Antonia Gil

Gas-particle flow inside cyclone diplegs with pneumatic extraction

This paper presents a detailed flow analysis inside cyclone diplegs equipped with bottom gas extraction. Up to now, little experimental work has been done related with these devices, specially used for hot gas cleaning applications, such as pressurized fluidized bed combustion (PFBC). Tests varying inlet solid loading and gas extraction flow rate were carried out in a one-fifth cold-flow model of a PFBC cyclone. Velocity and pressure measurements along cyclone dipleg have been carried out. Results from experimental measurements reveal that the swirling flow penetrates inside the dipleg, deeper than can be anticipated by literature predictions on conventional cyclone designs. This effect is caused by the high inlet velocities of this kind of cyclones and the gas suction at dipleg bottom. Dipleg pressure coefficient is shown to be a function of the inlet solid loading and the tangential to axial velocity ratio. Although for standard cyclone designs it has been claimed that underneath the vortex end there is a stagnant region where solid recirculation and reentrainment can occur, it has been experimentally verified that even with a small percent of gas extracted at the bottom a substantial tangential velocity component is induced at dipleg bottom. This velocity assures solids conveyance to the extraction device. As solid loading is increased, an upward movement of the vortex end is detected from wall pressure measurements. The solid loading causes an important decrease of the vortex energy and, consequently, a weakening of the dipleg tangential velocity. A new method for measuring the vortex penetration in dipleg is presented.

Assessment of groundwater vulnerability to nitrates from agricultural sources using a GIS-compatible logic multicriteria model.

In the present study an overlay method to assess groundwater vulnerability is proposed. This new method based on multicriteria decision analysis (MCDA) was developed and validated using an appropriate case study in Aragon area (NE Spain). The Vulnerability Index to Nitrates from Agricultural Sources (VINAS) incorporates a novel Logic Scoring of Preferences (LSP) approach, and it has been developed using public geographic information from the European Union. VINAS-LSP identifies areas with five categories of vulnerability, taking into account the hydrogeological and environmental characteristics of the territory as a whole. The resulting LSP map is a regional screening tool that can provide guidance on the potential risk of nitrate pollution, as well as highlight areas where specific research and farming planning policies are required.

Effect of the Solid Loading on a PFBC Cyclone with Pneumatic Extraction of Solids

This paper presents the effects of solid loading on the performance of a cyclone with pneumatic extraction of solids. The cyclone is a non-conventional design, especially used for hot-gas cleaning applications such as pressurized fluidized bed combustors (PFBC). A scaled-down cold-flow model was employed for the research. Experiments were conducted at 9–14 m/s inlet gas velocities, inlet solid loadings ranging from 30 to 230 g/kg gas, and bottom gas extraction percentages from 0.3 to 1.5%. Experimental results of pressure drop resistance coefficients and collection efficiency were compared with literature predictions. At PFBC operating conditions, cyclone geometry and solid concentration are the main parameters influencing cyclone pressure drop and collection efficiency. The vortex penetration in dipleg causes lower pressure drop values and higher collection efficiencies than predicted. These parameters can be suitably predicted for PFBC cyclones by introducing a modified penetration length in Muschelknautzs model [1]. For the present cyclone design, a new correlation of pressure drop, including the influence of solid loading, is proposed. A new method for detecting cyclone fouling, not previously addressed, is also presented, based on the evolution of the pressure drop resistance coefficient. An enhanced separation efficiency has been found, related to collection efficiency, which is especially important for particle sizes below 10 μm revealing agglomeration effects.

Thermal valorization of post-consumer film waste in a bubbling bed gasifier

The use of plastic bags and film packaging is very frequent in manifold sectors and film waste is usually present in different sources of municipal and industrial wastes. A significant part of it is not suitable for mechanical recycling but could be safely transformed into a valuable gas by means of thermal valorization. In this research, the gasification of film wastes has been experimentally investigated through experiments in a fluidized bed reactor of two reference polymers, polyethylene and polypropylene, and actual post-consumer film waste. After a complete experimental characterization of the three materials, several gasification experiments have been performed to analyze the influence of the fuel and of equivalence ratio on gas production and composition, on tar generation and on efficiency. The experiments prove that film waste and analogue polymer derived wastes can be successfully gasified in a fluidized bed reactor, yielding a gas with a higher heating value in a range from 3.6 to 5.6 MJ/m3 and cold gas efficiencies up to 60%.

A CAPE-Taguchi combined method to optimize a NPK fertilizer plant including population balance modeling of granulation-drying rotary drum reactor

Abstract In this work, a detailed model of a real NPK fertilizer plant has been developed to optimize operation strategies, in order to reduce sensibly the thermal and electrical consumptions, as well as the recycle ratio. Granulation is a very complex process that involves changes in the particle properties and depends on several factors as drum speed and design, binder conditions and material properties. Furthermore, simultaneously to granulation process, a drying process takes place. In consequence, due to its complexity, a novel comprehensive semi-empirical population balance model of an industrial co-current rotary drum reactor has been developed to model the PSD evolution, including granular dynamics and the particle growth by granulation and the size reduction due to the effect of particle-particle and particles-bed attrition. The granulation model is coupled with a drying model, taking into consideration mass and energy balances, including combustion and the bed and reactor heat and mass transfer mechanisms. Granulator model (developed in Matlab) has been coupled to auxiliary equipment modelled in AspenPlus by means of MSExcel intermediate files. Global and local models have been validated with plant data. Additionally, a robust Taguchi Design of Experiments (DoE) has been applied to evaluate the effect of each process parameter in the Key Performance Indicators. From the results of the analysis, it is possible to discriminate what process parameters are critical in the quality of the product and in the use of the resources.