, the influence of tube arrays on fluid elastic instability is examined by experiments. As a result, it is clarified that the tube vibrations become large as T/D increases and L/D decreases, and the tube vibrations strongly depend on the dynamic characteristics of tubes such as the natural frequency and the damping ability.