Wet Scrubber Engineering
Wet scrubbers are air cleaning devices where a dust-laden air stream is brought into contact with a scrubbing liquid (generally water) and the fine particulates are captured by the liquid droplets and, hence, removed from the air. Dirty water exits the device, but the cleaned air will still retain a fine mist. Therefore, it is necessary for a wet scrubber to have a second stage, called a mist eliminator, to remove these fine droplets. Wet scrubbers can also be used to absorb noxious constituents from the gas, but the design criteria for gas absorption can be quite different from that for particulate removal.
BCE Low energy wet scrubbers are used to collect particles greater than 5 microns. An example of this type is a spray tower. This is a cylindrical vessel fitted with rows of water pipes to spray down on rising inlet air. To prevent droplets from being entrained with the rising air stream, the droplet size must be relatively large (500-1000 microns) compared to high-energy scrubbers and the air velocity must be low (1-4 ft/sec). The larger droplets reduce efficiency and the low air velocity makes this type scrubber larger than others at the same air volume. Other types of low-energy scrubbers are orifice scrubbers and dynamic wet precipitators.
BCE High-energy wet scrubbers are used to collect submicron particles. Two common designs of high-energy wet scrubbers are the venturi scrubber and the packed tower, both designed to provide effective contact of water droplets with the dust-laden inlet air.
The BCE Venturi Scrubber, as the name implies, contains a converging section, throat and diverging section. Dust-laden air enters at the top of the converging section and the scrubbing liquid is injected either at the entrance of the converging section or at the throat. As a result of the area reduction from the venturi entrance to the throat, the air reaches a high velocity where it strips the water from the scrubber wall, forming countless numbers of very small droplets, which capture the particles in the venturi throat. The mist eliminator of a BCE Venturi Scrubber is usually a cyclonic separator directly coupled to the scrubber.
The packed tower consists of a single cylindrical vessel where the inlet air and water contact each other countercurrently in a packed bed and the mist eliminator is in the top of the vessel to remove the fine droplets before the cleaned air exits through the top outlet. Packed beds are commonly used in a variety of applications where a large area of contact is necessary to promote intimate contact between gas and liquid phases.
The following are some advantages and uses of BCE Wet Scrubbers:
- Can handle high-temperature gas streams
- Low initial cost
- Small space to install
- Separates explosive solids from gas streams
- Reduces temperature of exhaust stream
- Capable of high collection efficiency