10/08/10 

B&V E-15 

PNM Response to EPA Question from Joe Kordzi, via email, dated 

September 29, 2010 

Question: 

“PNM agreed to provide sulfuric acid mist stack test data and any other data related to 

supporting the boiler outlet SO3 emission rate of 0.011 lb/MMBtu.” 

Response: 

Item 1 – Sulfuric Acid Mist Stack Tests

Enclosed as Attachment 1 of this document are the results of sulfuric acid gas testing 

performed on San Juan Generating Station Units 1 and 3 in March 2009. These tests 

were conducted for informational purposes only and were not conducted for regulatory 

compliance. Additionally, Units 2 and 4 were not tested as they are considered similar to 

Units 1 and 3, respectively. 

It should be noted that PNM is providing this information to be responsive to EPA’s 

questions from September 29, 2010. However, the results of this testing are invalid. As 

EPA reviews the enclosed testing information, please note the following: 

 The results of testing on Unit 1 vary dramatically from Test Run No. 1 to Test 

Run No. 3. Test Run No. 1 indicates H2SO4 emissions of 25 lb/hr while Test Run 

No. 3 indicates H2SO4 emissions of 1.5 lb/hr. This is 1,500 percent difference 

between the test runs. 

 The testing results for Unit 3 show essentially no H2SO4 emissions. 

The test method used for the H2SO4 testing is National Council of the Paper Industry for 

Air and Steam Improvement (NCASI) Method 8A (a EPA conditional test method 013), 

for ”Determination of Sulfuric Acid Vapor or Mist and Sulfur Dioxide Emissions from 

Kraft Recovery Furnaces”. This method (included as Attachment 2) was not specifically 

developed for coal fired power plants but is often used to measure coal fired power plants 

H2SO4 emissions. One key point to using this test method is that the probe temperature is 

maintained above 350 °F by heating it so that none of the H2SO4 in the flue gas 

condenses into the probe. Then the H2SO4 is collected in a condenser, where the 

temperature (and therefore the condensation of H2SO4) can be controlled. The condenser 

is then rinsed and the rinse water from the condenser is analyzed for H2SO4 using 

titration. Because of this condenser, this method is often called the “controlled 

condensation method”. If the probe temperature is not maintained above 350 °F to 

revaporize the acid gas to allow the vapor to pass through the filter, H2SO4 can collect on 

the probe and filter and not reach the condenser. This is an important point as coal fired 

power plants with wet scrubbers have stack gas temperatures well below 350 °F. 

In Appendix 2 of the report, the field data shows that the probe temperature was not 

maintained above 350 °F for the duration of the tests. Table 1 summarizes the probe 

temperatures for the six test runs conducted for Units 1 and 3. 
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B&V E-15 

Table 1 

Emission Test Probe Temperatures 

SJGS Unit 1 

Test Run 

Probe Temperature 

Range 

(°F) 

1 350-351 

2 346-348 

3 349-350 

SJGS Unit 3 

Test Run 

Probe Temperature 

Range 

(°F) 

1 346-351 

2 347-350 

3 346-348 

As can be seen by this summary, only one test run (out of six) had a temperature that met 

the requirements of the method. When the probe temperature is allowed to go below the 

350 °F temperature required by the method, H2SO4 condenses in the probe instead of in 

condenser. The testing contractor indicates in the report that they rinsed the condenser 

but does not indicate they rinsed the probe. It appears unlikely that they analyzed the 

probe rinse solution. As a result, it is probable that all the H2SO4 that condensed in the 

probe or was trapped on the filter was lost to the measurement results, leading to 

inaccurately low H2SO4 emissions measurements. It is telling that only Unit 1, Test Run 

1 of 3, where the probe temperature was maintained at 350 °F in accordance with the 

method, resulted in higher levels of H2SO4 emissions than any of the other test runs 

conducted. 

Because of the probe temperature issues and inconsistencies in the results, the tests were 

not properly performed and the resulting H2SO4 emissions are not considered valid. 

Item 2 – Boiler Outlet SO3 Emissions

In the Design Basis shown in Appendix A of the June 2007 BART submittal, B&V 

assumed that the boiler would oxidize 1 percent of the SO2 in the flue gas to SO3. This 

forms the basis of the SO3 emissions shown in the design basis at the exit of the 

economizer. This assumption was used to assess the ammonium bisulfate condensation 

temperature entering the SCR catalyst. The ammonium bisulfate condensation 

temperature sets the minimum flue gas temperature where ammonia can be injected into 

the flue gas for NOx control. Below this temperature, ammonia and SO3 will combine to 

form ammonium bisulfate and will foul the catalyst, making it unavailable for NOx 

reduction. This calculation is important because it determines whether or not an 

economizer bypass will be required for low load SCR operation. From this evaluation, 
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B&V E-15 

B&V determined that economizer bypass was not required at the San Juan Generating 

Station Units. Therefore, based on this assessment, no costs were included in the SCR 

estimate for an economizer bypass. The economizer outlet SO3 emissions, based on the 

assumption of 1 percent oxidation rate of SO2 to SO3 by boiler shown in Appendix A, 

were not used for any other purpose in the BART analysis. 

To determine the H2SO4 emissions exiting the stack, B&V used the National Park Service 

particulate speciation method. The detailed calculation, using the NPS method, is 

presented in the June 2007 BART submittal in “Appendix E - Section 4, NPS Speciation 

Spreadsheets”. A summary of these calculations can be found in Appendix D of the June 

2007 BART submittal. The emission values in Appendix D were the values used in the 

visibility modeling performed for the BART analysis. 

 
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B&V E-15 

Attachment 1 

March 2009 

Sulfuric Acid Mist Stack Testing Report for 

San Juan Generating Station 

































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B&V E-15 

Attachment 2 

NCASI Method 8A 
METHOD 8A - DETERMINATION OF SULFURIC ACID VAPOR

OR MIST AND SULFUR DIOXIDE EMISSIONS FROM

KRAFT RECOVERY FURNACES

NCASI

Southern Regional Center

December 1996
i

Acknowledgments

This method was prepared by Ashok K. Jain, Regional Manager at the NCASI Southern Regional

Center.

For more information about this method, contact:

Ashok K. Jain

NCASI

P. O. Box 141020

Gainesville, FL 32614-1020

(352) 377-4708, ext. 226

FAX (352) 371-6557

For information about NCASI publications, contact:

Publications Coordinator

NCASI

P. O. Box 13318

Research Triangle Park, NC 27709-3318

(919) 558-1987

National Council of the Paper Industry for Air and Stream Improvement, Inc. (NCASI). 1997.

Methods Manual, Method 8 - Determination of Sulfuric Acid Vapor or Mist and Sulfur Dioxide

Emissions from Kraft Recovery Furnaces, Research Triangle Park, N.C.: National Council of the

Paper Industry for Air and Stream Improvement, Inc.

© 1997 by the National Council of the Paper Industry for Air and Stream Improvement, Inc.

NCASI’s Mission

To serve the forest products industry as a center of excellence for providing technical

information and scientific research needed to achieve the industry’s environmental goals.
ii

Disclaimer

The mention of trade names or commercial products does not constitute endorsement or

recommendation for use.
 1 December 1996

METHOD 8A - DETERMINATION OF SULFURIC ACID VAPOR

OR MIST AND SULFUR DIOXIDE EMISSIONS FROM

KRAFT RECOVERY FURNACES

1.0 Introduction

This method was developed as an alternative to EPA Method 8 for determining sulfuric

acid emissions from kraft recovery furnaces. When testing recovery furnaces, EPA

Method 8 is subject to significant interference from sulfates, which are present in the

particulate matter, and sulfur dioxide. The alternative method uses a quartz in-line filter

to remove particulate matter from the gas stream prior to capturing sulfuric acid. The use

of a controlled condensation technique eliminates the potential for interference from

sulfur dioxide. 

EPA approved the use of Method 8A in December 1996 for the determination of acid

vapor or mist and sulfur dioxide emissions from kraft recovery furnaces.

2.0 Method Description

2.1 Principle and applicability

2.1.1 Principle - A gas sample is extracted from the sampling point in the recovery

furnace stack. The sulfuric acid vapor or mist (including sulfur trioxide) and the

sulfur dioxide are separated, and both fractions are measured separately by the

barium-thorin titration method.

2.1.2 Applicability - This method is applicable for the determination of sulfuric acid

vapor or mist (including sulfur trioxide, and in the presence of other particulate

matter) and sulfur dioxide emissions from kraft recovery furnaces. Tests have

shown the minimum detectable limits of the method are 0.50 milligrams/cubic

meter (3.1 x 10-8 lb/ft3) for sulfur trioxide. No upper limits have been established.

 Based on theoretical calculations, for 200 mL of 3% hydrogen peroxide solution,

the upper concentration limit for sulfur dioxide in a 1.0 m3

 (35.3 ft3) gas sample is

about 12,500 mg/m3 (7.7 x 10-4 lb/ft3). The upper limit can be extended by

increasing the quantity of peroxide solution in the impingers.

Possible interfering agents of this method are fluorides, free ammonia, dimethyl

aniline and recovery furnace salt cake.

2.2 Apparatus

2.2.1 Sampling - A schematic of the sampling train used in this method is shown in

Figure 1. Component parts are discussed below. The schematic is similar to the

EPA Method 6 (see Appendix A) train except that the impingers are not the midget

type but larger as in the EPA Method 8 (see Appendix C) train. Also, the
 Method 8A - Determination of Sulfuric Acid Vapor or Mist and Sulfur Dioxide Emissions

 2 December 1996

impingers are preceded by a heated sampling probe, a heated quartz filter holder

and a heated H2SO4 condenser.

2.2.1.1 Probe - Quartz, straight tube approximately 12-mm inside diameter,

with a heating element and a stainless steel jacket. A thermocouple

taped on the quartz tube and insulated with glass wool allows for

measurement of the probe temperature.

2.2.1.2 Sulfuric acid sampling box - Insulated box with heating elements for

filter holder and H2SO4 condenser.

(a) Filter holder - Quartz, as described in Figure 2. Filter medium

is Tissuequartz filter paper with a 37-mm diameter (Pallflex

Corporation). Filter holder is always maintained at

temperatures >260°C (500°F) by a cylindrical heating mantle.

(b) H2SO4 condenser - Modified Grahm condenser, with Type C

glass frit and 200 cm of 5-mm ID glass tubing for condenser

coil, as shown in Figure 3. Condenser filled with water and

temperature maintained between 75 and 85°C (167 to 185°F)

with a cylindrical heating mantle.

2.2.1.3 Thermocouples - Copper-constantan thermocouples to measure

temperatures at the probe end, after the filter holder and after the

H2SO4 condenser (see Figure 1).

2.2.1.4 Impingers - Three, as shown in Figure 1. The first and third

impingers shall be of the Greenburg-Smith design with standard tips. 

The second shall be of the Greenburg-Smith design, modified by

replacing the insert with an approximately 13 mm (0.5 in.) ID glass

tube, having an unconstricted tip located 13 mm (0.5 in.) from the

bottom of the flask. 

2.2.1.5 Metering system - Same as EPA Method 6, Sections 2.1.5 to 2.1.10,

except rotameter should be capable of measuring flow rate to within

2% of the selected flow rate of about 10,000 cc/min (and not 1,000

cc/min).

2.2.1.6 Barometer - Same as EPA Method 6, Section 2.1.11.

2.2.1.7 Vacuum gauge and rotameter - Same as EPA Method 6, Section

2.1.12.

2.2.2 Sample Recovery - Same as EPA Method 8, Section 2.2.

2.2.3 Analysis - Same as EPA Method 8, Section 2.3.
 Method 8A - Determination of Sulfuric Acid Vapor or Mist and Sulfur Dioxide Emissions

 3 December 1996

2.3 Reagents

2.3.1 Sampling

2.3.1.1 Filters - Tissuequartz filter papers with a 37-mm diameter (Pallflex

Corporation).

2.3.1.2 Silica Gel, Water, Hydrogen Peroxide, Crushed Ice - Same as

described in EPA Method 8, Section 3.1.3 to 3.1.6.

2.3.2 Sample Recovery - Water. Same as for EPA Method 8, Section 3.2.

2.3.3 Analysis

2.3.3.1 Water, thorin indicator, barium perchlorate and sulfuric acid

standard - Same as for EPA Method 8, Section 3.3.

2.4 Procedure

2.4.1 Sampling

2.4.1.1 Preparation of collection train - Measure 100 mL of 3% hydrogen

peroxide into each of the first two impingers. Pour 100 mL of distilled

deionized water into the third impinger. Retain a portion of each

reagent used as a blank solution. Assemble the train as shown in

Figure 1. Adjust probe heater to maintain probe temperature above

177°C (350°F) to prevent condensation of H2SO4 in the gas passing

through the probe. Adjust heaters to the quartz filter and sulfuric acid

condenser to the desired temperatures given in Sections 2.2.1.2 (a) and

2.2.1.2 (b). Place crushed ice around the impingers.

2.4.1.2 Leak-check procedure - Follow the procedure laid out in EPA

Method 8, Section 4.1.4. 

2.4.1.3 Sample collection - Record the initial dry gas meter reading and

barometric pressure (see data sheet, Figure 4). To begin sampling,

position the tip of the probe at the sampling point at right angles to

direction of gas flow, connect the probe, filter and condenser assembly

to the first impinger, and start the pump. Adjust the sample flow to a

constant rate of about 10.0 L/min as indicated by the rotameter. 

Maintain this constant rate (+10%) during the entire sampling run. 

Sample for a minimum of 30 minutes and take readings (dry gas meter,

temperatures at dry gas meter, probe, filter and condenser) at least

every five minutes (Figure 4). Add more ice during the run if needed.

At the conclusion of each run, turn off the pump, remove probe from

the stack, and record the final readings. Conduct a leak check as
 Method 8A - Determination of Sulfuric Acid Vapor or Mist and Sulfur Dioxide Emissions

 4 December 1996

described in Section 2.4.1.2. (This leak check is mandatory.) If the

post-leakage rate exceeds the specified acceptable rate (see Section

4.1.4 of EPA Method 8), the tester shall either correct the sample

volume, as specified in Section 6.3 of EPA Method 5 (see Appendix

B), or shall void the run.

Drain the ice bath and, with the probe disconnected, purge the

remaining part of the train by drawing clean ambient air through the

system for 15 minutes at the average flow rate used for sampling (see

Section 4.1.5 of EPA Method 8 for details). 

2.4.2 Sample recovery - Disconnect the impingers after purging. Rinse separately the

probe, quartz filter holder and the H2SO4 condenser with deionized water using

multiple rinses for good washing. Collect the condenser wash solution in

Container No. 1, and the No. 1 and No. 2 impinger solutions in Container No. 2. 

Note levels of liquids in each container.

2.4.3 Sample analysis - Note the level of liquid in containers 1 and 2, and confirm

whether or not any sample was lost during shipment; note this on the analytical

data sheet. If a noticeable amount of leakage has occurred, either void the sample

or use methods, subject to the approval of the administrator, to correct the final

results.

2.4.3.1 Container no. 1 - Transfer the entire contents of Container no. 1 into a

250 mL Erlenmeyer flask, add enough isopropyl alcohol to give an

80% isopropyl alcohol solution. Pipette a 100-mL aliquot of this

solution into a 250-mL Erlenmeyer flask, add 2 to 4 drops of thorin

indicator, and titrate to a pink end point using 0.0100 N barium

perchlorate. Repeat the titration with a second aliquot of sample and

average the titration values. Replicate titrations must agree within 1%

or 0.2 mL, whichever is greater. Caution: The H2SO4 concentrations in

kraft recovery furnace stacks are typically so low that at times almost

the entire sample in Container no. 1 may have to be used during the

titration.

2.4.3.2 Container no. 2 - If concurrent SO2 concentrations in the stack are

desired carry out the following. Thoroughly mix the solution in

Container no. 2 which holds the contents of the 1st and 2nd impingers.

 Pipette a 10-mL aliquot of this solution into a 250-mL Erlenmeyer

flask. Add 40 mL isopropanol, 2 to 4 drops of thorin indicator, and

titrate to a pink end point using 0.0100 N barium perchlorate. Repeat

the titration with a second aliquot of sample and average the titration

values. Replicate titrations must agree within 1% or 0.2 mL,

whichever is greater.
 Method 8A - Determination of Sulfuric Acid Vapor or Mist and Sulfur Dioxide Emissions

 5 December 1996

2.4.3.3 Blanks - Prepare blanks by adding 2 to 4 drops of thorin indicator to

100 mL of 80% isopropanol. Titrate the blanks in the same manner as

the samples.

2.5 Calibration - Same as Section 5 of EPA Method 8.

2.6 Calculations - Same as Section 6 of EPA Method 8, except that equation 8-1 should be

replaced by equation 6-1 of EPA Method 6, and references to isokinetic sampling in this

section should be omitted. Recovery furnace stack gas temperatures are expected to be

higher than the estimated dewpoint of H2SO4 in the stack gas, and H2SO4 is expected to

be present in vapor phase only. Consequently, neither isokinetic sampling nor a stack

traverse is required.

2.7 Alternative procedures - Not applicable to this method.

2.8 References

National Council of the Paper Industry for Air and Stream Improvement, Inc. (NCASI). 

1980. A study of SOx measurement procedures and their use at kraft recovery furnaces.

Atmospheric Quality Improvement Technical Bulletin No. 106. Research Triangle Park,

NC: National Council of the Paper Industry for Air and Stream Improvement, Inc.
 Method 8A - Determination of Sulfuric Acid Vapor or Mist and Sulfur Dioxide Emissions

 6 December 1996

2.9 Tables, diagrams, flowcharts, and validation data

Figure 1. SO Sampling Train X

Heated Probe 

with Quartz Tube

Stack Wall

Insulated Box

Quartz Filter Holder

High Temperature 

Heating Elements

H SO Condenser 2 4

Thermocouple

Teflon Tube

Silica Gel 

Drying Tube

Water

3% Hydrogen 

Peroxide

Rate Meter

Thermometer

Ice Bath

Greenburg-Smith 

Impingers

Needle 

Valve

Pump

Dry Gas 

Meter
 Method 8A - Determination of Sulfuric Acid Vapor or Mist and Sulfur Dioxide Emissions

 7 December 1996

28/15 Ball

Spring Attachment 

Hooks

Tissue Quartz 

Filter Thermocouple Well

28/15 Socket

Extra Coarse 

Quartz Fit

Standard Taper 

Quartz 40/50

Seal Extension to 

Std. Taper Joint

Figure 2. Quartz Filter Holder
 Method 8A - Determination of Sulfuric Acid Vapor or Mist and Sulfur Dioxide Emissions

 8 December 1996

Glass Jacket

Gas Sample In

Sintered Glass Filter

Figure 3. H SO Condenser 2 4
 Method 8A - Determination of Sulfuric Acid Vapor or Mist and Sulfur Dioxide Emissions

 9 December 1996

Source ____________ Date _________________

Run No. __________ Furnace Load ________________

Stack Gas Temp. _____________ Atmospheric Pressure _________

Final Dry Gas Meter Reading _________

Initial Dry Gas Meter Reading _________

Volume Sampled ____________________

Temperature, °F

Dry Gas Meter

Time (min) Probe Filter Condenser In Out

0

5

10

15

20

25

30

Figure 4. SO3 Measurement Field Data Sheet
 Method 8A - Determination of Sulfuric Acid Vapor or Mist and Sulfur Dioxide Emissions

 10 December 1996

Figure 5. EPA Approval Letter