Dynamic modelling, validation and analysis of coal-fired subcritical power plant

Coal-fired power plants are the main source of global electricity. As environmental regulations tighten, there is need to improve the design, operation and control of existing or new built coal-fired power plants. Modelling and simulation is identified as an economic, safe and reliable approach to reach this objective. In this study, a detailed dynamic model of a 500 MWe coal-fired subcritical power plant was developed using gPROMS based on first principles. Model validations were performed against actual plant measurements and the relative error was less than 5%. The model is able to predict plant performance reasonably from 70% load level to full load. Our analysis showed that implementing load changes through ramping introduces less process disturbances than step change. The model can be useful for providing operator training and for process troubleshooting among others

Application of a portable FTIR for measuring on-road emissions

The objective of this work was the development of an onroad in-vehicle emissions measurement technique utilizing a relatively new, commercial, portable Fourier Transform Infra-Red (FTIR) Spectrometer capable of identifying and measuring (at approximately 3 second intervals) up to 51 different compounds. The FTIR was installed in a medium class EURO1 spark ignition passenger vehicle in order to measure on-road emissions. The vehicle was also instrumented to allow the logging of engine speed, road speed, global position, throttle position, air-fuel ratio, air flow and fuel flow in addition to engine, exhaust and catalyst temperatures. This instrumentation allowed the calculation of massbased emissions from the volume-based concentrations measured by the FTIR. To validate the FTIR data, the instrument was used to measure emissions from an engine subjected to a real-world drive cycle using an AC dynamometer. Standard analyzers were operated simultaneously for comparison with the FTIR and the standard analyzer results showed that most pollutants (NOx, CO2, CO) were within ~10% of a standard analyzer during steady state conditions and within 20% during transients. The exception to this was total HC which was generally 50% or less than actual total HC, but this was due to the limited number of hydrocarbons measured by the FTIR. In addition to the regulated emissions, five toxic hydrocarbon species were analyzed and found to be sensitive to cold starts in varying proportions. Finally, FTIR data was compared to results from a commercially available on-road measurement system (Horiba OBS- 1000), and there was good agreement

A dynamic mathematical model of a shell-and-tube evaporator. Validation with pure and blend refrigerants

[EN] This work presents a mathematical model of a shell-and-tube evaporator based on mass continuity, energy conservation and heat transfer physical fundamentals. The model is formulated as a control volume combination that represents the different refrigerant states along the evaporator. Since the model is based on refrigerant and secondary fluid states prediction, it can be easily adapted for modelling any type of evaporator. The strategy of working with physical fundamentals allows the steady- and dynamic-state analysis of any of its performance variables. The paper presents a steady-state validation made with two pure refrigerants (HCFC-22, HFC-134a) and with a zeotropic blend (HFC-407C), and a dynamic validation with transient experimental tests using HCFC-22. The model prediction error is lower than 5% and it is well in accordance with actual dynamic behaviour.Llopis, R.; Cabello, R.; Navarro-Esbrí, J.; Torrella Alcaraz, E. (2007). A dynamic mathematical model of a shell-and-tube evaporator. Validation with pure and blend refrigerants. International Journal of Energy Research. 31(3):232-244. doi:10.1002/er.1243S23224431

Simplification of detailed rate-based model of post-combustion CO₂ capture for full chain CCS integration studies

As post-combustion CO₂ capture (PCC) technology nears commercialisation, it has become necessary for the full carbon capture and storage (CCS) chain to be studied for better understanding of its dynamic characteristics. Model-based approach is one option for economically and safely reaching this objective. However, there is need to ensure that such models are reasonably simple to avoid the requirement for high computational time when carrying out such study. In this paper, a simplification approach for a detailed rate-based model of post-combustion CO₂ capture with solvents (rate-based mass transfer and reactions assumed to be at equilibrium) is presented. The simplified model can be used in model-based control and/or full chain CCS simulation studies. With this approach, we demonstrated significant reduction in CPU time (up to 60%) with reasonable model accuracy retained in comparison with the detailed model

Modelling and simulation of intensified absorber for post-combustion CO₂ capture using different mass transfer correlations

This paper studied mass transfer in rotating packed bed (RPB) which has the potential to significantly reduce capital and operating costs in post-combustion CO₂capture. To model intensified absorber, mass transfer correlations were implemented in visual FORTRAN and then were dynamically linked with Aspen Plus® rate-based model. Therefore, this represents a newly developed model for intensified absorber using RPB. Two sets of mass transfer correlations were studied and compared through model validations. The second set of correlations performed better at the MEA concentrations tested as compared with the first set of correlations. For insights into the design and operation of intensified absorber, process analysis was carried out, which indicates: (a) With fixed RPB equipment size and fixed Lean MEA flow rate, CO₂ capture level decreases with increase in flue gas flow rate; (b) Higher lean MEA inlet temperature leads to higher CO₂ capture level. (c) At higher flue gas temperature (from 30 °C to 80 °C), the CO₂ capture level of the intensified absorber can be maintained. Compared with conventional absorber using packed columns, the insights obtained from this study are (1) Intensified absorber using rotating packed bed (RPB) improves mass transfer significantly. (2) Cooling duty cost can be saved since higher lean MEA temperature and/or higher flue gas temperature shows little or no effect on the performance of the RPB

Minimizing Tracer Interference to Assess in vivo Hepatic Metabolism with Glutamine-generated Mass Isotopomers

Stable isotope tracers are widely used to study the in vivo kinetics of central carbon metabolism in diseases such as obesity, type 2 diabetes mellitus (T2DM) and non-alcoholic fatty liver disease (NAFLD). However, despite their common use, 13C-labeled acetate, lactate, and propionate have led to large incongruities and inconsistencies in their in vivo measurement of hepatic metabolism. To resolve major discrepancies and recent controversies of hepatic metabolism we developed and validated [1,2-13C2]-L-glutamine as a novel tracer strategy for measuring hepatic central carbon metabolism. In our rodent studies [1,2-13C2]-L-glutamine generated a straightforward labeling pattern of key metabolites suitable for the interpretation of LC-MS/MS spectra using Mass Isotopomer Multi Ordinate Spectral Analysis (MIMOSA) principles and thereby enabled an unencumbered independent assessment of Krebs cycle fluxes. In a head-to-head comparison, we found that [1,2-13C2]-L-glutamine had many favorable qualities and few liabilities compared to the other tracer strategies. Additionally, given that in vivo NMR studies of mitochondrial metabolism often depend on the signal for glutamate and other abundant metabolites that act as label-trapping pools for Krebs Cycle intermediates, we were able to directly measure α-Ketoglutarate-Glutamate exchange rate (Vx) and show evidence for the assumption that the intramitochondrial metabolite pool is in rapid exchange with NMR observable cytosolic metabolites. Here we report the development and in vivo kinetic and steady state validation of [1,2-13C2]-L-glutamine as an independent tracer of hepatic metabolism

EXPERIMENTAL SETUP AND CONTROLLER DESIGN FOR AN HCCI ENGINE

Homogeneous charged compression ignition (HCCI) is a promising combustion mode for internal combustion (IC) engines. HCCI engines have very low NOx and soot emission and low fuel consumption compared to traditional engines. The aim of this thesis is divided into two main parts: (1) engine instrumentation with a step towards converting a gasoline turbocharged direct injection (GTDI) engine to an HCCI engine; and (2) developing controller for adjusting the crank angle at 50% mass fuel burn (CA50), exhaust gas temperature Texh, and indicated mean effective pressure (IMEP) of a single cylinder Ricardo HCCI engine. The base GTDI engine is modified by adding an air heater, inter-cooler, and exhaust gas recirculation (EGR) in the intake and exhaust loops. dSPACE control units are programmed for adding monitoring sensors and implementing actuators in the engine. Control logics for actuating electronic throttle control (ETC) valve, EGR valve, and port fuel injector (PFI) are developed using the rapid control prototyping (RCP) feature of dSPACE. A control logic for crank/cam synchronization to determine engine crank angle with respect to firing top dead center (TDC) is implemented and validated using in-cylinder pressure sensor data. A control oriented model (COM) is developed for estimating engine parameters including CA50, Texh, and IMEP for a single cylinder Ricardo engine. The COM is validated using experimental data for steady state and transient engine operating conditions. A novel three-input three-output controller is developed and tested on a detailed physical HCCI engine plant model. Two type of controller design approaches are used for designing HCCI controllers: (1) empirical, and (2) model-based. A discrete sub-optimal sliding mode controller (DSSMC) is designed as a model-based controller to control CA50 and Texh, and a PI controller is designed to control IMEP. The results show that the designed controllers can successfully track the reference trajectories and can reject the external disturbances within the given operating region

Model development and simulating of a spinning cone evaporator : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology at Institute of Technology and Engineering, Massey University, Palmerston North, New Zealand

The idea of milk pre-concentration at the farm has attracted worldwide interest for many years. A new pilot-scale evaporator (called spinning cone evaporator), which can be operated on the farm and has a compact and efficient design, has been developed at Massey University. However, there is a shortage of knowledge on the design, operation and control of this new evaporator. The main goal of this thesis is to develop a dynamic mathematical model in order to better utilize this evaporator and make further developments. This thesis consists of three parts. Firstly, a first-principles model of a pilot scale spinning cone evaporator is developed using the sub-system modelling techniques of the evaporator from the Laws of Thermodynamics and the general mass and energy balances. The model is dynamic and includes the evaporator, the compressor, the condenser and the product transport sections. The system model describes the dynamic relationships between the input variables (cooling water flowrate, M c , speed of compressor, N comp , feed flowrate, M f , feed temperature, T f and mass composition of feed dry matter, W f ) and the output variables (outlet temperature of cooling water, T co , evaporating temperature, T e , mass composition of product dry matter, w p and product flowrate, M p ), Secondly, the evaporator model was implemented using the software package Matlab along with its dynamic simulation environment Simulink. The differential equations for the evaporator model are embedded in a block diagram representation of the evaporator system. The evaporator Simulink model is divided into three levels, the blocks at the top represent the overall model and global constants used in it. The second level contains the individual sub-systems and the bottom level elements within each sub-system. Results of the model verification are satisfactory. Finally, the model validation is presented for both steady state and dynamic comparisons. The product flowrate (except in the case of feed temperature changes) and evaporation temperature can be predicted at a given time, and the outlet temperature of cooling water and product dry matter composition can also be predicted at a steady state. It can be seen that the results predicted using this spinning cone evaporator model, which accounts for the varying concentrate flowrate and evaporation temperature with time, are in good agreement with experimental data. This model provides a valuable tool to predict performance in a spinning cone evaporator and to modify the design parameters

Modelling and operational analysis of coal-fired supercritical power plant integrated with post-combustion carbon capture based on chemical absorption under UK grid requirement

Fossil-fuel fired power plants are subjected to stringent operational regime due to the influx of renewable resources and the CO2 emission reduction target. This study is aimed at modelling and analysis of supercritical coal-fired power plant (SCPP) integrated with post-combustion CO2 capture (PCC) and its response electricity grid demand constraints. Current status of dynamic modelling of SCPP integrated with PCC was reviewed to identify the gaps in knowledge. It was observed that no accurate dynamic model of an SCPP integrated with PCC had been reported in open literature. A steady state model of the SCPP integrated with PCC was developed with Aspen Plus®. The model was validated with the reference plant and it was found that the relative error is about 1.6%. The results of the conventional and advanced exergetic analysis showed that the energy/exergy consumption and the efficiency of the integrated system can be improved by recovering the avoidable exergy destruction in the whole system.Dynamic models of SCPP once-through boiler based on lumped parameter and distributed parameter approaches were compared. The distributed parameter model gave a more accurate prediction of the SCPP boiler dynamics at different load levels. Analysis of the strategies for operating the SCPP under the UK grid requirement as regards to primary frequency response was performed using the validated SCPP model. The results show that using turbine throttling approach, extraction stop or condensate stop individually was not sufficient to meet the grid requirement. A combination of turbine throttling, extraction stop and/or condensate stop can achieve a 10% increase in maximum continuous rating (MCR) of the power plant within 10 seconds to 30 seconds of primary frequency change as required by the UK grid.The dynamic model of SCPP was integrated with a validated and scaled-up model of PCC. Analysis of the strategies for operating the SCPP integrated with PCC under the UK grid requirement as regards to primary frequency response was undertaken. The results show that the stripper stop mechanism is not sufficient for the 10% MCR required for the primary response. The results show that the combination of stripper stop mechanism with extraction stop can meet the 10% MCR requirement for integrated plant operating at above 75% of its full capacity. The throttling and stripper stop configuration only barely meets the demand at full load capacity. The condensate stop combination with the stripper stop mechanism on the other hand could not meet the frequency response requirement at any load level

Predicting NOx emissions in diesel engines via sigmoid NARX models using a new experiment design for combustion identification

Diesel engines are still widely used in heavy-duty engine industry because of their high energy conversion efficiency. In recent decades, governmental institutions limit the maximum acceptable hazardous emissions of diesel engines by stringent international regulations, which enforces engine manufacturers to find a solution for reducing the emissions while keeping the power requirements. A reliable model of the diesel engine combustion process can be quite useful to search for the best engine operating conditions. In this study, nonlinear modeling of a heavy-duty diesel engine NOx emission formation is presented. As a new experiment design, air-path and fuel-path input channels were excited by chirp signals where the frequency profile of each channel is different in terms of the number and the direction of the sweeps. This method is proposed as an alternative to the steady-state experiment design based modeling approach to substantially reduce testing time and improve modeling accuracy in transient operating conditions. Sigmoid based nonlinear autoregressive with exogenous input (NARX) model is employed to predict NOx emissions with given input set under both steady-state and transient cycles. Models for different values of parameters are generated to analyze the sensitivity to parameter changes and a parameter selection method using an easy-to-interpret map is proposed to find the best modeling parameters. Experimental results show that the steady-state and the transient validation accuracies for the majority of the obtained models are higher than 80% and 70%, respectively