D B Jambhale
Consuting Sugar Technologist,
former Technical adviser, VSI PUne,
Pune Maharashtra India,
Flash tank for treated juice:
The
treated juice generally being heated above 103°C and if it send directly to the
clarifier as it is opened to atmosphere flashing or self evaporation starts and
vapor bubbles that are evolved. These vapour bubbles pass upward and disturb
the precipitate. Therefore the settling mud by gravity gets disturbed.
Therefore before sending the juice to
clarifiers it is passed through a flash tank. In the flash tank the flashing
effects occurs rapidly due to whirling velocity of the juice in the flash tank
and the temperature of the juice comes down below the boiling point of the
juice. Then the juice is send to the clarifier at a slow rate. Now in some factories heating of the juice is
done up to 97-99°C only. In such case flashing of the juice does not occur.
Fig. 1 - flash tank
Fig. 2 - flash tank
Flash tank size:
We will calculate the flash tank inlet
outlet diameter and tank size for a 5000 TCD (230 tch) plant here under
Assumptions:
|
Crushing
rate TCH |
230
|
|
mixed juice
% cane |
110
|
|
Mixed juice
quantity mt/hr |
253
|
|
Filtrate return (17%) mt/hr |
39
|
|
Total
Juice quantity mt/hr |
292
|
|
Juice
density at 99°C |
1.02 |
|
Juice
volume m3/hr |
286.3 |
|
Juice
volume m3/sec |
0.080
|
Flash tank juice inlet pipe
diameter:
In calculating the inlet pipe diameter the velocity of the juice
is assumed as 1.5 m/sec. The diameter can be calculate by the following formula
p
D2
V =
-------------- X v
4
Where
V
=
Volume of juice flow (m3/sec)
D
=
Diameter of the inlet pipe
n
=
Velocity of juice (m/sec.)
Putting the value of V and v
3.142 D2
0.080 = -------------- X 1.50
4
Solving the above equation we get D = 0.261 m.
The standard pipelines available are of sizes 10” or `12” in
diameter. Considering higher crushing rate 12” diameter pipeline can be used.
Flash
tank dimensions:
The flash tank volume should be
about 6 m3/100 tch for venting out vapours. For as 500 tcd (230 tch)
plant it should be 13.8 m3 say 14 m3. Now considering height to diameter ratio of
the tank as 1.35 we will calculate height and diameter of the tank.
p
D2
V =
-------------- X h
4
Where
V
=
Volume of flash tank
D
=
Diameter of of the flash tank
h = Height
of flash tank = 1.35D
Putting the value of V and v
3.142 D2
14.0 = ------------------
X 1.35 D
4
14.0 X 4
Or D3 = ---------------------------------
3.142
X 1.35
Solving
the above equation we get D = 2.37 or
say 2.40 m.
Thus
the diameter of the flash tank will be 2.40 m and height will be 3.24 m.
Outlet
pipe diameter:
The
velocity of the juice pass from flash tank to clarifier through a U siphon
should be around 0.5 m/sec. so that the
floc formed will not be distrurbed. Therefore considering the juice velocity
0.5m/sec. we will calculate the diameter of the outlet and siphon.
p
D2
V =
-------------- X v
4
Where
V
=
Volume of juice flow (m3/sec)
D
=
Diameter of the inlet pipe
n
=
Velocity of juice (m/sec.)
Putting the value of V and v
3.142 D2
0.080 = -------------- X 0.50
4
Solving the above equation we get D = 0.450 m.
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