Physical characteristics of subglacial tills

A regional database of the physical properties of glacial tills has been interrogated to produce characteristic design values and baseline construction values. Glacioterrestrial glacial till, one of the most distributed deposits in the world, is typically a heterogeneous mixture of clays, silts, sands, gravels and cobbles, which can contain remnants of earlier till including glaciolacustrine and fluvioglacial deposits that have been gravitationally compacted and sheared. This results in a complex deposit, which is spatially variable both in composition and fabric to the extent that the selection of design profiles is challenging. A study of the intrinsic properties of the tills in the North East of England together with a statistical analysis has led to the identification of two distinctly different, heavily overconsolidated tills that have profiles of strength, water content and density that lead to characteristic values based on the regional database and baseline values based on the local database that provide a priori knowledge for future investigations. This a priori knowledge has been used to determine the characteristic and baseline values for a new dataset from the region after demonstrating that the data fit with the regional database

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 %

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

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

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

Techno‐economic assessment on the fuel flexibility of a commercial scale combined cycle gas turbine integrated with a CO2 capture plant

Post‐combustion carbon capture is a valuable technology, capable of being deployed to meet global CO2 emissions targets. The technology is mature and can be retrofitted easily with existing carbon emitting energy generation sources, such as natural gas combined cycles. This study investigates the effect of operating a natural gas combined cycle plant coupled with carbon capture and storage while using varying fuel compositions, with a strong focus on the influence of the CO2 concentration in the fuel. The novelty of this study lies in exploring the technical and economic performance of the integrated system, whilst operating with different fuel compositions. The study reports the design of a natural gas combined cycle gas turbine and CO2 capture plant (with 30 wt% monoethanolamine), which were modelled using the gCCS process modelling application. The fuel compositions analysed were varied, with focus on the CO2 content increasing from 1% to 5%, 7.5% and 10%. The operation of the CO2 capture plant is also investigated with focus on the CO2 capture efficiency, specific reboiler duty and the flooding point. The economic analysis highlights the effect of the varying fuel compositions on the cost of electricity as well as the cost of CO2 avoided. The study revealed that increased CO2 concentrations in the fuel cause a decrease in the efficiency of the natural gas combined cycle gas turbine; however, rising the CO2 concentration and flowrate of the flue gas improves the operation of the capture plant at the risk of an increase in the flooding velocity in the column. The economic analysis shows a slight increase in cost of electricity for fuels with higher CO2 contents; however, the results also show a reduction in the cost of CO2 avoided by larger margins

A Lattice Study of the Magnetic Moment and the Spin Structure of the Nucleon

Using an approach free from momentum extrapolation, we calculate the nucleon magnetic moment and the fraction of the nucleon spin carried by the quark angular momentum in the quenched lattice QCD approximation. Quarks with three values of lattice masses, 210, 124 and 80 MeV, are formulated on the lattice using the standard Wilson approach. At every mass, 100 gluon configurations on 16^3 x 32 lattice with \beta=6.0 are used for statistical averaging. The results are compared with the previous calculations with momentum extrapolation. The contribution of the disconnected diagrams is studied at the largest quark mass using noise theory technique.Comment: 14 pages, 3 figures, Talk given at Lattice2001, Berlin, German

Patterned hydrophobic gas diffusion layers for enhanced water management in polymer electrolyte fuel cells

Flooding of the cathode due to water accumulation is one of the biggest limiting factors in the performance of polymer electrolyte fuel cells (PEFCs). This study therefore attempts to solve this issue by fabricating gas diffusion layers (GDLs) with differently patterned hydrophobic regions. The GDLs in three different patterns (triangular, diamond, and inverted-triangular) were prepared by brushing a Polytetrafluoroethylene (PTFE) solution onto commercial carbon papers through a mask and tested in PEFCs. The patterned GDLs results in superior performance in all cases compared to a uniformly PTFE-treated GDL. Notably, the oxygen transport resistance is significantly reduced, indicating that the water accumulation in the cathode is avoided. This is attributed to the patterned hydrophobicity gradient providing distinct pathways for water and oxygen. The GDL with triangular patterning displays the highest peak power density, due to the fact that the untreated less hydrophobic region is in direct contact with the cathode outlet in this case, facilitating the removal of excess liquid water. Overall, the study confirms that the GDLs with patterned hydrophobicity could be used to enhance the performance of commercial PEFC systems by facilitating water management, potentially leading to improved efficiency and durability

Role of methyldioxy radical chemistry in high-pressure methane combustion in CO2

The combustion chambers of direct-fired supercritical CO2 power plants operate at pressures of approximately 300 bar and CO2 dilutions of up to 96%. The rate coefficients used in existing chemical kinetic mechanisms are validated for much lower pressures and much smaller concentrations of CO2. Recently, the UoS sCO2 1.0 and UoS sCO2 2.0 mechanisms have been developed to better predict ignition delay time (IDT) data from shock tube studies at pressures from 1 to 260 bar in various CO2-containing bath gas compositions. The chemistry of the methyldioxy radical (CH3O2) has been identified as an essential combustion intermediate for methane combustion above 100 bar, where mechanisms missing this species begin to vastly overpredict the IDT. The current literature available on CH3O2 is very limited and often concerned with atmospheric chemistry and low-pressure, low-temperature combustion. This means that the rate coefficients used in UoS sCO2 2.0 are commonly determined at sub-atmospheric pressures and temperatures below 1000 K with some rate coefficients being over 30 years old. In this work, the rate coefficients of new potential CH3O2 reactions are added to the current mechanism to create UoS sCO2 2.1 It is shown that the influence of CH3O2 on the IDT is greatest at high pressures and low temperatures. It has also been demonstrated that CO2 has very little effect on the chemistry of CH3O2 at 300 bar meaning that CH3O2 rate coefficients can be determined in other bath gases, reducing the impact of non-ideal effects such as bifurcation when studying in a CO2 bath gas. The updated UoS sCO2 2.1 mechanism is then compared to high-pressure IDT data and the most important reactions which require reinvestigation have been identified as the essential next steps in understanding high-pressure methane combustion