Which Air Pollution Control Method is Most Effective?
Category: Air Pollution Control Methods | 17/02/2009 - 15:05:00
Concerns about global air pollution levels are increasing, and for business owners feeling the pressure, the growing area of air pollution control can be pretty cloudy itself. Enviro News explores the day-to-day methods available to modern industries to help minimise air pollution using practicable systems.
Volatile Organic Compounds (VOCs)
One of the major causes of both indoor and outdoor air pollution are Volatile Organic Compounds (VOCs). VOCs are found within a wide range of consumer products, including solvent-based paints, printing inks and petrol products. Due to the proven contribution of VOCs to air pollution (and ultimately smog) VOC control regulations are enforced around the world to protect the environment against them.
Activated Carbon is a popular air pollution control method. One of the most common forms of carbon treatment in air pollution control is carbon adsorption. This method sees the use of dry chemical scrubbing media such as carbon filters for the adsorption of fumes from the air.
Biofilters: Clearing the Air
Biofiltration is a method of pollution control in which process pollutants are biologically degraded using microorganisms. The most common air pollution control application of biofilters is the microbiotic oxidation of contaminants in the air. Biofilters use living materials to degrade pollutants when immobilized in the biofilm. Applications of this method include treatment of the off-gas from wastewater treatment plants, after painting and during the manufacture of food products.
Although capable of treating large airflows, one of the disadvantages of biofilters is the requirement of a large amount of physical space. In recent years efforts have been made to reduce the amount of space needed, meaning that footprint reductions have been seen.
Various systems are used to ensure that sufficient moisture levels are maintained throughout the system. Air is humidified before entry to the bed using humidification chambers, bioscrubbers and water spray systems. Biofilters are cost-effective and straightforward options for pollutants capable of biodegrading reasonably easily. The absence of further pollution from biofilters is another positive associated with this method of air pollution control.
Driving Towards Cleaner Emissions
Car engine emissions are recognized as one of the leading causes of air pollution. Catalytic Oxidizers are placed in the exhaust system of cars to reduce emissions from the exhaust pipe. The ideal byproducts of a car’s engine are carbon dioxide, some water and nitrogen. However in reality engines continue to release unburned hydrocarbons which damage the environment. Catalytic oxidizers now oxidize many of the unburnt hydrocarbons from an engine, leading to cleaner emissions from cars.
The Big Problem: CO2 Emissions
One of the challenges associated with catalytic oxidizers is the necessary operation speed to catch the unburnt hydrocarbons before they leave the exhaust pipe. Standards of catalytic oxidizers are increasing each year, although carbon dioxide emissions still pose a problem. It is not possible to oxidize CO2 emissions into anything less harmful to the environment.
We’ve all seen Gas Flares (or flare stacks) burning off unwanted substances and releasing them into the environment. Gas flares burn excess and flammable gases and liquids from plant equipment in an elevated chimney.
Examples of gas flare usage include chemical plants, landfills and oil rigs. Their most common purpose is to protect against unplanned over-pressuring of the plant equipment. The gases we see leaving the chimneys are released automatically whenever any piece of plant equipment becomes over-pressurised. The released substances are burned as they exit the flare stacks.
One of the world’s largest gas flaring sites (and a major source of concern for environmentalists) is the Niger Delta, which sees more natural gas flaring during crude oil production than any other country.
Air Pollution vs Noise Pollution
Efforts have been made to reduce the impact of gas flares on air pollution levels. The injection of steam into the flame can serve to reduce the amount of black smoke released during gas flaring, although one problem with this is an increased level of noise during the burning which can lead to complaints from those living within earshot. Some environmentalists argue that this is an easy choice to make in light of the urgency to lower air pollution levels.
Acid Gas Control - SO2
Several systems for dry scrubbing are available, including Spray Dryer Absorbers (SPAs) and Dry Sorbent Injectors (DSIs). Usually known as spray dryers, SPAs remove the presence of acid gases from the environment through absorption in the dryer.
Wet or Dry Scrubbers?
DSIs are mainly used in medical waste applications and involve the injection of an alkaline into a gas stream. This causes a reaction to create solid salts which can then be removed. The ability of DSIs to reduce air pollution is limited in the less advanced systems.
Dry scrubbers are ideal for air pollution reduction applications in which the lowest level of water involvement is vital. They are particularly suited to the removal of aerosol mist, metal finishing and battery wet and dry charging.
Whilst dry scrubber methods do not rely on saturation of the gas stream, wet scrubber air pollution control methods see contact between the stream of polluted gas and a scrubbing liquid. The gas is stripped of its pollutants as it is pushed through the liquid.
Advantages associated with wet scrubbers in air pollution control applications include their capacity to withstand high temperatures and moisture levels, they necessitate a smaller operating space due to compact equipment and they have the ability to neutralize corrosive gases. Applications of wet scrubbers include exhaust cleaning, the treatment of industrial process gas streams and the incineration of medical waste.
Drawbacks of this method include corrosion and the requirement of treatment on the spent liquid. Worth noting, is the fact that the disposal of the water must be handled according to the current wastewater regulations, which can be time consuming. Additionally, the need for high pressure during operation makes the powering of wet scrubbers costly for businesses.
Inspection of the various VOC control solutions available demonstrates that whilst there are plenty of options, none of them are flawless. Advice on the best VOC control solution for the individual business can be gained by contacting suppliers with the working knowledge of air pollution reduction technology to help you make the right choice - both for your business and the environment.