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Home / Blog / Nitric Oxide Scrubber: Danger NOx, Wet Scrubbers, Design, Chemicals, Materials

Nitric Oxide Scrubber: Danger NOx, Wet Scrubbers, Design, Chemicals, Materials

Author: Michael Klepik, Chief Executive Officer
Nitrogen (N) is not only a non-hazardous chemical element but also essential for the human body. It is an organogenic compound, as it is a constituent of amino acids that form proteins. Additionally, it is part of the building material of DNA, hormones, hemoglobin, most vitamins, and other essential substances for life support. It is a non-combustible, non-explosive, and non-toxic inert gas, ranking fourth among chemical elements in abundance. In solid and liquid environments, its concentration is about 2-3% of the total amount of organic matter. However, when combined with oxygen, its volume and toxicity increase.

Industrial enterprises utilize sodium hydroxide NOx scrubbers to mitigate atmospheric pollution.

Such devices are commonly used at power plants, chemical production facilities, and elsewhere, where reducing emissions of harmful substances into the atmosphere is important for compliance with environmental regulations and standards.
Emissions of NO2 into the atmosphere
Emissions of NO2 into the atmosphere.

The Danger of Nitrogen Oxides

Firstly, it should be mentioned that nitrogen forms several oxides.
Purifying air from nitrogen oxide (I) is not an important or necessary task. It is rarely produced in large quantities in industry. Rather, the industry intentionally produces this type of N2O for medical, food, aviation, and automotive industries. In medicine, for example, it is utilized as an anesthetic under the well-known name "laughing gas."
Molecules of Nitrogen Oxides
Molecules of Nitrogen Oxides
Cleaning air mixtures from nitrogen oxide (II) is also not a necessary task, as this oxide cannot exist in the air; it immediately oxidizes to NO2.

N2O3 is a dark blue liquid. It forms nitrous acid upon interaction with water.

Let's start with the highest degree of N2O5 — a volatile, gaseous, toxic compound. It is stable only at temperatures not exceeding 50°F. It becomes explosive when combined with organic substances. Handling of this oxide is usually carried out in laboratories. Upon decomposition, it yields NO2.

Now let's focus on NO2 — a toxic gas of brown color with an unpleasant odor. Emissions are highly toxic, causing irritation of mucous membranes. They cause significant damage to the lungs and respiratory system, alter blood composition, and reduce hemoglobin levels. They can also contribute to acid rain.

The main sources of nitrogen dioxide (IV) formation are the byproducts of fuel combustion in furnaces and the operation of internal combustion engines.

Wet Scrubbers NOx Removal

Absorption is a universally applicable method. It allows achieving a high degree of purification — up to 99.99%. The method is based on the interaction of gas with water and neutralizers. A huge advantage is that substances suitable for further use in agriculture and various industries are formed as a result.

NOx gas scrubbers are the best filters in this case. Their principle of operation is as follows:
  1. Contaminated gas enters the inlet flange and passes into the column apparatus to the nozzles.
  2. The packing material is continuously sprayed from several nozzles positioned above, creating a cleansing layer that purifies the incoming gas. In the column apparatus, there are 35.315–52.973 cubic feet of intricately shaped nozzles, designed to maximize the contact area between water and gas, thus increasing the filtration efficiency.
  3. The nozzles are sprayed with water or a special liquid, depending on production needs.
  4. Then the purified air with water enters the mesh droplet collector.
  5. It is expelled outside with the help of a fan.

The TORNADO series — a nitric oxide scrubber with a multistage droplet capture system. Designed for air purification from most acids, alkalis, and their mixtures. Specially developed for use in the chemical industry. Vertical nitrogen oxide scrubbers from the TORNADO series offer a range of designs, including venturi, foam, nozzle, and packed bed units. Renowned for their efficiency, these NOx caustic scrubbers achieve purification rates of up to 99.9%, effectively removing pollutants from the air.
The BOREAS series NOx wet scrubbers are ideal for purification. The undeniable advantage of the horizontal column layout is its compactness and ease of maintenance. The types of devices in this lineup include: spray scrubbers, random packing scrubbers, and Ion-Exchange Fiber-Bed scrubbers.
How Does a Venturi Scrubber Work
Devices incorporating a Venturi tube. The performance ranges from 600 to 175,000 cfm. Versatile industrial scrubbers for wet air purification. The gas cleaning system is based on mass exchange processing that occurs inside the Venturi tube throat. Design options: With a Cyclonic Separator, Fluidized Packed Bed


The sodium hydroxide NOx scrubber design is a crucial component in industrial air pollution control systems. This system is designed to remove nitrogen oxides from industrial emissions by utilizing a chemical reaction with sodium hydroxide (NaOH). The equipment operates by passing the polluted air stream through a tower filled with a sodium hydroxide solution. In this process, substances react with sodium hydroxide to form harmless sodium nitrate (NaNO3) and water vapor.

Key considerations in the design of a NOx fume scrubber include the selection of appropriate materials resistant to the highly corrosive nature of sodium hydroxide, such as corrosion-resistant alloys or specially coated surfaces. Additionally, the design must optimize contact between the stream and the sodium hydroxide solution to ensure efficient NOx removal while minimizing energy consumption and operational costs.

The efficiency of the configuration depends on various factors such as gas flow rate, temperature, and the concentration of sodium hydroxide solution. Proper monitoring and maintenance are essential to ensure the scrubber's continued effectiveness in reducing NOx emissions and maintaining compliance with environmental regulations.
Polypropylene Packed Bed Scrubber
Polypropylene Packed Bed Scrubber

NO2 Removal Process

NO2 removal in a scrubber is a critical process in industrial air pollution control systems. NO2 is a harmful pollutant emitted from various industrial processes, combustion engines, and other sources. A NO2 fume scrubber designed for physical absorption is used to capture and neutralize the pollutant.

Chemical scrubbers employ reactive substances, such as sodium hydroxide (NaOH) or calcium hydroxide (Ca(OH)2), which react with NO2 to form harmless compounds like sodium nitrate (NaNO3) or calcium nitrate (Ca(NO3)2). These reactions typically occur in a tower or vessel filled with the scrubbing solution, where the polluted air stream is passed through.

Physical scrubbing system, on the other hand, rely on the absorption of NO2 molecules onto a surface or into a liquid. This process often involves the use of activated carbon or other porous materials with high surface areas that can effectively capture NO2 molecules as the air stream passes through.
Tornado ST | Spray Tower Scrubber | Spray Chamber Scrubber


NOx scrubber chemicals are essential components in industrial purification systems. These reagents are widely used in industry for cleaning emissions from NOx:
  • Ammonia (NH3) is widely used in system. The reaction looks as follows: 4NO+4NH3+O2→4N2+6H2O
  • Urea (NH2CONH2) is also an effective reagent. When it reacts with NOx, it forms nitrogen and water. The reaction is similar to the reaction with ammonia.
  • Sodium carbonate (Na2CO3) or baking soda, is also utilized as a reagent for cleaning. When it interacts with NOx, it also leads to the formation of N and H2O.
  • Sodium hydroxide (NaOH), or caustic soda, is utilized to neutralize acids and form nitrates or nitrites.

Chemical reagents are typically introduced into the NOx fume scrubber using specialized delivery systems, which may incorporate pumps, sprayers, or other devices to dose and spray the reagents into the air stream passing through it. Depending on the specific design and the process requirements, the reagents can be introduced in the form of solutions, dry powders.

For example, ammonia or urea can be introduced into the NO2 gas scrubber in the form of aqueous solutions. This solution is then sprayed into the air stream passing through the equipment, where it reacts with nitrogen oxides.
The process of delivering and dosing reagents is typically controlled by automatic control systems, which ensure the optimal ratio of reagents and effective removal of NOx emissions.

Robust Materials for Aggressive Environments

In scrubbers designed to process aggressive chemical compounds, materials resistant to chemistry are often utilized, including certain types of plastics. Here are several types of plastics that are suitable for use:
  • Polypropylene (PP) is widely used in various industrial applications. It has good resistance to various acids, alkalis, and solvents.
  • Polyethylene (PE) also has high caustic resistance and is utilized in nitrogen oxide gas scrubber for processing aggressive environments.
  • Polyvinyl chloride (PVC) has good resistance to acids and alkalis.
  • Polytetrafluoroethylene (PTFE) also known as Teflon has high chemical resistance and inertness to most substances, making it a suitable material for some parts of equipment, especially as a coating.

In purification devices, special types of steel are often used, which possess chemical resistance and corrosion resistance. Some of them include:
  • Stainless steel, such as AISI 304 or AISI 316, is often used due to its high corrosion resistance and chemical stability.
  • Duplex steel, such as SAF 2205, has a dual-phase structure, providing high strength and corrosion resistance.
  • Galvanized steel is employed in some parts to protect against corrosion.
  • Nickel steel, such as Inconel or Hastelloy, has high corrosion resistance and chemical stability. It is widely used in aggressive environments, such as in NOx scrubbing.
These materials are applied in various combinations and forms, depending on the specific operating conditions and the type of aggressive compounds being processed.
Venturi TORNADO-FB Fluidized Bed Scrubber
Venturi TORNADO-FB Fluidized Bed Scrubber

Other Purification Methods

Adsorption (chemisorption processes)
This method is suitable only for a small volume of air. The main reagent, as in most cases, is activated carbon. Silica gel, peat alkaline reagents are also applied. An important condition for proper cleaning is maintaining the temperature regime (176-266°F). The degree of purification with this method reaches 90%.

Catalytic reduction
This purification method is based on a reaction that forms molecular nitrogen. Hydrogen, natural gas, and carbon monoxide act as reducing agents.

Depending on the temperature, the decomposition of NO is divided into high-temperature, selective, and heterogeneous. The efficiency will depend on the catalyst used (platinum group metals, alloys based on rhodium/palladium). These catalysts are expensive, making the filtration process unaffordable for many enterprises.

Combustion process regulation
This method is suitable only if the temperature regime is between 1562°F and 2012°F. The degree of purification is not very high — 70%.

The process includes two stages: technological measures and the operation of units integrated into the furnaces. At the second stage, it is necessary to reduce excess air, lower the temperature of oxygen preheating, maintain circulation of flue gases, ensure combustion in two stages, and use water instead of steam.

Carbide method
This method allows gas to be cleaned from nitrogen dioxide by 95%. The advantage of the method is the independence of the reaction from the concentration of the oxide and the absence of the need for pre-treatment of the gas.

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