1. LECTURE #7b Particulate Scrubbers
March 6, 2017
ATMO.5230

2. Introduction Collect: fumes, mists, suspended dusts
Classified as: f(liquid contacting mechanism)
Spray-chamber scrubber (use spray nozzles / preformed spray scrubbers)
Cyclone spray chambers (influent enters tangentially)
Orifice & wet-impingement scrubbers (self-induced or gas atomized spray)
Venturi & Venturi jet scrubbers (maximizes relative velocity between liquid droplet and suspended particles)
Classified by energy:
Low-, moderate- or high-energy units
Energy requirements expressed:
Pressure drop (inches / centimeters of water)
Level of contacting power (hp/1000 cfm or kWh/1000 m3 treated)
Liquid circulation rates:
gallons per 1000 cf3 (1 gal/1000 ft3 = L/m3)

3. Advantages/disadvantages
Can handle flammable/explosive dusts
Provide gas absorption and dust collection in single unit
Can handle mists
Provide cooling of hot gases
CE can be varied/optimized
Corrosive gases/dusts can be neutralized
Disadvantages
High potential for corrosion
Effluent liquid can create water disposal problems
May need protection against freezing; need for exhaust reheat
Contaminated collected particulate
Disposal of waste sludge may be expensive

4. Spray-chamber scrubbers
Like a packed tower only with spray nozzles
Optimized water droplet size separates particles from gas stream
Maintenance: nozzle clogging
CE of 90% on particles > 8um
Applications: paper dust control, latex aerosol control in fiberglass production
Power consumption: low  1 – 4 inches water (0.5-2 hp/1000acfm) at Vg of 3-6 fps

5. Cyclone spray chamber
Influent enters tangentially allowing higher Vsuperficial
Centrifugal force promotes droplet separation  smaller size w/ greater CE (95% at 5um)
Vg(in) = fps; Vsuperficial =10 fps
Liquid recirculation: 2-10 gal/1000 ft3
Pressure drops: 4-8 inches water
Power inputs: hp/1000 cfm

6. Orifice and wet-impingement scrubbers
Self induced or gas atomized spray where combined air-droplet mixture impinges on solid surface
Orifice:
air impinges on liquid surface then on baffles
Low water recirc., 0.5 gal/1000ft3
P drop: 8-12 inches water
Power inputs: 2-4 hp/1000 cfm
Impingement:
air-droplets flow through perforated tray with liquid/froth then impinges on plate
Same P drop
Liquid requirements: 2-3 gal/1000ft3
Power input: 2-4 hp/1000 acfm

7. Typical Venturi Scrubber
CE = f(relative velocity between liquid-particle and particle size)
Water injected at low P at throat with Vg of fps  CE of 98% at 0.5 um)
Power: 3-12 hp/1000 cfm
Liquid recirculation rate of 3-15 gal/1000ft3
Venturi jet scrubbers:
Water injected in throat at high velocities
P drop: 2-4 inches water
Water rates: gal/1000 ft3
Nozzle pressures: psig
CE of 92% for 1 um particles

8. Contacting power approach to design

9. Energy dissipated / unit volume of gas

10. Effective friction loss

11. CE as f(particle size & pressure) in Venturi scrubber

12. Typical scrubber applications

13. Other considerations Elimination of liquid entrainment
Humidification of scrubbed gases
Cost
High-energy Venturi .
Low-energy Venturi

14. Power plants: coal to gas &end-of-pipe controls

15. China halts coal power plants

16. China offers bonus to curb emissions