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FOOD ENG I NEER I NG DES I GN AND ECONOM I CS CHAPTER II GENERAL CONSIDERATIONS IN A PLANT DESIGN Plant location Plant layout Plant operation and control Utilities Structural design Storage Materials handling Waste disposal Health and safety Patents Plant Location

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general considerations in a plant design
GENERAL CONSIDERATIONS IN A PLANT DESIGN
  • Plant location
  • Plant layout
  • Plant operation and control
  • Utilities
  • Structural design
  • Storage
  • Materials handling
  • Waste disposal
  • Health and safety
  • Patents
slide3
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.

slide4
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
slide5
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.

slide6
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.

slide7
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.

slide8
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.

slide9
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.

slide10
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.

slide11
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.

slide12
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.

slide13
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.

slide14
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.

slide15
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.

2 plant layout
2. Plant Layout
  • 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”
slide20
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.

slide21
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.
slide22
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. Three-dimensional models are also beneficial for orientation after the plant is completed.

+ “empty area”

slide23
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.
slide24
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.
slide25
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
3. Plant Operation and control
  • 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.
slide27
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.

slide28
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
4.Utilities
  • 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.
slide30
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
5. Structural Design
  • 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.
slide32
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.
  • 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.
slide33
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.
slide34
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
6. Storage
  • 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.
slide36
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.
slide37
in all storage areas;
  • 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.
7 materials handling
7. Materials Handling
  • 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.
      • 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.
slide39
Factors that must be considered in selecting such equipment include:
  • Chemical and physical nature of material being handled
  • Type and distance of movement of material
  • Quantity of material moved per unit time
  • Nature of feed and discharge from materials handling equipment
  • 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.

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
8. Waste Disposal
  • 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
    • 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 control device
    • 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.
slide41

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.
slide42
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.
slide43

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.

  • 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.
slide44
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.

slide45
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;
      • 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.
slide46
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:
    • 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 solutionflows 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;

    • 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.
slide47
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
    • 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 de-ionized 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)
slide48
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 pre-concentrated with RO from 6% total solids to 10-20% total solids beforeultrafiltration(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.
slide49
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.
slide50
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.

slide51
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)

slide52
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.

slide53
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 aerobic-anaerobic 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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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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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 extra-cellular 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.

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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.

  • 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 aprocess 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.

  • 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
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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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;

  • External plant considerations
  • Internal plant structure and service considerations
  • In-plant physical and organizational considerations.
9 health and safety
9. Health and Safety
  • 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
10. Patents
  • 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.