Cost effective greenhouse gas reductions in the steel industry from an Organic Rankine Cycle

Large quantities of low grade heat (LGH) are generated within many process industries, and the recovery of LGH is a potentially significant means of improving process efficiency, but it is often difficult to find an appropriate internal heat load. One alternative is to use appropriate technologies to convert the low grade heat to electricity for use on site. This paper describes the environmental and techno-economic evaluation of a case study examining the potential application of an Organic Rankine Cycle (ORC) to generate electricity from LGH from the stacks of a coke oven used in steel production. 21 MW of LGH was available for recovery at the plant and resource accounting and lifecycle analysis methods were used to evaluate the environmental and economic benefits of the operation of an ORC. The results showed that between 1 and 3% of the CO(2) emitted directly through the production of coke would be offset by installation of an ORC, with lifecycle environmental impacts of coke production reduced by less than 1 %, although this was sufficient to offset over 10,000 t CO(2) annually. However, the amount of electricity generated was sufficient to replace all currently imported electricity and economic analysis indicated a relatively attractive discounted payback period of between 3 and 6 years, suggesting this may be a commercially viable option, which could present a relatively cost effective method of achieving greenhouse gas savings in the process industries

The influence of emotional valence on word recognition in people with aphasia

Although several studies have demonstrated that emotional valence facilitates lexical processing in neurotypical adults, there has been limited work involving people with aphasia. This study explored the effects of valence (valenced/neutral) and polarity (positive/negative) on single word processing. Twenty people with chronic aphasia and 20 neurotypical controls completed a written lexical decision task in which valence was manipulated. An effect of valence (i.e. better performance for valenced vs. neutral words) was found in both accuracy and response time in the aphasic group and in response time for controls. Both groups showed an effect of polarity, with aphasic participants generating fewer errors for positive (vs. negative and neutral) stimuli, and controls responding more quickly to positive (vs. neutral) stimuli. Additionally, performance with positive words was impacted less by aphasia severity than negative and neutral words. The results highlight the importance of valence as a psycholinguistic factor in aphasia assessment and intervention

Infrared dust emission in the outer disk of M51

We examine faint infrared emission features detected in Spitzer Space Telescope images of M51, which are associated with atomic hydrogen in the outer disk and tidal tail at R greater than R_25 (4.9', ~14 kpc at d=9.6 Mpc). The infrared colors of these features are consistent with the colors of dust associated with star formation in the bright disk. However, the star formation efficiency (as a ratio of star formation rate to neutral gas mass) implied in the outer disk is lower than that in the bright disk of M51 by an order of magnitude, assuming a similar relationship between infrared emission and star formation rate in the inner and outer disks.Comment: 13 pages in manuscript form, 2 figures; download PDF of manuscript with original-resolution Figure 1 at http://www.eg.bucknell.edu/physics/thornley/thornleym51.pd

The Opacity of Spiral Galaxy Disks VIII: Structure of the Cold ISM

The quantity of dust in a spiral disk can be estimated using the dust's typical emission or the extinction of a known source. In this paper, we compare two techniques, one based on emission and one on absorption, applied on sections of fourteen disk galaxies. The two measurements reflect, respectively the average and apparent optical depth of a disk section. Hence, they depend differently on the average number and optical depth of ISM structures in the disk. The small scale geometry of the cold ISM is critical for accurate models of the overall energy budget of spiral disks. ISM geometry, relative contributions of different stellar populations and dust emissivity are all free parameters in galaxy Spectral Energy Distribution (SED) models; they are also sometimes degenerate, depending on wavelength coverage. Our aim is to constrain typical ISM geometry. The apparent optical depth measurement comes from the number of distant galaxies seen in HST images through the foreground disk. We measure the IR flux in images from the {\it Spitzer} Infrared Nearby Galaxy Survey in the same section of the disk that was covered by HST. A physical model of the dust is fit to the SED to estimate the dust surface density, mean temperature, and brightness in these disk sections. The surface density is subsequently converted into the average optical depth estimate. The two measurements generally agree. The ratios between the measured average and apparent optical depths of the disk sections imply optically thin clouds in these disks. Optically thick disks, are likely to have more than a single cloud along the line-of-sight.Comment: 31 pages, 5 figures, 4 tables, accepted for publication in A

Gaps in the cloud cover? Comparing extinction measures in spiral disks

Dust in galaxies can be mapped by either the FIR/sub-mm emission, the optical or infrared reddening of starlight, or the extinction of a known background source. We compare two dust extinction measurements for a set of fifteen sections in thirteen nearby galaxies, to determine the scale of the dusty ISM responsible for disk opacity: one using stellar reddening and the other a known background source. In our earlier papers, we presented extinction measurements of 29 galaxies, based on calibrated counts of distant background objects identified though foreground disks in HST/WFPC2 images. For the 13 galaxies that overlap with the Spitzer Infrared Nearby Galaxies Survey (SINGS), we now compare these results with those obtained from an I-L color map. Our goal is to determine whether or not a detected distant galaxy indicates a gap in the dusty ISM, and hence to better understand the nature and geometry of the disk extinction. We find that distant galaxies are predominantly in low-extinction sections marked by the color maps, indicating that their number depends both on the cloud cover of {\it Spitzer}-resolved dust structures --mostly the spiral arms--and a diffuse, unresolved underlying disk. We note that our infrared color map (E[I-L]) underestimates the overall dust presence in these disks severely, because it implicitly assumes the presence of a dust screen in front of the stellar distribution.Comment: 22 pages, 2 figures, 3 tables, accepted for publication in A

Star Formation in Disk Galaxies. I. Formation and Evolution of Giant Molecular Clouds via Gravitational Instability and Cloud Collisions

We investigate the formation and evolution of giant molecular clouds (GMCs) in a Milky-Way-like disk galaxy with a flat rotation curve. We perform a series of 3D adaptive mesh refinement (AMR) numerical simulations that follow both the global evolution on scales of ~20kpc and resolve down to scales ~<10pc with a multiphase atomic interstellar medium (ISM). In this first study, we omit star formation and feedback, and focus on the processes of gravitational instability and cloud collisions and interactions. We define clouds as regions with n_H>=100cm^-3 and track the evolution of individual clouds as they orbit through the galaxy from their birth to their eventual destruction via merger or via destructive collision with another cloud. After ~140Myr a large fraction of the gas in the disk has fragmented into clouds with masses ~10^6 Msun and a mass spectrum similar to that of Galactic GMCs. The disk settles into a quasi steady state in which gravitational scattering of clouds keeps the disk near the threshold of global gravitational instability. The cloud collision time is found to be a small fraction, ~1/5, of the orbital time, and this is an efficient mechanism to inject turbulence into the clouds. This helps to keep clouds only moderately gravitationally bound, with virial parameters of order unity. Many other observed GMC properties, such as mass surface density, angular momentum, velocity dispersion, and vertical distribution, can be accounted for in this simple model with no stellar feedback.Comment: 21 pages ApJ format, including 16 figures, accepted to Ap