Product Announcement from Branch Environmental Corp.

Technologies for Removing NOx -Image

Selective Catalytic Reduction

SCR systems use our catalytic design to react ammonia injected into the air stream with the NOx present. This approach requires an operating temperature of 320-700º F (160-320º C) depending on the catalyst used.

For flue gas that is already in this range, the SCR system will be a good choice. Systems use about .4 wt. NH3/wt. NOx .

Because there are so many variables, please contact us for specific information.

Wet Phase Catalyst

To avoid the problem of high chemical cost, a special surface catalyst media was developed to be used at ambient temperatures. This unit uses conventional scrubber chemistry with a caustic solution, operates at ambient temperature, and can handle variable loads.

This surface catalyst is relatively expensive initially, so the best choice will depend on concentration of NOx, temperature, required efficiency...

Wet Scrubbing

The lowest initial cost system will be a wet scrubber. However, as NOx absorbs in water, it reacts to form NO (insoluble form) which will slowly reoxidize to NO2. In a conventional scrubber, 60-70% removal occurs. To improve this, several possible chemicals can be introduced into the towers combined with a very long contact time.

The disadvantage of this approach is the cost of the special chemicals required. Additionally, there will be a waste water treatment requirement.

How does SCR work?

Catalysts perform by lowering the temperature required to allow a chemical reaction to occur. In this case, a reduced nitrogen compound (ammonia or urea) is introduced into the air. The "oxidized" chemical (NO or NO2 or both) then reacts with the other nitrogen compound forming elemental nitrogen and water.

The two common sources of neutralizing chemical are either ammonia, which is a gas at room temperature or urea, which is normally used as a solution and must be atomized into the air.

Selective Catalytic Reduction (SCR)

SCR technology is often used where high temperatures, low concentrations or high percentage of NO are encountered.

The catalyst used is normally coated on a ceramic substrate. Various configurations are used including lose pieces of ceramic media and structured honeycomb shapes. The structured shape is the most common because of its lower pressure drop. It is also easier to install and replace.

Different catalysts can operate over different temperature ranges. The minimum range in temperature can be as low as 500°F or as high as 1000°F.

Other temperature considerations include the presence of sulfur dioxide and the concentration of NOx.

At lower temperatures, ammonium sulfate can form. The ammonium sulfate salt can deposit on the catalyst effectively blocking off its activity and reducing the NOx scrubbing efficiency. The catalyst usually be regenerated by heating above the point where the ammonium sulfate becomes volatile again, but you cannot operate in this temperature range continuously.

There is a heat of reaction between ammonia and NOx. Care must always be used when designing an SCR system to avoid excessive temperature rise. Excessive is defined as anything that takes the temperature higher then the design range for the catalyst. Excessive temperatures will rapidly deteriorate the effectiveness of a catalyst.

Ammonia Reaction
NH3 + NOx + O2 → N2 + H2O + CO2

Urea Reaction
(NH2)2CO → NH3 + HNCO
HNCO + NOx + O2 → N2 + H2O + CO2

NOx removal

There are several techniques for removal of oxides of nitrogen (NOx) depending on the composition/temperature/removal efficiencies.

N0x Abatement

N0x Control on Gas Turbines

Branch Environmental supplies custom built pollution control equipment for industry. Our air pollution control equipment can clean up acids, organics, aerosols and mist to meet any emission control standards. Our equipment is also used for water treatment, including removal of volatile organics, ammonia and other gases.


Branch Environmental supplies custom built scrubbers and systems for air pollution control. From small units to large custom designed systems, you receive competitive pricing with the highest reliability and assurance that the equipment will work right the first time.

Branch can provide standard design or custom built oxidation systems for thermal destruction of volatile organic compounds (VOC) and other gases that can be eliminated by thermal destruction.

Branch provides custom built Air Stripper units for removal of voc, ammonia, hydrogen sulfide and other volatile components from water. With our experience in complete systems, we can provide you with all of the related components and controls for a trouble free installation.

Branch designs and builds custom fabricated mass transfer equipment for gas absorption and removal.

Branch Environmental can provide several different technologies for removing oxides of nitrogen (NOx) from air or flue gas. The best treatment method for your application will depend on the conditions of operation.

When extremely small particles are present, the energy required for scrubbing will increase tremendously. If the particles are oil, acid mist, or a soluble salt, a Fiberbed may be the best answer

 Contact us

We would appreciate the opportunity to help you in any way. If you have a question or comment, please email us at 


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