References of "Dewallef, Pierre"
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See detailSimulation and optimization of a CHP biomass plant and district heating network
Sartor, Kevin ULg; Quoilin, Sylvain ULg; Dewallef, Pierre ULg

in Applied Energy (2014), 130

Biomass Combined Heat and Power (CHP) plants connected to district heating (DH) networks are recognized nowadays as a very good opportunity to increase the share of renewable sources into energy systems ... [more ▼]

Biomass Combined Heat and Power (CHP) plants connected to district heating (DH) networks are recognized nowadays as a very good opportunity to increase the share of renewable sources into energy systems. However, as CHP plants are not optimized for electricity production, their operation is profitable only if a sufficient heat demand is available throughout the year. Most of the time, pre-feasibility studies are based on peak power demand and business plans only assume monthly or yearly consumption data. This approach usually turns out to overestimate the number of operating hours or oversize the plant capacity. This contribution presents a methodology intended to be simple and effective that provides accurate estimations of economical, environmental and energetic performances of CHP plants connected to district heating networks. A quasi-steady state simulation model of a CHP plant combined with a simulation model of the district heating network installed on the Campus of the University in Liège (Belgium) is used as an application framework to demonstrate the effectiveness of the selected approach. Based on the developed model and actual consumption data, several scenarios for energy savings are considered and ranked. The potential energy savings and resulting energy costs are estimated enabling more general conclusions to be drawn on the opportunity of using district heating networks in urban districts for Western Europe countries. [less ▲]

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See detailAnalysis versus synthesis for trending of gas-path measurement time series
Borguet, Sébastien ULg; Léonard, Olivier ULg; Dewallef, Pierre ULg

in Proceedings of ASME Turbo Expo 2014 (2014, June)

Gas-path measurements used to assess the health condition of an engine are corrupted by noise. Generally, a data cleaning step occurs before proceeding with fault detection and isolation. Classical linear ... [more ▼]

Gas-path measurements used to assess the health condition of an engine are corrupted by noise. Generally, a data cleaning step occurs before proceeding with fault detection and isolation. Classical linear filters such as the exponentially weighted moving average filter are traditionally used for noise removal. Unfortunately, these low-pass filters distort trend shifts indicative of faults, which increases the detection delay. The present paper investigates two new approaches to non-linear filtering of time series. On one hand, the synthesis approach reconstructs the signal as a combination of elementary signals chosen from a pre-defined library. On the other hand, the analysis approach imposes a constraint on the shape of the signal (e.g., piecewise constant). Both approaches incorporate prior information about the signal in a different way, but they lead to trend filters that are very capable at noise removal while preserving at the same time sharp edges in the signal. This is highlighted through the comparison with a classical linear filter on a batch of synthetic data representative of typical engine fault profiles. [less ▲]

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See detailPrediction of SOx and NOx Emissions from a Medium Size Biomass Boiler Biomass and Bioenergy
Sartor, Kevin ULg; Restivo, Yannick ULg; Ngendakumana, Philippe ULg et al

in Biomass and Bioenergy (2014), 65

While small and medium size biomass combined heat and power (CHP) plants (i.e., up to 5 MW of electrical rated power) represent an attractive option to exploit locally available biomass resources at low ... [more ▼]

While small and medium size biomass combined heat and power (CHP) plants (i.e., up to 5 MW of electrical rated power) represent an attractive option to exploit locally available biomass resources at low cost, the corresponding investment per unit of rated power significantly rises when the installed power decreases. In these cases, secondary pollutant emissions control measures are most of the time not economically viable and primary emissions control must be used alone to avoid the formation of undesired compounds such as $NO_x$ and $SO_x$. Primary control measures require the careful optimization of fuel quality and combustion process. For plant operators, being able to accommodate biomass quality changes in order to minimize the fuel cost can be of great importance in order to guarantee the profitability of the plant. This contribution is dedicated to the development of a zero-dimensional (input-output) combustion simulation model able to predict the pollutants emissions resulting from complete and incomplete combustion with respect to varying combustion operation (ambient temperature, humidity, fumes recirculation,..). This tool is intended to be integrated in a global simulation model of the CHP plant and the attached district heating network installed on the University campus in Liège. Doing so, the plant operation can be optimized with respect to economic as well as environmental and energetic aspects (3E approach) thus ensuring the sustainability of the approach. [less ▲]

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See detailMethods to Increase the Robustness of Finite-Volume Flow Models in Thermodynamic Systems
Quoilin, Sylvain ULg; Bell, Ian ULg; Desideri, Adriano ULg et al

in Energies (2014), 7(3), 1621-1640

This paper addresses the issues linked to simulation failures during integration in finite-volume flow models, especially those involving a two-phase state. This kind of model is particularly useful when ... [more ▼]

This paper addresses the issues linked to simulation failures during integration in finite-volume flow models, especially those involving a two-phase state. This kind of model is particularly useful when modeling 1D heat exchangers or piping, e.g., in thermodynamic cycles involving a phase change. Issues, such as chattering or stiff systems, can lead to low simulation speed, instabilities and simulation failures. In the particular case of two-phase flow models, they are usually linked to a discontinuity in the density derivative between the liquid and two-phase zones. In this work, several methods to tackle numerical problems are developed, described, implemented and compared. In addition, methods available in the literature are also implemented and compared to the proposed approaches. Results suggest that the robustness of the models can be significantly increased with these different methods, at the price of a small increase of the error in the mass and energy balances. [less ▲]

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See detailUnveiling the mystery of Combined Heat & Power (cogeneration)
Verbruggen, Aviel; Dewallef, Pierre ULg; Quoilin, Sylvain ULg et al

in Energy (2013), 61

The article unveils the mystery of cogeneration. Cogeneration is an add-on or embedded activity in thermal power plants, with as merit the use of part or whole of their point source heat exhausts. EU's ... [more ▼]

The article unveils the mystery of cogeneration. Cogeneration is an add-on or embedded activity in thermal power plants, with as merit the use of part or whole of their point source heat exhausts. EU's talk of “high-efficiency cogeneration” is an unfounded transfer of responsibility from the hosting thermal power generation plant onto CHP (Combined Heat & Power) activity. The quality of a CHP activity is univocally defined by its design power-to-heat ratio σ, a tombstone parameter derived from the design characteristics of the power plant. A thermal power plant may house more than one cogeneration activity. Identifying σ requires positioning the bliss point in the electricity–heat production possibility set of the cogeneration activity. The bliss point is where after electric output is maximized, the sum of that output and the maximum recoverable quantity of heat occurs. Once CHP's mystery of virtual bliss points is unveiled, the proper σ are found. With known σ by CHP activity, the quantity of cogenerated electricity is reliably assessed as best indicator of cogeneration performance. Our analysis is applicable on all relevant thermal power cycles that host CHP activities, and illustrated with a numerical example. Our lean method is necessary and sufficient for proper CHP regulation. [less ▲]

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See detailImproved District Heating Network Operation by the Integration of High Temperature Heat Pumps
Sartor, Kevin ULg; Lemort, Vincent ULg; Dewallef, Pierre ULg

in Digital proceedings of the 8th Conference on Sustainable Development of Energy, Water and Environment Systems - SDEWES (2013, September 23)

Biomass Combined Heat and Power (CHP) plants connected to district heating networks are a very good opportunity to increase the share of renewable sources into energy systems. Frequently, important ... [more ▼]

Biomass Combined Heat and Power (CHP) plants connected to district heating networks are a very good opportunity to increase the share of renewable sources into energy systems. Frequently, important consumers are connected to ensure a stable base demand of heat throughout the year but they often have higher requirements in terms of temperature (i.e., steam) which involves high level of temperatures in the district heating network during the whole year and high levels of heat losses in the network. This contribution presents the possibility to decrease the level of temperature at which the district heating network operates and to use high temperature heat pumps connected locally at the consumption point to produce steam when needed. An investigation of the global design and integration through thermodynamic simulation models is realized for the University of Liège district heating network. This study is intended to determine the heat pump coefficient of performance and, therefore, to assess the balance between the savings in terms of heat losses and the additional heat pump electricity consumption. [less ▲]

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See detailSimulation and optimization of a CHP biomass plant and district heating network
Sartor, Kevin ULg; Quoilin, Sylvain ULg; Dewallef, Pierre ULg

Conference (2013, July)

Biomass Combined Heat and Power (CHP) plants connected to district heating (DH) networks are recognized nowadays as a very good opportunity to increase the share of renewable sources into energy systems ... [more ▼]

Biomass Combined Heat and Power (CHP) plants connected to district heating (DH) networks are recognized nowadays as a very good opportunity to increase the share of renewable sources into energy systems. However, as CHP plants are not optimized for electricity production, their operation is profitable only if a sufficient heat demand is available throughout the year. Most of the time, pre-feasibility studies are based on peak power demand and business plans only assume monthly or yearly consumption data. This approach usually turns out to overestimate the number of operating hours or oversize the plant capacity. This contribution presents a methodology intended to be simple and effective that provides accurate estimations of economical, environmental and energetic performances of CHP plants connected to district heating networks. A quasi-steady state simulation model of a CHP plant combined with a simulation model of the district heating network installed on the Campus of the University in Liège (Belgium) is used as an application framework to demonstrate the effectiveness of the selected approach. Based on the developed model and actual consumption data, several scenarios for energy savings are considered and ranked. The potential energy savings and resulting energy costs are estimated enabling more general conclusions to be drawn on the opportunity of using district heating networks in urban districts for Western Europe countries. [less ▲]

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See detailOptimization of the operating conditions of an existing biomass CHP plant with respect to pollutants levels
Sartor, Kevin ULg; Restivo, Yannick ULg; Ngendakumana, Philippe ULg et al

in Proceedings of 21st Biomass Conference and Exhibition (2013, June 03)

While small and medium size biomass combined heat and power plants (i.e., up to 5 MW of electrical rated power) represent an attractive option to exploit locally available biomass resources at low cost ... [more ▼]

While small and medium size biomass combined heat and power plants (i.e., up to 5 MW of electrical rated power) represent an attractive option to exploit locally available biomass resources at low cost, the corresponding investment per unit of rated power significantly rises when the installed power decreases. In these cases, secondary pollutant emissions control measures are most of the time not economically viable and primary emissions control must be used alone to avoid the formation of undesired compounds such as $NO_x$ and $SO_x$. Primary control measures require the careful optimization of fuel quality and combustion process. For plant operators, being able to accommodate biomass quality changes in order to minimize the fuel cost can be of great importance in order to guarantee the profitability of the plant. This contribution is dedicated to the development of zero-dimensional (input-output) combustion simulation model able to predict the pollutants emissions resulting from complete and incomplete combustion with respect to varying combustion operation (ambient temperature, humidity, fumes recirculation,..). This tool is intended to be integrated in global simulation model of the CHP plant and the attached district heating network installed on the University campus in Liège. Doing so, the plant operation can be optimized with respect to economic as well as environmental and energetic aspects (3E approach) thus ensuring the sustainability of the approach. [less ▲]

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See detailTechno-economic survey of Organic Rankine Cycle (ORC) systems
Quoilin, Sylvain ULg; van den Broeck, Martijn; Declaye, Sébastien ULg et al

in Renewable & Sustainable Energy Reviews (2013), 22

New heat conversion technologies need to be developed and improved to take advantage of the necessary increase in the supply of renewable energy. The Organic Rankine Cycle is well suited for these ... [more ▼]

New heat conversion technologies need to be developed and improved to take advantage of the necessary increase in the supply of renewable energy. The Organic Rankine Cycle is well suited for these applications, mainly because of its ability to recover low-grade heat and the possibility to be implemented in decentralized lower-capacity power plants. In This paper, an overview of the different ORC applications is presented. A market review is proposed including cost figures for several commercial ORC modules and manufacturers. An in-depth analysis of the technical challenges related to the technology, such as working fluid selection and expansion machine issues is then reported. Technological constraints and optimization methods are extensively described and discussed. Finally, the current trends in research and development for the next generation of Organic Rankine Cycles are presented. [less ▲]

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See detailA Methodology to Improve the Robustness of Gas Turbine Engine Performance Monitoring Against Sensor Faults
Dewallef, Pierre ULg; Borguet, Sébastien ULg

in Journal of Engineering for Gas Turbines and Power (2013), 135(5),

For turbine engine performance monitoring purposes, system identification techniques are often used to adapt a turbine engine simulation model to some measurements performed while the engine is in service ... [more ▼]

For turbine engine performance monitoring purposes, system identification techniques are often used to adapt a turbine engine simulation model to some measurements performed while the engine is in service. Doing so, the simulation model is adapted through a set of so-called health parameters whose values are intended to represent a faithful image of the actual health condition of the engine. For sake of low computational burden, the problem of random errors contaminating the measurements is often considered to be zero-mean, white and Gaussian random variables. However, when a sensor fault occurs, the measurement errors no longer satisfy the Gaussian assumption and the results given by the system identification rapidly become unreliable. The present contribution is dedicated to the development of a diagnosis tool based on a Kalman filter whose structure is slightly modified in order to accommodate sensor malfunctions. The benefit in terms of the diagnostic reliability of the resulting tool is illustrated on several sensor faults that may be encountered on a current turbofan layout. [less ▲]

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See detailVariable Renewable Energy integration and the balancing challenge: Flexibility assessment in Belgium
Quoilin, Sylvain ULg; Dewallef, Pierre ULg; Verbruggen, Aviel

Poster (2012, November)

The world is facing a historical increase in energy demand and energy consumption. Variable Renewable Energy (VRE) sources are considered as a solution to both environmental issues and energy demand, even ... [more ▼]

The world is facing a historical increase in energy demand and energy consumption. Variable Renewable Energy (VRE) sources are considered as a solution to both environmental issues and energy demand, even though they present high variability and low predictability. Variability and uncertainty are familiar aspects of all power systems. However, the increase of the share of renewable sources leads to new needs in terms of flexible resources. These resources can be provided by four different means: 1. Dispatchable power plants (i.e. with ramp up and ramp down capabilities) 2. Storage systems, mainly in the form of pumping stations. 3. Grid interconnections between countries 4. Demand side management. The present work focuses on the Belgian transmission grid. In order to assess its flexibility, both the technical flexible resource available and the flexibility requirement are evaluated in the considered area and the Present Variable Renewable Energy penetration Potential is calculated. [less ▲]

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See detailAdaptive estimation algorithm for aircraft engine performance monitoring
Léonard, Olivier ULg; Borguet, Sébastien ULg; Dewallef, Pierre ULg

in Journal of Propulsion and Power (2008), 24(4), 763-769

In the frame of turbine engine performance monitoring, system identification procedures are often used to adapt a simulation model of the engine to some observed data through a set of so-called health ... [more ▼]

In the frame of turbine engine performance monitoring, system identification procedures are often used to adapt a simulation model of the engine to some observed data through a set of so-called health parameters. Doing so, the values of these health parameters are intended to represent the actual health condition of the engine. The Kalman filter has been widely used to achieve the identification procedure in real-time onboard applications. However, to achieve a proper filtering of the measurement noise, the health parameters are often assumed to vary in time relatively slowly, preventing any abrupt accidental events from being tracked effectively. This contribution presents a procedure called adaptive filtering. Based on a covariance-matching method, it is intended to automatically release the health parameters once an accidental event is detected. This enables the Kalman filter to deal with both continuous and abrupt fault conditions. [less ▲]

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See detailA way to deal with model-plant mismatch for a reliable diagnosis in transient operation
Borguet, Sébastien ULg; Dewallef, Pierre ULg; Léonard, Olivier ULg

in Journal of Engineering for Gas Turbines & Power (2008), 130(3),

Least-squares health parameter identification techniques, such as the Kalman filter, have been extensively used to solve diagnosis problems. Indeed, such methods give a good estimate provided that the ... [more ▼]

Least-squares health parameter identification techniques, such as the Kalman filter, have been extensively used to solve diagnosis problems. Indeed, such methods give a good estimate provided that the discrepancies between the model prediction and the measurements are Zero-mean, white, Gaussian random variables. In a turbine engine diagnosis, however this assumption does not always hold due to the presence of biases in the model. This is especially true for a transient operation. As a result, the estimated parameters tend to diverge from their actual values, which strongly degrades the diagnosis. The purpose of this contribution is to present a Kalman filter diagnosis tool where the model biases are treated as an additional random measurement error. The new methodology is tested on simulated transient data representative of a current turbofan engine configuration. While relatively simple to implement, the newly developed diagnosis tool exhibits a much better accuracy than the original Kalman filter in the presence of model biases. [less ▲]

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See detailA Way to Deal with Model-Plant Mismatch for a Reliable Diagnosis in Transient Operation
Borguet, Sébastien ULg; Dewallef, Pierre ULg; Léonard, Olivier ULg

in Proceedings of the ASME Turbo Expo 2006 (2006, May)

Least-squares health parameter identification techniques such as the Kalman filter have been massively used to solve the problem of turbine engine diagnosis. Indeed, such methods give a good estimate ... [more ▼]

Least-squares health parameter identification techniques such as the Kalman filter have been massively used to solve the problem of turbine engine diagnosis. Indeed, such methods give a good estimate provided that the discrepancies between the model prediction and the measurements are zero-mean, white random variables. In turbine engine diagnosis, however, this assumption does not always hold due to the presence of biases in the model. This is especially true for transient operation. As a result, the estimated parameters tend to diverge from their actual values which strongly deteriorates the diagnosis. The purpose of this contribution is to present a Kalman filter diagnosis tool where the model biases are treated as an additional random measurement error. The new methodology is tested on simulated transient data representative of a current turbofan layout. While relatively simple to implement, the newly developed diagnosis tool exhibits a much better accuracy than the original Kalman filter in the presence of model biases. [less ▲]

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See detailCombining classification techniques with Kalman filters for aircraft engine diagnostics
Dewallef, Pierre ULg; Romessis, C.; Léonard, Olivier ULg et al

in Journal of Engineering for Gas Turbines & Power (2006), 128(2), 281-287

A diagnostic method consisting of a combination of Kalman filters and Bayesian Belief Network (BBN) is presented. A soft-constrained Kalman filter uses a priori information derived by a BBN at each time ... [more ▼]

A diagnostic method consisting of a combination of Kalman filters and Bayesian Belief Network (BBN) is presented. A soft-constrained Kalman filter uses a priori information derived by a BBN at each time step, to derive estimations of the unknown health parameters. The resulting algorithm hers improved identification capability in comparison to the stand-alone Kalman filter. The paper focuses on a way of combining the information produced by the BBN with the Kalman filter. An extensive set of fault cases is used to test the method on a typical civil turbofan layout. The effectiveness of the method is thus demonstrated, and its advantages over individual constituent methods are presented. [less ▲]

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See detailOn-Line Transient Engine Diagnostics in a Kalman Filtering Framework
Borguet, Sébastien ULg; Dewallef, Pierre ULg; Léonard, Olivier ULg

in Proceedings of the ASME Turbo Expo 2005 (2005, June)

A common assumption made in the performance assessment of a turbine engine for aircraft propulsion consists in restricting the data processing to steady-state data. This especially holds for on-board ... [more ▼]

A common assumption made in the performance assessment of a turbine engine for aircraft propulsion consists in restricting the data processing to steady-state data. This especially holds for on-board performance monitoring of a commercial aircraft which spends up to 90% of the time in cruise flight where such conditions are satisfied. The present contribution is intended to investigate the ability of a diagnosis method to process unsteady data rather than steady-state data. The aim of this unsteady approach is to strongly reduce the time and the efforts spent to obtain a reliable diagnosis. In order to assess the improvements in terms of diagnosis efficiency and engine operability, the resulting diagnostic method is tested for different degradations that can be expected on commercial turbofans. The results are also compared to those obtained from cruise flight steady-state data in order to balance the two approaches. [less ▲]

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See detailCombining classification techniques with Kalman filters for aircraft engine diagnostics
Dewallef, Pierre ULg; Léonard, Olivier ULg; Mathioudakis, Kostas et al

in Proceedings of the ASME Turbo Expo 2004 (2004, June)

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See detailOn-Line Aircraft Engine Diagnostic Using a Soft-Constrained Kalman Filter
Dewallef, Pierre ULg; Léonard, Olivier ULg; Mathioudakis, Kostas

in Proceedings of the ASME Turbo Expo 2004 (2004, June)

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See detailOn-Line Performance Monitoring and Engine Diagnostic Using Robust Kalman Filtering Techniques
Dewallef, Pierre ULg; Léonard, Olivier ULg

in Proceedings of the ASME Turbo Expo 2003 (2003, June)

In this contribution, an on-line engine performance monitoring is carried out through an engine health parameter estimation based on several gas path measurements. This health parameter estimation makes ... [more ▼]

In this contribution, an on-line engine performance monitoring is carried out through an engine health parameter estimation based on several gas path measurements. This health parameter estimation makes use of the analytical redundancy of an engine model and therefore implies the knowledge of the engine state. As the latter is a priori not known the second task is therefore an engine state variable estimation. State variables here designate working conditions such as inlet temperature, pressure, Mach number, rotational speeds, . . . Estimation of the state variables constitutes a general application of the Extended Kalman Filter theory, while the health parameter estimation is a classical recurrent regression problem. Recent advances in stochastic methods [1] show that both problems can be solved by two Kalman filters working jointly. Such filters are usually named Dual Kalman Filters. The present contribution aims at using a dual Kalman filter modified to provide robustness. This procedure should be able to cope with as much as 20 to 30% of faulty data. The resulting online method is applied to a turbofan model developed in the frame of the OBIDICOTE 1 project. Several tests are carried out to check the performance monitoring capability and the robustness that can be achieved. [less ▲]

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