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Article Number , December 2016
CFD Modelling of Pulverized Coal Combustion in Blast Furnace Test Rig
Ari Vuokila1, Riitta L. Keiski1, Esa Muurinen1, Olli Mattila2
1. University of Oulu, Finland
2. SSAB Europe, Finland
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Pulverized coal is the most common auxiliary fuel used in blast furnaces. Auxiliary fuels are used to replace expensive coke as a reducing agent for iron oxides. High amounts of pulverized coal injection lead to permeability changes in a blast furnace shaft together with an excess amount of unburnt coal. Permeability issues can be tackled with an adjusted charging program, but poor pulverized coal combustion will not enable cost efficient substitution of coke with coal. The only way to overcome this limit is to improve the conditions in pulverized coal combustion. The aim of this study was to create a combustion model for pulverized coal, which could be used to locate limiting factors in auxiliary fuel combustion in the actual blast furnace. Experimental results were used to validate the combustion model. The CFD model had a good agreement with experimental results with different types of coals. According to this study, this kind of combustion model can be used to study the blast furnace operation.
CFD, blast furnace, coke, auxiliary fuel
* Corresponding Author:
Article Number 201602, November 2016
Investigation of modelling approaches for scattering and absorption properties of particles in pulverized coal combustion
Tim Gronarz1, Martin Habermehl1, Oliver Hatzfeld1, Reinhold Kneer1
1. Institute of Heat and Mass Transfer
RWTH Aachen University, Augustinerbach 6, 52056 Aachen, www.wsa.rwth-aachen.de. email@example.com
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For the combustion of solid fuels, thermal radiation is of high importance. Numerical simulation of these processes requires a detailed description of thermal radiative transport. The present paper investigates the scattering of thermal radiation by particles in numerical simulations. Mie theory is assumed to provide an exact description for radiative properties. As the evaluation of the equations obtained from Mie theory is very time consuming, approximate phase functions are used to describe scattering of radiation by particles. These approximations can be evaluated very fast at the expense of shortcomings in precision. To match the accuracy achieved by elaborate models for other sub-processes of coal combustion, new models with an increased precision must be identified. In this work, a quantitative investigation of the effect of commonly used approximate phase functions (Henyey-Greenstein and Delta-Eddington) on the distribution of thermal radiation was carried out. Integration over a discrete spectral interval was performed. The influence of particle size distribution and also varying refractive indices of the particles were taken into account. The results of the approximated methods were compared to the exact solutions obtained by Mie theory. It was found that the choice of the phase function has a significant influence on the distribution of radiation. After integration, a deviation of about 10-20 % was observed for forward scattering, while for other angular directions, the results differed up to a factor larger than 3 compared to the Mie theory reference case. For the spectral discretization into a low number of bands, an influence of the distribution of radiation within each band on the total scattered intensity was found. Therefore, the use of a distribution function based on black body radiation is proposed. Furthermore, a tabulation and interpolation approach for the representation of radiative properties is presented and discussed. Finally, different approximations for the scattering phase function are applied in a heat transfer calculation and the influence is discussed.
scattering, phase functions, particles, coal, ash, solid fuel combustion, numerical simulation, Mie theory
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Article Number 201601, March 2016
Online Alkali Measurement for Fuel Quality Control in Biomass-operated Boilers
Tomas Leffler1, Magnus Berg1, Tomas Leffler2, Christian Brackmann2, Zhongshan Li2, Marcus Aldén2
1. Vattenfall Research and Development AB
2. Division of Combustion Physics, Lund University
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Today’s power plants are shifting their combustion toward a more complex fuel mix on grounds of environmental impact, cost, availability and regulations. New types of fuel can be classified into the following groups: herbaceous material (straw and grass), agricultural by-products (pits, shells and hulls), wood and waste fuels. These fuels contain various amounts of alkali metals, mainly potassium and sodium, as well as chlorine and sulphur, which are easily vaporised in the combustion process and involved in processes that cause severe slagging, fouling and high-temperature corrosion problems in the furnace and further downstream in the boiler. In order to evaluate fuel quality in terms of generating harmful alkali chlorides, an online alkali-chloride-monitoring instrument provides valuable information. This has been achieved using an online alkali-monitoring device that measures the sum of alkali chlorides (potassium chloride and sodium chloride) based on ultraviolet absorption. Combustion of three different biomass fuel mixes has been investigated in a circulating fluidized bed boiler. In addition, two batches of wood biomass fuel were compared during combustion in a full-scale powder fuel boiler. In all cases the impact of changes in fuel composition on alkali-chloride formation levels could be monitored quantitatively with a time resolution in the order of seconds, allowing for analysis and countermeasures. Thus, the employment of an online alkali monitoring device to prevent alkali-chloride problems is a cost-efficient, sustainable solution that extends the operational time and reduces the maintenance costs of the boiler.
alkali metals, prevention of slagging, fouling and high-temperature corrosion, reduced maintenance cost
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