vacuum filtration experiment

7/24/2019 Vacuum filtration experiment

1/26

1

ABSTRACT

This study was intended to investigate the flow characteristics of constant

pressure filtration operation and impact of vacuum pressure on the specific resistances

of filter cake and medium. The calcium carbonate slurry, prepared from 1.25g of

calcium carbonate powder and 75mL of distilled water, was used in this eperiment.

The assembled e!uipment set comprising of the filtration bottle, filter paper, vacuum

pump, air compressor, burette, waste fluid flask and stopwatch was utili"ed. #or

pressure drops of 1$$mm%g, 2$$mm%g, &$$mm%g and '$$mm%g, the time taken

for attaining certain filtrate volumes was recorded for calculation of filtration rates.

(nalytical calculations were also conducted to estimate the specific resistances of

filter cake and filter medium. #rom this study, it was observed that the filtration rate

for constant pressure drop was the highest initially and gradually decreased as the

filter cake thickness increased. The estimated values of specific resistances of filter

cake and filter paper were 7.)7*+1$1$mkg and 5.$2- 1$1$m1respectively. The

specific resistances of filter cake and filter medium were independent of vacuum

pressure variation. The observation above implied that calcium carbonate wasincompressible.


2/26

2

TABLE OF CONTENTS

(/0T(T........................................................................................................i

T(/L3 4# 4T3T0...................................................................................ii

L60T 4# T(/L30............................................................................................iii

L60T 4# #6830..........................................................................................iv

493L(T83...........................................................................................v

1 6T4:8T64.......................................................................................1

1.1 4/;3T630 4# T%3 0T8:=..................................................................2

1.& 066#6(3 4# T%3 0T8:=.....................................................2

2 L6T3(T83 366>L30 4# #6LT(T64.............................................&

2.2 T%3 ((L=060 4# #6LT(T64....................................................'

& 93T%4:4L4=......................................................................................)

&.1 (>>((T80 (: 9(T36(L0.......................................................)

&.2 >43:83 #4 3@>3693T...................................................)

' 308LT0 (: :6080064..................................................................7

5 4L8064..........................................................................................17

3#3330.................................................................................................1-

(>>3:6@......................................................................................................1*


3/26

&

LIST OF TABLES

Table 4.1aw data for the mass of filter cake calculation..........................................12

Table 4.2aw data for the moisture ratio calculation.................................................12

Table 4.30ummary of calculated results.....................................................................1'


4/26

'

LIST OF FIGURES

Figure 2.1#ilter cake formation A/%0 #iltration, 2$th:ec 2$1$B................................'

Figure 4.1


5/26

5

NO#ENCLATURE

C>, :>


6/26

1

1 INTRO$UCTION

6n another class of mechanical separations, placing a screen in the flow

through which they cannot pass imposes virtually total restraint on the particles above

a given si"e. The fluid in this case is subDect to a force that moves it past the retained

particles. This is called filtration. The particles suspended in the fluid, which will not

pass through the apertures, are retained and build up into what is called a filter cake.

0ometimes it is the fluid, the filtrate that is the product, in other cases the filter cake.

The fine apertures necessary for filtration are provided by fabric filter cloths,

by meshes and screens of plastics or metals, or by beds of solid particles. 6n some

cases, a thin preliminary coat of cake, or of other fine particles, is put on the cloth

prior to the main filtration process. This preliminary coating is put on in order to have

sufficiently fine pores on the filter and it is known as precoat.

1.1 OB%ECTI&E OF T'E STU$(

The obDectives of this study shall comprise of the followingE

i. To characteri"e the flow through the cake in a simple laboratory test.


7/26

2

1.2 SCO)ES OF T'E STU$(

The scopes of this study shall comprise of the followingE

i. 6nvestigating the trend of filtrate flow rate variation with timeF

ii. 0tudying the relationship between the specific resistance of filter cake

and the vacuum pressure.

iii. 0tudying the relationship between the specific resistance of the

medium and the vacuum pressure.

iv. 3stimating the values of specific filter cake and filter medium

resistances.

1.3 SIGNIFICANCE OF T'E STU$(

This study was designed to investigate the effect of vacuum pressure on the

filtration rate, and deduce the impact of vacuum pressure on the specific resistances of

calcium carbonate filter cake and filter medium Ai.e. filter paperB. The outcome may

be applicable for the design of efficient batchwise filtration operation. The estimated

values of specific resistances could be used to predict the pressure drop re!uired to

attain specific filtration rate. 9oreover, this study was also helpful in investigating the

compressibility of calcium carbonate.


8/26

&

2 LITERATURE RE&IE*

#iltration is a separation of solid particles from the fluid of li!uid or gas where

the suspended solid particles in the fluid are physically or mechanically removed by

using a porous medium that retains the particles as a separate phase or cake and

passes the clear filtrate Aeankoplis, 2$$&B. There are two general methods of

filtration which are gravity filtration and vacuum filtration. erlmutter, 2$1'B.

ake filtration consists of feed containing a solid suspension AslurryB through a

porous medium or septum Ae.g. a porous membrane, a woven wireB. The solids in the

slurry are retained on the surface of the medium where they build up, forming an

increasing thicker cake. (s more slurry is filtered the solids retained on the medium

provide most of filtering action. %ead losses in the cake will control the filtrate flow

rate. 6n cake filtration the cake is the real filtering element.


9/26

'

thickness is kept well below its theoretical maimum and the driving force is not the

maimum available. This is true in general, but especially so in those cases where the

solids have to be washed, etracted or subse!uently impregnated.

Figure 2.1#ilter cake formation A/%0 #iltration, 2$th:ec 2$1$B

2.2 T'E ANAL(SIS OF FILTRATION

The analysis of filtration is largely a !uestion of studying the flow system.

The fluid asses through the filter medium, which offers resistance to its passage,

under the influence of force which is the pressure differential across the filter. Thus,we can write the familiar e!uationE

ate of filtration I driving forceresistance

esistance arises from the filter cloth, mesh, or bed, and to this is added the

resistance of the filter cake as it accumulates. The filtercake resistance is obtained by

multiplying the specific resistance of the filter cake that is its resistance per unit

thickness, by the thickness of the cake. The resistances of the filter material and pre

coat are combined into a single resistance called the filter resistance. 6t is convenient

to epress the filter resistance in terms of a fictitious thickness of filter cake. This

thickness is multiplied by the specific resistance of the filter cake to give the filter

resistance. Thus the overall e!uation giving the volumetric rate of flow d


10/26

5

(s the total resistance is proportional to the viscosity of the fluid, we can

writeE

I mrALc J LB

where is the resistance to flow through the filter, m is the viscosity of the fluid, r is

the specific resistance of the filter cake, Lc is the thickness of the filter cake and L is

the fictitious e!uivalent thickness of the filter cloth and precoat, ( is the filter area,

and :> is the pressure drop across the filter.

6f the rate of flow of the li!uid and its solid content are known and assuming

that all solids are retained on the filter, the thickness of the filter cake can be

epressed byE

Lc I w


11/26

)

3 #ET'O$OLOG(

3.1 A))ARATUS AN$ #ATERIALS

6n this eperiment, the vacuum filter device was used to characteri"e the flow

through the cake. The device and apparatus were set up which consist of filter

housing, pipet, vacuum pump, filter paper, petri dish, stopwatch, and conical flask for

discharge purpose. #our sets of filter paper with petri dish were weight before the

eperiment began.

#or the material preparation, the 1.25 grams of calcium carbonate was mied

with 75 mL of tap water. #our sets of these solutions will be the slurry samples.

3.2 )ROCE$URE FOR E+)ERI#ENT

(t the beginning of the eperiment, the filter housing was filled up with

weight filter paper. Then, the slurry was poured into the device and the pipette valve

was closed. The power supply and vacuum pump were switched on and the valve was

adDusted to set the desired vacuum pressure. (fter that, time for every 5 cm & of water

that filled in the pipette was recorded until all the slurry was filtered.

Lastly, the vacuum pump and power supply were switched off after the each

set of eperiment was done. The pipette valve was opened to drain the water into the

conical flask.

Then, the filter cake on the filter paper with petri dish was weight and dried in

the oven for &$ minutes. (fter that, the mass of petri dish with dry filter cake was

weighed. The same steps were repeated by using another three sets.


12/26

7

4 RESULTS AN$ $ISCUSSION

The filtration rate was observed to be maimum initially in the graph of


13/26

-

Figure 4.3


14/26

*

$ 1$ 2$ &$ '$ 5$ )$ 7$$

1$2$

&$

'$

5$

)$

$

$.2

$.'

$.)

$.-

1

1.2

1.'

olynomial A


15/26

1$

(ccording to the armenMo"enyHs relation, the rate of filtration can be

related to the pressure drop and the resistance arose from the filter cake and filter

medium as in e!uation belowE

dV

dt= A P

mr[w (VA )+L]

where ( I filter area

m I viscosity of the fluid

r I specific resistance of filter cake

L I fictitious e!uivalent thickness of filter cloth and precoat

P I pressure drop across filter

w I fractional solid content per unit volume of filtrate

#or constant pressure, constant r and incompressible cake, by inverting the

e!uation and undergoing the integration, the filtration e!uation is

t

V= mrw

2A2

P V+

mrL

A P

6n this case, the specific resistance of the filter medium, mwill be e!uivalent

to rNL in the rightmost term of the e!uation above. The e!uation can also be epressed

in term of filtration constant, M>Asm)B and / Asm&B

t

V=KP

2 V+B

whereKP=

mrw

A2

P

B= mrL

A P=

m R m

A P


16/26

11

/ased on the e!uation above, a linear graph is to be epected by plotting t


17/26

12

$ 1$ 2$ &$ '$ 5$ )$$

$.5

1

1.5

2

2.5

&

&.5

'

'.5

fAB I $.$& J 2.)*


18/26

1&

$ 1$ 2$ &$ '$ 5$ )$$

$.2

$.'

$.)

$.-

1

1.2

fAB I $.$1 J $.72


19/26

1'

%owever, there are some value of parameters have to be determined prior to

the calculation above. 0ome raw data for the calculation are tabulated in Table '.1and

Table '.2.

Table 4.1aw data for the mass of filter cake calculation

Mass of wet filter cake=Mass of petri dishfilter medium withwet filter cakeMass of petri dishfilter

Mass of dry filter cake=Mass of petri dishfilter mediumwith dry filter cakeMass of petri dishfilter

Table 4.2aw data for the moisture ratio calculation

where m I mass of wet cake mass of dry cake

9ass of a4& used I 1.25g

(t 25 O, density of water, P used is $.**7$- gmL A**7.$- kgm&B

Aeankoplis, 2$$&B.

9 I total mass of slurry filtered

I 1.25 g J A75 mLN$.**7$- gmLB

I 7).$&1 g

s I mass fraction of solid in slurry

I 1.25 g 7).$&1 g

>ressure :rop

Amm%gB

9ass of petri dish

and filter medium

without filter cake

9ass of petri dish

and filter medium

with wet filter

cake

9ass of petri dish

and filter medium

with dry filter cake

1$$ &1.*)7 &'.-2* &&.1&&

2$$ &$.'-) &&.')- &1.)&-

&$$ &2.'&7 &5.'1' &&.5*1

'$$ &$.2*5 &&.175 &1.'5)

>ressure :rop

Amm%gB

9ass of wet filter

cake AgB

9ass of dry filter

cake AgB

9oisture ratio,

m1$$ 2.-)2 1.1)) 2.'5'5

2$$ 2.*-2 1.152 2.5--5&$$ 2.*77 1.15' 2.57*7

'$$ 2.-- 1.1)1 2.'-$)


20/26

15

I $.$1)''

Let w be the fractional solid content per unit volume of filtrate.

w= s

1mR s

6n case of Q> I 1$$ mm%g, w I 17.$- kg solid m&of filtrate

6n case of Q> I 2$$ mm%g, w I 17.12 kg solid m&of filtrate

6n case of Q> I &$$ mm%g, w I 17.12 kg solid m&of filtrate

6n case of Q> I '$$ mm%g, w I 17.$* kg solid m&of filtrate

6n this eperiment, the diameter of filter area is '$.2 mm.

( I R:2'

I 1.2)*2 1$&m2

(t 25O, the viscosity of water, m is about -.*&7 1$'kgmNs Aeankoplis, . ;.,

2$$&B.

(fter getting all the information needed, the calculation have been carried out

and the results were tabulated in Table '.&.


21/26

Table 4.30ummary of calculated results

>ressure drop,

Q> Amm%gB

>ressure

drop, Q> A>a

or m2B

radient,

1$12

yintercept,

1$)

#iltration onstant0pecific

resistance of the

filter cake, r

1$1$AmkgB

m 1$1$

A1mBM> 1$12 / 1$)

1$$ 1&&&2.2&7 $.$2-&25 2.)-5$ $.$5))5$ 2.)-5$ 7.*7$5 5.$-&-

2$$ 2)))'.'7' $.$1&1'5 1.1*'5 $.$2)2*$ 1.1*'5 7.&-$5 '.52&&

&$$ &***).711 $.$$-2-&5 $.---& $.$1)5)7$ $.---& ).*7)' 5.$'57

'$$ 5&&2-.*'7 $.$$7'572 $.72$- $.$1'*1'' $.72$- -.&--7 5.'5*$


22/26

17

et, in order to investigate the effect of vacuum pressure Ai.e. the pressure

drop across the filterB on the specific resistance of the filter cake and the specific

resistance of the filter medium, two graphs of specific resistance of the filter cake

versus pressure drop and specific resistance of the filter medium versus pressure drop

were plotted as shown in #igure '.1$and #igure '.11respectively.

1$$$$ 2$$$$ &$$$$ '$$$$ 5$$$$ )$$$$$.$$$$3J$$

5.$$$$3J1$

1.$$$$3J11

1.5$$$3J11

2.$$$$3J11

2.5$$$3J11

&.$$$$3J11

r vs. Q>

Q> A>aB

r AmkgB

Figure 4.1"0pecific resistance of the filter cake versus pressure drop

1$$$$ 2$$$$ &$$$$ '$$$$ 5$$$$ )$$$$$

2$$$$$$$$$$

'$$$$$$$$$$

)$$$$$$$$$$

-$$$$$$$$$$

1$$$$$$$$$$$

12$$$$$$$$$$

1'$$$$$$$$$$

m vs. Q>

Q> A>aB

m A1mB

Figure 4.110pecific resistance of the filter medium versus pressure drop


23/26

1-

(s shown in both graphs above, the specific resistance of the filter cake and

specific resistance of the filter medium are independent of the pressure drop where the

gradient of both graphs are almost hori"ontal. >ressure drop across the filter have no

effect on both of the parameters.

The independence of specific resistance of the filter cake from the pressure

drop is due to the incompressibility of the calcium carbonate in the slurry. 6n other

words, calcium carbonate is a rigid incompressible solid in the slurry.

/esides, the filter medium specific resistance was observed to be independent

of the pressure drop. There was no penetration of particles into the filter paper which

can avoid the plugging of the pores of filter paper A:oran, 2$12B. 0ince the pore si"es

of the filter medium remain unchanged, the specific resistance of filter medium will

not vary with the increasing vacuum pressure.


24/26

1*

5 CONCLUSION

The conclusions of this eperiment are as followsE

i. The average values of specific filter cake resistance, r and specific

filter medium resistance, mwere estimated to be 7.)7*+1$1$mkg and

5.$2- 1$1$m1respectively.

ii. The filtration rate was found to be maimum initially due to the

absence of solid deposition at the very beginning of filtration process.

6t would decrease with the increasing thickness of filter cake.

iii. alcium carbonate was found to be incompressible and the specific

filter medium resistance, mwas observed to be independent of the

vacuum pressure.

iv. 6t can be concluded that there was no permeation of calcium carbonate

particles to the apertures of the filter medium.


25/26

2$

REFERENCES

>auline 9. :oran. A2$12BBioprocess Engineering Principles. 8nited 0tatesE

(cademic >ress.

eankoplis, . A2$$&B. Transport processes and separation process principles

(includes unit operations) App. *$'*$5B. 8nited 0tates of (mericaE >rentice

%all >ress.

eankoplis. A2$$&B Transport Processes and Separation Process Principles. >earson

3ducation.

>erlmutter, /. (. A2$1'B.Dilute Stream Solid-Liquid Separations Using Continuous

Vacuum Filtration Tecnologies. /%0#iltration 6nc.


26/26

21

A))EN$I+

(? :(T( :4893T(T64

vacuum filtration experiment

Documents