Wet Dust scrubbing
Applications of the Vane-cage scrubber
Scrubbers are designed and built by Dahlman for several industrial purposes. In general, scrubbers can be divided into two groups; scrubbers for dust removal (venturi scrubbers, Vane-cage scrubbers etc.) and scrubbers for vapour absorption (packed columns). Scrubbers for dust removal do not have enough contact surface to reach the efficiencies on vapour absorption like packed columns. On the other hand, a packed column is less efficient on dust fines and very vulnerable for blockings compared to a good dust scrubber.
A Vane-cage scrubber is designed as a solution for difficult dust emissions (sticky, abrasive, fines etc.) and proved to be more economical and more effective than a venturi scrubber. Because of his excellent efficiency we also apply this scrubber for dust removal in combination with ‘easy’ absorption jobs like SO2 SO3, NH3, HCl etc. This way two scrubbing processes systems can be integrated on one system.
Working principle of the Vane-cage scrubber
Gas enters the Vane-cage scrubber tangentially and is forced into a centrifugal motion. The washing liquid (e.g. water) is injected directly into the vane-cage through an open pipe. The contact between the washing liquid and the centrifugal gas inside the vane-cage creates a spinning cloud of very fine droplets. Part of this cloud is forced outwards through slits in the vane-cage, creating a wet cyclone and coating every part of the scrubber with a moving water film (cleaning itself continuously!).
The scrubbing liquid captures the contaminants (dust or vapour) in three distinct scrubbing steps:
Scrubbing step 1:
The gas enters the scrubber tangentially, while crossing a vortex of water droplets. In this wet cyclone, the gas is saturated with water and, the main part of the bigger particles are captured.
Scrubbing step 2:
The stationary vane-cage acts as a number of small venturies, working parallel to wash the gas stream at a low-pressure drop.
Scrubbing step 3:
The dense cloud of very fine water droplets in the vane-cage forms the most efficient washing step. When the contaminated gas flows through this cloud it is in intense contact with the water droplets.
In this process, very fine particles as well as vaporous or gaseous emissions are separated from the gas stream.
After capturing the contaminant with water droplets, the final efficiency of the scrubber is determined by the separation of the remaining droplets from the gas stream.
After the vane-cage a stationary de-entrainer forces the gas into a quick spinning motion, which efficiently removes all droplets at a low pressure drop. Scrubbing and droplet separation in one single motion!
- Dust emission control
- Sticky/ abrasive particles
- High temperature
- High explosion risk
- Chemical scrubbing combined with a(sticky) dust load. e.g. SO2/ SO3with fly ashes, NH3)
- Emission limits below 10 –5 mg/m3
Advantages Vane-cage scrubber:
- High efficiency at relatively low pressure drop
- Completely self cleaning
- Can handle high dust loading
- No risk of Explosion
- Less energy consumption and better efficiency (compared with venturi scrubbers in similar processes)
- Low water consumption
- No moving parts, spray nozzles or demister pad required
- Minimal maintenance costs
- Small footprint compared with filters