Document ID: EPA-R08-OAR-2017-0062-0004
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2017-04-14T04:00Z

Aaron:

History is always harder to reconstruct and explain than expected, so this has taken a bit longer that I had hoped given all of the other activities going on.  I hope that my answers below will inform your decision making process for the RH FIP in Montana.

As I noted during our call, Ash Grove formally commented on the EPA's assertions related to transferability of SNCR performance results from one long wet kiln to another based on the data from Midlothian's three wet kilns at the time.  We continue to believe that the data affirms our comments and experience at Montana. While we cannot confirm the uncontrolled NOx emissions at Montana due to an obligation to operate SNCR at all times, we believe that uncontrolled NOx rates being experienced now are lower than previously observed due to our efforts to optimize kiln operations through the mandated consent decree "test and set" process.  Bear in mind that part of that process has involved the installation of new, certified, CEMS in the stack, where previously the uncertified CEMs were located in the smoke box.  We do not believe it has been demonstrated that 50% control can be achieved on any long kiln thru the use of SNCR alone. Many variables exist when comparing one kiln or kiln feed mix chemistry to another. My comment letter of June 19, 2012 provides further detail on this, but the concluding paragraph is below:
      In summary, we continue to believe that an SNCR system at Montana City cannot be assumed to reach greater than 35 percent control efficiency and that EPA has produced no credible evidence in the record for supporting a different conclusion. While we recognize that our initial BART submittal listed 50 percent control as achievable for the combination of a low NOx burner and SNCR at the Montana City kiln, based on the actual operating results we have achieved at Midlothian since 2006/2007, we can no longer be confident that 50 percent is achievable at Montana City since we cannot get to that level on all three kilns at Midlothian. ...

I understand your interest in ammonia CEMS information, but you should realize that pretty significant advances have been made since 2007 in that arena.  While our monitors for the old kiln stacks at Midlothian were the latest technology at the time, they were difficult to maintain due to stack optical path length variability (caused by temperature changes and its impact on alignment), significant stack gas moisture content (wet process kilns have higher moisture stack gas), and lack of reliable support from the CEM manufacturer.  It should also be noted that no established CEM certification method existed in 2007 and still does not today. Some of our kilns today have been equipped with newer technology monitors that are calibrated daily and believed to provide a more representative value than the data we were able to obtain in the period you are interested in, but that is not helpful with respect to the wet process kilns in Midlothian as they were never equipped with this type of monitor.  Furthermore, the data we collected both then and now is a total ammonia concentration value, representing variability of both naturally occurring ammonia in the raw materials and that from ammonia slip due to SNCR use. It is not possible to discern the source of the ammonia and it is clear that there is significant variability in the raw material influence on emissions.  It is difficult to conclude how much ammonia slip came from SNCR when the naturally occurring ammonia emissions fluctuate between 5 and 25 ppm, while the "slip" allowance was an additional 10 ppm above background.

I have provided answers to your questions below, after restating the questions.

      1) The NOx emissions (lb/ton clinker) in 2009-2010 returned to, or were even higher than, the pre-SNCR levels in 2006 and 2007.  Can you explain why this occurred?  (I understand that Kiln 1 operated with SNCR during the 2007 ozone season.)
          
I think what you are seeing here is the difference in what was required versus what was voluntary. The initial Kiln 1 SNCR installation was in 2007, but the facility was not yet required to operate SNCR for any specified time or achieve a particular NOx emission limit. This work was done in preparation for the 2009 SIP limit, but since SNCR had not yet been tried on a long wet kiln, the period between installation and the SIP limit was used to understand how the system would operate once a lower NOx limit was imposed on the plant.  In 2008 the plant was in the process of evaluating performance parameters and control capabilities for the system.  In 2009 and 2010 the plant operated in line with the requirements of the SIP, operating SNCR only during ozone season and only as necessary to comply with the site-wide SIP limit of 4.41 tons/day.  Bear in mind that during 2009 and 2010, cement demand was sharply lower than in 2007, so our site-wide SIP limit could often be met without the use of SNCR because one or more of the kilns was idle.  After the March 11, 2011 agreement was finalized with the Cities, the plant was required to achieve 3.6 lb/ton clinker on a 30 day rolling average basis for each kiln, so more SNCR use was necessary to comply.
          
      2) The NH3 emissions (lb/ton clinker) in 2009-2010 were much lower than in 2008?  Can you explain why this occurred?  Is it indication that far less reagent was being used?  Was the amount of reagent constrained by ammonia slip?  Or was the goal to comply with the non-attainment area NOx emission limit, but otherwise to limit reagent injection?
          
Correct, as explained above, less reagent was used during 2009-2010 because we were able to idle kilns due to low demand and achieve the SIP limit without SNCR.  
          
For periods before the City agreement, the plant only operated the SNCR systems during ozone season and as needed to comply with other requirements that were not as stringent. Also, while the facility had a plant-wide SIP daily total NOx emissions limit, the limit  only applied during ozone season (March 1 through November 31 -  TCEQ state rule 117 defines this period). The SIP allowed 4.41 tons of NOx per day, regardless of production rate or number of kilns operating.  Once the 3.6 lb/ton limit of the City agreement applied, the facility operated in such a way that both limits were complied with at all times.

      3) Can you share the ammonia slip that the Midlothian kilns experienced when the SNCRs were operated (in ppm, all years)?
      
We had a baseline ammonia rate of 25.1 ppmv and an additional 10 ppmv for ammonia slip.  The Texas rules allowed for this alternative limit. This limit came in to play March 1, 2009 and later.  We cannot tell the difference between slip from SNCR use and raw material related ammonia emissions.  The average ammonia emission was 9.5 ppm with a standard deviation of 5.2 without ammonia injection.  The average value was based on daily average values collected between December 2008 and February 2009.
      
Note that annual ammonia emissions were quantified on the emissions inventories you provided, so one can see the variation, but keep in mind the value represents total ammonia emissions, not just slip.
      
      4) Can you share NOx and NH3 emissions data for the three kilns after 2010 and prior to their retirement?
          
Annual emission rates by kiln are included in the attached spreadsheet.  Kilns 1 and 2 operated through September 2014, while Kiln 3 did not operate in 2014 as it was being reconstructed.
      
      5)      Can you share the molar ratio (NH3:NOx) for the three kilns during SNCR operation?
      
We do not know the molar ratio, only the emission rate and injection rate.
      
      6) Also, I was wondering if you could verify some information that I obtained from Shaun Burke in regard to the Montana City kiln in the nearer term.  We have a reagent (19% aq. NH3) usage rate for Montana City of 0.545 gal/ton clinker as a long-term average.  Is that accurate? 
      
      YTD the number is 0.547 gal/ton clinker for 2016.
 
Thanks in advance.  Please call if you have any questions.