ISSN 1070-4272, Russian Journal of Applied Chemistry, 2007, Vol. 80, No. 3, pp. 495 ! 497. + Pleiades Publishing, Ltd., 2007.
Original Russian Text + N.F. Fedorov, M.A. Andreev, 2007, published in Zhurnal Prikladnoi Khimii, 2007, Vol. 80, No. 3, pp. 499!501.
Specific Features of Thermal Dissociation of Magnesite
in Calcination in Furnaces with a Solid Metallic
N. F. Fedorov and M. A. Andreev
St. Petersburg State Institute of Technology (Technical University), St. Petersburg, Russia
Received April 4, 2006; in final form, September 2006
Abstract-The kinetics of thermal decomposition of magnesite in a furnace in which the gaseous heat-transfer
agent is replaced with a solid metallic heat-transfer element was studied.
Decarbonation processes are the most energy-con-
suming stage of thermal treatment in manufacture of
technical products, such as lime, portland cement,
caustic magnesite, and caustic dolomite. In the con-
ventional firing technology, raw materials are decom-
posed in rotary kilns by the energy of flue gases. It
has been suggested [13 4] to intensify the thermal de-
composition of the material by using a liquid metallic
heat-transfer agent, which provides a thermal-shock
action on a material being fired. However, this solu-
tion involves a number of negative factors, the main
of which are the complicated choice and high cost of
the liquid metallic heat-transfer agent, intricate ap-
paratus and stringent requirement to this equipment,
contamination with the heat-transfer agent of the
material being treated, and loss of the heat-transfer
agent with a porous material.
All these factors preclude wide industrial use of
liquid heat-transfer agents and require that alternative
modes of heat treatment by thermal shock should be
sought for. A possible solution is replacement of a
liquid metallic heat-transfer agent with a solid one.
Even though the coefficient of heat transfer from a
solid metal to a material being processed is inferior to
that in transfer of thermal energy from a molten metal
to a solid substance, the former is still sufficiently
high and markedly exceeds that for a gaseous heat-
transfer agent. This is the principal factor responsible
for the acceleration of solid-phase transformations.
In addition, the possibility of using induction heating,
which is known to provide the highest efficiency in
conversion of electric energy into heat, counts in favor
of the solid metallic heat-transfer agent. Finally, it is
necessary to take into account the fact that replace-
ment of a liquid metallic heat-transfer agent with
a solid one shows promise of a less intricate equip-
ment of the firing device.
In view of the aforesaid, it seems appropriate to
study thermal decomposition of inorganic substances
under conditions of a thermal shock produced when
a material to be thermally treated is brought in contact
with a solid metal heated to a prescribed temperature.
We consider the process of magnesite decomposi-
tion by thermal-shock calcination to magnesium
oxide, whose application area includes such branches
of chemical industry as technology of building ma-
terials, refractories, binders, and materials for elec-
tronics and electrical engineering, medicine, and
cosmetology [5, 6].
We used magnesite of composition (wt %) SiO
1.5, CaO 0.49, MgO 46.14, R
1.27, and calcina-
tion loss 50.60, from the Savinskoe deposit. The
dependence of the degree of decomposition of mag-
nesite on its residence time in the furnace and on the
calcination temperature was studied. The starting
magnesite was placed, in the form of 335-mm lumps,
to produce a monolayer on the metallic heat-transfer
agent heated to the temperature of the experiment and
was kept there for a prescribed time. The temperature
range 7003900oC was studied. In parallel, we per-
formed thermal treatment with a gaseous heat-transfer
agent, for which purpose a sample was placed in
a heated muffle surface. For the calcined material, we
evaluated the degree of conversion by measuring the
calcination loss (900oC, 1 h).
Figure 1a shows kinetic curves of thermal decom-
position of magnesite at various temperatures on a