Experimental study of the SO_2 removal efficiency and volumetric mass transfer coefficients in a pilot-scale multi-nozzle spray tower

摘要

The spray tower is an industrial device widely employed for liquid-gas contact. In these towers, liquid is sprayed to generate droplets that provide a large interfacial area for heat and mass transfer between the continuous and dispersed phases. The performance of a spray tower is difficult to predict due to the complex hydrodynamics of system. This performance is influenced by several factors, such as droplet size and distribution, droplet velocity, collision and coalescence between droplets, internal recirculation, oscillation and distortion of the droplets, the relationship between different variables, and gas and liquid flow rates. Although spray towers are very common, there are few methodologies for their design, which is typically based on empirical or one-dimensional models. Experimental studies on gas absorption in spray towers have been carried out for years. However, all these studies used a single spray nozzle, whose configuration differs from that used in typical industrial spray towers, thus making the results of these studies difficult to apply in practice. The present work consisted of experimentally determining the volumetric mass transfer coefficient, k_ga, in a lab-pilot spray tower absorbing SO_2, employing different operating conditions and two nozzle configurations, one involving the simultaneous use of a set of five spray nozzles and the other one, a single spray nozzle. New correlations to predict the coefficient k_ga are proposed, including two new parameters: the diameter of the spray nozzle orifice and the exit velocity of liquid from the orifice, as well as the superficial gas and liquid velocities, which have been used traditionally in other studies.