‫اسکرابرهای تر‬
‫• اساس کار این روش شستشوی گاز به کمک یک حالل می باشد‪.‬‬
‫• در این روش بطور هم زمان گازها و ذرات حذف می گردند‪.‬‬
‫• در هنگام کاربرد این روش باید به تصفیه پساب حاصل نیز فکر شود‪.‬‬
Wet Scrubbers
Principle
 Wet scrubbers are used for removal of
particles which have a diameter of the order
of 0.2 mm or higher.
 Wet scrubbers work by spraying a stream of
fine liquid droplets on the incoming stream.
 The droplets capture the particles
 The liquid is subsequently removed for
treatment.
Wet Scrubbers
Construction and Operation
 A wet scrubber consists of a rectangular or
circular chamber in which nozzles are
mounted.
 The nozzles spray a stream of droplets on the
incoming gas stream
 The droplets contact the particulate matter,
and the particles get sorbed.
 The droplet size has to be optimized.
Wet Scrubbers (contd.)
o Construction and Operation (contd.)
 Smaller droplets provide better cleaning, but are
more difficult to remove from the cleaned stream.
 The polluted spray is collected.
 Particles are settled out or otherwise removed from
the liquid.
 The liquid is recycled.
 Wet scrubbers are also used for the removal of gases
from the air streams.
Types of scrubbers
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Spray towers
Venturi scrubbers
Cyclone scrubbers
Packed scrubbers
Mechanical scrubbers
Impingement Plate Scrubbers
Spray Tower Scrubbers
• This is the simplest type of particulate wet scrubber
in commercial service.
• Sets of spray nozzles located near the top of the
scrubber vessel generate water droplets that impact
with particles in the gas stream as the gas stream
moves upwards.
Spray towers
Venturi Scrubbers
 The dirty gas is led in to the chamber at high inlet
velocities.
 At the inlet throat, liquid at low pressure is added to the
gas stream
 This increases the relative velocity between the gas and
the droplets, thus increasing the efficiency of removal.
 Efficiencies of the range of 95% for particles larger than
0.2 mm have been obtained.
Venturi Scrubber
Absolute Pressure Drop
Δp = pressure drop ( cm of water)
ug = gas velocity (cm/s)
Qt = liquid volume flow rate
Qg = gas volume flow rate
Problem
• Water is introduced into the throat of a
venturi scrubber. The air velocity through
the scrubber is 550 fps and the liquid to
gas ratio is 8.5 gal/1000 actual ft3.
Determine the pressure drop?
• Δp = 4.8
Venturi Scrubbers
Cyclone Spray Chambers
 These scrubbers combine a cyclone with a spray nozzle.
 The added centrifugal force permits good separation of
the droplets, hence a smaller droplet size can be used.
 Cyclone spray chambers provide up to 95% removal of
particles > 5 micron.
Cyclone scrubber
Mechanical scrubbers
Packed scrubbers
Impingement Plate Scrubbers
• These scrubbers usually have one to three horizontal
plates, each of which has a large number of small
holes.
• The gas stream accelerating through the holes
atomizes some water droplets in the water layer
above the plate.
• Particles impact into these water droplets.
Efficiency
where,
k = Scrubber coefficient (m3 of gas/ m3 of liquid)
R = Liquid-to-gas flow rate (QL/QG)
ψ = internal impaction parameter
• Internal impaction parameter
where,
c = Cunningham correction factor
ρp = particle density (kg/m3)
Vg = speed of gas at throat (m/sec)
dp = diameter of particle (m)
dd = diameter of droplet (m)
μ = dynamic viscosity of gas, (Pa-S)
Collection Efficiency of Wet Scrubbers
• The velocities of the particle-laden gas stream and the liquid targets
vary substantially.
• There are substantial differences in the ability of particulate wet
scrubbers to collect particles less than approximately 5
micrometers.
• If a significant portion of the particulate matter mass is composed
of particles < 5 micrometers, care is needed to select the type of
scrubber that is effective in this size range.
• It should be noted that some types of wet scrubbers have limited
capability to remove particles in the less than 0.3-micrometer
range.
• These particles are so small that their movement is influenced by
collisions with individual molecules in the gas stream.
Scrubber Operating Principles
• The ability of a particulate wet scrubber to
remove particles depends on two or more of the
following variables:
• The size (aerodynamic diameter) of the particle
• The velocity of the particle
• The velocity of the droplet.
Advantages of Wet Scrubbers
 Wet Scrubbers can handle incoming streams at high
temperature, thus removing the need for temperature control
equipment.
 Wet scrubbers can handle high particle loading.
 Loading fluctuations do not affect the removal efficiency.
 They can handle explosive gases with little risk.
 Gas adsorption and dust collection are handled in one unit.
 Corrosive gases and dusts are neutralized.
 Hot gases can be cooled down.
 Corrosive gases can be recovered and neutralize.
Disadvantages of Wet Scrubbers
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High potential for corrosive problems
Effluent scrubbing liquid poses a water pollution problem.
Poses freezing problem in cold countries.
Maintenance cost is high when corrosive materials are
collected.
 they require make-up water to replace the water vaporized
into the gas stream and lost to purge liquid and sludge
removed from the scrubber system.