ChE 304

Chemical engineering laboratory - III Experiment No. 6 Group No. 03 (A2)

Name of the experiment:

CONSTANT PRESSURE FILTRATION

Submitted by:

Md. Hasib Al Mahbub Student Id: 0902045

Level: 3; Term: 2

Section: A2

Date of performance: 25/02/2014

Date of submission: 04/03/2014

Partners’ Student Id. 0902041

0902042

0902043

0902044

Department of Chemical Engineering.

Bangladesh University of engineering and technology, Dhaka.

Summary

The purposes behind this experiment were to study the filtration phenomena and to calculate

the flow rate, resistance of the performed filtration process. For these above objectives slurry

of CaCO3 was pumped through filter press at a constant pressure (10psig for & 20 psig). The

plate-and-frame filter presses were arranged properly for one directional flow of slurry. The

plots of cumulative volume vs. cumulative time were drawn for both pressures which show the

nature of filtrate with time progress. For determine the filtration constant two bar diagram (t

/V) vs. cumulative volume (V) for both pressures were plotted. The optimum volumes of

filtrate per cycle found from the experiment were 0.450 m3 and 0.557 m3 and optimum filtration

times were 2255.78 sec and 6017.03 sec for 10 and 20 psig respectively. The specific cake

resistances were found to be 1.95× 1010 m/kg and 9.31× 1010 m/kg respectively.

Experimental setup

Figure 1: Schematic diagram of a typical Plate-and-Frame Filter Press.

Plate Fram

e

Movable

head

Closing

device

Side rails

Filter cloths

Slurry in

Stan

d

Fixed

head

Clear

filtrate out

Figure 2: Sketch of a plate and a frame.[Badger,1997,Page-561]

Observed Data

Mass of bucket no. 01 = 0.700g

Mass of bucket no. 02 = 0.550g

Table 1: Observed data for constant pressure filtration at 10 psig.

Observation No. Bucket No. Mass of filtrate

collected+bucket

(kg)

Time (sec)

01 1 3.5 30

02 2 3 30

03 1 2.8 30

04 2 2.3 30

05 1 2.3 30

06 2 2 30

07 1 2.1 30

08 2 1.75 30

09 1 1.75 30

10 2 1.5 30

11 1 1.5 30

12 2 1.2 30

13 1 1.4 30

14 2 1.2 30

15 1 1.3 30

16 2 1.1 30

1st down time=10 min 25 sec

Table 2: Observed data for constant pressure filtration at 20 psig.

Observation No. Bucket No. Mass of filtrate

collected+bucket

(kg)

Time (sec)

01 1 3.5 30

02 2 3.2 30

03 1 2.7 30

04 2 2.3 30

05 1 2.15 30

06 2 1.9 30

07 1 1.95 30

08 2 1.8 30

09 1 1.85 30

10 2 1.6 30

11 1 1.7 30

12 2 1.5 30

13 1 1.6 30

14 2 1.45 30

15 1 1.6 30

16 2 1.35 30

2nd down time = 4 min 25 sec

Calculated Data

Table 3: Calculated data for cumulative volume of filtrate and filtration time at 10 psig.

Obs.

No.

Volume of

filtrate

(m3 )

Time

(s)

Cumulative

volume

(m3)

Cumulative

time

(s)

Δt

(s)

ΔV

(m3)

t/V

(s/m3)

01 0.002806 30 0.002806 30 30 0.002806 10690.39

02 0.002455 30 0.005262 60 30 0.002455 12217.59

03 0.002105 30 0.007366 90 30 0.002105 14253.86

04 0.001754 30 0.00912 120 30 0.001754 17104.63

05 0.001604 30 0.010724 150 30 0.001604 18708.19

06 0.001453 30 0.012177 180 30 0.001453 20643.52

07 0.001403 30 0.01358 210 30 0.001403 21380.79

08 0.001203 30 0.014783 240 30 0.001203 24944.25

09 0.001052 30 0.015835 270 30 0.001052 28507.71

10 0.000952 30 0.016787 300 30 0.000952 31508.53

11 0.000802 30 0.017589 330 30 0.000802 37416.38

12 0.000651 30 0.018241 360 30 0.000651 46050.92

13 0.000702 30 0.018942 390 30 0.000702 42761.57

14 0.000651 30 0.019594 420 30 0.000651 46050.92

15 0.000601 30 0.020195 450 30 0.000601 49888.5

16 0.000551 30 0.020746 480 30 0.000551 54423.82

Table 4: Calculated data for cumulative volume of filtrate and filtration time at 20 psig.

Obs.

No.

Volume of

filtrate

(m3 )

Time

(s)

Cumulative

volume

(m3)

Cumulative

time

(s)

Δt

(s)

ΔV

(m3)

t/V

(s/m3)

01 0.002806 30 0.002806 30 30 0.002806 10690.39

02 0.002656 30 0.005462 60 30 0.002656 11295.51

03 0.002004 30 0.007467 90 30 0.002004 14966.55

04 0.001754 30 0.009221 120 30 0.001754 17104.63

05 0.001453 30 0.010674 150 30 0.001453 20643.52

06 0.001353 30 0.012027 180 30 0.001353 22172.67

07 0.001253 30 0.01328 210 30 0.001253 23946.48

08 0.001253 30 0.014532 240 30 0.001253 23946.48

09 0.001153 30 0.015685 270 30 0.001153 26028.78

10 0.001052 30 0.016737 300 30 0.001052 28507.71

11 0.001002 30 0.01774 330 30 0.001002 29933.1

12 0.000952 30 0.018692 360 30 0.000952 31508.53

13 0.000902 30 0.019594 390 30 0.000902 33259

14 0.000902 30 0.020496 420 30 0.000902 33259

15 0.000902 30 0.021398 450 30 0.000902 33259

16 0.000802 30 0.0222 480 30 0.000802 37416.38

Table 5: Calculated data for ekscsesc tsesereccs ceps at 10 psig.

Observation

no

Filtration

time

t

sec

Qavg Resistance

of cake

Rc

m

Resistance

of filtering

medium

Rm

m

Specific

cake

resistance

m/kg

01 28.98415757 9.54561E-06 43318907.19

1.95× 1010

8.33× 108

02 54.35634984 1.64761E-05 81222950.98

03 76.11215506 2.15953E-05 113712131.4

04 94.24778315 2.53873E-05 140786448.4

05 110.8335354 2.85337E-05 165540109.6

06 125.8681741 3.11541E-05 187973115.1

07 140.3878062 3.34995E-05 209632568.7

08 152.8358865 3.53798E-05 228197814.7

09 163.7299872 3.69354E-05 244442404.9

10 173.5881874 3.82761E-05 259139891.2

11 181.8910329 3.93591E-05 271516721.9

12 188.6379049 4.02098E-05 281572896.7

13 195.9045792 4.1098E-05 292402623.5

14 202.6529594 4.18979E-05 302458798.4

15 208.8828781 4.26161E-05 311741421.4

16 214.5941804 4.3258E-05 320250492.4

Table 5: Calculated data for ekscsesc tsesereccs ceps at 20 psig.

Obs.

No.

Filtration

time

t

sec

Qavg Resistance of

cake

Rc

m

Resistance of

filtering

medium

Rm

m

Specific cake

resistance

m/kg

01 28.98415757 9.54561E-06 43318907.19

9.31× 1010

9.53× 108

02 56.42800471 1.69935E-05 84317158.64

03 77.14833486 2.18228E-05 115259235.2

04 95.28426375 2.55925E-05 142333552.2

05 110.315164 2.84396E-05 164766557.7

06 124.3126991 3.08924E-05 185652459.4

07 137.2761729 3.30112E-05 204991257.2

08 150.2423324 3.49974E-05 224330055.1

09 162.1735711 3.6718E-05 242121749.1

10 173.0692961 3.8207E-05 258366339.3

11 183.4479389 3.95577E-05 273837377.6

12 193.3092417 4.0784E-05 288534864

13 202.6529594 4.18979E-05 302458798.4

14 211.9980695 4.29681E-05 316382732.9

15 221.3445718 4.3997E-05 330306667.3

16 229.6537427 4.48789E-05 342683498

Sample Calculation

A sample calculation has been shown for observation number 5 at 20 psig

Weight of (Filtrate + Bucket1) =2.15 kg

Weight of Bucket1 = 0.70 g

Weight of Filtrate = (2.15-.70) g

= 1.45 kg

Density of Water at Room Temperature = 997.77 kg/m3

Volume of Filtrate = (1.45/997.77) m3

=1.453×10-3 m3

Cumulative Volume Flow = (2.806+2.66+2.00447+1.754+1.453) ×10-3 m3

= 10.674×10-3 m3

Cumulative Time = (30+30+30+30+30) sec

= 150 sec.

dt/dv = (150-120) / 1.453×10-3

= 20643.52 s/m3

From graph (plotted for 20-psig pressure)

It is found that the constants of filtration are:

Slope of curve, a = 1711.2 s/m6

Intercept at y axis, b = 10326 s/m3

Down time = 4 min 25 sec

= 460+25 sec

= 265 sec

The optimum volume of filtrate per cycle,

Vopt = (2td/a)

= (2265/1711.2)

= 0.557 m3

The optimum filtration time,

topt = avopt2/2+bvopt

= 1711.2× (0.557)2 ×0.5+10326×0.557

= 6017.03 s

Theoretical time, t = 𝑎

2× 𝑉2 + 𝑏 × 𝑉

= 1711.2

2× 0.0106742 + 10326 × 0.010674

= 110.32 sec

Qavg = 𝑉

𝑡+𝑡𝑑

= 0.010674

110.32+265

= 2.84×10-5 m

3 /sec

Solubility of CaCO3 in water = 16.6 kg/L

So, concentration of CaCO3, C = 16.6

16.6+1 = 0.9432

Plate height= 9.5 inch

Plate width= 9.5 inch

Area of plate, A = (9.5× 9.5) in2

= 90.25 in2

= 0.05823 m2

Specific cake resistance, α=𝑎𝐴2∆𝑃

𝐶𝜇

= 1711.2×0.058232×137857.14

0.9432×0.00089

= 9.53× 108 m Kg-1

Mass of the cake, w = 𝐶𝑉

𝐴

= 0.9432×0.010674

0.05823 kg

= 0.1729 Kg

Cake Resistance, Rc = αw

= 9.53× 108×0.1729

= 1.65× 107 m

Resistance of the filtering medium, Rm = 𝑏𝐴∆𝑃

𝜇

= 10326×0.05823×137857.14

0.00089 m

= 9.31× 1010 m

y = 2993.5x + 4339.3

0

10000

20000

30000

40000

50000

60000

Graphical Presentation

Cumulative volume×103, m3

Figure 3: Reciprocal of Filtration Rate (V

t

) vs. Cumulative Volume graph at 10 psig

Rec

ipro

cal

of

filt

rati

on r

ate,

Δ t

/ Δ

V (

sec/

m3)

Cumulative volume×103, m3

Figure 4: Reciprocal of Filtration Rate (V

t

) vs. Cumulative Volume graph at 20 psig

y = 1711.2x + 10326

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

Rec

ipro

cal

of

filt

rati

on r

ate,

Δ t

/ Δ

V (

sec/

m3)

Cumulative time, t (s)

Figure 5: Cumulative Volume vs. Cumulative Time graph

0

0.005

0.01

0.015

0.02

0.025

0 100 200 300 400 500 600

10 psig

20 psig

Cum

ula

tive

volu

me×

10

3, (m

3)

Results

Pressure

psig

optimum

filtration time,

topt

sec

Optimum

volume of

filtrate,

Vopt

m3

Resistance of

filtering

medium

Rm

m

Specific cake

resistance

m/kg

10 2255.78 0.450 1.95× 1010

8.33× 108

20 6017.03 0.557 9.31× 1010 9.53× 108

Discussions

Plate and frame filter press is the most fundamental design among all the other filter presses,

and majority nowadays refer it as “membrane filter plate”. In this experiment we used filter

press consists of three plates and frames assembled alternately with the supports of a pair

of rails. Presence of a gear pump ensured the remaining suspended solids do not settle in

the system and its main function was to deliver the suspension into each of the separating

chambers in the plate and frame filter. For each of the individual separating chambers, there

was one hollow filter frame separated from two filter plates by filter clothes. The introduced

slurry flows through a port in each individual frame, and the filter cakes are accumulated

in each the hollow frame. As the filter cake becoming thicker, the filter resistance increases

as well. The filtrate that passes through filter cloth are collected through collection pipes

and stored in the filter tank. Whereas filter cakes (suspended solids) accumulation occurs

at the hollow plate frame, then being separated at the filter plates by pulling the plate and

frame filter press apart. At the end of each run, the cloth are cleaned using wash liquid and

ready to start the next cycle.

The experiment was conducted very carefully and calculations were performed sincerely.

From the calculated data, three graphs showing the change of Cumulative volume of filtrate

with filtration time and of reciprocal filtration rate with Cumulative volume of filtrate.

Figure 3 and 4 shows the change of reciprocal of filtration rate with cumulative volume of

filtrate for pressure 10 and 20 psig respectively. These are bar charts instead of a straight

line because in actual equation the time difference was differential but in the calculation

procedure, finite time differences were used. So the bar chart indicates that the value (Δt

/ΔV) represents the average rate during the interval between V and V+ΔV. From the bar

diagram a trend line was drawn and the values of constants of filtration, a and b were

determined from the equation of the line. Optimum volume of filtrate and optimum

filtration time were determined in this experiment. Also Resistance of filtering medium and

specific cake resistance was determined.

The cumulative volume vs. cumulative time plot for both the two pressures shows

decreasing slope. The significance of the decreasing slope is that the rate of filtrate

collection was decreased with the aid of time. Because the resistances to flow increased

with time as the filter medium become blocked by filter cakes building up. As the operating

pressure remains constant, the volumetric flow of filtrate diminished.

The main feature of this experiment is that it is constant pressure filtration. But, it was not

truly possible to maintain a constant pressure. Moreover, instead of a centrifugal pump, a

gear pump was used for pumping the slurry because they are particularly effective with

high viscosity liquids, including greases, molasses and paints. They can operate in moderate

pressure ranges and have small to medium capacities. In order to keep the mixture

homogeneous the slurry was continuously stirred manually.