REFRACTORY MATERIALS FOR THE LINING
OF THERMAL POWER UNITS
I. D. Kashcheev
Translated from Novye Ogneupory, No. 1, pp. 70 – 75, January, 2005.
Refractory and heat-insulating materials perform a major
function in industrial power engineering — preserving heat
and maintaining a stable operating temperature. The use of
advanced heat-insulating refractory materials allows preserv
ing heat and significant economy of energy reserves. At pres
ent, a larger part of industrial heating units and furnaces in
Russia are severely depreciated and are badly in need of up
dating ; for this reason, preserving heat and economizing
energy reserves is an issue of urgent concern which requires
a prompt solution.
Two parameters are important for evaluating the heat-in-
sulating property of a refractory material: (i) long-term ser-
vice temperature and (ii) cumulative capacity . The latter
quantity comprises the major thermophysical properties of a
material; it is expressed by the heat build-up factor b,
W × sec
× K), which is defined by the formula
where l is the heat conductivity, W/(m × K); c is heat capa
city, kJ/(kg × K), and r is the density, kg/m
For practical analysis by Eq. (1), the heat conductivity
and heat capacity of refractory materials of average composi
tion are typically used. Formulas for l and c available from
the literature may look somewhat different depending on the
interpolation expressions used.
It should be kept in mind, however, that the heat capacity
is mainly a function of the refractory composition, and in
practical calculations one can use the additivity rule with
quite acceptable accuracy:
is the mass fraction of the ith components for a par
ticular refractory composition and c
is the average heat ca
pacity of the ith component, kJ/(kg × K).
The heat conductivity of a refractory material is con
trolled mainly by the composition and pressure of the gas
medium in the furnace. Quoted handbook data on heat con
ductivity refer typically to standard atmospheric conditions.
Still, the heat conductivity of a material is also a function of
the material’s phase composition, density, porosity, and other
factors. However, the actual heat conductivity may differ
from tabular data by 50% even within the same production
batch. For practical calculations, the semi-empirical formula
= a + bT + cT
is widely used, where l
is the effective heat conductivity,
W/(m × K); a, b, and c are empirical constants specific of
each particular refractory; T is the temperature, K. The con-
stants parametrize effects due to all kinds of heat conductivity.
During long-term service under comparatively stable
temperature conditions, the refractory heat conductivity tends
to increase by 10 – 15%, whereas under variable temperature
conditions, the heat conductivity tends to decrease because
of the refractory’s structural degradation (development of
microcracks). Proceeding from the assumption that the heat
conductivity of a refractory is an additive function of the
phase composition and, at high temperatures, is independent
of the macrostructure, heat capacities and heat conductivities
of refractory materials have been calculated using relation
ships given in . Relevant data are given in Tables1–3.
Numerical analysis of the thermophysical properties of
refractories as those in Tables 1 – 3 is an arduous task. For
one thing, the structure of actual refractory materials is sel
dom (if ever) regular; typically, it features a wide range of
heterogeneities (phase inclusions, pores, grain boundaries,
etc.) differing in shape and size and varying in concentration
(in size, inclusions may be of the same order of magnitudes
as the spacing between them). In size, heterogeneities may
vary from some tenths of a micrometer to tens and hundreds
Refractories and Industrial Ceramics Vol. 46, No. 2, 2005
1083-4877/05/4602-0147 © 2005 Springer Science+Business Media, Inc.
Ural State Technical University, Ekaterinburg, Russia.