Modeling for Scrubbing and Collection Efficiency

In wet scrubbing, water droplets collide with particles in three flow modes of operation (1) cross-flow (2) cocurrent flow and (3) countercurrent flow. Here the mathematical 

A model for wet scrubbing in a cross-flow is illustrated in Fig. 7.21. Consider a rectangular scrubbing domain of length L, height H, and width of unity in Cartesian coordinates. Assume that the gas-solid suspension flow is moving horizontally, and that the solid particles are spherical and of uniform size. The particle concentration across any plane perpendicular to the flow is assumed to be uniform. The water droplets fall vertically and are uniformly distributed in the flow system. 

The mass balance of particles in the volume element in Fig. 7.21 can be given as 

Equation (7.76) indicates that the collection efficiency increases with the height of the scrubbing chamber and with increasing ratio of flow rate of droplets to flow rate of particles. 

For the vertical countercurrent scrubbing system shown in Fig. 7.22, the gas-solid suspension flows upward from the bottom of the chamber and the water droplets fall downward. It is assumed that both the gas-solid suspension velocity and droplet velocity are unchanged in the process of scrubbing. It is also assumed that the no-slip condition exists between the particles and gas. The particle concentration across any horizontal plane is assumed to be uniform. 

---