7 Quencher Design
7 Quencher Design
7 Quencher Design
CHAPTER No.7
DESIGN OF QUENCHER
7.1 QUENCHER:-
The word quencher means sudden cooling. It may be used for various purposes, e.g. for
hardening of solid surfaces, for stopping further reactions etc. In our case quenching of
the reactor product is needed for sudden cooling, for removing impurities and to avoid
side reactions. Cooling by liquid quenching is essentially accomplished by introducing
the hot gases into a liquid contacting device.
When the liquid evaporates the energy necessary to vaporize the liquid is obtained at the
expense of hot combustion gases, resulting in a reduction of gas temperature. The
temperature of the combustion gases discharge from the quencher is at the adiabatic
saturation temperature of the combustion gases if the operation is adiabatic and the gas
leaves the quencher saturated with water vapors.
3. Packed towers
Spray tower is selected from the above mentioned types of quencher as:
1. Spray towers can be used for gas absorption, which removes impurities.
2. The main advantage of spray towers over other scrubber is their completely open
design. It is simple to construct. This feature eliminates many of the scale build up
and plugging problems associated with other scrubbers.
3. This is an inexpensive controlled device primarily used for gas conditioning
(cooling or humidification).
4. It requires very little space and only that amount of water is used that is needed to
maintain the desired temperature of the gases at the discharge.
5. Their installation and operation cost are generally considered to b less than that for
other cooling method.
6. Spray towers are very effective in removing pollutants (particles from reactor) if
the pollutants are highly soluble.
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Production of Acrylonitrile
DESIGN OF QUENCHER
countercurrent flow. Countercurrent flow exposes the outlet gas with the lowest pollutant
concentration to the freshest scrubbing liquid.
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Production of Acrylonitrile
DESIGN OF QUENCHER
1. Hydraulic spray:
The hydraulic spray nozzle utilizes the liquid kinetic energy as the energy source to break
the liquid into droplets. This type of spray is less energy consuming than a gas atomized
or twin-fluid spray nozzle. As the fluid pressure increases the flow increases and the drop
size decreases. But this leads to problems in selecting a droplet size and to achieve a
certain flow rate at a given pressure. To overcome this situation a special hydraulic nozzle
(Lechler Spillback Nozzle) has been developed. This nozzle can vary the liquid flow rate
at a particular droplet size and pressure. This nozzle creates a better and optimum control
on the liquid spray and in certain applications can eliminate the need of expensive
compressed air.
Air, steam or other gases can break up a liquid to form a spray, with the gas providing a
source of energy.
I. Internal mixing
The gas atomized spray utilizes a gaseous source to break the liquid to the droplets. The
internal mixed twin fluid spray can utilize two different ways for spraying liquid:
In the first type, the liquid impinges upon a surface for impact to break the liquid stream
and then the air is mixed to atomize it. The advantage of this process is to reduce the
amount of air required to generate the droplets but the downside is that the over time the
impact surface becomes eroded and effects the spray droplet size pattern. The nozzle life
can be very short if the liquid has impurities in it.
In the second type, the liquid is broken into droplets by using only gas. The advantage of
this type is that the nozzle lasts longer but the downside is that this type of spray needs
more gas to generate the same size of droplets.
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Production of Acrylonitrile
DESIGN OF QUENCHER
This type of spray nozzle may require more air, but the mixing and atomization of liquid
takes places outside the nozzle. If a liquid is atomized using any gas which may react
with the liquid, it is possible that the reaction may damage the inside of the nozzle. This
type of nozzle is most beneficial for a liquid which may evaporate inside the mixing
chamber of an internal mix nozzle or using steam to atomize the liquid. Also this nozzle
is suitable of spraying viscous fluid.
Rotary atomizers use a high speed rotating disk, cup or wheel to disperse the liquid into a
hollow cone spray. The rotational speed controls the drop size. Spray drying and spray
painting are the most common uses of this technology.
4. Ultrasonic:
Ultrasonic atomizers This type of spray nozzle utilizes high (20 kHz to 50 kHz)
frequency vibration to produce nearly narrow drop size distribution and low velocity
spray from a liquid. The vibration of a piezoelectric crystal causes capillary waves on the
nozzle surface liquid film.
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Production of Acrylonitrile
DESIGN OF QUENCHER
Area = WG / 3600 Vs G
Area = 114798/ 3600 x 0.5 x 6.9428
A = 9.186 m2
A = D2 / 4
9.186 = 3.1416 x D2 / 4
D = 3.419 m
T LMTD = T1 - T2
ln ( T1/ T2)
T LMTD = 82.1 oC
L= 19124
9.186
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Production of Acrylonitrile
DESIGN OF QUENCHER
Where
mo = molar flow rate of liquid stream = 4985.94 kmol /hr
q = heat rate required to vaporize the water to discharge temperature
Cp = 7.53 J /kmol .K
T = 82.1 oC
q = 3003929.131 J/hr
Z= height of Quencher
U = Heat Transfer Coefficient
Volume of Quencher :
V = q / U x T LMTD
..equation 5
V=Ax Z
..equation 6
Z 0.5 = 3.5539
Z = 12.63 m
Volume of Quencher:
V =A x Z ; V = 116.019 m3
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DESIGN OF QUENCHER
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