Full Plant Model Research Articles

Multi-physics analysis of SBLOCA by coupled Neutronics/Thermal-Hydraulics full plant model

With the development of computational tools, the accident analysis would be performed by best estimate approaches. The employment of multi-physics codes would be considered as new calculation procedure to obtain high valuable results by improving calculations with specialized codes. The small break loss of coolant accident (SBLOCA) is an accident that has typically been analyzed using system codes with a limited number of Thermal-Hydraulics (TH) channels in the core region, neglecting the use of multi-physics calculations. This approach results in insufficient accuracy and resolution in both neutronics and TH calculations within the core zone. To address this issue, this study proposes the implementation of a Neutronics/Thermal-Hydraulics coupling with one-to-one mapping in the core zone, achieved through the development of a comprehensive plant TH model. This approach aims to enhance the accuracy and resolution of calculations, enabling the identification of local phenomena, parameters, and feedback during accident simulations, and the incorporation of these effects on the macroscopic cross-sections at each time step. The results of SBLOCA simulation reveals the effects of conservative/best estimate approach on the sequence of events, the initiation time of the safety systems, the critical controlled parameters of the power plant, and the precise understanding of the accident. Also, it was found that the radial power distribution becomes disrupted and loses its symmetry immediately after the SCRAM leading to different characteristics of steam generators (SGs) and natural circulation flow rate in each loop of primary side.

Wave-induced reconfiguration of and drag on marsh plants

Salt marshes are a common feature in coastal regions and have been noted for their ability to attenuate wave energy, providing an important first line of coastal defense. Marsh plants usually consist of multiple leaves distributed along a central stem. This paper constructed a model predicting wave force on a marsh plant by modeling the reconfiguration of both the leaves and stem in waves. The individual leaf and stem models and the full plant model were validated with experimental measurements of drag and plant motion using both live and dynamically-similar model plants under a range of wave conditions. Although the leaves exhibited greater reconfiguration than the stem, they contributed more than 70% of the plant drag. Plant reconfiguration produced a drag force that had a weaker than quadratic dependence on wave velocity. A simplified model, which combines scaling laws for the stem and individual leaves, is proposed and validated. Wave drag on a variety of marsh species with different morphology and rigidity were estimated and compared.

Modular simulation model for falling film evaporators with novel approach to manage dominant time-varying transport delays

A modular simulation model of the evaporator is developed by dividing it into design-independent subsystems. By introducing this modularity, numerous different evaporator designs, system parameters, operating points or control concepts can be configured and simulated. The plant operation or design can therefore be easily tested and costs for staff and experiments can be particularly reduced.A large challenge to create valid simulation tools consists of modeling the product transport within connecting pipes and during the evaporation process within the tubes, which in a dynamic process both lead to time-varying delays. As previously published models only include constant transport delays, they are disadvantageous to simulate real plant operation. In order to improve the simulation validity, a detailed dynamic full plant model is developed, which is able to illustrate dominant time-varying transport delays. A comparison with measured data of an existing falling film evaporator shows the validity of the proposed model.

Bio-CH4 from palm empty fruit bunch via pyrolysis-direct methanation: Full plant model and experiments with bio-oil surrogate

Abstract A promising, cleaner alternative process of thermochemical conversion of lignocellulosic biomass to biomethane is proposed and rigorously investigated via modelling and experiments for the first time. Using a conventional nickel on calcium aluminate catalyst, operated in bench scale at 1 atm, 400 °C, and with a feed molar steam to carbon ratio of 2, the Low Temperature Steam Reforming of acetic acid, representing a single compound bio-oil surrogate, achieves a promising 81.9% fuel carbon conversion to gases with a methane yield of 15.7 wt% of the feed. This compares to 21 wt% methane yield at equilibrium, thus demonstrating encouraging first time performance and scope for future catalyst optimisation. A comprehensive Aspen Plus model is developed for the first time for an industrial plant producing biomethane from palm empty fruit bunch (50 wt% initial moisture), an under-used agro-industrial waste produced in vast amounts in South-East Asia and Sub-Saharan Africa. Dependency on external heating is completely eliminated by heat recovered from combusting 25% of the gas product. Based on the simulation results of the autothermal plant, a final gas product consisting of 99.2 wt% of CH4 and 0.8 wt% of H2 is predicted with a plant thermal efficiency of 80.6%, i.e., comparable to modelled efficiencies found in the literature for wood gasification to biomethane plants that generate syngas as a necessary intermediate.

Control of two Electrical Plants

AbstractIn this paper, a controller is recommended for the regulation of two electrical plants. Since electrical plants generate electricity all the time, the regulation to get that all the plant states reach constant behaviors is important. Two main characteristics of the introduced method are: (i) it is based in the separation of the plant model equations, only some model equations are chosen for the regulation while the other model equations are ignored, it avoids the difficulty in the consideration of the full plant model; (ii) the Lyapunov strategy is employed to analyze the stability of the selected model equations in the electrical plant, it lets to ensure the regulation purpose. The advised method is applied in a gas turbine and a wind turbine for the electricity generation.

Comprehensive analysis on the performance of an IGCC plant with a PSA process integrated for CO2 capture

The main goal of this paper is to provide a comprehensive overview on the performance of an integrated gasification combined cycle (IGCC) implementing CO2 capture through a pressure swing adsorption (PSA) process. The methodology for integrating a PSA process into the IGCC plant is first defined and then a full-plant model is developed. A reference case is outlined both for the PSA-based plant and for an absorption-based plant. Physical absorption is considered the benchmark technology for the application investigated. The full-plant model allowed an assessment of the potentials of PSA in this framework. The plant performance obtained was evaluated mainly in terms of energy penalty and CO2 capture efficiency. Several process configurations and operating conditions were tested. The results of these simulations demonstrated the influence of the PSA process on the overall performance and the possibility to shape it according to specific requirements. A sensitivity analysis on the adsorbent material was also carried out, aiming to establish the possible performance enhancements connected to advancements in the material. Improving the properties of the adsorbent demonstrated to have a strong impact not only on the CO2 separation process but also on the performance of the entire plant. However, nor modifications in the process or in the material were able to fully close the gap with absorption. In this sense a synergetic approach for addressing further performance enhancements is outlined, based on the close collaboration between process engineering and material science.

Code improvement and model validation for Ascó-II Nuclear Power Plant model using a coupled 3D neutron kinetics/thermal–hydraulic code

This paper provides a Best Estimate validation calculation with a coupled thermal–hydraulic and 3D neutron kinetic model for Ascó-II Nuclear Power Plant. Common NRC codes have been used for its purpose. TRACE is the code used for the thermal–hydraulic system calculations; PARCS is the code used for the 3D neutron kinetics calculations. Cross section calculations were performed with the HELIOS lattice physics code, finally GenPMAXS was used to convert the cross section into the PARCS format. A simplified three dimensional 3D neutronics model of the Ascó II NPP is used as a core kinetics model. A 3D cylindrical thermal–hydraulic vessel plus 1D representation of the remainder of the full plant model is used as the thermal–hydraulic model. The transient selected to ensure the model validation is an actual 50% Loss of Load. This transient is characterized by space–time effects and was used to validate different thermal–hydraulic system models for the GET university group in the past. The scenario is also good to ensure the validation of a coupled 3D neutron kinetics code since it provides a transient situation between two stable regions at 100% and 50%. From the current code versions used, some source code modifications have been carried out in order to ensure the correct feedback between thermal–hydraulic and neutron kinetics code. In that sense, a dynamic control rod movement between TRACE and PARCS has been implemented. This is a complete control rod position feedback during transient scenarios. After all the work was performed, the important TH and NK time trend parameters were compared to the plant data and the comparison was reasonable with some discrepancy, thus the developed system models and the code modifications are robust enough to be used for future safety analysis. New coupled code capability has been tested and found as a required capability, when validating 3D NK–TH coupled calculations.

Efficiency evaluation procedure of coal-fired power plants with CO2 capture, cogeneration and hybridization

In an energy landscape undergoing great change with regard to CO2 emissions, the evaluation of solutions allowing a drastic reduction of the anthropogenic emissions are carried out for more than a decade. Among them, CO2 capture and storage on coal power plants has been identified as a particularly promising solution but other options such as heat and electricity cogeneration and power plant hybridization with solar of biomass can also reduce the carbon footprint of electricity production. However, the implementation of an external process on a power plant impacts its electric production. Post- and oxy-combustion CO2 capture, cogeneration for industries or districts, or hybridization are all examples of processes either demanding thermal and electrical energy or providing heat valorization opportunities. To identify the true potential of those systems, the evaluation of the performance of the integrated system is necessary. Also, to compare different solutions, a common framework has to be adopted since the performance of those systems are often highly dependent of the considered hypotheses.This paper presents a full integration procedure suited for both new built and retrofit coal-fired power plants by means of easy-to-use correlations, which links heat demand to production loss and waste heat availability to production increase, taking their exergy content into account. This correlative approach provides an analytical tool allowing a quick and realistic evaluation of a given concept or process layout, without the need of a detailed full power plant model. Examples are given for CO2 capture, cogeneration and hybridization, illustrating the interest of the approach to evaluate and compare several technologies on a consistent manner. An Excel spreadsheet with the calculation procedure is available online (see supporting information).

Adaptive control design under structured model information limitation: A cost-biased maximum-likelihood approach

Networked control strategies based on limited information about the plant model usually result in worse closed-loop performance than optimal centralized control with full plant model information. Recently, this fact has been established by utilizing the concept of competitive ratio, which is defined as the worst-case ratio of the cost of a control design with limited model information to the cost of the optimal control design with full model information. We show that an adaptive controller, inspired by a controller proposed by Campi and Kumar, with limited plant model information, asymptotically achieves the closed-loop performance of the optimal centralized controller with full model information for almost any plant. Therefore, there exists, at least, one adaptive control design strategy with limited plant model information that can achieve a competitive ratio equal to one. The plant model considered in the paper belongs to a compact set of stochastic linear time-invariant systems and the closed-loop performance measure is the ergodic mean of a quadratic function of the state and control input.

Optimal design of large‐scale chemical processes under uncertainty: A ranking‐based approach

An approach for the optimal design of chemical processes in the presence of uncertainty was presented. The key idea in this work is to approximate the process constraint functions and model outputs using Power Series Expansions (PSE)‐based functions. The PSE functions are used to efficiently identify the variability in the process constraint functions and model outputs due to multiple realizations in the uncertain parameters using Monte Carlo (MC) sampling methods. A ranking‐based approach is adopted here where the user can assign priorities or probabilities of satisfaction for the different process constraints and model outputs considered in the analysis. The methodology was tested on a reactor–heat exchanger system and the Tennessee Eastman process. The results show that the present method is computationally attractive since the optimal process design is accomplished in shorter computational times when compared to the use of the MC method applied to the full plant model. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3243–3257, 2014

Active control of adaptive optics system in a large segmented mirror telescope

For a large adaptive optics system such as a large segmented mirror telescope (SMT), it is often difficult, although not impossible, to directly apply common multi-input multi-output (MIMO) controller design methods due to the computational burden imposed by the large dimension of the system model. In this article, a practical controller design method is proposed which significantly reduces the system dimension for a system where the dimension required to represent the dynamics of the plant is much smaller than the dimension of the full plant model. The proposed method decouples the dynamic and static parts of the plant model by a modal decomposition technique to separately design a controller for each part. Two controllers are then combined using the so-called sensitivity decoupling method so that the resulting feedback loop becomes the superposition of the two individual feedback loops of the dynamic and static parts. A MIMO controller was designed by the proposed method using the H ∞ loop-shaping technique for an SMT model to be compared with other controllers proposed in the literature. Frequency-domain analysis and time-domain simulation results show the superior performance of the proposed controller.

Fractional order and BICO disturbance observers for a run-of-mine ore milling circuit

Grinding mill circuits are hard to control due to poor plant models, large external disturbances, uncertainties from internal couplings, and process variables that are difficult to measure. This paper proposes a novel fractional order disturbance observer (FO-DOB) for a run-of-mine (ROM) ore milling circuit. A fractional order low pass filter ( Q-filer) is used in the DOB to offer an additional degree of freedom in tuning for set-point tracking performance and disturbance rejection performance. Another disturbance observer is introduced in which a Bode ideal cut-off (BICO) filter is used for the Q-filter. A full non-linear plant model is used for evaluation of the performance gained over the ubiquitous PI controller. The simulation results show that the FO-DOB and BICO-DOB schemes are useful additional tools for ROM ore milling circuit control implementations.

A reduced order full plant model for oxyfuel combustion

The linkage of models generated in different commercial and/or proprietary software packages is becoming the state-of-the-art for the investigation of power generation applications. Here, a sophisticated process modelling software package, gPROMS, has been linked with a commercial CFD code, ANSYS FLUENT version 12, in order to create a reduced order model (ROM) for oxyfuel combustion. This is the first such application, and represents a vital step in the evaluation of the impact of oxyfuel operation on a conventional pulverised fuel plant. In order to use existing steam cycle technology, the heat duties to the furnace walls and heat exchangers must match those of conventional combustion. Evidence from experiments conducted by Smart et al. (Fuel 89 (2010) 2468–2476) at 0.5MW scale indicate that this is possible; however there is no operating experience of full-scale technology.A full plant model of a 500MWe sub-critical UK power station has been adapted for oxyfuel combustion. In order to relate heat transfer in the boiler to the level of oxygen enrichment and recycle ratio, a CFD-generated database of results for air and oxyfuel combustion with an excess oxygen value of 5% in both cases has been developed. Non-linear correlations of heat duties for various heat transfer sections of the plant are developed from the database, and linked to the full plant model. The plant model was then investigated over a range of oxygen concentrations from 25% to 35% by volume at the furnace inlet, which corresponds to a dry recycle ratio range of 66–77%. The aim in this case was to assess the potential for fitting oxyfuel burners to an existing plant. The optimum level of oxygen enrichment is found to be 32% and this corresponds to a recycle ratio of 70%. For these conditions the steam temperatures and heat duties closely match those of the conventional air-firing operation.