Fan types for wet scrubbers
Fan types for wet scrubbers
(OP)
(I originally posted this on the HVAC forum, but I believe this is a more appropriate forum, since it is a scrubber-specific problem).
Up to now, we have used radial type centrifugal fans in our scrubbers (blades extend from the hub straight out). We want to evaluate the use of backward-curved blades for our scrubber ID fans, could somebody point me to some web pages on the subject? I understand that radial fans are less prone to solids build-up, but I recently visited a plant whose scrubber uses backward-curved fans, and they are doing OK, with smaller fan motors for comparable applications.
Also, is there a rule of thumb for approximately how much less power you need on a particular application when using a backward-curved fan instead of radial fan? What about fan speeds, in general a backward would work faster or slower than a radial, for comparable sizes?
Last, any references of fan suppliers for scrubbers or other types of corrosive/abrasive environment applications?
Thanks a lot for your help.
Up to now, we have used radial type centrifugal fans in our scrubbers (blades extend from the hub straight out). We want to evaluate the use of backward-curved blades for our scrubber ID fans, could somebody point me to some web pages on the subject? I understand that radial fans are less prone to solids build-up, but I recently visited a plant whose scrubber uses backward-curved fans, and they are doing OK, with smaller fan motors for comparable applications.
Also, is there a rule of thumb for approximately how much less power you need on a particular application when using a backward-curved fan instead of radial fan? What about fan speeds, in general a backward would work faster or slower than a radial, for comparable sizes?
Last, any references of fan suppliers for scrubbers or other types of corrosive/abrasive environment applications?
Thanks a lot for your help.





RE: Fan types for wet scrubbers
Forward curve blades will maximize the velocity of fluid leaving the fan. This allows for greater air speed, lower fan diameter, and greater presure output if velocity head is converted to pressure head. Due to turbulence it can be noisy. They collect dirt. Most common type for air.
Radial blades are simple, inexpensive and can be made very robust. They are easy to clean and shed dirt well. They are not the most aerodynamically efficient.
Backward curved blades do not generate much velocity or pressure but are quiet because they don't generate much turbulence. They require more diameter to move the same amount of air. They would be less prone to erosion due to particulates or liquid drops. Probably more energy efficient for moving air with no pressure output, like axial fans. Liquid pump impellers have backward curved blades.
RE: Fan types for wet scrubbers
RE: Fan types for wet scrubbers
Backward inclined straight blades are preferred over backward inclined curved blades. The curved blades have a concave side where solids will build up causing vibration and changing the fan characteristics. The build up isn't the problem, the sloughing off of large chunks of the build up on a random basis is.
Also, if airfoil blade shapes are used, they are made hollow and the noses erode and then solids build up (unevenly of course) inside the hollow spaces. This can be mitigated by making the nose of the airfoil shape out of round bar of a hard (very hard) material.
Airfoil shapes with flat (rather than curved) inside surfaces have been successful. Not quite as efficient as the pure 'curved both sided' airfoil shape, but better than a flat blade design.
Boy, this question cleared out a lot of cobwebs. I hope this helps.
rmw
RE: Fan types for wet scrubbers
Thanks for your help....
RE: Fan types for wet scrubbers
A backwardly inclined fan blade is a non overloading design but a radial bladed fan's power curve is wicked. It balances off the two effects.
rmw