How does Selective Catalytic Reduction Work?

How does Selective Catalytic Reduction Work?

Selective Catalytic Reduction (SCR) is an advanced active emissions control technology system that injects a liquid-reductant agent through a special catalyst into the exhaust stream of a diesel engine. The DEF can be rapidly broken down to produce the oxidizing ammonia in the exhaust stream.

What is the main purpose of selective catalytic reduction?

SCR technology is designed to permit nitrogen oxide (NOx) reduction reactions to take place in an oxidizing atmosphere. It is called “selective” because it reduces levels of NOx using ammonia as a reductant within a catalyst system.

What is the difference between DPF and SCR?

A DPF’s core can be made of a few different materials but the most common are cordierite composites. An SCR catalyst has valuable filter contents in the form of ceramic materials and precious metals.

What is catalytic reduction in chemistry?

Abstract: In the selective catalytic reduction (SCR) process, NOx reacts with ammonia, which is injected into the flue gas stream before the catalyst. Ammonia-SCR has been used in industrial processes, in stationary diesel engines, as well as in some marine engines.

Why is NOx bad?

NOx can cause serious health damage to humans, including respiratory diseases. NOx is also responsible for smog and the typical brown cloud that covers larger cities and produces poor air quality. NOx reacts with volatile organic compounds in the presence of sunlight and forms ground-level ozone.

When was selective catalytic reduction invented?

1957
Selective catalytic reduction of NOx using ammonia (NH3) as the reducing gas was patented in the United States by Englehard Corporation in 1957 [48].

Can an SCR catalyst be cleaned?

Catalyst systems can contain potentially harmful contaminants that are difficult to reach or remove using traditional cleaning methods. The catalyst system remains sedentary while units are air-blast cleaned using regulated pressures and OEM-approved proprietary nozzles.

What is ammonia slip?

Ammonia slip is an industry term for ammonia passing through the SCR unreacted. This occurs when ammonia is injected in excess, temperatures are too low for ammonia to react, or the catalyst has degraded. Temperature is SCR’s largest limitation.

What comes first DOC or DPF?

The DOC protects the DPF. Vapor can interfere with the DPF’s ability to trap and remove particulate matter, so manufacturers route the exhaust through the DOC first, then into the DPF.

What is NOx reduction?

Exhaust Gas Recirculation technology is able to reduce diesel nitrogen oxide (NOx) emissions by taking a carefully controlled portion of the inert exhaust gases, cooling it and re-introducing it to the combustion chamber when conditions are right to do so.

What does NOx do to your body?

NOx has direct and indirect effects on human health. It can cause breathing problems, headaches, chronically reduced lung function, eye irritation, loss of appetite and corroded teeth. Indirectly, it can affect humans by damaging the ecosystems they rely on in water and on land—harming animals and plants.