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1 

### The Air Emissions Impact of Bu rning Railroad Tie-Derived Fuel

Introduction

Wood is treated with creosote when preparing railroa d cross ties (railties) in order to prolong the useful life of the ties by protecting them against insect and fungal attack. Wood exposed to the outdoor atmosphere and in direct contact with soil or water is more prone to decay and therefore usually requires treatment. At the end of their useful life, treated wood products like railties must be landfilled, reused beneficially, or burned for energy recovery. This paper summarizes available information on the air emission impact of burning railties in industrial boile rs, specifically those equipped with stokers. A full comparison of the contaminants (trace metals, organics, etc.) in railties with those in traditional fuels such as coal, biomass and fuel oil was carried out earlie r and submitted to EPA in support of the NonHazardous Secondary Material (NHSM) rule (AF&PA 2013).

A. Testing at an Electricity Generating Unit (EGU) at McBain, MI

Under EPA’s supervision, elaborate emission test s were conducted on the Viking Energy, McBain, MI wood-fired stoker (with ESP) when burning chipped cr eosote-treated railties and several other treated wood wastes (EPA 1994). The test results for chipped creosote-treated railtie burning are summarized in Table 1. The boiler typically fired about 600 tons per day of virgin and recycled untreated wood in chip form. However, a baseline run with 100% untreated wood was not conducted during this study. Table 1 provides a comparison of the mean emissions when firing railties in the McBain boiler against ranges and/or means of emissions from firing 100% untreated wood residues in stoker units with ESPs, the latter being obtained from Boiler MACT and other recent test data that were summarized in NCASI Technical Bulletin No. 1013 (NCASI 2013). Sampling was con ducted for dioxins/furans (PCDD/Fs), several polyaromatic hydrocarbons (PAHs), trace metals, par ticulate matter (PM), HCl, formaldehyde, acrolein,

NO
x 

### , CO, SO 2 

### and VOCs.

A comparison of emissions resulting from burning 29.0 wt% creosote-treated wood (remainder being virgin and recycled untreated wood) in the Viking boiler with emissions from burning 100% untreated wood residues in stoker units (NCASI 2013) indicates that there is no discernible difference due to the
addition of railties to the untreated wood fuel. In f act, most emissions when burning creosote-treated wood are lower than the averages for 100% wood burning, including those of PAHs. Emissions of 2- methylnaphthalene from 29% creosote substituted wood burning were comparabale to the maximum values from untreated wood burning. However, the emissi ons of all other PAHs were closer to the lower end of the range. (NCASI 2005, 2013). This obser vation is not surprising given that PAH emissions
reduce when the robustness of combustion increases. The use of dry fuels with high heat value, like railties, generally improves combustion, thereby redu cing products of incomplete combustion like PAHs.

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2 Table 1. Trial Burns of Creosote-Treated Ra ilties in a Wood-Fired Boiler (EPA 1994)

Baseline CreosoteUntreated Wood 1 Treated 2, 3
Range Mean Co-firing Rate (% wt) 29.00 Load (lb/hr steam) 157,990 Dioxins (ng/m 3 ) 4 0.0017 to 0.375 0.164 PAHs (ng/m 3 )

Naphthalene 14 to 599,295 917.2 2-Methylnaphthalene 50 to 3,679 3,704 Acenaphthene 3 to 10,214 67.7 2-Chloronaphthalene 2.95 5 1.29 Acenaphthylene 11 to 38,517 38.1 Fluorene 4 to 32,857 145.4 Phenanthrene 11 to 43,071 499.1 Anthracene 4 to 32,857 30.4 Fluoranthene 7 to 13,044 87.0 Pyrene 7 to 32,857 49.9 Benzo(a)anthracene 1 to 445 2.5 Chrysene 3 to 619 2.56 Perylene 1 to 110 0.53 Trace Metals ( μ g/m 3 )

Arsenic 0.2 to 11.5 ND
Cadmium 0.09 to 1.66 ND
Chromium 0.12 to 11.6 ND Copper 3.13 to 13.5 5 13.8
Lead 0.44 to 35.6 ND Mercury 0.1 to 8.2 0.68
Nickel 0.24 to 18.2 ND
Zinc 20.6 to 872 5 87.8

Mean Mean Part. Matter (gr/dscf) 0.029 5 0.0087 HCl (mg/m 3 ) 5.37 ND Formaldehyde ( μ g/m 3 ) 1,255 76.0 Acrolein ( μ g/m 3 ) 320 ND

NO
x (ppm) 136 168

NO
x (lb/10 6 Btu) 0.21 0.23 CO (ppm) 765 120

SO 2 (lb/10 6 Btu) 0.011 0.027 VOC (ppm) 11.0 0.8

1 NCASI TB 1013 - factors available for 100% wood combustion in a st oker unit with ESP in units of lb/MMBtu were converted assuming F factor of 9,280 dscf @ 0% O 2 /10 6 Btu, 6% O 2 in stack and 8,400 Btu/lb dry wood; 2 concentrations for the McBain unit are expressed at stack O 2 which varied from 4 to 5%; 3 29% creosote-treated wood, remain der untreated and recycled wood;

4 mass (not TEQ) basis; 5 same as AP-42 Chapter 1.6

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3 B. Pilot-Scale Tesing of Creoste-Treated Wood With Coal

Freeman et al. (2002) conducted a pilot-scale study co -firing creosote-treated woods with coal to provide data for pre-permitting evaluations by utilities inter ested in co-firing bioma ss as a means of increasing renewable energy use. The results of these tests ar e summarized in Table 2. Substances tested for included PCDD/Fs, PAHs, several heavy metals, formal dehyde and other VOCs, HCl and particulates. These emissions represented “uncontrolled” emissions from the combustor “upstream of flue gas cleanup
devices.”

From the results presented in Table 2, the author s concluded that creosote-treated wood could be successfully co-fired in coal-fired utility boilers at 10% heat input without increases in most air toxic
emissions relative to the baseline with 100% eastern bitu minous coal firing. Compared to the baseline test results with 100% coal, the results with 10% creosote -treated wood (rest coal) consistently showed lower levels (often non-detectable) of dioxins/furans, P AHs, heavy metals, formaldehyde and other aldehydes, ketones and total hydrocarbons. The slightly higher levels of HCl emissions measured (61 vs 44 ppm) appears to be an anomaly since creo sote-treated wood has much lower ch lorine levels than most coals, being similar to those in virgin wood fuels (<0.07%).

Table 2. Emissions from Creosote Treated Wood Cofiring with Coal (Freeman et al. 2002)

Baseline
UF Coal 10% Creosote
Wood 1

Flue Gas ( dr y basis @ 3% O 2 ) SO 2 (pp m ) 1209 1120 N O
x (pp m ) 574 474 CO (pp m ) 92 75 HCl (pp m ) 44 61 Total H y drocarbons (pp m ) 2 2.0 1.6 Particulate (g /dN m 3 ) 8.9 5.5 VOCs ( dr y basis @ 3% O 2 )) Acetaldeh y de (pp b ) <1.4 <2.7 Aceto p henone (pp b ) <1.5 <1.2 Formaldeh y de (pp b ) ~2.3 2.4 Iso p horone (pp b ) <0.21 <0.18 Pro p ionaldeh y de (pp b ) <0.53 <0.46 PCDD/Fs ( n g /dN m 3 @ 3% O 2 ) Total PCDD/Fs 0.0463 0.0039 WHO TE Q s 0.0014 N D Total PAHs ( μ g /dN m 3 @ 3% O 2 ) 0.134 0.079 Heav y Metals (g /MJ ) Antimon y 7.36E-06 6.38E-06 Arsenic 4.21E-04 3.42E-04 Cadmiu m 5.84E-06 4.65E-06 Cobal t 2.38E-04 1.14E-04 Lea d 1.34E-04 9.96E-05 Man g anese 1.17E-03 6.68E-04 Mercur y 9.18E-06 9.40E-06 N ickel 2.01E-04 1.23E-04 Seleniu m 6.61E-05 3.96E-05

1 10% creosote treated wood, remainder coal; 2 as propane; ND – non-detect

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4 C. Chipped Railroad Tie Burning in a Pulp Mill Bark Boiler

In 2003, a southwestern pulp mill conducted extensive tests on its bark boiler by replacing the entire wood fuel with chipped railroad ties. The boiler was tested with 100% railti es for several criteria pollutants, particulate matter (PM), six trace metals (As, Cd, Cr, Pb, Cu and Zn), several semi-volatile organics (SVOCs), PCDD/Fs, and several speciated VOCs. CO, THCs, NO
x 

### and SO 2 

### were also measured during a baseline test with 100% bark/wood residues (N CASI File Information). These emissions data are compared in Table 3. For comparison purposes, the emission data from this study are compared against mean and range of emissions when firing 100% untreated wood residues in stoker units with ESPs (NCASI 2013). Once again, the emissions data with 1 00% railtie combustion in a stoker unit are routinely
lower than for 100% untreated wood combustion.

Table 3. Criteria and Non-Criteria Pollutants From Burning Railties in a Bark Boiler

100% Bark 100% Untreated Wood Railties Range or Mean 5

RTDF feed rate tons/h r 0 24.7 Steam KPPH 520 430 CO ppm@8%O 2 316 117 663 THC as C ppm@8%O 2 56 7 9.5 NO
x lb/MMBtu 0.20 0.21 0.21 SO 2 lb/MMBtu 0.00 0.01 0.011 PM gr/dscf@7%O 2 0.026 -- PCDD/Fs ng/dscm@7%O 2 5.01E-04 1 7.21E-03 5

As μ g/dscm@7%O 2 11.0 0.2 to 11.5 Cd μ g/dscm@7%O 2 4.8 0.09 to 1.66 Cr μ g/dscm@7%O 2 5.8 0.12 to 11.6 Cu μ g/dscm@7%O 2 45.2 3.13 to 13.5 6
Pb μ g/dscm@7%O 2 107.8 0.44 to 35.6
Zn μ g/dscm@7%O 2 764.7 20.6 to 872 6
SVOCs Naphthalene μ g/dscm@7%O 2 2.98 11.4 Bis(2-ethylhexyl)phthalate μ g/dscm@7%O 2 1.90 0.1 Benzyl alcohol μ g/dscm@7%O 2 4.10 No data Benzoic acid μ g/dscm@7%O 2 152.4 49.5 All Others 3 μ g/dscm@7%O 2 ND -- VOCs Methyl chloride μ g/dscm@7%O 2 9.34 628.0 Chloroform μ g/dscm@7%O 2 19.97 23.1
Benzene μ g/dscm@7%O 2 38.84 1125.0 Toluene μ g/dscm@7%O 2 4.96 24.2 Xylenes (total) μ g/dscm@7%O 2 4.04 6.0 Ethyl Benzene μ g/dscm@7%O 2 1.35 453.5 Styrene μ g/dscm@7%O 2 1.4 547.6 All Others 4 μ g/dscm@7%O 2 ND --

1 I-TEF/89 units; 2 WHO-TEF 2005 units; 3 over a hundred other compounds including phenol, 1,2-dichlorobenzene, 1,2,4- trichlorobenzene, 2,4,6-trichlorophenol, hexachlo robenzene, pentachlorophe nol, and several PAHs; 4 over 50 other VOCs including chloromethane, vinyl chloride, carbon tetrachloride, 1,1,2-trichloroethane, trichloroethene, tetrachloroethylene;

5 NCASI TB 1013 - factors available for 100% wood combustion in a stoker unit with ESP in units of lb/MMBtu were converted assuming F factor of 9,280 dscf @ 0% O 2 /10 6 Btu and 8,400 Btu/lb dry wood; 6 same as AP-42 Chapter 1.6

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5 The emissions of Cd, Cu, and Pb from 100% railtie burning were higher than the maximum values from untreated wood burning. However, it should be noted that emissions of PM and trace metals are generally a function of the PM control device efficiency. Un less the fuel combusted is believed to contain a particular trace metal in unusually large concentr ations (not the case with railties), a comparison of resulting emissions should made with care as it ignor es any variability in effectiveness of the control
device. It is also worthwhile to note that the 100% railtie substitution scenario is a highly atypical worstcase boundary condition – railtie substituti on levels in industrial boilers typically range between 5 and
30%.

D. Emissions from Combustion of Railties in Several EGUs – A 1995 Study

Holtzman and Atkins (1995) reported on air emissions data from the burning of railties in several large independent wood-fired power plants (EGUs) a nd one coal-fired plant (EGU). The treated wood emissions data from each of the test programs are also compared to emissions from combusting clean
wood or coal in these boilers. The wood-fired EGUs ra nged in size from 20 to 50 MW, were of a spreader stoker design, and had either a baghouse or ESP for PM control. Table 4 provides an emissions comparison between burning clean wood with and without various levels of railties at 3 different sites, 25 to 50% railties at Site A, 20% railtie at Site B, and 10% railtie at Site C. The emissions measured included criteria pollutants PM, NO
x 

### , CO, SO 2 

### and THCs, trace metals As, Be, Cd , Cr, Cu, Pb, Mn, Hg, Ni, Se and Zn, acid gases HCl and H 2 

### SO 4 

### , PCDD/Fs and several organics. The comparison clearly shows that burning railties at various levels in these stokers al ong with clean wood had no discernible bearing on the air emissions of most criteria and non-criteria pollutants (SO 2 

### emissions continued to be negligible but were marginally higher; Among trace metals, onl y arsenic emissions were somewhat higher).

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6 Table 4. Emissions Comparison of EGUs Burning Clean Wood With and Without Railroad Ties

Site A Site B Site C

Clean 25-50% Clean 20% Clean Wood 10%

All emissions are in units of lb/MMBtu
Particulate Control MC ESP MC ESP ESP ESP MC ESP MC ESP Emissions Control Heat Input (MMBtu/hr) 339 339 711 681 286 295 Particulate Matter 1.68E-03 1.31E-03 2.63E-02 2.80E-02 PM - Back Half 9.84E-03 3.94E-03 3.55E-03 6.27E-03 Nitrogen Oxides 1.44E-01 1.22E-01 2.08E-01 2.07E-01 1.96E-01 2.00E-01 Carbon Monoxide 2.65E-01 5.21E-01 4.30E-01 4.04E-01 2.68E-01 1.39E-01 Sulfur Dioxide 2.54E-03 4.07E-02 7.33E-03 2.08E-03 4.30E-02 Hydrocarbons 3.62E-03 5.72E-03 5.07E-03 3.62E-03 Arsenic 1.44E-07 7.97E-07 1.64E-05 3.07E-05 Beryllium <2.87E-07 <1.91E-06 Cadmium <2.87E-07 <1.53E-06 1.20E-06 1.29E-06 Chromium <6.37E-07 <2.87E-06 3.36E-05 4.09E-05 Hexavalent Chromium * Not Tested 1.62E-06 Copper 1.59E-05 3.51E-06 Lead 1.59E-05 1.12E-06 9.64E-06 2.20E-05 Manganese 3.01E-05 1.43E-06 8.59E-05 1.18E-04 Mercury 3.19E-07 4.30E-07 Nickel <2.87E-06 <1.34E-05 3.97E-06 1.98E-06 Selenium <2.87E-06 <3.62E-06 5.53E-07 4.36E-07 Zinc 1.12E-05 4.30E-06 Hydrogen Chloride 5.60E-05 5.60E-05 Sulfuric Acid 1.63E-02 2.25E-02 2,3,7,8-TCDD 7.80E-11 3.51E-11 1.66E-12 3.66E-12 Acetaldehyde 7.57E-05 2.54E-05 5.11E-04 1.54E-04 Acrolein 1.85E-04 5.74E-06
Benzene 2.45E-04 1.55E-04 2.18E-04 2.40E-04 Benzo(a)anthracene <5.00E-09 <6.00E-09 2.73E-07 2.82E-07 Benzo(a)pyrene <5.00E-09 <6.00E-09 2.98E-07 3.21E-07 Chlorophenols 1.94E-05 2.11E-05 Clorobenzenes 1.19E-05 1.28E-05 Chloroform <3.64E-05 <2.14E-05 Chrysene/Triphenylene <5.00E-09 <6.00E-09 2.98E-07 3.08E-07 Formaldehyde 2.800E-04 1.32E-04 2.36E-03 7.20E-04 Naphthalene 7.05E-06 3.28E-06 Phenol 2.27E-05 4.58E-06 Toluene <2.97E-05 <4.49E-05 2.29E-05 3.07E-05 Dioxins <6.48E-12 <1.83E-11
Furans <2.05E-11 <1.99E-10 *Blank indicates no data

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7 Table 5 provides an emissions comparison between burning coal with and without railties at low and high loads at a coal-fired EGU. The emissions meas ured included criteria pollutants PM, NOx, CO, and

SO 2 

### , trace metals As, Be, Cd, total Cr, Cr +6 

### , Cu, Pb, Hg, Ni, and Zn, acid gas HCl, PCDD/Fs, PCBs, PAHs, total chlorophenols, and formaldehyde. Once agai n, most emissions were comparable or lower as a result of co-firing railties in this coal-fired unit (form aldehyde and arsenic emissi ons were a bit higher).

Table 5. Baseline and Railtie ombustion Emission Test Summary, Hickling Station, East Corning, NY

Low Load (lb/hr) High Load (lb/hr)

Test Parameters Baseline c Creosote Treated d Baseline c Creosote Treated d

Total particulate 35.63 2.06 133.43 5.37 Carbon monoxide (CO) 13.9 12.9 9.9 24.0 Nitrogen oxides (NO
x ) 66.6 94.3 206.3 156.3 Sulfur dioxide (SO 2 ) 686.5 439.6 1436.6 724.5 Arsenic (As) a a 1.72E-03 6.24E-02 Beryllium (Be) a a <2.54E-04 <7.04E-04 Cadmium (Cd) a a 4.52E-04 1.10E-04 Total Chromium (Cr) a a 7.74E-03 5.90E-03 Hexavalent Chromium (Cr +6 ) a a <4.08E-03 5.90E-04 e Copper (Cu) a a 8.56E-03 8.82E-03 Lead (Pb) a a 3.24E-03 1.18E-03 Mercury (Hg) a a 2.88E-02 1.33E-02 Nickel (Ni) a a 2.58E-03 b 3.39E-04 Zinc (Zn) a a 1.86E-02 3.31E-03 Formaldehyde (HCHO) a a 0.012 0.028 Hydrogen chloride (HC1) a a 48.7 13.44 2,3,7,8 TCDD Tox. Equiv. a a 4.81E-09 1.696E-08

Total PAHs 4.56E-04 <1.26E-02 6.44E-04 b <2.12E-02
Total PCBs a a <2.44E-05 <1.23E-03 Total chlorophenols a a 9.17E-05 <2.42E-02

Source: Unit 1 Creosote Treated Wood/Co al CO-Fired Feasibility Project a Indicates no source testing was conducted for these test parameters. b Estimated emission rate. When 1 or 2 of the 3 sample runs demonstrated emissions below the detection limit, one-half of the detection limit for each of the ND test runs was used to calculate the average emission rate. c Baseline emissions (coal only) testing performed by Galson Corporation in June 1992. d Creosote treated wood testing performed by TRC Environmental Corporation in November 1993. e Chromium +6 values were calculated assuming 10% of total chromium was chromium +6.

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8 Summary

The data presented in this paper indicate that the air emission impact of burning creosote-treated railroad ties (railties) along with either virgin, untreated biomass or coal in stokers is not any different than that from the burning of untreated biomass or coal in th ese units. The organic constituents in the creosote appear to oxidize completely during combustion on the gr ate and above the grate in such boilers such that the emission of VOCs, SVOCs, PCDD/Fs and other pr oducts of incomplete combustion would be similar in magnitude as the baseline fuel. Further, the metals content of the railties are known to be similar to those in virgin wood fuels and thus the trace metals air emission impact of co-firing these fuels in a given
boiler would be no different than those measured wh en firing predominantly untreated wood fuel in the
same boiler.

References

AF&PA (American Forest & Paper Association) 2013. “Comparison of Contaminant Concentrations in Cross Tie-Derived Fuel with Traditional Fuels”, s ubmitted to EPA on March 28, 2013 as Attachment A

Freeman, M.C., O’Dowd, W.J., Brown, T.D., Harg is, R.A. Jr., James, R.A., Plasynski1, S.I., Walbert, G.F., Lowe, A.F., and Battista, J.J. Jr. 2002. Pilot-scale air toxics R&D assessment of creosote-treated and PCP-treated wood cofiring fo r pulverized coal utility boiler applications. http://www.netl.doe.gov/osta/techpapers/ 2002-710.pdf (accessed September 2005).

Holtzman, M. I. and Atkins, R. S. 1995. Emissions from Combustion of Treated Wood Fuel and Tires in
Industrial Boilers. Presented to the Air and Waste Ma nagement Association Annual Meeting, June 18-23,

1995.

National Council for Air and Stream Improvement, Inc. (NCASI). 2005. Alternative fuels used in the forest products industry: Their co mposition and impact on emissions. Technical Bulletin No. 906. Research Triangle Park, N.C.: National Counc il for Air and Stream Improvement, Inc.

National Council for Air and Stream Improvement, Inc. (NCASI). 2013. A Comprehensive Compilation and Review of Wood-Fired Boiler Emissions. Technical Bulletin No. 1013. Research Triangle Park, N.C.: National Council for Air and Stream Improvement, Inc.

Smith, S. T. 2002. Environmental Issues Related to the Use of Creosote Wood Preservative. AcuAeTer, Inc. Helena, MT (May 28, 2002) ( http://home.earthlink.net/~stephentsmith/site buildercontent/sitebuilderfiles/Env-Issues.pdf )