1 July 1 5 , 2011

ncasi 

### Developing an Alternative CO Limit f or Biomass Stoker Unit s Having a CO CEMS
T he current biomass stoker subcategory CO limit is 490 ppm at 3 % O 2 for existing units. As discussed in the companion NCASI paper Review of the Biomass Stoker CO Limits and Suggestions for Revisions , there are several reasons why this limit needs revision. The key reason is that additional Method 10 tests have been located for some of the best performer s in this sub category, and these additional tests provide a more complete picture of the variability in CO emissions amongst biomass stokers
. Still, this is a 3 hour average limit, and it is well documented that routine biomass stoker operations are such that frequent spikes in CO concentrations occur. A boiler equipped with a CO CEMS would record such elevated emissions , thus providing credible evidence of exceedances of the 490 ppm limit. EPA has acknowledge d that a n alternative CEMS

- based CO limit is a possible solution for this dilemma. This limit would have a n averaging time considerably longer than 3 hours in order to minimize the impact of temporary spikes and provide sufficient time for boiler operators to make appropriate adjustments to lower CO levels. To establish a CO limit for a longer period than 3 hr, EPA Metho d 10 tests are unsuitable and CEMS data are needed. EPA strongly favors using CEMS data from the best performing units in a subcategory, as identified from Method 10 data, to develop such a limit. Since none of the current or prospective best performers in the biomass stoker subcategory have a CO CEMS, this leaves only two options, namely (1) install a CO CEMS on one or more of the top performers and gather several months of data, or (2) demonstrate that a non

- best performer stoker boiler with CO CEMS dat a has CO emissions that are equivalent to or less than those measured during Method 10 tests at the best performers. Generating New Data If it is assumed any biomass stoker boiler with a Method 10 test average of 210 ppm at 3% O 2 or less (when 90% or more of the heat input during the test came from biomass) will be a best performer for CO in the biomass stoker subcategory after EPA completes its review of new information submitted by July 15, potential candidate boilers in the forest products industry for additional CO sampling using a temporary CEMS are: **•** WVWeyerhaeuserBuckhannon **•** ARWestFraserHuttig **•** IDChilcoLakeSawmill **•** IDRileyCreekLumber **•** MSShuqualakLumber (uncertain if it belongs in subcategory) Company representatives for these facilities have been co ntacted. A t least two have expressed interest in having a temporary CO CEMS installed for the purpose of gathering additional data. AF&PA and AWC would provide funding for testing contractors, and NCASI would be responsible for overseeing the effort and analyzing the resulting data.2 July 1 5 , 2011

ncasi If EPA adheres to its timetable for proposing and promulgating changes to the Boiler MACT rule by April 30, 2012 , results from a 4

- month sampling effort c ould be provided to EPA around March 1 if there are no unforeseen problems with the testing program. This timing might allow EPA to issue a quick Notice of Data Availability or include a reference in the preamble to the final rule, noting that the alternative CO standard with a longer averagin g time described in the proposed rule was still under consideration and development . Four months of CEMS data from at least two boilers is the absolute minimum amount of data needed to make a credible case for an alternative 24 hr block or 7 day average s tandard. Obtaining similar CEMS data from additional boilers would be highly desirable. However, four months of CEMS data would likely be insufficient to support a 30 day average standard

– at least 12 months should be obtained from a minimum of at least two boilers to represent the full year of variability including winter and spring months when biomass fuels are typically wetter and average CO emissions higher than in summer and fall. Using Existing CEMS Data There are at least 26 stoker boilers that burn biomass in the forest products industry that have CO CEMS. Outside of the forest products industry, there are at least 18 biomass stoker units operated by electricity generating firms with CO CEMS, but t he ma jority of the se boilers are at facilities which are not major sources of hazardous air pollutants , or the boilers burn some biomass materials which may be classified as solid wastes
. It is understood that EPA will not use any data from boilers that will b e subject to GACT or CISWI standards to set MACT limits. As previously mentioned, n one of current or potential best performers have a CEMS. Thus to use existing CEMS data to develop an alternative standard with a longer averaging time , it would have to b e shown that CO emissions from a non

- best performer are substantially similar to those of best performers. Presumably EPA’s benchmark for comparisons will be Method 10 test results from the best performers. Relative to u sing CO CEMS data for revising t he current biomass stoker subcategory CO limit or establishing an alternative limit with a longer averaging time for those units having a CEMS, EPA suggested CEMS data from non

- best performers might be considered if (1) the CEMS for CO and O 2 met certain Q A/QC criteria, e.g. PS

- 4 and PS

- 3 provisions and annual RATAs and periodic calibration and drift tests, (2) at least 90% of the boiler heat input came from biomass during each 3

- hr block average , and (3) a significant fraction of the 3

- hr block averages were at or below the maximum 3

- hr average Method 10 concentrations measured in tests conducted at the best performers. Regarding the last condition, 210 ppm at 3% O 2 is currently the cutoff test average va lue for the best performing units in the biomass stoker subcategory. NCASI ha s gather ed and continues to gather more information on the installed monitors and boiler fuel use in biomass stoker units to see what data meeting EPA’s criteria can be obtained. Thus far, NCASI has obtained hourly average CO CEMS data f or sixteen biomass stoker s (1 3 in the forest products industry and 3 at electricity generating facilities ) for periods ranging from 6 to 18 months
. After screening the data to remove hourly averages associated with startup/shutdown conditions and monitoring equipment failure or calibration s , 3

- hour block average s were calculated and averages of all such blocks were estimated for the 16 boilers
.3 July 1 5 , 2011

ncasi Table 1 summarizes the 3 hr bl ock averages for these 16 units along with the duration of the data and the fuel mix. Five of the 16 boilers had a long

- term 3 hr block average of less than 210 ppm (Boiler Nos. 1, 3, 8, 12 and 14). However, Boiler Nos. 13 and 14 burned less than 30% b iomass on an annual average basis, the rest being coal, oil and gas. Boiler No. 8 burned 81% biomass and 19% gas. However, besides clean wood residues, the biomass material included sludge and paper materials , and may have included chipped railroad ties and industrial wood waste. Thus it is uncertain whether this boiler would be subject to CISWI or Boiler MACT standards
. Two of the 16 boilers (Boiler Nos. 1 and 3) had a mean 3 hour average CO value of 208 an d 202 ppm @ 3% O 2 , respectively. Boiler No. 1 ( Boise Paper, Wallula, WA ) burned hog fuel and natural gas (78% biomass annual average). Boiler No. 3 ( Genessee Power, Flint, MI) burned 100% biomass which included small amounts of animal bedding (wood shavi ngs and manure) . For Boiler No. 1, n early 3.0% of the hourly data were eliminated before computing three

- hour block averages (periods of startup/shutdown , no steam production, and CEMS malfunction s/calibrations )
. Of the remaining 97.0%, 7.7% corresponded to periods when biomass firing exceeded 90% of total heat input (rest gas), and 65.2% of these were less than 210 ppm @3% O 2 . For Boiler No. 3 that burned 100% biomass, 9. 8 % of the data were eliminated ( 8.3% for periods of shutdown with no steam producti on, and the remainder for startup/shutdown conditions or CEMS malfunctions/ calibrations ) before computing three

- hour block averages
. Of the remaining 90.2 %, nearly 65% corresponded to periods when CO emissions were less than 210 ppm @3% O 2 . Thus, these two boilers equipped with CO CEMS should be represent ative of the “best performer” boilers in the biomass stoker s ubcategory and their data should be appropriate for determining a CEM

- based CO limit for biomass stokers. Table 1. Long

- Term CO CEMS 3

- Hr A verages For 16 Biomass Stoker Units
No. Fuel Mix Data Duration 3 Hr

- Avg CO, ppm @ 3% O 2 1 Wood Residues (78%), Gas (22%) 1

- 1

- 10 to 1

- 1

- 11 207.8 2 Wood Residues (100%) 12

- 1

- 99 to 12

- 31

- 00 335.3 3 Wood Residues (100%)

- EGU 6

- 1

- 10 to 5

- 31

- 11 201.5 4 Wood Residues & Sludge (97.5%), Gas (2.5%) 1

- 1

- 10 to 1

- 1

- 11 605.0 5 Wood Residues (100%)

- EGU 9

- 1

- 07 to 12

- 18

- 08 482.9 6 Wood Residues (100%)

- EGU 6

- 1

- 09 to 11

- 4

- 09 995.8 7 Wood Residues (91.2%), Sludge (8.8%) 1

- 1

- 08 to 10

- 31

- 08 334.9 8 Wood Residues (81%), Gas (19%) 1

- 11

- 08 to 1

- 10

- 09 43.4 9 Wood Residues (75%), Gas (18%), Oil (7%) 1

- 1

- 09 to 6

- 11

- 10 703.7 10 Wood Residues (73%), Gas (27%) 1

- 1

- 00 to 12

- 31

- 00 211.5 11 Wood Residues, Gas 1

- 1

- 09 to 12

- 31

- 09 387.7 12 Wood Residues, Coal, Gas 1

- 5

- 09 to 12

- 21

- 09 1389.9 13 Wood Residues (28%), Coal (49%), Oil (12%), Gas (12%) 1

- 1

- 09 to 6

- 11

- 10 155.1 14 Wood Residues (29%), Coal (44%), Oil (13%), Gas (14%) 1

- 1

- 09 to 6

- 11

- 10 143.6 15 Wood Residues (100%) 1

- 1

- 08 to 12

- 31

- 08 302.1 16 Wood Residues (100%) 1

- 1

- 01 to 5

- 31

- 01 311.74 July 1 5 , 2011

ncasi Table 2 summarizes the 99.0 and 99.9 percentile value of CO emissions using the combined hourly average CO CEMS data for the above two “best

- performing” biomass stokers. The 99 .0 and 99.9%ile values are shown for 3

- h r, d aily, weekly and monthly averages . Also shown are a “never

- to
- exceed” value which simply corresponds to the maximum value in the data set. Table 2 . 99 .0%ile and 99.9%ile Values For Two “Best Performing” Biomass Stokers With Long

- Term CO CEMS Data Using 3 Hr, Daily, Weekly and Monthly Averages 3 Hr

- Avg Daily Average Weekly Average Monthly Average 99.9 %ile 1 99.0 %ile 1 99.9 %ile 1 99.0 %ile 1 99.9 %ile 1 99.0 %ile 1 99.9 %ile 1 99.0 %ile 1 ppm CO @ 3% O 2 990 680 650 550 470 440 420 420 Never

- to
- Exceed ppm CO @ 3% O 2 1540 680 470 420

1 99.9 or 99.0%ile value from rank ordering the data points Illustration of How Limits Shown in Table 2 Compare With Available Emission Profiles for Two Biomass Stokers In this section, the 3

- hour, daily, weekly and monthly average CO emission profiles are compared for two of the biomass stokers listed in Table 1 with the limits derived in Table 2
. Boiler No. 2 ( 12 - 1 - 99 to 12 - 31 - 00 ) Although this boiler had a 3 h r annual a verage CO emission concentration of 335 ppm , as seen from the profile in Figure 1A, stack CO levels were often much higher. Thus, e ven though the 99%ile, 99.9%ile or “not

- to
- exceed” values for the 3

- h r average s in Table 2 are significantly higher than those for the daily, weekly or monthly averages, on multiple occasions these 3

- hr values would have been exceeded. Attempting to adjust boiler operating conditions to sufficiently reduce CO levels to meet a 3

- hr limit is generally not possible; the timeframe is too short.

Figure 1A. 3 - Hr Average CO Emissions For Boiler No. 2 0.0 1000.0 2000.0 3000.0 4000.0 5000.0

12/01/99 01/19/00 03/07/00 04/21/00 06/07/00 07/31/00 10/25/00 12/12/00CO (ppm @ 3% O2) 

### 3 Hr Averages Limit Not To Exceed = 1540 ppm 99.9 & 99%ile = 990 & 680 ppm5 July 1 5 , 2011

ncasi The daily average CO profile shown in Figure 1B also shows how the 99%ile, 99.9%ile or “not

to
- exceed” 24

- hr values in Table 2 were often exceeded . However, 24 hours would provide more time f or modifying boiler operations to lower CO levels
.

Figure 1 B . Daily Average CO Emissions For Boiler No. 2
The weekly average CO profile shown in Figure 1C shows how the 99%ile, 99.9%ile or “not

- to
exceed” 7

- day average values in Table 2 would have been exceeded four times (8%) during the entire year. More importantly, sufficient time would have been available for modifications to be made to boiler operations to lower CO levels
.

Figure 1C . Weekly Average CO Emissions For Boiler No. 2 Finally, t he monthly average CO profile shown in Figure 1D demonstrates the 99%ile, 99.9%ile or “not

- to
- exceed” 30

- day average values in Table 2 would have been exceed ed once during the entire year . The 30

- day averaging time provides more flexibility for adjusting boiler operating conditions to minimize CO emissions. 0.0 200.0 400.0 600.0 800.0 1000.0

12/02/99 03/04/00 06/02/00 10/15/00CO (ppm @ 3% O2) 

### Daily Average Limit Not To Exceed = 680 ppm 99.9 & 99%ile = 650 & 550 ppm

0.0 200.0 400.0 600.0 800.0 1000.0

12/08/99 02/16/00 04/26/00 07/05/00 10/11/00 12/20/00CO (ppm @ 3% O2) 

### Weekly Average Limit Not To Exceed = 470 ppm 99.9 & 99%ile = 470 & 440 ppm6 July 1 5 , 2011

ncasi Figure 1 D . Monthly Average CO Emissions For Boiler No. 2 Boiler No. 13 ( 1 - 1 - 09 to 6 - 11 - 10 ) This boiler had a 3 h r annual a verage CO emission concentration of only 15 5 ppm . Yet Figure 2A shows how the stack CO levels were sometimes 5 to 10 times hi gher. Thus, e ven though the “not

- to
- exceed” 3

- hr average value of 1540 ppm is exceeded just once, the 99.0 and 99 .9%ile values are excee ded multiple times
. I n sufficient time would have been available to adjust boiler operating conditions to lower CO emissions to these values
.

Figure 2A . 3 - Hr Average CO Emissions For Boiler No. 13 The daily average CO profile shown in Figure 2B also shows how the 99%ile, 99.9%ile or “not

to
- exceed” 24

- hr average values in Table 2 would have often been exceeded
. 0.0 200.0 400.0 600.0 800.0

01/01/00 03/01/00 05/01/00 07/01/00 09/01/00 11/01/00CO (ppm @ 3% O2) 

### Monthly Average Limit Not To Exceed = 420 ppm 99.9 & 99%ile also 420 ppm

0.0 200.0 400.0 600.0 800.0 1000.0 1200.0 1400.0 1600.0

12/8/2008 3/8/2009 6/6/2009 9/4/2009 12/3/2009 3/3/2010 6/1/2010CO (ppm @ 3% O2) 

### 3 Hr Averages Limit Not To Exceed = 1540 ppm 99.9 & 99%ile = 990 & 680 ppm7 July 1 5 , 2011

ncasi Figure 2 B . Daily Average CO Emissions For Boiler No. 13
The weekly average CO profile shown in Figure 2C shows how the 99%ile, 99.9%ile or “not

- to
exceed” 7

- day average values in Table 2 would have been exceed ed only three times (6%) during the entire year. More importantly, sufficient time would have been available for modificat ions to be made to boiler operations to sufficiently lower CO concentrations
.

Figure 2 C . Weekly Average CO Emissions For Boiler No. 13 Finally, t he monthly average CO profile shown in Figure 2D demonstrates the 99%ile, 99.9%ile or “not

- to
- exceed” 30

- day average values in Table 2 would have been exceeded once during the entire year
. A mple time would be available for adjusting boiler operations to achieve these values
. 0 200 400 600 800 1000

12/8/2008 3/8/2009 6/6/2009 9/4/2009 12/3/2009 3/3/2010 6/1/2010CO (ppm @ 3% O2) 

### Daily Average Limit Not To Exceed = 680 ppm 99.9 & 99%ile = 650 & 550 ppm

0 200 400 600 800

12/8 3/8 6/6 9/4 12/3 3/3 6/1CO (ppm @ 3% O2) 

### Weekly Average Limit Not To Exceed = 470 ppm 99.9 & 99%ile = 470 & 440 ppm8 July 1 5 , 2011

ncasi Figure 2 C. Monthly Average CO Emissions For Boiler No. 13 Conclusion EPA technical staff believe using CO CEMS data obtained on the best performing units already used to calculate the current short

- term limit would be the most legally defensible approach for developing an alternative CO CEMS

- based limit. If temporary CEMS were installed on some of these units to obtain just four month s of data, the data could not be provided to EPA until shortly before EPA’s antici pated date for promulgating changes to the Boiler MACT rule. Thus the collection of additional CEMS data would only be worthwhile if EPA commits to waiting for the new data before making final decisions on an alternative CEMS

- based CO limit for the biomass stoker subcategory. Because of the timing issue, EPA encouraged the forest products industry to investigate how existing CO CEMS data could be used to develop an alternative limit. NCASI has done that. CEMS data from two biomass stoker boilers substantially similar to those in MACT floor for this subcategory were analyzed. Based on 12 months of data for each of these boilers, the analysis would support the following numerical limits for a CEMS

- based longer

- term alternative standard: 1. A daily average of 650 ppm @ 3% O 2 to be exceeded only once per calendar year (based on 99.9%ile value.) 2. A daily average of 550 ppm @ 3% O 2 to be exceeded only four times per calendar year (based on 99.0%ile value.) 3. A daily average of 1540 ppm @ 3% O 2 never - to
- be

- exceeded in a calendar year (based on the “never

- to
- exceed” value.) 4. A weekly average of 470 ppm @ 3% O 2 to be e xceeded only once per calendar year (based on 99.9%ile and “never

- to
- exceed” value.) 5. A weekly average of 440 ppm @ 3% O 2 to be exceeded only four times per calendar year (based on 99.0%ile value.) 6. A monthly average of 420 ppm @ 3% O 2 never to be exce eded in a calendar year (based on the 99.0%ile, 99.9%ile and /or “never

- to
- exceed” value.)

0.0 100.0 200.0 300.0 400.0 500.0

12/8 3/8 6/6 9/4 12/3 3/3 6/1CO (ppm @ 3% O2) 

### Monthly Average Limit Not To Exceed = 420 ppm 99.9 & 99%ile also 420 ppm9 July 1 5 , 2011

ncasi There is no way to predict if limits based on data that would be obtained in a four month study on boilers currently in the MACT floor would be the same as these numerical values. Nevertheless the available CEMS data show an alternative to the current sho rt
- term standard for biomass stoker boilers equipped with a CEMS is essential.