INTRODUCTION:-A Wet scrubber is an air pollution control device that removes pollutants material from waste gas stream of stationary point sources .The pollutants are removed primanily through the impaction, diffusion, interception or absorption of the pollutant onto droplets of liquid. The liquid containing the pollutant is than collected for disposal.
Wet scrubber system have some advantage over ESP in bagasse fired boilers, wet scrubber are smaller and more compact than ESP .they have lower capital cost and comparable operation and maintenance costs.
CENTRIFUGAL WET SCRUBBER
dust ladan gas stream is introduced tangentially into the lower portion of the cylindrical part of the scrubber, while water drops are injected into the flow stream from sprays directed outwards these droplets are caught in the spinning gas stream and thrown towards the wall by centrifugal force .during the motion the droplets collide with dust particles and capture them. The scrubber liquid along with the particles flow down the wall to the bottom of the scrubber ,from where it is discharged into the hopper .at the top of the separator cleaned gas is discharged into the atmosphere. Separated dust mixed with water is discharged from the scrubber into drainage or into the slurry tank.
CENTRIFUGAL/VANE WET SCRUBBER
This unit is subtable for low pressure drop application involving heavy inlet dust loading and slurry recycling its achieves high collection efficiencies in the 2-4 micron range with low liquid rates .it utilizes a tangential gas inlet and stationary scrubbing vanes to induce centrifugal motion of the gas for removed of dust .there are no moving parts .its non clogging ,self draining design makes it an ideal choice for many application
Scrubbing liquid is introduced on top of the lower scrubbing vane assembly to ensure complete coverage, a centrifugal vane type demister is provided to minimize liquid carry over problems. gases are exhausted via the top outlet.
CONVERSION OF OLD TRAY TYPE WET SCRUBBER INTO CENTRIFUGAL/ VANES TYPE WS:-
This type of wet scrubber, the gas passes up through the opening in the perforated plates( tray) which hold a bed of liquid. The secret is in the scrubber design which uses an impingement baffle above each individual hole .the tiny droplets created by the wetted baffles are the heart of the collection process, gas velocity 60 to 75 feet/sec through the holes result in thousands of jets which atomize the liquid into droplets on the order of 100 in diameter, to clean the contaminated gas this entraps the particles in the scrubbing liquid
But this type of wet scrubber created these problems include
1.Blockages of tray holes( downward of stream) that increase the pressure drop across the scrubber, due to low water flow over the tray .this reduces the gas flow through the boiler and therefore boiler steam output.
2.Droplets carryover that causes buildup on and wear of boiler induced draft fans,this reduces collection efficiency of pollutants. Highly deposition of induced draft fan unbalanced the impeller and generated vibration, due to high vibration fan may be damage.
3.critical operation, backwash problems etc.
4.low efficiency about 60% to 70%
Avoiding this type of problems we provided conversion of old tray type wet scrubber into centrifugal/vanes type wet scrubber
Advantage of centrifugal/vanes wet scrubber.
* low pressure drop
*low water flow required
*easy and smooth operation
*no blockage of internal parts of wet scrubber
* no any deposition at ID Fans
* high efficiency about 99 %
* conversion cost very low according to new W.S
*Flexible design engineering
Shell:- mild steel ,cast steely
Internals:- 304 ss,409 ss,316ss, etc