اساس کار این روش شستشوی گاز به کمک یک حلال 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 ID: 397058
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Slide1
اسکرابرهای تر
اساس کار این روش شستشوی گاز به کمک یک حلال 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.Slide2
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.
Slide3
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. Slide4
Wet Scrubbers (contd.)
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. Slide5
Types of scrubbers
Spray towers
Venturi
scrubbers
Cyclone scrubbers
Packed scrubbers
Mechanical
scrubbers
Impingement Plate Scrubbers Slide6
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.Slide7
Spray towers Slide8
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. Slide9
Venturi Scrubber
Absolute Pressure Drop
Δp
= pressure drop ( cm of water)
u
g
= gas velocity (cm/s)
Q
t
= liquid volume flow rate
Q
g
= gas volume flow rate
Slide10
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 ft
3
. Determine the pressure drop
?
Δp
= 4.8Slide11
Venturi Scrubbers Slide12
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. Slide13
Cyclone scrubber Slide14
Mechanical scrubbers Slide15
Packed scrubbersSlide16
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.Slide17Slide18
Efficiency
where,
k = Scrubber coefficient (m
3
of gas/ m
3
of liquid)
R = Liquid-to-gas flow rate (Q
L
/Q
G
)
ψ
= internal impaction parameter
Internal impaction parameter
where,
c = Cunningham correction factor
ρ
p
= particle density (kg/m
3
)
Vg = speed of gas at throat (m/sec)
d
p
= diameter of particle (m)
d
d
= diameter of droplet (m)
μ
= dynamic viscosity of gas, (Pa-S)
Slide19
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.Slide20
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.Slide21Slide22
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.Slide23
Disadvantages of Wet Scrubbers
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.