Assessing the potential of yield improvements, through process scrap reduction, for energy and CO2 abatement in the steel and aluminium sectors

Targets to cut 2050 CO2 emissions in the steel and aluminium sectors by 50%, whilst demand is expected to double, cannot be met by energy efficiency measures alone, so options that reduce total demand for liquid metal production must also be considered. Such reductions could occur through reduced demand for final goods (for instance by life extension), reduced demand for material use in each product (for instance by lightweight design) or reduced demand for material to make existing products. The last option, improving the yield of manufacturing processes from liquid metal to final product, is attractive in being invisible to the final customer, but has had little attention to date. Accordingly this paper aims to provide an estimate of the potential to make existing products with less liquid metal production. Yield ratios have been measured for five case study products, through a series of detailed factory visits, along each supply chain. The results of these studies, presented on graphs of cumulative energy against yield, demonstrate how the embodied energy in final products may be up to 15 times greater than the energy required to make liquid metal, due to yield losses. A top-down evaluation of the global flows of steel and aluminium showed that 26% of liquid steel and 41% of liquid aluminium produced does not make it into final products, but is diverted as process scrap and recycled. Reducing scrap substitutes production by recycling and could reduce total energy use by 17% and 6% and total CO 2 emissions by 16% and 7% for the steel and aluminium industries respectively, using forming and fabrication energy values from the case studies. The abatement potential of process scrap elimination is similar in magnitude to worldwide implementation of best available standards of energy efficiency and demonstrates how decreasing the recycled content may sometimes result in emission reductions. Evidence from the case studies suggests that whilst most companies are aware of their own yield ratios, few, if any, are fully aware of cumulative losses along their whole supply chain. Addressing yield losses requires this awareness to motivate collaborative approaches to improvement. © 2011 Elsevier B.V. All rights reserved.

The role of the surfaces in the photon absorption in Ge nanoclusters embedded in silica.

The usage of semiconductor nanostructures is highly promising for boosting the energy conversion efficiency in photovoltaics technology, but still some of the underlying mechanisms are not well understood at the nanoscale length. Ge quantum dots (QDs) should have a larger absorption and a more efficient quantum confinement effect than Si ones, thus they are good candidate for third-generation solar cells. In this work, Ge QDs embedded in silica matrix have been synthesized through magnetron sputtering deposition and annealing up to 800°C. The thermal evolution of the QD size (2 to 10 nm) has been followed by transmission electron microscopy and X-ray diffraction techniques, evidencing an Ostwald ripening mechanism with a concomitant amorphous-crystalline transition. The optical absorption of Ge nanoclusters has been measured by spectrophotometry analyses, evidencing an optical bandgap of 1.6 eV, unexpectedly independent of the QDs size or of the solid phase (amorphous or crystalline). A simple modeling, based on the Tauc law, shows that the photon absorption has a much larger extent in smaller Ge QDs, being related to the surface extent rather than to the volume. These data are presented and discussed also considering the outcomes for application of Ge nanostructures in photovoltaics.PACS: 81.07.Ta; 78.67.Hc; 68.65.-k.

Light absorption in silicon quantum dots embedded in silica

The photon absorption in Si quantum dots (QDs) embedded in SiO2 has been systematically investigated by varying several parameters of the QD synthesis. Plasma-enhanced chemical vapor deposition (PECVD) or magnetron cosputtering (MS) have been used to deposit, upon quartz substrates, single layer, or multilayer structures of Si-rich- SiO2 (SRO) with different Si content (43-46 at. %). SRO samples have been annealed for 1 h in the 450-1250 °C range and characterized by optical absorption measurements, photoluminescence analysis, Rutherford backscattering spectrometry and x-ray Photoelectron Spectroscopy. After annealing up to 900 °C SRO films grown by MS show a higher absorption coefficient and a lower optical bandgap (∼2.0 eV) in comparison with that of PECVD samples, due to the lower density of Si-Si bonds and to the presence of nitrogen in PECVD materials. By increasing the Si content a reduction in the optical bandgap has been recorded, pointing out the role of Si-Si bonds density in the absorption process in small amorphous Si QDs. Both the photon absorption probability and energy threshold in amorphous Si QDs are higher than in bulk amorphous Si, evidencing a quantum confinement effect. For temperatures higher than 900 °C both the materials show an increase in the optical bandgap due to the amorphous-crystalline transition of the Si QDs. Fixed the SRO stoichiometry, no difference in the optical bandgap trend of multilayer or single layer structures is evidenced. These data can be profitably used to better implement Si QDs for future PV technologies. © 2009 American Institute of Physics.

In-Situ grown carbon nanotubes for enhanced CO2 detection in non-dispersive-infra-red system

Non-dispersive-infra-red (NDIR) sensors are believed to be one of the most selective and robust solutions for CO2 detection, though cost prohibits their broader integration. In this paper we propose a commercially viable silicon-on-insulator (SOI) complementary metal-oxide (CMOS) micro-electro-mechanical (MEMS) technology for an IR thermal emitter. For the first time, vertically aligned multi walled carbon nanotubes (VA-MWCNTs) are suggested as a possible coating for the enhancement of the emission intensity of the optical source of a NDIR system. VA-MWCNTs have been grown in situ by chemical vapour deposition (CVD) exclusively on the heater area. Optical microscopy, scanning electron microscopy and Raman spectroscopy have been used to verify the quality of the VA-MWCNTs growth. The CNT-coated emitter demonstrated an increased response to CO2 of approx. 60%. Furthermore, we show that the VA-MWCNTs are stable up to temperatures of 500°C for up to 100 hours. © 2013 IEEE.

Dependence of dye regeneration and charge collection on the pore-filling fraction in solid-state dye-sensitized solar cells

Solid-state dye-sensitized solar cells rely on effective infiltration of a solid-state hole-transporting material into the pores of a nanoporous TiO 2 network to allow for dye regeneration and hole extraction. Using microsecond transient absorption spectroscopy and femtosecond photoluminescence upconversion spectroscopy, the hole-transfer yield from the dye to the hole-transporting material 2,2′,7,7′-tetrakis(N,N-di-p- methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD) is shown to rise rapidly with higher pore-filling fractions as the dye-coated pore surface is increasingly covered with hole-transporting material. Once a pore-filling fraction of ≈30% is reached, further increases do not significantly change the hole-transfer yield. Using simple models of infiltration of spiro-OMeTAD into the TiO2 porous network, it is shown that this pore-filling fraction is less than the amount required to cover the dye surface with at least a single layer of hole-transporting material, suggesting that charge diffusion through the dye monolayer network precedes transfer to the hole-transporting material. Comparison of these results with device parameters shows that improvements of the power-conversion efficiency beyond ≈30% pore filling are not caused by a higher hole-transfer yield, but by a higher charge-collection efficiency, which is found to occur in steps. The observed sharp onsets in photocurrent and power-conversion efficiencies with increasing pore-filling fraction correlate well with percolation theory, predicting the points of cohesive pathway formation in successive spiro-OMeTAD layers adhered to the pore walls. From percolation theory it is predicted that, for standard mesoporous TiO2 with 20 nm pore size, the photocurrent should show no further improvement beyond an ≈83% pore-filling fraction. Solid-state dye-sensitized solar cells capable of complete hole transfer with pore-filling fractions as low as ∼30% are demonstrated. Improvements of device efficiencies beyond ∼30% are explained by a stepwise increase in charge-collection efficiency in agreement with percolation theory. Furthermore, it is predicted that, for a 20 nm pore size, the photocurrent reaches a maximum at ∼83% pore-filling fraction. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cost-effectiveness of alternative powertrains for reduced energy use and CO2 emissions in passenger vehicles

This work analysed the cost-effectiveness of avoiding carbon dioxide (CO2) emissions using advanced internal combustion engines, hybrids, plug-in hybrids, fuel cell vehicles and electric vehicles across the nine UK passenger vehicles segments. Across all vehicle types and powertrain groups, minimum installed motive power was dependent most on the time to accelerate from zero to 96.6km/h (60mph). Hybridising the powertrain reduced the difference in energy use between vehicles with slow (t z - 60 > 8 s) and fast acceleration (t z - 60 < 8 s) times. The cost premium associated with advanced powertrains was dependent most on the powertrain chosen, rather than the performance required. Improving non-powertrain components reduced vehicle road load and allowed total motive capacity to decrease by 17%, energy use by 11%, manufacturing cost premiums by 13% and CO2 emissions abatement costs by 15%. All vehicles with advanced internal combustion engines, most hybrid and plug-in hybrid powertrains reduced net CO2 emissions and had lower lifetime operating costs than the respective segment reference vehicle. Most powertrains using fuel cells and all electric vehicles had positive CO2 emissions abatement costs. However, only vehicles using advanced internal combustion engines and parallel hybrid vehicles may be attractive to consumers by the fuel savings offsetting increases in vehicle cost within two years. This work demonstrates that fuel savings are possible relative to today's fleet, but indicates that the most cost-effective way of reducing fuel consumption and CO2 emissions is by advanced combustion technologies and hybridisation with a parallel topology. © 2014 Elsevier Ltd.

Fast response CO2 sensor for automotive exhaust gas analysis

A fast response sensor for measuring carbon dioxide concentration has been developed for laboratory research and tested on a spark ignition engine. The sensor uses the well known infra-red absorption technique with a miniaturized detection system and short capillary sampling tubes, giving a time constant of approximately 5 milliseconds; this is sufficiently fast to observe changes in CO2 levels on a cycle-by-cycle basis under normal operating conditions. The sensor is easily located in the exhaust system and operates continuously. The sensor was tested on a standard production four cylinder spark-ignition engine to observe changes in CO2 concentration in exhaust gas under steady state and transient operating conditions. The processed sensor signal was compared to a standard air-to-fuel ratio (AFR) sensor in the exhaust stream and the results are presented here. The high frequency response CO2 measurements give new insights into both engine and catalyst transient operation. Copyright © 1999 Society of Automotive Engineers, Inc.

A coupled hydro-mechanical analysis for prediction of hydraulic fracture propagation in saturated porous media using EFG mesh-less method

The details of the Element Free Galerkin (EFG) method are presented with the method being applied to a study on hydraulic fracturing initiation and propagation process in a saturated porous medium using coupled hydro-mechanical numerical modelling. In this EFG method, interpolation (approximation) is based on nodes without using elements and hence an arbitrary discrete fracture path can be modelled.The numerical approach is based upon solving two governing partial differential equations of equilibrium and continuity of pore water simultaneously. Displacement increment and pore water pressure increment are discretized using the same EFG shape functions. An incremental constrained Galerkin weak form is used to create the discrete system of equations and a fully implicit scheme is used for discretization in the time domain. Implementation of essential boundary conditions is based on the penalty method. In order to model discrete fractures, the so-called diffraction method is used.Examples are presented and the results are compared to some closed-form solutions and FEM approximations in order to demonstrate the validity of the developed model and its capabilities. The model is able to take the anisotropy and inhomogeneity of the material into account. The applicability of the model is examined by simulating hydraulic fracture initiation and propagation process from a borehole by injection of fluid. The maximum tensile strength criterion and Mohr-Coulomb shear criterion are used for modelling tensile and shear fracture, respectively. The model successfully simulates the leak-off of fluid from the fracture into the surrounding material. The results indicate the importance of pore fluid pressure in the initiation and propagation pattern of fracture in saturated soils. © 2013 Elsevier Ltd.

Development of low-pH cements for immobilisation of intermediate level radioactive waste: Achievements and challenges

Although cementation is a widely recognized solidification/ stabilization process for immobilisation of Intermediate Level Radioactive Waste (ILRW), the low resistance to hyperalkaline pore waters compromises the effectiveness of the process when Portland Cement (PC) is employed. Moreover the manufacture of PC is responsible for significant CO2 emissions. In this context, low pH cements are environmentally more suitable and have emerged as a potential alternative for obtaining secure waste forms. This paper summarises the achievements on development of low-pH cements and the challenges of using these new materials for the ILRW immobilisation. The performance of waste forms is also discussed in terms of radionuclides release. Reactive magnesium oxide and magnesium phosphate cements are emphasised as they feature important advantages such as consumption of available constituents for controlling acid-base reactions, reduced permeability and higher density. Additionally, in order to identify new opportunities for study, the long-term modelling approach is also briefly discussed. Copyright © 2013 by ASME.

Post-earthquake behaviour of footings employing densification to mitigate liquefaction

In situ densification is a popular technique to protect shallow foundations from the effects of earthquake-induced liquefaction, current design being based on semiempirical rules. Poor understanding of the mechanisms governing the performance of soil-structure systems during and after earthquakes inhibits the use of narrow densified zones, which could contribute to optimise the use of densification if the increase in post-earthquake settlement is restrained. Therefore this paper investigates the long-term behaviour of a footing built on densified ground and surrounded by liquefiable ground, centrifuge experiments being used to identify the mechanisms occurring in the ground during and after a seismic simulation. The differential excess pore pressure generated in the ground during the shaking and the processes of vertical stress concentration and subsequent redistribution observed under the footing dominate the system behaviour. The results enlighten the complex mechanisms determining the post-earthquake settlement when densification is carried out to mitigate liquefaction effects. The improvement in performance resulting from widening the zone of densification is rationally explained which encourages the development of new design concepts that may enhance the future use of densification as a liquefaction resistance measure. © 2007 Thomas Telford Ltd.

Nanotube-based passively mode-locked Ytterbium-pumped Raman laser

Over the past decades mode-locked fibre lasers have been extensively refined and developed, with most research efforts focussing on employing rare-earth doped fibres as the active elements [1]. This presents the problem that operation is limited to regions of the spectrum where such elements exhibit gain [1]. Raman amplification in silica fibre is an attractive way to overcome this spectral limitation, with gain available across the entire transparency window (300 nm - 2300 nm) [2-4]. There have been a number of reports utilising Raman gain in ultrashort pulse sources [2-4], however none using a broadband saturable absorber, such as carbon nanotubes [5-7] and graphene [7-9]. A broadband saturable absorber is an essential pre-requisite in order to fully exploit the wavelength flexibility provided by the Raman gain in short pulse mode-locked fiber lasers. © 2011 IEEE.

Identification of Materials from Construction Site Images Using Content Based Image Retrieval Techniques

The capability to automatically identify shapes, objects and materials from the image content through direct and indirect methodologies has enabled the development of several civil engineering related applications that assist in the design, construction and maintenance of construction projects. Examples include surface cracks detection, assessment of fire-damaged mortar, fatigue evaluation of asphalt mixes, aggregate shape measurements, velocimentry, vehicles detection, pore size distribution in geotextiles, damage detection and others. This capability is a product of the technological breakthroughs in the area of Image and Video Processing that has allowed for the development of a large number of digital imaging applications in all industries ranging from the well established medical diagnostic tools (magnetic resonance imaging, spectroscopy and nuclear medical imaging) to image searching mechanisms (image matching, content based image retrieval). Content based image retrieval techniques can also assist in the automated recognition of materials in construction site images and thus enable the development of reliable methods for image classification and retrieval. The amount of original imaging information produced yearly in the construction industry during the last decade has experienced a tremendous growth. Digital cameras and image databases are gradually replacing traditional photography while owners demand complete site photograph logs and engineers store thousands of images for each project to use in a number of construction management tasks. However, construction companies tend to store images without following any standardized indexing protocols, thus making the manual searching and retrieval a tedious and time-consuming effort. Alternatively, material and object identification techniques can be used for the development of automated, content based, construction site image retrieval methodology. These methods can utilize automatic material or object based indexing to remove the user from the time-consuming and tedious manual classification process. In this paper, a novel material identification methodology is presented. This method utilizes content based image retrieval concepts to match known material samples with material clusters within the image content. The results demonstrate the suitability of this methodology for construction site image retrieval purposes and reveal the capability of existing image processing technologies to accurately identify a wealth of materials from construction site images.

A simple diesel engine air-path model to predict the cylinder charge during transients: Strategies for reducing transient emissions spikes

Simple air-path models for modern (VGT/EGR equipped) diesel engines are in common use, and have been reported in the literature. This paper addresses some of the shortcomings of control-oriented models to allow better prediction of the cylinder charge properties. A fast response CO2 analyzer is used to validate the model by comparing the recorded and predicted CO2 concentrations in both the intake port and exhaust manifold of one of the cylinders. Data showing the recorded NOx emissions and exhaust gas opacity during a step change in engine load illustrate the spikes in both NOx and smoke seen during transient conditions. The predicted cylinder charge properties from the model are examined and compared with the measured NOx and opacity. Together, the emissions data and charge properties paint a consistent picture of the phenomena occurring during the transient. Alternative strategies for the fueling and cylinder charge during these load transients are investigated and discussed. Experimental results are presented showing that spikes in both NOx and smoke can be avoided at the expense of some loss in torque response. Even if the torque response must be maintained, it is demonstrated that it is still possible to eliminate spikes in NOx emissions for the transient situation being examined. Copyright © 2006 SAE International.