----- Forwarded by Melanie King/RTP/USEPA/US on 08/05/2010 04:41 PM

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>--------------------------------------------------------------------------- ---------------------------------------------------------------| |"Bromberg, Kevin L." <kevin.bromberg@sba.gov> |

>--------------------------------------------------------------------------- ---------------------------------------------------------------| |------------> | To: | |------------>

>--------------------------------------------------------------------------- ---------------------------------------------------------------| |Melanie King/RTP/USEPA/US@EPA, RobertJ Wayland/RTP/USEPA/US@EPA |

>--------------------------------------------------------------------------- ---------------------------------------------------------------| |------------> | Cc: | |------------>

>--------------------------------------------------------------------------- ---------------------------------------------------------------| |"Higgins, Cortney" <Cortney_Higgins@omb.eop.gov>, "Kymn, Christine J." <Christine_J._Kymn@omb.eop.gov>, Michael Horowitz/DC/USEPA/US@EPA, | |Fred Talcott/DC/USEPA/US@EPA |

>--------------------------------------------------------------------------- ---------------------------------------------------------------| |------------> | Date: | |------------>

>--------------------------------------------------------------------------- ---------------------------------------------------------------| |08/03/2010 05:15 PM |

>--------------------------------------------------------------------------- ---------------------------------------------------------------| |------------> | Subject: | |------------>

>--------------------------------------------------------------------------- ---------------------------------------------------------------| |FW: NOx Reductions vs. HCHO Reductions - More Technical Information - can be shared with EPA |

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I told Peter that I would share this with EPA so we can get its comments in a timely manner. This affects the NOx benefits from 4SRB engines.

Cortney – I’m working on a consolidated document to share with EPA. This has more details on the NOx issue than that document will have.

Kevin

From: Bromberg, Kevin L. Sent: Monday, August 02, 2010 1:31 PM To: 'Higgins, Cortney'; 'Kymn, Christine J.' Cc: 'Lee, Amanda I.'; 'Nancy.Johnson@hq.doe.gov'; 'Zwicke, Greg - Portland,

OR' Subject: NOx Reductions vs. HCHO Reductions - More Technical Information - can be shared with EPA

If you get NOx reduction with NSCR it is usually relatively high – e.g., 90% or more. The problem is that the NOx performance is very sensitive to the air to fuel ratio (AFR) and the stream needs to be “more rich” (i.e., more fuel rich or air deficient). A lesser NOx reduction (e.g., 20 – 60% NOx reduction) with NSCR is typically not seen, because the performance curve (versus AFR) is very steep – meaning that you go from no NOx reduction to relatively high NOx reduction (e.g., 80% or more) with very small changes to AFR. Similarly, if set for “richer” operation with NOx reduction, relatively small changes in AFR can move the AFR more lean and significantly impact NOx performance. Thus, if an operator installs NSCR to meet a NOx limit, the set to provide a better assurance of emission performance is often accomplished by establishing a “richer” setpoint (which can result in significant ammonia emissions). In this scenario,

there is more of an operating window before minor AFR changes can move “too lean” and significantly compromise NOx performance. Those richer set point also result in lower efficiency / higher fuel use, more hydrocarbon (HC) emissions, and hotter operation – and these conditions affect maintenance requirements because the HC and higher temps impact performance and increase maintenance frequency (and related costs).

An example of NOx (post NSCR catalyst) versus AFR for a RB with NSCR is provided here. Note the “stoichiometric ratio” (SR) is the theoretical amount of air relative to the amount required to burn all of the fuel – i.e., at 1.00 there is just enough air to burn all the fuel. From the scale on the x-axis, a change in the amount of air by 1 or 2% dramatically changes the NOx emissions (and ammonia and CO emissions). This level of AFR control is difficult to maintain on a continuous basis. It’s also not reasonable to operate in a region of the “NOx curve” that provides intermediate levels of NOx reduction so in general NOx reduction with NSCR close to an all or nothing proposition. Also – as a reminder, the definition of “rich burn” is an engine with a stoichiometric ratio up to 1.10 (beyond the scale of this graph). As you can see from the graph, the NOx emissions on the right side of the graph (from SR of about 0.99 or higher) have high NOx indicative of very little or no NOx reduction. This relates to our discussion that NOx reductions cannot be presumed with NSCR – and operators can achieve better efficiency, lower fuel use, and lower greenhouse gas emissions by running leaner where NSCR will not reduce NOx.

Also for the NOx data – the marginal relative change in the 3 data points to the right (from about 2100 to about 2650 ppmv) is due to changes in the inlet NOx and not from NSCR reduction – i.e., the inlet NOx versus AFR is also dependent on AFR at this operating threshold where you cross from “rich” to “lean”, and the NOx reduction across the catalyst is insignificant. Note that the one NOx point at about 850 ppmv is 58% reduction and the three low NOx points on the left are about 98% reduction for these tests.

(Embedded image moved to file: pic09770.gif) Since facilities will be attempting to meet a HCHO standard in the neighborhood of 3.7 ppm, the preferred operation will use a stoichiometric ratio of 0.99 or more, which
would be on the “fuel lean” side (right hand side) of the graph. However, the NOx reductions will only occur on the rich side (left hand side) of the graph – in this case approximately 0.98 or less. In addition to good HCHO emissions performance, there are additional reasons for being on the lean side of the curve – reduced fuel consumption, associated reductions in greenhouse gas emissions (i.e., lower CO2 and methane), reduced maintenance, and avoidance of ammonia and CO emissions. The NOx reductions go very quickly from roughly 98% to 0% once you
move from richer settings to leaner operation above about 0.98. Also, the air to fuel ratio differences are very small and given some instability of the settings of these engines, maintaining a precise setpoint is difficult and you will need to set an even leaner setting optimize engine operability and effieciency – or, conversely, set a richer setting to ensure NOx reductions. The above graph is from a rich burn engine tested by Colorado State University. Unless EPA is also setting a NOx limit with the HCHO limit, these desired NOx reductions are unlikely to occur.

EPA may wish to review additional data to see how under what AFR ratios, both the HCHO number and the desired NOx reductions can occur (by how much and whether these overlap), although I don’t know how this result can be achieved
under the current standard.

This argues that our NOx reductions will be lower for the 300-500 HP major sources and the >500 HP area sources, and reinforces our argument to drop the NSCR for sources <750 HP and in rural America.