FLUIDISED BED SCRUBBERS

Description

A fluidised bed scrubber can be an efficient method of particulate removal and trace gas transfer. Fluidised bed scrubbers are filled with mobile hollow plastic or glass spheres or ellipsoids supported on grids. Scrubbing liquor is sprayed from above, countercurrent to the flow of dirty gas that fluidises the bed.

The intimate mixing of the gas and the scrubbing liquor over the large surface area of the packing spheres allows for efficient trace gas absorption and particulate impingement. The dynamic nature of the bed allows any solids to be removed from the spheres efficiently and prevents blockage of the bed. Similarly, scale deposits, which can be a problem in wet scrubbing systems, are avoided.

When used to remove particulate material, a fluidised bed scrubber will produce a slurry that may require further treatment before disposal. For the removal of trace gases, various scrubbing liquors may be used such as sulphuric acid, caustic soda or water.

The cleaned gas stream is passed through a mist eliminator before release to the atmosphere. As with all wet scrubbers, the increased moisture content of the gas plume may increase its visibility and thus cause problems.

Application

FFluidised bed scrubbers are used to remove particulate material down to 1 µm with an efficiency of more than 90 %. Applications for particulate separation are found within various industrial processes including foundries, pulp mills and chemical and food processing plants. Fluidised bed scrubbers are also capable of simultaneous removal of trace gases and can achieve mass transfer efficiencies of up to 99‰.

Sizing

Fluidised bed scrubbers offer high mass transfer efficiencies for a low power consumption. For example, a typical scrubbing liquor pump would be rated at 15 kW and, for gas streams that require additional propulsion, each 12,000 m3/hour of gas flow would require about 17 kW of fan power. Additional beds of mobile packing can increase the efficiency of mass transfer but have little effect on particulate removal.