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March 25, 2010

Ms. Elineth Torres

Environmental Protection Specialist

U.S. Environmental Protection Agency

OAQPS/SPPD/Program Design Group

109 T.W. Alexander Dr.

Durham, NC 27711

RE: PCA Letter Responding to EPA’s Email of February 23, 2010 Regarding ISIS

Model Related Questions on SO2 Performance

Dear Ms. Torres:

With this letter, the Portland Cement Association (PCA) is responding to several questions you 

posed regarding SO2 emission intensities and control equipment performance in your email to 

me of February 23, 2010. We previously provided responses to the other questions posed in your 

email; this letter completes our response. We continue to appreciate the opportunity to provide 

you with information that will improve the accuracy with which EPA’s ISIS model simulates the 

U.S. cement industry.

Portland cement is the powder which acts as the glue or bonding agent that, when mixed with 

water, sand, gravel and other materials, forms concrete. Cement is produced from various 

naturally abundant raw materials, including limestone, shale, clay, and silica sand. Portland 

cement is an essential construction material and a basic component of our nation’s infrastructure. 

It is utilized in numerous markets, including the construction of highways, streets, bridges, 

airports, mass transit systems, commercial and residential buildings, dams, and water resource 

systems and facilities. The low cost and universal availability of portland cement ensure that 

concrete remains one of the world’s most essential and widely used construction materials.

Your email of February 23 was in part to follow up on an EPA/PCA conference call on January 

20, 2010. EPA’s notes summarizing this conference call provide the most detailed summary of 

your questions to which we are responding in this letter. The following is the relevant section 

from EPA’s conference call notes. 
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We have the following comments on these topics.

NOx Emission Intensities

We have not reviewed the baseline NOx emission intensity factors (pounds per ton of clinker) 

that are included in the ISIS model. Nor have we reviewed the NOx control effectiveness 

estimates that are included in ISIS for various control measures and process changes (e.g., for 

mid-kiln firing, low NOx burners, etc.). NOx emissions have not been at issue with respect to 

the proposed the Portland Cement NESHAP, and we have not reviewed any elements of the ISIS 

model that deal with NOx. We cannot now provide any review on NOx issues within the time

frame that EPA contemplates for developing revisions to ISIS.

Section of EPA minutes from 1/20/10 conference call

- Appendix 11 page 5- Emission Intensities (ton pollutant/ton clinker)

o PCA to revise emission intensities for NOx (by kiln type and perhaps state) and SO2 (by 

kiln type and state). EPA to provide tables of emission intensities –input spreadsheet

o Can PCA provide baseline SO2 emissions- data derived from PCA's Labor Energy Survey

- Appendix 11 page 7 -SO2 removal performance

o Is the report that specifies SO2 removal performance from PCA’s consultant available for 

EPA review? 

• Bob? /Dan? / Christa? –from vendors information

o Can we get real performance (emissions) and control efficiency for the 5 kilns with wet 

scrubbers?

• Years of scrubbers being installed? 

- Appendix 12 page 3

o EPA needs background materials that back-up control performance assumptions used by 

PCA
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SO2 Emissions Intensities and Baseline

You sent for our review an Excel workbook that includes a new set of SO2 emission estimates 

for kilns for 2005 that EPA now proposes to use in ISIS. The new estimates were developed by 

EPA from the 2005 National Emissions Inventory (NEI). The workbook includes 3 tabs or 

worksheets: Emission Intensities, Units, and Emissions. Notes in the worksheets request PCA 

comments at various points and also, in Column B of the Emissions worksheet, EPA identifies 

specific kilns for which the Agency is uncertain about how to interpret the available 2005 NEI 

emissions estimates for SO2. We have marked in green color in the workbook our responses on 

all these issues, and have emailed you the revised workbook file titled “ISIS Units and Emission 

Spreadsheet for PCA Review_Following January 20,2010 Conference Call – PCA 

Comments.xls”. In the following paragraphs we summarize our comments on EPA’s workbook 

and new SO2 emission estimates.

Background on SO2 emissions estimates and PCA’s Labor & Energy survey data for SO2

In the 2009 NESHAP version of ISIS-Cement, EPA developed two different sets of SO2

emission estimates for all cement kilns in the country, derived in different ways. The first set 

was derived from 2002 NEI data, and updated to 2005 in some manner. The second set was 

developed based on applying estimated regional emission intensities (lbs SO2 emitted per ton of 

clinker produced – estimated by EPA’s consultant Andover Technology Partners) to estimated 

2005 clinker production for each kiln.

In commenting on the proposed NESHAP in September, 2009, PCA compared the two sets of 

EPA’s SO2 emission estimates for 2005 in ISIS against data obtained by PCA in PCA’s Labor & 

Energy (LE) Survey for 2005. The LE data is on a plant (not kiln-by-kiln) basis, and it covered 

75 cement plants. For the 75 cement plants that provided SO2 emissions estimates for 2005 via 

the LE Survey, total estimated emissions were 119,379 tons, relative to EPA’s ISIS estimates for 

these 75 plants of 149,533 tons (2002 NEI updated to 2005). PCA commented based on this LE 

data that EPA in ISIS thus apparently overestimated 2005 baseline SO2 emissions by about 25%.

PCA believes that the SO2 emissions estimates from the LE Survey are, in general, more 

accurate than those developed by EPA via either of the methods used for the 2009 NESHAP 

version of ISIS-Cement. 80% of the cement plants that provided data for the 2005 LE Survey 

indicated that their estimates of 2005 SO2 emissions were developed based on CEMs and/or 

stack tests, while 20% were based on application of AP-42 or other emission factors. PCA 

believes that these detailed information sources are likely more reliable than either of EPA’s 

approaches used in ISIS for estimating SO2 emissions -- the procedure based on updating 2002 

NEI figures or the procedure based on use of average regional emission factors. However, 

although we believe the LE Survey data to be generally of good quality, the LE Survey data 

would not represent a 100% satisfactory set of estimates for actual kiln-by-kiln SO2 emissions in 

2005 for several reasons.

• There are roughly 25 cement plants that did not provide LE Survey responses, and 

emissions somehow need to be estimated for ISIS for these plants also.
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• The LE Survey data is on a plant-by-plant basis rather than kiln-by-kiln, and ISIS 

ultimately needs kiln-by-kiln estimates. There can be some difficulties in apportioning 

an emission estimate for an entire plant among the plant’s individual kilns.

• A small portion of the LE Survey data derives from likely less accurate sources (e.g., 

application of general emission factors), and for a few plants, it is possible that EPA’s 

estimates based on either 2002 NEI or the estimated regional emission factors may be 

more accurate than those from the LE Survey.

However, the major issue associated with perhaps using PCA’s LE Survey data for ISIS is that 

the LE Survey data have been provided by cement companies to PCA on a confidential basis. 

The LE Survey data for individual plants cannot be revealed by PCA without violating the 

confidentiality agreements under which the data was provided to PCA. One of our major 

objectives in reviewing EPA’s proposed SO2 emission estimates for ISIS and suggesting 

improvements to these estimates is thus to find a way to somehow provide the generally high 

quality LE Survey data to EPA, but to do so in a manner that respects the confidentiality 

agreements and avoids providing LE Survey data to EPA at the individual plant level.

PCA review of EPA’s new estimates for ISIS of baseline SO2 emissions in 2005

We find EPA’s new estimates of kiln SO2 emissions based on 2005 NEI data to be much more 

accurate than and preferable to either of EPA’s previous sets of estimates [estimates based on 1) 

updating 2002 NEI estimates; or 2) application of regional emission factors.] We base this 

conclusion on a comparison of EPA’s new and old estimates against our LE data for the 75 or so 

cement plants for which all four sets of emission estimates exist. The four sets of estimates 

being: 1) Old ISIS based on 2002 NEI updated to 2005; 2) Old ISIS based on regional SO2

emission factors applied to estimated 2005 clinker production; 3) Potential new ISIS based on 

2005 NEI; and 4) PCA LE Survey. Again, we regard the PCA LE Survey data to be the most 

accurate of the 4 data sets, and we judge the accuracy of the three alternative sets of EPA 

estimates by how closely each matches against the LE estimates. The following table shows a 

comparison of the three alternative sets of EPA estimates against the LE estimates for those 

plants for which all four sets of emissions estimates exist. 

Comparison

# of Plants with 

Emission Estimates 

Differing

by > 500 tpy

Total SO2 Emissions 

Across All Plants

Old ISIS (NEI 2002) vs. LE Survey 29 + 27% net

Old ISIS (Regional emission factors) vs. LE 

Survey

32 +17% net

Potential new ISIS (NEI 2005) vs. LE Survey 14 -6% net

EPA’s suggested new set of SO2 emissions estimates based on NEI 2005 is much closer to the 

LE Survey data than are the Agency’s previous sets of estimates, both in terms of the numbers of 

plants for which large differences in estimates exist (>500 tpy SO2) and in terms of the total 

emissions estimated across all plants. In general, then, we much prefer EPA’s potential new set 

of estimates to either of the previous sets of estimates considered for ISIS. However, there are 
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still some plants (11) for which the NEI 2005 and the LE Survey emission estimates differ 

substantially.

We suggest that EPA adopt in ISIS the following approach to estimating baseline (2005) SO2

emissions from cement kilns:

1. For those particular cement plants for which EPA’s new SO2 emission estimates (based 

on 2005 NEI) are reasonably close to PCA LE Survey estimates (i.e., ≤500 tpy 

difference), EPA should use the Agency’s new 2005 NEI-based estimates. In the Excel 

workbook that you sent us for review and that we are returning, we have noted the 

particular cement plants for which EPA’s new estimates are close to the PCA LE Survey 

estimates. We have also provided some notes for many of these plants that respond to 

instances marked in the “Units” worksheet (column B) where EPA has had some 

difficulty in interpreting 2005 NEI information with regard to allocation of total plant 

emissions among the individual kilns at the plant.

2. For those particular cement plants for which EPA’s new SO2 emission estimates (based 

on 2005 NEI) are not close to PCA LE Survey estimates (i.e., >500 tpy difference), we 

suggest that EPA should not use the Agency’s new estimates. In these instances where 

2005 NEI and PCA LE Survey estimates disagree substantially, we expect that the LE 

estimates are likely more accurate than the 2005 NEI data, but we cannot provide EPA 

with the LE Survey estimates for these individual plants. Instead, we have developed a 

set of national emission intensity factors (pounds of SO2 emitted per short ton of clinker 

produced, by type of kiln) that we suggest EPA use in estimating SO2 emissions for this

set of plants, instead of the 2005 NEI data for these plants and instead of EPA’s previous 

regional emission intensity factors. We have developed this set of national emission 

intensity factors by analyzing the particular set of 64 cement plants for which the PCA 

LE Survey data are close to (i.e., within 500 tpy of) EPA’s 2005 NEI estimates. We will 

say more below about this new set of national emission intensity factors that we have 

developed.

3. For nearly all the remaining cement plants for which EPA has developed 2005 NEIbased emissions estimates and for which no PCA LE Survey data has been collected, we 

suggest that EPA use the 2005 NEI-based emissions estimates. For these particular 

plants, PCA has no basis (absent substantial additional data gathering) to believe that the 

2005 NEI estimates are inaccurate or to improve them, and we further believe that the 

plant-specific nature of the 2005 NEI estimates makes them likely more accurate for 

individual plants than either our new national emission intensity estimates or EPA’s 

previous regional emission intensity estimates.

4. For any new cement plants simulated in ISIS or for any other plants for which 2005 NEI 

emission estimates do not exist, we suggest that EPA estimate baseline SO2 emissions by 

using the national emission intensity estimates we have developed.

5. For a handful of cement plants, EPA posed questions in the Excel workbook we were 

asked to review about how to interpret available emissions estimates from the 2005 NEI. 

Most of these questions involved difficulties in determining whether an NEI data entry 
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represents emissions from a single kiln or from multiple kilns at a plant venting to a 

single stack. For these plants, we have provided in the workbook some information that 

will assist EPA in interpreting the data available through NEI.

We have edited the workbook to indicate for each cement plant and kiln which of these five

approaches we suggest that EPA use in estimating baseline SO2 emissions.

Here is further detail on the new national emission intensity estimates that we have developed 

and that we suggest EPA use for some plants.

We believe that the LE Survey provides the most accurate source of estimates of baseline SO2

emissions for individual cement plants. However, we recognize that some of the LE Survey 

estimates, for some plants, are based on less accurate data sources (e.g., AP-42 emission factors, 

etc.). We believe the most accurate of all the LE Survey estimates are likely to be those for 

which the LE Survey estimate for 2005 and the 2005 NEI estimate developed by EPA 

correspond closely. There are 58 cement plants for which these two estimates of 2005 SO2

emissions are within 500 tpy of each other. We have used the LE Survey data for these 58

cement plants to estimate a set of national emission intensity factors in terms of pounds of SO2

emitted per ton of clinker produced, for wet, long dry, preheater and preheater/precalciner kilns. 

These estimated emission factors are as follows:

Type of Kiln SO2 Emission Factor

(lbs SO2/ton clinker)

Wet 4.89

Long dry 4.78

Preheater 1.18

Precalciner 1.12

The estimated emission factors represent the averages (not medians) across the four subsets of 

the58 cement plants, consistent with how EPA estimated the Agency’s regional emission factors 

previously proposed as one alternative for ISIS. In this calculation, each plant’s emission factor 

is estimated as:

• The plant’s 2005 SO2 emissions reported to PCA in the LE Survey (in short tons)

• Divided by the plant’s estimated 2005 clinker production, estimated as follows. (Note 

that this procedure for estimating a plant or kiln’s clinker production responds to one of 

EPA’s requests in the Excel workbook that you sent us regarding how to estimate this 

quantity.) PCA does not collect data on clinker production by plants or kilns from 

member companies, but we do collect data on annual clinker capacity. This data is 

reported publicly in PCA’s biennial Plant Information Summary. We crosswalked plant 

capacity information from the Plant Information Summary with information generated by 

USGS on clinker production by district (generally States) for the corresponding year in 

the USGS annual Minerals Yearbook, Cement in order to estimate capacity utilization by 

district. We then applied this estimated district capacity utilization figure to the clinker 
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capacity figures for all cement plants in the district (from the Plant Information 

Summary) in order to estimate clinker production for each cement plant in that district.1

We then averaged the emission factors obtained for each plant across all plants of that sort (wet, 

long dry, etc.) in order to obtain an average national emission factor for plants of each sort. 

Some plants include kilns of differing sorts (e.g., one plant consisting of several long dry kilns 

and one precalciner kiln); in which case we classified the plant in a group according to the kiln 

type for the largest capacity kiln at the plant.

We have sent to EPA an edited version of the Excel workbook on SO2 emissions that you 

originally sent to us for comment. The comments in the workbook should be self explanatory, 

but we will be pleased to explain them further if you wish. In summary, the comments include:

• In response to your request (“Emission Intensities” worksheet) for review of EPA’s 

previous regionally based emission intensity factors, we have provided instead a set of 

nationally-based emission factors developed from analysis of emissions data from those 

58 plants for which LE Survey emission estimates and NEI 2005 estimates do not differ 

by more than 500 tpy.

• In response to your request (“Units” worksheet) for a procedure for estimating 2005 

clinker production on a plant or kiln basis, we have provided the suggested methodology 

combining information from PCA’s Plant Information Summary and the USGS Minerals 

Yearbook, Cement.

• In response to your indication of some plants/kilns where there are difficulties in 

interpreting the 2005 NEI information in terms of which kilns at a plant are included in 

the estimates, we have provided a series of clarifying comments in a text column toward 

the right edge of the “Emissions” worksheet.

• In response to your request for review of the current EPA SO2 emissions estimates for 

individual kilns (based on 2005 NEI), we have provided in the rightmost column of the 

“Emissions” worksheet an indication of which of 5 methods of estimating emissions we 

recommend for each particular plant/kiln. The five methods, as we discussed earlier in 

this paper are:

1. Based on a close match between the 2005 NEI estimate for this plant/kiln and the LE 

Survey estimate, we recommend using the 2005 NEI estimate for this plant/kiln.

2. Based on a significant disparity between the 2005 NEI estimate for this plant/kiln and 

the LE Survey estimate, we recommend developing an emissions estimate based on 

application of our national emission intensity factors.

3. Based on the absence of a LE Survey estimate for this kiln but the existence of a 2005 

NEI estimate, we recommend using the 2005 NEI estimate.

 1

 Here’s an example of this calculation. In the “Maryland” district, as USGS defines districts, the Plant Information 

Summary for 2004 (used to represent 2005 conditions, since no report was published for 2005) reports 3 plants with 

a total of 4 kilns and total annual clinker capacity of 2,538,000 metric tons per year. The USGS Minerals Yearbook, 

Cement for 2005 reported total clinker production from plants in the Maryland district as 2,458,000 metric tons. 

These figures imply capacity utilization of 96.8% on average in 2005 for cement plants in the Maryland district. We 

applied this district-wide average to the reported capacity of each plant in the Maryland district in order to estimate 

clinker production in 2005 for each of these plants.
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4. For the remaining kilns for which there exist neither an LE Survey estimate nor a 

2005 NEI estimate (e.g, new kilns since 2005), we recommend developing an 

estimate based on application of our national emission intensity factors.

5. For approximately ten plants for which EPA noted in the worksheet that the Agency 

has difficulty interpreting 2005 NEI data, we have provided information that should 

clarify the meaning of the NEI data. For these plants, we recommend that the Agency 

use the additional information that we provide in the worksheet in order to develop an 

estimate of baseline SO2 emissions.

PCA Control Efficiency Assumptions

SO2

On behalf of the PCA, representatives of Schreiber, Yonley & Associates (SYA) met with 

representatives of MECS USA, the supplier of DynaWave Scrubber systems, on January 28, 

2010, to discuss the control efficiencies for their scrubber systems. During this meeting, 

DynaWave representatives confirmed that the lower limit for their initial performance guarantees 

for SO2 scrubbers for the cement industry is 10 to 12 ppm SO2 for a scrubber using limestone or 

CKD as the scrubber reagent. The initial performance guarantee is considered representative of 

the long-term performance, or performance over the useful life, of the LWS systems. Therefore, 

for a scrubber inlet concentration of 100 ppm SO2 and an outlet of 10 to 12 ppm SO2, the control 

efficiency will be 88 to 90%, not 95%. In addition, they also confirmed that facilities with 

significant HCl concentrations will have to treat and dispose of liquid effluent in order to remove 

the CaCl2 from the scrubber system. This treatment and disposal aspect was not included in 

prior assessments by EPA and would represent a significant cost burden to part of the industry. 

Additional comments from PCA related to various cost aspects of EPA’s economic benefit 

analysis and technology effectiveness analysis were included in Appendix 11 and 12, 

respectively, of the September 4, 2009 submittal. Previous PCA comments and calculations 

were based on a range of 10 to 15 ppm and used the 15 ppm for calculations. The following 

table presents a revised example of the expected performance based on the vendor guarantee of 

12 ppm.

Uncontrolled 

SO2

Concentration

(ppm)

Cumulative 

Percentage of 

Kiln Population 

Less Than 

Stated 

Uncontrolled 

Concentration

SO2

Control 

Level if 

90% 

Reduction 

is Obtained

(%)

Controlled SO2

Concentration 

if 90% 

Reduction is 

Obtained

(ppm)

SO2

Control 

Level if 

95% 

Reduction 

is Obtained

(%)

Controlled SO2

Concentration 

if 95% 

Reduction is 

Obtained

(ppm)

12 24 0 - 0 -

25 29 52 12 52 12

50 39 76 12 76 12

100 56 88 12 88 12

120 59 90 12 90 12

240 67 90 24 95 12

500 84 90 25 95 25

1000 94 90 100 95 50
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The wet scrubbers currently utilized for SO2 control at U.S. cement plants are not typically 

equipped with continuous SO2 monitors at the scrubber inlet. Therefore, there is no continuous 

measurement of the scrubber efficiencies. Of the 5 existing wet scrubbers, one began operation 

in 2001, two in 2002 and two in 2004. The design control efficiencies for these scrubbers varied 

depending upon the limits of the individual permits. Therefore, one of them was designed for 

and achieves a control efficiency of 95% while others were designed for control efficiencies of 

less than 90%.

PCA previously provided comments that the ISIS model used incorrect gas flows for costing wet 

scrubbers. The equipment sizing criteria for add-on or tailpipe control technologies is normally 

based upon the actual flow of the exhaust gas to be treated as the equipment has to be capable of 

handling the actual volume of gases being exhausted. The following source information is 

provided to give an example of the magnitude of error than is introduced by specifying the size 

of the control equipment with the flow in DSCFM versus ACFM.

Parameter Units

Operating Condition

Minimum Average Maximum

Flow Rate acfm 195000 260000 325000

Temperature F 550 575 600

Moisture Content % 27 27 27

Flow Rate dscfm 74394 96796 118140

Error % 38 37 36

Mercury

Wet scrubber The 50% control efficiency was based upon the assumption that 50% of 

the mercury emissions are elemental and will not be controlled by a wet 

scrubber.

ACI The 75% control efficiency was based upon testing at Ash Grove, Durkee, 

Oregon.

ACI – Wet scrubber The 85% combined control efficiency assumes that the ACI controls 75% 

of the total mercury emissions, and the scrubber would then remove about 

half of the remaining non-elemental portion (50% of the remaining 25%).

HCl

Wet Scrubber PCA agrees with EPA’s assumed control efficiency for a wet scrubber 

with one qualifier. At least one of the operating scrubbers, which are 

designed and operated for SO2 control, cannot comply with the proposed 

HCl limits. Therefore, it is not appropriate to assume that the installation 

of a wet scrubber will assure compliance with the proposed emission 

limits for HCl.
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THC

ACI The 50% control efficiency was based upon operating experience at one 

facility.

Wet Scrubber –ACI PCA’s assumption is consistent with EPA’s assumption, no additional 

THC control credited for the addition of a wet scrubber.

RTO The 95% control efficiency was based upon discussions with two different 

vendors, and experience from one facility. Vendor quotes referencing 

non-methane VOC were adjusted to account for methane and ethane, 

especially where natural gas firing is necessary to maintain RTO 

temperatures. The standard normally guaranteed by equipment vendors 

for this type of application (inlet concentrations below 500 ppmv) is an 

outlet non-methane VOC concentration of 10 ppmv.

We appreciate the opportunity to work with EPA in improving ISIS, and look forward to 

continuing this collaboration. Please call me if you have any questions about the data that we 

have provided.

Sincerely:

Tyrone Wilson, Ph.D.

Director, Regulatory Affairs, Energy & Environment

cc: Andy O’Hare, PCA