The present invention relates to a process for manufacturing silica refractory bricks for
tall coke ovens. More particularly the subject invention pertains to a process for the
manufacture of silica bricks for use in tall coke ovens which are characterized by high
thermal conductivity, high bulk density and extreme low porosity, resulting in a
procedure having considerable economic viability.
BACKGROUND OF THE INVENTION
In recent years demand for coke in iron and steel industries has steadily been on
the rise due to an increase in the production capacities of steel making. Modern
day coke ovens are built with a height of 7 Mtr or more, which are called "Tall
Coke Ovens", to enhance the productivity of coke making. Coke ovens which
produce coke from coal happen to be an integral part of steel plants, which produces
coke, one of the important fuel constituents of blast furnaces. Another aspect of
coke making consists in increasing productivity further by reducing coke making
time from 20-24 hours to 15-18 hours. It has been found from literature and from
different experiments that by increasing the height from 4mts to 7mts and width from
13 mts to 17 mts, the weight per charge is increased from 20 to 40 MT, which
consequently decreases the number of openings of door by 50% and reduces emission of
toxic gases like SO2, NOx, PAH and BTX (benzene, toluene and xylene).
It has been reported that the temperature of coke oven combustion chamber, wall
thickness and width of coking chamber remaining same, increase of thermal conductivity
of silica refractory bricks from 1.08 to 1.21 Btu/ft/hr °F(1.87 to 2.09 w/Mk), increased
the through-put by around 10 percent. If the same is further increased to 1.68 Btu/ft/hr °F
(from 1.87 to 2.9 W/Mk), the throughput is increased by about 50%, as tabled below.



Generally silica bricks are used for coke oven construction. To achieve higher
thermal conductivity in silica bricks, the said bricks should have very high bulk
density, more than 2.00 gm./cc with a corresponding lower "Apparent Porosity",
lower than 12%.
PRIOR ART
(i) US Patent No-2599236 describes a process for the manufacture of silica bricks
where pre-fired non quartzite siliceous materials have been used along with other
mineialis.ers to manufacture silica bricks.
(ii) US Patent No-4183761 describes a process for the manufacture of silica bricks
with high thermal conductivity and low gas permeability using nitride and carbide
of silicon metals.
(iii) US Patent No-4988649 describes a process for making silica bricks with increased
bulk density from a starting mix containing graded granular quartzite (silica) and
elemental silicon.
(iv) EU patent No.-05449130B1 is related to a method of producing silica bricks from
sand stone with addition of soda-lime glass making powder additives suitable for
building or repairing different industrial furnaces such as coke ovens, hot blast
stove and glass kilns.
(v) Indian Patent No. 163883 describes a process for manufacture of silica bricks using
nitride and carbide of silicon.

OBJECTIVES OF THE PRESENT INVENTION
The principal object of the present invention is to provide a process for the manufacture
of silica refractory bricks for TALL COKE OVENS from aggregates of specific quartzite
deposits and with addition of SiO2- yielding compounds to achieve required high bulk
density, low apparent porosity and high thermal conductivity.
A further object pf this invention is to provide a process for the manufacture of improved
refractory bricks from aggregates of various siliceous stone materials with a mixture of
SiO2-yielding compounds with a view to making high density silica bricks.
A still further object of this invention is to provide a process for the manufacture of
improved silica refractory bricks wherein a mixture of silicon carbide of varying particle
sizes is employed as SiO2-yielding compounds, with particle sizes varying between 40
nm and 0.0070 nm.
Another object of this invention is to provide a process for the manufacture of silica
refractory bricks of improved performance wherein there is included one or more
inorganic or organic binder, with an optional addition of an additive in the form of one or
more oxide of iron.
Yet another object of this invention is to provide a process for making silica refractory
bricks having high thermal conductivity, high bulk density and extreme low porosity
wherein green bulk density of the processed bricks varies between 2.36 and 2.40 gm./cc,
and such bricks are. pressed in hydraulic presses having capacity between 400 and 800
MT, followed by firing at a temperature between 1350°C and 1500°C.

SUMMARY OF THE INVENTION
Due to their specific desirable properties, silica refractory bricks are used for construction of various
types of coke ovens including tall coke ovens. For manufacture of silica refractory bricks, siliceous
stones are used as principal raw material. The main mineral phase of all siliceous stone is quartz. During
firing of silica brick, the quartz converts into high temperature silica polymorphs such as cristoballite and
tridymite leaving a very low amount of residual quartz. The amount of mineral phases such as quartz,
cristoballite and tridymite during firing of silica bricks is governed by type of siliceous stone used, its
crystal size, conversion rate, types and amount of additive used and firing schedule and type of kiln used.
Further, during filing the green bricks expand to around 15% by volume and having apparent porosity in
the range of 18 % to 23%, bulk density inthe range of 1.75 to 1.85 and thermal conductivity in the range
of 1.6-1.8w/Mk.
Therefore selection of quality/type of silica bricks plays an important role in performance of a coke .
oven. Siliceous stone materials having different chemical composition, crystal grain sizes and different
conveision rates as shown in Table-1 were crushed and ground to different grain sizes before mixing.



In the present invention, the mixture of Si02-yielding compounds comprises a
mixture of various particle sizes of silicon carbide (SiC) as shown in Table-2 below.

It has been found that the addition of 0.5 to 5% by wt. of a mixture of aforesaid SiO2—
yielding compounds to in aggregate of aforesaid siliceous material produces silica bricks
having low porosity, high bulk density, high cold crushing strength, high thermal conductivity
and low residual quartz. Thus the aforesaid mixture of SiO2-yileding compounds help to
enhance quartz conversion and produces dense silica bricks with enhanced thermal conductivity.
According to this invention, there is provided a process for manufacture of silica refractory
bricks which comprises adding 0.5 to 5 parts bywt. of a mixture of Si02-yielding compounds
as herein described to 100 part by wt. of particles of quartzite, sandstone, silica grog end like
siliceous materials with the addition of organic and/or inorganic binder is an amount not
exceeding 7 parts by wt. of the reaction mass, and with an optional addition of an additive,
intimately mixing the ingredients with water to a mouldable consistency, moulding the wet
. mix into shape of bricks, drying and firing the said bricks at a temperature between 1350 °C and
1500°C.

According to a further feature, the mixture of SiO2—yielding compounds is added in an
amount of 0.5 to 3 parts by wt., preferably 0.5 to 5 parts by wt. to 100 parts by wt. of the
siliceous materials.
The organic binder comprises sulphite lye, molasses and dextrin powder. The inorganic
binder comprises calcium bearing materials, such as calcium hydroxide, milk of lime, calcium
oxide and calcium carbonate. The aforesaid binder is added in an amount of up to 7 parts by
wt. of the composition reaction mass.
The other additive comprises iron oxide powder having particle size below 75 microns or a
mixture thereof. It has been ascertained that the SiCVyielding compounds maximizes quartz
conversion and also densities the final product. During firing of the bricks, the SiO2-
yielding compounds yield finely divided SiO2 of different modifications. Thus the
formation of SiO2 in situ helps densification of the bricks and enables the bricks to attain
higher strength at normal and higher temperatures as well as higher thermal conductivity.
The invention is further defined by the following examples as shown in Table - 3, which
are given by way of illustration and not by way of limitation.



In each of the above examples, the ingredients were intimately mixed with requisite
quantity of water. Thereafter, the mix was moulded into the shape of bricks, dried and
then fired at 1450°C. The test properties of the fired bricks are given below in Table -


The bricks prepared according to this invention are ideally suitable for lining of high
capacity "Tall Coke Ovens".
Further, the following Example 5 shown in Table - 5, corresponding to Example 1,
shows comparative data wherein the process has been carried out without the
addition Of SiO2.yieilding compounds, while other ingredients being present in same
amounts as in Example 1:


The bricks prepared from the above example were dried and fired at 1450 C. The test
properties of these fired bricks are given in Table-6 shown hereinbelow.

Thus by comparing Example 4 with Example 1, it may be inferred that the addition of a
mixture of SiO2-yielding compounds considerably help the silica bricks to attain superior
properties.
ADVANTAGES
(a) Provision of silica refractory bricks having high thermal conductivity, high bulk
density and extreme low porosity enhances the life of coke ovens, including tall
coke ovens.

(b) Use of a tall coke oven enhances quantum of steel production with consequent
saving of cost of operation.
(c) The subject process employs indigenously available raw materials and the steps
followed are user-friendly.
As the present invention may be embodied in several forms without deviating or
departing from the spirit or essential characteristics thereof, it should be understood that
the above-described features/examples are not limited by any of the details of the
foregoing description, unless otherwise specified, but rather should be construed broadly
within its spirit and scope as defined in the following claims, and therefore all changes
and modifications that fall within meets and bounds of the claims, or equivalences of
such meets and bounds intended to be embraced by the claims appended hereafter.

We claim:
1. A process for manufacturing silica refractory bricks characterized in that the said
process comprises adding 0.5 to 5 parts by wt. of mixture of SiO2-yielding
compounds as herein described to 100 parts by wt. of particles of quartzite, sandstone,
silica grog and like siliceous materials with the addition of organic and/or inorganic
binders, in an amount not exceeding 7 parts by wt. of the reaction mass, and with an
optional addition of an additive, intimately mixing the ingredients with water to a
mouldable consistency, moulding the wet mix into shape of bricks, drying and firing
the said brick at a temperature between 1350 °C and 1500°C:
2. A process as claimed in Claim 1, characterized in that SiO2-yielding compounds
comprise a mixture of silicon carbides (SiC) of varying particle sizes.
3. A process as claimed in Claims 1 and 2, characterized in that the particle size of
silicon carbide varies from 40 nm to 0.0070 nm.
4. A process as claimed in Claim 1, characterized in that the SiO2-yielding compounds
are added in an amount of 0.5 to 3 parts by wt. preferably 0.5 to 1.5 parts by wt. to
100 parts by wt. of the said siliceous materials.
5. A process as claimed in any of the Claims 1 to 3, characterized in that the inorganic
binder comprises calcium bearing materials such as calcium hydroxide, milk of lime,
calcium oxide, calcium carbonate or a mixture thereof.
6. A process as claimed in any of the preceding claims, characterized in that the organic
binder comprises sulphite lye, molasses and dextrin.
7. A process as claimed in any of the preceding claims, characterized in that the additive
comprises iron oxide or a mixture thereof.

8. A process as claimed in any of the preceding claims, characterized in that the green
bulk density of pressed bricks is in the range of 2.36 to 2.40 gm. /cc.
9. A process as claimed in any of the preceding claims, characterized in that the green
bricks are pressed in hydraulic presses having capacity between 150 and 800MT,
followed by firing at a temperature varying between 1300°C and 1500°C.