Product Announcement from Branch Environmental Corp.
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.
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
There are several techniques for removal of oxides of nitrogen (NOx) depending on the composition/temperature/removal efficiencies.
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.
Wet Scrubbers have been used on a variety of applications. Their ability to remove both solids and gases makes them suited to handle difficult applications.
The most common types of scrubbers we supply include:
Where insoluble organic vapors are present, Scrubbers will not work. Such vapors can be removed by thermal destruction. The result is usually harmless gases including water and carbon dioxide.
The most common types of systems we supply include:
- Thermal Oxidizers.
- Regenerative Thermal Oxidizers RTO
- Catalytic Oxidizers.
- Selective Catalytic Reduction.
For ground water or wastewater cleanup. Trace organics can be stripped out of the water by air moving countercurrent to the water.
Air Strippers come in several configurations. They can be provided as part of a package with vapor phase control, if necessary.
The most common types of Air Strippers we supply include:
The removal of oxides of nitrogen (NO/NO2) is a unique problem because of the difficulty.
Our selective catalytic reduction system uses ammonia to react with the NOx resulting in nitrogen and water.
Alternative systems using wet scrubbing are also available
Where difficult to remove aerosols are present in the air, a Fiberbed mist eliminator maybe the answer.
Fiberbeds are able to remove oil mist and smoke sized droplets from air.
Aeration Columns
We design and build custom fabricated mass transfer equipment for gas absorption and removal.
The most common type of aeration devices we provide are:
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