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.
Combustion profiles of coal-limestone-paper blends were studied using thermogravimetric/ Fourier transform infrared spectroscopy
(TG/FTIR). The role of limestone in promoting the initial combustion of coal-paper blends and its ability to absorb sulphur
oxides were examined.
Limestone and monocrystalline calcite tempers (grains) are abundant in ancient pottery. In pottery from the Canaan area the
former is common in Iron Age storage and table-ware vessels and the latter is present in cooking pots. Limestone is much more
widespread than monocrystalline calcite and the potters used it often as tempers when manufacturing pottery vessels, but usually
not for cooking pots. While defects appear frequently around limestone tempers, they do not appear around monocrystalline
calcite ones. This study examines the reason for using the latter tempers rather than the former ones.
Raw materials of carbonate tempers in a clay matrix were fired and the decarbonation process was followed by quantitative
IR thermospectrometry. The results indicate that the monocrystalline calcite tempers prevent formation of defects in the cooking
pots during firing or during use. The reasons for this are higher thermostability at elevated temperatures, lower intensity
of decarbonation, and retention of grain shape, as compared to limestone tempers.
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.
Authors:S. Felder-Casagrande, H. Wiedemann, and A. Reller
The calcination of limestone is one of the oldest technical processes and it is still of actual interest. Very early calcitic
mortars from Turkey have been investigated and compared with materials of other early civilisations i.e. with Egyptian mortars
containing gypsum as well as medieval dolomite-based mortars from alpine regions. Contemporary calcination procedures, in
particular the cement production, range among the most important global industrial processes causing non neglectable environmental
problems. Sustainable, solar energy assisted calcination technologies and the conversion of product CO2 into useful commodities are discussed.
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.
Authors:V. F. Rahhal, E. F. Irassar, M. A. Trezza, and V. L. Bonavetti
/flocculation state of the particles [ 7 ], the type and amount of mineral addition used [ 8 , 9 ], the presence of chemical admixtures [ 10 ] and the curing temperature [ 11 ].
The production of Portland limestone cement (PLC) rises around the world due to