Air Pollution Control

View A Video on Air Pollution Control - A Quick Introduction

Visit our Recycling Equipment page

To remain in compliance with federal emissions regulations, facilities must install emission control systems to keep air pollution output below levels specific to facility size and pollutant type. Oxidizers perform a process in which air pollutants such as hydrogen sulfide are broken up and reformed into safe, non-toxic carbon; this process, called oxidation, is performed by burning air pollutants and is at the heart of most of these systems. Depending on the type of air pollution being controlled, facilities may also use wet scrubbers or dry air scrubbers, mist collectors, electrostatic precipitators, odor control systems or simply air filtration systems. Automotive, agricultural, petrochemical processing, mining, pharmaceutical and most industrial manufacturing facilities require air pollution control systems to regulate air purity inside the facility and without. To recuperate the some of the cost of running this equipment, many manufacturers use heat recovery systems as well.

Oxidizers may be thermal or catalytic, using either high heat or elemental additives to catalyze oxidation, or burning of VOCs (which is one common method of VOC abatement). Catalytic oxidizers typically wash polluted air in platinum or palladium, causing oxygen to separate from VOCs and create non-toxic bi-products such as nitrogen and oxygen, as opposed to nitric oxide. Both catalytic and thermal oxidizers may be regenerative or recuperative. Recuperative oxidizers use ceramic heat transfer beds to recover as much energy as possible from the oxidization process -- often as much as 90% to 95%. These heat transfer beds act as heat exchangers, coupled to a retention chamber where the organics are oxidized. Regenerative thermal oxidizers recover up to 90-95% of the heat energy released from oxidation processes with ceramic heat transfer beds. Recuperative oxidizers use a plate, shell, tube or other conventional type of heat exchanger to preheat VOC-contaminated process gas in an energy recovery chamber. A catalyst - either heat or elemental additives - oxidizes the VOCs, which then release enough energy to allow self-sustained operation.

Non-oxidizing air pollution control equipment uses a variety of filtering methods to separate volatile organic and inorganic compounds from processed air. Air scrubbers may be dry scrubbers or wet scrubbers; dry scrubbers remove acid gases such as sulfuric oxide and hydrogen chloride using dry sorbent alkaline materials, while wet scrubbers clean flue gas of larger pollutants and dust using water or other liquid reagents. Electrostatic precipitators clean pollutants and dust particles from polluted air using electrical ionizing fields and tightly woven fabric filters to remove particulate from boiler flue gas and other process air. Electrostatic precipitators often filter process smoke, mist or other large liquid or solid particle contaminants in a process called mist collection. Mist collectors and oxidizers are often used as odor control systems for high methane producing facilities such as pulp and paper or livestock processing. Nitrogen oxide controls include the processes of selective catalytic reduction, which controls emissions of nitrogen oxides from stationary sources, and selective non-catalytic reduction, which changes oxides of nitrogen (NOx) into molecular nitrogen (N2). If VOCs have recovery value, carbon adsorption, scrubbing and condensation are typical techniques may recuperate materials. Thermal and catalytic oxidation and biofiltration are common VOC controls utilized when the VOC stream has no recovery value.
 
The Environmental Protection Agency has stipulated federal regulations regarding industrial facility air pollution emissions which limit the type and quantity of Volatile Organic Compounds and Hazardous Air Pollutants industrial manufacturing facilities may emit during processing. VOCs and HAPs pose threats not only to the safety of the environment and local ecosystems, but to human health as well. 188 HAPs have been regulated which are suspected or proven to cause cancer, birth defects and other serious health effects. Based on the federal regulations laid down in the Clean Air Act, the National Ambient Air Quality Standards (NAAQS) is a set of emissions standards based on scientific studies spanning several years designed to protect the health and safety of the environment and public. Most of these standards are recent, having been implemented only within the last ten to twenty years. Facilities may use data-providing Continuous Emissions Monitoring Systems (CEMS) to aid in the control, monitoring and reporting of pollutant emissions. VOC and HAP emissions have significantly decreased as a result of these strict regulations, but the emission of carbon, a non-volatile organic compound, is becoming of greater concern to environmentalists, lobbyists, state and federal legislators in recent years due to global climate change. Recent and proposed state and federal emissions regulations are beginning to concentrate on lowering carbon emissions further, a regulation which may require manufacturers to seek alternatives to oxidizers and incinerators.

Air Pollution Control Equipment and Air Pollution Control Images Provided by Air-Clear LLC	Air Pollution Control Equipment and Air Pollution Control Images Provided by Anguil Environmental Systems, Inc.	Air Pollution Control Equipment and Air Pollution Control Images Provided by APC Technologies, Inc.

---

Air Pollution Control Equipment Types

• Air filtration systems remove impurities from the air with a number of different filtration and purification schemes.
• Air scrubbers consist of a fan containing several filters that separate contaminants from clean air and recirculate the air into the atmosphere.
  
• Catalytic oxidizers utilize a metal catalyst, such as platinum, within the unit to speed the break down of hazardous compounds. The use of a catalyst allows the substance breakdown to occur at a lower temperature than that of a thermal oxidizer.
  
• Dust collectors use an online process to either retrieve usable granular solid or powder from process streams or to eliminate granular solid pollutants from exhaust gases before they are vented into the atmosphere.
  
• Electrostatic precipitators utilize grounded electrodes called collection plates to ionize and capture dust and particulate matter in contaminated air. These systems are often used prior to other pollution control equipment.
  
• Emission control systems are devices that monitor and diminish harmful byproducts of combustion and other processes.
• Gas scrubbers use a high-energy liquid spray to remove gaseous pollutants, such as sulfur, from an air stream, either by absorption or chemical reaction.
  
• Heat recovery systems includes any method that recaptures heat generated as the byproduct of one process and reuses it for another process.
• Ionizing wet scrubbers remove acid gases and fine particulate that can include a variety of heavy metals such as antimony, lead and zinc from the air stream.
  
• Mist collectors, which consist of a filter containing mesh and steel wire, capture mists of water and oil created during industrial applications.
  
• Odor control systems neutralize unpleasant smelling gases.
  
• Oxidizers are chemicals that readily yield oxygen and can be used to start or to feed fires.
  
• Particulate control systems utilize systems, such as electrostatic precipitators (ESPs), baghouses, wet particulate scrubbers, mechanical/inertial collectors (cyclones/mutilcyclones) and high temperature/high pressure (HTHP) particulate control systems, to control ash that is emitted into the atmosphere through combustion, industrial processes, fugitive emissions and natural sources.
  
• Pollution control equipment is any device that removes and eliminates a wide variety of impurities from the air.
• Rotary concentrators compress air and gas streams containing small amounts of VOCs into concentrating streams containing greater volumes of VOCs, which makes it easier for oxidizers to break down.
  
• Thermal oxidizers heat contaminated air in order to break down hazardous compounds into carbon dioxide and water vapor, a process called oxidation. In order to conserve energy, many thermal oxidizers contain a heat exchanger (http://www.heatexchangers.org) that recovers and reuses the heat from incoming polluted air.
  
• Venturi scrubbers are wet scrubbers that collect extremely tiny (less than a micron) dust particles from the gas stream in a slurry system using an orifice to spray water into the vortex in the cyclone section.
  
• VOC abatement is a process in which VOCs are rendered inert by removing them from the point of generation, subjecting them to high temperature and long residence time and then discharging the resulting treated gas into atmosphere.
  
• VOC destruction is the oxidation process in which VOCs are heated by incineration or subjected to microorganisms (biodegradation) to produce carbon dioxide and water.
  
• Wet Scrubbers are devices in which exhaust air is forced into a spray chamber wherein the water particles cause the dust to drop from the air stream.
  

---

Air Pollution Equipment Terms

Adsorption - The attachment of concentrated liquid or gaseous molecules to a solid or liquid surface. Unlike absorption, the substances, such as active carbon and silica gel, do not permeate one another.
 
Baghouse (Fabric Collector) - Dust collector (http://www.iqsdirectory.com/dust-collection) containing fabric bags, which trap dust while allowing gases to move through the collector.

Certified Energy Manager (CEM) - International professional designation available through training and testing by the Association of Energy Engineers (AEE).

CFC (Chlorofluorocarbon) - Family of chemicals used as refrigerants, being tightly regulated and phased out of production due to stratospheric ozone depletion potential. Examples: R-11, R-12, R-113, R-114, R-115.
 
Cyclone Separator - Device that extracts fine particles from air or gas by centrifugal means.
 
Destruction Efficiency - The effectiveness by which an oxidizer eliminates VOCs exhausted from by the oxidization process.
 
Hazardous Air Pollutant (HAP) - A specific category of 189 particularly harmful volatile organic compounds (VOCs) designated as such by the EPA's Clean Air Act.
 
Heat Exchanger Bypass - A system that will automatically modulate dampers in a thermal oxidizer to provide a safe route for the process exhaust in case there is a solvent overload.
 
Hydrocarbon - An organic compound composed of hydrogen and carbon. Many hydrocarbons are considered stable, as they only evaporate during heating and cooling processes, though some are considered volatile, because they evaporate under moderate conditions.
 
HEPA (High Efficiency Particulate Air) Filter - Air filter capable of trapping a minimum of 99.97% of particles at least .3 microns in size. HEPA filters are a common component of air scrubbers.
 
Hopper - In pollution control systems, the area in which the collected particulate is stored.
 
Lower Explosive Limit (LEL) - The lowest concentration of pollutants that would lead to combustion if ignited.
 
Nitrogen Oxides (NOx) - A group of air pollutants released during industrial combustion applications that contribute to smog and acid rain.
 
Oxidation - Process involving the transformation of harmful compounds into safer compounds through the application of oxygen and heat.
 
Rapper - Part of an electrostatic precipitator that transfers dust from the collection plates to the hopper.
 
Rotor Concentrator - An add-on available for oxidation technology that reduces air volume and increases concentration of VOCs by directing the process stream through a continuously rotating wheel impregnated with adsorbent. The VOCs are adsorbed, the clean air is exhausted into the atmosphere and the wheel is then regenerated by passing through a stream of warm, low volume desorption gas, producing a concentrated stream, which an oxidizer can more efficiently destroy.
 
Tubular Precipitators - High-voltage electrostatic precipitators consisting of cylindrical collection plates that rotate around the discharge electrodes.
 
Turbulence - A fixed condition that is built into the equipment design in order to make sure that there is the correct mix of VOCs and oxygen for combustion.
 

Volatile Organic Compounds (VOCs) - A group of pollutant compounds consisting primarily of carbon that, in combination with the sun's radiation and oxygen, form ozone. VOCs are those substances, such as gasoline, alcohol, ethers and esters, that form a gas or vapor under moderate temperature and pressure conditions.

---

---