The method of fundamental solutions for detection of cavities in EIT

In this paper, the method of fundamental solutions (MFS) is used to solve numerically an inverse problem which consists of finding an unknown cavity within a region of interest based on given boundary Cauchy data. A range of examples are used to demonstrate that the technique is very effective at locating cavities in both two- and three-dimensional geometries for exact input data. The technique is then developed to include a regularisation parameter that enables cavities to be located accurately and stably even for noisy input data

CO2-enhanced and humidified operation of a micro-gas turbine for carbon capture

As greenhouse gas emissions are a key driver of climate change, sources of CO2 must be mitigated, particularly from carbon-intensive sectors, like power production. Natural gas provides an increasingly large percentage of electricity; however its lower carbon intensity is insufficient to make proportional reduction contributions to circumvent 2 °C global warming. The low partial pressure of CO2 in its flue gas makes post-combustion capture more challenging – increasing the CO2 in the exhaust assists in enhancing capture efficiency. This paper experimentally investigates the impact of the combination of humidified air turbines and exhaust gas recirculation to increase CO2 partial pressures, with the aim of evaluating their effects on emissions and turbine parameters at various turndown ratios. It was found that CO2 levels could be increased from 1.5 to 5.3 vol%, meaning more efficient post-combustion capture would be possible. CO2 and steam additions increased incomplete combustion when used together at high levels for low turndown ratios (below 60%), with CO increasing from 49 to 211 ppm and CH4 from 2.5 to 52 ppm; this effect was negated at higher power outputs. Turbine cycle humidification resulted in net improvements to the turbine efficiency, by up to 5.5% on a specific fuel consumption basis

A unifying computational fluid dynamics investigation on the river-like to river-reversed secondary circulation in submarine channel bends

A numerical model of saline density currents across a triple-bend sinuous submerged channel enclosed by vertical sidewalls is developed. The unsteady, non-Boussinesq, turbulent form of the Reynolds Averaged Navier-Stokes equations is employed to study the flow structure in a quasi-steady state. Recursive tests are performed with axial slopes of 0.08°, 0.43°, 1.5°, and 2.5°. For each numerical experiment, the downstream and vertical components of the fluid velocity, density, and turbulent kinetic energy are presented at four distinct locations within the channel cross section. It is observed that a crucial change in the flow pattern at the channel bends is observed as the axial slope is increased. At low values of the axial slope a typical river-like pattern is found. At an inclination of 1.5°a transition starts to occur. When the numerical test is repeated with an axial slope of 2.5°, a clearly visible river-reversed secondary circulation is achieved. The change in the cross-sectional flow pattern appears to be associated with the spatial displacement of the core of the maximum downstream fluid velocity. Therefore, the axial slope in this series of experiments is linked to the velocity structure of the currents, with the height of the velocity maximum decreasing as a function of increasing slope. As such, the axial slope should be regarded also as a surrogate for flows with enhanced density or sediment stratification and higher Froude numbers. The work unifies the apparently paradoxical experimental and numerical results on secondary circulation in submarine channels

Estimation of the Pitzer Parameters for 1–1, 2–1, 3–1, 4–1, and 2–2 Single Electrolytes at 25 °C

The Pitzer model is one of the most important thermodynamic models to predict the behavior of aqueous electrolyte solutions, especially at high ionic strengths. However, most of the parameters in the Pitzer equations have to be obtained experimentally and this represents an important drawback to this model. Therefore, in order to make the Pitzer equations less dependent on experimental data and more dependent on the properties of the solution, new equations that correlate the Pitzer equations with the properties of the solution have been successfully developed for 1-1, 2-1, 3-1, 4-1 and 2-2 electrolytes. In particular, these equations were developed for two cases: (i) considers the original Pitzer equations and (ii) considers some simplifications to the Pitzer equation (assuming CMX , BMX (2) and 2 = 0). In particular, for case (ii), the second virial coefficients BMX (0) and BMX (1) of the Pitzer equations were re-estimated using published experimental data of the osmotic coefficient obtained from the literature. As a conclusion, both the simplified and the original Pitzer equations presented a very good match with this published experimental data for the osmotic coefficients. Additionally, the second virial coefficients BMX (0) and BMX (1) for both cases were successfully correlated with the ionic radius and the ionic charge, and this is confirmed by the very high coefficients of determination achieved (R2>0.96). However, these new equations are valid only to cases in which no significant ion association occurs, which is also the basic premise of the original Pitzer model

Optimal Process Design of Commercial-Scale Amine-Based CO2 Capture Plants

Reactive absorption with an aqueous solution of amines in an absorber/stripper loop is the most mature technology for postcombustion CO2 capture (PCC). However, most of the commercial-scale CO2 capture plant designs that have been reported in the open literature are based on values of CO2 loadings and/or solvent circulation rates without an openly available techno-economic consideration. As a consequence, most of the reported designs may be suboptimal, and some of them appear to be unrealistic from practical and operational viewpoints. In this paper, four monoethanolamine (MEA) based CO2 capture plants have been optimally designed for both gas-fired and coal-fired power plants based on process and economic analyses. We have found that the optimum lean CO2 loading for MEA-based CO2 capture plants that can service commercial-scale power plants, whether natural-gas-fired or coal-fired, is about 0.2 mol/mol for absorber and stripper columns packed with Sulzer Mellapak 250Y structured packing. Also, the optimum liquid/gas ratio for a natural gas combined cycle (NGCC) power plant with a flue gas composition of approximately 4 mol % CO2 is about 0.96, while the optimum liquid/gas ratio for a pulverized-coal-fired (PC) power plant can range from 2.68 to 2.93 for a flue gas having a CO2 composition that ranges from 12.38 to 13.50 mol %

Effect of the CO2 enhancement on the performance of a micro gas turbine with a pilot-scale CO2 capture plant

Gas turbines are a viable and secure option both economically and environmentally for combined heat and power generation. Process modelling of a micro gas turbine for CO2 injection and exhaust gas recirculation (EGR) is performed. Further, this study is extended to assess the effect of the CO2 injection on the pilot-scale CO2 capture plant integrated with a micro gas turbine. In addition, the impact of the EGR on the thermodynamic properties of the fluid at different locations of the micro gas turbine is also evaluated. The micro gas turbine and CO2 injection models are validated against the set of experimental data and the performance analysis of the EGR cycle results in CO2 enhancement to 5.04 mol% and 3.5 mol%, respectively. The increased CO2 concentration in the flue gas, results in the specific reboiler duty decrease by 20.5 % for pilot-scale CO2 capture plant at 90 % CO2 capture rate for 30 wt. % MEA aqueous solution. The process system analysis for the validated models results in a much better comprehension of the impact of the CO2 enhancement on the process behaviour

A porous media model for CFD simulations of gas-liquid two-phase flow in rotating packed beds

The rotating packed bed (RPB) is a promising advanced reactor used in industrial gas-liquid two-phase reaction processes because of its high phase contact efficiency and mixing efficiency. Investigation of RPBs using CFD simulations will improve the understanding of physical behaviours of gas and liquid flows in such reactors. Currently, CFD simulations on the RPBs only focus on the volume of fluid (VOF) method. However, the VOF method is not suitable for simulations of pilot-scale 2D and 3D RPBs due to the limitations in computer resources, while the Eulerian method using a porous media model is a promising alternative method but it is rarely reported. The reason is that there are no suitable porous media models that accurately describe the drag force between the gas and liquid, the gas and solids and the liquid and solids due to the high porosity and the stacked wire screen packing used in RPBs. Therefore, the purpose of this paper is to propose a new model for modelling RPBs. The new proposed model is based on the Kołodziej high porosity wire screen one-phase porous media model. In this work, two experimental counter-current gas–liquid flow cases from the literatures have been used for validating the CFD simulation results. Finally, the new model has been compared with the current porous media models for traditional spherical or structured slit packed beds, which are the Attou, Lappalainen, Iliuta and Zhang models. The simulation results show that the proposed new model is the most appropriate and accurate model for the simulation of RPBs among all the models investigated in this paper

Modelling of CO2 absorption in a rotating packed bed using an Eulerian porous media approach

The rotating packed bed (RPB) is a promising reactor for CO2 capture with liquid amine because of its high mass transfer rate and energy and space savings. The CFD simulations of RPBs generally use the volume of fluid (VOF) method, but this method is prohibitively expensive for 3D simulations, in particular for large-scale reactors. The Eulerian method is a promising and effective method; however, there are still several difficulties, such as the settings for the porous media models in the gas-liquid counter-current flow and the interfacial area between the gas and liquid. To overcome these difficulties in the Eulerian method, this paper uses a new porous media model, a novel liquid generation-elimination model for numerically investigating the gas-liquid counter-current flow in RPBs and a new interfacial area model derived from the VOF simulation. These new models, incorporating the two-film reaction-enhancement mass transfer model, have successfully simulated the CO2 capture process with monoethanolamine (MEA) solutions in a RPB under both low (30 wt%) and high (90 wt%) concentration conditions. The results show that the overall gas phase mass transfer coefficient (KGa) increases with increasing the rotation speeds and the liquid to gas mass flow rate (L/G ratio). The simulations were validated by the experimental data and the results were analysed and discussed

Dynamic economic and emission dispatch model considering wind power under Energy Market Reform: A case study

With the increasing issues in the environmental and the high requirement for energy, the Energy Market Reform (EMR) was introduced by the UK government. This paper develops a novel Dynamic Economic and Emission Dispatch (DEED) model for a combined conventional and wind power system incorporating the carbon price floor (CPF) and the Emission Performance Standard (EPS) that is supported by the EMR. The proposed model aims to determine the optimal operation strategy for the given system on power dispatch taking into account wind power waste and reserve and also the environmental aspect, especially the CPF of greenhouse gases and the emission limit of the EPS for different decarbonisation scenarios. Case studies for the demand profile in the Sheffield region in the UK with different time intervals is presented. The results indicate that renewable power is superior in both the economics and emissions to a mid to long-term energy strategy in the UK

Techno-economic process design of a commercial-scale amine-based CO2 capture system for natural gas combined cycle power plant with exhaust gas recirculation

Post-combustion CO2 capture systems are gaining more importance as a means of reducing escalating greenhouse gas emissions. Moreover, for natural gas-fired power generation systems, exhaust gas recirculation is a method of enhancing the CO2 concentration in the lean flue gas. The present study reports the design and scale-up of four different cases of an amine-based CO2 capture system at 90% capture rate with 30 wt.% aqueous solution of MEA. The design results are reported for a natural gas-fired combined cycle system with a gross power output of 650 MWe without EGR and with EGR at 20%, 35% and 50% EGR percentage. A combined process and economic analysis is implemented to identify the optimum designs for the different amine-based CO2 capture plants. For an amine-based CO2 capture plant with a natural gas-fired combined cycle without EGR, an optimum liquid to gas ratio of 0.96 is estimated. Incorporating EGR at 20%, 35% and 50%, results in optimum liquid to gas ratios of 1.22, 1.46 and 1.90, respectively. These results suggest that a natural gas-fired power plant with exhaust gas recirculation will result in lower penalties in terms of the energy consumption and costs incurred on the amine-based CO2 capture plant