Search

Oxygen production processes using adsorbents for application to CCS technologies (Carbon Capture and Storage) offer potential cost benefits over classical cryogenics. In order to model adsorption processes an approach using three size scales has been developed. This work is being conducted in the framework of the DECARBit European research project. The first scale is at the size of the oxygen adsorption bed to be modelled as a vertical cylinder filled with pellets. Its length is 0.2 m (scale 10-1 m). The bed is homogeneous in the transversal direction so that the problem is 1D (independent variables t, x). The physics in the process include gas species (Cbk (t, x)) convection and dispersion, thermal convection and conduction (T(t, x)) and hydrodynamics (v(t, x)). The gas constituents involved are N2, 02, CO2 and H2O. The second scale is at the size of the pellets that fill the adsorber and which are assumed to be of spherical shape with a typical radius of 5 mm (scale 10-3 m). The independent variable for the pellets is the radius “rp”. At a certain height (x) down in the adsorber all the pellets are the same and are surrounded by the same gas composition but inside the pellets the concentrations may vary. The state variables for the inner part of the pellets are the gas concentrations Cpk(t, x, rp). The pellets are so small that they are assumed to have a uniform temperature. This leads to a 2D transient model for the pellets linked to the 1D transient model for the bulk. The third scale looks into the detailed structure of the pellets that are made of perovskite crystallites. The latter are assumed to be spherical. Oxygen adsorption occurs in the crystallites which have a radius of about 0.5 pm (scale 10-7 m). All the crystallites at the same radius in a pellet are supposed to behave the same and because they are spherical, the only independent variable for a crystallite located at (x, rp) is its radius “rc”. The state variables for the crystallites are then the adsorbed oxygen concentration Cc2 (t, x, rp, re). The crystallites are so small that they are assumed to have a uniform temperature. This leads to a third transient model that is 3D for the crystallite and is linked to the 2D transient model for the pellets which is itself linked to the 1D transient models for the bulk. From the larger to the lower scales, the links between the three models are the following: the bulk concentration and temperature give the boundary conditions surrounding the pellets. The pellet concentration gives the boundary conditions for the crystallites. We chose to solve this multiscale approach that requires the coupling of models of different dimensions in Comsol Multiphysics. The simulator was built to gain knowledge from laboratory experiments in order to estimate whether oxygen separation from air is realistic or not.

CLC is a new promising combustion process for CO2 capture with less or even no energy penalty compared to other processes. Up to now, most of the work performed on CLC was conducted with gaseous or solid fuels, using methane and coal and/or pet coke. Liquid fuels such as heavy fuels resulting from oil distillation or conversion may also be interesting feedstocks to consider. However, liquid fuels are challenging feedstock to deal with in fluidized beds. The objective of the present work is therefore to investigate the feasibility of liquid feed injection and contact with oxygen carrier in CLC conditions in order to conduct partial or complete combustion of hydrocarbons. A batch experimental fluidized bed set-up was developed to contact alternatively oxygen carrier with liquid fuels or air. The 20 mm i.d. fluidized bed reactor was filled up with 45 g of NiAl0.44O1.67 and pulses of 1-2 g of liquid were injected in the bed at high temperatures up to 950˚C. Different feedstocks have been injected, from dodecane to heavy fuel oils No.2. Results show that, during the reduction period, it is possible to convert all the fuel injected and there is no coke remaining on particles at the end of the reduction step. Depending upon oxygen available in the bed, either full combustion or partial combustion can be achieved. Similar results were found with different liquid feeds, despite their different composition and properties. Le CLC est un nouveau concept prometteur appliqué à la combustion qui permet le captage de CO en minimisant la pénalité énergétique liée au captage. Jusqu’à présent, l’essentiel des travaux de recherche dans le domaine du CLC concerne les charges gazeuses (méthane) et solides (charbon et coke). Les charges liquides, et particulièrement les résidus pétroliers, sont des charges également intéressantes à considérer a priori. La mise en oeuvre de ces charges en lit fluidisé est cependant délicate. L’objet de ce travail est d’étudier la faisabilité de la combustion partielle ou totale des charges liquides dans les conditions du CLC au contact d’un matériau porteur d’oxygène. Un petit réacteur en lit fluidisé opérant en batch a été développé pour permettre alternativement le contact du matériau porteur d’oxygène avec une charge liquide ou de l’air. Le réacteur de 20 mm de diamètre est rempli de 45 g de particules de NiAl0.44O1.67. Environ 1-2 g de charge liquide est injecté par pulse dans le lit à des températures allant jusqu’à 950˚C. Différentes charges liquides ont été étudiées, du dodécane au fioul lourd n˚2. Les résultats montrent que pendant la période de réduction du matériau porteur d’oxygène, il est possible de convertir tous les hydrocarbures injectés. À l’issue de cette phase, il ne subsiste pas de dépôt de coke à la surface des particules. En fonction de la quantité d’oxygène disponible dans le lit, on effectue une combustion totale ou partielle des hydrocarbures injectés. Des résultats similaires sont obtenus pour les différents hydrocarbures testés, malgré leurs propriétés a priori très différentes.

The asphalt concrete constructability analyses indicate that the proposed objective of Caltrans to rebuild 6 lane-kilometer of truck lanes within a 55-hour weekend closure has a low probability of success. Material delivery resources, especially dump trucks for demolition and delivery trucks for asphalt concrete supply, were the major constraints limiting the production. 2 The total layer thickness for asphalt concrete proved to be a major determining element on the production capability. For example, the production capability of Full-Depth AC Replacement is just about 60 percent of CSOL production within a weekend closure for a scenario in which the two truck lanes need to rehabilitated. However, CSOL requires rehabilitation of all lanes including shoulders on both sides, thereby limiting its effective productivity. Different rehabilitation working methods, determined by the construction access, lane closure tactics, and paving procedures, also have a significant effect on the production capability of the rehabilitation. The comparison of different construction windows, (i.e., a weekend closure versus continuous closure) was also examined to see the effect of different construction windows on production capability. Continuous closure/continuous operation enables the CSOL project to be finished 15 percent faster and the Full-Depth AC Replacement project to be finished 12 percent faster compared to weekend-only closures. However, the total duration of the closure for continuous closure/daytime operation was longer than that for the weekend-only closure. This study concludes that efficient lane closure tactics designed to work with the pavement profile can minimize non-working time, such as the time waiting for the AC to cool, and increase the production capability of the project. The constructability analysis for AC developed in this study will aid transportation agencies in their decision-making processes for prioritizing the number of rehabilitation projects on their backlogs, selecting optimal strategies, and effectively communicating project duration with the public and other project stakeholders, such as local governments.

A case study was performed on a Caltrans concrete rehabilitation project near Los Angeles on Interstate 10. The project was unique in that the contractor had to remove and replace 2.8 lane-km of concrete pavement in a 55-hour weekend closure. The existing cement treated base was not removed except in places where it had deteriorated, and a fast setting hydraulic cement concrete with a 4-hour opening strength was used for the surface concrete. The contractor used a concurrent working method in which demolition and concrete paving occurred simultaneously and only a single lane was removed and replaced. The contractor had only one standard width construction access lane (3.7 m) and a shoulder width of less than 3.0 m. The contractor successfully completed this 2.8 lane-km objective in 55 hours and was eligible for a $500,000 bonus per the contract. The demolition operation took 76 percent longer than planned, but it did not delay the overall progress of the project. The concrete paving activities, especially the concrete delivery and discharge, controlled the overall progress of the 55-hour weekend project. In terms of the number of slabs replaced per hour, the 55-hour weekend closure was 54 percent faster than the average nighttime closure conducted by the same contractor. The amount of the rehabilitation work performed over the 55-hour extended closure would have normally taken 2.5 weeks (16.4 days) of nighttime lane closures. If no work stoppages in the concrete paving had occurred, the maximum amount of rehabilitated road would have been 3.5 lane-km. In 10-hour nighttime closures, the contractor was able to remove and replace 50 slabs on average compared with 15 slabs for 7-hour nighttime closures. During weekend daylight hours, traffic through the construction zone was reduced by 30 to 60 percent compared with normal weekend traffic volume. During construction, the percentage of traffic diverting to other routes doubled over normal diversion in the daylight hours, but was only approximately 5 percent more than normal during the nighttime hours. The reduced traffic volumes passing the construction site indicated driver awareness of the weekend construction window and traffic lane closures. Caltrans did an excellent job of informing the public of the project through local media outlets (radio, newspapers, and television), signage, and brochures. The construction productivity data from the demolition and paving operation was used to validate a constructability and productivity analysis software coded by the University of California Berkeley (UCB). The average results from a deterministic and stochastic analysis were in agreement with the actual project productivity. The stochastic analysis showed that the expected range for the project productivity was between 2.2 and 3.4 lane-km for a 68-percent confidence interval with the average productivity being 2.8 lane-km.

One of the main objectives of the Caltrans Long Life Pavement Rehabilitation Strategies for rigid pavements (LLPRS-Rigid) is to have a construction productivity of approximately 6 lane-kilometers within a 55-hour construction window. This productivity objective must not conflict with the other two main LLPRS-Rigid objectives: to provide 30 plus years of pavement service life and to minimize pavement maintenance. This report describes the processes and results of a constructibility and productivity analysis for the Caltrans LLPRS-Rigid project, focusing on optimizing the maximum production capability within a 55-hour weekend closure. The analyses explored the effect of the following parameters on the concrete pavement construction productivity in California: pavement design profile, curing time, number and capacity of resources, number of lanes to pave, type of construction scheduling, and alternative lane closure tactics. The typical construction processes for concrete pavement rehabilitation were modeled with input from California concrete paving contractors, Caltrans, and academia.

Interferon-gamma receptor deficiency is a recently described immunodeficiency that is associated with onset of severe mycobacterial infections in childhood. We describe the occurrence of symptomatic and often severe viral infections in 4 patients with interferon-gamma receptor deficiency and mycobacterial disease. The viral pathogens included herpes viruses, parainfluenza virus type 3, and respiratory syncytial virus. We conclude that patients with interferon-gamma receptor deficiency and mycobacterial disease have increased susceptibility to some viral pathogens.