Mass Transfer 2
CPB 20104
Experiment 4 PLATE AND FRAME FILTER PRESS ______________________________________________________________________________________ INTRODUCTION Filtration is the removal of solid particles from a fluid by passing the fluid through a filtering medium on which the solids are deposited. Industrial filtrations range from simple straining to highly complex separations. The fluid maybe a liquid or a gas, the valuable stream from the filter may be the fluid or the solids or both. In industrial filtration the solids content of the feed ranges from a trace to a very high percentage. Fluid flows through a filter medium by a virtue of a pressure differential across the medium. Filters are also classified, therefore into those that operate with pressure above the atmospheric level on the upstream side of the filter medium and those that operate with atmospheric pressure on the upstream side and a vacuum on the downstream side. Pressures above the atmospheric level may be developed by a pump or blower. Many industrial filters are pressure filters, vacuum filters or centrifugal separators. Filters are divided into 3 types: cake filters, clarifying filters and cross flow filters. Cake filters separate relatively large amounts of solids as a cake of crystal or sludge. Filter presses are pressure filters designed to de-water chemically conditioned sludge on a batch basis using mechanically applied pressure to achieve high solid content sludge cakes. The The filter consists of a series of parallel plates, each dressed dressed with a filter cloth and rigidly held together in a structure frame. The filter plates are placed between the stationary and moving platens. In operation, the hydraulic closing device compresses the plate pack. The recessed chamber between the individual plates forms the cake space in which the suspended solids are then retained. The slurry to be filtered is fed by slurry pump which pressure subjected to the allowable pressure needed for filtration. During the filtration cycle, the filtrate passes through the filter cloth and drains a long a grooved rib of the plates while the solid is retained within the cake chamber. Once the filtration pressure is reached and the filtrate discharge is reduced, the compressed air is introduced to inflate the membrane to speed up the filtration process. Once the filtrate is reduced to droplets the compressed air is released, releasing the hydraulic pump then opens up the press and shifting the filter plates either manually or mechanically discharges the cake. In industrial filtration a common filter medium is canvas cloth. Synthetic fabrics such as nylon, polypropylene and various polyesters are also highly resistant chemically. Filter aids are used in the filtration of very fine solids or slimy to increase the porosity of the cake to permit the passage of the liquor at a reasonable rate. Filter aids are diatomaceous silica, perlite or other inert porous solids. The filter aids are percoated on the filter medium. Precoats prevent gelatinous solids from plugging the filter medium as well as giving a c learer filtrate. filtrate.
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FG/Exp4/Jan2015
Mass Transfer 2
CPB 20104
OBJECTIVES
To study the operation of f ilter press for filtration of calcium carbonate slurry. To determine filter medium resistance and specific cake resistance from filtration data obtained.
MATERIALS AND ANCILLARY EQUIPMENTS REQUIRED a) Materials Calcium Carbonate powder (commercial grade) Water in the tank 100 litres for making calcium carbonate slurry b) Ancillary Equipments 2 beakers of at least 5 litres capacity 2 stop watches for recording time Dissolve 3.0 kg of calcium carbonate in a container and transfer it to the slurry tank. In 100 litres of water it will be 3% wt calcium carbonate slurry.
EXPERIMENTAL PROCEDURES Procedures: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
Open the air regulator outlet valve Check the pressure gauge setting Release the hydraulic pump air valve and operation valve (knob) anticlockwise to release the hydraulic pressure. Pack the filter press by pushing it towards the stationary platen. At the same time dress up the filter cloths with creases. Move the moving platen towards the filter plate pack. Lower down the trust bar and alignment it inline with the hydraulic piston. Move the hydraulic piston towards the trust bar by pumping the hydraulic pump using the lever. Check the filter pack alignment and the cloths to en sure no crease is formed. In order to have a proper good sealed compression. Pull the PVC drip tray towards the stationary platen at the bottom of the filter pack. To contain a ny dripping during filtration process if occur. Start pumping the hydraulic ram until it reach to the require working pressure. Then lock it by turning the operation valve (knob) clockwise.
Check to ensur e that the slurr y tank s h ad enoug h slur r y before oper atin g the pu mp, never r un th e pu mp i n a dr y con di ti on even for a f ew r evolu ti ons or th e s ta tor wi ll be damag ed. 11.
12.
On the control panel, press the feed pump “start” button and the R UN light will light. This indicates that the process of feeding the slurry into the filter press has started. When feeding of the slurry into the filter press had reached the preset timing or pressure by the consolidation timer and feeding p ressure gauge. Which ever come first the pump will be stopped and RUN light will be off.
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Mass Transfer 2
CPB 20104
Caution: Do not release the hydraulic pump pressure before operating the squeeze process. Also, ensure that the feed process is completed. Do not inflate the rubber membrane when there is no solids in the filter pack. 13.
14. 15. 16. 17. 18. 19. 20. 21. 22.
Close the air regulator valve and SLOWLY open the inlet valve. This will let the compressed air in so as to inflate the rubber membrane SLOWLY. These processes will squeeze the water out of the filtrate or cake. Upon completion, close the air regulator inlet valve and o pen the outlet valve slowly to deflate the rubber membrane slowly. Do not release the hydraulic pump pressure until the compress air outlet valve is fully opened. Shift the drip tray away from the bottom of the filter pack. Release the hydraulic pump pressure by turning the operation valve (knob) anticlockwise. The hydraulic piston will retract back to the body. Swing the trust bar back to the stopper and hold. Push the moving platen back towards the hydraulic piston. Move the end filter plate i.e the one next to moving platen towards the hydraulic piston. Let the solid cakes drop onto a receptable at the bottom of the filter press. Subsequently unpack the rest of the filter plate one by one. Clean the residue from the filter c loth by mean of a plastic scrapper.
Do not use any s har p object to clean th e fil ter cloth; i t can damage the f i lter cl oth . 23.
24.
Ensure that all the sealing edges are clear of residues especially the bottom area. It is to prevent any improper sealing during the next filtration compression process. Upon completion, for the next filtration process subsequently repeat the operating process.
Data:
The volume of filtrate collected, V in litres collected at different time intervals are recorded at a given pressure drop. Record all the data in the data sheet. Filter area in cm2 is noted down. The mass of solid per unit volume of filtrate is also noted. Note down the weight of wet cake. Dry the wet cake in the oven, overnight and note down the weight of the dry cake.
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Mass Transfer 2
CPB 20104
Table of Results: Weight fraction of calcium carbonate in slurry
: _________________ %
Weight of wet cake
Tray 1 Tray 2 Tray 3
: _________________ g : _________________ g : _________________ g
Weight of dry cake
Tray 1 Tray 2 Tray 3
: _________________ g : _________________ g : _________________ g
Weight ratio of wet cake to dry cake (
m F
mc
)
Viscosity of filtrate ( ) Density of filtrate ( ) Density of calcium carbonate Total active filter area Pressure drop (ΔP) Total filtration time Total volume of filtrate
: _________________ : _________________ Pa.s : _________________ : 2.93 g/cm3 : 47 cm x 470 cm : _________________ : _________________ s : _________________ litre
Filtrate Volume, V (L) 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 100
Time, t (s)
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FG/Exp4/Jan2015
Mass Transfer 2
CPB 20104
RESULTS AND DISCUSSION: Discuss all your results. The questions below only serve as a guideline. Your discussion s h ould not only limited to these questions. 1. 2.
3.
Plot the data relating t/V versus V to obtain a st raight line graph. The slope of each line is
qo K c
1 qo
from the intercept
R m
A( P) c
A
2
P
Where A P
c
5.
2
in seconds per litre and
of the line. Obtain the value of filter me dium resistance (Rm) and cake resistance ( ) from the equations below:
1
4.
K c
= = = =
viscosity of filtrate filter area pressure drop mass of solid deposited in the filter per unit volume of filtrate (kg/L)
Explain briefly how filter medium resistance can affect the pressure in filtration process. Explain three advantages and disadvantages of plate and frame filter press.
REFERENCES 1. 2. 3. 4.
Svarovsky, L. “Solid-Liquid separation” Butterworths, 3rd Edition (1990). Rushton, A. “Mathematical models and de sign methods in solid-liquid separation” Martinus Nijhoh, (1985). Geankoplis, Transport process and unit operation 3rd Edition, Prentice Hall (1993). McCabe, Smith and Harriott, Unit operations of Chemical Engineering, McGraw Hill 6th edition (2000).
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