Combustion characterization of coals for industrial applications. Final technical report, January 1, 1981-May 29, 1985

Nsakala, N.Y.; Patel, Rajeshriben; Lao, T.C.

doi:10.2172/5880865

Cited by 4 publications

(7 citation statements)

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“…The bulk ash chemistry analyses were renormalized excluding SO 3 , since SO 3 is also accounted for in the ultimate analysis. A calculation was then performed to determine the amount of air (oxygen and nitrogen) required to combust an amount of coal containing 1 gram of ash at 20% excess air.…”

Section: Fact Descriptionmentioning

confidence: 99%

Coal Slagging and Reactivity Testing

McCollor¹,

Eylands²,

Laumb³

2003

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Union Fenosa's La Robla I Power Station is a 270-MW Foster Wheeler arch-fired system. The unit is located at the mine that provides a portion of the semianthracitic coal. The remaining coals used are from South Africa, Russia, Australia, and China. The challenges at the La Robla I Station stem from the various fuels used, the characteristics of which differ from the design coal. The University of North Dakota Energy & Environmental Research Center (EERC) and the Lehigh University Energy Research Center (LUERC) undertook a program to assess problematic slagging and unburned carbon issues occurring at the plant.Full-scale combustion tests were performed under baseline conditions, with elevated oxygen level and with redistribution of air during a site visit at the plant. During these tests, operating information, observations and temperature measurements, and coal, slag deposit, and fly ash samples were obtained to assess slagging and unburned carbon.The slagging in almost all cases appeared due to elevated temperatures rather than fuel chemistry. The most severe slagging occurred when the temperature at the sampling port was in excess of 1500°C, with problematic slagging where first-observed temperatures exceeded 1350°C. The presence of anorthite crystals in the bulk of the deposits analyzed indicates that the temperatures were in excess of 1350°C, consistent with temperature measurements during the sampling period.Elevated temperatures and "hot spots" are probably the result of poor mill performance, and a poor distribution of the coal from the mills to the specific burners causes elevated temperatures in the regions where the slag samples were extracted. A contributing cause appeared to be poor combustion air mixing and heating, resulting in oxygen stratification and increased temperatures in certain areas. Air preheater plugging was observed and reduces the temperature of the air in the windbox, which leads to poor combustion conditions, resulting in unburned carbon as well as slagging.A second phase of the project involved advanced analysis of the baseline coal along with an Australian coal fired at the plant. These analysis results were used in equilibrium thermodynamic modeling along with a coal quality model developed by the EERC to assess slagging, fouling, and opacity for the coals. Bench-scale carbon conversion testing was performed in a drop-tube furnace to assess the reactivity of the coals.The Australian coal had a higher mineral content with significantly more clay minerals present than the baseline coal. The presence of these clay minerals, which tend to melt at relatively low temperatures, indicated a higher potential for problematic slagging than the baseline coal. However, the pyritic minerals, comprising over 25% of the baseline mineral content, may form sticky iron sulfides, leading to severe slagging in the burner region if local areas with reducing conditions exist.Modeling results indicated that neither would present significant fouling problems. The Australian coal was expected to s...

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Section: Fact Descriptionmentioning

confidence: 99%

Coal Slagging and Reactivity Testing

McCollor¹,

Eylands²,

Laumb³

2003

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“…Kinetic values were determined from the gravimetrically determined carbon loss data in Tables 3-2a-c using the formulation of Field (5, 6) as modified by Nsakala et al (7). The calculations are based on surface area, employing a shrinking core model.…”

Section: Kinetic Calculations and Modelingmentioning

confidence: 99%

“…[3][4][5][6][7][8][9] where K diff is the diffusional reaction rate coefficient and K s is the surface reaction rate coefficient. Units on K diff and K s are g/(cm 2 -s-atm).…”

Section: -11mentioning

confidence: 99%

“…[3][4][5][6][7][8][9][10] where AW is the atomic weight of carbon (12 g/mole); N is the molar ratio of product gases to reactant gases (equivalent to 2 for the reaction O 2 + 2C →2CO); D is the binary diffusion coefficient of oxygen in nitrogen in cm 2 /s; X is the average particle diameter in cm at time t; R is the ideal gas constant, 82.06 cm 3 atm /mole K; and T m is the temperature of the boundary layer in K (equivalent to T g when calculation was based on gas temperature and [T g + T particle ]/2 when calculation was based on calculated particle temperature).…”

Section: -11mentioning

confidence: 99%

“…[3][4][5][6][7][8][9][10][11][12][13][14][15] where , is the emissivity of particle and wall, taken as 0.8; F is the Stefan-Boltzmann constant, 1.36 × 10 -12 cal/cm-s K; and T wall is the furnace wall temperature in K. For these calculations, T wall = T g .…”

Section: -11mentioning

confidence: 99%

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Reducing Power Production Costs by Utilizing Petroleum Coke

Galbreath¹,

Toman²,

Zygarlicke³

1999

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EXECUTIVE SUMMARYThe effects of blending petroleum shot cokes with Powder River Basin (PRB) subbituminous coals on grindability, combustion reactivity, fouling/slagging, and electrostatic precipitator (ESP) fly ash collection efficiency were investigated over a 2-year period. Testing was conducted using three different laboratory-scale downfired combustion systems. Fly ash and deposit samples were analyzed using a variety of techniques, including inductively coupled plasma-atomic emission spectroscopy, x-ray diffraction, x-ray absorption fine-structure spectroscopy, wavelengthdispersive x-ray fluorescence spectrometry, scanning electron microscopy, electron probe microanalysis, and digital image analysis.A PRB subbituminous coal with a Hardgrove grindability index (HGI) of about 56 at 26 wt% moisture and a petroleum shot coke with an average HGI of 38 were used for testing the effects of parent fuel hardness on PRB coal-petroleum coke blend grindability. Samples of the PRB coal, petroleum shot coke, and coal-coke blends of 95:5 and 85:15 (on a weight basis) were pulverized under identical conditions. Ni and V analyses of three size fractions (<45 µm, $45 µm but <75 µm, and $75 µm) for each pulverized fuel indicate that the finest particle-size fraction of the petroleum coke is significantly enriched in V and Ni, whereas V and Ni are uniformly distributed among the three particle-size fractions of the pulverized PRB coal. The finest particle-size fractions of the coal-coke blends are not enriched in V and Ni relative to their coarser size fractions, suggesting that the softer Ni-and V-depleted coal particles are preferentially fractioned into the finest size fractions during pulverization.Combustion kinetic testing in a drop-tube furnace of a PRB coal, petroleum coke, and an 80 wt% PRB coal-20 wt% petroleum coke blend indicates that the parent fuels essentially burn independently of each other. It was demonstrated that the combustion kinetics of a given coalpetroleum coke blend in the drop-tube furnace can be predicted from those of the parent fuels because of the two-stage combustion process.Measurements of deposits (i.e., initial slagging temperatures, crushing strengths, and ash fouling deposition rates) produced from burning PRB coal-petroleum coke blends (coke blends of 0%, 10%, and 20% on a weight basis) in a drop-tube furnace under slagging and high-temperature fouling conditions indicate that petroleum coke blending with PRB coal impedes the rate of fouling deposit growth but promotes slagging and slag deposit strength. Although petroleum coke blending slows the rate of ash fouling deposition, it promotes ash sulfation and the formation of an anhydrite-rich base layer on tube surfaces.Testing of a PRB coal and two (95:5 and 85:15) coal-coke blends in a 42-MJ/hr (40,000 Btu/hr) downfired combustion system indicates that the primary effect of petroleum coke blending on flue gas composition is a significant increase in sulfur concentration. Sulfur speciation analyses using U.S. Environmental Protection Agenc...

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