Effective NOX Pollution Control and Removal Techniques
July 28, 2020 Welcome
Much of the industrial process equipment today uses fossil fuels and hydrocarbons to drive their processes. The combustion of hydrocarbons in the air usually produces a mixture of gaseous nitrogen compounds. These gases are detrimental to the environment when they react with moisture, sunlight, and other volatile gases to produce acid rain and photochemical smog.
The Environmental Protection Agency (EPA) has long recognized the negative effects of these airborne pollutants and fixed emission levels for all industrial processes. To help meet the NOx Control Regulations set by the EPA, NOx abatement technologies can reduce the level of waste gases produced by burning fossil fuels.
What Is NOx Gas?
NOx is a term used to describe a group of toxic, extremely reactive gases produced by the combustion of hydrocarbon compounds in atmospheric oxygen. These gases include nitric oxide (NO) and nitrogen dioxide (NO2). Nitric acid can further react with water vapor to produce a weak nitric acid solution (acid rain).
Although NOx can be produced during a natural lightning strike, the main source of this gas is from man-made processes that burn hydrocarbons.
Common Sources of NOx Pollution
NOx gas can be generated from different domestic and industrial sources. The most common sources are listed below:
- Power generation plants
- Industrial boilers
- Construction equipment
- Automobiles, trucks
- Sea vessels and marine equipment
- Residential oil and gas combustion
- Metal finishing procedures
Impact of NOx Pollution on the Environment
NOx gases have serious detrimental effects on the environment into which they are released. These gases play a role in increasing the greenhouse effect and escalating global warming, by forming ozone at ground level rather than the upper atmosphere where it is protective. Ozone formed in the lower atmosphere will readily react with volatile organic compounds to form a very potent toxin with serious health implications for humans.
Further, NOx gases are responsible for the formation of smog and acid rain which can be harmful to plants, trees, and aquatic life.
How to Reduce Nitrogen Dioxide Pollution
Various NOx pollution control measures can limit the impact of toxic gas on the environment. The most effective NOx removal technologies are listed below:
- Overfire air combustion modification
- Low-NOx burning
- Recirculation of NOx in flue gas
- Off-stoichiometric combustion
- Selective noncatalytic reduction
- Selective catalytic reduction
Overfire Air Combustion Modification
This NOx elimination technique involves the use of a stream of air which is maintained just above the primary fuel burner. This “over fire” method can be effectively employed in boilers to regulate air/fuel ratio, maintain lower combustion temperatures, and prevent the formation of NOx gases.
This method prevents the formation of NOx gas by inhibiting a critical step in the chemical reaction. NOx gas is formed at very high temperatures that force nitrogen molecules to recombine with oxygen. Low-NOx burners prevent fuel mixtures from reaching the critical temperatures at which NOx can be formed, by combusting fuel under lower thermal conditions.
Recirculating of NOx in Flue Gas
Flue gas recirculation is an efficient NOx scrubbing method. A portion of the flue gas being produced is simply channeled back into the combustion chamber to help cool the process and maintain peak flame temperatures below the critical levels required for NOx formation.
Reburning is a highly effective way to reduce the level of nitrogen dioxide formed from the burning of hydrocarbon compounds. This technique involves three stages of burning which ensures that the primary fuel undergoes complete combustion. A main fuel-rich zone burns approximately 85% of the primary fuel under low air conditions while the leftover fuel is channeled to a second stage/reburning zone where a reduction reaction occurs. The final stage of the reburning setup is an overfire air zone that completes the burning process.
Modifying how a boiler is set up can significantly reduce the amounts of NOx gas it produces. This technique known as off-stoichiometric combustion can be used in boiler configurations including:
- Over fire air burners
- Low excess air systems
- Biased firing burners
- Burners out of service
Selective Non-catalytic Reduction (SNCR)
Selective non-catalytic reduction involves the introduction of ammonia (NH3) or urea into a heated gas zone containing NOx, under high temperatures and in the presence of oxygen. This reaction breaks down the NOx into nitrogen (N2) and water (H2O).
Selective Catalytic Reduction (SCR)
There are many SCR/SNCR similarities, but SNCR requires a catalyst. SCR involves the introduction of ammonia (NH3) or urea into a flue gas zone which is channeled over a catalytic bed. The NOx gases present will readily react with oxygen in the presence of a catalyst to form nitrogen (N2) and water (H2O).
IFS Has the NOx Pollution Control Solutions You Need
Our team of process skid manufacturers at Integrated Flow Solutions provide the best NOx pollution control technologies to help you remain compliant with all EPA emission regulations.