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

Author: Michael Klepik, Chief Executive Officer

Firstly, it should be mentioned that nitrogen forms several 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.

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.

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

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.

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.

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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