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Byline: Blas Melissari, Stavros A. Argyropoulos This paper deals with the identification of transition convective regimes in liquid metals by means of the numerical simulation of the melting of solid spheres in uniform flow baths. The cases of forced convection with 'aiding' and 'cross-flow' natural convection are investigated. The fluids studied have Prandtl numbers between 10-3 and 101. A three dimensional mathematical model has been developed using the SIMPLER algorithm to study the melting of a spherical addition initially at room temperature subjected to a uniform flow of liquid metal. The melting times are obtained as a function of the bath temperature and velocity. The model is validated against experimental results in water and liquid Aluminium, showing good agreement with the existing data.

Biomass is regarded as a renewable source of energy and is playing a role in future fuel supply trend, with great acceleration. However, due to the chemical composition of the ash of certain types of biomass (particularly short rotation crops like grasses, canes and straws), boiler related problems have occurred systematically in the past. These fuels are rich in alkaline metals (potassium, phosphorus, chlorine and sodium) which form complex eutectic salts that effectively lower the melting point of the ashes during combustion and cause fouling and slagging problems, especially in superheater tubes. This work reviews the latest investigations regarding the prediction of these problems through the evaluation of the ashes in the laboratory and discuss their mitigation by fuel leaching and blending. As a means to demonstrate the methodology, experimental data related to the evaluation of the Common Cane are presented, resulting from our own laboratory tests. These include fusion/sintering tests of ashes sampled from canes in the as-is and water-leached condition and the comparisons with other more traditional biomasses. The results show that the as-is state would be unacceptable to burn, but leaching with water and/or blending with more stable ashes reduces the detrimental effects on boiler components to a tolerable level. [ABSTRACT FROM AUTHOR]

Biomass as a source of energy is key to the progress of developing countries like Uruguay, since the application of a safe and efficient burning technology uses a renewable source of energy, relieves the dependence on imported crude oil, generates more employment than traditional sources and has a zero net greenhouse gas effect. Knowledge of the characteristics of the fuel and its behaviour in combustion systems is very important, since the installations are subject to chemical and physical attack from its ashes. The ash content and composition must be measured and analyzed, and its impact evaluated. In particular, cereals and other short-rotation plants have ashes with a high tendency to form deposits and enhance corrosion processes. This paper focuses on the effects that some kinds of fuels have on the physical and chemical damage of boiler components, particularly Chlorine enhanced corrosion. Recommendations for the remediation of critical situations are provided. [ABSTRACT FROM AUTHOR]

The present paper analyzes the different biomass burner technologies used in Uruguay from the combustion process standpoint, seen as a system of processes with highly non linear mechanisms of mass, momentum and energy transfer phenomena. Technologies based on fixed, moving and fluidized bed are compared and contrasted, with a special emphasis on the effect that fuel quality has on the choice of technology, given the variations found in the biomass quality, in terms of its size distribution and composition. The problem of designing equipment for any given chemical process is stated and the inherent difficulty when scaling an existing installation is proven. The need to acquire knowledge of the processes and the relationships between them is essential for a successful scale-up. In the majority of cases, the geometry has to be altered, dramatically affecting the mechanisms within. The highly coupled non linear system renders analytical solutions impossible, so approximate numerical solutions are sought. Numerical results of a study of the sensitivity of bed permeability on combustion stability are shown. [ABSTRACT FROM AUTHOR]