bluuebunny/crossref_metadata_2025 huggingface dataset:
Control of a 420 kN Discrete Displacement Cylinder Drive for the Wavestar Wave Energy Converter
Authors: Hansen Rico H. , Andersen Torben O. , Pedersen Henrik C. , Hansen Anders H.
Published: November 2014

To improve the power production of their 1 MW wave energy converter, Wavestar is developing a new transmission based on discrete hydraulics. The discrete hydraulic system allows all cylinders to supply a common accumulator storage while maintaining low-loss individual force control of the 20 absorbers. The system is implemented using multi-chambered cylinders, where the different chambers may be switched between three pressure lines using a manifold with fast on/off valves. Resultantly, a Discrete Displacement Cylinder (DDC) is obtained, where force control is implemented by shifting between different area/pressure combinations. Currently, a 420 kN DDC prototype has been implemented and tested at the newly commissioned full size wave energy testbench at Aalborg University. The initial design and control of the DDC had poorly damped switching transients. These issues treated in this paper. This leads to a new control, which gives a smooth operating DDC, while meeting the requirements to the efficiency of the drive.
A Robust Multi-Input Multi-Output Control Strategy for the Secondary Controlled Hydraulic Hybrid Swing of a Compact Excavator With Variable Accumulator Pressure
Authors: Busquets Enrique , Ivantysynova Monika
Published: November 2014

Over the last decade, a number of hybrid architectures have been proposed with the main goal of minimizing energy consumption of excavator swing drives. One of the most notorious architectures is the secondary controlled hydraulic swing drive. One of the advantages of this system is that, through the installation of a hydraulic accumulator, energy which otherwise would be wasted can be stored and reutilized on demand. However, the fact that the hydraulic motor in this architecture operates under a constant high pressure at all times diminishes the overall system efficiency significantly. Therefore, to investigate machine power management strategies, it is imperative to formulate a controller that overcomes this weakness. In this paper, a robust multi-input multi-output controller is synthesized for the control of the hybrid swing velocity and for first time the control of the accumulator state of charge. The simplified plant is tested using a high fidelity nonlinear model developed in the Simulink-Matlab environment. The proposed controller is then tested and compared against a PI controller using the optimal accumulator pressure obtained from dynamic programming and the desired cab velocity. Results show satisfactory tracking of the swing drive velocity and pressure. In addition, a study of the nominal stability, robust stability and robust performance of the controlled system reveals the advantages of the H∞ controller.
Heat Storage Enhanced in Solar Chimney Power Plant Model by Using PCM Material
Authors: Albaldawi Rafea A. H. , Shyaa Aseel K. , Nuri Haider S.
Published: November 2014

Solar energy is a renewable energy source that can generate electricity. When there is much solar radiation, there is not always a need for all the energy from the solar, and when the weather is cloudy there may be too little energy to meet demand. Thus, it is often wise to implement energy storage in systems with a large share of renewable energy. Latent heat storage is one of the most efficient ways of storing thermal energy. Sodium Sulfate Decahydrate (Glauber’s salt) has a larger energy storage density and a higher thermal conductivity. So the present work, built solar chimney power plant of 2m-radius of collector and a 4m chimney height integrated by phase change materials. Aim of designing and building solar chimney to estimate the effect of adding phase change materials as well as to examine the effect of inclination angle (16°, 8°). The results show that maximum temperature difference between collector exit and the ambient reached to 23.7°C for case (i) and for 17.7°C case (ii), the maximum air velocity reached 2.25 m/s that in case (ii) and reached 2.05 m/s in case (i).and maximum collector efficiency can be reached to 8.925% in case (ii).
Hydropower Generation by a Self-Circulating Solar Thermosyphon
Authors: Yoshida Hiro , Imada Haruhiko , Hagino Naoto
Published: November 2014

A self-circulating solar thermosyphon (TS) was applied to hydropower generation for the first time. A TS consists of a solar thermal collector, condenser, buffer chamber, hydropower section, heat exchanger, and recuperator. In the present study, the power output level was 10−6 W for the solar irradiation input of 102 – 103 W. The coefficient is 10−9. Considering the Carnot’s coefficient, 0.13, for the heat source and sink of temperatures 70°C and 25°C, there is room for remarkable improvement in TS hydropower generation. Moreover, the solar thermosyphon hydropower generation may provide us with new ways of utilizing heat below a temperature of 100°C, which until now has been merely used for things such as hot water supply and floor heating.
Role of Toluene and Carbon Dioxide on Sulfur Recovery Efficiency in Claus Process
Authors: Ibrahim Salisu , Chardonneau Marie , AlShoaibi Ahmed S. , Gupta Ashwani K.
Published: November 2014

Examination of the effect of toluene and carbon dioxide accompanying acid gases (mainly H2S) in the sulfur recovery process is very critical to determine the optimum operating temperature for enhanced sulfur recovery. Experimental and simulation were used to quantify the conversion efficiency with the addition of different amounts of toluene and carbon dioxide/toluene mixtures to the H2S gas stream. The results showed similar trends between predictions and experimental data, which revealed a decrease in conversion efficiency with increase in toluene or carbon dioxide/toluene addition to the H2S gas stream in a reactor. Further simulations were carried out to seek for the effect of toluene and CO2 addition to acid gas stream on the more favorable operating temperature of the reactor. The results showed that toluene increases the optimum reactor temperature at which enhanced sulfur recovery occurs, whereas it reduces the optimum operating temperature in the presence of CO2. The presence of toluene and CO2 in the acid gas stream affects the sulfur recovery efficiency by altering the optimum temperature of the reactor. These results reveal the importance of reactor temperature and its excursion on sulfur recovery in a Claus process. The effect of mean reactor temperature and its role on detailed chemical speciation from within the reactor as well as the role of key species formed in the process on sulfur recovery are presented.
Human Information Processing and Cognition: Applications to Improve Reliability, Availability, and Maintainability (RAM)
Authors: Bishop Heath , Everline Shannon , Banghart Marc
Published: November 2014

Human cognition, bias and error have been studied significantly over the past few decades and are utilized in several fields, including reliability and safety engineering. Research has indicated that both man-machine interfaces and training are critical during human intervention. Additionally, it has been shown that humans contribute significantly to failures, and thus downtime. This trend is likely to continue as systems become more complex. Several methods, such as Human Reliability Assessment (HRA) and Probabilistic Risk Assessment (PRA), had been proposed and utilized throughout industry. These methods are both qualitative and quantitative and aim to understand, and thus improve, human performance within the system. Additionally, much of the research is focused on risk reduction — for example, design of a power plant to maximize redundancy in human performance during a mishap. Human error is a complicated process in itself and closely tied to cognition, information processing, system automation, team dynamics and biases inherent to humans. It cannot be eliminated by training and familiarity alone, and system design plays a major role in susceptibility to error. The digital age has spurred many advances in processing power, sensor technology and data capture. These advances have resulted in situations where a very large amount of data can be captured and presented to the user. The large amount of information has to be processed with limited attention resources, which can result in human error. This contribution will discuss human error and information processing along with the role of humans in modern power plants. Finally, trends in information overload will be discussed with applications to reducing human error in power plants.
Mill Steam Inerting System Review and Performance Validation
Authors: Lin Qingsheng , Collins Todd
Published: November 2014

NFPA 85, Chapter 9.5.4 states “A pulverizer that is tripped under load shall be inerted and maintained under an inert atmosphere until confirmation that no burning or smoldering fuel exists in the pulverizer or the fuel is removed”. Pulverizer systems with the potential for a resident inventory of combustible material upon trip must be designed and equipped with an inerting system that is capable of maintaining an inert atmosphere to meet this requirement. Proper design of the inerting system and operating procedure, integrated with the mill operation during start-up, shut down and emergency trip is critical for safe mill operation.

This paper presents a mill steam inerting system review and performance validation. The technology has been applied to ball tube mill systems at Hoosier Energy’s Merom Generating Station. A testing technique, used to validate performance of the steam inerting system at this generating plant, is described. It quantifies the compliance of the steam inerting system to meet NFPA requirements during start-up and shut down of the pulverizer. This type of operation is considered to be the most difficult for inerting as the primary air is flowing through the system. The developed testing approach can be applied to evaluate the performance of either existing or newly installed steam inerting systems. The validation technology, developed based on a ball tube mill system, can be readily applied on other types of mill systems, since the steam inerting principle is the same and inerting system requirements are similar, regardless of different mill types.
Introducing ASME PTC 48
Authors: Le Galudec Olivier , Oszewski James , Preston John , Thimsen David
Published: November 2014

In the field of Power Generation, Operators — Plant Owners, Utilities, IPPs … — have had to face severe constraints linked not only with price of electricity and cost of fuel, but also with more and more demanding environmental constraints. It appears that the next atmospheric emission coming under scrutiny is CO2. Some small scale laboratory size experiments and pilot scale tests demonstrating the ability to capture CO2 before it reaches the atmosphere have already been conducted, and some industrial scale demonstrators are already at the permitting stage and will soon reach construction.

In order to anticipate the needs of Performance Tests within this coming market, ASME decided to form a new committee in order to prepare and deliver ASME Performance Test Code – PTC 48 “Overall Plant Performance with Carbon Capture” test code. This new code may be seen as an evolution of ASME PTC 46 “Performance Test Code on Overall Plant Performance” 1996 (currently under revision), which goes beyond the sole verification of components to provide guidelines for testing a full Plant.

Capturing CO2 from fuel–fired power plants will have a significant impact on net capacity and net heat rate of the plant. Such plants will, in addition to the Power Block and Steam Generator, also include systems not commonly included in non-CO2 capture power plants. The addition of an ASU (Air Separation Unit, for oxy-combustion with CO2 capture) and/or CPU (CO2 Purification Unit, for oxy-combustion or post-combustion CO2 capture) has made necessary the preparation of a dedicated test code based upon same guiding principle than PTC 46, i.e. treating the plant globally as a “Black Box”. This approach allows correction of output and efficiency at the plant interfaces, but at the exclusion of internal parameters. It is anticipated that the code can inform development of regulations that define the rules and obligations of Operators.

Currently, the proposed PTC 48 aims at fossil fuel fired Steam-electric power plants using either post-combustion CO2 capture or oxy-combustion with CO2 capture technologies. Combined cycles and Integrated Gasification Combined Cycles — IGCCs — are not addressed.
An Engineering Systems Sensitivity Analysis Model for Holistic Energy-Water Nexus Planning
Authors: Lubega William , Farid Amro M.
Published: November 2014

The energy-water nexus is an area of increasing global concern and research. In several existing publications on the subject, the challenges of water use for power plant cooling and energy use for water supply are handled seperately. There is however also a need to consider the totality of interactions between the different elements of the engineered water and electricity systems, thus creating a system-of-systems model. A model of this form integrates water use for electricity supply and electricity use for water supply into a single framework, thus elucidating a wide range of interactions which can be influenced by policy and management decisions to achieve desired objectives. An engineering model capturing these interactions and based on first-pass models of the underlying physics of the various coupling and boundary points has been developed in previous work. In this work, the Jacobian of the resulting system of equations has been determined for a particular illustrative case. This Jacobian enables a sensitivity analysis of the inputs and outputs of this system-of-systems to changes in water and electricity demand to be carried out. As a concrete example, the Jacobian is used to examine the effect of a 10 % growth in both electricity and water demand on the set of system inputs and outputs.
Optimum Heating of Thick Wall Pressure Components of Steam Boilers
Authors: Dzierwa Piotr , Taler Dawid , Taler Jan , Trojan Marcin
Published: November 2014

A method for determining time-optimum fluid temperature changes is presented. In contrast to present standards, two points at the edge of the opening are taken into consideration. The optimum fluid temperature changes are assumed in the form of a simple time function. It is possible to increase the fluid temperature stepwise and then the fluid temperature can be increased with a constant rate at the beginning of the heating process. Due to the stepwise increase in fluid temperature, heating time of a thick-walled component is of the same order as in the case of calculations according to EN 12952-3 European Standard, but the total circumferential stresses on the edge of the hole do not exceed the allowable value.
Performance Predictions of Axial Turbines for Organic Rankine Cycle (ORC) Applications Based on Measurements of the Flow Through Two-Dimensional Cascades of Blades
Authors: Hasselmann Karsten , Reinker Felix , aus der Wiesche Stefan , Kenig Eugeny Y. , Dubberke Frithjof , Vrabec Jadran
Published: November 2014

The Organic-Rankine-Cycle (ORC) offers a great potential for waste heat recovery and use of low-temperature sources for power generation. However, the ORC thermal efficiency is limited by the relatively low temperature level, and it is, therefore, of major importance to design ORC components with high efficiencies and minimized losses. The use of organic fluids creates new challenges for turbine design, due to real-gas behavior and low speed of sound. The design and performance predictions for steam and gas turbines have been mainly based on measurements and numerical simulations of flow through two-dimensional cascades of blades. In case of ORC turbines and related fluids, such an approach requires the use of specially designed closed cascade wind tunnels. In this contribution, the specific loss mechanisms caused by the organic fluids are reviewed. The concept and design of an ORC cascade wind tunnel are presented. This closed wind tunnel can operate at higher pressure and temperature levels, and this allows for an investigation of typical organic fluids and their real-gas behavior. The choice of suitable test fluids is discussed based on the specific loss mechanisms in ORC turbine cascades. In future work, we are going to exploit large-eddy-simulation (LES) techniques for calculating flow separation and losses. For the validation of this approach and benchmarking different sub-grid models, experimental data of blade cascade tests are crucial. The testing facility is part of a large research project aiming at obtaining loss correlations for performance predictions of ORC turbines and processes, and it is supported by the German Ministry for Education and Research (BMBF).
Numerical Simulation and Analysis of the Two-Sided Windcatcher Inlet\Outlet Effect on Ventilation Flow Through a Three Dimensional Room
Authors: Niktash Amirreza , Huynh B. P.
Published: November 2014

A windcatcher is a structure placed on the roof of a building for providing natural ventilation for interior space working by wind power. It draws out the inside stale air to the outside and supplies the outside fresh air for the building’s interior space.

In this paper, the effect of different types of windcatcher’s inlet\outlet on the air flow, flow velocity and flowrate through a three-dimensional room fitted with a two-sided windcatcher is observed numerically, using a commercial computational fluid dynamics (CFD) software package. The standard RANS K-ε CFD method is used in the simulations. The flow pattern, flow velocity and flowrate of the inside ventilation flow is considered for the six different types of a two-sided windcatcher’s inlet\outlet.

It is found that the shape of the inlet\outlet of windcatcher strongly affects flow pattern, flow velocity and flowrate and the performance of square windcatcher is higher than the circular one specially in ventilating the living area (lower part) of a room.
Cost Performance Tradeoff Study of Low-Carbon System Concepts
Authors: Goudarzi Navid , Pavlak Alex
Published: November 2014

Achieving higher emission reductions on one hand and employing lower cost concepts on the other hand are desirable in designing future power generator systems. Hence, interdisciplinary studies in a form of system concept modeling should be employed to conceptualize and construct economic and efficient low-carbon system concepts. The concept modeling starts with simple idealized models that preserve the key structural features of a system and adds complex features in the following stages to elucidate principles, relationships, and interfaces. For wind systems, the essential features for concept modeling are wind and load variations, and the main goal is to obtain the cost of electricity delivered by the system as a function of wind penetration (emission reduction); more complex features (storage, photovoltaic, transmission, etc.) are added in the following stages. In this work, an interdisciplinary concept modeling is provided to estimate the magnitude of cost versus performance using the wind/load data from Pennsylvania New Jersey Maryland Interconnection (PJM) LLC, and cost estimations published by the Energy Information Agency. The results show that system total cost increases modestly at low penetration, and it increases more rapidly when wind curtailment becomes significant. Eventually storage becomes cheaper than curtailment. The key question that should be answered in this modeling is the magnitude of electricity cost for high penetration, low emission systems.
Diversification From a Combined Heat and Power Plant Owner to an Operations and Maintenance Service Provider
Authors: Judd Ian
Published: November 2014

The aim of this paper is to introduce readers to the UK’s Combined Heat and Power (CHP) industry, whilst identifying the key influences to the industry’s steady decline and the future diversification from an asset owner to a credible CHP or Utilities Operations and Maintenance (O&M) Service provider. There is a lack of research specific to the CHP and Utility O&M sectors that identify how to focus on attaining service excellence that adds real value to customers and stakeholders.

The Service–Profit Chain (SPC) model developed by J. Heskett et al[1] is a recognised theory and business model that established the connection between profitability, customer loyalty, employee satisfaction and productivity. The application of the SPC model to the CHP and Utilities market sectors has identified a possible shortfall with the SPC model framework; in that it requires additional links to the resource support infrastructure and customer service cycle, whilst including the organization’s strategic service vision.

Going beyond the application of the SPC model, this study will identify the additional management tools required to enhance and support the diversification process. An O&M SPC implementation model and a site specific Key Performance Indicator (KPI) model have been designed to complement the organization’s diversification. In addition to this, 10 golden rules have been developed in conjunction with a six tier approach to attain a meaningful O&M Service culture, which should ensure a sustainable future for an O&M Service provider.
Opportunities for Distributed Electricity Generation at Wastewater Facilities
Authors: Liner Barry , Tarallo Steve , Fillmore Lauren , Peot Chris
Published: November 2014

“Wastewater treatment plants are not waste disposal facilities but are water resource recovery facilities that produce clean water, recover nutrients (such as phosphorus and nitrogen), and have the potential to reduce the nation’s dependence on fossil fuels through the production and use of renewable energy and the implementation of energy conservation.” This quote from the 2011 WEF Renewable Energy Position Statement clearly calls attention to the role of wastewater management through Water Resource Recovery Facilities (WRRF) to address the needs of the Utility of the Future.

The water resources utility of the future will integrate these three major concepts of Nutrients, Energy and Water, and many cutting edge utilities are already implementing this management goal of resource recovery. This focus may initially have been internal to the water or wastewater utility, investigating sustainable energy management through energy conservation, increased renewable energy production (where feasible), and focus on overall energy management. The overall societal benefit of the resilience improvement through distributed generation is starting to be realized. The fact that a water resource recovery facility (wastewater plant) that generates its own energy can operate when the power is out is an asset during extreme events. In addition, this capacity can be coordinated with electric utilities to address peak loads and other system needs. Valuable energy products generated on-site at wastewater plants can also supply a portion of energy demand within their respective service areas.

On average, the energy content of wastewater (chemical, hydraulic and thermal) is five times greater than the energy required for treatment. The most common opportunity for on-site power generation is through biogas created through anaerobic digestion. However, technologies such as gasification, pyrolysis, and incineration may be used to generate electricity or fuel. District energy systems, facilities to generate renewable diesel or aviation fuel, hydrogen fuel cells, and in-line hydropower are all being installed today.

However, becoming net energy positive is not the only goal. Optimizing overall sustainability may actually require using more energy or producing less energy onsite. Treating water to higher standards is often more energy intensive. Similarly, using biogas as a transportation fuel reduces onsite power production and increased energy use is required to further process biosolids to maximize reuse potential and to recover nutrients and minerals (e.g., nitrogen, phosphorous, magnesium).

A number of utilities worldwide have already taken the leap and begun this transformation towards resource recovery. While it is not practical for all water resource recovery facilities to become energy positive or neutral, all can take steps towards increasing sustainability while also improving resilience in the energy sector.
Model Centric Approach for Monte Carlo Assessment of Storm Restoration and Smart Grid Automation
Authors: Cheng Danling , Onen Ahmet , Arghandeh Reza , Jung Jaesung , Broadwater Robert , Scirbona Charlie
Published: November 2014

A model centric approach for Monte Carlo simulation for evaluating the economic and reliability benefits of automated switches for storm restoration is presented. A very detailed circuit model with over 20,000 individual customers modeled is used in the simulation. The simulation uses non-constant equipment failure rates based upon actual utility measurements. As part of the Monte Carlo storm simulation, a reconfiguration for restoration algorithm is employed in determining the response to each outage. The reconfiguration for restoration algorithm can work with either manual or automated switches, or both. System reliability with and without automated switching devices is investigated. Cost benefits as well as reliability benefits are considered.
Parametric Effects on Exergetic Efficiency During H2-O2 Combustion Including Singlet Oxygen
Authors: Washington DeVon A. , Shapiro Howard N.
Published: November 2014

Previous work conducted by the authors showed that for a stoichiometric inlet fuel-oxidizer ratio at 1 atm and 1200 K, an optimal range of exergetic efficiency exists for H2 combustion when singlet oxygen composes 0–20% of the oxidizer; with the maximum occurring at approximately 10%. Additionally, in the optimal range, 60% of the total exergy destruction occurs before ignition. These results provide encouraging evidence that it is possible to improve the exergetic efficiency of combustion inherently and thereby reduce fuel usage for a desired energy transfer. The focus of this study is to determine if the exergetic efficiency of combustion can be further optimized by varying other combustion parameters in addition to the inlet concentration of singlet oxygen.

The chemical kinetics simulation was accomplished by developing an adiabatic plug flow reactor model in CHEMKIN-PRO® and employing the Moscow State University H2-O2 mechanism. The ranges of parameters considered were: equivalence ratio 0.7–1.3, inlet temperature 1100–1300 K, inlet concentration of singlet oxygen 0–20%, and diluent type (Ar, N2, no dilution). Pressure was held fixed at 1 atm. The calculated quantities were: exergetic efficiency, exergy destruction before ignition, molar conversion of H2, exit temperature, ignition temperature, and ignition distance.

Results of the study show that over the optimum range the maximum exergetic efficiency occurs for an equivalence ratio of 1.3, with no dilution at 1300 K. Furthermore, the data show that for 20% inlet singlet oxygen there is significant variability in exergy destruction before ignition, ignition temperature, and ignition distance. Understanding how varying traditional combustion parameters impacts the enhancing effect that singlet oxygen has on the exergetic efficiency of H2 combustion provides a framework for directing future research efforts for hydrocarbon combustion under a broader range of operating conditions of practical engineering interest.
High Pressure Feedwater Heater Cup Forging Alteration
Authors: Muldoon Thomas R. , Cashner Bob , Vestfals Sara
Published: November 2014

American Exchanger Services, Inc (AM-EX) performed a 2012 repair of a vertical head-up High Pressure (HP) Feedwater Heater breech lock channel during a shop based re-tube for the American Electric Power (AEP) Wilkes Power Plant, Unit 1. The 48 year old channel is a carbon steel cup-forging that had 1-1/2″ deep circumferential cracks extending radially into the tight knuckle radius at the channel barrel to tubesheet junction. A small area was also found on the backside of the tubesheet which had corroded to a depth of 7/16″.

Several methods to repair these types of failures may be employed, such as grinding out the crack and weld repair, grinding or machining out the crack, leaving as is and performing regular inspections and monitoring crack propagation, or leave as is and perform a fitness for service analysis (API 579-1/ASME FFS-1). A repair was chosen that reduced the stresses in the highly stressed corner radius and was validated using modern calculations. The channel barrel was in the re-tube process so immediate access to a vertical lathe was available and this, in part, lead to the crack removal approach. The design alteration was to machine a pocket to completely remove the crack, verify tubesheet stresses are within allowable stress limits by Finite Element Analysis (FEA), and prescribe future Nondestructive Examination (NDE) to monitor potential future cracking. The size of the machined “pocket” was determined by the actual crack length “as measured” and the repair was verified using FEA. The machined pocket was Dye Penetrant Tested (PT) in September of 2013 (after approximately one year of returning to service), and no defects were noted.

This is not a new repair method; in fact it was researched by Electric Power Research Institute (EPRI) in 1988 symposium [1], and based on an EPRI 1985 [2] similar repair. In the 1985 repair similar methods of FEA were employed, however using less sophisticated forms of the calculation. Modern computing allows for 3D analysis with more complex geometries, and more conservative meshing. This analysis demonstrates that the earlier papers were correct in their understanding of the problem and the proposed solutions. The Wilkes HP feedwater heater was repaired in a similar manner with a machined radius that sufficiently reduced stresses to safe levels allowing an alteration of the vessel to be in compliance with National Board Inspection Code (NBIC) [3] and American Society of Engineers Boiler and Pressure Vessel Code (ASME B&PV CODE) [4].
Modelling Chemical and Microstructural Evolution Across Dissimilar Interfaces in Power Plants
Authors: Clark J. W. G. , McCartney D. G. , Saghafifar H. , Shipway P. H.
Published: November 2014

Dissimilar metal welds between different grades of ferritic steels or between ferritic steel and austenitic nickel alloys are used extensively in power plants. When such weldments are exposed to high temperature conditions, as might be found in service in a thermal power plant, local microstructural evolution will occur. This is due to diffusion, driven by chemical potential gradients, of solute atoms. Such diffusion can cause major changes in hardness and mechanical properties of joints and can lead to the formation of embrittling phases and/or softened zones. This can potentially lead to premature component failure by, for example, high temperature creep.

Whilst finite element modelling of mechanical behavior and damage evolution is well established this is not the case for chemical diffusion and microstructural evolution at weld interfaces. In the present study, the general purpose linked thermodynamic and kinetic software packages Thermo-Calc and DICTRA have been applied to simulate chemical diffusion and precipitation/dissolution (i.e. phase fraction evolution) in dissimilar weld joints using commercially available thermodynamic databases TCFE7 and TTNI6. Two approaches for modelling multiphase, multicomponent systems using this software will be presented and discussed and their implementation will be illustrated.

The paper will present results on modelling a range of dissimilar metal interfaces of both the ferritic-ferritic type and the ferritic-austenitic type (for example, grade 22 to grade 91 steel and grade 22 to Inconel 625). Ferritic-ferritic case studies will compare model predictions with a number of previously published experimental studies and it will be shown that the current approach can give good quantitative agreement in terms of carbon composition profiles and carbide depleted/carbide enriched zones. The results obtained from modelling a grade 22 steel-Inconel 625 system where the crystal structure of the matrix is different on either side of the weld will be compared with experimental observations on a weld overlaid tube component. The experimental results will include scanning and transmission electron microscopy studies of the weld interface regions and it will be shown that the predictions of diffusion and precipitate formation compare well with observations made experimentally following exposure at 650 °C. Also discussed are the options for further refining the computational model based on empirically observed phenomena, such as the unmixed zone of a weld.
Simulations of Pressurized Fluidized Circulating Bed Based Combined Cycle (PFCB)
Authors: Omar Hossin , Elmnefi Mohamed
Published: November 2014

The Pressurized Fluidized Circulating Bed (PFCB) combined cycle was simulated. The simulations balance the energy between the elements of the unit, which consists of gas turbine cycle and steam turbine cycle. The PFCB is used as a combustor and steam generator at the same time. The simulations were carried out for PFCB combined cycle plant for two cases. In the first case, the simulations were performed for combined cycle with reheat in the steam turbine cycle. While in the second case, the simulations were carried out for the PFCB combined cycle with extra combustor and steam turbine cycle with reheat. For both cases, the effect of steam inlet pressure on the combined cycle efficiency was predicted. It was found that increasing of steam pressure results in increase in the combined cycle thermal efficiency. The effect of the inlet flue gases temperature on the gas turbine and on the combined cycle efficiencies was also predicted. The maximum PFCB combined cycle efficiency occurs at a compression ratio of 18, which is the case of utilizing an extra combustor. The simulations were carried out for only one fuel composition and for a compression ratio ranges between 1 to 40.
Admission of Bypass Steam Into a Water Cooled Condenser and Air Cooled Condenser: Similarities, Differences and Areas of Concern
Authors: Nadig Ranga , Sanderlin Dave
Published: November 2014

In power plant locations with adequate supply of cooling water the steam from the steam turbine is condensed in a water cooled condenser. In most instances circulating water from the cooling tower is used to condense the turbine exhaust steam. In other instances once through cooling is deployed wherein water from a lake, river or sea is used to condense the turbine exhaust steam. In water challenged locations or locations where wet cooling cannot be deployed due to permitting or regulatory issues, the steam from the steam turbine is condensed in an air cooled condenser (ACC) wherein ambient air is used to cool and condense the turbine exhaust steam. In a combined cycle plant, during normal operation, the water or air cooled condenser condenses the turbine exhaust steam. During bypass operation, when the steam turbine is out of service, the high-pressure steam from the HRSG is attemperated in a pressure reducing/desuperheating (PRD) valve and then admitted into the water cooled or air cooled condenser. The bypass steam flow is substantially higher than the design turbine exhaust steam flow and the duration of bypass operation can vary from a few hours to several weeks.

The requirements for admission of bypass steam into a water cooled condenser are substantially different from that for an air cooled condenser. In a water cooled condenser the bypass steam is admitted in the steam dome. The bypass steam as well as the turbine exhaust steam is condensed outside the tubes. In an air cooled condenser the bypass steam is admitted in the large diameter steam duct. The bypass, as well as the turbine exhaust steam (normal operation), is condensed inside the tubes. There are similarities and differences in the requirements for admission of bypass steam into a water cooled and air cooled condenser. The differences must be identified and addressed to ensure safe and reliable performance of the condenser.
Degradation of Mechanical Properties for Polyethylene by Small-Deformation Damage
Authors: Jar P-Y Ben
Published: November 2014

Polyethylene (PE) has now been widely used to make plastic pipe for gas transportation. Because of its excellent ductility, processes for repair and maintenance of PE pipe allow squeeze-flattening the pipe to reduce the gas flow. Our previous study has shown that stretch of PE, even at a low strain level, can cause damage of the material, and significance of the damage depends on the strain rate. This paper presents results from a follow-up study, to investigate the possibility of quantifying the influence of damage on the mechanical properties. Coupon specimens used in this study have the same geometry as that used previously. Each specimen was tested twice. The 1st test was to introduce the damage, by stretching the specimen at a crosshead speed of 1 mm/min; the 2nd test to characterize the influence of the damage on the mechanical properties, by stretching the specimen at 1 μm/min. The two crosshead speeds were chosen because the former (1 mm/min) is known to introduce much more damage than the latter (1 μm/min) at a same strain level. Therefore, change in mechanical properties observed from the 2nd test should mainly come from the damage generated in the 1st test. To avoid influence of viscous recovery from the 1st test on the results from the 2nd test, the two tests were conducted more than one month apart. Test results show that even by stretching the specimen to a strain level below the yield point in the 1st test (i.e. with the strain less than 0.1), damage introduced to the specimen can cause a detectable decrease in the mechanical properties, such as the tangent modulus at the strain 0.01 and the stress response at the strain 0.1, from the 2nd test. The results also show that the rate of decrease of the above values with the increase of strain becomes significant when the strain level introduced in the 1st test is above the yield point. By stretching the specimen to a strain level about 0.5 in the 1st test, though yet to cause apparent necking or stress whitening, the tangent modulus and the stress response in the 2nd test are decreased by about one-third of the values for the virgin specimen. This amount of change is significant and should not be ignored for long-term applications such as for gas transportation.
The Role of Weld Processing on the Integrity Assessment of Bimetallic Girth Welds
Authors: Testa Gabriel , Bonora Nicola , Carlucci Antonio , Ruggiero Andrew , Iannitti Gianluca
Published: November 2014

Current design standards and codes do not provide specific guidance how to perform engineering criticality assessment with bi-metallic girth weld in lined or clad pipe. Recently, Bonora et al. (Proc. ASME 2013 32nd OMAE conf.) proposed the equivalent material method (EMM) which allows one to still use current design assessment routes. The method consists in considering instead of three materials in the weld joint, a single “equivalent” material with a flow curve defined as the interpolated lower bound of the three weld joint material flow curves. In this work, the applicability of the EMM was verified considering the effect associated to weld residual stresses. To this purpose, two flaw geometry configurations have been investigated. Particular relevance was given to the multi-pass weld process simulation. Numerical results indicate that the EMM always provides reasonable results in terms of applied J with respect to those obtained considering the effective multimaterials configuration in the weld joint.
An Integrated Creep Model Based on Internal Stress Evolution
Authors: Bonora Nicola , Esposito Luca
Published: November 2014

In creep design, not only secondary creep but also primary and tertiary creep regimes become important for an accurate creep life prediction and need to be accounted for in more sophisticated models. Mechanism-based theories showed a better potential since they usually leads to more accurate prediction over wider range of stress and temperature. It has long been recognized that the mechanics and kinetics of the deformation and recovery processes occurring at the microscale are determined by, amongst other things, the local effective stress while, at macroscopic level, it may still possible to discern an effective stress, which is different from the applied stress that drives the creep strain accumulation, [1]. Recently, the authors proposed an internal stress based model for primary creep, which is independent on the creep rate formulation at the steady state, ensuring the continuity of the creep curve at the transition between primary and secondary creep stages, [2]. In this work, in order to account for all creep stages, this modeling framework is extended further. In particular, for tertiary creep stage, it is assumed that the occurrence of microstructural modifications (such as fine particle dissolution, secondary phase precipitations, etc.) is the process responsible for the reduction of the internal stress and consequent increase of the creep rate as result of the increment of the effective stress. The possibility to derive the internal stress decay function from tertiary creep data is discussed. The proposed model has been applied to P91 high chromium steel and preliminary results are presented in this work.
Application of ASME Piping Code Through a Stress Analysis Procedure and Comparison With the Italian Code
Authors: Grisolia Ottaviano , Scano Lorenzo
Published: November 2014

A previously-developed procedure applies to evaporator section of bottom-supported heat-recovery steam generators (HRSG): The procedure features methods to use on pressure internal parts designed according to Section I, as required by the Boiler & Pressure Vessel (B & PV) Code. It uses ASME Power Piping Code B31.1, which is for external piping, to evaluate additional concerns on pressure parts that have already met Section I. This mainly because other sections of B & PV code do not cover flexibility analysis: Procedure includes classical methods for the static analysis of the lower header and a computer-modeled flexibility analysis. They investigate the stability of the harp high-temperature components, which may be critical because of their longitudinal dimensions, thermal expansions and loading: Preliminary stress evaluation showed that Italian pressure formula is largely conservative.

Methods’ application to a worked example using both ASME and Italian pressure formulae shows now that the pressure contribution is the greatest. Also, the maximum stress found out on the header in sustained case appears consistent with that from numerical model, though bending contribution the greatest; Sustained case appears less critical than thermal. So, the design should be safe from risks of static instability due to longitudinal pressure stress: deformation occasionally observed in field on the lower headers may be correctly imputed to thermal expansion. Herein, a bottom-supported HRSG double-width unity of combined cycle power plant is considered as the worked example.
Energy Saving for a Chinese Crude Oil Pipeline
Authors: Yu Yang , Wu Changchun , Xing Xiaokai , Zuo Lili
Published: November 2014

The Dongying-Linyi Crude Oil Pipeline, transporting the crude oil from Shengli Oilfield to the outside, is one of the most important pipelines in East China. It is of great significance for saving energy, reducing emissions and improving the economy by optimizing pipeline operation. By analyzing the daily operation reports and monthly energy consumption reports, the energy consumption situation of the pipeline is revealed. Then the crude oil from Shengli Oilfield is collected, and its physical property is tested and researched. Based on the topological structure, the technological process and the operation philosophy of the pipeline, the mathematical models for the optimal operation and the energy consumption are built and the corresponding algorithm is introduced. With the models and the algorithms mentioned above, a computer software is developed for the operation simulation and optimization of the pipeline. Combining with practice, three energy-saving measures for the pipeline are analyzed, including reduction of oil heating temperature, operation matching with peak-valley electricity price and operation matching with the combination of flow rates in a planned operation period. In addition, these energy-saving measures are evaluated by the software with several examples. It turns out that: the first measure can considerably reduce the energy consumption and the energy consumption cost of the pipeline; the second could reduce the energy consumption cost of the pipeline a lot, while may make the energy consumption go higher a little; the third could slightly lower the equivalent energy consumption and the energy cost at the same time, but the effect of it is not obvious.
Study of Safety Reserve Factor for Defect Acceptance Criteria in ASME BPV Code
Authors: Chen Zhao-he
Published: November 2014

With some typical pressure vessel materials commonly used for fabrication of pressure retaining Code items and fracture mechanics assessment methods stipulated in Chinese standard GB/T19624, assessment for safety reserve factor for defect acceptance criteria stipulated in ASME Codes, some suggestion for revision to acceptance criteria has been pointed out.
Brittle Fracture Assessments of Offshore PSVs
Authors: Subramanian Kannan , Penso Jorge , Pordal Harbi , McVinnie Graham , Garic Greg
Published: November 2014

Pressure safety relief valve needs to be designed and operated to assure metal temperatures are not lower than the Minimum Allowable Temperature (MAT) to prevent brittle fractures. Design and fitness for service codes include general procedures to prevent brittle fractures. Design procedures in the codes are very conservative whereas fitness for service codes in some cases lack details. In the absence of a detailed brittle fracture assessment procedure for valves subject to significant low temperatures as a result of either Joule-Thompson effect or auto-refrigeration, an approach involving pressure based stress ratio method of ASME/API 579, Part 3 has been adopted and implemented. The initial and very conservative approach involved a worst case combination of the upstream pressure while calculating the stress ratio and a comparison of the newly established MAT with the downstream temperature. This conservative approach resulted in the disqualification of numerous PSVs studied in this work. Valve replacement and associated lost production time leads to high costs. A sophisticated and appropriately conservative brittle fracture assessment approach involving the use of computational fluid dynamics (CFD) followed by finite element method analysis (FEA) based stress analysis was adopted based on the concepts defined in ASME/API 579 and is presented in this paper.

Predictive CFD analysis establishes more realistic temperatures and pressures in relation to the actual operating conditions. The CFD predicted pressure and temperature field is used to determine the stresses in the valve body using FEA methods. The stress analysis is followed by an intermediate brittle fracture assessment based on the procedures described in API 579 Part 3 using the actual PSV body metal temperatures and stresses established using the stress analysis. A discussion on the allowable stresses and stress components to be used in this intermediate assessment is also presented. If the PSVs cannot be qualified with this intermediate brittle fracture assessment, fracture mechanics evaluations are carried out to establish the limiting flaw sizes for the valves. In addition, the flaw tolerances of the valves are also established using reference flaw approach described in API 579, Part 9.