### Background: 

## Summary Report for USS On NOx reduction for Kilns #6 and 7 S. Londerville 10/26/11

Coen Co. has been actively involved in supplying burners for reduced NOx to U.S.S. working with U.S.S. consultants (Hatch). The NOx reduction is difficult due to secondary air preheat of over 2100 deg Fat over 300% excess air (EA). Both EA and high temperature contribute to high thermal NOx formation. Further, high excess air contributes to higher fuel bound nitrogen conversion in the coal fuel. The main source ofNOx in the system is thermal NOx and partial contribution from fuel bound nitrogen in the coal. The kilns are used for the ore induring process requiring high radiant heat transfer with pellet exit temperatures of@ 2265 Deg F. Two kilns (line 6 and 7) have been retrofitted to reduce NOx by adding additional cold dilution combustion air. The addition of cold combustion air will negatively impact kiln efficiency. Each kiln produces about 9400 Long tons/day of product. The line 7 burner is arranged with coal on the outside part of the burner and cold combustion air on the inside. The line 6 burner is arranged with cold combustion air on the outside part of the burner and coal on the inside. In both cases natural gas or oil is introduced in a center fire injectors/atomizers and both units have high, over 2100 Deg F secondary air introduced outside of the burner via the hood from the cooler. Normally for kilns, the fuel is introduced on the axial centerline with a minimal amount of cold combustion air for optimal performance. When the secondary air is not excessively high, typical NOx reduction techniques used are various forms of staging. Staging is accomplished by reducing the primary burner air to lengthen the flame, increase luminosity and reduce the entraimnent of hot secondary air while the flame decreases in temperature, thus limiting peak flame temperatures and NOx. In the case of extremely high secondary air, staging cannot be used because the peak temperatures and NOx will increase with reduced primary air. 

### NOx Objectives: The proposed limit is 180# N02/hr for all fuels. Natural gas has been able to meet the 180#/hr proposed limit with the addition of about 100 % stoichiometric cold combustion air at 200 MMB. Coal has been quite variable and generally has an average value of220 to 270 # N02/hr with 240 # N02 the average at 200 MMB when fired with NG. It is useful to convert the proposed limit and achieved limits to help understand what else can be done. The plot below compares NOx achieved vs proposed as a function of firing rate. Normally the unit is firing at @ 200 MMB requiring a NOx emission rate of @0.9 #/MMB to meet 180#/hr.3 2.5

2 al**~ ~** 
......... 1.5 N 0 z # 1 0.5

0 #N02/MMB vs firing rate 

# !Ill lllJ I I I II**~~ '**  ', 1 

# l l illJ I 

# lllL ll[ I**~~; ~:** **,,~~** 

# /IIIII 1111 1 111 I II I I**~ ~**  

# m±-1- c- -c-c1 1 

# r r- 11 I , I I
.

# -~ ... I""' 

# I 

# I I I I I'"" x 3 + 9E

-05x 2

- 0.0285x + 3
. 8783 R

2 = 0
. 9991

- 180#/hr target

- 200#/hr

- 240#/hr --Poly. (180#/hr target)

100 150 200 250 MMB Fired 300 350 400

Fig I #N02/MMB Vs Firing rate The proposed hourly limit of 180 #/hr will require reduced NOx in # N02/MMB as a function of firing rate. Generally this is not a practical approach as NOx will increase with firing rate. Ultimately as the unit efficiency decrea ses with added primary air, the firing rate must increase to maintain production. As a reference point for what to expect as base line we refer the EPA document AP-42 (refS). The NOx emission factor is 1.5 # N02/ton production. Using line 6 and 7 normal capacity of 9400 long tons/day this EPA emission factor results in a base line emission rate of 646#N02/hr. The emission factor is rated " D", meaning "below average" and may have variability. This EPA emission factor i s equivalent to 3.29# N02/MMB at 200 MMB firing rate . Using the proposed limit and AP-42 base line estimat e, line 6 and 7 would require@ 73% reduction in NOx. Latter in this review we discover the base line on NG is actually about 800#/hr or 4# N02/MMB. Thus, requiring a 78% reduction from baseline. The writer would like to review the results to date and provide explanations for the se results and recommendations forward
. But prior to this it may be inst ructive to review some b as ic background on NOx f01mation.

### Background on NOx Formation, Thermal NOx Therm al NOx i s for med at h igh temp era t ure s when mo l ecul ar N 2 and 0 2 disso ci ate and re act to form NO
. For formation , The Ze ld ovich equ ation is u sed as follows :

and 

### d(NO) = 

### 2AJ - 

# :T Jro) (N ) dt \ eq 2
( ) Ko ( )0
. 5 0 eq = (RT)0.5 02 eq One generally accep te d pr actice is to assume 

### o 2 in equilibriu m w ith 0 and 0 2 concen tration using the Westenburg results for K 0 see We stenberg, "Turbulence Modeling for CFD ." (l) foro 2 equilibr ium and Zeldovi ch con stants , A and E as measured by Bowman " Kinetics of Pollution Formation and Des truction in Combustion."(2). Th e 1 mal NOx in creases exponentially with temp erature as sh own in F i g 2 and 3. 

### NOx and CO vs time,Temperature at10°/oEA premixed 5 

### 4 "'-.**~** I\ -+-CO .0 1sec 

### 3

## ~ 

# \ W""" 

### H 2 

### 1\ 1 \ '\ 

# Arv 

# v ----- CO .05 sec 

### v**~**

### ~v v a. 

### 0 

## 1 \ -V CO
. 1 sec a. 

# r- \ v**1** 

# _.**+- ___!** **~ Nox**  .01 

### -2 

# 1 \ sec 

### -3 

# \ ::1( Nox .05sec



### -4 -5 --.- Nox
. 1 sec



### 1400 1900 2400 2900 3400 Deg F
Fig2 NOx and CO formation/destruction vs Temperature for premix Nat gas at 10%EA#N02/MMB vs Time a n d Temperature at 10% E A 3.5

3 2.5 al :!: 2 :!:

........ N - 3000 DegF 0 1.5 z 

# '"' - 3200 DegF 1 - 3400 Deg F 0.5

0 0 0
. 2 0.4 0.6 0.8 Seconds Fig 3 NOx E missions as a function of Temperature and Time using refl and 2

USS line 6 and 7 generally opera te on Coal with N G support. The S e condary air i s abo ut 2 100 De g F. The follo wing chart #4 compa res the adia b atic flame temp erature o f Coal v s n atural gas vs exces s air and combustion air temperature.

u.. bO QJ c Adiabatic Flame VS Excess air for coal and NG vs Air Preheat 5000 4500 4000

- NG 80 Deg air 3500

- NG 2000 Deg air 3000

- coal 80 D e g air 2500

- coal 2000 Deg air 2000 0 20 40 60 80 100 Excess air F ig 4 Adiab atic Flame t emper ature vs exc ess air and air preheat fo r C o a l and NG

### What is clear is that the thermal component of both Coal and NG have similar adiabatic flame temperatures vs excess air. For gaseous fuels we expect similar results ofNOx reduction with dilution when the flame temperatures are similar. As we will see, solid fuels behave differently with dilution. The residence time of the high NOx zone in a Kiln flame is on the order of 0.05 to 0.1 seconds depending on many variables. Given that the NOx target is near .95#/MMB (at 200 MMB) and by inspection of fig 3 we can determine that a target adiabatic flame temperature should be near 3400 Deg F. By inspection of Fig 4, we see that a viable solution is to add ambient dilution air to the burner knowing that we cannot change the secondary 2100 Deg F hot air. This was the direction taken on both Line 6 and 7 to reduce NOx. The burners were modified to significantly increase cold primary air to the burner at the expense of unit efficiency. 

### Prompt NOx formation Another NOx formation mechanism is prompt NOx. This occurs at the flame front and is responsible for no more than 20 ppm NOx in most applications. The mechanism can be summarized as: CH +N,-+ HCN BCN X

- 

### (not balanced) HCN B CN+0 2 

### -+NO+ CO+ H (not balanced) Both of these reactions are very fast and do not require high temperature. It 

### would appear that one way to reduce NOx fi·om the prompt mechanism would be to dilute the HCN and CN species on the fuel side of the combustion zone, or reduce the available oxygen. The use of premix combustion is very effective for prompt NOx reduction. The fornmtion of Prompt NOx was not a consideration in the NOx reduction program at U.S.S. 

### Fuel Bound NOx Conversion:
The fuel-bound NOx mechanism is similar to prompt NOx and proceeds through the same HCNCN chemistry. However, the fuel-bound mechanism differs in the following ways. 1. The fuel-bound mechanism requires nitrogen as part of the fuel molecule. 2. At low fuel-nitrogen concentrations, all of the bound nitrogen converts to NOx in gaseous fuels. 3. The fuel-bound mechanism can be responsible for hundreds of ppm NOx, depending on the amount of nitrogen bound in the fuel. For liquid and solid fuels the conversion ranges from 80 to 10 % 

### depending on the concentration and excess air in the flame. The first steps in the chemistry dit1er in that the intermediates are formed directly from pyrolysis of the parent molecule. Ambient nitrogen is unimportant. (not balanced)Fuel NOx contribution is a function of% FBN and stoichiometric conditions in the flame zone. For medium temperature low 02 conditions , Coal FBN conversion is about 25 % Ref 3
. With increasing E.A. this conversion will increase. For example, Given Coal at 

### HHV=10300 BTU/lbm, 

### ( . 6 lbmN ) (1lbmoleN) (1lbmoleNOz) (46 lbmNOz) ( 1lbm Fuel) ( 10 6 

### BTU )

100 lbmFuel 14 lbmN 1lbmole N lbmoleN0 2 

### 10300 BTU million BTU lbmNOz lbm 

# = Ol. 9 

### 10 6 

### BTU (ZS%) 

# = '47 10 6 

### BTU


### Evaluation of Line 6 and Line 7 results NG firing:
We will review the results ofNatural Gas firing first as it is simpler and clearer to the reader. A s ignificant amount of data was taken by plant personnel. Figures 5 and 6 is the raw NOx data plotted as a function of burner stoichiometry.



### Line 6 raw data Nox Emmissions (lbs/hr) 185 MMB Avg NG

600.00 550.00 500.00 450
.00 X**~** 400.00



## ... :E. 350.00 # 300.00**'i).--- t--t--t--t--t--t--1---l** **~** Line 6 Nox Em missions (lbs/hr) 250.00**+-+-+-+- +-+-+-+--+--** **-+--'111~ H--** **+-+-+---i** Poly. (Line 6 Nox Em mi ss ions 200.00 (lbs/hr)) 150.000.55 0.75 0.95 1
. 15 Stoc air
Fig 5 raw NOx data fi·om Line 6LINE 7 Raw data NOX (lbs/hr} 192 MMb avg NG with SKPPH atm air 300.00 .-------.-------.-------,- -- ----;- - ----;r-------,

260.00**~lr-4~ +-** **-- -:** **----+-- -v-::-~~1x.?.** ...**~- <1760.5x**  + 1394 R

2 = d.8611

160.00 140.00 120.00 LINE 7 NOX (lbs/hr) -Po l y. {LINE 7 NOX (lbs/hr))

100.00 +--- -t----1- -- --i- ----+----ir------i 0.90 0
.95 1.00
Fig 6 Raw NOx data fi·om line 7 1.05 Stoc air 1.10 1.15 1.20

We can clearly see a lot of scatter in the data. T ltis could be real or not. Pl otted is a best fit curve for both line 6 and 7 indicating signific ant NOx reduction with added dilution air. We compare the best fit and re-plot in figure 7. We see that both lines perform similar with line 6 achieving @180 #/hr at 1.1 stoc and line 7 at 1.05 stoc. Figure 8 is a comparison in# N02/MMB. We observe line 7 has slightly better perfonnance at uti lization of dilution air to reduce NOx although considered insignificant by the writer. When firing NG , Line 7 has a slight advantage to reduce thermal NOx. Originally we thought line 6 may have an advantage due to cool air on the outside. However with the data scatter and so m any variables, it is difficult to draw any concrete conclusions.500 450 400
X 350 0**~** 300 ..c

........ # 250 200 150 100 #/hr NOx vs Stoc air line 6 185 MMB up with a i r/line 7 192 MMB down with air

- #/hr NOx line 6

- #/hr NOx line 7 --Poly
. (#/hr NOx line 6) --Poly. (#/hr NOx line 7)

0.5 0.7 0.9 1.1 Stoc air Fig 7 Compari s on of line 6 and 7 NO firing in #/ ill:



### #NOx/MMB 

### line 6 vs 7 NG 

### only@ 190 MMB

3 2.5 lXI

- line 6 #/MMB :i: 2 :i:

- Line 7#/MMB ........ N 0 1.5 z --Poly. (line 6 #/MMB) # 1

-- Poly. (Line 7#/MMB) 0.5 0.7 0.8 0
. 9 1 1.1 1.2 y = 2 .6851x 2

- 8.5287x + 6
. 9029 R

2 = 1 Stoc air
Fi g 8 Compari s on of line 6 and 7 firing N G in # N02/ MMBFigure 9 be lo w is an extension of the NG data to provide some credibility to the reported base line data in the EPA document AP-42. We see the AP-42 factor of 658# N02/hr would correspond to a burner stoc air of@ 0.5. Typically we would expect stoc air with NG to be@ 0.4 cmresponding to 800# N02/hr baseline. But we need to recall the AP-42 NOx factor has a "D" rating. So the expected base line is closer to 800# N02 /hr or 4 # N02/MMB. Extrapolated Line 6 and 7 NOx NG Data 1200 1000

.... 800 ..r. 

# - N 600 0 

### z # 400 200

0 

# I I I I I I I

# ~ 

# I I I 

# I I**~** 

# '"I I I I ""''III

## ~ 

# I

....... 

# I .......

# i'k I I I**~** - NOxline6

- NOxline7

0.2 0.4 0.6 0.8 1 1.2 Stoc air Fig 9 Extension of line 6 and 7 data for clarity and suppOtt of EPA

- AP-42 NOx factor



### Background on Coal Combustion: The oxidation mechanism for coal involves heat up (fast) to devo litization and fmal char burnout (longer). These mechanisms define the flame v olume and the emissions. However, coal fuels exhibit an unusual flammability characteristics not found in other liquid or gaseous fuels. The rich limit offlammability is almost infinite for solid fuel/air mixtures. This is due to the fact that all of the air is present but much of the fuel still exists as un-reacted char or volatiles. The air simply does not see all the fuel in the firs t pa1i of the flame. Also the range of local stoichiometric mixtures near and around the solid particle is wide r anged from high exc ess air to near zero when reacting. The situation can be quantified by the measurements of Smoot, Hmion and Willams, 1976 ref6 plotted in figure10
. The result, coal stability is not tolerant of h igh excess air and has almost no rich limit. The tests indicate coal firing can experience reduced fl ame speeds and po s sible in stabilitie s at excess air above 20% or so. A further difference from gaseous fuels is the time required for char oxidation. See F ig 11. The char pa rticle takes s ignificant time for oxidation. Based on the fact that the char surface is oxidizin g at ne ar stoc conditions and oxidize over significant time, coal particl es do not re act to dil ution like g aseo us fuels.35 30 25

() <II 1/) 

# - 20 E 15 () 10 5 0 0 Coal Dust Velocity vs Equivalence Ratio Sto i ch i ometric (F/A)mass

2 4 6 8 10 12 Equivalence Ratio [ --.-. em/sec [

Fi g 10 Coal flame velocity (related to flammabi lity) VS E.R
. = (F /A) O%EA= l, 100% EA= .5
Burnout for Subbituminous Coal Char at 15% EA 100**~** 

# H1 I 

# u J e ' 

### /**~** 

## ...- 90 

## ,.,. 

# 'I**)~** I' 1
. , :;. 80 i ' 

# I 70 

## .... 

# v . :I 0 60 !:

- 100 Micron 

## ... 

# I :I .0 50

- 1 50 Micron


### .... I !: <II 40 

# 1! - 200 Micron (.) - 

## ... (I) ll. 30

- 20

## ~ 10 I



## o , 

# I 0 0.2 0.4 0.6 0.8 1 Seconds Figure 11 Sub b ituminous Cha r Burnout Coen code A = 60 and E = 17,150

### Evaluation of Line 6 and Line 7 results Coal firing: Figures 12 and 13 summarize the raw NOx data taken from line 6 and 7. In fig 12, Line 6 , the burner coal nozzle is on the inside and stabilized by NG and a small amount of atomizing air near the gas injectors at high swirl. Although NOx appears to decrease with increasing air, the amount is minor and only about 270 to 240 #/hr. At stoc levels @.55 we see large variations in NOx. The reason is unknown, but the writer speculates that at low air rates the atomizing air spinner alternately stabilizes coal or NG with a precessing vortex core. It could also be due to measurement issues that the writer is not aware of. Result , over the 50% EA range, the NOx indicates a slight decrease of maybe 30#.hr or @12%. Completely insignificant compared toNG. The variabil ity+/-@ 20 #/hr could be real or not. In fig 13, Line 7 the burner nozzle is on the outer part of the burner and stabilized by hot secondary air. NOx again appears to decrease from 250#/hr to 225 #/hr or so. Result, over 50% EA range the NOx seems to decrease @25#/hr or@ 10%. Again insignificant compared toNG. The variability is about the same as line 6 +/- 20#/hr and could be real or not. Both units indicate little change with EA. Figures 14 and 15 show NOx plotted as #/MMB
. Line 6 indicates a slight decrease from 1.35 to 1.2# N02/MMB or maybe 12%. Line 7 indicates a minimum at .75 stoc. We conclude that large changes in excess air has l ittle impact on coal firing dilution and NOx above .5 stoc.
Line 6 Raw Data NOx Emmissions (lbs/hr}@lOOMMB Coal 95 MMB NG with 3KPPH Atm air 340.00
320
. 00
300.00 l: 280.00

......... N 0 z # 260
. 00
240.00
220.00

0.50**~~· t---1"** **'-' --'1~** **&- l-----:---** **--::L...o.___** Line 6 Nox Emm i ssions ( l bs/hr)**111- --+-:llk--** **-- +--** **--- ----+** **~Orl:.l lll---** **-l- ----=r----Po**  ly. ( Li ne 6 Nox Emmiss i ons ( l bs/hr))

0.60 0.70 0.80 Stoc air 

### o_go 1.00 Fig 12 Line 6 N02 #/hr vs Stoc air in burner270.00
260
. 00
250.00
240.00 )( 0 :: 230.00 ..c**~** 220.00
210.00
200
. 00
190.00 LINE 7 Raw Data NOX (lbs/hr)@ 130 MMB coal 30 to 50 MMB NG No Atm air
J l = -25lj i7 8
. 9J I +

# 6~**6.1x** 4769.7x + 1467.7**+-- i--11-.,...._.** **--:-- -:** **--- --+--** **-+ ---i--~** **"'** = 0.236

# I

# ~ i\

## I

# ~ 

# II I 

# I

... 

## I 

## -,........4

# ~**""~** 

## " "" 

# ' I 

# [**LINE** 7 NOX (lbs/hr)

# 1~ - Poly. (LINE 7 NOX (lbs/hr)) 

### <J1 

# i/**~ ~**  

# I 

# L**~**

0.50 0.60 0.70 0.80 0.90 1 .00 Stoc air 

### Fig 13 Line 7 Raw N02 #/ hr vs Stoc i n burner# N02/MMB Coai+NG line6 lOOMMB coai+95MMB NG 1.60 .-------.-----.- - ----.- - --,-- ---, 1 ·5° -r--t'l-H l- - -l- -f- -+---+--- Y -t

- 6.7923x 3 -17.127x 2 + 13.508x1.40 2.0019**~** R 2 = 0
. 5304**~** 1
. 30 

# -**~** 1.20 z # 1.10 1.00 +- --+ -- +-- --+ -- -+--- ----1 0.90 +---+----1----+--+------i 0.50 0.60 0.70 0.80 0.90 1.00 Stoc air Fig 14 Line 6 Plotted in# N02/MMB - #N02/MMB -Po ly
. (# N02/MMB)

Line 7# N02/MMB 130 MMB coal+30 to SO MMB NG 1.60 

### I y = 2
. 73x 2

- .0041x + 2.7852 1.50**+- ---** **A.' ---** **+- ----** **----t----A-~)..1.3742** al**~** 1.40 

# - N**~** 1.30 +---:-+-FtJ-M;;;I;;;!i #

1.10 0.50 0.60 0.70 0.80 0.90 1.00 Stoc air Fig 15 Line 7 Plotted in #N02/MMB - #N02/MMB

-- Poly.(# N02/MMB)

We will explore the fate of coal fuel bound nitro gen (FBN) to determine the impact on NOx and if this explains the slight decrease in NOx with added air and what impact FBN h as at all. Figure 16 shows FBN convers ion for coal under me dium thermal environments vs stoc air. Fi gure 17 shows the #/MMB NOx contribution vs stoc air for the FBN.FBN Converstion 

### 0.6% FBN Coal No Air Preheat**45 ~~·~~~** **~~~~n** 40 

### 5 30 ·.;::;**~** 25 (I)**~** 20 0 u '?R 15**-!--+-!--+-+::.~ :**  10

5**~-++-+--+-+-+-- -t-'-L....L..!.-+-"--"--'--'** **-t-'--'-'-~---'-'- ...L.f-L...L....l..** **--'--j** 0 0.5 1 1.5 2 2.5 Stoc air - FBN Converstion

- Poly. (FBN Converstion)

Fi g 16 FB N conversation vs stoc air medium the 1 mal environments #N02/MMB 

### 0.6% FBN Coal No Air Preheat

0.7 z [f 0. 6 +-+ -+-+-+-: E 

## .g 0.5**~** 0.4**~** 0.3**+-+--H -+** **~** N**~** 0. 2 +-+-- .l.,.-1-H-+-+-H-+-+-H-+-+-' - #N 02/MMB

- Poly. (#N02/MMB) :It 0.1**~~~ ~~~~**  0 0. 5 1 1.5 2 2
. 5 Stoc air Fig 17 #N02/MMB vs stoc a ir from fig 16 Fig 18 Co nverts t he #N02/MMB to #N02/hr vs stoc a ir and coal firing rate. Our intent is to take the curve flt data and subtrac t out the FBN to determine what the thermal NOx is do ing
.14jl =
120
100



## ... 80 ..1:

......... N 0 

### z =II: 60
40
20

0 ... "'**~** FBN Contribution vs Stoc and firing rate 0.6% FBN Coal no APH



## .... ,) ...



# -

j**-~** Rz

:- ... 

## ..**·~ ·** **~· ~**  

### I , , -r-- 

# I 1 ,.... 

# ,.**~** =

# ~**~/ -1t~~** **l** 1 /

_ ., I 

# I 19 56x 2 + 3
. 3526x + 21.812 R

2 

### = 1 

# o

rrrp

- 75MMB

- 100MMB

- 130MMB

- 170MMB 

# ml { {l llJ- I
__ r-

## ~ 

# v .,,. I 

## I 

# lJl l.t,.J-rl**l--~ 1**  

# ...........**~** I I

# -- r- r-+ / 

# 1 ./

# ~w**~** 

# : - L,-V

# v"l% 

# /1 

# = Trl T 

# lrt:n r -Po ly. (75MMB) -Pol y. (100MMB)

0

## .....-**~** •••

## ..~.....

## ~ R z = 8 -Poly. (130MMB) -Poly. (170MMB)



# _ ...**~** 

# ITT,= 

# 1, , 

# +t'**,'** 

# g t, + 12.584
0.5 1 1.5 2 2.5 Stoc air Fig 18 FBN contribution vs stoc air and firing rate

Figure 19 and 20 are charts cmTected for FBN contribution. We plot the average curve fitted NOx obtained from Figs 12 and 13. We also plot the FBN contribution from fig 18. The contribution in line 6 is more since the coal is under medium thermal environments. Line 7 has the coal on the outside and the FBN conversion is conected for the hot thermal environments. We then subtract the FBN cont ribution from the total measured NOx. The re sults are plotted over stoc 0.5 to 1.0
. We discover th a t the FBN contribution i s small but significant relative to the proposed limit of 180#/ln. We fmiher note that the thermal NOx emission at stoc =1.0 is about what the NG emission is,@ 180 #/hr. Thus the difference in coal fired NOx vs NG fued NOx is directly related to the FBN contribution.

### ... ..c:

....... 300 250 200**~** 150 

### z :It 100 

### so

0 Line 6 lOOMMB Coal95 MMB NG with 3KPPH atm air 

## ./"" -r-....... 

# V" 

# __

# , - I 

# ---

- total NOx

- FBN contribution 

## I I 

# I

- Thermal NOx I
0.5 0.6 0.7 0.8 0.9 1 Stoc air Fig 19 Line 6 estimates ofthermal and FBN contribution



### ... ..c:

....... 300 250 200**~** 150 z :It 100 

### so

0 

### Line7 130 MMB Coal30 to SO MMB NG**~ ~~**  

# I Ill Ill I I I**,, ~**  I 

### I**~~**

# II ...**~"-1"-** 

# I I II I I - totaiNOx

- FBN contribution 

# Il l I I 

# I I

- Thermal NOx I I I I I 

### I 

## I 0.5 0.6 0.7 0.8 0.9 1 Stoc air Fig 20 Line 7 estimates ofthermal and FBN contribution

### Conclusions: Both Line 6 and line 7 respond about the same with good NOx reduction on natural gas vs stoc air in the burner down to 180 # N02/hr (@ .9#N02/MMB) at 200 MMB using@ 100% combustion air in the burner. This will have a significant impact on unit efficiency, but this has not been addressed. For the san1e air levels the coal thermal NOx is about the same as NG and the total is higher directly due to the FBN conversion as shown in Fig 19 and 20. Due to stability issues with coal at high excess air it is not recommended to increase air to the burner fmiher than stoichiometric knowing the secondary air is 300% EA plus. This was also observed during testing, coal instability near I 00% combustion air in burner and as illustrated in fig I 0. 

### Recommended NG Emissions As discussed, an hourly limit of 180#/hr for NG requires a 73 to 78% reduction at 200 MMB firing rate. The reduction requirements will be higher if the load need to increase. See Fig I. This limit already requires I 00% combustion air to the burner. It is recommended to limit the NOxon NG to 1.0#/MMB as opposed to an hourly limit. This will correspond to a 75% reduction over baseline and allow for variations in measurements as indicated in figs5 and 6. Fmiher this limit will allow load changes as unit efficiency is decreased. 

### Recommended Coal Emissions Coal is fired with NG and as shown the FBN contribution is significant. Coal fired results have greater variability than NG fired as expected. Adding dilution air increases the FBN contribution. From figures 12 -15 it recommend that the NOx limit be set at 1.5#N02/MMB. Anything lower will result in non compliance due to variability, limit load and cause flame instabilities.References:
I. Westenberg, A. E. "Turbulance Modeling for CFD." Combustion Science and Technology 4 (1971):59-67 2. Bowman, C. T. "Kinetics of Pollution Formation and Destruction in Combustion." Progress in Energy and Combustion Science 1 (1975): 33-45 3. Application ofNOx Control technologys to Power Boilers, A. Rawdon and S. Johnson 4. Coen Internal Documents 5. EPAdocumentAP42 Section 11.23 Feb 1997 Table 11.23-4 6. Smoot L.D., Hmton M.D. and Williams, G.A. "Propagation of Laminar Pulverized Coal-Air Flames" 16'h Symposium International on Combustion, The Combustion Institute, Pittsburgh, PA. 375 (I976)