بنام خدا

1. بنام خدا با سلام

2. انتظار میرود دانشجو در پایان جلسه بتواند: 1- اساس كار رسوب دهنده هاي ثقلي را شرح دهد. 2- اساس كار سيكلونها را توضيح دهد. 3- اساس كار الكترو فيلترها را توضيح دهد. 4- اساس كار فيلترهاي پارچه اي را شرح دهد. 5- مزايا و معايب دستگاههاي فوق را بيان كند.

3. AIR POLLUTION CONTROL Environment technologies 2. AIR POLLUTION CONTROL

4. AIR POLLUTION CONTROL Environment technologies • CONTENTS • Background • Equipment • Techniques • Factors • Selecting technology

5. AIR POLLUTION CONTROL Environment technologies • BACKGROUND • Controlling the emission of pollutants from industrial and domestic sources is important in protecting the quality of air. Air pollutants can exist in the form of particulate matter or as gases. • Air cleaning devices have been reducing pollutant emissions from various sources for many years. • Originally, air cleaning equipment was used only if the contaminant was highly toxic or had some recovery value.

6. AIR POLLUTION CONTROL Environment technologies • EQUIPMENT • Equipment used to control particulate emissions are: • Gravity settlers (often referred to as settling chambers) • Mechanical collectors (cyclones) • Electrostatic precipitators (ESPs) • Scrubbers • Fabric filters • Hybrid systems

7. AIR POLLUTION CONTROL Environment technologies • EQUIPMENT • Gravity settlers (often referred to as settling chambers) • Gravity settlers, or gravity settling chambers, are used industrially for the removal of solid and liquid waste materials from gaseous streams. • Advantages accounting for their use are simple construction, low initial cost and maintenance, low pressure losses, and simple disposal of waste materials. • Mechanical collectors (cyclones) • Centrifugal separators, commonly referred to as cyclones, are widely used in industry for the removal of solid and liquid particles (or particulates) from gas streams.

8. AIR POLLUTION CONTROL Environment technologies • EQUIPMENT • Electrostatic precipitators (ESPs) • They are satisfactory devices for removing small particles from moving gas streams at high collection efficiencies. They have been used almost universally in power plants for removing fly ash from the gases prior to discharge. • Two major types of high-voltage ESP configurations currently used are tubular and plate. Tubular precipitators consist of cylindrical collection tubes with discharge electrodes located on the axis of the cylinder. Vast majority of ESPs installed are of the plate type. • Collected particles are usually removed by rapping.

9. AIR POLLUTION CONTROL Environment technologies • EQUIPMENT • Scrubbers (venturi scrubbers) • Wet scrubbing involves the technique of bringing a contaminated gas stream into intimate contact with a liquid. • Wet scrubbers include all the various types of gas absorption equipment. • The term "scrubber" will be restricted to those systems which utilize a liquid, usually water, to achieve or assist in the removal of particulate matter from a carrier gas stream.

10. AIR POLLUTION CONTROL Environment technologies • EQUIPMENT • Fabric filters (bag houses) • Filtration process may be conducted in many different types of fabric filters.Differences may be related to: • Type of fabric • Cleaning mechanism • Equipment • Mode of operation • Gases to be cleaned can be either "pushed" or "pulled" through the bag house. • In the pressure system (push through) the gases may enter through the cleanout, hopper in the bottom or through the top of the bags. • In the suction type (pull through) the dirty gases are usually forced through the inside of the bag and exit through the outside.

11. AIR POLLUTION CONTROL Environment technologies • EQUIPMENT • Hybrid systems are defined as those types of control devices that involve combinations of control mechanisms-for example, fabric filtration combined with electrostatic precipitation. • Four of the major hybrid systems found in practice today include: • Wet electrostatic precipitators, • Ionizing wet scrubbers, • Dry scrubbers, and • Electrostatically augmented fabric filtration.

12. AIR POLLUTION CONTROL Environment technologies Absorption Combustion Condensation • TECHNIQUES • Applicability of a given technique depends on the physical and chemical properties of the pollutant and the exhaust stream. • More than one technique may be capable of controlling emissions from a given source • Techniques used to control gaseous emissions are: Adsorption

13. AIR POLLUTION CONTROL Environment technologies • TECHNIQUES • Absorption • Mass transfer operation in which a gas is dissolved in a liquid. • A contaminant (pollutant exhaust stream) contacts a liquid, and the contaminant dif­fuses from the gas phase into the liquid phase. • The liquid most often used for absorption is water. • Reagents can be added to the absorbing water to increase the removal efficiency of the system. Gas absorbers or wet scrubbers are designed to provide good mixing of the gas and liquid phases. • The devices used for gas absorption are often the same as those used in particulate emission scrubbing. • These include packed towers, plate towers, spray columns, and venturi scrubbers.

14. AIR POLLUTION CONTROL Environment technologies • TECHNIQUES • Adsorption • Mass transfer process that involves removing a gaseous contaminant by adhering it to the surface ofa solid. • It can be classified as physical or chemical. In physical adsorption, a gas molecule adheres to the surface of the solid due to an imbalance of natural forces (electron distribution). • In chemisorption, once the gas molecule adheres to the surface, it reacts chemically with it. • The major distinction is that physical adsorption is readily reversible whereas chemisorption is not.

15. AIR POLLUTION CONTROL Environment technologies • TECHNIQUES • Combustion • Combustion is defined as rapid, high-temperature gas-phase oxidation. • Simply, the contaminant (a carbon-hydrogen substance) is burned with air and converted to carbon dioxide and water vapor. • The operation of any combustion source is governed by the three T's of combustion; temperature, turbulence, and time. • Combustion devices can be categorized as flares, thermal incinerators, or catalytic incinerators

16. AIR POLLUTION CONTROL Environment technologies • TECHNIQUES • Condensation • Process in which the volatile gases are removed from the contaminant stream and changed into a liquid. • It is usually achieved by reducing the temperature of a vapor mixture until the partial pressure of the condensable component equals its vapor pressure. • Requires low temperatures to liquefy most pure contaminant vapors. • It is affected by the composition of the contaminant gas stream. • Condensers are normally used in combination with primary control devices. • Condensers can be located upstream of (before) an incinerator, adsorber, or absorber.

17. AIR POLLUTION CONTROL Environment technologies Economic Environ mental Engineering • FACTORS • There are a number of factors to be considered prior to selecting a particular piece of air pollution control hardware.

18. AIR POLLUTION CONTROL Environment technologies Environ mental • FACTORS • Environmental factors • Equipment location • Available space • Ambient conditions • Availability of adequate utilities (i.e., power, water, etc.) and ancillary system facilities (i.e., waste treatment and disposal, etc.) • Maximum allowable emissions (air regulations) • Aesthetic considerations • Contribution of air pollution control system to wastewater and solid waste • Contribution of air pollution control system to plant noise levels

19. AIR POLLUTION CONTROL Environment technologies Economic • FACTORS • Economic • Capital cost (equipment, installation, engineering, etc.) • Operating cost (utilities, maintenance, etc.) • Expected equipment lifetime and salvage value

20. AIR POLLUTION CONTROL Environment technologies Engineering • FACTORS • Engineering • Contaminant characteristics (i.e., physical and chemical properties, concentration, particulate shape and size) • Gas stream characteristics (i.e., volume flow rate, temperature, pressure, humidity, composition, viscosity, density, reactivity, combustibility, corrosivity, toxicity, etc.) • Design and performance characteristics of the particular control system(i.e., size and weight, fractional efficiency curves, etc)

21. AIR POLLUTION CONTROL Environment technologies • SELECTING TECHNOLOGY • Final choice in equipment selection is usually dictated by that equipment capable of achieving compliance with regulatory codes at the lowest uniform annual cost (amortized capital investment plus operation and maintenance costs). • In order to compare specific control equipment alternatives, knowledge of the particular application and site is essentials. • A preliminary screening, however, may be performed by reviewing the advantages and disadvantages of each type of air pollution control equipment.