Online boiler convective heat exchanger monitoring: a comparison of soft sensing and data-driven approaches

Online monitoring supports plant reliability and performance management by providing real time information about the condition of equipment. However, the intricate geometries and harsh operating environment of coal fired power plant boilers inhibit the ability to do online measurements of all process related variables. A low-cost alternative lies in the possibility of using knowledge about boiler operation to extract information about its condition from standard online process measurements. This approach is evaluated with the aim of enhancing online condition monitoring of a boiler’s convective pass heat exchanger network by respectively using a soft sensor and a data-driven method. The soft sensor approach is based on a one-dimensional thermofluid process model which takes measurements as inputs and calculates unmeasured variables as outputs. The model is calibrated based on design information. The data-driven method is one developed specifically in this study to identify unique fault signatures in measurement data to detect and quantify changes in unmeasured variables. The fault signatures are initially constructed using the calibrated one-dimensional thermofluid process model. The benefits and limitations of these methods are compared at the hand of a case study boiler. The case study boiler has five convective heat exchanger stages, each composed of four separate legs. The data-driven method estimates the average conduction thermal resistance of individual heat exchanger legs and the flue gas temperature at the inlet to the convective pass. In addition to this, the soft sensor estimates the average fluid variables for individual legs throughout the convective pass and therefore provides information better suited for condition prognosis. The methods are tested using real plant measurements recorded during a period which contained load changes and on-load heat exchanger cleaning events. The cleaning event provides some basis for validating the results because the qualitative changes of some unmeasured monitored variables expected during this event are known. The relative changes detected by both methods are closely correlated. The data-driven method is computationally less expensive and easily implementable across different software platforms once the fault signatures have been obtained. Fault signatures are easily trainable once the model has been developed. The soft sensors require the continuous use of the modelling software and will therefore be subject to licencing constraints. Both methods offer the possibility to enhance the monitoring resolution of modern boilers without the need to install any additional measurements. Implementation of these monitoring frameworks can provide a simple and low-cost contribution to optimized boiler performance and reliability management

Safety analysis in large volume vacuum systems like tokamak: Experiments and numerical simulation to analyze vacuum ruptures consequences

The large volume vacuum systems are used in many industrial operations and research laboratories. Accidents in these systems should have a relevant economical and safety impact. A loss of vacuum accident (LOVA) due to a failure of the main vacuum vessel can result in a fast pressurization of the vessel and consequent mobilization dispersion of hazardous internal material through the braches. It is clear that the influence of flow fields, consequence of accidents like LOVA, on dust resuspension is a key safety issue. In order to develop this analysis an experimental facility is been developed: STARDUST. This last facility has been used to improve the knowledge about LOVA to replicate a condition more similar to appropriate operative condition like to kamaks. By the experimental data the boundary conditions have been extrapolated to give the proper input for the 2D thermofluid-dynamics numerical simulations, developed by the commercial CFD numerical code. The benchmark of numerical simulation results with the experimental ones has been used to validate and tune the 2D thermofluid-dynamics numerical model that has been developed by the authors to replicate the LOVA conditions inside STARDUST. In present work, the facility, materials, numerical model, and relevant results will be presented. © 2014 A. Malizia et al

Implementation of a Cascade Fault Tolerant Control and Fault Diagnosis Design for a Modular Power Supply

The main objective of this research work was to develop reliable and intelligent power sources for the future. To achieve this objective, a modular stand-alone solar energy-based direct current (DC) power supply was designed and implemented. The converter topology used is a two-stage interleaved boost converter, which is monitored in closed loop. The diagnosis method is based on analytic redundancy relations (ARRs) deduced from the bond graph (BG) model, which can be used to detect the failures of power switches, sensors, and discrete components such as the output capacitor. The proposed supervision scheme including a passive fault-tolerant cascade proportional integral sliding mode control (PI-SMC) for the two-stage boost converter connected to a solar panel is suitable for real applications. Most model-based diagnosis approaches for power converters typically deal with open circuit and short circuit faults, but the proposed method offers the advantage of detecting the failures of other vital components. Practical experiments on a newly designed and constructed prototype, along with simulations under PSIM software, confirm the efficiency of the control scheme and the successful recovery of a faulty stage by manual isolation. In future work, the automation of this reconfiguration task could be based on the successful simulation results of the diagnosis method.This research was funded by the Tunisian Ministry of Higher Education and Scientific Research

FAST : a fault detection and identification software tool

The aim of this work is to improve the reliability and safety of complex critical control systems by contributing to the systematic application of fault diagnosis. In order to ease the utilization of fault detection and isolation (FDI) tools in the industry, a systematic approach is required to allow the process engineers to analyze a system from this perspective. In this way, it should be possible to analyze this system to find if it provides the required fault diagnosis and redundancy according to the process criticality. In addition, it should be possible to evaluate what-if scenarios by slightly modifying the process (f.i. adding sensors or changing their placement) and evaluating the impact in terms of the fault diagnosis and redundancy possibilities. Hence, this work proposes an approach to analyze a process from the FDI perspective and for this purpose provides the tool FAST which covers from the analysis and design phase until the final FDI supervisor implementation in a real process. To synthesize the process information, a very simple format has been defined based on XML. This format provides the needed information to systematically perform the Structural Analysis of that process. Any process can be analyzed, the only restriction is that the models of the process components need to be available in the FAST tool. The processes are described in FAST in terms of process variables, components and relations and the tool performs the structural analysis of the process obtaining: (i) the structural matrix, (ii) the perfect matching, (iii) the analytical redundancy relations (if any) and (iv) the fault signature matrix. To aid in the analysis process, FAST can operate stand alone in simulation mode allowing the process engineer to evaluate the faults, its detectability and implement changes in the process components and topology to improve the diagnosis and redundancy capabilities. On the other hand, FAST can operate on-line connected to the process plant through an OPC interface. The OPC interface enables the possibility to connect to almost any process which features a SCADA system for supervisory control. When running in on-line mode, the process is monitored by a software agent known as the Supervisor Agent. FAST has also the capability of implementing distributed FDI using its multi-agent architecture. The tool is able to partition complex industrial processes into subsystems, identify which process variables need to be shared by each subsystem and instantiate a Supervision Agent for each of the partitioned subsystems. The Supervision Agents once instantiated will start diagnosing their local components and handle the requests to provide the variable values which FAST has identified as shared with other agents to support the distributed FDI process.Per tal de facilitar la utilització d'eines per la detecció i identificació de fallades (FDI) en la indústria, es requereix un enfocament sistemàtic per permetre als enginyers de processos analitzar un sistema des d'aquesta perspectiva. D'aquesta forma, hauria de ser possible analitzar aquest sistema per determinar si proporciona el diagnosi de fallades i la redundància d'acord amb la seva criticitat. A més, hauria de ser possible avaluar escenaris de casos modificant lleugerament el procés (per exemple afegint sensors o canviant la seva localització) i avaluant l'impacte en quant a les possibilitats de diagnosi de fallades i redundància. Per tant, aquest projecte proposa un enfocament per analitzar un procés des de la perspectiva FDI i per tal d'implementar-ho proporciona l'eina FAST la qual cobreix des de la fase d'anàlisi i disseny fins a la implementació final d'un supervisor FDI en un procés real. Per sintetitzar la informació del procés s'ha definit un format simple basat en XML. Aquest format proporciona la informació necessària per realitzar de forma sistemàtica l'Anàlisi Estructural del procés. Qualsevol procés pot ser analitzat, només hi ha la restricció de que els models dels components han d'estar disponibles en l'eina FAST. Els processos es descriuen en termes de variables de procés, components i relacions i l'eina realitza l'anàlisi estructural obtenint: (i) la matriu estructural, (ii) el Perfect Matching, (iii) les relacions de redundància analítica, si n'hi ha, i (iv) la matriu signatura de fallades. Per ajudar durant el procés d'anàlisi, FAST pot operar aïlladament en mode de simulació permetent a l'enginyer de procés avaluar fallades, la seva detectabilitat i implementar canvis en els components del procés i la topologia per tal de millorar les capacitats de diagnosi i redundància. Per altra banda, FAST pot operar en línia connectat al procés de la planta per mitjà d'una interfície OPC. La interfície OPC permet la possibilitat de connectar gairebé a qualsevol procés que inclogui un sistema SCADA per la seva supervisió. Quan funciona en mode en línia, el procés està monitoritzat per un agent software anomenat l'Agent Supervisor. Addicionalment, FAST té la capacitat d'implementar FDI de forma distribuïda utilitzant la seva arquitectura multi-agent. L'eina permet dividir sistemes industrials complexes en subsistemes, identificar quines variables de procés han de ser compartides per cada subsistema i generar una instància d'Agent Supervisor per cadascun dels subsistemes identificats. Els Agents Supervisor un cop activats, començaran diagnosticant els components locals i despatxant les peticions de valors per les variables que FAST ha identificat com compartides amb altres agents, per tal d'implementar el procés FDI de forma distribuïda.Postprint (published version

A review of physics-based models in prognostics: application to gears and bearings of rotating machinery

Health condition monitoring for rotating machinery has been developed for many years due to its potential to reduce the cost of the maintenance operations and increase availability. Covering aspects include sensors, signal processing, health assessment and decision-making. This article focuses on prognostics based on physics-based models. While the majority of the research in health condition monitoring focuses on data-driven techniques, physics-based techniques are particularly important if accuracy is a critical factor and testing is restricted. Moreover, the benefits of both approaches can be combined when data-driven and physics-based techniques are integrated. This article reviews the concept of physics-based models for prognostics. An overview of common failure modes of rotating machinery is provided along with the most relevant degradation mechanisms. The models available to represent these degradation mechanisms and their application for prognostics are discussed. Models that have not been applied to health condition monitoring, for example, wear due to metal–metal contact in hydrodynamic bearings, are also included due to its potential for health condition monitoring. The main contribution of this article is the identification of potential physics-based models for prognostics in rotating machinery

Development, Optimization and Testing of High Performance Cooling Systems for Fusion Devices

One of the fundamental components for the full scientific exploitation of future fusion experiments is the Neutral Beam Injectors (NBI). Such devices shall operate in ITER and DEMO experiments at particle energy levels, heating power and steady state working conditions that have never been simultaneously reached before in other experimental facilities. In addition to the challenging technological and manufacturing aspects, NBIs coupled with future fusion reactors should be characterized by much demanding efficiency, availability and reliability factors, composing and additional set of critical issues that claim for an accurate and robust design. The research activity of this PhD thesis focuses on particular components of the negative ion beam source, the accelerating electrostatic grids, which are characterized by high heating power and highly focused power densities, and hence require a continuous active cooling in order guarantee proper heat removal and temperature control. Present research aims to verify the present solution applied inside the NBI accelerator grids realized in PRIMA facility (i.e. MITICA experiment) and to perform further improvements in the heat transfer process with an acceptable pressure drop and reliable manufacturing process. The main advantages rely on the possibility to extend the fatigue life-cycle of different high thermal stress components and to investigate the possibility to employ alternative dielectric fluids instead of water. Such design solutions would in fact allow the exploitation of less performing fluids in terms of cooling capability. This is particularly relevant in view of DEMO and future power plants characterized by higher efficiency and reliability. The research activity is not only limited to numerical analyses but includes the manufacturing of the prototypes of the accelerator grid cooling channels where the novel channel design solutions have been implemented. In order to characterize the experimental thermo-fluid dynamic behaviour of the samples the hydraulic performances and the cooling efficiency in transient operations have been tested in a specific plant for thermo-hydraulic measurements, called Insulation and Cooling Experiment (ICE). In order to support further optimization design activity and the implementation of the cooling solutions inside full-scale models of the electrostatic accelerating grid in future injector beam source the experimental results have been obtained and compared both with Computational Fluid-Dynamic models in order to validate the numerical realized predictions. The thesis is organized in five chapters. The first one is an introduction to nuclear fusion and magnetic confinement. The second chapter gives a description of the NBI devices, both from the conceptual point of view and technology of its components. The third chapter tackles the development of the novel cooling solution designs on a single channel and single beamlet group sub-modelling of the electrostatic grid system. The fourth chapter confronts the numerical obtained results to the experimental ones performed in the specific test-bed facility. In the fifth chapter the different developed designs have been upgraded to the electrostatic grid full scale model and a general scheme for further design improvement is introduced. Final general conclusions are drawn in the last dedicated section of the work. An outline of dealt topics is placed at the beginning of each of the different five chapters

Employing Additive Manufacturing for Fusion High Heat Flux Structures

The commercial realisation of nuclear fusion power will require advanced engineering solutions including high heat flux components with higher performance, greater reliability, and longer lifetimes. Additive manufacturing (AM) provides opportunities to produce components with previously unachievable geometries in new and hard-to-manufacture materials. This project introduces the state of the art of fusion high heat flux components and AM and then focuses on applying laser powder bed fusion to high temperature divertor designs. Much of the work was carried out in parallel to the EU FP7 AMAZE project (Additive Manufacturing Aiming towards Zero waste and Efficient production of high-tech metal products). A review of material selection for divertor applications is carried out with an emphasis on the cooled substructure. A parallel, strengths-based approach is undertaken concluding in a series of SWOT (strengths, weaknesses, opportunities, threats) analyses rather than a traditional linear down-selection. Material properties including strength, ductility, thermal expansion, and thermal conductivity are graphically presented as well as derived figures of merit for thermal stress and thermal mismatch with tungsten armour. Radiation damage and compatibility with operational and manufacturing environments are considered and historical summaries of availability and cost are given. By emphasising high temperature operation and acknowledging the inevitability of some nuclear activation beyond the usual 100 year limit, refractory metals and their alloys present themselves as promising candidates, particularly those based on vanadium, tantalum, and molybdenum. A shortage of data for these materials is highlighted, particularly under fusion neutron irradiation, as well as the need for greater understanding of corrosion under relevant conditions. Two novel divertor cooling schemes are then presented and evaluated via concept-level tile-type geometries. The first is a design with multiple small pipes fed from the rear of the component via an in-built manifold and the second employs an enclosed pin-fin array drawing inspiration from the electronics industry. Both highlight features made feasible only by employing AM and use tantalum as the structural material to demonstrate the effect of high-temperature operation on performance. 1D analytical calculations and simple finite element modelling with 150◦C and 600◦C coolant and up to 10 MWm−2 heat flux loading demonstrate improved heat transfer coefficients and more uniform temperature distributions. Performance improvement over conventional designs is likely to be marginal without significant further design optimisation, but the up to 80% reduction in material use compared with conventional concepts, higher thermal efficiency, and opportunity to reduce or relocate pipe joints are highlighted as more significant advantages. Work to develop laser powder bed fusion of tungsten, molybdenum, and tantalum is then presented. First, a summary of context and recent related work is given. A through-lifecycle approach to component development is detailed with the aim of giving an insight into critical issues related to supply chain, process development, material testing, and component build trials. Basic characterisation of size, morphology, and flowability of a selection of powders is used to demonstrate the high variability of current supply. This is followed by determination of first-order build parameters and energy density required for consolidation. Persistent cracking is found, particularly in tungsten and molybdenum, and causes including oxidation and residual stress are posited with suggestions for possible approaches to mitigating these. The results of material testing of small samples are given, including dilatometry, laser flash, and small punch. Small sample numbers and high variability prevent definitive conclusions from being drawn, but trends towards increased brittleness and decreased thermal conductivity are shown and there are indications that the extreme thermal conditions during processing produce β and ω phases of tantalum. Finally a description of a new facility is given, HIVE (Heating by Induction to Verify Extremes), as well as the results of comparative high heat flux testing of two simple copper components - one produced by electron beam melting (EBM) and the other conventionally manufactured. HIVE can apply a constant 10 MWm−2 to a 30 mm x 30 mm test-piece in vacuum which can be cooled using a 200◦C cooling water supply. Thermocouples, thermography, and water calorimetry provide instrumentation. This facility acts as a strategic and previously unavailable intermediate concept validation step between analytical modelling and plasma-surface interaction testing or in-situ qualification. The results presented suggest that convective heat transfer is enhanced by the rough surface of the AM copper part, but that the component’s lower thermal conductivity through the AM copper and across the brazed joint compared to the conventional results in a higher bulk temperature for the same input power indicating a lower overall heat flux handing capability. The project concludes with a summary of key findings and suggestions for future work

Review of selection criteria for sensor and actuator configurations suitable for internal combustion engines

This literature review considers the problem of finding a suitable configuration of sensors and actuators for the control of an internal combustion engine. It takes a look at the methods, algorithms, processes, metrics, applications, research groups and patents relevant for this topic. Several formal metric have been proposed, but practical use remains limited. Maximal information criteria are theoretically optimal for selecting sensors, but hard to apply to a system as complex and nonlinear as an engine. Thus, we reviewed methods applied to neighboring fields including nonlinear systems and non-minimal phase systems. Furthermore, the closed loop nature of control means that information is not the only consideration, and speed, stability and robustness have to be considered. The optimal use of sensor information also requires the use of models, observers, state estimators or virtual sensors, and practical acceptance of these remains limited. Simple control metrics such as conditioning number are popular, mostly because they need fewer assumptions than closed-loop metrics, which require a full plant, disturbance and goal model. Overall, no clear consensus can be found on the choice of metrics to define optimal control configurations, with physical measures, linear algebra metrics and modern control metrics all being used. Genetic algorithms and multi-criterial optimisation were identified as the most widely used methods for optimal sensor selection, although addressing the dimensionality and complexity of formulating the problem remains a challenge. This review does present a number of different successful approaches for specific applications domains, some of which may be applicable to diesel engines and other automotive applications. For a thorough treatment, non-linear dynamics and uncertainties need to be considered together, which requires sophisticated (non-Gaussian) stochastic models to establish the value of a control architecture

Magnetic Resonance Imaging Techniques for Thermofluid Applications

In this PhD thesis, Magnetic Resonance Imaging (MRI) techniques were applied to thermofluid applications. Magnetic Resonance Velocimetry (MRV) was utilized to measure the three-dimensional, three-component mean velocity field in forced convection flows. Flow models were investigated that contain complex internal structures (e.g. compact heat exchangers) that would not be measureable with conventional optical velocity measurement techniques. The effects of the internal structures on the fluid flow were analyzed to understand the flow physics and to introduce further improvements in performance. Modern three-dimensional manufacturing processes, such as direct polyamide laser sintering, were used to manufacture MR compatible flow models of arbitrary complexity. Measuring velocity fields in such flow models highlights the unique features of MRV. Magnetic Resonance Thermometry (MRT), based on the temperature-dependent Proton Resonance Frequency (PRF) shift of the water molecule, is a comparatively novel approach with which the scalar temperature difference field can be measured. Novel experimental setups meeting the requirements given by MRT were developed and applied to MRT and MRV. The chosen flow models were taken from thermofluid sciences and exhibit mixed convection flows, whereby temperature-induced buoyancy forces play an important role. In their velocity and temperature fields three-dimensional structures develop. The three-dimensional temperature and velocity vector fields were measured utilizing optimized adjustments of both techniques. The results show the applicability of MRT and MRV to thermofluid applications and demonstrate these MRI techniques as valuable engineering measurement tools

Controle reconfigurável de processos sujeitos a falhas em atuadores : uma abordagem baseada no MPC em duas camadas

Orientadores: Flávio Vasconcelos da Silva, Thiago Vaz da CostaDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia QuímicaResumo: Plantas industriais modernas estão suscetíveis a falhas em equipamentos de processo e em instrumentos e componentes da malha de controle. Tais eventos anormais podem acarretar danos a equipamentos, degradação do desempenho do processo e até cenários extremos como a parada da planta e acidentes graves. Em vista disso, o emprego de sistemas de controle tolerante a falhas visa a elevar o grau de confiabilidade e segurança do processo por meio do tratamento e mitigação de eventos anormais, evitando que evoluam para situações críticas. Nesse sentido, este trabalho tem como objetivo desenvolver uma técnica de controle reconfigurável tolerante a falhas para processos sujeitos a falhas em atuadores. A presente proposta é baseada em abordagens por atuadores virtuais e ocultação da falha. Essas técnicas consistem no recálculo das ações de controle e na ocultação da falha do ponto de vista do controlador nominal, permitindo que o mesmo seja mantido após a reconfiguração da malha de controle. Na presente proposta, o atuador virtual é baseado na estrutura do controlador preditivo em duas camadas. Uma camada consiste no cálculo de referências para as variáveis de entrada e para o desvio previsto entre o comportamento da planta nominal e com falha. A outra camada, por sua vez, é responsável por conduzir as variáveis de processo para as referências calculadas na etapa anterior. Ambas as camadas são baseadas em problemas de programação quadrática e levam em consideração as restrições do processo, como limites de atuadores e desvios permissíveis em relação ao comportamento nominal da planta. Essa técnica possibilita a consideração de cenários de falhas nos quais não há graus de liberdade suficientes para a manutenção de variáveis controladas em valores desejados. Assim, a estimativa de perturbações permite que novas referências atingíveis sejam calculadas, ainda que haja erros de identificação do modelo pós-falha do processo. Por fim, a estrutura de controle proposta foi aplicada em simulações utilizando um processo de tanques quádruplos, bem como em experimentos conduzidos em uma planta de neutralização de pHAbstract: Modern industrial plants are susceptible to faults in process equipment and in instruments and components of the control loop. Such abnormal events can lead to equipment damage, degradation of process performance and even extreme scenarios such as plant shutdown and serious accidents. Thus, the use of fault-tolerant control systems aims to increase process reliability and safety by treating and mitigating abnormal events, preventing them from evolving to critical situations. In this sense, this work aims to develop a reconfigurable fault tolerant control technique for processes subject to actuator faults. The present proposal is based on the virtual actuator and fault hiding approaches. These techniques consist of recomputing control actions and hiding the fault from the nominal controller perspective, allowing it to be maintained after the control loop reconfiguration. We propose a virtual actuator based on the two-layer model predictive control structure. One layer consists of calculating references for input variables and for the predicted deviation between the nominal and faulty plant behaviors. The other layer, in turn, is responsible for driving process variables to the references calculated in the previous step. Both layers are based on quadratic programming problems and take into account process constraints such as actuator limits and permissible deviations from the nominal plant behavior. This technique allows the consideration of fault scenarios in which there are not enough degrees of freedom for the maintenance of controlled variables in desired values. Thus, disturbance estimation allows the calculation of new achievable references, even though there are identification errors in the post-fault model. Finally, the proposed control structure has been applied to an experimental pH neutralization plant. Finally, the proposed control structure was applied in simulations to a quadruple-tank process as well as in experiments conducted in a pH neutralization plantMestradoSistemas de Processos Quimicos e InformaticaMestre em Engenharia Química130952/2015-0CNP