Comparative data are presented on the absorption rate and capacity for SO2 capture by a natural Polish limestone with and without sodium chloride additive. Two sets of experiments were carried out, under dry and wet conditions during limestone calcination and sulphation.
The role that can be played in the elucidation of the limestone sulphation mechanism by thermal analysis methods with some
specific procedures is discussed. Contrasting examples of applications of thermoanalytical techniques using the variable conditions
are provided. These examples deal with the programmed thermal analysis using different gas sequences, the influence the calcination
and sulphation conditions on the capture of SO2, the effect of catalysts on limestone sulphation and the thermal stability of CaSO3. Two proposed mechanisms were supported by the phase identification of the solid products.
The effects of the presence of a Pt catalyst on the limestone/lime sulphation process were investigated by thermal analysis methods to provide a better understanding of the factors limiting gas desulphurization when Ca-based sorbents are used. It was found that for the Pt-catalysed sulphation of precalcined limestone the weight increase is above 100% higher under isothermal and dynamic conditions (up to 830°C). These results are direct evidence that Pt catalyses the CaO-SO2-O2 reaction. It can be presumed that the process proceeds through a gaseous intermediate, SO3, a highly reactive gas, which explains the increased rate of sulphation. SO3 then reacts with CaO to form CaSO4 directly, in contrast with the non-catalysed oxidation of SO2 to SO3, where CaSO3 formation is the most probable early stage of sulphation. The proposed mechanisms were supported by the phase identification of the products.
Properties of limestone related to SO2/SO3 reactivity were investigated. Limestone calcined under different conditions (temperature, time and with/without additives)
yield calcines of distinctly different physical structures. The amount of pores and the size of the pores formed during calcination
The main purpose of the present work was to gain a better understanding and more reliable explanation of the temperature regime
for gas desulphurization using Ca-based sorbents in atmospheric fluidized-bed combustors.
Pore size, surface area and pore volume of each calcine were determined by mercury porosimetry and BET methods. At higher
calcination temperature and during longer time, sintering became significant and the obtained calcine had a smaller internal
surface area and thereby the average pore radius increased. The additives such as NaCl also accelerated sintering thus increasing
the pore size. The measurements of porosity were supplemented by scanning electron microscopic observations employed for qualitative
description of the pore structure. SEM micrographs are presented.
The reactions occurring between CaCO3/CaO and SO2/SO3 in oxidizing atmospheres are discussed. Calcination and sulphation were
carried out in a thermobalance under conditions relevant to atmospheric fluidized bed combustion. It is suggested that the
quality of limestones as potential SO2 sorbents can be assessed on the basis of tests carried out in a TG apparatus adapted
for use with corrosive gases. Limestone calcined under different conditions including the treatment with NaCl leads to changes
in surface texture. Sulphated samples were examined in a SEM by energy dispersive X-ray and backscattered electron imaging.
Two sulphur-bearing solids (CaSO4 and CaS) were identified. The sulphation rate and extent are determined by the product layer
diffusion. The amount of CaS present at the end of the process depends on the particle size of the sorbent.
It has been presented that the bulk mechanical alloying occurring in the Ni-hydroxycarbonate-aluminium mixture can produce
homogeneously refined composite of nickel aluminides with aluminium oxide. The control of mechanochemical phenomenon was carried
out by phase identification of milling products as well as their structural and morphological characterization. As a result
the thermoanalytical and X-ray powder diffraction measurements as well as scanning electron microscopy with backscattered
electron images (BSE) and X-ray energy dispersive spectroscopy (EDS) were applied. It was found that the kinetics of mechanochemical
reactions depends on the chemical nature of initial salt.</o:p>
A study of the kinetics of the thermal dehydration of syngenite was carried out using the isothermal gravimetric method. Weight changes of the samples were followed by means of a Mettler Thermoanalyzer. The applicability of nine equations commonly used to describe the thermal decomposition of solids was investigated. The experimental results can be best represented, over the whole temperature range of the change, by the Avrami equation I