Co-firing of coal and cattle feedlot biomass (FB) fuels. Part I. Feedlot biomass (cattle manure) fuel quality and characteristics☆

Fuel 82 (2003) 1167–1182 www.fuelfirst.com

Co-firing of coal and cattle feedlot biomass (FB) fuels. Part I. Feedlot biomass (cattle manure) fuel quality and characteristicsq John M. Sweetena, Kalyan Annamalaib,*, Ben Thienb, Lanny A. McDonaldc a

Texas Agricultural Experiment Station (TAES), Agricultural Research and Extension Center, Texas A&M University, Amarillo, TX 79106, USA b Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843-3123, USA c Agricultural Research and Extension Center, Texas A&M University, Amarillo, TX 79106, USA Received 1 November 2002; revised 12 December 2002; accepted 16 December 2002; available online 29 January 2003

Abstract The use of cattle manure (referred to as feedlot biomass, FB) as a fuel source has the potential to solve both waste disposal problems and reduce fossil fuel based CO2 emissions. Previous attempts to utilize animal waste as a sole fuel source have met with only limited success due to the higher ash, higher moisture, and inconsistent properties of FB. Thus, a co-firing technology is proposed where FB is ground, mixed with coal, and then fired in existing pulverized coal fired boiler burner facilities. A research program was undertaken in order to determine: (1) FB fuel characteristics, (2) combustion characteristics when fired along with coal in a small scale 30 kWt (100,000 BTU/h) boiler burner facility, and (3) combustion and fouling characteristics when fired along with coal in a large pilot scale 150 kWt (500,000 BTU/h DOE– NETL boiler burner facility). These results are reported in three parts. Part I will present a methodology of fuel collection, fuel characteristics of the FB, its relation to ration fed, and change in fuel characteristics due to composting. It was found that FB has approximately half the heating value of coal, twice the volatile matter of coal, four times the N content of coal on heat basis, and due to soil contamination during collection, the ash content is almost 9 – 10 times that of low ash (5%) coal. The addition of , 5% crop residues had little apparent effect on heating value. The main value of composting for combustion fuel would be to improve physical properties and to provide homogeneity. The energy potential of FB diminished with composting time and storage; however, the DAF HHV is almost constant for ration, FB-raw, partially composted and finished composted. The fuel N per GJ is considerably high compared to coal, which may result in increased NOx emissions. The N and S contents per GJ increase with composting of FB while the volatile ash oxide% decreases with composting. Based on heating values and alkaline oxides, partial composting seems preferable to a full composting cycle. Even though the percentage of alkaline oxides is reduced in the ash, the increased total ash percentage results in an increase of total alkaline oxides per unit mass of fuel. The adiabatic flame temperature for most of the biomass fuels can be empirically correlated with ash and moisture percentage. q 2003 Elsevier Science Ltd. All rights reserved. Keywords: Feedlot biomass; cattle manure, compost; Higher heating value

1. Introduction Since 1978, the average number of animal units, thus animal waste has increased by 56% (cattle) to 176% (poultry). Large concentrated animal feeding operations have expanded in many parts of the country including Texas. The Texas Panhandle region covering adjacent parts of Oklahoma and New Mexico is the largest cattle feeding region in the nation, producing about 7.2 million fed cattle, annually (32% of the fed cattle produced and slaughtered in * Corresponding author. Tel.: þ 1-979-845-2562; fax: þ1-979-862-2418. E-mail address: [email protected] (K. Annamalai). q Published first on the web via Fuelfirst.com—http://www.fuelfirst.com

the US) and contributing $14 billion per year to the regional economy. The cattle feeding industry in the Texas Panhandle area is growing at the rate of approximately 100,000 head per year. The feedlot industry is also a major industry in several other major farming areas of United States. Each animal fed leaves approximately 1 ton (over a five month period) of collectable manure containing 35% moisture and 65% solids (combustibles þ ash) on an as collected basis. In many cases, the production of manure from one or more animal species is in excess of what can safely be applied to farmland in accordance with nutrient management plans, and stockpiled waste poses economic and environmental liabilities. Hence, the animal bio-waste can contribute to surface or ground water contamination and

0016-2361/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0016-2361(03)00007-3

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Nomenclature AFT ash fusion temperature ATP Texas Advanced Technology Program ARS Agricultural Research Services BTU British Thermal Unit CAFO concentrated animal feeding operations CFB coal:feedlot biomass (cattle manure) CTE Commercial Testing and Engineering Company CRADA Cooperative Research and Development DAF dry ash free EPA Environmental Protection Agency FB feedlot biomass (cattle manure) FC fixed carbon air pollution problems with the release of CH4 (a greenhouse gas), NH3, H2S, amides, volatile organic acids, mercaptans, esters, and other compounds. With irrigation water tables declining, the number of cattle on feed gradually increasing in the Southern Great Plains region, and EPA adoption of more stringent land application regulations, the development of alternative uses for feedlot manure may become more attractive in some cattle feeding areas in the future. Since the manure contains combustibles, it could be fired in utility type boiler burners providing an energy source. Various technologies, which utilize feedlot biomass (FB) as a sole energy source, are summarized in tabular form in Refs. [2,7]. The sole source biomass technologies have met with only limited technical success [9]. The limitations were primarily due to relying on manure as the sole-source of fuel, despite the highly variable properties (high ash, high moisture, salt composition, etc.) of manure and the associated flame stability problems. Another technology used for the reduction of feedlot waste is anaerobic digestion. Unfortunately, anaerobic digestion is a slow process that results in the release of emissions over a longer period of time (10 – 30 days). Anaerobic digestion also requires liquefaction and the use of precious water; there is difficulty in transporting digested slurry; and the ash content of the slurry solids poses chronic mechanical problems. While the ash is 2 –10% in woody biomass and 10% in coal, the ash in FB can range from 20 to 50%, leading to low British Thermal Unit (BTU) content. Most of these problems could be eliminated by blending biomass with coal and firing it in existing boiler burners since feedlot waste can be readily combusted in the presence of high heating value coal. The blend technology is particularly advantageous for fuel with highly variable properties and high moisture, and the possibility is high for rapid technology transfer [4,5]. The reader is referred to a recent review article which summarizes various biomass fuel properties, their combustion behavior, existing literature on co-firing, fundamental concepts related to coal:biomass blend combustion, and modeling studies [7]. Apart from the disposal of waste, other advantages of co-firing coal with

FBC FiC HHV NETL PC SPS

fluidized bed combustor finished composted higher heating value National Energy Technology Laboratory partially composted Southwestern Public Service Company (now known as Xcel Energy) TAMU Texas A&M University TAES Texas Agricultural Experiment station TGA thermo-gravimetric analysis USDA US Department of Agriculture USDOE US Department of Energy VM volatile matter

biomass are: (i) reduction of fossil fuel based CO2, (ii) reduction in NOx, (iii) reduction in fuel costs since biomass is cheaper than coal, (iv) minimization of waste and reduction of soil, water, and air pollution depending on the biomass fuel blended with coal, (v) potential to use biomass as a reburn fuel, as FB contains N in the form of NH3, and (vi) reduction of the anaerobic release of CH4, NH3, H2S, amides, volatile organic acids, mercaptans, esters, and other chemicals since storage time is reduced. In order to demonstrate the performance of boiler burners with co-firing, fuel properties and combustion and fouling performance data need to be generated. Hence an interdisciplinary research program was undertaken to obtain the combustor performance when firing coal:FB blends. Part I of the paper presents a database of physical and chemical properties of FB and coal:feedlot biomass (cattle manure) (CFB) fuels while part II presents the results of co-firing a blend of 90% pulverized Wyoming coal from the Powder River Basin (used by Southwestern Public Service (SPS) Company) and 10% (weight basis) dry pulverized partially composted (PC) feedlot manure in a small scale 30 kW (100,000 BTU/h) boiler burner facility located at Texas A&M University (TAMU). Additional combustion tests involving a blend of cattle feedlot manure and coal were conducted in a 150 kW (500,000 BTU/h) pilot plant test at the National Energy Technology Laboratory (NETL) at the US Department of Energy (USDOE) and the experimental data is reported in part III of the paper. These tests were conducted under a Cooperative Research and Development Agreement (CRADA) established between DOE/NETL and the Texas Engineering Experiment Station (TAMU).

2. Fuel procurement and protocol 2.1. Procurement Arrangements were made with a commercial cattle feedlot (housing , 45,000 cattle) and an adjacent commercial manure composting operation near Hereford,

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TX, to collect manure from two pens in early December 1998 using wheel loaders, and to then compost the manure in two windrows of 136 Mg (150 tons) each with a Scarab composting unit. One windrow was prepared containing , 5% admixed crop residues (cotton burs and hay on a volumetric ratio) and another windrow was prepared without added crop residues. Large 0.9 Mg (1 ton) samples of these materials were collected from each windrow on day 1 (raw FB or unprocessed manure, following an initial mixing only), day 31 (PC or FB-32), and day-125 (finished composted, or FiC or FB-125). The two windrows received the last turning on April 6, 1999; 123 days after the windrows were first placed and material was sampled from the windrows on April 8, 1999 (125 days after initiation of composting). Two bulk samples (three loader buckets equally spaced along the windrow) were extracted, loaded into a partitioned bobtail truck, hauled, and unloaded in storage under a shed on April 8th.

c.

d. 2.2. Protocol for collection and sampling The protocol for manure collection and sampling was as follows: a.

b.

Manure source. Typical well-drained feed-pens were selected at the commercial feed-yards in which cattle had been on a normal finishing ration. Relatively dry manure was harvested from the top 1/2 to 2/3 of the existing manure pack, with an effort to maintain an undisturbed manure pack of approximately 25 – 12.5 mm (1 in. – 1/2 in.) to minimize ash (soil) entrainment. The pen numbers used for the source manure were recorded, along with animal numbers, weight, time of occupancy since last collection, and a printout of finishing ration. Windrows. Upon removal, the manure was placed in two parallel windrows of normal cross-sectional size and at least 45 m (150 ft) long. One of the windrows was mixed with organic matter as a carbon source while the other windrow was mixed without crop residues. For the manure/carbon source windrow, the mixture was made following commercial compostor standard practice which involves , 5% crop residue by volume. Crop residues included a small amount of cotton gin trash and forage sorghum straw but no inoculants were used. The estimated weight of manure in the windrows was about 3 Mg/m (1 ton/ft) running length. (1) Manure with crop residues. Manure that came out of two pens on 12/3/98 was placed into one windrow. The 45 m (150 ft) test section of the windrow had about 3/4 of a wheel loader bucket of cotton burs and 1/4 of a loader bucket of forage sorghum straw. (2) Manure with no crop residues. The manure only windrow (45 m, 150 ft) contained manure

e.

f.

g.

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from two adjacent pens, collected on 5th December. Initial sampling. Within 24 –48 h of placement, both windrows were mixed once, and sampled by extracting a minimum of 15 sub-samples, mixing them, and then removing three composite subsamples. Then a 1.9 –2.3 m3 (2 12 – 3 yd3) sample weighing approximately 0.9 metric ton 1.4 Mg (1 ton) was taken from each windrow by wheel loader. The large samples were taken with the wheel loader at three places equally spaced along the 45 m (150 ft) windrow section. The large bulk samples were placed in a bobtail truck with a partition to separate the two manure bulk samples and transported to the Texas Agricultural Experiment Station (TAES), James Bush Research Farm, Bushland, near Amarillo, for storage in a wooden bin inside an equipment shed. Interim sampling. Both windrows were turned according to established practice by the commercial compostor. Immediately following the fourth turning, the windrows were again sampled. The same windrow sub-sampling and large batch sampling procedures were followed for both windrows. Final sampling. When the compost site manager determined the two windrows ready for the final turning, he notified project personnel who sampled each windrow within 24 h after the final turning. Sample analysis. Manure sub-samples were analyzed for the following parameters: moisture, ash, higher heating value (HHV), total carbon, total nitrogen, sulfur, potassium, and sodium. Shipment for combustion tests. Manure from the bulk samples stored at Bush Farm was reloaded in small drums for shipment to Vortec Industries for grinding and then to the National Energy Technology Laboratory, US Department of Energy, Pittsburgh, PA.

The 0.9 metric ton (1 ton) samples hauled to Bushland, TX, were stored in pallet bins under an equipment shed at TAES – Bush Farm, Bushland, TX. These bulk samples were periodically sampled and characterized as per protocol. Sub-samples were taken and sent to two laboratories: Southwestern Public Service Company (SPS)/New Century Energies, Amarillo, TX, which conducted proximate and elemental analyses and to Commercial Testing and Engineering Co., (CTE), Denver, which provided the ultimate analyses. Larger sub samples of 4.5 kg (10 lb) were collected and shipped periodically, from the bin-stored materials, for combustion testing at the 30 kWt (100,000 BTU/h) smallscale (150 mm, 6 in. diameter) Texas A&M University Boiler Burner Laboratory, College Station and to USDOE – NETL for material handling and feeding tests leading up to the January 2000 test burn in the 480 mm (19 in.)

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diameter 150 kW (500,000 BTU/h) pilot plant combustor at Pittsburgh. The moisture content of the PC bulk manure samples at 30– 32% moisture were reduced by thin-bed drying in a greenhouse at USDA – ARS in Bushland. Previous records showed that the drying of FB does not cause significant loss in heating values [6]. In October 1999, a 570 kg (1260 lb) sample of the PC manure without crop residues was prepared for the test burn at TAMU (see part II for results) and DOE – NETL by (a) solar drying to 3% (w.b.) moisture in a stirred thin-bed on a concrete floor of a greenhouse at Bushland, (b) containerized shipment to Vortek Industries, Long Beach, CA (c) grinding to 2 50 mesh particle size [10] and (d) reshipment in metal drums to NETL in Pittsburgh. Similar steps in handling, preparation, and grinding (, 20 mesh) were applied to the Wyoming coal materials supplied by SPS, Amarillo. About 80% of coal particles and 75% of FB passed through a 74 mm (200 mesh) sieve. After arrival of the coal and manure samples at NETL, in mid-December, they were blended together in a 90:10 ratio (as-received weight basis) and mixed in a cement mixer. The blend was sealed in plastic bags and stored in sealed barrels prior to test firing during the pilot plant tests on January 20– 22, 2000.

3. Results and discussion 3.1. Proximate and ultimate analyses of ration and fuel The manure analyses in Table 1 show the results of the proximate analyses provided by SPS on feed bunk ration and 3 sub-samples taken from a composite of 20 or more random probes into the 136 Mg (150 ton) windrows of test manure that were collected from typical, adjacent cattle pens. These initial samples were taken immediately after the first mixing with the Scarab composter on 5th December 1998 (day 1), but before pronounced heating occurred with the onset of composting. Ultimate analyses were provided by the Commercial Testing and Engineering Company (CTE), which analyzed only one composite sample of the three sub-samples submitted to SPS. According to SPS results, manure moisture contents were about 4% lower and ash content about 4% higher for the windrow with crop residues added than for the manure-only windrow. Similarly, initial volatile matter, VM (dry basis) and fixed carbon, FC (dry basis), were slightly higher for the manureonly windrow than for the , 5% crop residue windrow. Since FC has a higher heat values than VM, fuels with high FC tend to have a higher heat value. Accordingly, the initial

Table 1 Analysis summary for initial raw/feedlot manure (RM) and feed ration samples (December 5, 1998; day 1) I. Ultimate analysis by Commercial Testing and Engineering Co. (CTE), Denver, CO Parameter

Feedlot manure

As-received Moisture% Carbon% Hydrogen% Nitrogen% Sulfur% Ash% Oxygen% (differential)

Dry basis

38.6 18.2 2.06 1.57 0.50 24.8 14.3

Total

Feedlot manure þ 5% crop residues

Feedbunk ration

As-received

As-received

xxxx 29.60 3.35 2.55 0.81 40.40 23.30

100.0

Dry basis

36.20 18.90 2.19 1.48 0.51 27.30 13.50

100.0

xxxx 29.60 3.43 2.32 0.80 42.80 21.10

100.0

Dry basis

19.80 35.90 4.96 1.63 0.08 3.60 34.00

100.0

100.0

xxxx 44.80 6.18 2.03 0.10 4.50 42.40

II. Proximate and elemental analysis by Southwestern Public Service Co. (SPS), Amarillo, TX Parameter

Mean ^ SD

Mean ^ SD

Mean ^ SD

Mean ^ SD

Mean ^ SD

Mean ^ SD

Moisture% Ash% Sulfur% Heat of combustion (kJ/kg) (BTU/lb) Sodium% of ash Magnesium% of ash Potassium% of ash Calcium% of ash

40.2 ^ 1.0 21.5 ^ 0.4 0.45 ^ 0.02 8010 ^ 200 (3450 ^ 90) – – – –

–

35.8 ^ 0.2 25.6 ^ 0.1 0.47 ^ 0.02 7620 ^ 120 (3280 ^ 50) – – – –

–

20.2 ^ 0.2 4.2 ^ 0.4 0.26 ^ 0.0 14,700 ^ 100 (6340 ^ 40) – – – –

–

33.3 ^ 0.5

Subtotal Ash%, db (above) Volatiles% (db)

35.9 ^ 0.1 0.76 ^ 0.03 13,400 ^ 500 (5760 ^ 220) 2.93 ^ 0.12 5.08 ^ 0.02 11.7 ^ 0.2 13.6 ^ 0.4

– –

35.9 ^ 0.1 50.2 ^ 0.9

40.0 ^ 0.01 0.73 ^ 0.04 11,900 ^ 200 (5100 ^ 70) 3.30 ^ 0.11 4.34 ^ 0.15 10.7 ^ 0.3 11.7 ^ 0.0 30.0 ^ 0.60

– –

40.0 ^ 0.1 47.6 ^ 1.1

5.2 ^ 0.5 0.33 ^ 0.01 18,500 ^ 100 (7950 ^ 40) 2.12 ^ 0.06 7.19 ^ 0.09 13.5 ^ 0.4 23.0 ^ 0.2 45.8 ^ 0.3

– –

5.2 ^ 0.5 72.9 ^ 0.1

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Fig. 1. HHV of ration and animal based biomass fuels. Table 2 Analysis summary for PC feedlot manure (January 5, 1999; 32 days of composting) I. Ultimate analysis by Commercial Testing and Engineering Co. (CTE), Denver, CO Parameter

Feedlot manure þ 5% crop residues

Feedlot manure As-received

Moisture% Carbon% Hydrogen% Nitrogen% Sulfur% Ash% Oxygen% (differential)

Dry basis

32.00 19.80 2.20 1.67 0.56 30.70 13.10

Total

As-received

xxxx 29.00 3.23 2.46 0.82 45.10 19.30

100.0

30.70 20.00 2.16 1.62 0.53 28.50 16.50

100.0

100.0

Dry basis xxxx 28.80 3.12 2.34 0.76 41.20 23.80 100.0

II. Proximate and elemental analysis by Southwestern Public Service Co. (SPS), Amarillo, TX Parameter

Mean ^ SD

Mean ^ SD

Mean ^ SD

Mean ^ SD

Moisture% Ash% Sulfur% Heat of combustion (kJ/kg) BTU/lb Sodium% of ash Magnesium% of ash Potassium% of ash Calcium% of ash

32.5 ^ 3.7 30.3 ^ 2.1 0.51 ^ 0.03 7350 ^ 380 (3160 ^ 160) – – – –

–

31.7 ^ 2.5 30.6 ^ 2.6 0.49 ^ 0.06 7450 ^ 380 (3200 ^ 160) – – – –

44.7 ^ 2.3 0.71 ^ 0.02 10,900 ^ 900 (4700 ^ 390) 2.55 ^ 0.17 4.53 ^ 0.09 8.90 ^ 0.48 11.6 ^ 0.4

44.6 ^ 1.2 0.75 ^ 0.03 10,800 ^ 90 (4660 ^ 90) 2.18 ^ 0.03 4.40 ^ 0.36 8.95 ^ 0.27 12.3 ^ 0.5

Subtotal

–

27.8 ^ 0.7

–

27.6 ^ 0.6

Ash%, db (above) Volatiles% (db) Fixed carbon% (db)

– – –

44.6 ^ 1.2 42.3 ^ 1.3 10.1 ^ 0.2

– – –

44.7 ^ 2.3 42.8 ^ 0.5 9.4 ^ 0.2

Total

–

97.0 ^ 0.6

–

96.9 ^ 1.7

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Fig. 2. (a) Variation of ash and total alkaline oxide matter with composting time. (b) Variation of alkaline oxide% in ash with composting time.

HHV was higher on both as-received and dry basis in the manure-only sample. The CTE data corroborated the SPS findings of higher ash and lower moisture for the crop residue windrow, and showed identical initial carbon contents. Because crop residues generally have higher VM and lower ash than FB, the differences between manure with crop residue and without crop residue in the experiment are more likely due to the variations in properties of the manure harvested from the feed-pens, including any entrained soil or debris, resulting from manure collection, than to any effects of incorporating the crop residues. 3.2. Higher heating values The cattle ration samples taken from feed-bunks adjacent to three pens from which manure had been removed showed

much lower ash and much higher values of total carbon, FC, VM, and heating values than either manure windrow (Table 1). The ration had a much higher HHV value (as-received and dry-basis) compared to FB-raw due to its reduced moisture and ash content (HHV as-received, Fig. 1). However, on a dry ash free (DAF) basis, the heating value was similar for ration (19,500 kJ/kg, 8390 BTU/lb), manure-only (20,900 kJ/kg, 8990 BTU/lb), and manure/crop residue (19,800 kJ/kg, 8500 BTU/lb). Dry ash percentage of ration was only 4.5%. If a metabolic efficiency of 20% is assumed, then the ash content is expected to increase slightly. However, the ash percentage on a dry basis is 40% in manure indicating a large collection of soil from the feedlots and/or substantial degradation in situ in the feedlot; therefore, resulting in the loss of VM with time before collection (120 – 150 days typical).

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On January 5, 1999, 32 days after the initial mixing and early stages of composting, the windrows were re-sampled following the same protocol as before. In order to determine the extent of loss of combustibles, the ash percentage on dry basis was determined. Results of the PC manure (without crops) analysis (Table 2) indicated that moisture decreased from 39% (Table 1) to about 32% (Table 2) for both windrows while ash content increased from 40% (dry basis) to 45%. The moisture reduction should increase the heat value. The ash increased with composting time (Fig. 2a), indicating a loss of combustibles and hence a reduction in HHV on dry basis (See HHV-dry in Fig. 1). However; the DAF HHV remained almost constant at about 19,500 kJ/kg (8400 BTU/lb) for ration, FB, and PC and 19,800 kJ/kg (8500 BTU/lb) for manure mixed with crop residue. The HHV decreased by 19% for the manure-only windrow and 8% for the manure/crop residue windrow, to a level of about 10,900 kJ/kg (4700 BTU/lb) dry basis for both windrows. After 125 days of composting (Table 3), ash content was higher for FiC biomass than at days 1 and 32 (Fig. 2a), moisture was slightly lower, and the heating value was 7 – 9% lower (10,000 and 9930 kJ/kg or 4310 and

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4270 BTU/lb dry basis, respectively) for the manure-only and manure-crop residue compost. Volatiles were lower as well, along with total carbon, but FC was slightly lower for the manure-only windrow and higher for manure with crop residue. There was a large variation in HHV on as-received basis, but the HHV on a DAF basis was approximately constant. In essence, DAF HHV did not show significant change until 32 days, even though there was combustible loss. However, after 125 days, the DAF HHV decreased slightly indicating a loss of the high heating value components of the combustibles. The DAF heating values of raw FB-raw (1 day), PC (32 days), and FiC (125 days) are compared in Fig. 1. 3.3. Fuel composition A direct comparison of ultimate analysis of composted manure after 1, 32, and 125 days is provided in Table 4 (ultimate analysis, CTE) and Table 5 (proximate and elemental analysis, SPS). The higher H/C ratio, lower O/C ratio, and lower ash content likely were responsible for

Table 3 Analysis summary for FiC (April 8, 1999; 125 days of composting) I. Ultimate analysis by Commercial Testing and Engineering Co. (CTE), Denver, CO Parameter

FiC manure-only As-received

Moisture% Carbon% Hydrogen% Nitrogen% Sulfur% Ash% Oxygen% (differential) Totals

Dry basis

FiC manure þ 5% v/v crop residues

SPS coal sampled 6/7/99

As-received

As-received

Dry basis

Dry basis

31.20 16.80 1.65 1.61 0.60 33.40 14.80

0.00 24.40 2.40 2.34 0.87 48.50 21.50

27.30 17.60 1.82 1.69 0.60 38.10 12.90

0.00 24.20 2.50 2.33 0.83 52.50 17.70

26.90 50.80 3.33 0.75 0.31 5.30 12.60

0.00 69.50 4.56 1.03 0.42 7.30 17.20

100.00

100.00

100.00

100.00

100.00

100.00

II. Proximate and elemental analysis, Southwestern Public Service Co. (SPS), Amarillo, TX Parameter

n ¼ 3; sub-samples As-received mean (SD)

Moisture% 32.4 (0.3) Ash% 32.9 (0.98) Sulfur% 0.51 (0.01) Heat of combustion (kJ/kg) 6850 (390) BTU/lb 2940 (170)) Ash%, db (above) Volatiles% (db) Fixed carbon% (db) Sodium% of ash Magnesium% of ash Potassium% of ash Calcium% of ash

n ¼ 3; sub-samples Dry basis mean (SD) 0 (0) 48.7 (1.64) 0.75 (0.01) 10,000 (360) 4310 (160) 48.7 (1.6) 39.1 (0.6) 9.45 (0.43) 2.44 (0.07) 4.53 (0.19) 8.66 (0.03) 12.8 (0.4)

n ¼ 1; sub-samples

As-received mean (SD)

Dry basis mean (SD)

28.5 (1.8) 38.9 (2.41) 0.49 (0.02) 7100 (30) 3050 (10)

0 (0) 54.4 (2.3) 0.68 (0.01) 9930 (270) 4270 (120) 54.4 (2.3) 37.9 (0.5) 9.70 (0.58) 2.20 (0.11) 4.00 (0.13) 8.18 (0.36) 13.2 (0.8)

Subtotals

28.5 (0.5)

27.6 (0.4)

Totals

97.3 (0.7)

102.0 (1.8)

As-received

27.5 4.89 0.35 20,400 8760 4.89 30.7 36.9

Dry basis

0.00 6.74 0.48 28,100 12,100 6.74 42.30 50.90

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Table 4 Comparison of ultimate analysis of feedlot manure after 1, 32, and 125 days of windrow composting Parameter

No. of days of composting

FiC manure-only

FiC manure þ 5% v/v crop residues

Concentration

Concentration

As-received, n ¼ 1 I. Ultimate analysis by Commercial Testing and Engineering Co. (CTE), Denver, CO Moisture% 1 38.6 32 32.0 125 31.2 18.2 19.8 16.8

Dry basis, n ¼ 1

As-received, n ¼ 1

Dry basis, n ¼ 1

0 0 0

36.2 30.7 27.3

0 0 0

29.6 29.0 24.4

18.9 20.0 17.6

29.6 28.8 24.2

Carbon%

1 32 125

Hydrogen%

1 32 125

2.06 2.20 1.65

3.35 3.23 2.40

2.19 2.16 1.82

3.43 3.12 2.50

Nitrogen%

1 32 125

1.57 1.67 1.61

2.55 2.46 2.34

1.48 1.62 1.69

2.32 2.34 2.33

Sulfur%

1 32 125

0.50 0.56 0.60

0.81 0.82 0.87

0.51 0.53 0.60

0.80 0.76 0.83

Ash%

1 32 125

24.8 30.7 33.4

40.4 45.1 48.5

27.3 28.5 38.1

42.8 41.2 52.5

Oxygen% (differential)

1 32 125

14.3 13.1 14.8

23.3 19.3 21.5

13.5 16.5 12.9

21.1 23.8 17.7

the higher HHV in FB-raw fuels (Fig. 3a and b). The trends toward decreasing moisture, carbon (total and fixed), hydrogen, volatiles, and heating value with increasing composting time are readily evident. Simultaneously, on a dry basis, ash content increased (both as-received and dry basis) while nitrogen and oxygen slightly decreased or remained constant. However, the H/C ratio decreased monotonically while the O/C ratio first decreased and then increased (Fig. 3b) with composting. Typically high O/C ratios and low H/C ratios correspond to a low heating value. Thus, the DAF heating value of PC was almost the same as 1 day FB. The DAF heating value of FC had a slightly lower value as compared to PC and FB, indicating that the volatile components of high heat content were lost. There was very little S and low N, kg per GJ, in the ration (Fig. 4a). After metabolism in the cattle, both the N and S jumped to a high value. The N% increased on dry basis while C and H% decreased, indicating loss of combustibles relative to nitrogen. Thus the N/C and S/C continued to increase with composting. On a DAF basis, both the N/C and S/C ratios increased after 30 days of composting, which indicated that S and N were not lost with the volatiles (Fig. 3b). Since DAF heating values were approximately constant, the S and N contents, kg per GJ, increased as

shown in Fig. 4b. Regardless of composting, values of S and N were much higher than for coal (Fig. 4a). 3.4. Effect of storage After cessation of windrow composting on April 8, 1999, the 0.9 metric ton (one ton) lots of FiC were stored continually under a roof in open bins until late October 1999, when preparation began for the first combustion tests in January 2000. The lots were stored alongside similar batches placed in storage under roof on days 1 and 32. During the storage, further chemical and physical changes occurred in the manure. The analyses for samples taken on 29th October 1999 are shown in Table 6 (ultimate and proximate analysis) and Table 7 (elemental analysis of ash from manure samples). As compared to data for day 125 in Tables 4 and 5, data in Table 6 for bin-stored manure or compost showed large reduction in moisture (below 23% w.b.), similar carbon and volatiles, lower heating values (9630 and 8340 kJ/kg, or 4140 and 3756 BTU/lb dry basis), slightly higher ash (dry basis), slightly higher sulfur, and similar nitrogen. The ash analyses revealed very small differences between mineral oxide values as a function either of time in storage or the addition of crop residue.

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Table 5 Comparison of proximate and elemental analyses of composted feedlot manure after 1, 32, and 125 days of composting manure analysis summary for coal/manure combustion tests Parameter

No. of days of composting Concentration ðn ¼ 3Þ

Concentration ðn ¼ 3Þ

As-received mean (SD) Dry basis mean (SD) As-received mean (SD) Dry basis mean (SD) I. Proximate and elemental analysis by Southwestern Public Service Co. (SPS), Amarillo, TX Moisture% 1 40.2 (1.0) 0.0 (0) 32 32.5 (3.71) 0.0 (0) 125 32.4 (0.3) 0.0 (0)

35.8 (0.2) 31.7 (2.5) 28.5 (1.8)

0.0 (0) 0.0 (0) 0.0 (0)

Ash%

1 32 125

21.5 (0.4) 30.3 (2.1) 32.9 (1.0)

35.9 (0.1) 44.6 (1.2) 48.7 (1.6)

25.6 (0.1) 30.6 (2.6) 38.9 (2.4)

40.0 (0.1) 44.7 (2.3) 54.4 (2.3)

Sulfur%

1 32 125

0.45 (0.02) 0.51 (0.03) 0.51 (0.01)

0.76 (0.03) 0.75 (0.03) 0.75 (0.01)

0.47 (0.02) 0.49 (0.06) 0.49 (0.02)

0.73 (0.04) 0.71 (0.02) 0.68 (0.01)

Heat of combustion (BTU/lb)

1 32 125

3450 (90) 3160 (160) 2940 (170)

5760 (220) 4660 (90) 4310 (160)

3280 (50) 3200 (160) 3050 (10)

5100 (70) 4700 (390) 4270 (120)

Sodium% of ash

1 32 125

2.93 (0.12) 2.18 (0.03) 2.44 (0.07)

3.30 (0.11) 2.55 (0.17) 2.20 (0.11)

Magnesium% of ash

1 32 125

5.08 (0.02) 4.40 (0.36) 4.53 (0.19)

4.34 (0.15) 4.53 (0.09) 4.00 (0.13)

Potassium% of ash

1 32 125

11.7 (0.2) 8.95 (0.27) 8.66 (0.03)

10.7 (0.3) 8.90 (0.48) 8.18 (0.36)

Calcium% of ash

1 32 125

13.6 (0.4) 12.3 (0.5) 12.8 (0.4)

11.7 (0.0) 11.6 (0.4) 13.2 (0.8)

Volatiles% (db)

1 32 125

50.2 (0.9) 42.3 (1.3) 39.1 (0.6)

47.6 (1.1) 42.8 (0.5) 37.9 (0.5)

Fixed carbon% (db)

1 32 125

11.3 (0.3) 10.1 (0.2) 9.5 (0.4)

10.4 (0.2) 9.4 (0.2) 9.7 (0.6)

3.5. Volatile matter and higher heating values of volatile matter On DAF basis, the VM percentage remained between 75 and 83% (Fig. 5). Table 8 shows the results of ultimate and proximate analyses on 90:10 (mass) coal:PC manure blends. If the heat of pyrolysis is negligible (about 420 kJ/kg of volatiles), [3]. HHVfuel ¼ HHVvol VM þ ð1 2 VMÞHVFC

(6500 BTU/lb) as manure is composted, while the HHVvol of coal is about 26,700 kJ/kg (11,500 BTU/lb) One can estimate the %heat contribution by volatiles using the following relation: %Heat contribution by volatiles ¼ VM £ HHVvol =HHVfuel

ð2Þ

ð1Þ

Where HHVfuel and HHVvol are the HHVs for the fuel and volatiles, respectively. Knowing HHV fuel, VM, and HVFC ¼ 32,800 kJ/kg (14,100 BTU/lb), then one can estimate the HHVvol for FB, PC, FiC, and coal as shown in Fig. 6a. It is seen that the heating values of volatiles ranged from 17,400 kJ/kg (7500 BTU/lb) to 15,100 kJ/kg

While the VM of manure is almost twice that of coal, the percentage of heat contributed by volatiles from manure ranges from 60 to 70% while in coal it contributes only 40% of total heating value (Fig. 6b). The volatiles, from FB, are released more rapidly in manure (part II) at lower temperatures compared to coal, the flame is expected to be more stable when firing a coal:FB blend.

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Fig. 3. (a) Variation of hydrogen to carbon and oxygen to carbon ratios for ration and FB or manure with composting time. (b) Variation of hydrogen to carbon and oxygen to carbon ratios of FB with composting time.

3.6. Adiabatic flame temperatures The HHV on a DAF basis was almost constant (< 20,000 kJ/kg) for raw-FB, ration, and PC (Fig. 1). Heat contents were reported to be linearly related to ash and

moisture contents [8] and the results are re-plotted in Fig. 7. The DAF heating value when extrapolated to zero ash percentage yields 21,900 kJ/kg (9350 BTU/lb), which is 1800 kJ/kg (780 BTU/lb) higher than the current data shown in Fig. 1. Most biomass fuels including FB fuel have varying

J.M. Sweeten et al. / Fuel 82 (2003) 1167–1182

1177

Fig. 4. (a) Nitrogen and sulfur contents on a heat basis vs. fuel type. (b) Change in nitrogen and sulfur contents on a heat basis with composting.

amounts of oxygen accompanied by variations in heating value and stoichiometric air. It has been reported that the DAF HHV per unit of stoichiometric air is roughly constant for most biomass fuels at 3800 kJ/kg [7]. Thus, if DAF biomass fuels are fired into a boiler, they will all have similar adiabatic flame temperatures under identical air:fuel ratio conditions. Hence, variations in flame temperatures for biomass fuels are essentially due to variation in the ash and moisture contents of the biomass fuels. From simple theory on adiabatic combustion of stoichiometric air:fuel (with ash and moisture) mixtures, it can be shown that if HVDAF per unit stoichiometric air is constant for most of the biomass fuels then the adiabatic flame temperature (K) should have

the following approximate correlation Temp ðKÞ ¼ A þ B £ H2 O ð%moistureÞ þ C £ ash ð%ashÞ þ D £ H2 O ð%moistureÞ £ ash ð%ashÞ2 þ E £ H2 O ð%moistureÞ2 þ F £ ash ð%ashÞ2 ð3Þ where A; B; C; D; E; and F are the coefficients. A THERMOLAB spreadsheet based combustion program assuming equilibrium concentrations was run for many agricultural and animal-based biomass fuels with varying, moisture and ash [1]. The curve fit for many

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Table 6 Uncomposted, PC, and FiC following 6–11 months of bin-storage under roof (October 29, 1999) Parameter

Uncomposted manure (day 1)

PC manure (day 32)

FiC (Day 125)

0% Crop residues

,5% Crop residues

0% Crop residues

,5% Crop residues

0% Crop residues

5% Crop residues

As-rec eived

As-rec eived

As-rec eived

As-rec eived

As-rec eived

As-rec eived

Dry basis

Dry basis

Dry basis

I. Ultimate analysis by Commercial Testing and Engineering Co. (CTE), Denver, CO Moisture% 23.0 – 10.8 – 9.1 – Fixed 23.7 30.8 26.4 29.6 23.9 26.3 carbon% Hydrogen% 2.60 3.37 3.04 3.41 2.58 2.84 Nitrogen% 2.21 2.87 1.98 2.22 2.03 2.23 Sulfur% 0.72 0.94 0.73 0.83 0.73 0.80 Ash% 33.0 42.8 39.8 44.7 45.0 49.5 Oxygen% 14.8 19.2 17.2 19.3 16.7 18.4 (differential) Totals 100.0 100.0 100.0 100.0 100.0 100.0

Dry basis

Dry basis

Dry basis

17.9 21.9

– 26.7

20.9 21.9

– 27.6

20.1 19.6

– 24.6

2.41 1.86 0.65 40.1 15.2

2.93 2.26 0.79 48.8 18.5

2.35 2.00 0.68 39.4 12.8

2.97 2.53 0.86 49.8 16.2

2.03 1.81 0.63 42.5 13.2

2.54 2.27 0.79 53.3 16.6

100.0

100.0

100.0

100.0

100.0

100.0

II. Proximate and elemental analysis by SPS Co., Amarillo, TX Moisture% 23.3 – 10.9 – 9.3 – 18.1 – 20.9 – 20.5 – Ash% 32.3 42.1 39.6 44.5 44.6 49.2 40.1 49.0 40.2 50.8 41.2 51.8 Sulfur% 0.61 0.79 0.54 0.61 0.64 0.70 0.57 0.70 0.68 0.86 0.64 0.81 Heat of 9040 11,800 9570 10,740 8710 9600 8060 9840 7620 9640 6940 8740 combustion (kJ/kg) BTU/lb (3890) (5060) (4120) (4620) (3740) (4130) (3460) (4230) (3280) (4140) (2990) (3760) Ash%, db – 42.1 – 44.5 – 49.2 – 49.0 – 50.8 – 51.8 (above) Volatiles% – 46.5 – 45.0 – 41.3 – 41.3 – 39.9 – 38.8 (db) Fixed – 11.4 – 10.5 – 9.5 – 9.7 – 9.3 – 9.4 carbon% (db) Totals – 100.0 – 100.0 – 100.0 – 100.0 – 100.0 – 100.0

Table 7 Mineral analysis of manure ash (%dry basis) after composting and bin storage vs. coal ash Mineral analysis% Uncomposted (dry basis) manure (day 1)

PC manure (day 32) FiC (day 125)

Mean (^ SD)

0% Crop 5% Crop 0% Crop 5% Crop 0% Crop 5% Crop 0% Crop residues residues residues residues residues residues residues Sodium oxide Magnesium oxide Aluminum oxide Silica Sulfur trioxide Potassium oxide Calcium oxide Titanium oxide Ferric oxide Strontium oxide Barium oxide Total

4.26 8.63 8.67 41.8 3.62 13.6 17.8 0.43 0.95 0.10 0.08 100.0

4.09 7.72 9.29 45.8 3.34 12.0 16.2 0.48 1.02 0.09 0.08 100.0

3.71 7.16 9.84 45.6 3.20 11.1 17.4 0.49 1.35 0.11 0.10 100.0

4.13 7.05 9.68 47.5 2.77 11.4 15.6 0.48 1.20 0.09 0.07 100.0

4.26 7.19 9.64 46.2 3.19 11.6 16.0 0.49 1.27 0.10 0.10 100.0

Analysis provided by Southwestern Public Service Co., Amarillo, TX.

3.39 6.47 9.57 48.0 3.09 10.5 17.0 0.48 1.35 0.09 0.08 100.0

4.08 (0.32) 7.66 (0.84) 9.38 (0.63) 44.5 (2.4) 3.34(0.25) 12.1 (1.3) 17.1 (1.0) 0.47 (0.03) 1.19 (0.21) 0.10 (0.01) 0.09 (0.01) 100.0

SPS coal sample 6/7/99, n ¼ 1 5% Crop residues 3.87 (0.42) 7.08 (0.63) 9.51 (0.20) 47.1 (1.2) 3.07 (0.29) 11.3 (0.7) 16.2 (0.7) 0.48 (0.00) 1.19 (0.17) 0.09 (0.00) 0.08 (0.01) 100.0

Combined 0% and 5% crop residues 3.97 (0.35) 7.37 (0.73) 9.45 (0.42) 45.8 (2.2) 3.20 (0.28) 11.7 (1.2) 16.7 (1.0) 0.48 (0.02) 1.19 (0.17) 0.10 (0.01) 0.09 (0.01) 100.0

0.94 5.53 19.08 28.7 9.86 0.5 27.9 1.34 5.58 – – 99.4

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Fig. 5. VM% on DAF basis.

different biomass fuels with moisture ranging from 0 to 45% and ash percentage ranging from 0 to 40% yields the following correlations (for 8C and 8F, respectively): T ð8CÞ ¼ 2010 2 1:89 ð%moistureÞ 2 5:06 ð%ashÞ 2 0:309 ð%moistureÞ ð%ashÞ 2 0:180 ð%moistureÞ2 2 0:108 ð%moistureÞ2

ð4Þ

T ð8FÞ ¼ 3650 2 3:40 ð%moistureÞ 2 9:10 ð%ashÞ 2 0:556 ð%moistureÞ ð%ashÞ 2 0:324 ð%moistureÞ2 2 0:194 ð%ashÞ

2

ð5Þ

ash (Table 9) for the coal –manure blend (dry basis) contained consistent levels of 11 minerals, especially silica (39.2 ^ 0.8%), aluminum oxide (19.6 ^ 0.5%), and calcium oxide (17.8 ^ 0.7%). Lower levels (2 – 6%) of sulfur . magnesium . iron . potassium . sodium were present. The remaining mineral oxides (titanium . strontium . barium) represented less than 1% each. While the ash percentage increased (Fig. 2a), the total alkaline oxide% (potassium, calcium, sodium, and magnesium) decreased during composting, (see alkaline oxides in Table 8 Analysis of coal (90%) and manure (10%) mixture (January 20 –21, 2000) Parameter

Fig. 8 shows a comparison of the exact results (data points) and the curves obtained by the above correlation. The R squared value for the curve fit is 0.991. The curves can provide the allowable moisture and ash contents of biomass fuels for any specified flame temperature required for flame stability. 3.7. Mineral matter The mineral matter (mm) analyses are extremely important for high ash FB since the mm affects the deposition rate, corrosion rate, and erosion rate of heat transfer tubes. The FB contains almost 45% ash while coal contains only 5% ash. Thus a 90:10 blend will essentially double the ash output compared to coal. Alkaline matter such as Na, K, etc. are believed to vaporize, react with SO2, and form Na2SO4, K2SO4, etc, which become sticky around 750 K. Higher alkaline oxide content results in a higher probability of fouling. Once ash is stuck to a metal surface, the oxide layers grow and are accompanied by an increase in surface temperature (as much as 1000 K), which will accelerate the deposition process. The mineral analysis of

As-received ðn ¼ 5Þ

Dry basis ðn ¼ 5Þ

Mean

Mean

SD

SD

I. Ultimate analysis by Commercial Testing and Engineering Co. (CTE), Denver, CO Moisture% 7.86 0.27 – – Carbon% 60.1 0.6 65.2 0.6 Hydrogen% 4.31 0.02 4.67 0.02 Nitrogen% 1.06 0.01 1.15 0.01 Sulfur% 0.50 0.01 0.54 0.01 Ash% 11.4 0.2 12.3 0.2 Oxygen% 14.8 0.4 16.1 0.5 (differential) Totals

100.0

–

100.0

–

II. Proximate and elemental analysis by SPS Co., Amarillo, TX Moisture% 8.40 0.16 – Ash% 10.8 0.11 11.8 Sulfur% 0.48 0.02 0.52 Heat of combustion 23,600 300 25,800 (kJ/kg) BTU/lb (10,200) (100) (11,100) Volatiles% (db) 37.8 0.4 41.2 Fixed carbon% (db) 43.0 0.6 46.9

(100) 0.5 0.6

Totals

–

100.5

–

100.4

– 0.11 0.02 300

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J.M. Sweeten et al. / Fuel 82 (2003) 1167–1182

Fig. 6. (a) Variation of heating values of volatiles. (b) The % heat contribution by volatiles.

Fig. 2b) possibly due to leaching from the outer layers of the windrow surface. Thus PC manure is preferable, compared to FB-raw. Note that the total alkaline oxide percentage in the fuel still increased due to an increased ash percentage in fuel, as shown in Fig. 2a. Ash fusion temperatures (AFT) depend upon the percent of ash acid (SiO2, Al2O3, TiO2, etc.) vs. the percent basic (Fe2O3, CaO, MgO, Na2O, and K2O, etc.). [11] Fig. 9 showed the percentage of acidic vs. basic oxides in ash as manure is composted. Higher the basic percentage, lower the AFT (that is typically lower than flame temperatures). Alkaline oxides ranged from around 40 – 44% for 0% crop-residues with

Fig. 7. Variation of dry heating values of manures with ash content [8].

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Fig. 8. Correlation of adiabatic flame temperature with moisture and ash content.

Table 9 Mineral analysis of ash from coal/manure (90/10%) blend (%dry basis) Mineral analysis% (dry basis) Sodium oxide Magnesium oxide Aluminum oxide Silica Sulfur trioxide Potassium oxide Calcium oxide Titanium oxide Ferric oxide Strontium oxide Barium oxide Total

Mean 2.39 4.64 19.6 39.2 6.36 4.23 17.8 0.99 4.43 0.20 0.18 100.0

dominant component being CaO and K2O, while for coal it is about 35% with the dominate compound being CaO.

SD 0.28 0.33 0.5 0.8 0.27 0.30 0.7 0.03 0.21 0.00 0.01

4. Summary 1. The main value of composting for combustion fuel was to improve physical properties. However, the energy potential of feedlot manure diminished with composting time and time in storage. The drop in heat value was not significant for PC compared to FiC. 2. The DAF HHV was almost constant for ration, FB-raw, PC, and FiC. 3. The N and S contents, per mmBTU, increased with composting.

Fig. 9. Ash acidic and basic percentage vs. composting time.

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4. The fuel N, per mmBTU, in FB, was high compared to coal which may result in increased NOx emission. 5. The alkaline oxide percentage decreased with composting. 6. On the basis of heating value and alkaline oxide, the PC is better fuel compared to raw-FB and FiC. Hence, partial composting seems preferable to a full composting cycle. 7. The addition of , 5% crop-residues had little effect on heating values. 8. Even though the percentage of alkaline oxides in ash decreased with composting, the total amount of alkaline oxides increased due to an increase in the percentage of the ash. 9. The adiabatic flame temperature for most of the biomass fuels can be empirically correlated with ash and moisture percentage.

5. Future work Co-firing experiments need to be performed in order to determine the combustion performance in a boiler burner. Particularly the NOx emissions and fouling behavior need to be determined. Parts II and III of this paper will address these issues using TAMU’s small-scale 30 MW (part II) and DOE-pilot scale 150 MW (part III) boiler burner facilities.

Acknowledgements The Texas Higher Education Coordinating Board (THECB) under the 1997 –1999 Advanced Technology Program (ATP) provided primary funding for the project, ‘Biosolid Fuel Blends for Power Generation and Reduction of Pollutants’. The services of personnel and equipment provided by DOE/FETC as in-kind contribution to the ATP project on coal/feedlot manure blends was very significant, as was a research grant from TCFA, and the in-kind contribution of laboratory analysis by Southwestern Public

Service Company/New Century Energy Company. Appreciation is extended to Mark Freeman and Dr Mehandra Mathur, DOE Energy Technology Laboratory, for their leadership in organizing and conducting pilot plant tests at Pittsburgh. The work is also partially supported by DOE – NETL DE-FG26-00NT40810 (2000 – 2002) and DOE – Nebraska WRBEP 55026 (1999 – 2001).

References [1] Annamalai K, Puri I. Advanced thermodynamics engineering. Boca Raton, FL: CRC Press; 2001. software at www.CRCpress.com/ Electronic download/Advanced Thermodynamics Engineering. [2] Annamalai K, Ibrahim MY, Sweeten JM. Experimental studies on combustion of cattle manure in a fluidized bed combustor. J Energy Resour Technol 1987;109(2):49– 57. [3] Annamalai K, Ryan W. Interactive processes in gasification and combustion. II. Isolated carbon coal and porous char particles. Prog Energy Combust Sci 1993;19:383 –446. [4] Annamalai K, Frazzitta S, Sweeten JM. Combustion of feedlot manure for energy recovery. Proceedings, Livestock Waste Streams: Energy and Environment, Texas A&M University System, Amarillo, TX; August 4, 1997. p. 34–43. [5] Frazzitta S, Annamalai K, Sweeten JM. Performance of a burner with coal and coal–biosolid fuel blends. J Propul Power 1999;15(2): 181 –6. [6] Rodriguez P, Annamalai K, Sweeten J. The effect of drying on the heating value of biomass fuels. Trans ASAE 1998;41:1083–7. [7] Sami M, Annamalai K, Wooldridge M. Cofiring of coal and Biomass Fuel blends. Prog. Energy Combust Sci 2001;27:171–214. [8] Sweeten JM, Egg RP, Reddell DL, Varani F, Wilcox S. Characteristics of cattle feedlot manure in relation to harvesting practices. Agricultural waste utilization and management. Proceedings of the Fifth International Symposium on Agricultural Waste, Chicago, IL, December 16–17, 1985. p. 329–37. [9] Sweeten JM, Korenberg J, LePori WA, Annamalai K, Parnell CB. Combustion of cattle feedlot manure for energy production. Energy Agric 1986;5:55–72. [10] Tang H. Personal communication. Long Beach, CA 90810: Vortec Industries. Tel.: þ1-310-537-6624; 1999. [11] Winegartner EC, Rhodes BT. An empirical study of the relation of chemical properties to ash fusion temperatures. J Engng Power-T, ASME’97 1975;3:395–406.