Selective Catalytic Converters (SCR’s)

What are Selective Catalytic Converters? And how do they work?

Selective Catalytic Converters or SCR’s are a group of systems which are used to remove Nitrogen Oxides (NOx) from flue gases by a process of selective catalytic reduction. During this process, a reducing agent, such as ammonia is added to the flue gas, which subsequently combines with the Nitrogen Oxide and converts it to water and Nitrogen.

3 NO2 + H2O → 2 HNO3 + NO

This process is typically catalysed in systems which are liable to producing significant amounts of Nitrogen Oxide, such as industrial boilers, diesel engines and gas turbines.If the NOx gases are allowed to enter the damp atmosphere they will react with water to form the very corrosive nitric acid. As Nitrogen Oxides are a family of gases which contribute to smog and acid rain formation, the importance of reducing NOx emissions is therefore becoming increasingly important.

What issues can affect Selective Catalytic Converters?

Selective Catalytic Converters are constructed by one or more honeycomb-shaped banks of catalytic blocks, through which the flue gas must flow. Ammonia is injected into these catalytic chambers to convert the NOx gas into harmless nitrogen and water. However, due to their honeycomb shape, catalytic chambers are incredibly prone to bonding and blockage issues, which can severely reduce Selective Catalytic Converter efficiency.

Particulate Build-up

Even though natural gas is considered a relatively clean fuel, fine particulates are commonly still present. If the surfaces of catalytic chambers present an insufficient amount of friction for particulates to slide along, they will slide against themselves instead, causing particulates to coagulate and form surface build up. By reducing the amount of flue gas that can flow through catalytic chambers, surface buildup can therefore severely decrease Selective Catalytic Converter efficiency.

Discharge Cross Contamination

Discharge Cross Contamination occurs in SCR’s when fresh particulates bind with particulates of older materials present in surface build up. If the accumulated material remains stationary for a significant period of time, the material may begin to degrade and produce conflicting gases. Due to the delicate composition of gases, even the smallest contamination can result in serious repercussions for your business, as this will cause an alteration of the resultant product in the catalytic reaction.

Blockages & pressure drop

When flue gas is drawn through the catalytic chambers, the SCR enforces a resistance to the flue gas flow, which causes a difference in pressure, between the inside and outside of the chambers. This difference in pressure is what is referred to as pressure drop, which if too high, can indicate that the resistance to gas flow is impeding the SCR’s ability to draw through flue gas.

The most common reason for an excessive pressure drop is surface buildup, with even a partially blocked chamber having the potential to severely disrupt flow, as gas is then forced through a very small number of catalytic chambers, thus reducing the effectiveness of SCR’s.

Selective Catalytic Converters are typically found on utility and industrial boilers.

Traditional methods of dealing with Selective Catalytic Converter issues:

Unless particulate build up is consistently dealt with and prevented, such problems will continue to cause disturbances to your business and affect the efficiency of Selective Catalytic converters.

However unlike Primasonics Acoustic Cleaners, traditional Selective Catalytic Converter cleaning methods, only target specific and current problem, meaning they do not prevent problems from reoccurring in the future, and in some cases will only exasperate additional issues

Steam Soot Blowers are incredibly costly to purchase, install, operate and maintain. However, their major flaw is that they are typically only used in 8 hour cycles, which allows materials to build up and cause damage during this period, before the Steam Soot Blower can even begin to operate. Furthermore, because this method of cleaning is unable to reach large areas, rather than cleaning the full circumference of a catalytic chamber, steam soot blowers will often only strike the very edge of the chamber, thus giving rise to the costly problem of structural damage.

How can Primasonics Acoustic Cleaners help to prevent Selective Catalytic Converter issues?

Primasonics Acoustic Cleaners are a non intrusive technology, which provide a long-term solutions to Selective Catalytic Converter blockages and buildup issues. Acoustic Cleaners create a series of high energy- low frequency sound waves, which penetrate material build up with rapid pressure fluctuations.

By using alternating frequencies, Acoustic Cleaners are able to target particles that have different masses and which therefore travel at different speeds. This causes compacted materials to vibrate at different rates to their surrounding environment, to the extent that they are detached from surfaces and carried along by the gas stream to a suitable filtration instead.

The Primasonics Quattro range

Preventative- Unlike Steam Soot Blowers, Acoustic Cleaners are used to ensure that particulates are always excited and therefore always preventing build up. Rather than dealing with a problem after it has progressed to a more problematic stage, Acoustic cleaners ensure that SCR’s are consistently running with performance.

Non Intrusive- Unlike vibrators and explosive cleaning methods, Acoustic Cleaners are designed to reflect sound from solid surfaces. Therefore, the powerful sound waves that they transmit will only penetrate targeted materials and not the catalytic chamber walls. This will prevent structural damage and the propagation of wear.

Health & Safety- In addition to the elimination of costly manual work and cleaning regimes, acoustic cleaners also eliminate the danger of sparking, as they are powered by compressed air rather than electricity.