INSTRUCTION MANUAL
Plate and Frame Filter Press
Plate and Frame Filter Press
Aim: To study the fundamental principle and method of operation of a plate and frame filter
press.
Objective: To determine specific cake resistance and medium resistance under constant pressure
operation.
Utilities Required:
Electricity supply: single phase, 220V AC, 50 Hz, 5-15 ampere socket with earth
Water supply (initial fill)
connection
Drain facility
CaCO3 = 2.5 kg
Theory:
Filtration is the removal of solid particles from a fluid (the original mixture is referred to
as slurry) by passing the fluid through a filtering medium, or septum (like filter cloth), on which
the solids are deposited. Filters are divided into three main groups: cake filters, clarifying filters,
and cross-flow filters. Cake filters separate relatively large amounts of solids as a cake of crystals
or sludge. They often include provisions for washing the cake and for removing some of the
liquid from the solids before discharge.
At the start of filtration in a cake filter, some solid particles enter the pores of the medium and
are immobilized, but soon others begin to collect on the septum surface. After this brief initial
period, the cake of solids does the filtration and not the septum. A visible cake of appreciable
thickness builds up on the surface and must be periodically removed.
Filter press is one of the most commonly used cake filter. A filter press contains a set of plates
designed to provide a series of chambers or compartments (frames) in which solids may collect.
The plates are covered with a filter medium such as canvas, filter cloth, etc. Slurry is admitted to
each compartment under pressure; liquor passes through the canvas and out a discharge pipe,
leaving a wet cake of solids behind.
Principles of cake filtration:
Since the cake forms a porous bed over the filter medium, the flow
of filtrate through the accumulated cake is analogous to fluid flow through a packed bed of
granular solids. In filtration, the flow resistance increases with time as cake builds up. The chief
quantities of interest are flowrate through the filter and pressure drop across the unit (p) and
thus filtration can be of two types:
Constant pressure filtration: p is constant and flowrate decreases with time due to
Constant rate filtration: p is increased with time in order to maintain a constant flowrate
increased flow resistance.
(less common).
Now in cake filtration, liquid passes through two resistances in series:
1. Resistance of cake
2. Resistance of filter medium
The overall pressure drop at any time is the sum of pressure drops over cake and medium:
p = pa pb = (pa p') + (p' pb) = pc + pm
where, pa = inlet pressure
(1)
pb = outlet pressure
p' = pressure at the interface between cake and medium
pc = u Rc = pressure drop over cake
pm = u Rm = pressure drop over medium
=
/ = cake resistance;
Substituting in (1),
= medium resistance
=
= specific cake resistance
+
(2)
If c = mass of solids deposited in filter cake per unit volume of filtrate
then, mass of cake = mc = V c; where V is the volume of filtrate collected in time t.
Filtrate is being collected with velocity,
Now rearranging Eq. (2),
(3)
Constant pressure filtration:
When p is constant, the only variables in Eq. (3) are V and t. When t = 0, V = 0 and p = pm
Hence,
1
(4)
where q0 is the initial volumetric flowrate.
Eq. (3) may therefore be written
1
(5)
where
Integration of Eq. (5) between the limits (0,0) and (t, V) gives
= 0.5
(6)
Therefore, the plot of t/V v/s V will be linear, with a slope equal to 0.5Kc and an intercept of 1/q0,
The resistances can be calculated as
Medium resistance,
Specific cake resistance,
(m-1) =
(m/kg) =
Experimental Procedure:
Experimental Set-up:
The filter press assembly comprises of 8 plates (P) and 7 frames (F) fixed alternatively on a
horizontal rim/axis (standing vertically). The slurry to be filtered is pumped to the press from a
feed tank provided with an agitator. The pressure gauge measures the pressure of the slurry
entering the press assembly. Both the open cross sections of a frame are covered with a filter
medium (filter cloth). Each plate is provided with an outlet to drain filtered water in the filter
tank.
Procedure:
1. Prepare slurry of CaCO3 in water and fed it in the feed tank.
2. Switch on the agitator of the feed tank.
3. Fix the plates and frames on the press.
4. Start the pump and allow the feed to enter the press.
5. Adjust the flowrate so as to maintain constant gauge pressure at 0.1 kg f/cm2
6. Collect the filtrate in the filter tank. Record the amount of filtrate collected (V) in time t.
7. Run the filtration till there is appreciable fall in the rate of filtrate collection.
Data:
Experimental Observation:
Internal diameter of feed tank, D = 60 cm
Height of feed tank (upto slurry free surface) = 60 cm
Cross sectional area of feed tank = 0.2829 m2
Weight of CaCO3 = 2.5 kg
Concentration of slurry, c = 14.732 kg/m3
number of plates = 8
number of frames = 7
Cross sectional area of frame = 13.5 X 13.5 cm 2
Total filtration area, A = 13.5 X 13.5 X 7 X 2 cm2 = 0.25515 m2
Viscosity of solvent (water) = 8.9 10
Pressure drop across the filter press,
= 0.1
= 0.1 10
Pa.s
= 0.1 10 9.80665
Time, t (s)
0
123.4
276.11
482.71
749.22
1065.42
1508.53
1987.79
2545.79
3179.79
3910
= 9806.65
Observation Table
Volume, V (m^3)
0
0.007
0.014
0.021
0.028
0.035
0.042
0.049
0.056
0.063
0.07
t/V
0
17628.57143
19722.14286
22986.19048
26757.85714
30440.57143
35917.38095
40567.14286
45460.53571
50472.85714
55857.14286
Calculation:
t/V
60000
y = 69116x + 7246.
50000
40000
30000
t/V
Linear (t/V)
20000
10000
0.02
0.04
Therefore,
Medium resistance,
0.06
0.5
(m-1) =
Specific cake resistance,
0.08
= 691168
1
(m/kg) =
= 7246.4
= 1382336
= 2.03727 10
= 6.73091 10
Result and Discussion:
Medium resistance and specific cake resistance are respectively found to be
= 2.03727 10
= 6.73091 10
Filtration begins as soon as the feed (slurry) is pumped into the filter press. The stopwatch is
switched on as soon as the filtrate starts to come out of the press and collected in the filter tank.
As the filtration proceeds, the solid particles get accumulated inside the frames and the cake
builds up gradually which consequently resists the flow thereby increasing the inlet pressure. But
we should remember that we have to operate the filtration at constant pressure. So we'll decrease
the inlet flowrate in order to maintain a constant pressure. This eventually increases the time
period to collect the filtrate i.e. every time period reading will be higher than its previous one for
a given volume of filtrate collected.
By conducting constant-pressure experiments at various pressure drops, the variation of
may be found. If
with
is independent of , the sludge is incompressible. Ordinarily,
increases with , as most sludges are at least to some extent compressible. For highly
compressible sludges,
increases rapidly with .
Empirical equations may be fitted to observed data for v/s , the commonest of which is,
where
and s are empirical constants. Constant s is the compressibility coefficient of the cake.
It is zero for incompressible sludges and positive for compressible ones. It usually falls between
0.2 and 0.8. The above relation should not be used in a range of pressure drops much different
from that used in the experiments conducted to evaluate
and s.
Sources of errors:
1. Improper cleaning of the whole equipment and its components like feed tank, plates,
frames and filter cloth.
2. Any leakage due to improper assembling of plates, frames and filter cloth.
3. Discontinuous electricity supply.
Precautions:
Proper cleaning of plates, frames and filter clothes is must.
Plates and frames should be properly tightened.
