What Are NOx Emissions? Effective Methods for NOx Removal
December 3, 2022 Welcome
Environmental pollution from fossil fuel use is a major negative consequence of industrialization. NOx gas release is one of the significant outcomes of burning fossil fuels with significantly negative environmental impacts. In this article, the experts at IFS will discuss various methods that can be used to eliminate NOx gases and preserve ecological balance.
What Are Nitrogen Oxides (NOx)?
Nitrogen oxides refer to two gaseous compounds: nitrogen dioxide and nitric oxide. These two compounds are also described as NOx gases and are significant environmental pollutants. NOx gases are produced primarily from fossil fuel combustion.
NOx emissions released into the atmosphere will not remain airborne indefinitely. At some point, nitric oxide will react with water and other chemicals to form acid rain. Acid rain will then contaminate water bodies and soil, harming both plant and animal life.
Common Sources of NOx Pollution
Most NOx emissions are generated globally from domestic and industrial sources. The most common sources are listed below:
- Power generation plants
- Industrial boilers
- Automobiles, trucks
- Construction equipment
- Sea vessels and marine equipment
- Metal finishing procedures
- Residential oil and gas combustion
Impact of NOx Pollution on the Environment
NOx gases have serious detrimental effects on the environment into which they are released. These gases increase the greenhouse effect and escalate global warming by forming ozone at the ground level rather than the upper atmosphere, where it is protective. In addition, 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 smog and acid rain formation, which can harm plants, trees, and aquatic life. Fortunately, power plant pollution control is possible.
Adverse Effects of High NOx Emissions
In addition to damaging the environment, the release of NOx gases also causes serious harm to human health. For example, people exposed to NOx emissions for longer periods typically develop respiratory problems.
Some major health changes associated with NOx gas exposure include irreversible lung tissue damage, worsening asthma, and an increased breast cancer risk.
7 Effective Methods for Reducing NOx Pollution
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. Outlined below are some of the most useful NOx emission control methods available.
- Low-NOx burning
- Natural gas reburning
- Flue gas treatment
- Excess air control
- Overfire air combustion modification
- Flue gas recirculation
- Off-stoichiometric combustion
1. Low NOx Burners
The installation of low NOx burning equipment in power plants is a good emission reduction strategy. This method prevents the formation of NOx gas by inhibiting a critical step in the chemical reaction. As a result, 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. Further, existing power plants can be retrofitted with these low NOx burners to reduce emission levels.
2. Natural Gas Reburning
Natural Gas Reburning (NGR) is a highly effective way to reduce the level of nitrogen dioxide formed from burning hydrocarbon compounds.
This technique involves three burning stages, ensuring that the primary fuel undergoes complete combustion. First, 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.
3. Flue Gas Treatment
This technique is highly efficient and uses methods such as selective catalytic reduction (SCR) with ammonia to convert NOx into nitrogen. Selective non-catalytic reduction (SNCR) processes can achieve a similar result to SCR NOx control but are less commonly employed.
- SNCR 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).
- SCR involves the introduction of NH3 or urea into a flue gas zone channeled over a catalytic bed. The NOx gases present will readily react with oxygen in the presence of a catalyst to form N2 and H2
4. Excess Air Control
Excess air refers to the amount of air in excess required to achieve 100% combustion. Tightly regulating the amount of air supplied to a combustion process is an effective emission-limiting strategy. Low excess air processes aim to regulate the amount of excess air available to a process within 20-30%. Lowering the excess air is associated with reduced NOx formation and cleaner energy generation.
5. Overfire Air Combustion Modification
This NOx elimination technique involves using a stream of air 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.
6. Flue-gas recirculation (FGR)
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.
7. Off-stoichiometric Combustion
Modifying how a boiler is set up can significantly reduce the amounts of NOx gas it produces. This technique, known as off-stoichiometric combustion (or staged combustion), can be used in boiler configurations including:
- Over-fire air burners
- Low excess air systems
- Biased firing burners
- Burners out of service
Discover IFS Solutions for NOx Emission Control
With so many negative effects of high NOx generation on humans and the natural environment, effective elimination strategies must be implemented and adhered to.
IFS is a leading provider of NOx elimination solutions easily modifiable to various industrial processes. Our products and services guarantee you remain compliant with emission regulations while optimizing your productivity.
Chat with our team today to learn more.