CFD Analysis of an FGD Absorber

A customer using an absorber for desulfurization of flue gas was trying to solve the problem of sediment on the wall of the absorber, which made the equipment parameters worse during the desulfurization process. A CFD analysis was applied on the current operational condition of the absorber in order to identify the causes of the sediment on the walls and in order to find solutions and modifications that – according to analysis results – lead to suppression of sediment creation and to better diffusion of suspension in the space of the absorber.

The aim of the analysis was to identify possible causes of the sediment (made of solid suspension particles) on the walls of the absorber. The calculations also concentrated on the way the suspension was sprayed, its effect on covering the cross-section of the absorber and possible impact on the efficiency of desulfurization. Moreover, the changes of geometry of inlet guide vanes were calculated with respect to the more intensive swirl of flue gas in the space of the absorber. The analysis included calculations of the current conditions under various operational circumstances, calculations of various modifications of the flue gas outlet and atomizer jets under various operational conditions of the absorber.

The CFD analysis proved that there was a reverse swirl and an increase in the local dampness of the walls, which contributed to sediment on the walls. It showed the influence of speed and potency of droplet streams in the atomizer on the flow and distribution of dampness in the absorber. Thanks to the CFD analysis, necessary modifications of the atomizer and internals took place to improve the working conditions of the absorber.

Some visualizations

Places with higher risk of on wall fouling

Velocity vectors, visualization of vortices close to the wall (before changes)

The radial velocity at the wall of the absorber, visualization of transport speeds deteriorating deposits (before changes)

Mass fraction of moisture on the walls of the absorber (before changes)

Mass fraction of moisture on the walls of the absorber (after change, 24 nozzles in atomizer)

 Effect of changes in the number of nozzles on the temperature field

The temperature field in the absorber (32 nozzles in atomizer)

The temperature field in the absorber (24 nozzles in atomizer)

 

Realization

After checking the impact of the changes in design, the customer used the findings of the CFD analysis and documentation to carry out modifications and achieved an improvement in the operation of his equipment.