REFRACTORIES IN HEATING UNITS
EFFECTIVE LINING FOR FURNACES USED TO MAKE COBALT
V. V. Slovikovskii
and A. V. Gulyaeva
Translated from Novye Ogneupory,No.12,pp.3–5,December, 2014.
Original article submitted October 13, 2014.
The reasons for the short life of the linings of furnaces used to make cobalt are analyzed along with the mecha
nism by which the refractories undergo wear. A refractory lining of a new composition and design has been de
veloped for Kuhlman furnaces. It is proposed that highly durable grade-MP periclase refractories based on
fused grains be used in the lining. Specific designs of lining have been developed for refractories of grades
MU and MP. The measures that were implemented have increased the durability of the linings of Kuhlman
furnaces at the combine “Yuzhuralnikel’” (in Orsk) by a factor of 1.8 – 2.0.
Keywords: fired refractories, fused refractories, chemical reactions, heat resistance, wear rate.
Metallic cobalt is produced in furnaces that have an inde-
pendent electric arc (a Kuhlman furnace) and are lined with
periclase refractories. The production process is carried out
at high temperatures (1550 – 1650°C) with abrupt thermal
cycling which takes place when the metal is tapped and when
the cold charge materials and wastes are charged onto the ex-
posed lining. The demanding operating conditions character-
istic of Kuhlman furnaces account for the short life of their
lining (8 – 12 heats), which is made of fired periclase re
fractories of grade MU.
Experience with the operation of metallurgical furnaces
shows that slag has the greatest effect on the wear of the re
fractory lining. The most heavily worn section of the lining
of Kuhlman furnaces is the area opposite the electric arc in
side the annular region of the furnace’s drum. This region is
up to 450 mm wide, i.e. it encompasses nearly two 230-wide
courses of the refractory. The thickness of the working layer
of the lining in Kuhlman furnaces is 80 – 85 mm by the end
of the campaign.
To determine the mechanism responsible for the failure
of the lining, we obtained specimens of the periclase refrac
tory that had been in use in a furnace lining for different peri
ods of time. Visual inspection of the used refractories re
vealed the presence of two zones: the working zone and a
transitional zone. The refractories contained roughly twice as
as they did originally, while their content of CaO
was more than five times greater than the initial value (Ta-
ble 1). The refractory also contained new phases: sulfur, flu-
orine, and cobalt.
Petrographic studies of the zones of the MU refractory
(Fig. 1) showed that the working zone consists of a loose
rose-colored material that readily crumbles into a powder
with a coarseness of 1 – 0 mm. The working zone has a
thickness of 15 – 20 mm and consists of fractured grains of
periclase with a size of 20 – 50 mm, silicates, and metallic in
clusions of cobalt. Accumulations of periclase grains that
form aggregates of up to 22 mm are seen in isolated loca
tions. Films of silicates are seen between the grains, these
Refractories and Industrial Ceramics Vol. 55, No. 6, March, 2015
1083-4877/15/05506-0495 © 2015 Springer Science+Business Media New York
Ural Federal University, Ekaterinburg, Russia.
TABLE 1. Chemical Composition of the Slag and Grade-MU
Refractories before and after Service
CaO MgO Fe
Slag I 9.85 54.34 9.22 1.64 2.87 6.5 12.39 —
Slag II 7.06 54.64 7.10 1.06 1.35 13.62 15.17 —
working zone 3.97 16.96 55.73 1.55 2.68 4.07 14.35 0.69
transitional zone 5.13 12.53 71.12 1.59 1.99 2.98 4.48 0.18
before service 2.4 1.7 92.94 1.3 — — — —