June 7 , 2012

1 **HAP Emissions and Relat i**  **on to CO Below 100 ppm for Coal and Oil**  **- Fired Industrial Boilers**  **1** Carbon monoxide (CO) results from incomplete oxidation of the carbonaceous fractions in fossil and non - fossil fuels. High levels of CO are generally associated with poor combustion. Solid fuels first undergo pyrolysis followed by oxidation of the pyrolys is products. Organic hazardous air pollutants (HAPs) are products of incomplete oxidation of the products of pyrolysis. Such incomplete oxidation has been historically associated with high levels of CO in the stack. As a result, CO is very often used as a surrogate for controlling HAPs and total hydrocarbon (THC) emissions from fuel combustion. However, while the evidence for CO as a HAP surrogate during biomass combustion may be considered to be reasonably sound, such evidence in the case of fossil fue l combustion is generally less forthcoming (except, of course, at very high stack CO levels). Coal, oil and natural gas combustion in boilers generally result in much lower CO emissions than biomass combustion. Thus, while in general the observation t hat high levels of CO (say >300 ppm) are indicative of higher levels of HAP emissions holds, impirical evaluation of CO data from the Industrial Boiler rule record , as shown in this paper, indicates that the correlation appears to b reakdown in the case of very low CO emissions from fossil fuel combustion (below about 100 ppm). In c onversation s between the AF&PA and the EPA BMACT team in February 2012, a consultant (Carl Bozzuto) with more than 4 0 years of boiler combustion design expertise offered an expla nation of a physical/chemical model within the combustion chamber of industrial boilers to explain why CO concentrations bel ow about 100 ppm ( or perhaps as high as the 200 to 300 ppm level traditionally indicative of “good combustion practice”) would not be expected to corr e late with combustion efficiency, nor be a controllable parameter indicative of increasing combustion efficiency in industrial boilers. In short, CO at these very low levels is largely a function of combustion zone inertial physics and boiler “ wall CO” and not the efficiency of combustion itself

. 2 The following plots for CO versus THC emissions from coal and oil combustion, generated from data reported to EPA and residing in EPA’s Boiler MACT database, demonstrate this point. Figure 1 is a plot of all data for CO versus THCs currently in EPA’s Boiler MACT database when essentially 100% coal was

1 Prepared by the National Council for Air and Stream Improvement 2 At low levels, “ w all CO” is not so much a function of combustion zone dynamics or efficiency since it occurs primarily outs ide the combustion zone. During pyrolysis of a solid fuel particle (and atomized liquid fuel droplet) , a small fraction of the pyrolysis products at the burner exit ( where fuel temperature begins to rise ) that are first oxidized to CO gets caught up in the eddy formed at the burner tip , and is directed towards the boiler wall. From here this “wall CO” drifts outside the strong gas circulation in the combustion zone and rises along the boiler wall to the flue. Because the boiler wall temperature s (~500 degrees F) are much less than the ignition temperature for CO (~1200 degrees F or higher) , this “wall CO” never has an opportunity to oxidize to CO 2 . Due to the inertia of the fule particles, other than the small volatile fraction subject to the eddy phenom e non , the rest of the pyrolysis products enter the combustion zone and are completely ox id ized, first to CO and then to CO 2 . The inference is that when stack CO is at high levels , this would be a result of less complete combustion in the combustion zone. At low levels of CO , time , temperature and turbulence in the combustion zone have much less influen ce, and CO concentrations are much more transient. Of course, each boiler’s fuel and load characteristics , combined with its physical arrangement and fluid dynamics , make it essentially unique. Individual boiler operation therefore is tuned or optimized to these unique characteristics. The transient load characteristics of industrial boilers further con s trains the combustion dynamics. These design con s traints (and others n ot brought into this very brief explanation) contribute to varying levels of wall CO , negating the basis for a b asic correlation between CO emissions and boiler combustion efficienc ies, especially at low stack CO levels. AF&PA and CIBO can make available the boiler combustion expertise needed to more fully explain these phycial/chemical phenomen a .June 7 , 2012

2 combusted. These pairs of tests (THC vs CO) corresponded to typically 3 short duration tests (29 boilers) . Only data corresponding to CO emissions of <100 ppm are shown, although this corresponded to the bulk of the data (70 of a total of 84 data points). Based on the extremely low coefficient of regression 3 , r 2 , i t is clearly seen that below about 100 ppm CO, there is simply no correl ation between THC and CO

.

Seven of the 29 boilers for which THC vs CO data are shown in Figure 1 represented units in the “best performing” floor ( AZCatalystPaperSnowflake , IAADMCornProcessingCR , IAUofNorthernIowa , INNotreDame , OHMortonSaltRittman , OKGPMuskogeeMill and TNEastman_NO_CBIDATA ). Figure 2 is a plot of just the data for these 7 boilers.

3 A correlation coefficient r 2 of between 0.0 and 0.04 implies slight to almost negligible correlation; from 0.04 to 0.16 it implies low, quite small correlation ; from 0.16 to 0.50 it implies moderate correlation; from 0.50 to 0. 80 it implies high correlation ; and from 0.80 to 1.00 it implies very high correlation. 

### y = 0.0045x + 1.7512 **R2 = 0.0029**



## 0 **1 2**  **3 4**  **5 6**  **7 8** 

**0 20**  **40 60**  **80 100** **S t** **a c** **k T** **H C** **, p** **p m** **@ 3** **% O** **2**



### Stack CO, ppm @ 3% O2 **Figure 1. CO V s T** 

**otal Hydrocarbons -**  **Boiler MACT Short Duration Te**  **st Data for 100% Coal**  **- Fired Industrial**  **Boilers -**  **CO < 100 ppm**June 7 , 2012

3 Figure 3 is a similar plot of all data for CO versus THCs currently in EPA’s Boiler MACT database when essentially 100% No. 6 fuel oil was combusted. Once again, only data corresponding to CO emissions of <100 ppm are shown, although this corresponded to the bulk of the data (23 of a total of 27 data points). Again, THC emissions show no correlation with CO at CO emission levels of < 100 ppm. 

### y = **- 0.0283x + 1.8194**  **R2 = 0.046**

**0 1**  **2 3**  **4 5**  **6**

**0 5**  **10 15**  **20 25**  **30 35** **S t** **a c** **k T** **H C** **, p** **p m** **@ 3** **% O** **2**



### Stack CO, ppm @ 3% O2 **Figure 2. CO V s THCs**  **- Boiler MACT Short Duration T**  **est Data for Seven "Best Performer" 100% Coal**  **- Fired Industrial**  **Boilers -**  **CO < 100 ppm**

**y = -**  **0.0089x + 1.8538 R2 = 0.0357** 

**0 1**  **2 3**  **4 5**  **6 7** 

**0 20**  **40 60**  **80 100**  **120 S** **t a** **c k** **T H** **C ,** **p p** **m @** **3 %** **O 2** 



### Stack CO, ppm @ 3% O2 **Figure 3. CO V s THC & HCHO**  **- Boiler MACT Short Duration T**  **est Data for 100% No. 6 Oil**  **- Fired**  **Industrial Boilers**  **- CO < 100 ppm** Figures 4 and 5 are plots of CEMS

- based

Washington Works coal

- fired stoker unit Boiler MACT database

. Both plo t s demonstrate how THC are a very poor function of CO at CO for coal or oil

- fired units will not achieve the desired end result of controlling HAPs.
**Figure 4**  **.** CO Vs THC Emissions For a Best

**Figure 5**  **.** Formaldehyde Vs THC Emissions For 0. 0 0. 5 1. 0 1. 5 2. 0 2. 5 3. 0 3. 5 4. 0 4. 5

0 10 20**T H** **C ,** **p p** **m** 

### WWks **Bo iler**  **5 THC**  **vs C**  **O**

0. 0 0. 2 0. 4 0. 6 0. 8 1. 0 1. 2 1. 4

0 10 20**H C** **O H** **, p** **p m**  

## WWks **Bo iler**  **5 HC**  **OH vs C**  **O**

4 based CO versus THC and formaldehyde data for the Dupont stoker unit which currently is a best performer in its category s demonstrate how THC and HCHO emissions, and therefore other PICs, are a very poor function of CO at CO levels below about 100 ppm and thus setting limits of <100 ppm CO

fired units will not achieve the desired end result of controlling HAPs.

CO Vs THC Emissions For a Best

- Performing Coal

- Fired Unit

- Boiler MACT Data

Formaldehyde Vs THC Emissions For a Best
- Performing Coal

- Fired Unit

- Boiler MACT Data y = 0. 0013x + 0. 1864 R2 = 0 .0 035

30 40 50 60 70

**CO, ppm**  

### WWks **Bo iler**  **5 THC**  **vs C**  **O**

y = 0. 0008x + 0. 5007 R2 = 0 .0 009

30 40 50 60 70

**CO, ppm**  

## WWks **Bo iler**  **5 HC**  **OH vs C**  **O** June 7 , 2012 for the Dupont best performer in its category with in EPA’s emissions, and therefore other PICs,

limits of <100 ppm CO

Boiler MACT Data

Boiler MACT Data y = 0. 0013x + 0. 1864 R2 = 0 .0 035

80 90

y = 0. 0008x + 0. 5007 R2 = 0 .0 009

80 90June 7 , 2012

5 **Analysis of Paired CEMS**  **Data Available in the EPA Boiler MACT Database as of May 30, 2012** A significant amount of paired CO and THC CEMS data for two coal

- fired boilers were posted on the EPA website on May 30, 2012. The two boilers included a PC unit (VAPhilipMorrisPark500) and a stoker unit (WVDuPontWashingtonWorks). A total of 13 14 4 data points for simultaneous CO and THC measureme n ts when burning 100% coal in these two boilers were available, of which 38 data points with stack oxygen content above 16% were eliminated for this exercise since they most likely represented boiler startup/shutdown conditions

. Figure 6 looks at all the data w here stack CO was < 100 ppm ( bulk of the data

- 1 292 of the 13 14 data points) . Once again, it is clearly seen from this f igure that there exists no correlation between THC and CO in industrial coal

- fired boilers for CO levels below 100 ppm.

4 38 data points with stack oxygen content above 16% were eliminated for this exercise since they mo st likely represented boiler startup/shutdown conditions 

### y = 0.0069x + 1.3074 **R2 = 0.0016**

**0 5**  **10 15**  **20 25** 

**0 20**  **40 60**  **80 100**  **120 S** **t a** **c k** **T H** **C @** **3 %** **O 2** 



### Stack CO @3%O2

**Figure 6. THC Vs CO for Two Coal -**  **Fired Boilers -**  **Boiler MACT CEMS**  **- Based Data**  **- May 30, 2012**  **- CO < 100 ppm (Stack O2 < 16%)**