Air Pollution Control Technology

Dr. Alex London, P.E.
January 1, 2006

Requirements
With the passage of clean air legislation and increased scrutiny of air emissions by federal, state and local regulatory agencies, well-designed and maintained air pollution control (APC) devices are no longer optional but mandatory. The greatest reason for developing and applying high efficiency APC technology is the tightening emission standards for Toxic Air Compounds.

State, regional and local regulations concentrate on both quantities of particulate emissions and opacity (or visibility) of stack exhausts. To meet current emission regulations, industrial and commercial technology must be equipped with high-efficiency emission control devices.

Criteria for APC equipment selection.
General

·  Expedient design and engineering, which decreases a size of the APC system..

·  Air cleaning efficiency

·  Initial costs of the APC system.

·  Maintenance, which represents the most laborious, unpleasant and time-consuming job: cleaning, costly repair, shutdowns and troubleshooting.

·  Operating costs.

·  Structural and space requirements for APC system.

Energy Conservation and Saving on:

·  Air pollution prevention by manufacturing process modernization.

·  Fuel consumption for contaminants burning.

·  Cooling for vapor condensing.

·  Energy for operating compressors, pumps, scrapers, etc.

·  Costs of filters replacement, water treatment chemicals, disposal, etc.

Safety:

·  Fire and explosion hazard prevention.

·  Smog removal provisions.

·  Preventing residues accumulation in local exhausts, ducts and fans, on the roof, etc.

Environmental

·  Water pollution prevention.

·  Noise and vibration attenuation.

·  Healthy conditions in the breathing zones and working places.

Recycling of trapped contaminants.

Bags or other types of dry filters entrap matter, which is exposed on them directly to fire or explosion hazard. All sprinklers should operate to control potential fires; the filters should not be used with spontaneous ignitable materials. Loaded filters reduce the exhaust air flow capacity. As result, filter materials must be replaced or cleaned. Non-uniform airflow creates turbulence and could increase pollutant concentration to exceed permitted levels.

Afterburners require a high initial investment in hardware, fuel gas line and electrical component wiring. The units have been unreliable in operation, often provoking major public relation problems concerning smoke and fire hazards. They also reduce cost-efficiency because of ongoing expenses for repair, parts and labor. Furthermore, high fuel gas consumption has become even more financially debilitating as energy prices rise.

Electrostatic precipitators are the most expensive devices. There are very few operators who can afford to keep these systems functioning and still maintain their profit margins. Their initial costs become insignificant when compared to the ongoing maintenance costs. Precipitators also are not applicable for contaminants with low electrical resistivity.

Catalytic and thermal oxidizers are a well-known and accepted method of handling hydrocarbon off-air treatment and destroying contaminants. Actual operating temperatures are typically 600˚F to 900˚F for catalytic incineration, and 1,350˚F to 2,000˚F for thermal incineration. However, they do require routine maintenance and troubleshooting by an experienced technician or engineer. Some oxidizers also have been known for short durability – about five years on average. They require a supplemental heat source, hot water-detergent solution and a fire hazard prevention system. Efficiency deteriorates over time and periodic element replacement is required. Finally, performance of the catalyst can be seriously affected by materials such as mercury, arsenic, zinc and lead that can poison it.

Wet collectors use water droplets formed by spray nozzles to remove pollutants. Encompassing a fairly diverse group of similar technologies, wet collectors have been used for air treatment for more than a century. The systems still have problems with clogs in piping, nozzles and/or pumps, troublesome sludge handling, and hazardous water pollution.

All of the above systems are complicated, have high initial capital costs and maintenance expenses. There continues to be a worldwide effort to develop an improved APC system that can overcome these problems. But until recently, most new technologies were basically minor refinements of the same old systems.

London Falls^TM is, in principle, different type of the Air Pollution Control Technology.

It consists of an air turbo-impactor (ATI) and an open sludge collector (SC) – just two welded sheet metal boxes, filled with liquid to the predetermined level. 

The ATI combines several principles of air cleaning: venturi, impaction, centrifugal separation, intermixing and abrupt expansion outlet.

The working substance can be water, oil, alkali, or other different chemical or physical solutions.

Sludge removal does not require draining the entire system; it cuts down on water pollution problems significantly.

The system provides air purification, liquid recirculation, safe contaminant containment, fire and explosion prevention, fire suppression, emergency smoke removal, resource and heat recovery, and water pollution prevention, without requiring power, moving or removable parts, pumps, nozzles, filters, valves, etc.

It requires little floor space and only the fluid levels need to be maintained.

Also, in compliance with NFPA-96, the ATI is “not restricted by covers, dampers or any other means which would reduce the operating efficiency of the exhaust system.” The systems satisfy EPA, OSHA, NFPA and other pertinent regulations.

The aerodynamic force of the exhausting air circulates a liquid-fall capture system in the ATI. Centrifugal force is exerted by rapid changes in flow direction, causing contaminants to precipitate and become permanently trapped. Clean air then leaves the ATI, while entrapped matter flows into the open SC. A quiet liquid flow assists in clarifying the liquid, which flows into the ATI for the next air cleaning cycle.

The technology is a big part of future air pollution control across a number of industries.

Literature:

• Air Pollution Engineering Manual, U. S. Environmental Protection Agency
• Air Pollution Engineering Manual, Air & Waste Management Association.
• Industrial Ventilation, American Conference of Governmental Hygienists.
• ASHRAE HANDBOOK, Equipment.
• HVAC Duct System Design, SMACNA.
• Air Movement and Control Association.
• NFPA.
• Foundamentals of Industrial Ventilation, Dr. V. V. Baturin, Moscow PROMISDAT