1. The SCR catalysts in Units 1 and 2 of the New Harquahala Generating Station are showing signs of premature degradation and reduced performance. 2. Data from lab tests and on-site inspections indicate that the catalysts are reaching the end of their useful life and will no longer be able to maintain emissions within design limits by fall 2009. 3. The catalysts have a reduced ability to control NOx emissions in the first few hours after startup when temperatures are transitional rather than optimal for NOx conversion, requiring more ammonia injection and risking emissions exceedances as the units struggle to warm up the catalysts.

1. Graphical Analysis of NHGC Unit
1 & 2 SCR Performance
The need to replace catalyst due to
premature performance degradation
and no further options for service life
optimization.

2. It is important to note that increases
in ammonia flow can be an direct Ammonium Hydroxide Flow Unit 1
representation of reduced catalyst
reactivity. Avg. NH3 Flow
700 Rate of Ammonia use increase
650 was minimized via better control
l 600 and prevention of overfeeding.
b
550
s
500
/
450
h
Improved/lower levels due to 400
r
installed catalyst seal 350
strips(2/9/09). 300
2006 2007 2008 2009 2010 2011
High levels due to historically high CT
emissions, flue gas bypassing the Ammonium Hydroxide Flow Unit 2
catalyst, and catalyst
masking/plugging. Avg. NH3 Flow
700
Rate of Ammonia use increase in
650
l 2011 was minimized via better
600 control and prevention of
b 550 overfeeding on start up.
s
500
/
450
Improved/lower levels due to h
400
installed catalyst seal strips r Further reductions realized due
350
(2/29/08), vacuuming catalyst to less cyclic operating profile.
surface, and improved CT 300
emissions. 2006 2007 2008 2009 2010 2011

3. Environex 2007 SCR Catalyst Evaluation Unit 1
The SCR catalyst in Unit 2 is approaching end of life based on catalyst performance and operating data. By fall
2009, the SCR catalyst will no longer maintain emissions within design limits. Environex 2008 SCR Catalyst Evaluation Unit 2
(Conclusions)
This audit of the New Harquahala Units 1 and 2 SCR catalyst shows that the catalytic potential of the SCR
catalyst, as measured by lab-scale testing, is at the performance threshold. The catalyst performance level is
currently at its end of life condition. Cormetech SCR and CO Catalyst Inspection and Performance Test Report 2009

4. 25
Unit 1 NOx following start up 2011 2.55
2.45
20.9
20 2.35
18.6
2.25
16.7 16.5 16.9
15.6 15.7 15.7
15
14.4 14.3 14.6 4.6
1 14.5 2.15
14 13.9 3.8
1 14 13.7 14.2 13.7
lbs/hr
13.6
13 12.6 12.8 12.5
12.4 12.3 12.3 12.4 2.3 12.7 12.2
1 12.3 1st hr NOx lbs
11.3 2.05
2.03 2.03 lb/hr Limit
10 2.00 2.00 .00
2
9.3 1.97 1.97 1.97 1st 3hr Avg ppm
1.95
1.93 1.93 1.93
7.4 1.90 1.90 3hr ppm Limit
1.87 1.87 1.87
1.85
5 1.83 .83 .83
1 1 1.83 1.83 1.83 1.83 1.83 1.83
1.80 1.80 1.80 1.80 1.80
1.77 1.77 1.77 1.77 1.77
1.75
0 1.65
7/2/2011
7/5/2011
7/6/2011
7/7/2011
7/8/2011
8/1/2011
8/2/2011
8/3/2011
8/4/2011
8/5/2011
8/8/2011
8/9/2011
9/1/2011
9/3/2011
9/6/2011
9/8/2011
6/22/2011
7/11/2011
7/12/2011
7/13/2011
7/18/2011
7/19/2011
7/20/2011
7/21/2011
8/10/2011
8/11/2011
8/15/2011
8/16/2011
8/17/2011
8/18/2011
8/19/2011
8/22/2011
8/26/2011
8/27/2011
8/29/2011
8/30/2011
Date
Units 1 and 2 (next page) both show a reduced ability to control NOx emissions during the first few hours after start up. The
catalyst at this time is within design operating temperatures though it has not yet reached normal operating temperatures
that optimize the NOx conversion efficiency. To counter act the reduced performance (due both to catalyst degradation and
transitional temperatures) during this time frame, NHGC must resort to feeding more aqueous ammonia into the SCR. While
the increased ammonia injection has a short term impact on decreasing stack NOx, in the long run it more negatively impacts
the emissions control efficiency by slowing the warm up process further hampering catalyst performance. This ultimately
results in stack emissions excursions. As we approach closer to the permitted emissions limits, the probability of exceeding
them increases as NHGC struggles to achieve adequate catalyst temperatures while injecting enough ammonia to meet stack
emission limits. Unit 2 has the most operating hours and worst catalyst performance and is more prone to these excursions.

5. 2.55
Unit 2 NOx following start up 2011
25
2.45
2.40
21.5
2.35
20.5
20
2.30
2.27
17.7 17.8 17.8 2.25
16.9 16.8 16.9
2.20 16.9
16.4 16.4
2.17 15.9 15.7
15 15.2 14.9 15 2.15
14.3 14.3 13.9 2.13 14.5 14.6
14.4
lbs/hr
14 14 14 14.1
13.5 13.6
2.10 1st hr NOx lbs
13.1 12.7
12.3 12.3
12.2 12.2 12.3 12.2
12.1 12.4
12.2 2.07
11.9 2.05 lb/hr Limit
2.03
11
10 10 1st 3hr Avg ppm
1.97 1.97 1.97
1.95 3hr ppm Limit
1.93 1.93 1.93 1.93
1.90 1.90 1.90
1.87 1.87 1.87 1.87 1.87 1.87
1.85
1.83 1.83 1.83
1.83 1.83
1.83 1.83
5
1.80 1.80 1.80
1.80 1.80
1.80
1.77 1.77
1.75
1.70 1.70
0 1.65
Date
Following this excursion on Optimizing the ammonia feed system included restricting ammonia flow while the system was still in
8/9/2011 caused by overfeeding “start up” status to allow faster warm up of the SCR system and SCR catalyst before “online” status is
ammonium hydroxide during start achieved and the emissions limits become more restrictive (as identified in the graph above).
up, NHGC optimized the system to Also, the flow rate increase of ammonia after “online” status is achieved was reduced to prevent
better prevent an exceedence. quenching of the SCR system and a resulting loss of control in NOx emissions.

6. Addition Pertinent Information
NHGC hired Siemens to tune Results and situations for 2011
both Units 1 and 2 made NHGC decide to do
Combustion Turbines on something to remedy
8/2/2011. An effort was catalyst performance.
made to specifically NHGC knew that catalyst
improve NOx emissions at needed to be replaced but
the inlet to the SCR catalyst. was hopeful that service life
Data and trends show that could be extended. When
the effort did not have any test results came back that
appreciable impact catalyst cleaning would
(increase or decrease) have a negative impact the
during and shortly after effort to replace the catalyst
start up. immediately became
imperative.

7. Catalyst History/Timeline
Accelerated Degradation Further
Complicated by CT Exhaust Emissions

8. 90% Fresh Surface area all units
Units 2&3 adequate activity
Silica Fouling on Unit 1 below Unit 2 Seal Strips Installed
design conversion and Catalyst vacuumed
June 2007 ~ Environex February 29, 2008
2007
2008 2009
Unit 2 below design conversion of 90%
Avg activity 54% (min 58%)
silica, aluminum, insulation fouling, less
than 90% surface area
AIG free of salt deposits
Unit 2 analysis April 2008 ~ Environex

9. February 2010
February 2009 Unit 3 operating at
92% conversion
Unit 1 Seal Strips (fresh sample 93%)
Installed and
Catalyst Vacuumed ~ Cormetech
2009 2010
September 2009 August 2010
Analysis shows Units 1 & 2 at or Units 1 & 2
below design NOx Reduction operating below
Efficiency of 90% 90% design
conversion rate
Unit 1 shows 25% blockage
Unit 2 no plugging ~ Cormetech
Seal strips in place
Units 1 & 2 ~ Cormetech

10. January 2012
Unit 2 sample shows insufficient
93% NOx NOx conversion margin for reliable
performance.
reduction
rate needed Significant surface loss found
February 2011 August 2011 caused by fouling and de-
at 35 ppm lamination of the catalyst affecting
Unit 3 Operating at NHGC optimized SCR logic per Fuel catalyst performance
design conversion Tech and tuned CT for optimum Unit 2 ~ Environex
Catalyst inlet conditions
2011 2012
November 2011
Analysis shows Units 1 & 2 at or
below design NOx Reduction
Efficiency of 90%
Unit 3 at design efficiency
Units 1, 2 & 3~
Cormetech