Alberto Gómez-Barea

Downstream evolution of unconfined vortices: mechanical and thermal aspects

We present a numerical study of the downstream evolution (mechanical and thermal) of vortex-jet cores whose velocity and temperature elds far from the axis match a family of inviscid and non-conducting vortices. The far-velocity eld is rotational, except for a particular case which corresponds to the well-known Long’s vortex. The evolution of the vortex core depends on both the conditions at a certain upstream station, characterized by the dimensionless value of the velocity at the axis, and a dimensionless swirling parameter L dened as the ratio of the values of the azimuthal and axial velocities outside the vortex core. This numerical study, based on the quasi-cylindrical approximation (QC) of the Navier{Stokes equations, determines the conditions under which the vortex evolution proceeds smoothly, eventually reaching an asymptotic self-similar behaviour as described in the literature (Fern andez-Feria, Fern andez de la Mora & Barrero 1995; Herrada, P erez-Saborid & Barrero 1999), or breaks in a non-slender solution (vortex breakdown). In particular, the critical value L = Lb(a) beyond which vortex breakdown occurs downstream is a function of a dimensionless parameter a characterizing the axial momentum of the vortex jet at an initial upstream station. It is found numerically that for very large values of a this vortex breakdown criterion tends to an asymptote which is precisely the value L = L predicted by the self-similar analysis, and beyond which a self-similar structure of the vortex core does not exist. In addition, the computation of the total temperature eld provides useful information on the physical mechanisms responsible for the thermal separation phenomenon observed in Ranque{Hilsch tubes and other swirling jet devices. In particular, the mechanical work of viscous forces which gives rise to an intense loss of kinetic energy during the initial stages of the evolution has been identied as the physical mechanism responsible for thermal separation.

Catalytic Seawater Flue Gas Desulfurization Model

A model of a seawater flue gas desulfurization process (SFGD) where oxidation of the absorbed SO(2) is catalyzed by activated carbon is presented. The modeled SFGD process is comprised of two main units, an absorption packed scrubber, where SO(2) absorption takes place, and an oxidation basin, where the absorbed SO(2) is catalytically oxidized to sulfate, a natural component of seawater. The model takes into account the complex physical-chemical features of the process, combining mass-transfer, kinetics and equilibrium equations, and considering the electrolyte nature of the liquid phase. The model was validated with data from a SFGD pilot plant and a sensitivity analysis was performed, showing its predictive capability. The model is a useful tool for designing industrial desulfurization units with seawater.

Implementation of waste-to-energy options in landfill-dominated countries: Economic evaluation and GHG impact

The economic and environmental impact of several waste-to-energy (WtE) schemes to produce electricity from municipal solid waste (MSW) refuse is evaluated and compared with landfill disposal. Both incineration and gasification alternatives are considered. The gasification option includes three different configurations: (1) a fluidized bed gasifier (FBG) with internal combustion engine (ICE), (2) a FBG with organic Rankine cycle (ORC) and (3) a grate gasifier with steam Rankine cycle (SRC). The study is primarily applied to regions where the management system is based on Mechanical Biological Treatment (MBT) plants, generating a large share of refuse (>70%), which is currently landfilled. The specific case of Andalusia, a region in the south of Spain with 23 MBT plants distributed over a region of 87.000 km2, where about 80% of municipal solid waste (MSW) is currently landfilled, is taken as main reference; thereafter, the study is further extended to preliminary assess other regions of some European landfill-dominated countries with similar characteristics. The results show that both incineration and gasification improve landfill disposal, contributing favorably to greenhouse gas (GHG) reduction and fulfilling EU environmental regulations, although the three gasification options analyzed yield lower GHG emissions than incineration. In addition, gasification enables better integration of WtE into existing MBT plants, especially in the particular case of Andalusia, where MBT plants are widespread on the region, making it a more promising option than incineration, which is mainly based on large centralized plants, and less socially accepted. From the options analyzed, the WtE scheme based on FBG with ICE gives the highest profitability for a given gate fee, due to much higher electrical efficiency. However, FBG with ORC seems to be a better option in the short-term for landfill-dominated countries, due to its higher technical reliability and the low gate fee currently available in these countries.

THE ROLE OF ADVANCED WASTE-TO-ENERGY TECHNOLOGIES IN LANDFILL MINING

Publicado en: WIT Transactions on Ecology and the Environment, Volume 224, Issue 1, 20 September 2017, Pages 403-409