EGR Vs SCR on diesel engines for generators

[wellandpower]

EGR (Exhaust Gas Recirculation) and SCR (Selective Catalytic Reduction) are the two technologies used to achieve the required reduction in NOx (nitrogen oxide).

Different manufacturers will be using different technologies initially. Both achieve the same aim of reducing the amount of NOx from the exhaust.

EGR works by reducing the amount of oxygen in the combustion process. This lowers the combustion tempurature (the hotter the combustion temperature, exponentially more NOx is produced) and reduces the amount of NOx in the exhaust.

SCR works by injecting urea into the exhaust. With a catalyst it transforms the NOx into nitrogen and water by first turning into ammonia and carbon dioxide and then breaking apart the NOx.

Both systems have advantages and disadvantages. Which can be generally viewed as follows:

SCR

Probably allows better fuel economy.
End result is harmless water, carbon dioxide and nitrogen.
Combustion remains optimal, as the tempurature can be maintained.
Most effective at continious loads and speeds.

Additional weight in the urea tank and accessories.
The additional cost of urea
Urea is a water polutant.

EGR

No intervention (ir filling urea tank) for compliance.
No extra hardware required.

Decreases the density of the power and the fuel economy.
Increases heat rejection, additional cooling capacity required.
Potential engine durability issues
Increase in particulates (ie soot).


Given the two technologies, in my opinion SCR will be the winner in the battle for the power generation market given it is effective at constant speed / load and that fuel consumption is maintained. The requirement to "AdBlue" (the name under which urea is marketed in Europe) and the difference in fuel consumption between the two systems will be key, along with the size of the cooling package that EGR may dictate is required.

[wellandpower]

It appears Perkins are opting for EGR.

http://www.allbusiness.com/legal/env...1774661-1.html

Although not the first to reveal its hand over technology for EPA Tier 4 Interim/EU Stage 3b off-highway engine emissions standards, Perkins has now detailed its plans.
The U.K. company and its parent group, Caterpillar, have invested heavily in Tier 4

preparation prior to the 2011 implementation date and have come out in favor of cooled exhaust recirculation (EGR) to meet the tougher emissions legislation--although Perkins is labeling its EGR process as N[O.sub.x] Reduction Technology. And at the same time it gave an apparently lesser estimation of the benefits of using selective catalytic reduction (SCR) to do the same job.

Perkins, based in Peterborough, England, has also taken the wraps off an impressive boost to its engine lineup with the emphasis on both enhanced power and fuel economy.
The company can perhaps afford to be in a fairly bullish mood, as 2008 was a record year for engine production--400,000 for the 12 months--and it is putting the final touches to a new crankcase manufacturing facility at its U.K. base. Added to that was the recent opening of its new Wuxi facility in China, where it will build its 400 and 1100 Series engines, with manufacture having begun at the end of 2008 and with initial volumes predicted to be around 60,000 units per annum.
Focusing on Tier 4 Interim/Stage 3b, the company said it had fully understood all of the emissions-tackling options open to it but added that it opted for EGR "with the customers' interests at heart."

[wellandpower]

Where as Volvo seem to have chosen SCR for their trucks and presumably everything else will go the same way.

http://trailer-bodybuilders.com/news...ks-SCR-062806/

Volvo Trucks North America will use selective catalytic reduction (SCR) to achieve 2010’s extremely rigorous standards for emissions of nitrogen oxides (NOx) by diesel engines.
SCR is an aftertreatment technology that involves injecting a water-based solution containing urea into the hot exhaust stream of an engine. The urea, in conjunction with a catalyst in the exhaust aftertreatment system, breaks down the NOx into harmless nitrogen and water vapor. Urea is an organic nitrogen-containing compound commonly used in agriculture as a fertilizer and is classified by the Environmental Protection Agency as a nonhazardous substance.
Volvo’s technology solution for 2010 will also include a diesel particulate filter (DPF) and exhaust gas recirculation (EGR). Volvo has employed EGR on its engines in North America since late 2002, while DPFs will be used starting in 2007 on Volvo’s new family of diesel engines.

[mikefills]

I was researching on this topic, and found your post, its a great post, thank you. I also think that SCR should always be given the preference because of its better fuel consumption.

[merryengineer]

Given that the fuel consumption seems to be better on SCR, SCR seems like a good choice.

Even better - neither of these technologies!