Air Pollution Control Methods and Devices

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Questions and Answers

Which of the following processes is NOT a method used to control air pollution?

Desorption (correct)

Condensation

Absorption

Combustion

What is a key factor in determining the appropriate control device for particulate emissions?

Particle size and chemical characteristics (correct)

Moisture content

Stack pressure

Exhaust gas temperature

Which control device is specifically designed to remove small particles from an exhaust stream?

Gravity settler

Mechanical collector

Fabric filter (correct)

Hybrid system

What characteristic of exhaust gas is important for determining the required control efficiency of an air pollution device?

Total exhaust gas flow rate (A) Signup and view all the answers

Which of the following is NOT a typical control device for capturing gases?

Pressure cooker (C) Signup and view all the answers

Which factor is critical when planning the installation of air pollution control equipment?

Availability of space (A) Signup and view all the answers

Which device is a commonly used method to remove large particles from an exhaust stream?

Cyclone (B) Signup and view all the answers

What aspect of exhaust gas characteristics relates to how it interacts with other materials?

Corrosiveness (B) Signup and view all the answers

What is a primary source of particulate matter in air pollution from stationary sources?

Incomplete combustion of fuel (D) Signup and view all the answers

Which of the following is NOT typically emitted by fossil fuel-fired boilers?

Iron oxides (C) Signup and view all the answers

What type of emissions are associated with auxiliary losses in industrial processes?

Volatile organic solvents (C) Signup and view all the answers

What causes malodorous emissions in industrial settings?

Oxidation processes (A) Signup and view all the answers

Which of the following types of pollutants is commonly generated by metallurgical plants?

Iron oxides (A) Signup and view all the answers

Which statement accurately reflects atmospheric releases from industrial operations?

They can include secondary components and impurities. (A) Signup and view all the answers

What factor contributes to the variability in emissions from different industrial plants?

The type of product being manufactured (B) Signup and view all the answers

Which emissions are associated with the production of rayon?

Hydrogen sulfide and carbon disulfide (A) Signup and view all the answers

What is the primary function of an electrostatic precipitator (ESP)?

To remove small particles from moving gas streams (A) Signup and view all the answers

Which of the following describes a characteristic of an electrostatic precipitator?

Operates effectively only in dry conditions (A) Signup and view all the answers

What distinguishes the tubular configuration of ESPs from the more common plate type?

Tubular configurations have cylindrical tubes (A) Signup and view all the answers

In what situations are wet scrubbers particularly effective?

In the presence of corrosive and hot gases (D) Signup and view all the answers

Which feature is NOT associated with the operation of wet scrubbers?

Uses high-pressure air to accelerate liquid (D) Signup and view all the answers

What method is commonly used to remove collected particles in an electrostatic precipitator?

Rapping effects (C) Signup and view all the answers

What is a key advantage of combining a venturi scrubber with a cyclone scrubber?

Increased efficiency in removing particulates (A) Signup and view all the answers

What voltage range is typically associated with the electric potential of an ESP?

30-75 kV (B) Signup and view all the answers

What is a primary advantage of using gravity settlers in industrial applications?

They offer low initial cost and maintenance. (A) Signup and view all the answers

Which type of filtration system is similar to a conventional home vacuum cleaner?

Baghouse filters (B) Signup and view all the answers

Which material is NOT suitable for use in fabric filters?

Wet air and corrosive gases (D) Signup and view all the answers

What temperature limit does fiberglass have when used as a fabric filter material?

260 oC (D) Signup and view all the answers

In a baghouse, how do dirty gases typically flow in a suction type system?

Forced through the inside of the bags. (B) Signup and view all the answers

Which cleaning mechanism is NOT commonly associated with fabric filters?

Reversed gravity (A) Signup and view all the answers

What characterizes hybrid systems in air pollution control?

They combine different filtration and control mechanisms. (C) Signup and view all the answers

What is the efficiency rate of baghouse filters for particles greater than 5 μm in diameter?

<blockquote> 99.5% (C) </blockquote> Signup and view all the answers

Which hybrid system is suitable for removing fine particles effectively?

Electrostatically augmented fabric filtration (A), Wet electrostatic precipitators (C) Signup and view all the answers

What is the primary function of a cyclone in air pollution control?

To remove particles larger than 10 μm (A) Signup and view all the answers

What characteristic of cyclones makes them cost-effective in particle removal?

Their simple design without moving parts (D) Signup and view all the answers

In the cut diameter equation, what does $d_{0.5}$ represent?

The particle size collected with 50% efficiency (C) Signup and view all the answers

For standard cyclone operations, what particle size range do they effectively handle?

10 μm to 100 μm (A) Signup and view all the answers

What parameter is needed to calculate the cut diameter in the cyclone equation?

Dynamic viscosity of gas (B) Signup and view all the answers

How does the gas flow rate ($Q_g$) affect the efficiency of a cyclone?

Higher flow rates generally decrease removal efficiency (D) Signup and view all the answers

What is the effective number of turns ($ heta$) in the cyclone equation used to solve for?

The aspect ratio of the cyclone design (B) Signup and view all the answers

What is the primary purpose of thermal incinerators?

To destroy volatile organic compounds (VOCs) (D) Signup and view all the answers

Which of the following factors does NOT influence VOC destruction efficiency in thermal incinerators?

Type of incinerator used (D) Signup and view all the answers

At what temperature are thermal incinerators typically designed to operate?

650° to 1100°C (C) Signup and view all the answers

What is the nominal residence time recommended for commercial incinerators to ensure high destruction efficiency?

0.75 seconds (C) Signup and view all the answers

Which pollutant is primarily destroyed by thermal incinerators?

Volatile organic compounds (VOCs) (B) Signup and view all the answers

Which of the following is a common result of incomplete combustion in thermal incinerators?

Generation of soot and particulate matter (A) Signup and view all the answers

What is a key design criterion impacting thermal incinerator performance?

Degree of mixing of the waste gas (A) Signup and view all the answers

What is the maximum destruction efficiency achievable by thermal incinerators for VOCs?

99.9% (C) Signup and view all the answers

Study Notes

Air Pollution Control of Stationary Sources

Stationary sources of air pollution result from incomplete fuel combustion or industrial processes.
Pollutants emitted depend on the specific process operations.
Examples include ash, sulfur dioxide, nitrogen oxides, mercury, and vanadium (in fuel). Metallurgical plants may emit metal dusts (like iron oxides), fluorides, and chlorides. Industrial plants manufacturing inorganic chemicals emit various waste gases dependent on their product. Odorous organic waste gases may also come from organochemical and petrochemical plants.

Industrial Pollutant Sources Categorization

Process Operations: Incomplete chemical reactions (combustion due to unconverted reactants, or reaction yield less than theoretical conversion).
Atmospheric Releases: Process secondary components or impurities of raw materials.
Auxiliary Losses: Compounds like volatile organic solvents from fugitive sources, inorganics like carbon disulfide and hydrogen sulfide, and fluorine compounds (in aluminum production) in rayon production.

Waste Emissions

Emissions of malodorous and oxidation compounds from oxidation, heating, drying processes.
Releases may originate from various emission points and not be centrally collected.
Air release emission points from industrial processes: stack, duct, vent, fugitive, and area.
Fugitive emission points are unconfined in a stack or duct before reaching the atmosphere.

Industrial Process Operation Air Emission Points and Categories

Process Operations: Reactors vents, Distillation systems, Vacuum systems, Combustion stacks, Blow molding, Spray drying and booths, Extrusion machines
Surface Area Sources: Pond evaporation, Cooling tower evaporation, Wastewater treatment, Land disposal
Fugitive Sources: Valves, Pump seals, Flanges/connectors, Compressors, Open ended lines, Pressure relief devices, Equipment cleaning/maintenance, Handling, Storage, Loading, Storage tank breathing losses, Loading/unloading, Line venting, Packaging and container loading

Pollution Control

Effective pollution control achieved by common sense solutions: installation of effective control technology, changes in production processes, and pollution prevention techniques.
Compliance with emission standards depends largely on the application of appropriate stationary source control measures.

PM Control Procedures

Control procedures include using tall smokestacks, changes in plant operations, and installing effective control devices.
Industrial environmental impact control strategy is a four-step process: elimination of the problem source, modification of the source operation, relocation of the source, and selection/application of appropriate control technology.

Exhaust Stacks

Exhaust stacks elevate the exhaust stream.
This reduces the local effects of pollution by dispersing the emission more effectively.
High stacks were an inexpensive solution, reducing near-community impact.
However, it may transfer the problem to another location (like acid rain).

Plant Operations

Compliance with emission standards may require control technology.
Many industrial operations have reduced emissions by changing operational methods.
Pre-treating process materials/fuel, material substitution, changes in manufacturing, and coal washing to reduce particulate/sulfur emissions.
Substituting cleaner fuels during refining (like natural gas or low-sulfur fuel oil) can decrease pollution from combustion.

Plant Maintenance

Reduced emissions from stationary sources may be achieved through increased attention to plant maintenance.
Improperly maintained equipment (especially combustion equipment) can release significant pollutants into the environment..
Adequately scheduled maintenance for exhausts and fugitive emissions from vats, valves, and transmission lines.

Control Technology

Advanced add-on control technologies can destroy/recover gaseous/particulate matter for proper disposal or re-use.
Pollution control operations include combustion, adsorption, absorption and condensation.
Control devices include thermal incinerators, catalytic incinerators, flares, boilers, process heaters, carbon absorbers, spray towers, and surface condensers.
Important parameters for selecting equipment: exhaust gas characteristics (from emissions tests), and process/site characteristics (from field surveys).

Exhaust Gas Characteristics

Total exhaust gas flow rate, exhaust gas temperature, required control efficiency, particle size distribution, particle resistivity, composition of emissions, corrosiveness of exhaust gas over operating range, moisture content, stack pressure, exhaust gas combustibility/flammability properties.

Process or Site Characteristics

Reuse/recycling of collected emissions, availability of space, availability of additional electrical power, availability of water, availability of wastewater facilities, frequency of startup and shutdowns, environmental conditions, anticipated changes in control regulations/raw materials, plant type (stationary/mobile).

Control Devices for Particulate Emissions

Technologies for removing particles from effluent gas streams.
Factors determining the appropriate device: particle size and chemical characteristics.
Common devices: gravity settlers, mechanical collectors (cyclones), electrostatic precipitators (ESPs), scrubbers, fabric filters, and hybrid systems.
Combinations of devices improve collection efficiency.

Equipment: Gravity Settlers/Chambers

Industrial use for removing solid/liquid waste materials from gaseous streams.
Advantages: Simple construction, low initial cost, low pressure losses, easy waste disposal.

Equipment: Mechanical Collectors (Cyclones)

Centrifugal separators widely used for removing solid/liquid particles (particulates) from gas streams.

Equipment: Fabric Filters (Bag Houses)

Filtration processes of varying fabric types, cleaning mechanisms and equipment.
Gases can be "pushed" or "pulled" through the bag house.

Baghouse Filter

Efficiency: >99.5% for <1µm diameter particles, >99.8% for >5µm.
Similar to conventional home vacuum cleaners.

Fabric Filter Materials

Natural fibers (cotton, wool); synthetics (acetates, acrylics); fiberglass
Temperature limitations
Cannot be used for wet air systems, corrosive gases.

Hybrid Systems

Defined as using combinations of control mechanisms, often fabric filtration combined with electrostatic precipitation.
Major types include: wet electrostatic precipitators, ionizing wet scrubbers, dry scrubbers, and electrostatically augmented fabric filtration.

Cyclones

Used for 50-100 µm size particles and down to 10 µm.
Simple, economical, no moving parts, relies on inertial effects.

Electrostatic Precipitator (ESP)

High efficiency, dry collectors of particulates.
High electrical direct current potential (30-75 kV).
Tubular and plate configurations.

Electrostatic Precipitators (ESPs)

Satisfactory devices for removing small particles from gas streams with high collection efficiency.
Commonly used in power plants for removing fly ash from gases before discharge, also to remove chlorinated compounds

Wet Scrubbers

Suitable for wet environments, corrosive gases and high temperatures.
Combines a venturi scrubber, cyclone to achieve higher efficiency.

Scrubbers (Venturi Scrubbers)

Involves bringing contaminated gas streams into close contact with a liquid (usually water).
Used for removing particulate matter from a carrier gas stream.

Control Devices for Gaseous Emissions:

Thermal incinerators, catalytic incinerators, flares, boilers and process heaters, carbon adsorbers, absorbers, condensers.

Thermal Incinerator

Destroys volatile organic compounds (VOC) by controlled high-temperature burning of liquid, solid or gaseous waste.
High efficiency (up to 99.9% possible).

Applicable Pollutants

Primarily volatile organic compounds (VOC), some particulate matter (soot).
Efficiency results from design criteria (reaction temperature, time, inlet VOC concentration).

Catalyst Temperatures

Required temperatures (in °F) for 99.99% destruction of various compounds.

Flares

Last resort for disposing of gases with low value or flammability.
Used in refineries, production, and chemical industry.

Boilers and Process Heaters

Commonly used by production facilities for heat and power.
Recycling pollutants as fuel can help control emissions.
Only pollutants that don't affect burner performance can be used for fuel.

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Description

Test your knowledge on various methods and devices used in air pollution control with this quiz. Focus on understanding particulate emissions, control efficiency, and typical sources of air pollutants. Challenge yourself with questions about specific control devices and their applications.