The aim of the paper is the petrographic characterization of coal from the Wieczorek mine and the residues after its gasification. The coal was subjected to gasification in a fluidized bed reactor at a temperature of about 900°C and in an atmosphere of oxygen and CO2. The petrographic, proximate, and ultimate analysis of coal and char was performed. The petrographic composition of bituminous coal is dominated by macerals of the vitrinite group (55% by volume); macerals of inertinite and liptinite groups account for 23% and 16.0%, respectively. In the examined char, the dominant component is inertoid (41% vol.). Mixed dense and mixed porous account for 10.9% and 13.5% vol., respectively. In addition, the examined char also contained unreacted particles such as fusinoids, solids (11.3% vol.), and mineroids (5.1% vol.). The char contains around 65% vol. of low porosity components, which indicates a low degree of carbon conversion and is associated with a low gasification temperature. The char was burned and the resulting bottom and fly ashes were subjected to petrographic analysis. Their composition was compared with the composition of ashes from the combustion of bituminous coal from the Wieczorek mine. Bottom ashes resulting from the combustion of bituminous coal and char did not differ significantly in the petrographic composition. The dominant component was mineroid, which accounted for over 80% vol. When it comes to fly ash, a larger amount of particles with high porosity is observed in fly ash from bituminous coal combustion.
Rare earth elements are characterized by the high risk of their shortage resulting from limited resources. From this reason REE constitute a group of elements of special importance for the European Union. The aim of this study was to evaluate ashes from the burning of coal in fluidized bed boilers as an potential source of REY . Twelve samples of fly ash and bottom ash taken from power plants in Poland were analyzed. Tests have shown that despite some differences in chemical composition, the fly ash and bottom ash from fluidized beds could be classified as the calsialic, low acid type. It was found that fly ashes contained more REY than bottom ashes. Among REY , the light elements (LREY ) had the highest share in the total REY content in both fly ashes and bottom ashes. Heavy elements (HREY ) had the lowest content. The normalized curves plotted for fly ash samples within almost all of their entire range were positioned above the reference level and these curves were of the L-M or H-M type. The content of the individual REY in these samples was even twice as high as in UCC . The normalized curves plotted for bottom ash samples were classified as of L, L-M or H type. They were positioned on the reference level or above it. The content of the individual REY in these samples was the same or up to about 4 times lower than in UCC. It was found that the content of critical elements and of excessive elements in fly ash and bottom ash differs, which has an effect on the value of the outlook coefficient Coutl, and which is always higher in the case of fly ash than in the case of bottom ash. Nevertheless, the computed values of the outlook coefficient Coutl allow both fly ash and bottom ash from fluidized beds to be regarded as promising REY raw materials.
The phase composition of the cement paste phase of concrete containing fly ash from circulating fluidized bed combustion (CFBC) was studied. The motivation was to broaden the knowledge concerning the microstructure and the durability of concrete containing new by-products from the power industry. Several air-entrained concrete mixes were designed with constant water to binder ratio and with substitution of a part of the cement by CFBC fly ash (20%, 30% or 40% by weight). X-ray diffraction tests and thermal analysis (DTG, DTA and TG) were performed on cement paste specimens taken from concrete either stored in water at 18° C or subjected to aggressive freeze-thaw cyclic action. The evaluation of the phase composition as a function of CFBC fly ash content revealed significant changes in portlandite content and only slight changes in the content of ettringite. The cyclic freeze-thaw exposure did not have any significant influence on the phase composition of concrete with and without the CFBC fly ash.
The objective of this investigation was comparing the penetration of chloride ions in ordinary and air-entrained concretes containing a waste material Fluidized Bed Combustion Fly Ash (FBCFA). All concretes were tested with 15% and 30% cement replacement by FBCFA, with the same water-binder ratio of 0.45. Two kinds of fly ash coming from fluid bed combustion in two power plants in Poland have been used. In this study the rapid chloride permeability test – Nordtest Method BUILD 492 method – was used. The microstructure of the concrete was analyzed on thin polished sections and the measurement of air voids sizes and their distribution, using digital image analysis, was carried on according to PN-EN 480-11:2008. Obtained results have shown a significant influence of partial cement replacement by FBCFA on the chloride ions movements in concrete. It has been found that this kind of addition reduced considerably the chloride ion penetration. The influence of air entrainment on the chloride diffusion coefficients was also measured and it was shown that application of air-entraining admixture for concretes with FBCFA reduce the chloride diffusion coefficient but it should be used with caution.