Typical Steam Research Articles

Constitutive Model-Based Efficient Creep-Fatigue Damage Computation Technique for Steam Turbine Rotors to Enhance Flexible Operational Capabilities

Abstract In the new era of renewable energy, flexible operation of conventional power plants is inevitable, causing high creep-fatigue life consumption. Conventional life assessment methods are deemed to be conservative to address the current requirements. The use of unified constitutive models for the analysis of damage evolution in steam turbine rotors in the past decade has shown promising results and is closely related to experimental data. However, identification of large number of material constants and high computational time hinder the widespread use of such models. In this paper, the latter is addressed using a novel representative input cycle (RIC) concept together with the noniterative asymptotic numerical method (ANM). Various startup shutdown sequences of a typical steam turbine rotor are studied using a unified constitutive model based on Chaboche's kinematic hardening including the damage parameter, Chaboche–Rousselier's isotropic hardening model including the damage parameter, Norton's viscoplastic flow model, Lemaitre's damage potential function and Kachanov–Rabotnov's creep damage law. First, a conventional finite element method (FEM) technique is used and then the proposed RIC method is used to study the evolution of inelastic variables. The reduction in computational time and the compromise in accuracy using the proposed method are studied.

Seismic analysis of a steam generator for Gyeongju and Pohang earthquakes

Safety qualification of a steam generator is a crucial issue related to faulted condition design loads, including earthquake loads, and it should be ensured that the structural integrity of a steam generator does not exceed its design load. Using data from the Gyeongju and Pohang earthquakes, the two most powerful recorded seismic events in Korea, seismic analyses of a typical steam generator are conducted in this study. The modal characteristics are used to develop an input deck for these analyses. With a time history analysis, the responses of the steam generator in the event of an earthquake are obtained. In particular, the displacement, velocity, and acceleration responses are obtained in the time domain, with these outcomes then used for a detailed structural analysis as part of the ensuing assessment. The response spectra are also generated to determine the response characteristics in the frequency domain, focusing on the response comparisons between the Gyeongju and Pohang earthquakes. Structural integrity can be ensured by performing additional analysis using results obtained from the time history analysis considering the input excitations of various earthquakes considered in the design.

METHODS TO REDUCE NOX FORMATION DURING GAS COMBUSTION IN BOILERS

A study of reduction of nitrogen oxides emissions using various methods and their combinations on operational typical steam and water heating boilers of Ukraine during combustion gas fuels was conducted. The experimental research of the power steam TGMP-314 boiler showed that when volume thermal stress of the firebox was reduced to qv » 0.09 MW/m3 (55 % of the nominal power), and the flue gas recirculation factor r = 17 %, the nitrogen oxides emissions were reduced by 75 % and they almost meet the requirements of the IED directive. This measure to reduce emissions of nitrogen oxides is also possible for other types of boilers, and it is advisable to implement for those combustion plants with an excess capacity of about 40–50 % and which have exhausted their factory-designated resource. On the water heating boiler KVGM-180, equipped with standard gas recirculation smoke exhauster, the research was conducted with aim to reduce of NOx emissions at combustion natural gas with recirculation of flue gases into the blowing air. NOx emissions were reduced by 67% to European standards, and the concentration of carbon monoxide in flue gases was below СО≤100 mg/Nm3 (at 3% O2) by a recirculation factor was of about r = 30%. The standard burners in the KVGM-180 boiler are two flow of air and can be considered a type of staged combustion burners. That is, in this case, a combination of the staged combustion burners and flue gas recirculation into blowing air was used. The research of combustion a methane and carbon dioxide mixture in the ratio of CH4 (76 %) and CO2 (24 %) (biogas) with regard to reduce the formation and emissions of nitrogen oxides in the DKVR-6.5-13 steam boiler was conducted. The obtained level of NOx in the flue gases is within the range of 63–76 mg/Nm3 (at 3 % O2), which fully complies with the EU standards for the operation of CP from 1 MW on natural gas and other gas fuels. Bibl. 34, Fig. 3, Tab. 1.

Pyrolysis of typical plastics and coupled with steam reforming of their derived volatiles for simultaneous production of hydrogen-rich gases and heavy organics

Pyrolysis is a thermochemical route for converting waste plastics into hydrocarbons that might be further upgraded to fine chemicals via the process such as hydrotreatment. In this study, the pyrolysis of five typical plastics (PE, PP, PVC, PS and PET) and steam reforming of their derived volatiles were coupled in one process, named as pyro-reforming. The reaction behaviors, especially the property of their derived cokes, in the pyro-reforming were investigated. The results indicated that the volatiles from the pyrolysis of PE had the highest reactivity with steam to produce H2 of the highest yield, followed by that of PP, PVC, PET and PS. The Cl in PVC promoted nickel sintering, enhanced formation of heavy aromatics through aromatization. Moreover, the existence of Cl interrupted formation of carbon nanotube, forming the highest amount of coke with hemp rope-like fiber form of very coarse surface. This was very different from the carbon nanotube form of coke with smooth surface and uniform outer/inner diameters from the pyro-reforming of PE or PP. The pyro-reforming of PET or PS generated mainly the aromatic intermediates that were chemically more inert in steam reforming, forming polymeric type of coke with no carbon nanotube morphology and very low crystallinity.

Mechanisms and Influence Factors of Downhole Electrical Heating-Assisted Steam-Assisted Gravity Drainage Production.

Approximately 70% steam-assisted gravity drainage (SAGD) wellpairs have entered into the production phase in China, while due to the fluvial sedimentation environment with strong reservoir heterogeneity, only 53% of the horizontal well section develops a steam chamber. In order to massively recover the bypassed oil and expand the steam chamber along the horizontal section, downhole electrical heating was proposed, and its mechanisms of high temperature-induced rock mechanics change and influence factors are investigated in this study using laboratory experiments and electrical steam hybrid numerical simulation. It is found that the electrical heating-assisted SAGD has four key mechanisms, namely, localized temperature elevation, development of a fixed point steam chamber, localized oil gravity drainage, and petrophysical property improvement. The influence factors include the static and operational factors, in which the permeability ratio is the primary factor for choosing SAGD wellpairs, while the steam injection rate, steam chamber operational pressure, injector and producer pressure difference, adjacent SAGD steam chamber pressure differential, heater surface temperature, and electrical heating period integrally influence the incremental production performance. Through carefully modifying the parameters, the typical SAGD wellpair steam chamber could expand from 67 to 100% along the horizontal section, with an incremental oil rate of 3–5 m3/day, and the cumulative steam/oil ratio decreases from 6.67 to 4.17. The downhole electrical heating is particularly efficient in improving steam chamber conformance in heterogeneous reservoirs and also has significant potential in similar reservoirs developed by horizontal wells.

Multi-criteria sensor placement determination in prognostics and health management using combined fault diagnosis, fault detection, and risk indexes

In framework of a prognostics and health management (PHM), a stochastic method is proposed for optimal sensor locations determination using three independent criteria indexes, reflecting the efficiency of sensor network: (i) the uncertainty of sensor information, the ability of fault diagnosis of a sensor network, (ii) the reliability of sensors, reflecting the fault detectability in sensor networks, (iii) risk of sensor failure including the consequence of sensor failure scenarios. The dynamic system failure model is developed and analyzed to consider the variation of environmental factors and their related failure threshold characterization along with statistical variance estimation as the information value that each possible sensor placement scenario provides through sensor information. A dynamic failure model is developed to incorporate the interaction of sensors and their corresponding components. It is demonstrated here that considering each criterion independently will not comprehensively determine the optimal placement scenario. An augmented index is formulated through Shannon Entropy theory, ranking all sensor placement scenarios based on proposed combined index. Optimization of sensor placement is demonstrated on a typical steam turbine. As shown in detail, the ranking based on each criterion provides different inconsistent rank for the location of the sensors. The combined index is found practically proper and recommended for rank and selection process.

Effect of Thermal Treatment on the Internal Structure, Physicochemical Properties and Storage Stability of Whole Grain Highland Barley Flour.

In this study, to improve the processing performance of whole grain highland barley flour (whole grain HB flour), they were prepared by sand-roasting, far-infrared baking, steam explosion, and extrusion, and the effects of on functional properties and storage characteristics were measured. The results indicated that sand-roasting, far-infrared baking, and steam explosion all caused cracks and honeycomb structures in the outer layer and endosperm of the highland barley. The XRD analysis results indicated that highland barley starch treated by far-infrared baking exhibited typical A-type crystal structure, while sand-roasting, steam explosion, and extrusion presented the typical V-type. The results of DSC analysis revealed that the onset temperature (To), peak temperature (Tp), gelatinization enthalpy (ΔH), peak viscosity (PV), trough viscosity (TV), and final viscosity (FV) decreased significantly, while the swelling power, water-holding capacity and oil-holding capacity increased significantly. During the storage period, the moisture content and lipase activity of the whole grain HB flour after thermal treatment remained at a low level; the fatty acid value, peroxide value, and malondialdehyde value increased; finally, the cooked whole grain HB flour was unstable during storage. The functional properties of whole grain HB flour can be improved by steam explosion, and will then have better storage stability.

HELB-induced blast wave evaluation based on mock-up tests and numerical analyses

Postulated high energy line breaks have been considered as a part of design of nuclear safety-related structures, systems and components for a long time. However, recently, technical controversy was raised over the adequacy in assumption of complex phenomena and assessment of dynamic loads. This study is to address blast wave evaluation under a typical main steam line break condition of 1,400MWe power plant. At first, a mock-up facility was developed and six tests were performed by changing rupture pressures and target distances. Corresponding computational fluid dynamics analyses were also carried out after optimization of numerical model. Finally, pressure – time histories caused by plant specific blast wave were generated in use of a theoretical correlation, which were applied to finite element analyses of neighboring steam generator and containment wall. Integrity assessment results as well as the details of tests and analyses data were provided, and their applicability was discussed.

Three-Dimensional CFD Model Development and Validation for Once-Through Steam Generator (OTSG): Coupling Combustion, Heat Transfer and Steam Generation

The current research studies the coupled combustion inside the furnace and the steam generation inside the radiant and convection tubes through a typical Once-Through Steam Generator (OTSG). A 3-D CFD model coupling the combustion and the two-phase flow was developed to model the entire system of OTSG. Once the combustion simulation was converged, the results were compared to field data showing a convincing agreement. The CFD analysis provides the detailed flow behavior inside the combustion chamber and the stack, as well as the two-phase flow steam generation process in the radiant and convective sections. The flame shape and orientation, the velocity, the species, and the temperature distribution at the various parts of the furnace, as well as the steam generation and the steam distribution inside the pipes were investigated using the developed CFD model

Calculations of complex chemical reaction equilibria using stoichiometric and non‐stoichiometric approaches in combination with arc‐length continuation

AbstractChemical equilibrium calculations—as they are required to evaluate the evolution limits of any reactive system—are fundamentally performed using either a reaction based stoichiometric (S) approach or a non‐stoichiometric (NS) method. One objective of the present paper is to check and discuss whether both methods lead to comparable solutions in the case of complex chemical equilibria encountered in high temperature and pressure combustion of hydrazine and propane and in steam gasification of glucose and cellulose. Within both calculation models various numerical methods can be used. We apply several techniques for each approach and discuss their easiness of implementation and usage, in particular when chemical equilibria are computed for reacting systems under a multitude of temperature and pressure conditions and feed compositions. In addition, we present a novel approach to perform sensitivity analyses based on a combination of S or NS methods and arc‐length continuation technique. For this purpose, three industrially relevant case studies are exposed: (1) synthesis of ammonia using the Haber process, (2) steam gasification of a typical biomass surrogate, glucose, and (3) steam gasification of cellulose. For all the above reacting systems, our results are benchmarked against their counterparts obtained either from the ubiquitous process simulator: ASPEN‐Plus® or from data available in the open literature.

Research on feature extraction of steam turbine shafting vibration signal

Vibration signal feature extraction is the primary problem of steam turbine condition monitoring and fault diagnosis. This paper focused on the analysis and recognition of vibration signal feature extraction, carried out model innovation on the basis of the existing status, and studied new modeling and solution methods. The vibration fault signals of typical steam turbine shafting were described respectively, and the time-frequency characteristics were studied by wavelet analysis

Flow-Induced Vibrations of a Rotated Square Tube Array Subjected to Single-Phase Cross-Flow

Abstract This paper investigates the flow-induced vibration (FIV) and possibility of fluidelastic instability occurrence in a rotated square geometry tube array through a series of experimental tests. All experiments presented here were conducted in water cross-flow. The array's pitch spacing ratio of approximately P/D = 1.64 is somewhat larger than that commonly found in typical steam generators. The stability of a single flexible tube as well as multiple flexible tubes was investigated. The tubes were free to vibrate purely in the streamwise direction or the transverse direction relative to the upstream flow. A single flexible tube, in the otherwise rigid tube array, was found to undergo large amplitude vibrations (up to 40% D) in the transverse direction. Tube vibration frequency analysis indicated the presence of two frequency components related to vorticity shedding in the array. This potential vorticity-induced vibration (VIV) and potential coupling between VIV and fluidelastic instability (FEI) are discussed in the paper. Test results for streamwise flow-induced vibrations are also presented. Results in water flow show a possible effect related to flow periodicity at low velocity. At significantly high flow velocities, the tubes are found to fully restabilize. This restabilization after VIV locking has not been previously reported as an unlocking result. The present results suggest that the flow-induced vibration of tubes in a rotated square array configuration is significantly more complex than in other geometries, particularly for the streamwise vibration case.

Numerical Study of the Deposition of Radioactive Nuclide (Aerosol) in Pressurized Water Reactor Steam Generator

Abstract This research presents a numerical study of deposition efficiency and decontamination factor of the radioactive nuclide in steam generator tubes of a typical 325 MWel pressurized water reactor (PWR). To find out the deposition of aerosol, the discrete phase model (DPM) has been used. The flow has been characterized as compressible, adiabatic, turbulent and wall-bounded. When steam generator tube gets ruptured, the radioactive nuclides can escape from primary side and create a radioactive field on the secondary side. This can be harmful at the personnel working at the plant. Therefore, in order to ensure the safety of the plant and personnel, it is important to study the particles deposition on the wall of steam generator tubes. In the present study, a computational fluid dynamics (CFD) methodology has been first developed and validated with the published results. After methodology validation, it has been applied to the U-tube of a typical PWR steam generator. It has been observed that due to the action of centrifugal force near the bent, the velocity magnitude is high toward the inner wall and the flow separates at the bent entrance. Furthermore, the flow inside the tube is rotational with vortices throughout the domain due to the presence of the bent. Finally, the deposition efficiency and decontamination factor have been calculated and it has been observed that both increase with the increase in particle size due to inertial effects.

Advanced technologies for electricity production in the sugarcane value chain are a strategic option in a carbon reward policy context

Sustainable bioenergy production is required to meet the growing demand and environmental concerns. This study addresses current and advanced options for biomass-based electricity generation integrated to a sugarcane ethanol distillery in Brazil and polices that would foster its deployment. The typical combustion and steam cycle system and the integrated gasification combined cycle are the options considered for lignocellulosic biomass conversion into heat and power, associated with carbon capture and storage technologies. Besides conventional sugarcane, eucalyptus and energy-cane are also examined as promising feedstocks to extend operational days and/or increase biomass yields. The considered biomass-based electricity options are able to mitigate climate change impacts and depletion fossil resources. However, decreasing costs is a challenge to overcome for its broader implementation. The assessed strategies may help to guide policymakers on how to feasibly deploy advanced technologies for electricity production from biomass, meeting the future demands for sustainable electricity. The choice of larger processing scales shows an important effect on reducing costs, as well as choosing energy-cane as feedstock, which is also favorable for reducing climate change and land use impacts. Likewise, government policies that reward climate mitigation, as RenovaBio in Brazil, have a prominent role to foster advanced biomass-based electricity production technologies.

The prediction of fluidelastic forces in triangular tube bundles subjected to a two-phase flow: The effect of the flow approach angle

The U-bend region in a typical steam generator is characterized by two-phase flow conditions and susceptible to damage due to fluidelastic instability excitation. To prevent such a destructive fluid–structure mechanism, numerous experimental and numerical works have been done to investigate, understand, and devise techniques to mitigate it. The effect of the flow approach angle on fluidelastic instability remains one of the topics which has not been fully resolved. This work aims to utilize flow numerical modeling techniques to gain an understanding of such an effect in a two-phase air–water flow. Various flow approach angles ranging from normal to parallel triangular arrays were investigated for various void fractions ranging from water to air flows. The results obtained revealed that the effect of a homogeneous air void fraction is very critical at very high values (99% and above). Moreover, at any intermediate flow approach angle between a normal and a parallel triangular array, the flow inside the array carries features of both normal and parallel triangular flow patterns. Based on this, a new FEI force-approach angle, semi analytical model is proposed to calculate the fluidelastic forces at any flow approach angle. The data obtained from this model were validated against information extracted from flow simulations and showed a good agreement.

Steady-State Thermal-Hydraulic Analysis of Steam Generator with Axial Economizer Based on Node Method

Based on the one-dimensional flow hypothesis, heat transfer hypothesis, and two-phase thermal equilibrium hypothesis, a lumped parameter method and a distributed parameter method are used to establish a one-dimensional steady-state thermal-hydraulic analysis model of the steam generator with axial economizer. Using C++ language programming, the calculation results are compared with the design values of the thermal-hydraulic parameters of a typical steam generator with axial economizer. The results show that the relative error of most of the overall parameter calculation results is within 3%, which verifies the rationality of the model. The analysis of the temperature, cavitation share, pressure and other parameters of the steam generator along the direction of the measured fluid flow trend consist well with the results of thermal hydraulics and qualitative mechanism analysis, indicating that the model and solution method established in this paper can accurately predict the steady-state thermal hydraulic parameter distribution of the steam generator with axial economizer.

Flow mapping using 3D full-scale CFD simulation and hydrodynamic experiments of an ultra-supercritical turbine’s combined valve for nuclear power plant

In a typical steam turbine generator system, electrical power output is related to the steam flow regulated by a control valve. Hence, to ensure adequate electrical load as well as the proper stability of the turbine, a linear operation of the control valve is desired. However, in reality, the control valve exhibits different flow characteristics (FCs), both linear and nonlinear, which stem from its complex shape of plug and stem lift. Therefore, precise estimation of FCs is of utmost importance for better controllability, reliability, and safety of the turbine system. In this study, experiments and CFD simulations were carried out to evaluate the hydrodynamic FCs of a combined emergency stop and control valve to be employed in an ultra-supercritical (USC) turbine system for power plant. A full-scale prototype valve was designed, fabricated, and tested for a vendor company. Experiments were performed in the so-called VELO (Valve Engineering Layout Operation) test bench, and CFD simulations were conducted using a commercial code STAR CCM+. Air was used for experiments and simulations for simple economic and safe operation. Hydrodynamic characteristics were analyzed, and the theoretical mass flow rate of the valve was estimated. Finally, the valve coefficient of the turbine system was determined from the obtained FC curves. The simulation and test data showed a scale deviation of 15–16% for the original model valve and the simplified test valve. The test valve required such scaled modification to match with the test bench and fabrication. The prospective future research and improvement were recommended. This study's findings would support improving the turbine system performance to ensure safer, reliable, and modular power conversion systems for nuclear and conventional fossil fuel-based power plants.

Study and Redesign of Aircooler System in a 16 MW Steam Turbine Surface Condenser at Neka Power Plant

According to the study of basic Rankin thermal cycle, the steam exhaust pressure of a typical steam turbine toward the condenser, plays a great role in the efficiency and the net output power of the steam turbine, so most surface condensers that are working in thermal power plants are kept at vacuum condition so that the maximum power of thermal cycle can be achieved. The vacuum pressure at condenser leads to the entering of air and Non-condensable gases from turbine gland seals to condenser so that the special air ejection equipment is being used to take apart air from steam and vent it to out of condenser. In this study, a special steam and air separator mechanism in an evacuating system called “Aircooler” at a 16 MW steam turbine condenser is being studied and the Fluent CFD software is utilized to analyze the behavior of steam plus air in a typical aircooler system of 16 MW steam turbine condenser of Neka power plant to find a way to reduce the risk of cooling tube rupture in aircooler ducts. The critical condition which tube rupture happens is determined and it is demonstrated that in hot seasons of year, by increasing the seawater cooling temperature and increasing in turbine steam exhaust pressure and temperature, the risk of tube rupture due to more mixture velocity at the first row of aircooler cooling tubes increases and also the effect of tube plugged condition on the performance of aircooler shows that the risk of other tubes rupture will increase and thus the efficiency of aircooler decreases due to more aircooler exhaust temperature. Finally, two modified plans at aircooler system design will be studied and simulated via Fluent CFD software which leads to reduce the risk of tube rupture. The results show that by modification of aircooler ducts and holes, the mixture air and steam flow velocity to first aircooler cooling tube row decreases significantly and causes the risk of tube rupture to decrease remarkably and also the exhaust temperature of aircooler decreases and causes the higher ejector performance.

Simulation of the HiPowAR power generation system for steam-nitrogen expansion after ammonia oxidation in a high-pressure oxygen membrane reactor

The EU project HiPowAR studies a novel power generation system based on ammonia flameless oxidation with pure oxygen in a high-pressure membrane reactor and expansion of the resulting high-temperature H2O-N2stream. The system combines the advantages of high temperature at expander inlet, typical of gas turbines, and small compression demand, typical of steam cycles. Water is injected into the reactor to control the very high adiabatic temperature, at the limited energy expenditure of liquid pumping. This work assesses the performance potential of the HiPowAR system under different design conditions, through simulations with a model developed in Aspen Plus®. The system shows a high efficiency (up to 55%) when operating at high temperature (e.g., 1350°C at expander inlet); hence, O2 membranes capable of working at very high temperature are required. The cycle features an optimal sub-atmospheric expansion pressure (in the range 0.1-0.2 bar), which requires the re-pressurization of the off-gas (steam-saturated nitrogen). The system also produces liquid water as a net output. A reduction of the expander inlet temperature to values acceptable by typical steam cycles (600°C) significantly limits the efficiency, despite allowing to demonstrate the process using conventional steam expanders.

Pressure drop and heat transfer of ZoneFlowTM structured catalytic reactors and reference pellets for Steam Methane Reforming

Structured catalytic reactors have the potential to combine reduced pressure drop and improved heat transfer compared to conventional pellets. In the present study, the pressure drop and heat transfer coefficient between the tube wall and the process gas were measured experimentally for annular structured ZoneFlowTM reactors of different design and for two commercial reference pellets. The ZoneFlowTM reactors differ by the design of the central rod that supports the near-wall annular casing. The experiments were carried out in a 1 m long reactor, at atmospheric pressure and with air flow rates from 70 to 330 Nm3/h. To measure the heat transfer coefficient, the furnace was set at a constant temperature that was varied in the range 100–500 °C and the axial profiles of the tube wall and gas temperatures were measured. Using the experimental data, correlations for the friction factor and the Nusselt number were derived and the introduced parameters estimated using non-linear regression. A correlation for the static contribution to heat transfer for the structured reactors was derived from 3D numerical simulations. The correlations were then used to evaluate the pressure drop–heat transfer advantage of the structured reactors compared to the reference pellets at typical industrial steam methane reforming conditions. The data show that ZoneFlowTM reactors can provide a roughly doubled heat transfer coefficient at comparable pressure drop than the tested reference pellets. Furthermore, modification of the central rod support structure was found an efficient way to balance the pressure drop–heat transfer advantage of ZoneFlowTM reactors using an identical design casing.