ASSIGNMENT

SUBJECT:

FLUID AND PARTICLE MECHANICS- II (LAB)

TOPIC:

PLATE AND FRAME FILTER PRESS

SUBMITTED BY:

GROUP# A-8

5TH SEMESTER (MORNING)

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GROUP MEMBERS

1. Sajjad Rasool Chaudhry

(M08-PG12)

2. Aqeel Abbas

(M08-PG01)

3. Muhammad Ayyaz

(M08-PG04)

4. Qaiser Abbas

(M08-CE29)

Table of Contents Page No.

Acknowledgment………………………………………………………….…..4

General introduction………………………………………………………..…5

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Objectives……………………………………………………………………...6

Literature review ……………………………………………...………..……..7

Introduction……………………………………………….………...….7

Working principle………………………………………..……………..8

Filter media……………………………………………………………..9

Types of filtration……..………………………………………………..11

Filtration equipment……………………………………………………13

General applications…………………………………………………………...14

Plate and frame filter press…………………………………………………….15

Experimental data……………………………………………………………...18

Operating procedure……………………………………………………18

Observations & Calculations ……………..………………………..…..19

Graph……………………………………………………………..….. ..20

References……………………..……………………………………………….21

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Acknowledgment

We are thankful to the all ICET library staff for helping us to search for and read most relevant books for preparing this assignment.

We are also thankful to Respected MISS RABIYA ASLAM and Mr. ABDUL BASIT for their constant guidance and kindness which encouraged us to work efficiently in Fluid and Particle Mechanics Lab during 5ht Semester.

General Introduction

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Liquid filtration is a unit operation which is used worldwide to separate solids from liquids and gases in laboratory and on industrial scale as well. Although many other processes such as sieving, centrifugal separation and electrostatic separation are also used for the same purpose in industry but filtration has its own merits due to ease of mechanism and low running cost as well as mechanical cost for the equipment. Two major types of filtration are know, one named as cake or surface filtration and other deep bed or depth filtration. Deep bed filtration has further two categories: i) Cross flow filtration and ii) dead end filtration.

Equipment used for filtration has a wide variety and selection depends on many factors, some of them are size distribution and shape of solid particles, properties of liquid holding solids (i.e. viscosity, density and corrosiveness etc), and concentration of suspension or slurry and its amount to be handled.

Keeping in view the importance of filtration, this document has been built to have a good discussion on filtration. First of all is an introduction of filtration. After introduction there general principals and techniques involved in filtration will be discussed. Different types of filtration equipments used at industrial scale will be discussed later. Then comes the main objective of this assignment and that is Plate and Frame Filter Press. This section includes a detailed description of the apparatus mentioned before including its working, science behind each operation, then its construction and where to use. After discussion, is our experimental work carried out in main unit operations lab on the same apparatus. This section includes procedure followed during the course of experimental work, its results and then graphical representation of the obtained results.

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Objectives

Objectives of this assignment are:

1. To have a review of liquid filtration, it’s working principle and types.

2. To discuss various equipments used in industry to carry out filtration.

3. To have a detailed discussion on plate and frame and filter press.

4. To discuss the experimental procedure and result obtain

5. Graphical representation of those results.

Literature Review

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iltration methods are often used to remove harmful substances from air or water, such as to reduce air pollution or to make water potable. Chemists often use filtration to separate

materials of different chemical compositions. On an industrial scale, filtration is used by the oil, gas, food and beverage, and pharmaceutical industries, among others. Municipalities use filtration techniques when treating sewage and purifying water. It is also an important and widely used as one of the unit operations of chemical engineering.

F

Filtration is a mechanical or physical operation by which solids are separated from fluids (liquids or gases) in a mixture with the help of a medium that is called a filter. When the mixture is brought in contact with a filter, the filter allows the fluid to pass through, but it retains at least part of the solid material. The fluid that passes through the filter is called the filtrate, and the solid material that remains on the filter is called the residue. Depending on the application, either one or both components may be isolated. In filtration processes it has to be kept in mind that the separation may not be complete. Solids will be contaminated with some fluid and filtrate will contain fine particles. And this degree of separation will depend on the pore size and the thickness of the filter medium as well as the mechanisms that occur during filtration.

Liquid Filtration, while used for a number of broad purposes is basically for two different but similar actions taken; to either, remove contaminates from a liquid, or for the collection of suspended solid particles from the liquid that may be valuable for another use. Many times in industrial applications filtration is done to accomplish both of these goals concurrently. Filtration is done mainly to:

• Prevent damage that can be caused by the contamination of a given liquid, either to people, machinery, or the environment

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• Produce a higher yield of the desired end product

• Create a more pure product which in turn is more valuable

• Recovery of material for use in other applications

• Lower operating costs

Filtration is essentially a mechanical operation and is less demanding in energy than evaporation or drying where the high latent heat of the liquid, which is usually water, has to be provided.

Working Principle:-

In the filtration, slurry or suspension flows through the filter medium by virtue of pressure drop across it. This pressure difference may be of two types. One is the case when pressure on upper side of the filter medium is greater than atmospheric pressure may be developed due to head of the liquid or by pump and on the other side; pressure is equal to atmospheric pressure. Other case of operation is where pressure on upper side is atmospheric and on the lower side, a vaccum is created. So it can be said that main driving force for filtration is pressure difference across the filter medium.

In general, the pores of the medium are larger than the particles which are to be removed, and the filter works efficiently only after an initial deposit has been trapped in the medium. In the laboratory, filtration is often carried out using a form of Buchner funnel, and the liquid is sucked through the thin layer of particles using a source of vacuum. In even simpler cases the suspension is poured into a conical funnel fitted with a filter paper. In the industrial equivalent, difficulties are encountered in the mechanical handling of much larger quantities of suspension and solids. A thicker layer of solids has to form to achieve highly efficient separation and, in order to achieve a high rate of passage of liquid through the solids, higher pressures are needed, and a far greater area has to be provided. As the cake gradually builds up on the medium and the resistance to flow progressively increases. During the initial period of flow, particles are deposited in the surface layers of the cloth to form the true filtering medium. This initial deposit may be formed from a special initial flow of precoat material. The most important factors on which the rate of filtration then depends will be:

• Drop in pressure from the feed to the far side of the filter medium.

• Area of the filtering surface.

• Viscosity of the filtrate.

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• Resistance of the filter cake.

• Resistance of the filter medium and initial layers of cake.

Some differences in general behavior may be expected, however, because the cases so far considered relate to uniform fixed beds, whereas in filtration the bed is steadily growing in thickness. Thus, if the filtration pressure is constant, the rate of flow progressively diminishes whereas, if the flowrate is to be maintained constant, the pressure must be gradually increased. So, it may be noted that there are two quite different methods of operating a batch filter. If the pressure is kept constant then the rate of flow progressively diminishes, whereas if the flowrate is kept constant then the pressure must be gradually increased. Because the particles forming the cake are small and the flow through the bed is slow, streamline conditions are almost invariably obtained The mechanical details of the operation, particularly of the flow channel and the support for the medium, influence the way the cake is built up and the ease with which it may be removed. A uniform structure is very desirable for good washing and cakes formed from particles of very mixed sizes and shapes present special problems. Although filter cakes are complex in their structure and cannot truly be regarded as composed of rigid non-deformable particles. Voidage of the cake, formed during course of filtration, is very important factor. And it depends on the nature of the support, including its geometry and surface structure, and on the rate of deposition. The initial stages in the formation of the cake are therefore of special importance for the following reasons:

• For any filtration pressure, the rate of flow is greatest at the beginning of the process since the resistance is then a minimum.

• High initial rates of filtration may result in plugging of the pores of the filter cloth and cause a very high resistance to flow.

• The orientation of the particle in the initial layers may appreciably influence the structure of the whole filter cake.

On the bases of Voidage, filter cakes may be divided into two classes: i) incompressible cakes and ii) compressible cakes. In the case of an incompressible cake, the resistance to flow of a given volume of cake is not appreciably affected either by the pressure difference across the cake or by the rate of deposition of material. On the other hand, with a compressible cake, increase of the pressure difference or of the rate of flow causes the formation of a denser cake with a higher resistance.

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Experimental work on the flow of the liquid under streamline conditions has shown that the flowrate is directly proportional to the pressure difference. It is the resistance of the cloth plus initial layers of deposited particles that is important since the latter, not only form the true medium, but also tend to block the pores of the cloth thus increasing its resistance. Cloths may have to be discarded because of high resistance well before they are mechanically worn. No true analysis of the buildup of resistance is possible because the resistance will depend on the way in which the pressure is developed and small variations in support geometry can have an important influence. It is therefore usual to combine the resistance of the cloth with that of the cake.

Filter media:-

Two main types of filter media are employed in the chemical laboratory, one is surface filter, a solid sieve which traps the solid particles, with or without the aid of filter paper (e.g. Büchner funnel, Belt filter, Rotary vacuum-drum filter, Crossflow filters, Screen filter), other one is a depth filter, a bed of granular material which retains the solid particles as it passes (e.g. sand filter). The first type allows the solid particles, i.e. the residue, to be collected intact; the second type does not permit this. However, the second type is less prone to clogging due to the greater surface area where the particles can be trapped. Also, when the solid particles are very fine, it is often cheaper and easier to discard the contaminated granules than to clean the solid sieve.

The function of the filter medium is generally to act as a support for the filter cake, and the initial layers of cake provide the true filter. The filter medium should be mechanically strong, resistant to the corrosive action of the fluid, and offer as little resistance as possible to the flow of filtrate. Woven materials are commonly used, though granular materials and porous solids are useful for filtration of corrosive liquids in batch units. An important feature in the selection of a woven material is the ease of cake removal, since this is a key factor in the operation of modern automatic units. When selecting the filter medium, one should consider whether the filter has the following properties:

• Ability to trap the solid particles • Minimum resistance for the filtrate to flow through • Resistance to chemical attack • Minimum cost • Long life

Filter media can be cleaned by rinsing with solvents or detergents. Alternatively, in engineering applications, such as swimming pool water treatment plants, they may be cleaned by

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backwashing. Self-cleaning screen filters utilize point-of-suction backwashing to clean the screen without interrupting system flow.

Types of Filtration:-

In general there are two types of filtration, described as follows:

1. Cake Filtration or Surface Filtration.

2. Depth Filtration or Deep Bed Filtration.

1. Cake Filtration:-

Cake filtration is perhaps the most widely used filtration system in industry. In cake filtration, the solid material separated from the liquid accumulates on the surface of the medium so that, after a short initial period, the deposited solids form a cake through which the liquid must pass. The cake in the form of diatomaceous earth is deposited initially on a coarse screen in the case of pressure leaf filters or pads in the case of plate and frame filters. Usually filter cloths made of cotton or other suitable synthetic fiber, such as nylon, are used. The process may continue, increasing the depth of the cake until the space available is filled or until the pressure differential becomes so great that the flow is reduced to an uneconomical level.

In order to improve the filtration characteristics of this system, the diatomaceous earth (D.E.) is sometimes used for precoating of the screen or filters pads as well as for a continuous

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proportioned body feed throughout the filtration cycle. By selecting the particle size of the D.E. used, different fineness of filtration can be achieved from rough filtration to polish filtration.

D.E. is composed of the fossil remains of microscopic marine plants called diatoms. Diatomaceous earths are processed at 1500-2000 degrees F to burn off all organic matter. This leaves a residue which is almost pure silica. There are various grades of D.E. depending on the fineness or particle size which range from about 2.5 to 38 microns. The finer particle size produces a more polished filtration. The amount of D.E. needed to deposit an effective precoat depends on the flow characteristics of the filter, the type of screens and filter pads used and the pump characteristics. The most effective amount can only be determined by actual experimentation.

Cake filtration is employed where large filtration areas are available and an separation of smallest solids without use of filter aids.

2. Depth Filtration:-

In Depth Filtration, depth filter media not only captures particles on its surface, but also makes use of its three-dimensional shape to trap them in its interior. By causing the particles to take a prolonged tortuous path through the entire interior of the media, it allows more time for particles to come into contact with the sidewalls of the filter pores. This process allows for particles that are even smaller than the mean pore size of the filter media to be captured. Depth Filters also have a much higher particulate holding capacity than Surface Filters. A larger pore volume and a long service life are also among Depth Filters noted advantages.

Another widely used depth filter design is the Deep Bed type. In this type of system the feed liquid enters much the same way as in a normal fabric depth filter from the top where it then proceeds to flow down through several layers (or beds) of packed porous material such as garnet, limonite, alumina, magnetite, anthracite, quartz and sand which is the most common. This design is primarily used to treat large amounts of contaminated water such as a municipality’s water supply. But they are also becoming an increasingly employed alternative to ceramic candle filters to treat dust-laded gases.

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Depth filtration is further categorized as:

a) Dead End Filtration: In dead-end filtration, fluid flow is perpendicular to the filter surface and the filter rapidly becomes clogged with particles. Particles may be retained by sieving when they are larger than the filter's pore size, or by hydrosol filtration4 when they are smaller than the pore size; in this case, the small particles stick to the elements of the filterb) Crossflow Filtration: In crossflow filtration, fluid flows parallel to the filter surface and particles become more concentrated as filtrate leaves through the filter's

pores.Filtration Equipment:-

Filtration equipment includes many types. Some of them are listed here.(1) Bed filters(2) Bag filters(3) Pressure leaf filters(4) Cartridge filters(5) Vaccum filters

i. Horizontal belt/band filtersii. Rotary drum filters

iii. Rotary disc filters(6) Filter press

i. Plate and frame filter press

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ii. Recessed (chamber) filter press

The main factors to be considered when selecting equipment and operating conditions are:

• The properties of the fluid, particularly its viscosity, density and corrosive properties.

• The nature of the solid—its particle size and shape, size distribution, and packing characteristics.

• The concentration of solids in suspension.

• The quantity of material to be handled, and its value.

• Whether the valuable product is the solid, the fluid, or both.

• Whether it is necessary to wash the filtered solids.

• Whether very slight contamination caused by contact of the suspension or filtrate• Whether the various components of the equipment is detrimental to the product.

• Whether the feed liquor may be heated.

• Whether any form of pretreatment might be helpful.

General Applications:-

Filtration methods are used in the home, in research laboratories, in industrial processes, and in controlling environmental pollution. For example:

• Coffee filters are used to separate brewed coffee from the grounds,• HEPA filters are used in air conditioners and vacuum cleaners. Some filters are used to

clean ambient air by removing dust from the atmosphere.• Chemists often use filtration to separate materials from mixtures of different chemical

compositions.• On an industrial scale, filtration is used by the oil, gas, food and beverage, and

pharmaceutical industries, among many others. • Municipalities use filtration techniques when treating sewage and purifying water.• Filtration cleans up river streams or other water streams. • Furnaces use filtration to prevent the furnace elements from fouling with particulates. • Pneumatic conveying systems often employ filtration to stop or slow the flow of material

that is transported, through the use of a baghouse.

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Plate and Frame Filter PressThis type of filter consists of plates and frames arranged alternately and supported on a

pair of rails. The plates have a ribbed surface and the edges stand slightly proud and are carefully machined. The hollow frame is separated from the plate by the filter cloth, and the press is closed either by means of a hand screw or hydraulically, using the minimum pressure in order to reduce wear on the cloths. A chamber is therefore formed between each pair of successive plates. The slurry is introduced through a port in each frame and the filtrate passes through the cloth on each side so that two cakes are formed simultaneously in each chamber, and these join when the frame is full. The frames are usually square and may be 100 mm–2.5 m across and 10 mm–75 mm thick.

The slurry may be fed to the press through the continuous channel formed by the holes in the corners of the plates and frames, in which case it is necessary to cut corresponding holes in the cloths which themselves act as gaskets. Cutting of the cloth can be avoided by feeding through a channel at the side although rubber bushes must then be fitted so that a leak-tight joint is formed. The filtrate runs down the ribbed surface of the plates and is then discharged through a cock into an open launder so that the filtrate from each plate may be inspected and any plate can be isolated if it is not giving a clear filtrate. In some cases the filtrate is removed through a closed channel although it is not then possible to observe the discharge from each plate separately.

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In many filter presses, provision is made for steam heating so that the viscosity of the filtrate is reduced and a higher rate of filtration obtained. Materials, such as waxes, that solidify at normal temperatures may also be filtered in steam-heated presses. Steam heating also facilitates the production of a dry cake. The optimum thickness of cake to be formed in a filter press depends on the resistance offered by the filter cake and on the time taken to dismantle and refit the press. Although the production of a thin filter cake results in a high average rate of filtration, it is necessary to dismantle the press more often and a greater time is therefore spent on this operation.

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A Plate with filter cloth Plate and frame

A process flow diagram for Plate and frame filter press

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Exploded view of Plate and frame filter press

Advantages of the plate and frame filter press:-

• Because of its basic simplicity the filter press is versatile and may be used for a wide range of materials under varying operating conditions of cake thickness and pressure.

• Maintenance cost is low.

• It provides a large filtering area on a small floor space and few additional associated units are needed.

• Most joints are external and leakage is easily detected.

• High pressure operation is usually possible.

• It is equally suitable whether the cake or the liquid is the main product.

Disadvantages of the filter press:-

• It is intermittent in operation and continual dismantling is apt to cause high wear on the cloths.

• Despite the improvements mentioned previously, it is fairly heavy on labour.

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Experimental work

Procedure:-

• Loosened the press by releasing the hydraulic pressure valve. Started from the back, lift out the makeup piece. Slide the next element away from the next moveable head plate carrying the filter cloth. Then carefully lift out the next plate which was a hollow cylinder.

• Washed all the plates and frames thoroughly with water after removing them to remove any cake already present. Also washed the filter cloth and holes at the corners of plates and frames.

• Refitted all these to the press in a way that PIPS on each edge were on the same side.

• Prepared 10 % slurry of calcium carbonate (CaCO3) in a drum with high homogeneity.

• Started the pump and opened the recirculation valve to help not the solids to settle down at the bottom of drum which may chock the suction and discharge lines and most importantly the impeller of the pump.

• Opened the main valve to filter press and partially closed the recirculation valve to drum.

• As filtrate started to flow out off the press, operated it for 2-3 minutes.

• Now started to collect the filtrate at various intervals of time.

• From the data obtained, plotted the volume of filtrate V (liters) against ∆t/∆V.

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Observations and Calculations:-

Room temperature = 31 Degree Celsius

Initial concentration of slurry = 10%

Table of Calculations

Sr. No.Time ‘’t’’

(s)

Volume ‘’V’’

(Liters)∆t ∆V ∆t/∆V

1 ti=0 0 5 0.6 8.33

2 t1=5 0.6 5 0.54 9.26

3 10 1.14 5 0.50 10.00

4 15 1.64 5 0.40 12.5

5 20 2.04 5 0.35 14.28

6 25 2.39 5 0.30 16.67

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Graphical Representation of Results:-

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References:-

1. Chemical Engineering (Vol. 2), 5th Ed., Coulson & J.F Richardson.

2. Unit Operations of Chemical Engineering, 5th Ed., W.L. McCabe & J.C. Smith

3. Encyclopedic Dictionary of Named Processes in Chemical Technology, 3rd Ed., A.E. Comynes

4. Handbook of Chemical Processing Equipment, Nicholas P. Cheremisinoff

5. Perry’s Chemical Engineers’ Handbook, 8th Ed., D.W. Green & R.H. Perry

6. Handouts for Fluid & Particle Mechanics Lab, ICET (Punjab University) Lahore.

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