STUDY OF ALKALI RESISTANCE OF REFRACTORY MATERIALS
USED IN BOILERS OPERATING ON WOOD FUEL
and P. Zdanevièius
Translated from Novye Ogneupory, No. 12, pp. 42 – 45, December, 2016.
Original article submitted April 6, 2016.
Using the ASTM C 454–83 method alkali resistance is studied for various refractories (chamotte brick, tradi
tional and medium-cement chamotte concrete) used most often in power generation boilers operating on wood
fuel. Resistance to alkali of medium-cement concrete developed by the authors with a filler prepared from
sinter grade Gorkal-50 (produced by the Gorka Plant, Poland) is also studied. It is established that use of
milled quartz sand additive improves resistance of the test cement significantly towards the action of alkaline
is used in the work) at 1100°C. It is shown that the test additive during action of alkali facilitates
formation of a protective layer that prevents penetration of K
decomposition products into the material
Keywords: refractory materials, concrete heat resistance, sinter filler, alkali resistance.
It is noted that in boilers operating on wood fuel refrac-
tory materials of a lining are subject to significant thermal,
mechanical, and chemical loads . It is quite often the case
when there is unexpected lining breakdown after
6 – 8 months of operation [2, 3]. This material breakdown
occurs due to combined action of the following factors: high
temperature, chemical action of wood fuel combustion prod
ucts, abrasive wear by solid particles (in boilers with a
fluidized bed or having a tube flushing system), thermal
shock with frequent boiler start-up and shut-down for ash
Lining breakdown is often observed with use of wood fuel
containing an increased amount of alkali (K, Na) compounds.
During burning of this fuel K and Na are released in a vapor
condition. They react with other fuel combustion products,
forming alkali compounds, acting on lining material. Mate
rial alkali corrosion, caused by reaction with wood ash, often
becomes one of the main reason for rapid breakdown of alu
minosilicate refractory materials. With ash sticking to the
surface of aluminosilicate refractory material there is reac
tion between the refractory minerals and alkali compounds.
As a result of this alkali reaction there is formation of
calcilite (K, Na)
, leucite K
feldspar minerals, etc. [4 – 6]. Formation of this class of ma-
terials occurs with an increase in mineral volume by
15 – 30%, and sometimes even by 55%. This causes stress
development in refractory material, and there is cracking that
leads to so-called alkali explosion .
In order to make penetration difficult into aluminosili
cate material enrichment with silicon oxide SiO
. During reaction of alkali at the surface of modified mate
rial there is formation of layer of glass of high viscosity,
which prevents further alkali penetration into the depth of
material. In some works it has been demonstrated that use of
adding silicon carbide filler [8, 9] also increases the resis
tance of aluminum silicate concrete to action of alkali salts.
Hard-burnt brick calcium aluminate filler in heat-resis
tant concretes is used extremely rarely, although these con
cretes exhibit good wear resistance . Research performed
in [10, 12] has shown that calcium aluminate filler is not re
sistant to action of alkali at 1100°C. It has been established
 that expansion of specimens prepared from different cal
cium aluminate phases (C
A, CA, CA
) during reaction with
O is 2 – 3%, and expansion of specimens of C
A is 15%.
The aim of this work is to study resistance to action of al
kali salt of aluminosilicate materials used most often in boil
ers operating wood biofuel, and also aluminosilicate concrete
developed by us with hard-burnt brick filler modified with
quartz sand additive.
Refractories and Industrial Ceramics Vol. 57, No. 6, March, 2017
1083-4877/17/05706-0651 © 2017 Springer Science+Business Media New York
Vilnius Gediminas Technical University, Vilnius, Lithuania.