Transcript Document 7131087

FOOD ENGINEERING
DESIGN AND
ECONOMICS
CHAPTER II
GENERAL CONSIDERATIONS
IN A PLANT DESIGN
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Plant location
Plant layout
Plant operation and control
Utilities
Structural design
Storage
Materials handling
Waste disposal
Health and safety
Patents
1.
Plant Location
The geographical location of the final plant can
have a strong influence on the success of an
industrial enterprise.
The plant should be located where the minimum
cost of production and distribution can be
obtained.
The choice of the final site should first be based
on a complete survey of the advantages and
disadvantages of various geographical areas.
An approximate idea for the plant location should
be obtained before a design project reaches
the detailed estimate stage.
1.1. Raw Materials
The source of raw materials is one of the most
important factors influencing the selection because
location near the raw materials source leads to
reduction in transportation and storage charges.
Attention should be given to the;
 purchased price of the raw materials
 distance from the source of supply
 freight or transportation expenses
 availability and reliability of supply
 purity of raw materials
 storage requirements
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1.2. Markets
The location of markets or intermediate
distribution centers affects the cost of product
distribution and the time required for shipping.
It should be noted that markets are needed for
by-products and end products as well as for
major final products.
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1.3. Energy Availability
Power and steam requirements are high in most
industrial plants and the fuel is ordinarily
required to supply these utilities. Consequently,
power and fuel can be combined as one major
factor in the choice of a plant site.
In addition, the presence and cost of electricity is
an important consideration for plant location. In
industrial areas the cost, voltage and
availability of electricity is different than in living
areas.
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1.4. Climate
Excessive humidity or extremes of hot or cold
weather can have a serious effect on
economic operation of a plant and these
factors should be examined when selecting a
plant site.
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1.5. Transportation Facilities
The common means of transportation used by
major industrial concerns are roads,
highways, railroads and water. For selection
careful attention should be given to “freight
rates”.
In food industry, raw materials and food
products are in huge amounts and not very
durable. Therefore, transportation should be
done with a great care and should be fast.
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1.6. Water Supply
The process industries use large quantities of water for
cooling, washing, steam generation, immobilized
conveying and as a raw material. Therefore, the
plant must be located where a dependable supply of
water is available.
Water sources can be tab water, rivers, lakes, deep
wells and artesian wells. If own sources are to be
used the level of existing water, seasonal
fluctuations, chemical, bacteriological content and
cost for supply and purification must be considered.
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1.7. Waste Disposal
The site selected for a plant should have adequate
capacity and facilities for correct waste disposal. In
recent years many legal restrictions have been
placed on the methods for disposing of waste
materials from the process industries. In choosing a
palnt site, the permissible tolerance levels for
various methods of waste disposal should be
considered carefully and attention should be given
to potential requirements for additional waste
treatment facilities.
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1.8. Labor Supply
The type and supply of labor available in the
vicinity of a proposed plant site must be
examined. Consideration should be given to
prevailing pay rates, restrictions on number of
hours worked per week, competing industries
that can cause dissatisfaction or high
turnover rates among the workers, the ethnic
distribution and variations in the skill and
intelligence of workers.
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1.9. Taxation and Legal Restrictions
Tax rates, health insurance rates and property
tax rates do not change depending on
position in our country. However, being a
governmental policy some places are
promoted for the development (as reduced
tax and interest rates). In industrial regions
permissions to be taken are important in cost
and time delays. For the abroad enterprises
local tax rates and promotions should be
considered.
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1.10. Site Characteristics
The characteristics of the land at a proposed plant site
should be examined carefully (topography and soil
structure).
The cost of land is important as well as local building
costs and living conditions. Future changes may
make it desirable or necessary to expand the plant
facilities.
The buildings that are constructed as a result detailed
land analysis, soil analysis and structural
calculations are very resistant to aging as well as
natural disasters like earthquakes.
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1.11 Flood and Fire Protection
Before choosing a plant site, the regional
history of natural events like floods or
hurricanes should be examined.
Protection from losses by fire is another
important factor for selection of plant location.
In case of a major fire, assistance from
outside fire departments should also be
available as well as fire protection systems.
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1.12. Community Factors
The character and facilities of a comunity can
have effects on the location of the plant.
Cultural facilities as schools, shops,
mosques, cafeterias, kindergartens, cinemas
are important for a progressive community. If
these facilities are not present it becomes for
the plant as a necessity to provide such
facilities.
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Approximate region determination for
preliminary survey
raw materials
markets
energy supply
climate
Reduction in possible areas
transportation facilities
water supply
raw materials
markets
energy supply
climate
Final selection
waste disposal
taxes and legal restrictions
site characteristics
flood and fire protection
community factors
raw materials, markets, energy supply, climate,
transportation facilities and water supply
2. Plant Layout
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After the process flow diagrams are
completed and before detailed piping,
structural and electrical design can begin, the
layout of process units in a plant and the
equipment within these process units must be
planned. This layout can play an important
part in determining construction and
manufacturing costs and thus must be
planned carefully with attention being given to
future problems that may arise.
“there is no ideal plant layout”
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A proper layout in each case will include arrangement of
processing areas, storage areas and handling areas in
efficient coordination and with regard to the following factors:
new site development or addition to previously developed site
type and quantity of products to be produced
type of process and product control
operational convenience and accessibility
economic distribution of utilities and services
type of buildings and building code requirements
health and safety considerations
waste disposal problems
auxiliary equipment
space available and space required
roads and railroads
possible future expansions.
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Preparation of the layout;
First, elementary layouts are prepared which shows
the fundamental relationships between storage
space and operating equipment (process).
The next step requires consideration of the
operational sequence and gives a primary layout
based on; flow of materials, unit operations,
storage, future expansion, administrative parts,
laboratories, sampling, change rooms, training
rooms, first aid , etc.
Finally, by analyzing all the factors that are involved
in plant layout, a detailed recommendation can be
presented and drawings and elevations, including
isometric drawings of the piping systems can be
prepared.
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While preparing the layout, three dimensional
models are often made. The main advantage
of three dimensional models is the possibility
of observing the problems that may be
missing in two-dimensional drawings. Threedimensional models are also beneficial for
orientation after the plant is completed.
+ “empty area”
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Considerable attention has to be given to auxiliary
departments and this should be done before the
manufacturing space has been planned in too much
detail. Time clocks, restrooms, washrooms and toilets
should be located so that they are convenient and
accessible to workers entering and leaving the plant.
General offices of the company should be located so as
to provide ready access to the public and freedom from
noise of the factory. In many cases it is desirable to keep
them adjacent to working areas for closer supervision.
Engineering and factory offices in particular should be
located adjacent to production areas. Some companies
separate these offices by a glass partition to isolate
sound but still keep a closer touch with the
manufacturing areas. This also improves a closer feeling
of unity between factory operating personnel and the
supervisory force.
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Layout design to minimize non-microbial contamination;
There should be enough empty space for de-boxing or de-palletizing of
raw materials and screening. Similarly space for storage of packaging
materials should be present.
Congestion in areas of open food production makes cleaning and
maintenance difficult to achieve without putting food products and other
equipments at risk.
There should be separate storage rooms for finished products. If they
have direct contact with raw material dirt and cross-infestation or odor
tainting may take place.
Insufficient space for maintenance operations will result in many
problems. Work benches in open production areas should never be
permitted. Fitters forced to work in cramped, dirty conditions will find it
difficult to conform to the required hygiene standards when working in
production areas. Lack of storage space for temporarily disused
equipment often results in it being kept in production areas. Such
equipment is frequently infested because it is not being cleaned before
and during storage.
If equipment cleaning centers are located too far from production areas,
there will be temptation to neglect cleaning schedules. An equal
temptation will be for cleaning materials including concentrated
detergents. The quantities of foodstuffs tainted by detergents should not
be under-estimated.
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There should be enough equipped smoking/snack rooms adjacent
to production areas. Otherwise, smoking near machinery or food
consumption in unauthorized parts of the factory may take place.
There should be short and direct routes for waste removal.
Sometimes returned goods are collected in plant. Such goods are
often infested and/or in a state of decomposition. Therefore, they
must be isolated from all raw material and production areas.
There should be;
Adequate surface drainage to avoid ponding
Provision of a surface that can be easily cleaned
A correct sitting and construction of waste-collection areas
A good housekeeping controls in nearby buildings
A control for weed growth
A correct sitting and control of effluent treatment
Control of stocks of surplus equipment (wood, empty containers,
etc.) which are often kept because “it might come in useful”.
3. Plant Operation and control
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In the design of an industrial plant, the
methods which will be used for plant
operation and control help for the
determination of many of the design
variables.
It should be remembered that maintenance
work will be necessary to keep the installed
equipment and facilities in good operating
condition.
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Instrumentation
Instruments are used in an industrial plant to
measure process variables such as; temperature,
pressure, density, viscosity, specific heat,
conductivity, pH, humidity, liquid level, flow rate,
chemical composition, moisture content, etc. By use
of instruments having varying degrees of complexity,
the values of these variables can be recorded
continuously and controlled within narrow limits.
Automatic control is widely used with resulting savings
in labor combined with improved ease and efficiency
of operations. (which overcomes the added expense
for instrumentation) This control is achieved through
the use of high speed computers.
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Maintenance
Maintenance work includes; repairs, equipment
upgrading, testing, field adjustment, etc. Many of the
problems involved in maintenance are caused by
the original design and layout of the plant and the
equipment.
In most cases the design engineer is concious only
of first costs and fails to recognize that maintenance
costs can easily overcome the advantages of a
cheap initial installation.
Sufficient space for maintenance work on equipment
and facilities must be provided in the plant layout
and the engineer needs to consider maintenance
requirements when making decisions on equipment.
4.Utilities
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Utilities are the process supplements of an industrial
plant as power, steam or water.
The most common sources of energy are oil, gas, coal
and nuclear energy. The decreasing availability of some
sources will necessitate the use of alternative forms of
energy.
In production industry the required power is primarily in
the form of electricity, other sources are steam engines,
internal-combustion engines and hydraulic turbines.
When a design engineer is setting up the specifications
for a new plant, a decision must be based on whether to
use purchased power or producing its own power. (if
both exist continuous operation is achieved)
The quantity of steam used in a process varies
depending on thermal and mechanical requirements and
should be generated from whatever fuel is cheapest.
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Water for industrial purposes can be obtained from
the plant’s own sources or a municipal supply. If the
demands for water are large, it is more economical
for the plant to provide its own water sources. Such
a supply may be obtained from drilled wells, rivers,
lakes, dammed streams or other supplies.
Before a company agrees to go ahead with a new
project, it must ensure itself of a sufficient supply of
water for all industrial, sanitary and safety demands
both present and future.
The value of an abundance of good water supplies
is reflected in the selling price of plant locations.
Treatment of water significantly increase the
operational cost for a plant. Increased cost of water
processing necessitates maximum yields for the
use of processed water. In general, high cost for
both processing and disposal of water lead to
minimum amount of utilization for water.
5. Structural Design
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For a successful structural design, it is necessary to know
the characteristics of the soil at a given plant site. The
allowable bearing pressure varies for different types of
soils and the soil should be checked at the surface and at
various depths to determine the bearing characteristics.
The purpose of foundation is to distribute the load so that
excessive or damaging settling will not occur. (footing with
plain concrete; foundation walls with reinforced concrete)
Although cost is important for the selection of materials of
construction, resistance to adverse effects and flexibility
of construction for future changes and expansions are
also important. Therefore, corrosive effects of the
process, cost of construction, possible future changes
and climacteric effects should be considered together.
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Floor design is worth considerable thought and high
initial investment. Concrete floors are used
extensively in the process industries and covering
materials should be used for making the floor
resistant to heat and chemical attacks and more
important in food industry ease of cleaning and
sanitizing. The disruption caused by defective floors
may be very costly and piecemeal repair is difficult to
achieve. Many floor defects arise from poor planning
and preparation and not from the actual finishing
material. Floorings which do not contain high-odor
materials should be used.
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The number of partition walls should be kept to the
minimum and used only to isolate operations which
otherwise lead to the spread of contaminants. Too
many separate rooms complicate inspection, control
and prevents the achievement of uniform standards.
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Correct floor drainage is important in the control
of insect infestation and odors. Covered
channels present major cleaning problems when
compared to open wall junction channels.
Similarly, it is unnecessary and undesirable for
equipment to drain directly on to the floor. This
spreads dirt into inaccessible areas and is
uncomfortable for operatives.
Water based cleaning systems are very much
restricted in dry production areas such as in
bakeries because of lack of drainage. This
requires the use of high pressure systems
usually applied in inefficient manual methods
which demand a greater level of supervision.
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The buildings are usually with flat roofs and special combinations are
outer coating in order to reduce effect of seasonal conditions. The
interior coating of the roofs is also important since water droplets
from condensed vapor on roofs may cause to contamination.
In conventional buildings ceilings are covered in a network of pipes,
lights, cable trays, heaters and channels (ducting). (overhead)
Maintenance work overhead may cause direct contamination to
product or contamination of equipment and subsequently to product.
This work should take place in out of work hours and production
lines are covered but in practice due to emergencies this cannot be
met.
For powdered materials a difficulty in cleaning occurs when such
materials settle on overheads. This cause subsequent mouse or
insect activity which in turn endangers production lines.
Overheads may also function as roosting for small birds where
droppings on equipment and raw materials are completely
undesirable.
These problems can be prevented by providing a separate service
floor which will house much of the channels (ducting), pipes etc. The
result is a clear ceiling which is easy to clean and the removal of
many activities, which could cause contamination to the separate
service area. Further it does not restrict maintenance work to outside
of working hours. This system is also flexible and allows direct feed
to be maintained after production line layout changes.
6. Storage
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In the operation of a process plant adequate storage
facilities for raw materials, intermediate products, final
products, recycle materials, off-grade materials, fuels,
cleaning agents, packaging materials and other items.
Storage of raw materials permits operation of the process
plant regardless of temporary supply of delivery difficulties.
Storage of intermediate products may be necessary during
plant shutdown for emergency repairs. this is not practical
for food systems since they are sensitive to contamination)
Storage of products makes it possible to supply the
customer even during a plant difficulty or unforeseen
shutdown.
An additional need for adequate storage is encountered
when it is necessary to meet seasonal fluctuations.
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Depending on the physical and chemical properties
of the materials storage conditions should be
determined.
Bulk storage of liquids is generally handled by
closed spherical or cylindrical tanks to prevent
escape of volatiles and minimize contamination.
High-pressure gas is stored in spherical or
horizontal cylindrical pressure vessels.
Solid products and raw materials are either stored in
air-tight tanks with sloping floors or in outdoor bins
or mounds. Solid products are mostly packed
directly on retail packages.
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in all storage areas;
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there must be a control unit (for controls and recording)
there should be necessary warnings (on doors, walls, instruments etc.)
ambient or cooled temperatures should be selected depending on the
properties of raw material and the products
depending on amount of material required storage area should be
determined
if long periods of storage are required coding systems should be used to
supply equal storage time for all materials.
if cold storage is to be used, to supply economic utilization of energy,
storage area can be divided into parts so that for each loading or
unloading temperature of whole area is not raised. For this purpose,
rooms may be formed by plastic curtains. by this way input and output of
materials could be done without energy losses.
in storage areas raw materials and products should be stored separately.
a constant temperature in storage area should be supplied with suitable
wall clearance and stack height.
storage should be made on transportation means to prevent contact with
basement.
there must be enough place to be walked for control purposes. these
controls are especially important for ambient temperature since spoilage
may take place more often.
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7. Materials Handling
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Materials handling equipment used for transportation of solids,
liquids and gases are divided into two main groups as continuous or
batch.
Liquids and gases are handled by means of pumps and blowers in
pipes and ducts and in containers such as drums or cylinders.
(hydraulic conveying)
Solids may be handled by conveyors, elevators, lift trucks and
pneumatic systems.
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Gravity or manually powered conveyors
Powered conveyors as; roller conveyors, belt conveyor, slat conveyors,
chain conveyors, vibratory conveyors, magnetic conveyors, screw
conveyors and flight conveyors.
Package elevators and bulk elevators
Trucks with low and high vertical lifts
Pneumatic equipment where air is used to reduce solid-solid friction,
either ‘air-cushion’ principle or solid fluidization or solid suspension.
The selection of materials handling equipment depends upon the
cost and the work to be done.
Factors that must be considered in selecting such equipment include:
1. Chemical and physical nature of material being handled
2. Type and distance of movement of material
3. Quantity of material moved per unit time
4. Nature of feed and discharge from materials handling equipment
5. Continuous and intermittent nature of materials handling
Depending on movement of raw materials and products outside of the
plant, some type of receiving and shipping facilities must be provided
in the design of the plant. In those facilities cleaning and sanitation
units should also be present.
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Safety considerations should involve unsafe conditions (insufficient
working space, inadequate aisle space, inadequate guarding of
running machinery, defective equipment, inadequate lighting and
ventilation, unsafe design or construction of equipment and bad floor
surfaces) and unsafe acts (unsafe loading and stacking, disregard
of traffic signals, carrying out repairs and adjustments on the run,
operating without authority, working at unsafe speeds, using incorrect
equipment, exceeding the capacity of equipment, failing to use
protective clothing and practical joking)
8. Waste Disposal
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Waste from an industrial plant in form of gas, liquid or solid
cause to pollution. In order to control this pollution several
factors should be evaluated as;
pollution source (pollutants and the total volume dispersed)
properties of pollution emissions
design of the collection and transfer systems
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selection of the control device
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the size of the equipment is directly related to the volume being
treated, therefore exhaust volume should be reduced to decrease
equipment cost. If a reduction in pollution source can be obtained
process or raw materials can be changed.
selection of the most appropriate control device requires
consideration of the pollutant being handled and the features of the
control device.
dispersion of the exhaust to meet applicable regulations.
i. Air Pollution Abatement: Air pollution control
equipments can be classified into two major categories,
those suitable for removing particulates and those
associated with removing gaseous pollutants.
Particulate removal
To obtain the greatest efficiency in particulate removal,
particular attention must be given to particle diameter
and the air velocity.
 Large diameter particles can be removed with low
energy devices such as settling chambers, cyclones and
spray chambers.
 Intermediate particles can be removed with impingement
separators or low energy wet collectors.
 Submicron particles must be removed with high energy
units such as bag filters or electrostatic precipitators.
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Noxious Gas removal
Gaseous pollutants can be removed from air streams either by
absorption, adsorption, condensation or incineration.
Condensation, is a method for removing a solvent vapor from air or
other gas if the concentration of the solvent in the gas is high and
the solvent is worth of recovery. Since condensation can not
remove all of the solvent, it can only be used to reduce the solvent
concentration in the carrier gas.
Gas liquid absorption processes are normally carried out in
vertical, countercurrent flow through packed, plate or spray towers.
For absorption of gaseous streams good liquid-gas contact is
essential, therefore proper equipment selection is important.
Adsorption is generally carried out in large, horizontal fixed beds
often equipped with blowers, condensers, separators and controls.
Dry adsorbents like activated carbon and molecular sieves are
used in removing final traces of objectionable gaseous pollutants.
Incineration is the simplest way when polluting gas has no value
and combustible. There are two methods in common use direct
flame and catalytic oxidations.
ii. Water pollution Abatement: since waste liquid
may contain dissolved gases or solids or it may be in
a form of slurry, physical, chemical or biological
treatment methods can be used.
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The problems of handling a liquid waste effluent are
considerably more complex than those of handling a
waste gas or solid effluent.
For applicable situations, recovery for reuse or sale
should be investigated.
If product recovery is not capable of solving the
problem, the design engineer should decide which
treatment, process or combination of processes will
give the best performance.
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Physical Treatment
The first step in any waste water treatment process is to remove large
floating or suspended particles. The size of solids is wide and several
separation methods are used. A common method involves the separation
of coarse material using screens. (bar screens, vibrating screens, rotary
drum screens etc) Screen apertures range from 25 mm down to
micrometer sizes depending on the application.
This is usually followed by sedimentation or gravity settling. Sedimentation
takes place in large open ponds if sufficient land area is available.
Otherwise gravity sedimentation tanks are used. Entering to those
cylindrical vessels the liquid stream slowly rises to the top of the tank to be
removed via an overflow launder as a clarified liquid stream. Denser solids
settle to the bottom as a thick sludge underflow. Slow speed scraper
blades help compact the sludge and drive it to the center off-take pipe for
removal. Usually residence times in these units are insufficient for
anaerobic decomposition to occur.
Certain food wastes contain large amounts of oils and fats. These organic
materials are immiscible with the aqueous effluent stream and float to the
surface. This layer can then be mechanically skimmed from the surface of
the bulk liquid. An alternative in this case is removal by aeration-floatation.
With controlled aeration small bubbles will be formed which will rise
through the liquid carrying grease and fine solids to the surface.
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Sludge from primary or secondary treatment that
has been initially concentrated in a clarifier or
thickener can be further concentrated by vacuum
filtration or centrifugation.
The dissolved materials like refractory organics,
toxic substances and color compounds can be
removed by adsorption process. The primary
forces for adsorption are a combination of;
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The hydrophobic nature of the dissolved organics in the
waste water
The affinity of the organics to the solid adsorbent due to
a combination of electrostatic attraction, physical
adsorption and chemical adsorption.
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The last stage of in-plant recovery involves different membrane processes like ultrafiltration,
reverse osmosis and electrodialysis.
In ultrafiltration, the separation is based primarily on the size of the solute
molecules which depending upon the particular membrane porosity can range
from about 2 to 10 000 millimicrons.
In this technique suspended solids and solutes with high molecular weight are
retained while water and low molecular weight solutes pass through the
membrane. The common membrane configurations are:
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Spiral wound (consists of large consecutive layers of membrane and support material around
a tube which maximizes the surface area, less expensive than the others but more sensitive
to pollution)
Hollow fiber (modules contain several small (0.6-2 mm in diameter) tubes or fibers, the feed
solution flows through the fibers and permeate is collected in the cartridge area surrounding
the fibers, the filtration can be carried out either “inside-out” or “outside-in”)
Tubular (the feed solution flows through the membrane core and the permeate is collected in
the tubular housing, system is not compact and it has high cost, used for viscous or bad
quality fluids.
Applications;
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dialysis and other blood treatments
concentration of milk before making cheese
fractionation of proteins
clarification of fruit juices
recovery of vaccines and antibiotics from fermentation broth
laboratory grade water production
waste water treatment
drinking water disinfection (including removal of viruses)
removal of endocrines and pesticides combined with suspended activated carbon treatment.
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In reverse osmosis, the size of the solute molecule is not the sole basis for
the degree of removal, since other characteristics of the solute such as
hydrogen bonding and valency affect the membrane selectivity.
This filtration process works by using pressure to force a solution through a
membrane, retaining the solute on one side and allowing the solvent pass
through to the other side. (the reverse of normal osmosis process)
Applications
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drinking water purification (household water purification systems are commonly used
for improving water for drinking and cooking, portable reverse osmosis purification
units are used in rural areas, in military applications, camping, in boats with the
addition of ultraviolet light or ozone treatment)
water and waste water purification (in industry reverse osmosis is used for
demineralization of boiler water since water is boiled and condensed so many times it
should be as pure as possible, rainwater collected from drains is purified with reverse
osmosis and used in landscape irrigation, it can also be used for the production of deionized water)
dialysis (reverse osmosis is similar to the technique used in dialysis, therefore dialysis
equipment mimics kidneys)
car washing (because of lower mineral content reverse osmosis water is used for final
rinse to prevent water spouting on the vehicle)
reef aquarium (reef aquarium keepers use reverse osmosis for their artificial mixture of
seawater, ordinary tap water can contain chlorine, chloramines, copper, nitrogen,
phosphates, silicates and many other chemicals that are detrimental for the sensible
reef organisms)
desalination (in areas where no or limited surface or underground water exist people
choose desalinate seawater, since no heating and phase change is required like other
treatments it is relatively cheap)
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In addition to desalination, reverse osmosis is a another economical
operation for concentrating food liquids (such as fruit juices) than
conventional heat-treatment processes. Research has been done
on concentration of orange juice and tomato juice. Its advantages
include a low operating cost and the ability to avoid heat treatment
processes, which makes it suitable for heat-sensitive substances
like the protein and enzymes found in most food products.
Reverse osmosis is extensively used in the dairy industry for the
production of whey protein powders and for the concentration of milk
to reduce shipping costs. In whey applications, the whey is preconcentrated with RO from 6% total solids to 10-20% total solids
before ultrafiltration(UF) processing. The UF retentate can then be
used to make various whey powders including whey protein isolate
(WPI) used in bodybuilding formulations. Additionally, the UF
permeate, which contains lactose, is concentrated by RO from 5%
total solids to 18–22% total solids to reduce crystallization and
drying costs of the lactose powder.
Although use of the process was once frowned upon in the wine
industry, it is now widely understood and used. An estimated 60
reverse osmosis machines were in use in Bordeaux, France in
2002.
Reverse osmosis is used globally throughout the wine industry for
many practices including wine and juice concentration, taint
removal; such as acetic acid, smoke taint and breyyanomyces taint;
and alcohol removal.
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In electrodialysis, the removal of the solute rather than the
removal of the solvent is employed and only ionic species are
removed.
Electrodialysis is used to transport salt ions from one solution
through ion exchange membranes to another solution under the
influence of an applied electric potential difference.
In electrodialysis process multiple electrodialysis cells are
arranged with alternaing anion and cation exchange membranes
forming the multiple electrodialysis cells.
Because the quantity of dissolved species in the feed stream
is far less than that of the fluid, electrodialysis offers the
practical advantage of much higher feed recovery in many
applications.
In application, electrodialysis systems can be operated as
continuous or batch production processes. In a continuous
process, feed is passed through a sufficient number of stacks
placed in series to produce the final desired product quality. In
batch processes, the dilute and/or concentrate streams are
re-circulated through the electrodialysis systems until the final
product or concentrate quality is achieved.
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Applications;
Deionization of aqueous solutions,(however, desalting of sparingly
conductive aqueous organic and organic solutions is also possible).
Large scale seawater desalination and salt production.
Small and medium scale drinking water production
Water reuse
Pre-demineralization (e.g., boiler makeup & pretreatment, ultrapure water
pretreatment, process water desalination, power generation,
semiconductor, chemical manufacturing, food and beverage)
Food processing
Agricultural water
Electrodialysis has inherent limitations, working best at removing low
molecular weight ionic components from a feed stream. Non-charged,
higher molecular weight, and less mobile ionic species will not typically be
significantly removed.
Electrodialysis systems require feed pretreatment to remove species that
coat, precipitate onto, or otherwise "foul" the surface of the ion exchange
membranes. This fouling decreases the efficiency of the electrodialysis
system. Species of concern include calcium and magnesium hardness,
suspended solids, silica, and organic compounds.
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Chemical Treatment
In wastewater treatment, chemical methods are generally used to remove
colloidal matter, color, odor, acids, alkalies, heavy metals and oil
compounds.
Coagulation is a process that removes colloids from water by the
addition of chemicals which upset the stability of the system by
neutralizing the colloid charge. For this purpose multivarient cations of Al
or Fe.
Emulsion breaking is similar to coagulation. The emulsions are
generally broken with a combination of acidic reagents and
polyelectrolytes.
Precipitation method is based on the common ion effect. In this case
an unwanted salt is removed from solution by adding a second soluble
salt to increase one of the ion concentrations. Coagulant aids may also
be needed to remove the precipitate.
Neutralization is treating acid and alkaline waste products with a
strong base or acid. Even though this method may change the pH of the
waste stream to the desired level it does not remove the sulfate, chloride
or other ions.
Depending on the composition chemical oxidation or reduction
methods can be used especially for organic materials which is hard to
separate from waste water stream. ( common chemical oxidizing agents
are chlorine, ozone and hydrogen peroxide)
Biological Treatment
In the presence of the ordinary bacteria found in water, many
organic materials will oxidize to form carbondioxide, water,
sulfates and similar materials. This process consumes the
oxygen dissolved in the water and may cause a depletion of
dissolved oxygen.
A measure of the ability of a waste component to consume the
oxygen dissolved in water is known as the Biochemical Oxygen
Demand (BOD). The BOD of polluted waters is the oxygen
reported as parts per million consumed during a set period of
time by bacterial action on the decomposable organic matter at
20oC.
Another measure of overall oxygen load is Chemical Oxygen
Demand (COD). COD is equal to the number of milligrams of
oxygen which a liter of sample will absorb from a hot, acidic
solution of potassium dichromate.
In determination of BOD some incubation period is
required, however, COD has the advantage of being measured
in a short time.
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The common biological treatment involves the use
of concentrated masses of microorganisms to break
down organic matter resulting in stabilization of
organic wastes. These organisms are broadly
classified as aerobic, anaerobic and aerobicanaerobic facultative.
Many organic industrial wastes are suitable for
biological treatment, however, some of them are
non-biodegradable. Process evaluation prior to
system design should center on characterization of
the waste stream, particularly to determine the
presence of inhibitory or toxic components relative
to biological treatment and the establishment of
pollutant removal rates, oxygen requirements,
nutrient requirements, sludge production and solids
settleability.
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Aerobic organisms require molecular oxygen for metabolism. The
aerobic biological process involve either the activated sludge process
or the fixed film process.
The activated sludge process is a continuous system in which aerobic
bacteria are mixed with wastewater and the resulting excess
flocculated suspension separated by gravity clarification or air
floatation.
Suspension is normally brought about by a combination of aeration
and mechanical agitation. As well as the particulate material, dissolved
organic matter is also adsorbed and then utilized by the aerobic
microorganisms part being oxidized to carbon dioxide and water and
part is assimilated to biomass. The “mixed liquor” leaving the reactor
passes to a settling tank. In the tank low BOD supernatant liquor (free
of suspended solids) and a thick sludge are produced. Part of the
sludge which contains viable microorganisms is recycled to maintain
the active microbial suspension in the aeration stage.
In the fixed film process, wastewater trickles over a biological film fixed
to an inert medium. Clarified waste liquor is fed on to the upper surface
of the bed by spray nozzles or rotator distributer arms. The large
surface area of the bed facilitates intimate contact between air, waste
liquor passing through the bed and attached active growth. The treated
liquors leaving the bed possess a much reduced content of dissolved
organic pollutory matter but will contain suspended biomass. The
solids are removed through a secondary sedimentation tank.
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ii.
Anaerobic organisms derive energy from organic compounds
and function in the absence of oxygen and methane and
carbondioxide are produced as the main products. Compared
to aerobic treatment the advantages of anaerobic
stabilization are the avoidance of expensive aeration facilities
and low production of stable solids. However, odorous,
unstable liquids are also produced and these may require
further treatment. In addition, anaerobic processes are slow
so long residence times in large reactors are necessary.
There are two main areas of application for anaerobic
processes in food waste treatment:
Food waste liquors with high contents of less degradable
solids (meat-processing wastes, starches, etc) are more
suitable to anaerobic than aerobic oxidation
Anaerobic digestion of primary and secondary sludges
associated with aerobic waste treatment is common in
municipal plants and treating food factory wastes with
sewage. This digestion produces a reduced volume of
relatively inert material having little unpleasant odour and and
can be dewatered easily.
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ii.
iii.
Since anaerobic fermentation is accompanied by the formation
of hydrogen sulphide unpleasant odours can arise. To minimise
odour problems as well as for the collection of combustible
gas in larger plants, digesters are usually covered.
Three stages of digestion have been identified;
Liquefaction: high molecular weight insoluble organic materials,
e.g., proteins, polysaccharides, etc. are hydrolyzed by extracellular enzymes produced by micro-organisms, being broken
down into soluble, low molecular weight substances
Acid fermentaton: The soluble organic material formed during
hydrolysis is metabolised by facultative and anaerobic
organisms, being converted into volatile lower fatty acids,
alcohols, carbon dioxide and hydrogen.
Methane fermentation: Under favorable conditions organic
acids are converted into methane, carbon dioxide and small
amounts of hydrogen by several species of strictly unaerobic
bacteria and new cells develop.
Sensitivity to pH makes anaerobic digestion process instable.
After digestion and settling, the reduced volume of sludge
solids is usually dewatered further before disposal. The
separated liquid is likely to have a high BOD and normally
requires aerobic treatment before discharge to a water course.
iii. Solid Waste Disposal: solid wastes differ
from air and water pollutants since the wastes
remain at the point of origin until they are
collected and disposed.
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Recycling and Chemical Conversion
Process wastes can be converted into saleable products or
innocuous materials that can be disposed of safely. Resource
recovery is an important factor in waste disposal. Some
specific chemicals may often be recovered by distillation,
leaching or extraction. Also valuable solids such as metals
and plastics can be recovered by magnets, electrical
conductivity or hand picking. In addition to these items,
hydrogenation of organics produce fuels and nitrogen or
phosphorus enrichment of wastes produce fertilizers.
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Incineration
The controlled oxidation of solid, liquid or gaseous
combustible wastes to final products of carbon dioxide,
water and ash is called incineration. Since sulfur and
nitrogen containing waste materials will produce their
corresponding oxides, they should not be incinerated
without considering their effect on air quality.
A properly designed and carefully operated incinerator can
be located adjacent to a process plant and can be adjusted
to handle a variety and quantity of wastes.
By using the heat evolved from this process in steam
generation operating costs are reduced and thermal
pollution control equipments are saved. Additionally, the
residue is a small fraction of the original weight and volume
of the waste and may be acceptable for landfill.
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Pyrolysis
Pyrolysis is the heating of wastes in an air free chamber at
temperatures as high as 1650 oC. Pyrolysis seems to
provide several advantages over incineration. These
systems encounter far fewer air pollution problems, handle
larger throughputs resulting in lower capital costs, provide
their own fuel and have added potential for recovering
chemicals or synthesis gas.
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Landfill
Sanitary landfill is basically a simple technique that involves
spreading and compacting solid wastes into cells that are
covered each day with soil. In this method it is important
that the wastes must be either or produces harmless
compounds by microbial attack. In addition the possibilities
of accumulation of hazardous materials which contaminate
surrounding groundwater and accumulation of flammable
gases produced during degradation should be eliminated.
iv. Thermal Pollution Control
The high temperature waste have several disadvantages as;
 Temperature effects nearly every physical property of concern in
water quality management including density, viscosity, vapor
pressure, surface tension, gas solubility and gas diffusion. The
solubility of oxygen is probably the most important of these
parameters since dissolved oxygen is necessary to maintain
many forms of aquatic life.
 Due to increased temperature assimilative capacity of organic
wastes is reduced.
 There exist some legal restrictions regarding the temperature of
wastewater.
all these problems lead the design engineer to investigate cooling
systems.
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In order to handle thermal discharges cooling towers are used
which may be classified on the bases of heat transfer medium
or power requirements.
In wet cooling towers the condenser cooling water an ambient
air are intimately mixed. Cooling results from the evaporation of
a portion of the water and to a lesser extent from the loss of
sensible heat.
In dry cooling towers, the temperature reduction of the
condenser water depends upon conduction and convection for
the transfer of heat from water to air.(in different channels)
Mechanical draft cooling towers force air which serves as the
heat transfer medium through the tower.
Natural draft cooling towers depend upon the density difference
between the air leaving the tower and the air entering the tower.
Cooling ponds are generally considered for removal of heat
when suitable land is available at a reasonable price
When land costs are high spray ponds often provide an
alternative to cooling ponds, which requires only 5 to 10 percent
of the area of a cooling pond.
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iv.
v.
vi.
vii.
HAZOP
The hazard and operability (HAZOP) study is a systematic
technique for identifying all plant or equipment hazards and
operability problems. For a HAZOP study of a specific
equipment the items are;
equipment reference and operating conditions
deviations from operating conditions
what event could cause this deviation
consequences of this deviation on the equipment under
consideration
additional implications of this consequence
process indications
notes and questions.
General safety checklist for identifying process hazards involves;
i.
External plant considerations
ii.
Internal plant structure and service considerations
iii.
In-plant physical and organizational considerations.
9. Health and Safety
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There are several health and safety hazards encountered in the
process industries. The design engineer should consider all those
items and should have precautions against them.
Chemical Hazards
Many chemicals can cause damages when come into contact with living
tissues. If such chemicals are used in the process the time and amount of
exposure should be determined and controlled by the design engineer.
Fire and Explosion Hazards
Hazardous operations should be isolated by location in separate buildings
or separated areas by brick-fire walls.
The design and construction of high pressure tanks should follow the
standards and should be tested at 1.5 to 2 times the design pressure.
In order to prevent fire, smoking, welding and cutting machines, open
electrical connections, heated materials and other ignition sources should
be eliminated. The installation of sufficient fire alarms, temperature alarms,
fire-fighting equipment and sprinkler systems are to be included in the
design. Fire protection systems are classified as active and passive
systems. Active systems include water sprays, foam and dry chemicals
which requires action to be taken either by plant personnel or by automatic
fire protection systems. Passive protection systems are designed and
installed at the construction stage and remain until needed. (like fire proof
insulating materials)
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Personnel Safety
In the design project, health and safety of plant personnel should be
considered.
All machinery must be equipped with control and warning devices.
Physical hazards if unavoidable must be clearly defined.
Protected walkways, platforms, stairs and work areas should be
provided.
Medical services and first aid must be readily available.
Noise Abatement
To attain efficient, effective and practical noise control it is necessary
to understand the individual equipment or other noise sources, their
acoustic properties and characteristics. Then it should be determined
that, how they interact to create the overall noise situation.
The design engineer should include noise studies in the design
stage of any industrial facility. If the acoustical problems are left for
field resolution, it costs roughly as much. Unnecessary costs
incurred in post-construction may include the replacement of
insulation, re-design of piping configuration to accommodate
silencers, modification of the equipment, additional labor costs and
possible down time for the plant to make necessary changes.
10. Patents
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A patent may be obtained on any new and useful process,
machine, method of manufacture, composition of matter or
plant, provided that it is not known or used by others before
the person applying for the patent made his invention or
discovery.
After a new design is developed application to Turkish
Patent Institution should be done. With necessary
investigations the institution determines the design as a
patent or not.
A patentee may treat the patent as personnel property with
the right to sell it or license it in any form desired.
The inventor can be paid by a lump sum, a periodic
payment, a percent of the profit, a set amount per each unit
produced or in any other way that is agreeable to the parties
involved.