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).
