Kinetic Modelling for Tar Evolution and Formation in a Downdraft Gasifier

Biomass gasification modeling is a powerful tool used to optimize the design of a gasifier. A detailed kinetic model was built by the current authors [1] to predict the behavior of air blown downdraft gasifier for a wide range of materials within the range of (38≤C≤52) %, (5.2≤H≤7) %, and (21.7≤O≤45) %. The model was verified and showed a good stability for a wide range of working parameters like equivalence ratio and moisture content. In the current research, 4 main tar species are added to the model to represent tar formation using detailed kinetic reactions. The yield of tar species is discussed for different zones of a gasifier based on temperature of each zone. Mass and energy balance are calculated. 18 different kinetic reactions are implemented in the kinetic code to predict the optimum working conditions that leads to the production of higher value producer gas. Results conclude that using ER of 0.3 with moisture content levels lower than 10% will lead to the production of higher yields of syngas with lower amounts of tar

Fokker-Planck Models of Star Clusters with Anisotropic Velocity Distributions. I. Pre-Collapse Evolution

The evolution of a spherical single-mass star cluster is followed in detail up to core collapse by numerically solving the orbit-averaged two-dimensional Fokker-Planck equation in energy-angular momentum space. Velocity anisotropy is allowed in the two-dimensional Fokker-Planck model. Using improved numerical codes, the evolution has been followed until the central density increased by a factor of $10^{14}$ with high numerical accuracy. The numerical results clearly show self-similar evolution of the core during the late stages of the core collapse. When Plummer's model is chosen as the initial condition, the collapse time is about 17.6 times the initial half-mass relaxation time. This is longer than the collapse time for the isotropic model by about 13%. As the result of strong relaxation in the core, the halo becomes to be dominated by radial orbits. The degree of anisotropy monotonically increases as the radius increases.Comment: 19 pages, latex, 7 postscript figures, uuencoded gzipped tar file. Submitted to PAS

Understanding the quantum Zeno effect

The quantum Zeno effect consists in the hindrance of the evolution of a quantum system that is very frequently monitored and found to be in its initial state at every single measurement. On the basis of the correct formula for the survival probability, i.e. the probability of finding the system in its initial state at every single measurement, we critically analyze a recent proposal and experimental test, that make use of an oscillating system.Comment: 9 pages, LaTeX, including 1 epsfigure, tar+gzip+uuencoded to appear in Phys. Lett.

On Damage Spreading Transitions

We study the damage spreading transition in a generic one-dimensional stochastic cellular automata with two inputs (Domany-Kinzel model) Using an original formalism for the description of the microscopic dynamics of the model, we are able to show analitically that the evolution of the damage between two systems driven by the same noise has the same structure of a directed percolation problem. By means of a mean field approximation, we map the density phase transition into the damage phase transition, obtaining a reliable phase diagram. We extend this analysis to all symmetric cellular automata with two inputs, including the Ising model with heath-bath dynamics.Comment: 12 pages LaTeX, 2 PostScript figures, tar+gzip+u