- 1 - 

### APS ANALYSIS OF EFFIC ACY OF LNB’S AND OFA

AT FOUR CORNERS

EPA has requested comment on ...”the potentia l efficacy of LNB + OFA on all Units at FCPP.” EPA assessed that Units 1, 2 and 3 have fireboxes (furnaces) too small to effectively utilize modern-day low-NOx burne rs (LNB) and separated overfire air (OFA) combustion-based NOx control technologies. In support, EPA correctly referenced the “considerable operational problems” experien ced on Unit 2 subsequent to retrofit of
Foster Wheeler LNB in late-1998. EPA concl udes that due to their small size (assumably meaning fireboxes or furnaces), Units 1 & 2 with LNB and Unit 3 with LNB + OFA will not provide significant NOx c ontrol beyond present-day levels . EPA further references
the cell-burner boiler classification of Units 4 & 5 and the higher presumptive levels of NOx control established by the EPA for this group of boilers. EPA concludes that because higher NOx standards were set for cell burner boilers that these units have “inherent design limitations” on the applicati on and effectiveness of OFA compared to conventional dry-bottom, wall-fired boilers. APS offers the following comments on the potential effectiveness of LNB + OFA on each of the different boilers at FCPP.

A. Units 1 & 2 - Units 1 & 2 are Riley Stoker pulver ized-coal (p.c.), dry-bottom, front wall fired boilers designed circa 1961 that went into commerci al service in February and May of 1963. Each unit is presently rated at an output of 170 MWNe. The unique features of the furnaces (fireboxes) on th ese two units with regards NOx control capability or limitations are: a) the closel y-pitched horizontal spacing (only 5’-5”) of burners in its 3 row x 6 column burner firing pattern; b) tangent-tube furnace construction with estimated 4% to 6% ‘tramp’ air infilt ration; c) very sma ll upper furnace residence time (only 0.41 sec.) for potential OFA additio n; d) a common furnace rear wall and convection-backpass front wall design that prevents the possibility of adding OFA ports to the rear wall; and e) an unfavorable , upper-furnace Radiant Superheat (RSH) design arrangement. By far the most problematic of these issues that constrain more aggressive
NOx reduction levels are the close horizontal burner spacing and the very small upper
furnace residence time. These two issues will now be discussed in some detail.

The furnace and convective back-pass design on Units 1 and 2 are shown in Figure 1-1. Each of the (18) p.c. fired burners on Un its 1 & 2 are designed for 102 million Btu/hr heat input with furnace wall throat openings on Unit 1 of 33” diameter (original design) and 38” diameter throat openings on Unit 2 with its LNB. The closely-pitched,
horizontal burner-to-burner thro at openings on Units 1 & 2 of only 5’-5” are much closer than industry standards [1] , and hence atypical of conven tional wall-fired-boiler burner array spacing of between 8 ft. to 9 ft. separa tion vertically and horiz ontally. Reference [ 2 ] submitted to “Environmental Organizations” including New Mexico Citizens for Clean

1 Coal Combustion , J. Tomeczek, Krieger Publishing, 1994. Reco mmended standard is horizontal pitch of 3 * throat diameter. Thus, desired Unit 1 & 2 horizontal burner spacing would equal 8.25 ft. (3* 33”) to 9.50 ft. (3* 38”).

2 Staudt, J.E., “ Assessment of Potential for Further NOx Reduction by Combustion-Based Control at Four Corners Steam Electric Station”; Final Report, April 2004, Andover Technology Partners (ATP)- 2 - Air and Water, and others, in April 2004 di scusses in some depth the importance of adequate separation between LNB in a multiple burner array and the significant risk of upsetting near-burner fuel:air mixing and comb ustion aerodynamics critical to optimal NOx control and combustion efficiency if burne rs are too closely spac ed. A key focus of discussion was on recognition of two alternate flame types, Type 1 and Type 3, produced by different, commercially-ava ilable LNB designs and their applicability to different furnace designs and burner spacing arrays. These flame types are redrawn and included herein as Figures 1-2 and 1-3. Type 1 LNB flames were discussed as slow-diffusion, low secondary air swirl designs with narrow flam e angle (of spread) and long, luminous flame zones caused by the full centerline penetration of the PA/coal jet (see Fig. 1-2). Flame attachment is achieved by bluff body flame stabilization [ 3 ]. The ATP report identified B&W and Riley Power LNB as having Type 1 flame characteristics, and noted the lengthened flames produced by these LNB were typically not compatible with older vintage, single wall fired furnaces having relatively shallow furnace depth and limited height such as Units 1 & 2. Type 3 low-NOx flames utilize strong secondary air swirl to create an annular, inte rnal recirculation zone (IRZ) in the near-burner region along the burner axis. In a properly de signed Type 3 LNB, the PA/coa l streams (jets) partially penetrate into the IRZ before being revers ed to flow backwards and along the outer boundary of the swirling recirculation zone. Near-burner flow patterns within Type 3 low NOx flames are illustrated in Figure 1-3. Type 3 flames have a wider flame angle (of spread) due to the strong sec ondary air swirl, shorter flame lengths due to the lack of central PA/coal jet pene tration, and are swirl stabilized for flame attachment. However, this flame type requires precise control of SA swirl levels and PA/coal jet velocity to
achieve the critical balanci ng of forward momentum forces from the PA/coal jets

3 Combustion Aerodynamics , Beer, J.M, Chigier, N.A., Krieger Publishing (1972).- 3 - Figure 1-1. Picture of F our Corners Units 1 & 2 Reheat Boiler (Side View)- 4 - Figure 1-2. Type 1 Low NOx p.c. Burner Flame on wall-fired boiler

Figure 1-3. Type 3 Low NOx pulveri zed coal flame on Wall-Fired burner

against the reverse velocity field of the IRZ. ATP identified Foster Wheeler and ALSTOM Power LNB as having Type 3 flame characteristics.- 5 - Based of these flame type discussions, th e ATP report recognized the likely adverse burner-to-burner flame interference occurring with the FW, high swirl type LNB installed on Unit 2. ATP assessed the ALSTOM low-NOx burner as a possible replacement for the FW burners, but was not able to rectify the high combustion air swirl design of this
burner with ALSTOM claims that the flames had a narrow angle of spread which avoided
burner-to-burner interferen ce in closely-pitched burne r arrays. The ATP report concluded there was no compelling evidence (including ALSTOM field experience) to suggest that the ALSTOM low-NOx burner w ould perform any better than the FW design in the tightly-spaced burner array on Units 1 & 2. It was also stated that ...”it may be possible that a different burne r design might resolve the cu rrent problems on Unit 2. But that will only be determined with time as the problems of Unit 2 become better
understood.”

In 2008 as part of BART evaluations fo r the FCPP under Regional Haze rules, APS’ engineering staff made an update d, detailed study of the tech nical feasibility and design practicability of retrofitting the latest, most-advanced LNB and LNB + OFA systems being supplied by U.S. manuf acturers on Units 1, 2 and 3 [ 4 ]. These evaluations were made to determine whether Units 1, 2 and 3 could achieve NOx emissions ≤ 0.42 lb/mmBtu (LNB only) or ≤ 0.32 lb/mmBtu (LNB + OFA) and simultaneously control PM emissions and stack opacity to acceptable le vels without jeopardi zing unit reliability, efficiency, or output capacit y. Central to these evaluations was identifying a commercially-proven LNB capable of achie ving optimal NOx performance without flame interference issues in a close-spaced burner array, and with acceptable luminous flame length. To this end, an extensive study was made of technica l papers published in the last ten years with an emphasis of evaluation and disc ussion on near-burner mixing patterns and combustion aerodynamics of comm ercial, p.c. fired U.S. LNB designs [ 5

, 6

, 7

, 8 ]. This work revealed th at a third low-NO burner flame t ype existed with near-burner flame aerodynamics in between Type 1 and Type 3 LNB flames. The aerodynamic flow patterns and ignition characteristics of this flame type (designated as Type 1-A) are shown in Figure 1-4. In Type 1-A low-NOx flames the overall swirl number (S) for collective secondary air and PA /coal streams is in the low-to-moderate range (0.2 < S < 0.45) which overlaps the swirl number of Type 1 slow-diffusion flames (0.2 < S < 0.3). [The swirl number is simply the normalized ratio of angular to axial momentum of the
combustion air and PA/coal flow streams exiti ng the burner throat ope ning.] The bluffbody flame attachment ring and SA diverter create a local IRZ i mmediately downstream of the burner exit driven by th e PA/coal jet, and strengthened by the swirl applied to the PA stream. Swirl primarily from the out er SA jet creates a second ERZ radially

4 Allen, C.D., “ Engineering Report on Low-NOx Burner + Overfire Air Application and Systems Design Options for Four Corners S.E.S, Units 1 – 5 Wall-Fired and Cell Burner Boilers”; Rev. 0, Sept. 2008,

. APS Privileged and Confidential report.

5 Gu, M., Zhang, M., et. al., “ The Effect of Mixing Characters of Primary and Secondary Air on NOx Formation in Swirling Pulverized Coal Flames “; June 2005.

6 Dorman, D., Courtemanche, B., Yilmaz, A., “ Reducing NOx Emissions and Commissioning Time on Southern Company Coal Fired Boilers with CFD Analysis ”; March 2003.

7 Hules, K.R., Yilmaz, A., “ Bunker to Stack: Cost Reduction an d Problem Solving Benefits of CFD for Utility Power Generation ”; Dec. 2002

8 Heap, M.P., Davis, K.A., Sarofim, A.F., et. al., “ Optimized Fuel Injector Design for Maximum InFurnace NOx Reduction and Minimum Unburned Carbon” ; Final Report 1998- 6 - displaced and slightly downstream from the PA-driven IRZ. As de picted in Figure 1-4, part of the fuel-rich PA/coal stream is re-cir culated back towards th e IRZ at the base of the flame while the remainder penetrates al ong the burner axis anal ogous to Type 1 nearburner flame aerodynamics shown in Figure 1-2. Type 1-A flames have a narrow flame angle of spread and normalized luminous flame lengths (flame length/throat diameter) in the range of 7 to 7.5 [ 9 ]. Riley Power Inc. (RPI) is th e primary U.S. manufacturer of LNB with Type 1-A flame char acteristics and a photo showi ng its actual flames in a tight-spaced burner layout is shown in Figure 1-5.

Figure 1-4. Type 1-A Low NOx Pulveriz ed Coal Flame on wall-fired burner

9 Hayes, J.M., Beer, J.M., “ Adrodynamic Modeling and Scale-Up of a Low NOx Oil Burner” ; ASME Conf., 1996.- 7 - Figure 1-5. Flame Zones at Branch U4 w ith 122 mmBtu/hr CCV-DAZ Burners in CloseSpaced Cell Burner Layout; note narrow flame angles.

Table 1-1 shows a summary comparison of key burner design parameters and flame types for commercial LNB developed from APS’ most recent studies. Also shown in the table are predicted NOx , CO, LOI, and PM emissions based on a retrofit of Units 1 & 2 with Riley Power CCV-DAZ low-NOx burners. Note that the Riley LNB is the only design APS now evaluates as being capab le of achieving NOx emissions ≤ 0.42 lb/mmBtu (LNB only) with acceptable flame length and reliab le, full-load boiler operation. Performance predictions for NOx, CO, etc. in Table 1- 1 are based on engineering analysis and regression correlation of field data collected from recent LNB retrofits on p.c. fired boilers with comparable (or more severe) fu rnace design parameters and firing similar or higher rank high-volatile bituminous co als as Units 1 & 2 at the FCPP [ 10 ]. NOx performance information supplied by vendor s was checked against the EPA Clean Air Markets database. Hence, in summary, APS believes it now has identified a LNB design that will provide significant NOx control improvements on Units 1 and 2 with burners only ( i.e., 46% additional reduction on Unit 1 and 34% additional reduction on Unit 2) with acceptable luminous flame length and combustion efficiency performance.

10 Reference: Louisville Gas & Elect ric, Cane Run Unit 5; and Georgi a Power, Harllee Branch Unit 4.- 8 - Table 1-1. Design Parameters and Flame types of Commercial LNB, and Predicted Performance of the RPI design burner on Units 1 and 2

Burner/Boiler Manufacturer

Parameter B&W/
DRB-4Z Riley /
CCV-DAZ FW / Vortex ALSTOM /
RSFC Siemens (ABT) / Opti-Flow
LNB

SA Swirl 0.2 – 0.3 0.2 – 0.45 0.6 – 0.9 0.6 – 1.1 Insuff. data

PA Swirl zero 0.2 zero 0.2 zero

PA Vel., ft/sec 65 – 85 65 – 85 85 – 110 about 100 Insuff. data

Quarl α , deg 25 25 22 25 / 0 ?

Flame Type 1 1-A 3 3 ?

Normalized Flame Length 8 – 9 7 – 7.5 5.5 – 6 ~ 6 ?

Applicable 4C
Boilers 4 & 5 1 – 5 3 – 5 3 – 5 ?

Predicted Performance on Units 1 and 2

Predicted NOx,
lb/mmBtu ≤ 0.42

Guarantied NOx by RPI, lb/mmBtu ≤ 0.40

CO at boiler exit,

ppm < 50 – 60

Pred. Avg. LOI, Wt.
% in ash 1.0

Avg. PM Emissions at stack, lb/mmBtu 0.033- 9 - The second major design constraint which limits NOx control effectiveness or reduction potential on Units 1 and 2 is the very small upper furnace residence time. EPA is correct in identifying this as a major concern. In fact, upper furnace residence time is the foremost factor governing the successful application of se parated OFA -- in conjunction with LNB. Upper furnace residence time (U FRT) is typically defined by the furnace volume between the OFA port elevation to th e apex of the furnace nose divided by the boiler flue gas flow rate [ 11 ]. OFA ports are typically placed on the firing wall and installed 8 to 10 ft. above the top burner row. Adequate upper furnace residence time is required for effective mixing of OFA with upward flowing furnace gases and unburned fuel (primarily CO and char particles), and combustion burnout of this un-reacted fuel. EPRI guidelines [ 12 ] and preliminary rules of thumb applied by U.S. boiler OEM’s for evaluating the feasibility of OFA application are roughly:

• UFRT > 1.0 sec. (ideal);

• 0.6 < UFRT < 1.0 sec. (acceptable to good);

• UFRT < 0.5 sec. (insufficient).

Upper furnace residence time on Units 1 & 2, calc ulated at a bulk average temperature of
2500°F and corrected for elevation above sea level, is only 0. 41 seconds. With this very short UFRT, if a conventional front-wall OF A system were applied to Units 1 & 2 it would be almost assured that significant in creases in CO emissions, increased unburned carbon in the ash, increased furnace exit ga s temperatures, and unacceptable PM emissions accompanied by noticeable incr eases in stack opacity would occur [ 13 ]. In fact the UFRT on Units 1 and 2 for potential a pplication of conventional front wall OFA systems is outside (below) the successful experience range of any U.S. LNB/OFA
manufacturer. This is the reason ATP c oncluded in 2004, and APS has confirmed with its most recent re-evaluations, that Un its 1 and 2 in their present furnace design configuration are not te chnically feasible candidates for OFA addition.

B. Unit 3 - Unit 3 is a Foster Wheeler p.c., dr y-bottom, front wall fired boiler also designed around 1961 – 1962 that went into co mmercial service in April of 1964. The rated output of Unit 3 is 220 MWNe. A side elevation view of the Unit 3 furnace and convective back-pass is shown in Fig 1- 6. The Unit 3 furnace has several advantages over Units 1 & 2 with regards to NOx contro l features: 1) it is designed with moreconventional, approximate 8 ft. horizontal a nd vertical burner spacing; 2) furnace walls are membrane construction versus tangent tube hence furnace ‘tramp’ air infiltration is not an issue; 3) the common furnace rear wa ll and convection back-pass front wall only

11 Some burner/boiler manufacturers apply an uppe r furnace volume effectiveness factor in calculating UFRT’s; another defines the furnace exit at the bottom elevation of fu rnace WW platens or RSH platens.

12 Eskinazi, D., “ Retrofit NOx Controls for Coal-Fired Utility Boilers”; EPRI Research Project 2916-7.

13 Trego, P., Kleisley, R, Panzera, P., “ Cromby Unit # 1: Challenges of Retrofitting Low NOx Combustion Technology to a Single Wall Fired Boiler ”; ASME Joint Power Conference, Oct. 1995.- 10 - Figure 1-6. Side Elevation Drawing of 4C Unit 3 Furnace and Convection Back-Pass OFA
Ports- 11 - extends 16 ft. below the apex of the furnace arch thereby allowing the potential of OFA ports addition in a revised burner firing pattern; and 4) the upper furnace Radiant Superheat design layout conforms to presen t-day utility boiler de sign standards (was redesigned/replaced in 1980). The two pr imary design issues presently limiting the
effectiveness of NOx control on Unit 3 ar e: incorrectly-designed, second-generation CF/SF type Foster Wheeler low-NOx burners ; and a very small upper furnace residence time (only 0.40 sec. as on Units 1 & 2) from where front wall OFA ports would have to
be located to the furnace exit.

The existing high swirl FW split-flame LNB in stalled on Unit 3 in 1990 were expected to
achieve NOx emissions of ≤ 0.45 lb/mmBtu at the furnace design burner zone heat release rate (BZRR) of 250 kBtu/hr-ft 2 [ 14 ]. This performance was never achieved, not due to any burner-to-burner flame interferen ce issues as on Units 1 & 2 but due to an incorrect SA-to-PA design velocity ratio at the burner throat. A typical design value for this ratio is around 1.0, based on APS’ detailed design review of ten (10) other front wall fired boilers equipped with Foster Wheeler CF/SF or I FS design LNB. Although FW added an insert piece into the burner no zzles on Unit 3 around 1992 to increase the PA/coal jet velocity, this was only able to lower the SA/PA velocity ratio to 1.35 – 1.40. The physical and aerodynamic effects of this mismatch in key burner design velocities are: 1) to increase shear-induced turbulence (and mixing) between the two steams at the base of the flame; and 2) to cause an earlier than desired breakup of the four, concentrated, fuel-rich PA/coal jets leaving the burner nozzle [ 15

, 8

, 16 ]. Both of these effects raise NOx emissions. Linear regres sion analysis performed on Unit 3 data for a regression of NOx on the SA/PA velocity rati o showed NOx emissions are increased by ~
0.08 lb/mmBtu due to this mismatch of SA a nd PA axial velocities at the burner exit.

Since the Unit 3 firebox does not have the tight burner spacing constraint of Units 1 & 2, two (2) alternate, modern-day low-NOx burner designs are assessed by APS to be most advantageous: either the Riley Power CCV-DAZ burner, or the Foster Wheeler “Vortex” burner (see Table 1-1). Based on APS’ review of other front wall fired furnaces with comparable design features to Unit 3 (e .g., BZRR, balanced draft, membrane wall, ≥ 8’ x 8’ burner spacing, BZRT ≥ 0.9 sec.), and firing similar high volative bituminous C or B grade coals, predicted NOx emissions with th ese latest, most-advanced (third-generation)
low-NOx burners would be ≤ 0.42 lb/mmBtu. This represents an additional 29% reduction in NOx levels (i.e., (0.59 – 0.42)/0.59 *100 = 29%) with a LNB only changeout on Unit 3.

Unit 3 does have an option for a more compact burner firing pattern to give space in the upper furnace for front- and/or rear-wall OFA ports and slightly improved upper furnace residence time for mixing and burnout. This approach involves de leting the two, top row “wing” burners and converting to a 4 x 4 fi ring pattern (16 burners versus 18). The existing three ball-tube mills would be retain ed with the top mill supplying four burners, and the bottom two mills each supplying six bur ners. Front and rear wall OFA ports,

14 Allen, C.D., “ Summary Engineering Report on Application of Foster Wheeler CF/SF Low-NOx Burners,
Four Corners Unit 3 ”; Oct. 1987.

15 Cremer, M., Davis, K., Letcav its, J. Vierstra, S., et. al., “ CFD-Based Development, Design, and Installation of Cost-Effective Control Strategies for Coal-Fired Boilers ”;

16 Low NOx System CFD Modeling and Design Study, Nevada Power – Reid Gardner 1 & 2; FWEC Confidential Report, 1997.- 12 - preferably in an interlaced (staggered) la yout, or rear wall only OFA ports (second option), would be located at the current elev ation of the top row bur ners (El 5403’-6’, see Figure 1-6). Analytical CFD modeling by Reaction Engineering (REI) and B&W has shown that front and rear wall OFA port de signs, followed by rear wall only OFA ports, provide the best mixing and CO/LOI burnout on front wall fired utility boilers with limited upper furnace residence time [ 17

, 13 ]. The UFRT on Unit 3 would be increased from 0.40 seconds to 0.52 seconds by the above described burner fi ring pattern redesign and OFA port layout.

Predicted Unit 3 full-load (220 MWNe) emissi ons performance with a 20% OFA system, as described above, in conjunction with eitherRiley CCV-DAZ or Foster Wheeler Vortex low-NOx burners is [ 18 ]:

1. NOx emissions ≤ 0.32 lb/mmBtu;

2. Average CO emissions ≤ 125 to 150 ppm at boiler exit;

3. Carbon in ash of 1.5% to 2.0%, by weight; (i.e., 50% to 100% increase).

4. PM emissions at stack with existin g VS in range of 0.040 – 0.044 lb/mmBtu.

In summary, APS believes that significan t additional NOx control reduction can be
achieved on Unit 3 – on the order of 46% fr om present day levels, with properly designed, modern-day low-NOx burners in a revised burner firing pattern and in conjunction with a front- and rear-wall designed 20% (of total combustion air) OFA system.

C. Units 4 & 5 - Units 4 & 5 are dry-bottom, opposed-f ired, cell burner boilers originally equipped with three-nozzle cells in a non-sy mmetrical firing array. In 1989 (U4) and 1991 (U5), the units were retrofit with “non-pl ug controls” for NOx (i.e., Foster Wheeler CF/SF low-NOx burners on approximate 9.0 ft. hor izontal and vertical burner spacing; 4 row x 6 column firing array). Both units are rated at a nominal 800 MWG electrical output and went into service in July, 1969 (U4) and July, 1970 (U5). The boilers on
Units 4 & 5 are B&W once-th rough, supercritical water/st eam pressure design with membrane-wall furnaces and a positive-pressu re, gas-side furnace design (versus balanced draft). The furnace design uses B&W’s three-pass Universal Pressure (UP) flow circuitry with multiple intermediate waterwall collection/distribution headers and interconnecting piping located in the upper regions of the windboxe s. EPA asserts that as cell burner boilers (EPA Phase II, Group 2) Units 4 and 5 have inherent design features
that limit the effectiveness of combustion-ba sed NOx control versus conventional wallfired burner boilers (EPA Phase II, Group 1) . As APS has commented in the past [ 19 ],
cell burner boilers are in fact no different in their baseline, uncontrolled NOx emissions or in the NOx control achieved by LNB only than wall-fired boilers in an opposed-wall

17 Davis, K.A., Eddings, J.R., Heap, M.P., “ Evaluating the Effects of Low-NOx Retrofits on Carbon in Ash
Levels ”; EPRI-DOE-EPA Combined Mega Symposium, Atlanta, 1999.

18 Reference: Gulf Power, Crist Unit 6 (R PI); FHI – Units LT3 and CCP2, China (FW).

19 See APS Comments dated March 19, 1996 on Proposed EPA NOx Acid Rain Program – 40 CFR Part 76, Docket No. A-95-28.- 13 - firing pattern. This is shown by the data and correlation shown in Figure 1-7 where uncontrolled NOx emissions of several wall-fired boilers (both single-wall fired and opposed-wall fired) are plotted along with unc ontrolled NOx emissions from several cell
burner boilers. This data was taken from EPA’s own database and extensive databases collected by the Edison Electric Institute (EEI) in the mid-1990’ s. It can be seen that baseline, uncontrolled NOx emissions from wall-fired burner boile rs with opposed-wall firing are in the same range as for cell burner boilers. The distingui shing feature of cell
burner boilers as a boiler population is that they are all opposed-wall fired with burner
zone heat release rates in the range of 300 – 500 kBtu/hr-ft 2 (FW definition basis for BZRR). On the other hand, the much larger wall-fired burner boile r population includes a significant percentage (~ 75 %) of single-wall fired units wi th burner zone heat release rates in the range of 150 – 300 kBtu/hr-ft 2 . Based on a relatively small sample size (n < 30) analyzed by APS back in 1996, single-wall fired boilers had uncontrolled mean NOx levels of 1.04 lb/mmBtu while the large r-sized, higher capacity opposed-wall fired
boilers had a mean uncontrolled NOx level of 1.25 lb/mmBtu. Thus the mean uncontrolled NOx for the entire populati on of “wall-fired burner boilers” is approximately 0.75 * 1.04 + 0.25 * 1.25 = 1.09 lb/mmB tu, while cell burn er boilers as a group have an approximate 1.25 lb/mmBtu mean uncontrolled NOx rate. Hence, cell burner boilers will always produce hi gher uncontrolled NOx emissions,

Uncontrolled NOx vs Burner Zone Release Rate

0 0.2 0.4 0.6 0.8

1 1.2 1.4 1.6

100 200 300 400 500 600

Burner Zone Release Rate, kBtu/hr-ft^2NOx Emissions, lb/mmBtu

Cell Burner Units

Opposed-Wall Fired

Single-Wall Fired

Fitted, Linear Regression NOx = 0.0009 (BZRR) + 0.81
R^2 = 0.533

Four
Corners
Units 4 & 5

Four
Corners Units 1,2 & 3

Figure 1-7. Uncontrolled (Base) NOx as a Function of Burner Zone Release Rate
for Wall-Fired boilers and Cell Burner Boilers

and in turn – whether retrofit on a plug-in or non-plug-in basis, higher controlled emissions when compared to the co nventional “wall-fired burner” boiler population

. However, cell-burner boiler s retrofit with non-plug-in co mbustion-based NOx control- 14 - and opposed-fired conventional wall-fired boilers ar e similar or analogous in burner firing pattern physical appearance, key furnace ke y parameters, and in their capability for comparable NOx reductions. For comparison to Units 1, 2 & 3 at the FCPP, Units 4 & 5 have a higher BZRR of 380 kBtu/hr-ft 2 (see Figure 1-7), but an upper furnace residence
time of 0.84 seconds.

As discussed herein it would be expected that LNB with Type 1 or Type 1-A narrow angle of spread luminous flames would be most successful if retrofit on cell burner boilers on a plug-in basis. In fact this is the case with Riley Power’s CCV and CCVDAZ low-NOx burners having achieved NOx reduc tions in the range of 50% - 60% using “burners only” in cell-fired configurations [ 6 ]. Riley claims they have retrofit over 7,000
MW of cell-burner-fired util ity boilers with their CCV or CCV-DAZ low-NOx burners [ 20 ]. B&W has also had some success in retr ofitting their DRB-XCL low-NOx burner on a plug-in basis for cel l burner boilers [ 21 ].

APS’ retrofit of Units 4 and 5 with Foster Wheeler second-generation CF/SF LNB in a non-plug-in design approach achieved NOx reduc tions of 50% - 52% with burners only.
Mean NOx emissions were reduced from 1.15 lb/mmBtu to around 0.53 lb/mmBtu [ 22

, 23 ]. Units 4 & 5 presently operate at an nual-average NOx emission of 0.49 lb/mmBtu with normal, full-load operation frequently ha ving one (1) pulverizer out of service but with its secondary air registers partially open. This creates a slight burner zone “staging” effect which further lowers NOx emissions by around 5%, depending on which of the eight (8) pulverizers is out of service. As shown in Table 1-1, the widened 9 ft. x 9 ft. horizontal and vertical burner spacing on Units 4 & 5, and the 42 ft. firing depth between front and rear walls, allows three (3) diffe rent modern-day, improved-performance LNB
to be considered: B&W’s D RB-4Z, Riley’s CCV-DAZ, and FW’s Vortex burner. All three of these burner designs, in conjuncti on with a conventional front- and rear-wall 20% to 25% OFA system are considered by APS to be “technically feasible” for application on Units 4 & 5. [T echnical feasibility is define d as being able to operate Units 4 & 5 with improved low-NOx emissions while maintaining good boiler operability and reliability.] APS’ review of comp arably-designed, opposed-wall fired, drum and supercritical pressure boilers with equiva lent BZRR’s, burner zone and upper furnace residence times, conventional 20% - 25% OFA, and firing high volatile bituminous coals of equal or higher rank than Four Corner s, showed NOx emissions performance of ≤ 0.35 lb/mmBtu with any of these three different LNB designs [ 4, 24 ]. This predicted NOx level represents a 28% reduction in NOx emissions , or over seven (7) million pounds of NOx reduction annually from each Unit.

20 See Babcock Borsig Power T echnical Bulletin No. B-97/02.

21 LaRue, A.D., Costanzo, M.A., et. al., “ Update of B&W’s Low NOx Burner Experience ”; ASME International Joint Power Conference, July, 2000.

22 Allen, C.D., “ Low-NOx Burner Evaluation at the Four Corners Station – Units 4 & 5, Comparative Emissions and Thermal Performance ”; EPRI Product RP2916-4, Final Report, July, 1994.

23 Allen, C.D., “ Review of NOx Emissions Performance Compared to Post-LNB Retrofit Baseline Data,
Four Corners Unit 5 ”; Generation Engineering Dept., March, 1995.

24 Reference: Mississippi Power, Jack Watson Unit 5 (R PI); Allegheny Power, Fort Martin Unit 2 and First Energy, East Lake Unit 5 (B&W); Tucson Electric, Sp ringerville U3 and Seminole Electric, Palatka Units 1 & 2 (FW).- 15 -