Air Pollution Control Equipment Quiz

Air Pollution Control of Stationary Sources

• Stationary sources of air pollution often result from incomplete fuel combustion or industrial processes.
• The types of pollutants emitted depend on the specific process.
• Examples of pollutants from fossil fuel boilers include ash, sulfur dioxide, nitrogen oxides, mercury, and possibly vanadium.
• Metallurgical plants may emit metal dusts like iron oxides, sometimes fluorides, and chlorides.
• Industrial plants producing inorganic chemicals release various gases depending on their product.
• Odorous organic waste gases can also come from organochemical and petrochemical plants.

Industrial Pollutant Sources

• Industrial pollutant sources can be categorized based on their process operations.
• Process Operations: Characterized by incomplete chemical reactions, leading to unconverted reactants or reaction yields lower than theoretical maximum.
• Atmospheric Releases: Results from the release of process secondary components or impurities from raw materials.
• Auxiliary Losses: Losses of compounds like volatile organic solvents, carbon disulfide, hydrogen sulfide, and fluorine compounds during various industrial processes.

Waste Emissions

• Emission points can originate from multiple points and may not be centrally collected.
• Air release points (e.g., stack, duct, vent) are categorized and can be fugitive or area point sources.
• Fugitive points are not confined by stacks or ducts before entering the atmosphere.
• Whether a source is considered a point or fugitive depends on emission confinement.

Industrial Process Operation Air Emission Points

• A table categorizing process operations and fugitive sources.
  • Process Operations: Reactors, distillation systems, vacuum systems, combustion stacks, blow molding, spray drying equipment, and extrusion machines
  • Fugitive Sources: Valves, pump seals, flanges, connectors, compressors, open-ended lines, pressure relief devices, equipment cleaning, handling, storage, loading, storage tank breathing losses, loading/unloading, line venting, packaging and container loading, surface area sources

Pollution Control

• Pollution control can include the implementation of effective control technology, changes in production processes, and pollution prevention measures.
• Compliance with emission standards depends on effectively applying appropriate stationary source control measures.

PM Control Procedures

• Control procedures for stationary pollution sources may involve using tall smokestacks, plant operation adjustments, and effective control devices.
• A four-step control strategy for industrial impacts may include eliminating the problem source, modifying it, relocating it, and choosing the right control technology.

Exhaust Stacks

• Exhaust stacks elevate emissions to disperse them more effectively, reducing local pollution impact.
• In the past, elevated stacks prevented nearby communities from experiencing pollutant impacts, despite not eliminating the problem but transferring it.
• Some concerns about regional and transboundary effects like acid rain led to shift in pollution control strategies.

Plant Operations

• Operational changes like pre-treating process materials, fuel or material substitutions, and modifications to manufacturing processes can reduce pollutant emissions.
• Coal washing is an example of pre-treatment to reduce particulate matter and sulfur emissions from coal.
• Clean fuel substitution during refining (e.g., natural gas, low-sulfur fuel oil) is another pollution control measure.

Plant Maintenance

• Plant maintenance plays a crucial role in reducing emissions from stationary sources.
• Improperly maintained equipment, particularly combustion equipment, frequently leads to significant pollutant releases.
• Scheduled maintenance for vats, valves, transmission lines helps reduce fugitive and exhaust emissions and prevent accidents.

Control Technology

• Advanced control technologies involve devices to destroy or recover gaseous/particulate matter.
• Controlling operations can include combustion, adsorption, absorption, and condensation.
• Control devices include thermal incinerators, catalytic incinerators, flares, boilers, process heaters, carbon absorbers, spray towers, and surface condensers.
• Selecting proper equipment depends on exhaust gas characteristics (flow rate, temp., efficiency, particle size & distribution), process, and site characteristics.

Exhaust Gas Characteristics

• Exhaust gas flow rate, temperature, control efficiency, particle size, distribution, particle resistivity, emission composition, corrosiveness, moisture, stack pressure, and combustibility/flammability properties.

Process or Site Characteristics

• Reuse/recycling of collected emissions, availability of space, electrical power, water, wastewater treatment facilities, frequency of start/stop, environmental conditions, control regulation changes, and raw material changes.

Control Devices for Particulate Emissions

• Technologies for controlling particulate matter aim to remove particles from exhaust streams.
• The choice for an appropriate device depends on various factors (e.g., particle size, composition).
  • Devices used include: gravity settlers, mechanical collectors (cyclones), electrostatic precipitators (ESPs), scrubbers, fabric filters, and hybrid systems.
  • Combining multiple devices often yields the best efficiency.

Equipment: Gravity Settlers/Chambers

• Gravity settlers/chambers, used industrially, remove solid/liquid waste from gas streams.
• Simple construction, low cost, maintenance, and waste disposal are their advantages

Equipment: Mechanical Collectors/Cyclones

• Centrifugal separators, commonly known as cyclones, are employed in industry to remove solid/liquid particles from gas streams.

Equipment: Fabric Filters/Bag Houses

• Filtration processes use various fabric filter types.
  • Differences include fabric type, cleaning mechanism, and equipment
  • Operation can be either push or pull through the bag house

Baghouse Filter

• Efficiency is similar to a home vacuum cleaner (e.g., >99.5% for <1 µm particles).
• Materials used for filters include natural fibers, synthetics, and fiberglass.
• Cleaning methods include shaker, reverse air, and pulse jet.

Hybrid Systems

• Hybrid systems combine various control mechanisms like fabric filtration and electrostatic precipitation.
  • Examples currently used include: wet electrostatic precipitators, ionizing wet scrubbers, dry scrubbers, and electrostatically augmented fabric filtration.

Cyclones

• Cyclones, economical devices, remove 50-100µm size particles, with simple designs and no moving parts; they rely on inertia.
• Their effectiveness extends to particles as small as 10µm.

Electrostatic Precipitator (ESP)

• High-efficiency, dry collectors for particulates.
• High electrical direct current potential (30-75 kV) used to charge particles that are then collected on plates and removed.
• Two common types: tubular, and plate.

Electrostatic precipitators (ESPs)

• Satisfactory for removing small particles from moving gas streams, commonly used in power plants to remove fly ash.
• Two types: tubular (cylindrical collection tubes) and plate (vast majority of installed).
• Removal occurs primarily through rapping.

Wet Scrubbers

• Used when air conditions are wet, corrosive, or hot.
  • Baghouses cannot be applied under these conditions.
  • Enhanced efficiency achieved in combination with a venturi scrubber and a cyclone.

Scrubbers (Venturi Scrubbers)

• Wet scrubbing involves bringing contaminated gas streams into intimate contact with liquids (usually water).
• This method is used to remove particulate matter from a carrier gas stream through gas absorption.

Comparison of Air Pollution Control Devices

• A graph comparing removal efficiency against particle size for various devices (settling chambers, simple cyclones, high-efficiency cyclones, ESPs, spray tower wet scrubbers, venturi scrubbers, and bag filters).

Effectiveness of Air Pollution Control Devices

• A diagram showing different control devices with their corresponding pollutant size ranges.

Gaseous Emissions Control

• The preferred method for controlling gaseous pollutants is using add-on devices for pollutant destruction or recovery.
• Control equipment includes thermal incinerators, catalytic incinerators, flares, boilers, process heaters, carbon absorbers, absorbers, and condensers.

Thermal Incinerator

• Used for destroying volatile organic compounds (VOCs) and waste by controlled high-temperature burning.
• High efficiency (up to 99.99%).

Catalytic Incinerator

• Similar to thermal incinerators but use catalysts to increase oxidation reaction rates at lower temperatures, leading to lower operating costs and smaller system size.
• Catalysts commonly used include platinum and palladium.

Flares

• Used as a last resort for disposing of gases with low recyclable value, or not easily combustible.
• Common in refineries, petroleum production facilities, and chemical plants to manage low MW VOCs

Boilers and Process Heaters

• Typically used for heat production.
• Useful in recycling pollutants with high heating values and sufficient amounts into combustion process (only for those that do not affect burner performance).