Spectral Thermal Radiation Characteristics of Coal Ashes and Slags: Influence of Chemical Composition and Temperature

2003 ◽  
Author(s):  
S. Linka ◽  
S. Wirtz ◽  
V. Scherer
Keyword(s):  
Heat Transfer ◽  
Chemical Composition ◽  
Thermal Radiation ◽  
Coal Ash ◽  
Spectral Emissivity ◽  
Department Of Energy ◽  
Radiation Characteristics ◽  
Transfer Rates ◽  
Inorganic Species ◽  
Coal Ashes

During the combustion of pulverized coal, ash particles (formed from inorganic species) can deposit on heat-transfer surfaces, resulting in a decrease in heat transfer rates and system efficiency. In addition to the knowledge of the thermal conductivity of the deposits it is necessary to obtain information on the thermal radiation characteristics of the furnace walls to predict the influence of ash sedimentation on heat transfer. At the Department of Energy Plant Technology investigations on the spectral emissivity of different coal ashes and slags were performed applying a spectral radiometer. The samples were electrically heated. Temperatures were varied between 600 and 1400 °C. Emissivities in the range of wavelengths from 1 to 15 μm have been determined. An essential result is that coal ashes show selective thermal radiation characteristics. The main factor of influence on the emissivity is the chemical composition. Therefore, measurements on the single phases SiO2, Al2O3 and MgO were carried out and compared with the emissivity of typical coal ashes and slags. Furthermore, the emissivity depends on temperature, mainly in the wavelength range from 1 to 6 μm.

Theoretical Predictions of Spectral Emissivity for Coal Ash Deposits

2013 ◽  
Author(s):  
Dong Liu ◽  
Yuan-Yuan Duan ◽  
Zhen Yang
Keyword(s):  
Heat Transfer ◽  
Chemical Composition ◽  
Coal Ash ◽  
Spectral Emissivity ◽  
Radiative Properties ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Chemical Compositions ◽  
Boiler Efficiency ◽  
Ash Deposit

Ash deposits decrease the boiler efficiency, reduce the generating capacity and cause unscheduled outages. The radiative heat transfer is the major heat transfer mechanism in utility boilers; thus, the ash deposit emissivity is critical to boiler efficiency and safety. This paper presents a radiative transfer model to predict the spectral emissivities of coal ash deposits. The model includes the effects of the microstructure, chemical composition and temperature. Typical ash deposit microstructures are generated using diffusion-limited aggregation (DLA). The radiative properties are then calculated using the Generalized Multiparticle Mie-solution (GMM). The combined GMM and DLA model predicts spectral emissivity better than the original Mie theory and Tien’s dependent scattering theory with the average relative difference between predicted results and experimental data decreasing from 17.7% to 8.1% for sample 1 and from 16.5% to 4.2% for sample 2. Maxwell-Garnett effective medium theory is used to calculate the ash deposit optical constants based on the chemical compositions to include the effect of chemical composition. Increasing temperatures increase the particle diameters and particle volume fractions and, thus, the spectral emissivities. The spectral emissivity ultimately remains constant and less than one. The homogeneous slab model gives the upper limit of the ash deposit spectral emissivity.

Theoretical Predictions of Spectral Emissivity for Coal Ash Deposits

2014 ◽  
Vol 136 (7) ◽  
Author(s):  
Dong Liu ◽  
Yuan-Yuan Duan ◽  
Zhen Yang ◽  
Hai-Tong Yu
Keyword(s):  
Heat Transfer ◽  
Chemical Composition ◽  
Coal Ash ◽  
Spectral Emissivity ◽  
Radiative Properties ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Chemical Compositions ◽  
Boiler Efficiency ◽  
Ash Deposit

Coal ash inevitably forms deposits as combustion residue on the walls and heat transfer surfaces of coal-fired boilers. Ash deposits decrease the boiler efficiency, reduce the generating capacity, and cause unscheduled outages. The radiative heat transfer is the major heat transfer mechanism in utility boilers; thus, the ash deposit emissivity is critical to boiler efficiency and safety. This paper presents a radiative transfer model to predict the spectral emissivities of coal ash deposits. The model includes the effects of the microstructure, chemical composition, and temperature. Typical ash deposit microstructures are generated using diffusion-limited aggregation (DLA). The radiative properties are then calculated using the generalized multiparticle Mie-solution (GMM). The combined GMM and DLA model predicts spectral emissivity better than the original Mie theory and Tien's dependent scattering theory with the average relative difference between predicted results and experimental data decreasing from 17.8% to 9.1% for sample 1 and from 18.6% to 4.2% for sample 2. Maxwell-Garnett (MG) effective medium theory is used to calculate the ash deposit optical constants based on the chemical compositions to include the effect of chemical composition. Increasing temperatures increase the particle diameters and particle volume fractions and, thus, the spectral emissivities. The spectral emissivity ultimately remains constant and less than one. The homogeneous slab model gives the upper limit of the ash deposit spectral emissivity.

scholarly journals Ash Characteristics and Selected Critical Elements (Ga, Sc, V) in Coal and Ash in Polish Deposits

Resources ◽  
2020 ◽  
Vol 9 (9) ◽  
pp. 115
Author(s):  
Barbara Bielowicz
Keyword(s):  
Chemical Composition ◽  
Bituminous Coal ◽  
Raw Materials ◽  
Coal Ash ◽  
Proximate Analysis ◽  
Petrographic Composition ◽  
Critical Elements ◽  
Icp Ms ◽  
Coal Ashes ◽  
The Relationship

The chemical composition of coal ash and the content of the critical elements Ga, Sc, and V in coal and ash are examined herein. In this study, lignite and bituminous coal from Polish deposits were used. The coals were subjected to ultimate and proximate analysis; the petrographic composition was determined based on maceral groups. The chemical composition of ash and the content of critical elements were determined using ICP-MS. The obtained results were correlated and Pearson’s linear correlation coefficient was determined. Based on the correlation analysis, the relationship between the chemical composition of ash and the proximate and ultimate analyses was demonstrated. The content of selected critical elements in the tested deposits was lower than the Clarke value in coal. However, in some deposits these contents are much higher in coal ashes. The higher levels of Ga, V, and Sc in the ash are associated with Al2O3. Therefore, it can be stated that ashes can be a potential source of some raw materials. The highest concentrations of critical elements in coal and ash were recorded in the Lublin Coal Basin. Supra-Clarke contents of Ga, V, and Sc were recorded in the Bogdanka coal mine.

Total Absorptivities and Emissivities of Particulate Coal Ash From Spectral Band Emissivity Measurements

1984 ◽  
Vol 106 (4) ◽  
pp. 771-776 ◽  
Author(s):  
T. F. Wall ◽  
H. B. Becker
Keyword(s):  
Radiative Transfer ◽  
Spectral Band ◽  
Flame Temperature ◽  
Coal Ash ◽  
Spectral Emissivity ◽  
Fe2o3 Content ◽  
Ash Layer ◽  
Coal Ashes ◽  
Emissivity Measurements

Previous measurements of the spectral emissivity of coal ashes are converted to total absorptivities and emissivities. Below the temperature at which ash sinters, the total absorptivity of an ash layer—which is necessary for the estimation of radiative transfer in furnaces—is shown to depend on both the source (flame) temperature and the ash temperature. Synthetic mixtures of the oxides Al2O3, SiO2, and Fe2O3 are shown to give the same trends as those for ashes of the same Fe2O3 content.

Thermal Radiation in Packed and Fluidized Beds

1988 ◽  
Vol 110 (4b) ◽  
pp. 1230-1242 ◽  
Author(s):  
C. L. Tien
Keyword(s):  
Heat Transfer ◽  
Thermal Radiation ◽  
Fluidized Beds ◽  
Radiative Properties ◽  
Phase Boundaries ◽  
Radiation Characteristics ◽  
Theoretical Predictions ◽  
Systems Models ◽  
Reflectance Data

The present work gives an overview of the existing knowledge on radiative transfer in packed and fluidized beds. Special emphasis is given to the proper usage and determination of radiation characteristics of the particles in these systems. Models that treat the particulate bed as a continuum are discussed along with those that consider the system as discontinuous, i.e., accounting for the phase boundaries between the gas and the particles. Existing experimental techniques for determining the radiative properties are presented, and the published bed transmittance and reflectance data are discussed and compared with the theoretical predictions. Interaction of radiation with other modes of heat transfer is also examined.

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