AECOM Peak-to-Mean Paper Machine HAP Emissions Ratios

Page 1 of 7 

## Peak-to-Mean HAP Emissions Ratios for Paper

Machine Sources

Prepared by David W. Heinold, CCM

AECOM Technical Services, Westford, Massachusetts

on behalf of the American Forest and Paper Association

February 15, 2011

In characterizing acute inhalation risk, the method outlined in EPA’s Risk Assessment and

Modeling - Air Toxics Risk Assessment Refer ence Library: Volume 2 - Facility-Specific

Assessment (EPA-453-K-04-001B, http://www.epa.gov/ttn/fera/risk_atra_vol2.html ) is to apply

HEM-3 to estimate maximum off-site concentrati ons due to a facility’s emissions. Because

emissions from some sources are more variabl e than others, EPA’s guidance indicates that to

provide a conservative estimate of acute exposur e and risk, the upper-limit short-term emissions

from all hazardous air pollutant (HAP) sources should be simultaneously modeled. The resultant

maximum 1-hour modeled off-site concentrations are then com pared to acute health effects

benchmarks. In the absence of direct estima tes of maximum hourly emissions EPA’s guidance

provides a default peak-to-mean emissions ratio of 10 to all HAP sources at a facility. This means

that the annual average emission rates which are used in HEM-3 to es timate cancer risks and

chronic hazard indices are all multiplied by te n for the acute risk assessment along with the

maximum modeled 1-hour average concentration. Espec ially for many sources at paper mills this

is a highly conservative met hod of estimating acute risk because it implies that operating

conditions that result in a 10-fold increase in em issions occur simultaneously for all mill sources

and that these conditions are also coincident with worst-case dispersion meteorology. Given that

modeling conducted by EPA has indicated that emissions from paper machines sources may

substantially contribute to maximum 1-hour av erage HAP concentrations, an investigation has

been undertaken by AF&PA to identify a peak-to-mean emission ratio that is more appropriate for

paper machines than the generic factor of 10.

In the absence of direct measurements, it is standard practice for HAP emissions from paper

machines sources to be computed by multiplying the air dried ton of finished product (ADTFP) by

an emission factor, e.g. those developed by NCASI for various types of paper products. Using

emission factors to estimate emissions, inherently assumes that emissions are proportional to the

production rate, which is a reasonable assumption based on available sampling data. This implies

hourly emission rates are determined by the production rate.

In addition to considering the variability in paper machine emission rates associated with

production rate fluctuations, the possibility that emission rates of gaseous organic compounds may

vary due to changes in process-related conditions has been considered. It would be desirable to

have continuous emission monitoring data or repeated manual stack sampling data to address thisAECOM Peak-to-Mean Paper Machine HAP Emissions Ratios

Page 2 of 7 possibility, but obtaining such data is extremel y difficult because paper machines have multiple

vents, and the concent rations of organic compounds of conc ern to acute risks (acetaldehyde,

acrolein, formaldehyde) are typically near or below instrumental or manual me thod detection limits

in the majority of these vents.

To help evaluate the degree to which paper-machine emissions vary due production rate and

other factors NCASI has provided data for a mill that it had in its possession in which methanol

sampling was conducted on multiple days on a paper machine to support the mill’s Clean

Condensate Alternative demonstration. In the Cl uster Rule, methanol is considered to be the

surrogate for all volatile organic hazardous air pollutants emitted from pulping, bleaching,

papermaking and wastewater treatment operations (MACT I sources). Tests were conducted on

five days for the 18 paper machine vents. Table 1 pr ovides the results of this testing on this paper

machine.

Table 1. Measurements of Paper Machine Methanol Emissions and Production

Date Production

(tons/hr) Methanol Emission

Rate

(lb/hr) Methanol Emission

Factor

(lb/ton)

09/06/08 35 28.3 0.81

09/10/08 43.5 28.1 0.65

09/12/08 49.9 31.5 0.63

09/18/08 54.8 30.8 0.56

09/20/08 34.8 18.4 0.53

Mean 43.6 27.4 0.64

Peak/Mean 1.26 1.15 1.26

The peak-to-mean production ratios for this machine for the five-day period were similar to those

for other machines over much longer periods of time. For this set of measurements, the data

indicate that the methanol emissions are highly co rrelated with production (correlation coefficient

of 0.73) and the computed emission factors ar e slightly negatively correlated with production

(correlation coefficient of -0.36). Thus, the peak-t o-mean ratio for methanol emission rate (1.15) is

less than the peak-to-mean ratio for paper machine production rate, indicating that using paper

machine production rate to evaluate variability of HAP emissions from paper machines is suitably

conservative.

In relation to production rate, other process-relat ed factors that might affect emission rates are

relatively constant – roof vent exhaust gas flow rates, dryer temperatures, pulp characteristics,

whitewater recirculation rates, as evidenced by wi th Table 1 which indicates that the variability ofAECOM Peak-to-Mean Paper Machine HAP Emissions Ratios

Page 3 of 7 the methanol emission rate is comparable and some what less than the variability in production

rate. There is also no reason to suspect e mission rates from paper machines would be higher

during startup or shutdown conditions, and paper ma chine malfunctions, which are extremely rare,

require prompt shutdown. Typically, paper machine upsets correspond to lack of production

(lowering average production value). Worst case scenario is pulp continues to go to machine,

then back in a loop and no paper is being made. Since HAP emissions from paper machines are

a function of the water carrying the pulp (HAPs ar e contained in solution), if there is no pulp

(water) going to the paper machine, there are no corresponding paper machine emissions.

Paper machines are typically operated at the max imum production possible for that specific grade

(unless limited by permit). Given that paper machines typically operate at a steady production rate

for up to several days, the daily variability of production rate for a mill throughout a year is

considered a reliable measure of the variability of the hourly producti on rate. As it is common for

mills to retain records of daily production, the peak-to-mean HAP emission ratio for each paper

machine can be readily computed as the ratio of the maximum daily production rate for the paper

machine to its annual production rate.

Several paper companies surveyed their produc tion records and computed the peak-to-mean

production ratio for each paper machine for twenty mills over the past three years (2008, 2009 and

2010). The results of this survey are provided in Table 2. Figure 1 shows the variation of the data

over the last three years and the distribution of peak-to-mean ratios among all paper machines is

provided in Figure 2. The median peak-to-mean rati o is 1.3, the maximum ratio is 2.1 and the 95 th

percent of the ratio values is less than 1.6.

The consistency of these paper machine producti on data and the evidence provided by NCASI in

Table 1 that the variability of HAP emissions from paper machines is comparable or less than the

variability in the production rate, supports a generic application of a peak-to-mean ratio for paper

machines that is much less than EPA’s default fact or of 10. Based on the variability in daily

production rate AF&PA recommends that EPA use a factor of 1.6 as it represents a highly

conservative estimate for the peak to mean ra tio for the vast majority of paper machines.AECOM Peak-to-Mean Paper Machine HAP Emissions Ratios

Page 4 of 7 Table 2 Daily Peak to Annual Average Paper Machine Production Ratios

Mill Year PM1 PM2 PM3 PM4 PM5

1 2008 1.30 1.31

1 2009 1.39 1.61

1 2010 1.27 1.20

2 2008 1.30 1.28 1.39 2.11

2 2009 1.19 1.32 1.30 1.74

2 2010 1.34 1.26 1.30 1.76

3 2008 1.43 1.41

3 2009 1.55 1.43

3 2010 1.56 1.97

4 2008 1.25

4 2009 1.26

4 2010 1.26

5 2008 1.27

5 2009 1.24

5 2010 1.32

6 2008 1.44 1.31

6 2009 1.37 1.35

6 2010 1.35 1.30

7 2008

7 2009 1.31 1.39 1.49

7 2010 1.96 1.99

8 2008 1.38 1.33 1.28 1.21

8 2009 1.28 1.49 1.31 1.49

8 2010 1.31 1.48 1.30 1.24

9 2008 1.22 1.27

9 2009 1.19 1.29

9 2010 1.16 1.30

10 2008 1.36 1.35 1.42

10 2009 1.41 1.30 1.29AECOM Peak-to-Mean Paper Machine HAP Emissions Ratios

Page 5 of 7 Table 2 (cont'd) Daily Peak to Annual Average Paper Machine Production Ratios

10 2010 1.24 1.31 1.27

11 2008 1.29

11 2009 1.31

11 2010 1.24

12 2008 1.28 1.40

12 2009 1.35 1.46

12 2010 1.29 1.32

13 2008 1.16 1.43

13 2009 1.24 NA

13 2010 1.19 1.32

14 2008 1.34 1.28

14 2009 1.32 1.27

14 2010 1.27 1.31

15 2008 1.33 1.47

15 2009 1.21 1.30

15 2010 1.35 1.31

16 2008 NA 1.18 1.19

16 2009 1.21 1.24 1.28

16 2010 1.19 1.24 1.33

17 2008 1.25

17 2009 1.32

17 2010 1.32

18 2008 1.22 1.15

18 2009 1.30 1.23

18 2010 1.26 1.19

19 2008 1.20 1.22

19 2009 1.09 1.08

19 2010 NA NA

20 2008 1.48 1.41 1.28

20 2009 1.55 1.49 1.56

20 2010 1.56 1.40 1.34

Note: NA indicates data not availableAECOM Peak-to-Mean Paper Machine HAP Emissions Ratios

Page 6 of 7 Figure 1: Peak

‐ to

‐ Mean Production Ratios for Each YearAECOM Peak-to-Mean Paper Machine HAP Emissions Ratios

Page 7 of 7 Figure 2: Distribution of Peak

‐ to

‐ Mean Production Ratios

0.00 0.50 1.00 1.50 2.00 2.50

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 

## Cumulative Distribution of Daily

Peak to Annual Average Ratios at 20 Mills

from 2008

‐ 2010