USE OF MINERAL COAL ASHES
IN INSULATING REFRACTORY BRICK
S. R. Bragança,
and C. P. Bergmann
Translated from Novye Ogneupory, No. 6, pp. 60 –63, June 2008.
Original article submitted December 19, 2007.
Coal ash from Candiota thermoelectric power plant in southern Brazil is a waste generated in great amount.
Current estimates indicate that coal ash production is likely to reach 2.000.000 tons per year. Of this total, only
10% are commercialized, so the price of this material is very low. In this work, it was investigated the use of
coal ashes in a composition of refractory insulating brick. In coal combustion process, fly ashes and bottom
ashes are generated. Bottom ashes are formed by partially fused ashes that precipitate to the bottom of the
boiler, due to their coarser particle size. Therefore, it was analyzed fly ash addition in a refractory body and the
addition of bottom ashes, partially replacing chamote (calcinated clay). The results showed that the effect of
the ash is small in the fired materials. In terms of technological characterization, the bricks formulates with
coal ash were considered suitable to commercial brick standards. Density and thermal conductivity of the
refractory bricks with coal ashes had revealed to be similar the commercial products. Then, the use of ash is
economical attractive and technical feasible.
Currently, one of the most important points for the
industry is energy conservation. Therefore, there is an
increase in the use of insulating bricks, made for different
temperature ranges, fully taking care of save energy require
ments. They are used in the thermal insulation of furnaces,
boilers, incinerators, etc, due to their structural resistance at
The new demand on the exploitation of waste materials
in industrial process must convert the discharged residues
(secondary raw material) into a commercial product. The ad
vantages to use residues are: saving energy, saving natural
resources, and to bring in return to the productive cycle what
it is put away. Engaged in this concept, is the use of coal
ashes, as a way of reducing the cost of refractory bricks.
In Candiota Thermoelectric Power Plant in southern
Brazil, just a part of generated ashes is commercialized,
manly to the cement industry, remaining approximately 90%
of the production returning towards to coal pit mine .
Therefore, a huge amount is available to make use of in a
product or by-product. In a consequence of this fact, ashes
present low commercial value, what make their use econo-
In this work, it was evaluated the utilization of coal
ashes, in a composition of refractory insulator body that
basically uses in its formularization kaolin, chamote and
sawdust. As it is known, kaolin generates refractory phases,
like mullite . Chamote facilitates the drying process and
reduces the retraction of the product. Sawdust is all elimi
nated during firing process, generating porosity in the
product. The coal ash effect in final product was evaluated
by performing technological properties, according to the
ASTM standards [3 – 5]. Coal ashes, being a fired product,
must show low reactivity to water in the forming body,
making easier the drying stage; therefore, it can be used as a
substitute to chamote. This fact was also investigated here.
MATERIALS AND METHODS
Technological properties of an industrial ceramic body of
insulating refractory bricks with the addition of fly ash were
evaluated. The composition of the commercial ceramic body
used in this work is composed of: kaolin 60%; chamote 20%
and sawdust 20%. Two ceramic bodies were prepared with
the addition of 5 and 10% weight of fly ash in the commer
Refractories and Industrial Ceramics Vol. 49, No. 4, 2008
1083-4877/08/4904-0320 © 2008 Springer Science+Business Media, Inc.
Materials Department, Federal University of Rio Grande do Sul,