Optimization of desulphurization process in a flue gas obsorber by adjusting flow patterns and rotary atomizer

Abstract

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.

Efficiency of desulphurization process in a flue gas absorber depends strongly on flow patterns of the continuous gas phase and interaction with water slurry phase that is injected into the absorber. The main task is to ensure that undesulphurized flue gas moves optimally to where a high concentration of water slurry in the form of droplets “flies”. In the paper, a model for desulphurization process is presented. The problem was solved using commercial CFD code StarCD into which a model for desulphurization was integrated. The model distinguishes between two phases of heat and mass transfer. One called “constant rate period” where the water droplet formed by an aggregate of calcium hydroxide particles encapsulated in water evaporates by convection mechanism and sulphur dioxide is transferred by the same mechanism. In this phase the spherical reaction front recedes as calcium hydroxide is converted. In the second phase called “falling rate period” water is contained only in the free space between solid particles of calcium hydroxide and sulphur dioxide is transferred by diffusion that is modified by tortuosity reflecting torturous paths inside the structure of particles. By the same mechanism water evaporates from the aggregate of particles. A model for age of flue gas was developed that shows residing time of flue gas in individual parts of the absorber. Together with values of water content and void fraction of water phase one can suggest different design modifications of the absorber (for example different inclination of inlet vanes that guide the flue gas into the absorber).