Designing of mechanical process such as separation process of filtration.pptx

Design of mechanical processes such as
separation process of filtration
Presented by: Md. Nazmus Salehin
M. Sc. In Food Processing and Preservation

Introduction to mechanical separation
Mechanical separation processes use physical forces to achieve separation of
components in mixtures. These include filtration, sedimentation, and
centrifugation, all commonly used in the food industry.
Filtration Sedimentation
Centrifugation

Definitions
 Sedimentation is a mechanical separation process where particles
suspended in a fluid settle under the influence of gravitational or
centrifugal forces, due to their density differences with the fluid.
 Centrifugation is a unit operation in which a mixture of immiscible
substances (typically solids and liquids, or two liquids) is subjected
to high-speed rotational motion, generating centrifugal force that
drives the denser components outward toward the periphery of the
rotating container, while less dense components remain closer to the
center.
 Filtration is a mechanical separation process in which solid
particles are removed from a fluid (liquid or gas) by passing the
mixture through a porous medium (filter) that allows only the fluid
and smaller particles to pass through while retaining the larger solid
particles.

Nature and applications of mechanical forces
Each process applies a specific force:
• Filtration: Pressure forces fluid through a medium.
• Sedimentation: Gravity settles denser particles.
• Centrifugation: Centrifugal force separates based on density.
Applications in Food Industry:
• Water treatment in the water treatment plant (Filtration)
• Clarification of juices (Sedimentation, filtration)
• Wastewater treatment (Sedimentation, filtration)
• Separation of molasses from sugar crystals (Centrifugation)

Introduction to Filtration
Filtration is a method to separate solids from fluids using a filter medium. It
is critical in both primary separations like curd removal and fine purification
processes.
There are two types of filtration process used in food industry,
1. Granular Filtration
2. Membrane Filtration
Schematic illustration of filtration process

Introduction to Granular Filtration
• Slow Sand Filters: Very fine filtration, low flow rate; used mainly for
water purification.
• Rapid Sand Filters: Higher flow rates, used in pre-treatment of water in
food processing.
• Precoat Filtration: A layer of filter aid (e.g., DE) is applied over a
support screen or cloth before filtration begins, allowing fine particle
capture.
1. Granular filtration is a type of depth filtration where the filter medium
consists of granular materials like sand, anthracite, activated carbon, or
diatomaceous earth. Instead of filtering purely at the surface, granular
filters allow the fluid to penetrate into the bed where suspended solids
are captured within the pores between granules.
Types of Granular Filters

Granular Activated Carbon Filter
Granular Bed Filter Media
• Activated Carbon
• Sand
• Pebbles
• Rocks
Design of a Granular Filtration Process

Parameter Typical Range Notes
Filtration Rate
5–15 m³/m²·h (rapid
filtration)
Slower rates (~1–5
m³/m²·h) for fine filters
Media Effective Size
(D )
₁₀
0.4–1.2 mm
Sand, anthracite, or
mixed media
Uniformity Coefficient < 1.7
Indicates media
uniformity
Bed Depth 0.6–1.5 meters
Deeper beds increase
holding capacity
Hydraulic Loading Depends on application
Food industry: may need
lower rates
Head Loss (Terminal)
2–3 meters of water
column
System designed to
handle this drop
Backwash Rate 30–50 m³/m²·h
To achieve 20–30% bed
expansion
Key Design Parameters

Components of the Granular Filtration System
a) Filter Vessel
• Material: Stainless steel (for food-grade processes) or concrete (for large
water treatment plants).
• Shape: Cylindrical or rectangular cross-section.
• Features: Inlet, outlet, backwash connections, pressure gauges, air
vents.
b) Filter Media
• Single media: Sand.
• Dual media: Sand + anthracite.
• Multi-media: Garnet (bottom) + sand (middle) + anthracite (top).
• Media selection depends on contaminant size and application.
c) Underdrain System
• Uniform distribution of influent and collection of filtrate.
• Equipped with nozzles or slotted pipes to prevent media loss during
backwash.
d) Instrumentation
• Pressure gauges (to monitor head loss).
• Flow meters.
• Valves for influent, effluent, and backwash lines.

 Basic Design Steps
1. Characterize the Feed Stream
• Determine particle size distribution, turbidity level, flow rate requirement.
2. Select Filter Media
• Choose appropriate media size, depth, and configuration based on
contaminant load.
3. Determine Filtration Area (A)
• A=Q/v
Where:
A = filtration area (m²)
Q = flow rate (m³/h)
v = filtration velocity (m³/m²·h)

4. Specify Bed Depth and Vessel Size
Sufficient to handle particle loading between backwashes.
5. Design the Backwash System
Ensure that the backwash flow rate expands the bed by 20–30%.
6. Establish Monitoring and Control Systems
Set up instrumentation for flow, pressure, and quality control.

 Advantages
1.Cost-effective – Lower installation and operational costs compared to
membranes.
2.High flow rates – Suitable for large-volume processing due to high
hydraulic loading capacity.
3.Simplicity – Operates without high-pressure systems; easier to maintain.
4.Long lifespan of media – Granular materials like sand or gravel can last
for years with proper backwashing.
5.Tolerance to suspended solids – More effective at handling water or
fluids with high turbidity.
 Disadvantages
1.Limited filtration fineness – Typically removes particles >10–20 µm; not
suitable for microbiological removal.
2.Backwashing required – Periodic cleaning is necessary to avoid clogging
and maintain efficiency.
3.Media degradation – Over time, granular media may become less
effective and need replacement.
4.Less effective for dissolved contaminants – Not suitable for removing
dissolved organics or salts unless activated carbon is used.
Advantages and Disadvantages of Granular Filtration Process

Membrane Filtration Processes
Membranes are porous filtration mediums, which can be cationic, anionic, or
nonionic in nature, and acts as a barrier to prevent mass movement of selected
phases, but allows passage of other remaining phases.
Introduction to Membrane Filtration
Membrane processes include the following five main categories for Food
processing, water and wastewater treatment:
1. Microfiltration (MF): MF is a pressure filtration process for the separation of
suspended solids in the particle size range of about 0.08–10 mm. The primary
function affecting solids separation from water is the size of the solids. The
hydraulic pressure applied in MF is about 1–2 bar, or 15–20 psi, for
overcoming the resistance of the “cake.”
2. Ultrafiltration (UF): UF is another pressure filtration process for the
separation of macromolecular solids in the particle size range of about 0.001–
0.1 mm. The hydraulic pressure required by UF for overcoming hydraulic
resistance of the polarized macromolecular layer on the membrane surface is
about 1–7 bar.

Introduction to Membrane Filtration
3. Nanofiltration (NF): NF membranes are multiple-layer thin-film composites of
polymer consisting of negatively charged chemical groups, and are used for
retaining molecular solids (such as sugar) and certain multivalent salts (such
as magnesium sulfate) at an operating pressure of about 14 bar or 200 psi.
The sizes of molecular solids and multivalent salts to be rejected by NF are
normally in the range of 0.0005–0.007 mm.
4. Reverse osmosis (RO): RO membranes are mainly made of cellulose
acetate (CA) with pore size of 5–20 Angstrom units. These membranes are
used for rejecting salts (as high as 98%) and organics (as high as 100%), at
an operating pressure of 20–50 bar or 300–750 psi. Sizes of molecular solids
and salts (multivalent as well as monovalent) to be rejected by RO are
normally in the range of 0.00025–0.003 mm.
5. Electrodialysis (ED): ED uses voltage or current as the driving force to
separate ionic solutes. The size of ionic solutes to be rejected or separated by
ED is normally in the range of 0.00025–0.08 mm. EDR is the electrodialysis
reversal (or reverse electrodialysis) process – which is similar to ED, but its
cathodes and anodes can be reversed for automatic cleaning operation.

Filtration application guide for membrane separation processes.

Separation capabilities of MF, UF, NF, and RO.

Separation capabilities of ED and EDR.

Membrane Filtration
 Basic Membrane System
The mass balance of flows is as follows:
Recovery or system conversion, Y in % is expressed as follows:
Where,
Qf = feed flow
Qp = permeate flow
Qr = retentate flow

Membrane Filtration
 Basic Membrane System
The feed water enters the membrane module at pressure Pi, and is split into
two streams: (a) permeate at pressure Pp and (b) retentate at pressure Po.
Simplified membrane process system.

Membrane Filtration
 Uniform Transmembrane Pressure (UTP) System
Uniform Transmembrane pressure
membrane (UTP) process system.
Pressure profiles and performance
characteristics of conventional MF and
UTP-MF
The process requires the simultaneous operation of a retentate pumping loop
and a permeate pumping loop, to simulate a backwashing operation, but in a
continuous manner rather than the periodic or intermittent traditional practice

 Advantages
1.High separation efficiency – Can remove very fine particles, bacteria,
viruses, and even dissolved ions (especially in RO).
2.Selective separation – Specific membrane types can target proteins, salts,
or microbes.
3.Compact design – Membrane systems occupy less space compared to
granular systems.
4.Consistent product quality – Precision in pore size ensures high-quality
output.
5.No chemical addition – Often operates without the need for coagulants or
flocculants.
 Disadvantages
1.High capital and operational costs – Membrane modules and pumps are
expensive and energy-intensive.
2.Membrane fouling – Susceptible to clogging, requiring frequent cleaning
and pretreatment.
3.Lower throughput – Limited flow rates, especially with tighter membranes
like RO.
4.Requires skilled operation – Membrane systems need careful monitoring
and maintenance.
Advantages and Disadvantages of Membrane Filtration Process

where the driving force is the pressure required to move the fluid through the filter
media and the resistance is dependent on several factors. The overall resistance can
be described by the following expression:
8.2
where represents a thickness of the accumulated solids in the filter cake, is the
𝐿𝑐 𝜇
fluid viscosity and is a fictitious thickness of the filter material or medium. The
𝐿
parameter in equation (8.2) represents the specific resistance of the filter cake
𝑟′
and will be a property of the particles forming the filter cake. Earle (1966)
describes by the following expression:
𝐿𝑐
8.3
where is the solids content of the fluid being filtered and is the volume which
𝑆 𝑉
has passed through the filter with cross-sectional area ( ). The thickness of the filter
𝐴
cake represents a somewhat fictitious value which would describe the total thickness
of all solids accumulated. In some filtration processes, this may approach the real
situation. Utilizing equations (8.2) and (8.3) the total resistance can be written in the
following manner:
8.4
8.1

Combining equations (8.1) and (8.4) an expression for the rate of filtration is
obtained as follows:
8.5
Equation (8.5) is an expression used to describe the filtration process and can be
used for scale-up if converted to appropriate forms.
The filtration process may occur in two phases: (a) constant-rate filtration, normally
occurring during the early stages of the process, and (b) constant-pressure filtration,
occurring during the final stages of the process.
(a) Constant-rate filtration.-Constant-rate filtration will be described by the following
integrated form of equation (8.5):
8.6
or:
8.7
which can be used to determine pressure drop required as a function of filtration
rate.

Equation (8.6) can be expressed in a different form if the thickness (L) of the filter
medium can be considered negligible. The following equation for pressure drop as a
function of time is obtained:
8.8
In many situations. equation (8.8) can be used to predict pressure drop requirements
for a filter during the early stages of the process.

Designing of mechanical process such as separation process of filtration.pptx

(b) Constant-pressure filtration.-An expression which describes constant-pressure
filtration can be obtained from the following form of equation:
8.9
Integration leads to the following design equation:
8.10
or the following equation if filter media thickness (L) can be assumed negligible:
8.11
Essentially, equation (8.11) indicates the time required to filter a given volume of fluid
when a constant pressure is maintained. Various procedures are utilized in the use of
this equation to obtain information in the equation which may not be readily
available. Such parameters as the specific resistance of the filter cake (r') may not be
known for specific types of solids and must be determined experimentally. Earle
(1966) presented procedures for determination of these parameters and Charm
(1978) has discussed determination of filtration constants which are somewhat more
difficult than those proposed in the above presentation.

 Remains as one of the most fundamental and widely applied unit
operations in food industry.
 Facilitates the removal of suspended solids, microorganisms, and other
undesirable components to ensure product quality, safety, and process
efficiency.
 Membrane filtration provides precision, selectivity, and the ability to target
specific contaminants at the micro- and nano-scale.
 Factors such as the nature of the feed material, desired product quality,
economic constraints, and regulatory requirements should be considered
while selecting a filtration process.
Conclusion

Designing of mechanical process such as separation process of filtration.pptx

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