1 

Discussion of SJGS Coal Ranking for 

BART NOx Presumptive Limit Determination 

Summary of NMED/US EPA review: 

In an e-mail transmittal on March 20, 2008 from the New Mexico Environment 

Department (NMED) PNM received an evaluation by US EPA of the San Juan coal that 

is combusted at the San Juan Generating Station (SJGS) units. The e-mail transmittal is 

attached as Appendix A. The evaluation was performed by the US EPA and was based 

on the ASTM D388 classification method (attached as Appendix B) to determine the coal 

ranking. Average coal analysis values referenced from the B&W Low NOx

Burner/Overfire Air (LNB/OFA) contract were used in this evaluation (attached as 

Appendix C). 

In the evaluation, EPA concedes that based on the average coal analysis, the coal 

classification falls into a gray area between subbituminous and bituminous. However, 

EPA is concerned that since the coal analysis is an average value, if the heating value of 

the coal is the lower half of the range, this would rank the coal as subbituminous. The 

EPA concludes that subbituminous rank should be assigned to the San Juan coal based on 

the following coal characteristics: 

1. Heating value = 9,502 Btu/lb (especially concerned with the lower range of 

heating value since this is an average value). 

2. Chlorine content = 0.03% is lower than typical bituminous coal (expected at 

0.1%). 

3. Volatile matter = 33.76% is higher than typical bituminous coal (expected at 

16%). 

Response: 

PNM agrees that the coal burned at SJGS falls into a gray area between 

subbituminous coal and bituminous coal. The main objective in investigating the ranking 

of the coal combusted at SJGS is to determine the applicable BART NOx presumptive 

emission limit. With respect to NOx combustion control performance, SJGS coal behaves 

more like a bituminous coal as the following discussion will illustrate. 

 New, state-of-the-art combustion controls are being retrofitted as a result of the 

consent decree upgrades. The LNB, OFA, and Neural Network (NN) being installed on 

each of the SJGS units are equivalent to the BART technology used to develop the 0.39 

lb/MBtu presumptive NOx limit for units combusting bituminous coal, or 0.23 lb/MBtu 

for units combusting PRB subbituminous coal in the BART Rule. 
 2 

The ASTM D388 classification method referenced by the EPA classifies coal 

based on the range of heating value (in Btu/lb) and the volatile matter content. The 

ASTM D388 method is based on the moist, mineral-matter free basis. The EPA 

compared the “as received” heating value of 9,502 Btu/lb to the classification table in 

ASTM D388. This is not a valid comparison because the “as received” heating value 

must be converted to a “moist, mineral-matter free” heating value. The Parr Formulas is 

used to convert the as-received heating value of 9,502 Btu/lb (as received) referenced by 

the EPA to a value of 12,443 Btu/lb (moist, mineral-matter-free), and is as follows: 

Moist, mineral-free Btu = (Btu – 50S) / {100 – (1.08A + 0.55S)} x 100, per lb 

where, 

 Btu = heating value per lb (as received) 

 A = ash, % 

 S = sulfur, % 

With the conversion of the San Juan coal heating value to the correct basis for 

classification using ASTM D388, the average coal heating value falls into the high 

volatile C bituminous rank. The San Juan coal does not fall into the subbituminous rank 

of ASTM D388. 

The EPA also indicates that a coal classification determined based on the average 

coal heating value will potentially neglect subbituminous ranked coal that may be 

combusted. In response to this comment, a detailed evaluation of the individual coal 

samples from the supply mine was made. The individual coal sampling period evaluated 

was from April 1, 2003 through February 29, 2008, which represented a total of 11,655 

individual delivery samples. Statistical analysis performed on these individual samples 

was made to group the data from each individual sample into the following: 

1. Overall total and average 

2. Daily average maximum 

3. Daily average minimum 

4. Single sample maximum 

5. Single sample minimum 

The results of this analysis are shown below: 
 3 

Daily Coal Sample Averages for April 2003 through February 2008

Tons Ave. %Moist. Ave. %Ash Ave. Btu/Lb. Ave. % Sulfur Parr # 3 Ave. PSO2 Overall total & averages

32,286,576 9.58 20.57 9,670 0.73 12,449 1.51 Overall total & averages

Tons Ave. %Moist. Ave. %Ash Ave. Btu/Lb. Ave. % Sulfur Parr # 3 Ave. PSO2 Daily averages max. and min.

69,272 10.91 25.56 10,170 0.88 12,866 1.86 Daily averages maximums

966 7.64 17.65 9,132 0.52 12,131 1.04 Daily averages minimums

Tons %Moist. %Ash Btu/Lb. % Sulfur Parr # 3 PSO2 Single sample max. and min.

4,710 12.99 31.99 10,415 1.07 13,098 2.19 Single sample maximums

454 6.83 16.50 7,994 0.50 11,811 0.99 Single sample minimums

In order to compare the results to ASTM D388, the “as received” heating value 

was converted to “moist, mineral-free” heating value (using Parr #3 formula). These 

results are provided above under the column labeled “Parr #3”. The results indicate that 

no samples from the all-underground supply period (from April 1, 2003 through February 

29, 2008) would be classified as subbituminous. The lowest coal heating value from the 

single sample minimum is 11,811 (moist, mineral-matter-free). In the ASTM D388 

classification, the high volatile C bituminous rank ranges from 11,500 to 13,000 Btu/lb 

(moist, mineral-matter-free). Therefore, essentially all the coal burned at SJGS would be 

considered bituminous coal according to ASTM D388. 

The second classification criteria that the EPA used was the average volatile 

matter content which for SJGS is 33.76% (as received). The SJGS value was compared 

with the properties of coal found in B&W’s Steam book (41st Ed., Chapter 9, Table 5, 

attached as Appendix D) for various US coals. EPA stated that the bituminous coals can 

have volatile matter content as low as 16%. It should also be noted, however, that in the 

same table, the range of volatile matter content for bituminous ranked coal ranges from 

16% to 40%. Therefore, the relatively high volatile matter content of the San Juan coals 

at 33.76% is within the range of expected content level for bituminous coals. In fact, it is 

higher than all the subbituminous coals listed in Table 5 and fits much better in the range 

of coals listed as bituminous. 

The chlorine content of the San Juan coals at 0.03% was also referenced by the 

EPA as differentiator in determining the coal ranking. While, it is true that the chlorine 

content is lower for the San Juan coals than other bituminous coals (EPA expected value 

of 0.1%), the chlorine content in coal does not impact the NOx emission level. Therefore, 

chlorine content is irrelevant for the determination of the presumptive NOx limit. 

In the PNM SJGS BART submittal to NMED in June 2007, Section 4.1.4 of the 

report (attached as Appendix E) discusses reasons why NOx emissions levels achieved 

using combustion controls at SJGS should not be compared to a PRB subbituminous coal 
 4 

for the purposes of establishing a NOx presumptive limit. The reasons provided are 

briefly recapped below: 

1. Oxygen content < subbituminous: SJGS coal oxygen content at 9.38%, is lower than 

bituminous coal (10.09%) and substantially lower than subbituminous coal (11.68%). 

Oxygen content in coal impacts NOx emissions because higher fuel oxygen content 

reduces the amount of additional air (i.e., nitrogen) required for combustion, reducing 

amount of nitrogen for formation of NOx. 

2. Moisture content < subbituminous: SJGS coal moisture content at 8.72%, is lower 

than bituminous coal (9.40%) and substantially lower than subbituminous coal 

(29.95%). Moisture content in coal impacts NOx emissions because higher fuel 

moisture content reduces the flame temperature and, therefore, reduces the formation 

of thermal NOx. 

3. Nitrogen content > subbituminous: SJGS coal nitrogen content at 1.08%, is higher 

than subbituminous coal (0.63%). Nitrogen content in coal impacts NOx emissions 

because of the oxidation of fuel-bound nitrogen to form NOx. 

4. SJGS boiler design (smaller effective boiler volume): the SJGS effective boiler 

volume is smaller when compared to boilers designed to combust PRB coal with 

similar steam output capacity. The smaller volume boiler will operate hotter, thus 

increasing thermal NOx formation. 

This fundamental understanding of the variation in NOx formation from different 

types of US coals and the inherent SJGS boiler design characteristics explains why the 

expected NOx rates of boilers burning the coal fired at SJGS cannot be as low as boilers 

firing PRB subbituminous coals. 

Conclusion: 

The discussions included here on the San Juan coal heating value, coal volatile 

matter content, coal combustion characteristics, and SJGS boiler design provide a strong 

basis for why the BART NOx presumptive limit for SJGS should not be based on the 

combustion of subbituminous coal. The proposed consent decree NOx control level of 

0.30 lb/MBtu is appropriately in between the BART NOx presumptive limit for 

subbituminous coal (at 0.23 lb/MBtu) and bituminous coal (at 0.39 lb/MBtu). In effect, 

the 0.30 lb/MBtu is equivalent (for SJGS) to the presumptive limit for PRB or eastern 

bituminous fuels. 

 
APPENDIX A 

NMED/EPA REVIEW OF COAL CLASSIFICATION 
Chang, Daniel

From: Norem, Nancy [Nancy.Norem@pnmresources.com]

Sent: Wednesday, April 30, 2008 5:10 PM

To: Fischer, Diane M.; Huggins, Roosevelt; Lucas, Kyle J.; Chang, Daniel

Subject: FW: PNM - NOx Information Review

5/8/2008

I am forwarding you a string of emails that the NMED sent me regarding SJ coal classification.

 

From: Trujillo, Rita, NMENV [mailto:rita.trujillo@state.nm.us] 

Sent: Thursday, March 20, 2008 4:38 PM 

To: Norem, Nancy 

Cc: Uhl, Mary, NMENV; Kuehn, Elizabeth, NMENV 

Subject: FW: PNM - NOx Information Review 

Hi Nancy -

 

I'm forwarding to you an e-mail from Sikander Khan from EPA regarding the classification of the San Juan coal as subbituminous. Based on our conversation with and this e-mail from Sikander, we believe that the coal burned in the San 

Juan Generating Station should be classified as sub-bituminous.

 

Rita

From: Kuehn, Elizabeth, NMENV 

Sent: Friday, March 14, 2008 3:06 PM 

To: Uhl, Mary, NMENV; Trujillo, Rita, NMENV; Schooley, Ted, NMENV; Mustafa, Sufi A., NMENV; Kim, Gi-Dong, NMENV 

Subject: RE: PNM - NOx Information Review 

AllBelow is a summary of our discussion with Sikander Khan at EPA regarding the coal classification at the SJGS.

 

Thanks, 

Liz

From: Khan.Sikander@epamail.epa.gov [mailto:Khan.Sikander@epamail.epa.gov] 

Sent: Wed 2/27/2008 2:42 PM 

To: Kuehn, Elizabeth, NMENV 

Subject: RE: PNM - NOx Information Review 

Liz, 

Here is a summary of what we discussed today: 

 ASTM D 388 sets the guidelines for classifying coals and, especially 

 for lignite, sub-bituminous and high-volatile bituminous coals, such 

 classification is based on the higher heating value. For other 

 coals, fixed carbon and volatile contents determine the exact class 

 of these coals. 

 PNM does not provide sufficient information with their coal analysis 

 to enable us to determine the exact classification of their coal. 

 They have provided only the average coal analysis. What we need is a 

 range of analyses as well as information on surface moisture and ash 

 mineral contents. With the given information, the coal appears to
 fall in a gray area, where it can be classified as either 

 sub-bituminous or high-volatile bituminous coal. However, since the 

 analysis provided by PNM is for the average coal, it appears that 

 some samples of this coal with heating values below the average may 

 fall squarely in the sub-bituminous column. Please note that, if the 

 analysis provided by PNM is average, chances are that half of the 

 samples of this coal would have heating values below the 9,502 Btu/lb 

 listed as an average. 

 The chlorine content and volatile matter of the average coal appear 

 to be a lot like what would be expected of sub-bituminous coals. The 

 chlorine content at 0.03% is too low (I would expect bituminous coal 

 chlorine to be generally higher than 0.1%). The average volatile 

 matter at 33.76% is fairly high and is more typical of sub-bituminous 

 coals. PNM also states that the minimum volatile matter would be 48% 

 on a dry, ash free basis, which is also very high and is 

 representative of a sub-bituminous coal. All of these numbers are 

 based on information provided in the contract PNM recently signed 

 with B&W for the supply of combustion controls. For examples of 

 analyses of US coals, you can refer to B&W's Steam book (41st 

 Edition, Chapter 9, Table 5). This table shows that the volatile 

 content of eastern bituminous coals can be as low as close to 16%. 

 The sub-bituminous coals would have volatile contents always 

 exceeding 30%. Given the low chlorine content, relatively low 

 heating value, and relatively high volatile content, the PNM coal can 

 be classified as sub-bituminous. 

 It is easier to combust a coal with a higher volatile content in a 

 boiler. This ease of burning for sub-bituminous coals is known to 

 improve efficiency of combustion controls employed to reduce NOx. 

 With the high volatile coal content, PNM can be expected to achieve 

 good performance from their new combustion controls. You can see the 

 projected differences in NOx reduction for bituminous and 

 sub-bituminous coals with combustion controls on the EPA website, 

 http://www.epa.gov/airmarkets/progsregs/epa-ipm/. Please scroll down 

 to the bottom area of this web page, under the Section, Documentation 

 for EPA Base Case 2006 (v3.0). Click on Section 3 and go to Table A 

 3-1:3. The last two columns of this table show the NOx reduction 

 efficiencies that can be achieved with different types of combustion 

 controls on bituminous and sub-bituminous coals. The difference in 

 the efficiencies in more pronounced if you use the formulae in the 

 second-last column. Here you can assume a baseline NOx rate (for 

 example 0.5 lb/MMBtu) without controls for the two coals and then 

 apply the formulae to see that the NOx reduction efficiency for 

 subbituminous coal is better than what you can achieve with 

 bituminous coal, with the same NOx controls. The last column is the 

 default efficiency that is still better for the sub-bituminous coals. 

 The main factor behind these projections is the coal volatile 

 content. 

 In one of your previous emails, you had referred to documents where 

 PNM and B&W had defined the above coal to fall under sub-bituminous 

 category. I believe that those documents provide another solid proof 

 that this coal should be considered sub-bituminous type. 

 The contact at our North Carolina office that I mentioned goes by the 

 name Ravi Srivastava and his phone number is 919-541-3444. 

I hope that the above is of some help to you in resolving the issues 

with PNM. Good luck. 

Sikander Khan 

US EPA 

5/8/2008
Telephone: 202-343-9781 

Fax: 202-343-2356 

Email Address: khan.sikander@epa.gov 

 

 

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5/8/2008
APPENDIX B 

ASTM D388 GUIDELINE 

APPENDIX C 

B&W LNB/OFA FUEL DESIGN CRITERIA 
Public Service Company of New Mexico December 20, 2006 o

San Juan Generating Station 

Unit 3 and Unit 4

EXHIBIT A PERFORMANCE GUARANTEES 

Proposal No.: P-005733 

Contract No.: 0635-169C (#3); 0635-169A (#4) Page 3 of 14

The Babcock & Wilcox Company a McDermott Company 

Table 1.2.1 – Burner Design/Guarantee Basis

Description Units Design Basis 

 

Total Heat Input from Fuel MBtu/hr 5485

Excess Air (Leaving Economizer) % 20 

Number of pulverizers in service (1) # 5 or 6 

Number burners in service # 35 or 42 

Primary Air to Coal Flow Ratio Lb-air/lb-coal 1.95 

Air Temperature Leaving Air Heater Deg F 579 

Feedwater Temperature Deg F 479 

Furnace Pressure Inches w.g. 9.9 

Windbox Pressure “ H2O 17.4 

Pulverizer Outlet Temperature Deg F 150 

Overfire Air Flow Mlb/hr 1,213 

 Note (1): BWC reserves the right to select which mill is out of service.

Table 1.2.2: Design/Guarantee Basis Fuel Criteria (1)

Fuel Type: Æ Design Coal 

Proximate Analysis: %wt. (as-fired) 

Moisture 8.93 

Ash 21.78 

Volatile Matter (VM) 33.76 

Fixed Carbon (FC) 35.53 

Total 100.00 

HHV (Btu/lb) 9,502

Ultimate Analysis: %wt. (as-fired) 

Moisture 8.93 

Ash 21.78 

Carbon 54.21 

Hydrogen 4.04 
Public Service Company of New Mexico December 20, 2006 o

San Juan Generating Station 

Unit 3 and Unit 4

EXHIBIT A PERFORMANCE GUARANTEES 

Proposal No.: P-005733 

Contract No.: 0635-169C (#3); 0635-169A (#4) Page 4 of 14

The Babcock & Wilcox Company a McDermott Company 

Sulfur 0.76 

Nitrogen 1.00 

Oxygen 9.28 

Chlorine 0.03 

Total 100.0 

Fuel Limits: 

% Volatile Matter

(%wt. dry, ash free) > 48.0 

% Oxygen 

(%wt. dry, ash free) > 13.0 

(1) Fuel samples shall be collected during the testing to confirm 

compliance with these criteria. The fuel analyses shall be performed in 

accordance with ASTM standard procedures. 

Table 1.2.3 – Flue Gas Analysis Entering Baghouse

ITEM

UNIT 3&4 

 PERFORMANCE 

CONDITION 

DESIGN COAL

Fuel Design coal Mass % 

Boiler Heat Input, 

MBtu/hr

5485.2

Flue Gas, lb/hr 

CO2 1,146,630 18.70 

H2O 324,454 5.29 

N2 4,268,137 69.60 

O2 320,453 5.23 

SO2 8,600 0.14 

HCl 210 0.003 

SO3 79 0.00 

Ash, lb/hr + PAC lb/hr 63,464 1.035 

Flue gas flow rate, lb/hr 

(w/solids) 

6,132,027 100% 
APPENDIX D 

US COAL PROPERTIES 

(B&W STEAM, 41ST EDITION, CHAPTER 9, TABLE 5) 

APPENDIX E 

PNM SJGS BART ANALYSIS (JUNE 2007) 

EXCERPT FROM SECTION 4.1.4
 SJGS fires a local New Mexico coal. The coal burned at SJGS has been referred 

to as both a subbituminous coal and a bituminous coal, since it possesses qualities that 

place it in a “gray area” between the bituminous and the subbituminous categories of 

coal. Based on these characteristics, the ASTM D388 classification would place the 

SJGS coal in either of the bituminous Group C or subbituminous Group A coal category. 

The difference between these two groups is not relevant, but the fact that the SJGS coal 

cannot be categorized as subbituminous Group C is very important in that subbituminous 

Group C includes PRB coals, which are known to produce very low NOx emissions when 

fired in utility boilers. Table 1 compares the fuel fired at SJGS to typical bituminous and 

PRB fuels. This fundamental understanding of the variation in NOx formation from 

different types of US coals explains why the expected NOx rates of boilers burning the 

coal fired at SJGS cannot be as low as boilers firing PRB subbituminous coals. 

The coal burned at SJGS is less volatile and has a lower oxygen and moisture 

content than PRB coals. The greater volatility and higher oxygen and moisture content 

found in PRB fuels are key to the lower NOx emissions seen in boilers combusting PRB 

coal. The high volatility in PRB coals reduces combustion time. The higher fuel oxygen 

content reduces the amount of additional air (i.e., nitrogen) required for combustion; the 

higher fuel moisture content reduces the flame temperature and, therefore, reduces the 

formation of thermal NOx. The nitrogen content in the fuel affects NOx generation 

because of the oxidation of fuel-bound nitrogen. As it relates to the amount of NOx

generated from combustion, the coal burned at SJGS is more similar to the low-sulfur 

bituminous coal than it is to PRB subbituminous coal. 

A comparison of the New Mexico subbituminous coal burned at SJGS to a typical 

subbituminous PRB (Bucksin, WY mine) and a typical low-sulfur bituminous coal 

(Twentymile, CO mine) is shown in Table 4-3. 

Another factor affecting the potential for NOx reduction at SJGS is the boiler 

design. Because of the HHV of the coal, the SJGS boilers are smaller in size (effective 

boiler volume) than similar output capacity boilers combusting PRB coal. This has a 

negative effect on potential NOx emissions reduction because a smaller volume boiler 

will operate hotter, thus increasing thermal NOx formation. Additionally, SJGS Units 1 

and 2 have limited flame length because of the high heat input burners on the front wall 

of the boiler. This reduces the effectiveness of the overfire air from the OFA ports. 
Table 1 

Coal Properties Comparison 

 Typical 

Subbituminous 

PRB 

SJGS 

New Mexico 

Subbituminous 

Typical LowSulfur 

Bituminous 

Ultimate coal analysis, as received 

Carbon, % 49.00 54.52 64.05 

Hydrogen, % 3.24 4.24 4.53 

Sulfur, % 0.35 0.77 0.50 

Nitrogen, % 0.63 1.08 1.63 

Oxygen, % 11.68 9.38 10.09 

Ash, % 5.15 21.29 9.80 

Moisture, % 29.95 8.72 9.40 

Total, % 100.00 100.00 100.00 

Higher Heating Value, Btu/lb 

(as received) 

8,400 9,692 11,400 

Volatile matter, % (as received) 30.25 34.3 35.8 

Volatile matter, % (dry) 43.18 37.6 39.5 

Notes: 

1. Typical subbituminous PRB analysis was based on Bucksin Mine (Wyoming). 

2. Low-sulfur bituminous analysis was based on Twentymile Mine (Colorado). 

3. SJGS New Mexico subbituminous analysis was based on BART analysis design 

basis. 

4. SJGS New Mexico subbituminous volatile matter is referenced from SJGS consent 

decree Environmental Project Design Criteria, Sargent & Lundy, June 15, 2006.