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Energy & Fuels 2006, 20, 2660-2665
Multi-utilization of Chicken Litter as Biomass Source. Part I. Combustion Nathan Whitely,† Riko Ozao,†,‡ Ramon Artiaga,†,§ Yan Cao,† and Wei-Ping Pan*,† Institute for Combustion Science and EnVironmental Technology, Western Kentucky UniVersity, Bowling Green, Kentucky, 42101 ReceiVed September 24, 2005. ReVised Manuscript ReceiVed May 28, 2006
Chicken litter disposal is a major economic and pollution concern. Poor waste management practices lead to air and water pollution. To produce a useful renewable resource for energy, optimal conditions for combustion were studied. Three samples differing in particle size were obtained from the chicken litter by drying, milling, and sieving, each at a recovery of (A) larger than 150 µm in size, 87.5%; (B) between 150 and 45 µm in size, 6.3%; and (C) below 45 µm in size, 6.3%. Sample A showed the highest calorific value (5 300 BTU lb-1) 12 320 kJ kg-1) and lowest ash content (ca. 25%), whereas sample C showed the lowest calorific value (2 900 BTU lb-1 ) 6 740 kJ kg-1) and highest ash content (ca. 54%). Evolved gas analysis (EGA) techniques, including thermogravimetric-mass spectrometry (TG-MS) and TG-Fourier transform infrared (TG-FTIR) were used to identify off-gases. Kinetic analyses using thermogravimetric analysis (TGA) were also performed to find that the combustion process proceeds in four stages (where E represents the activation energy): (I) release of absorbed water and ammonia stemming from ammonium salts (room temp (RT) ) 150 °C), E ) 61.72 kJ mol-1; (II) devolatilization (150-350 °C), E ) 71.43 kJ mol-1; (III) char precombustion (350-500 °C), E ) 148.5 kJ mol-1; and (IV) rapid char combustion (500-650 °C), E ) 157.6 kJ mol-1. In stage III, the combustion is retarded because N concentration is high.
Introduction Commercial chicken production is one of the largest agricultural industries in the United States. Over 16 million tons of chicken were produced within the United States during 2003, with nearly 85% of that chicken being consumed within the continental United States.1 In addition, chicken surpassed beef as the most consumed meat in the United States in 2003, with the average American consuming over 43 kg of chicken annuallysover one-third of total meat consumption.2 As individuals begin to become more health-conscious in their choice of diet, the amount of chicken consumption will increase by an estimated 5% per year. In commercial chicken production, flocks of ∼25 000 chickens are raised in large houses spanning up to 12 000 square feet of area.3 The chickens are raised and harvested in 5-7 weeks, and to promote hygiene within the flock, chicken houses are lined with bedding material, primarily composed of wood chips in thicknesses of up to 15 cm, which acts as an absorbent to remove excess moisture from the urine and feces of the flock. The wood chip and fecal matter mixture is termed litter and must be removed from the house floor * Corresponding author. Tel.: +1(270)745-2272. Fax: +1(270)7452221. E-mail:
[email protected]. † Western Kentucky University. ‡ Present address: SONY Institute of Higher Education, Atsugi, Kanagawa 243-8501, Japan. E-mail:
[email protected]. § Present address: Department Ingenieria Industrial II, Universidade da Coruna. (1) Poultry yearbook compiled by the United States Department of Agriculture Economic Research Service. http://www.ers.usda.gov/Data/sdp/ view.asp?f)livestock/89007/&arc)C. (2) Food availability spreadsheets compiled by the United States Department of Agriculture Economic Research Service. http://www.ers.usda.gov/ Data/foodconsumption/mtpoulsu. (3) North, Mack O. Commercial Chicken Production Manual; The Avi Publishing Company, Inc.: Westport, CT, 1984.
periodically to promote good health and hygiene among the flocks. Classically, chicken litter is spread onto agricultural land or composted in massive mounds as a means of disposal. Composted chicken litter is a significant threat to local and global air quality due to the release of methane and ammonia. At the local level, poorly managed chicken litter stockpiles can cause large effluents of malodorous compoundssprimarily ammoniasthat reduce air quality.4 Chicken litter composting also can cause large methane releases, from the bacterial decomposition of various compounds in the litter material.5-7 Spreading chicken litter as a fertilizer that is high in N and phosphorus (P) content provides a suitable, economic, and convenient supplement to inorganic fertilizers. However, overusage and neglect in proper fertilization and waste management practices have led to major water pollution concerns regarding chicken litter. Nitrogen is the limiting reagent of the chicken litter mixture when applied to cropland; thus, plant producers spread the chicken litter in quantities to meet the crops N requirements. Furthermore, this practice results in an excess of Pspresent as phosphatessapplication to the land. The excess P and N is quickly transported by runoff water into the neighboring rivers, lakes, and streams.8,9 Accumulation of P, N, and other plant nutrients into bodies of water is a natural (4) Siefert, R. L.; Scudlark, J. R.; Potter, A. G.; Simonsen, K. A.; Savidge, K. B. Characterization of Atmospheric Ammonia Emissions from a Commercial Chicken House on the Delmarva Peninsula. EnViron. Sci. Technol. 2004, 38, 2769-2778. (5) Brodie, H. L.; Carr, L. E.; Cardon, P. Poultry Litter Composting Comparisons. Biocycle 2000, 41, 36-40. (6) Georgakakis, D.; Krintas, Th. Optimal use of the Hosoya system in composting poultry manure. Bioresour. Technol. 2000, 72, 227-233. (7) Rao, P. P.; Seenayya, G. World J. Microbiol. Biotechnol. 1994, 10, 211-214. (8) Sharpley, A. N. Identifying sites vulnerable to phosphorus loss in agricultural runoff. J. EnViron. Qual. 1995, 24, 947-951.
10.1021/ef0503109 CCC: $33.50 © 2006 American Chemical Society Published on Web 07/12/2006
Combustion of Chicken Waste
aging process known as eutrophication; however, anthropogenic eutrophication is a serious problem resulting in accumulation of large concentrations of specific plant nutrients in a relatively short amount of time. When anthropogenic eutrophication occurs, algae present within the water reproduce excessively under aerobic metabolism, effectively using large quantities of the water’s dissolved oxygen. Accounts of destruction to the aquatic ecology due to anthropogenic eutrophication within the United States have been reported.10 Increasing occurrences of these outbreaks will compel the Environmental Protection Agency (EPA) to regulate the amount of chicken waste used per acre on agricultural land based on the local soil characteristics, weather conditions, and proximity to water systems.11 Much research has shown that chicken litter having calorific values equivalent to low-rank coals (on the order of 5 000 BTU lb-1 ) 11 600 J g-1)12,13 can be combusted to generate energy.14 Pilot studies have been executed to develop small reactors that will provide electricity to power chicken houses through burning chicken waste.15-17 Other research has shown that many useful chemicals and materials can stem from the thermal degradation of chicken waste.18 The possibilities of using chicken litter as a resource for energy are studied. Animal waste such as poultry litter is defined as “biomass”. Numerous studies have been made so far on the combustion of biomass and kinetic modeling. For instance, there is an overview by Nussbaumer;19 Gani et al.20 provide fundamentals of combusting low-rank coal mixed with biomass. Furthermore, thermogravimetric analysis (TGA) has been used in studying biomass char combustion reactivities for FBC,21 cocombustion of coal-sewage sludge mixture,22 and kinetic (9) Sharpley, A. N.; McDowell, R. W.; Kleinman, P. J. A. Phosphorus loss from land to water: Integrating agricultural and environmental management. Plant Soil 2001, 237, 287-307. (10) Geiselman, B. Okla. Farmers Polluted Water, Lawsuit Alleges. Waste News, Dec 24, 2001, p 5; Business Source Premier, Aug 15, 2004. (11) Ritchie, James D. Water, EPA, and You, July 2002; Today’s Farmer, Aug 15, 2004, http://www.mfaincorporated.com/todaysfarmer/index.asp. (12) Plasynski, S. I.; Goldberg, P. M.; Chen, Z.-Y. Using Animal Waste Based Biomass for Power and Heat Production while Reducing Environmental Risks. Presented at 19th Annual International Pittsburgh Coal Conference, Pittsburgh, PA, Sept 23-27, 2002. (13) Miller, B. G.; Miller, S. F.; Scaroni, A. W. Utilizing Agricultural By-Products in Industrial Boilers: Penn State’s Experience and Coal’s Role in Providing Security for our Nation’s Food Supply. Presented at 19th Annual International Pittsburgh Coal Conference, Pittsburgh, PA, Sept 2327, 2002. (14) Davalos, J. Z.; Roux, M. V.; Jimenez, P. Evaluation of poultry litter as a feasible fuel. Thermochim. Acta 2000, 394, 261-266. (15) Stranahan, S. Q. Farmers Face a Big Stinking Mess. Fortune, Apr 1, 2002, pp 32-34; Academic Search Premier, Aug 15, 2004. (16) Strutt, J. Fowl Source of Supply for New Power Scheme. The Australian, Dec 13, 2002, p 4; Newspaper Source, Aug 15, 2004. (17) McNeill, R. Study of Poultry Litter as Power Source of Interest to Oklahoma Farmers. The Daily Oklahoman, Apr 17, 2004; Newspaper Source, Aug 15, 2004. (18) Shinogi, Y.; Kanri, Y. Pyrolysis of plant, animal and human waste: physical and chemical characterization of the pyrolytic products. Bioresour. Technol. 2003, 90, 241-247. (19) Nussbaumer, T. Combustion and Co-combustion of Biomass: Fundamentals, Technologies, and Primary Measures for Emission Reduction. Energy Fuels 2003, 17, 1510-1521. (20) Gani, A.; Morishita, K.; Nishikawa, K.; Naruse, I. Characteristics of Co-Combustion of Low-Rank Coal with Biomass. Energy Fuels 2005, 19, 1652-1659. (21) Adanez, J.; deDiego, L. F.; Garcia-Labiano, F.; Abad A.; Ananades, J. C. Determination of Biomass Char Combustion Reactivities for FBC Applications by a Combined Method. Ind. Eng. Chem. Res. 2001, 40, 43174323. (22) Folgueras, M. B.; Diaz, R. M.; Xiberta, J.; Prieto, I. Thermogravimetric analysis of the co-combustion of coal and sewage sludge. Fuel 2003, 82, 2051-2055.
Energy & Fuels, Vol. 20, No. 6, 2006 2661
Figure 1. Sample preparation procedure. Table 1. Summary of Sample Identifications sample ID
particle size distribution
A B C mill
particles over 140 mesh (>150 µm) particles between 140 and 325 mesh (45-150 µm) particles below 325 mesh (500 °C, change in percent conversion with time was estimated at various temperatures to obtain the optimum condition of combustion. The results are given in Figure 3. Thermogravimetry-Mass Spectrometry (TG-MS). Approximately 10 mg samples were analyzed by TA Instruments 2960 simultaneous differential scanning calorimeter (DSC)thermogravimetric analyzer (TGA) (SDT) interfaced to a Fisons VG Thermolab mass spectrometer (MS) by means of a heated capillary transfer line. The capillary transfer line was heated to 120 °C, and the inlet port on the mass spectrometer was heated to 150 °C. The Fisons unit is based on quadrupole design operating at a pressure of ∼1 × 10-6 Torr. The sample gas from the interface was ionized at 70 eV, and a mass range of 1-150 amu was scanned. Breathing-quality air at a flow rate of 50 mL min-1 served as the carrier gases to the MS. Purges (30 min) preceded the heating programs, in which the samples were heated from room temperature to 1000 °C at a rate of 20 °C min-1. The MS continually samples the outgas, generating a temperature (or time) resolved MS spectrum for each of the individual masses. Thermogravimetry-Fourier Transform Infrared Spectroscopy (TG-FTIR). The samples were analyzed by a DuPont 951 TGA interfaced to a Perkin-Elmer 1600 series FTIR with a permanent 1 in. silicon transfer line. Approximately 25 mg litter samples were heated from room temperature to 1000 °C at heating rate of 20 °C min-1 in TGA. Breathing-quality air at a flow rate of 100 mL min-1 provided the combustion atmosphere. The purge gas carried the decomposition products from the TGA through an 80 mL sample cell with KBr crystal windows. The cell was placed in the FTIR scanning path for detection of the decomposition products. Wrapping the IR cell in heat tape held at 150 °C and the increased flow rate compared
If the function f(R) is constant for the entire reaction, the left-hand side plotted against 1/T yields straight lines for
(24) Cao, R.; Naya, S.; Artiaga, R.; Garcıa, A.; Varela, A. Logistic approach to polymer degradation in dynamic TGA. Polym. Degrad. Stab. 2004, 85, 667-674.
dR ) F(T)f(R) dt
(1)
The temperature dependence of the reaction rate function F(T) is generally described by the well-known Arrhenius equation
F(T) ) Z exp
(-E RT )
(2)
where R is the universal gas constant, E is the activation energy, and Z is the preexponential factor. In TGA, the runs are made under constant heating rate dT/dt ) β. Thus, eqs 1 and 2 can be rewritten and combined to give
-E dR Z ) exp f(R) dt β RT
( )
(3)
TGA runs differing in heating rate, i.e., in different β, are obtained to determine the kinetic parameters Z and E from the linearized transformation of eq 3:
ln
Z -E dR/dt ) ln + β RT f(R)
()
Combustion of Chicken Waste
Energy & Fuels, Vol. 20, No. 6, 2006 2663
Table 2. Summary of As-Received Proximate Analysis, CHN, S, and Gross Calorific Value of Litter Samples sample
moisture (wt %)
ash (wt %)
volatile matter (wt %)
C (wt %)
N (wt %)
H (wt %)
S (wt %)
BTU (lb-1)
mill A B C
10.59 10.43 11.43 9.44
26.58 25.27 34.62 53.85
54.72 54.43 49.25 34.83
29.09 30.66 26.13 16.75
3.44 3.35 4.74 3.68
5.11 5.07 4.69 3.35
0.80 0.76 1.28 1.24
5166 5299 4281 2915
Table 3. Summary of Major and Minor Element Data for Litter Samples wt % sample
SiO2
Al2O3
Fe2O3
CaO
MgO
Na2O
K2O
P2O5
TiO2
SO3
mill A B C
9.83 7.23 11.45 31.29
1.36 1.02 1.82 3.64
0.58 0.44 0.74 1.26
3.72 4.29 4.32 3.49
1.26 1.21 1.88 1.99
1.61 1.73 1.59 1.22
3.34 3.44 3.63 3.41
4.23 4.54 5.71 4.75
0.06 0.03 0.09 0.33
1.91 1.89 2.54 2.51
to the TG-MS experiments are required to limit condensation of high-boiling evolved products. The FTIR scans the frequency range of 4500-450 cm-1 at ∼25 s intervals providing temperature (or time) resolved FTIR spectra. To monitor the evolution of single gas moieties, the TG-FTIR data could be treated such that single frequencies of the FTIR spectra were monitored, generating plots of absorbance at a single frequency as a function of time.
Table 4. Kinetic Parameters for the Temperature Regions I-IV stages
preexponential factor log Z (min-1)
activation energy E (kJ mol-1)
I (RT ) 150 °C) II (150-350 °C) III (350-500 °C) IV (500-650 °C)
8.423 6.199 10.43 11.00
61.72 71.43 148.5 157.6
Sample Description. The mill sample that contains all particle sizes is approximately composed of 87.5% (volume percent) sample A, 6.25% sample B, and 6.25% sample C. Visual inspection of the litter samples indicates that sample A is primarily composed of wood-chip bedding material and sample C is composed of soil material. Sample B appears to be an intermediate between the two extremes. The as-received proximate analysis, CHN, S, and gross calorific value of the four chicken litter samples are shown in Table 2. The ash content of the litter samples is shown to increase with decreasing particle size; however, the calorific value and the volatile matter show an opposite trend, having the highest values for the larger particle sizes. Collectively, the ash, volatile matter, and the calorific value are indicative that the composition of the chicken litter resembles low-rank coal.25 By comparing the calorific and ash contents of sample A and the mill sample, one can deduce that removing particles under 140 meshssamples B and Csfrom the mill sample effectively acts to increase the productivity of the litter by increased energy content and a smaller ash content. The calorific value of the mill and sample A is similar to that of lignite.25 The elemental analysis shown in Table 3 as wt % in the litter supports the conclusions made from the proximate analysis. Sample C is comprised of 31.3% SiO2 by weight. The astounding concentrations of inorganic compounds such as SiO2, Al2O3, Fe2O3, and TiO2 suggest that sample C is primarily composed of soil matter. TGA. Figure 2 shows the TG curves of the samples obtained in flowing air. By curve separation according to the method of Cao et al.,24 it has been presumed that the mass loss occurs in four steps in the following temperature ranges: (I) room temperature to 150 °C; (II) between ca. 150 and 350 °C; (III) between ca. 350 and 500 °C; and (IV) between ca. 500 and 650 °C. The small mass loss found at temperatures >600 °C is attributed to mineral decomposition. The mass loss in temperature region I is approximately the same (∼10 wt %) for all of the samples. It is likely that desorption of moisture and volatile gases occurs in this region
for all of the samples, and hence, the rate equation should be the same for all the samples. The final mass % obtained on heating to 1000 °C is in fair agreement with the ash content above; the final mass % obtained by TG is ∼2% lower than those obtained by combustion testing, showing mass loss still occurring in the temperature range of 750-1000 °C on all samples. From the similarities in composition and the TG curves, it has been found that sample A represents the original milled sample. Thus, sample A is used for further study as a model sample for the original milled sample. Sample C contains much silica and alumina, and it can be considered as a starting milled sample diluted by thermally stable oxide minerals. In temperature region II, it is hypothesized that rapid devolatilization and subsequent oxidation, overlapping at some places, take place. That is, pyrolysis and oxidation take place conjointly. In particular, the maximum rate of reaction, i.e., the peak temperature for the derivative weight curve (DTG), is lower by 30 °C than the peak observed by DSC. That is, mass loss occurs first, with oxidation occurring shortly thereafter. Thus, in this temperature region, the presumption of independent reactions may not be applied; hence, the kinetic values are provided with lower reliability. In temperature region III, a plateau is observed in DTG, that is, the reaction rate is constant in this region. Diffusion and starting combustion of char, may be the rate-determining step. This region may be regarded as a precombustion or an introductory region26 and may be combined with region IV. In temperature region IV, mass loss ascribed to very rapid char combustion takes place. Table 4 shows the preexponential factors and activation energies obtained by kinetic analysis of temperature regions I-IV. The results are in fair agreement with the case of cocombustion of sewage sludge,20 which also contains ∼40 wt % ash. A typical coal has an activation energy of ∼60 kJ mol-1 in this temperature range, and the coal transformations involved in this stage are presumed to be devolatilization, ignition of volatiles, and reaction at the surface.22 Thus, because of high N present in the sample, ignition of volatiles and reaction at the surface are retarded, and this accounts for the high activation
(25) Nomura, M.; Suzuka, T. Modern Industrial Chemistry; Kodansha Scientific: Tokyo, Japan, 2004; pp 71-72.
(26) Chen, Y.; Mori, S.; Pan, W.-P. Estimating the Combustibility of Various Coals by TG-DTA. Energy Fuels 1995, 9, 71-74.
Results and Discussions
2664 Energy & Fuels, Vol. 20, No. 6, 2006
Figure 4. Overlay of the derivative weight curve (DTG) with selected MS intensity measurements (m/z 44, 32, 18) for sample A.
energy for stage III in the present sample. Further, by the kinetic analysis described in the section on TGA above, it was calculated that the char combustion is completed in ∼1.5 s at 700 °C (Figure 3). This value is close to the burnout time for char calculated by Ross et al.27 However, the present calculation is made on the hypothesis that the sample size is very small, and that the reactions occurring at lower temperatures, such as water desorption, devolatilization, and partial oxidation, are completed. Furthermore, for practical applications, isothermal runs by heating in an infinitesimal short time up to higher temperatures are necessary. The process of pyrolysis is, therefore, studied in detail and reported elsewhere.28 TG-MS. Because the TGA data indicates that the four samples are composed of the same compounds at different concentrations, the TG-MS data was only studied on samples A and C, which represent the extreme organic and mineral compositions, respectively. Monitoring the identity of the evolved gases allows development of generalized decomposition mechanisms characteristic to each of the four mass-loss events. Figure 4 is an overlay of the derivative weight curve (DTG) with selected intensity measurements from the MS for sample A. The DTG measures the rate of weight change and peaks within this curve, which indicates regions in which the sample is decomposing. Water (m/z ) 18) evolves in three different stages. The first correlates to bound water, while the following two water evolutions are due to devolatilization and combustion of organic matter. The carbon dioxide (m/z ) 44) evolutions occurring simultaneously with the second and third weight losses are indicative of devolatilization and char combustion, respectively, which is representative of the predictive behavior of highcarbon content materials. The decrease in oxygen intensity (m/z ) 32) supports the idea of char combustion of carbonaceous materials from the material and the solid decomposition products from devolatilization. Figure 5 shows the equivalent TG-MS data for sample C. This figure shows that samples A and C behave similarly; however, the evolutions of carbon dioxide, water, and oxygen are much weaker in sample C than in sample A. The disparity of the intensity in the evolution profiles can be attributed to the significant difference in the percentage of organic material composing each of the samples. Although samples A and C contain considerable amount of N, MS is not effective for identifying the oxides, because numerous m/z numbers apply (27) Ross, D. P.; Heidenreich, C. A.; Zhang, D. K. Devolatilisation times of coal particles in a fluidised-bed. Fuel 2000, 79, 873-883. (28) Whitely, N.; Ozao, R.; Cao, Y.; Pan, W.-P. Energy & Fuels. Multiutilization of Chicken Litter as a Biomass Source. Part II. Pyrolysis. 2006, 20, 2666-2671.
Whitely et al.
Figure 5. Overlay of the derivative weight curve (DTG) with selected MS intensity measurements (m/z 44, 32, 18) for sample C.
Figure 6. Change in absorbance for bands at 2359 (CO2), 3016 (CH4), and 965 cm-1 (NH3) of the FTIR spectra obtained for the gas evolved while heating sample A.
for NOx. Furthermore, the detection of S and P was unsatisfactory, which is described elsewhere.28 Figure 6 was generated by monitoring single frequencies in the time-resolved FTIR spectra of sample A. Carbon dioxide CO2 (g), methane CH4 (g), and ammonia NH3 (g) were investigated by monitoring the IR absorption bands at 2359 cm-1 (C-O asymmetrical stretching vibration), 3016 cm-1 (C-H symmetrical stretching vibration), and 965 cm-1(N-H out-ofplane stretching vibration) of the FTIR spectra, respectively. NH3 and CH4 have mass numbers of 17 and 16, respectively, and cannot be clearly distinguished from H2O (principal spectrum at m/z 18). However, by IR, it can be clearly seen that NH3 appears in four evolutions, two occurring below 215 °C as a result of the first weight loss and two occurring in conjunction with devolatilization and char combustion, respectively. The latter two would be related to the fragmentation of organic matter. CH4 is mainly found at temperatures higher than >200 °C, presumably as fragments generated by devolatilization. The carbon dioxide emission profile observed in Figure 6 is in good agreement with that obtained by MS (Figure 4). Figure 7 shows that sample C releases significantly less CH4; also, from Figures 6 and 7, it can be understood that sample C shows that the ratio of the relative absorption intensity at temperatures ca. 250 °C with respect to that at higher temperatures is reversed as compared with the case for sample A. This suggests that the NH3 evolution at lower temperatures can be attributed to the mineral matter, or ammonium salts, and that NH3 at high temperatures is released by fragmentation of organic
Combustion of Chicken Waste
Figure 7. Change in absorbance for bands at 2359 (CO2), 3016 (CH4), and 965 cm-1 (NH3) of the FTIR spectra obtained for the gas evolved while heating sample C.
matter. However, further study is necessary for determining the functionality of N. Conclusions Chicken litter was examined by a wide variety of ASTM D05 methods and was found to possess ∼20% moisture, with the
Energy & Fuels, Vol. 20, No. 6, 2006 2665
air-dry loss being ∼10%; a calorific value similar to a lowrank coal (∼5300 BTU lb-1 ) 12 320 kJ kg-1); and an ash value of ∼25%. Dividing the chicken litter into fractions based upon the particle size was shown as a physical means to alter the values of the calorific value and the ash content. On heating in air, chicken litter was found to decompose by four stages as follows (where E denotes activation energy obtained by kinetic analysis): I. Release of absorbed water and ammonia stemming from ammonium salts (room temperature (RT) ) 150 °C), E ) 61.72 kJ mol-1; II. Devolatilization (150-350 °C), E ) 71.43 kJ mol-1; III. Char precombustion (350-500 °C), E ) 148.5 kJ mol-1; IV. Char combustion (rapid) (500-650 °C), E ) 157.6 kJ mol-1. The higher activation energy for temperature region III as compared with a typical coal is presumably due to the increased presence of N, which retards combustion. Acknowledgment. This work is supported by the USDA-ARS Project No. 6406-12630-002-02S. EF0503109
