Claims:CLAIMS

1. An improved castable for roofs and curtain flame burners of sinter plant comprising a mullite forming high alumina castable with following composition:-

Chemical % age
Al2O3 % : 58-62
Fe2O3% (Max) 0.9
SiO2% (Max) 35
CaO% (Max). 3
PLC: +/- 1.0
Grain Size: mm 0-5
Water for casting: %, 10-12

2. The castable for roofs and curtain flame burners of sinter plant as claimed in claim 1, wherein 0.5-1% SS 304 type SS fibre fibres are added in the said castable for curtain flame burners for arresting cracks

3. The castable for roofs and curtain flame burners of sinter plant as claimed in claim 1, wherein the physical properties includes :

Physical %age
B.D., kg/cm3: (min at 110 deg.C/24hrs) 2.6
CCS at 110o C/24 hrs.,kg/cm2, (min) 275
at 800o C/3 hrs., kg/cm2, (min) 600
at 1400o C/3 hrs., kg/cm2, (min) 650

4. The castable for roofs and curtain flame burners of sinter plant as claimed in claim 1, wherein the heating schedule of the burners include:
Hour Temp.C
6 120
12 150
15 600
6 600
12 1200
2 1200

5. A process of manufacturing the castable as claimed in any of the preceding claims for roofs and curtain flame burners of sinter plant.

Dated: this 8th day of March, 2018.

(N. K. Gupta)
Patent Agent,
Of NICHE,
For SAIL

To,
The Controller of Patents,
The Patent Office, Kolkata.

, Description:IMPROVED CASTABLE FOR ROOFS AND CURTAIN FLAME BURNERS OF SINTER PLANT

FIELD OF INVENTION
The present invention related to an improved castable and its application process in Roofs and Curtain flame Burners of Sinter Plant. More particularly, the present invention an improved castable composition which is mullite forming high alumina castable which is thermal shock resistant, high strength material and with low thermal expansion during use.

BACKGROUND ART

Iron ore fines (-5mm) are not directly charged into blast furnace (BF) for iron making process. On the contrary, these iron ore fines added with lime and other binders are processed to make lump having sufficient strength for charging into BF from the top. The mixer of iron ore fines and binders are passed through ignition hearth furnace fired at around 1400oC temperature. The roof and burner blocks of this ignition hearth furnace are normally lined with 90% high alumina cement bonded castable. These type of high cement bonded castable needs high curing time after casting (2-3 days) and high pre-heating time (3-4 days) after installation at Sinter Plant.

Moreover, due to high structural load of the furnace and the thermal fluctuation, cracks and peeling off refractory starts from the day of operation of the furnace at 1400oC. These cracks and failure of refractory from the roof & burner blocks require intermediate repairs leading to reduced furnace availability. The roof and burner blocks are finally replaced after a life of 6-7 months. The existing shortcoming in the form of pictorial representation is illustrated in Figs 1 – 4.

In the prior art, a Japanese Patent Publication 2011-208344A discloses a molded inorganic fiber product fabricated by impregnating a needled inorganic fiber blanket with an inorganic sol and drying the blanket. The molded inorganic fiber product has a bulk density of 0.08 to 0.20 g/cm3. The said specification also describes the use of this product as a heat insulator for a burner tile. The castable disclosed in the specification has disadvantages in that delamination tends to occur when a laminated structure is formed.
In another prior art an International Publication WO 2013/035645 discloses a molded inorganic fiber product that includes inorganic fiber and inorganic binder particles and has at least one combination of a high fiber density region and a low fiber density region. The ratio of the binder particle content in the high fiber density region to that in the low fiber density region is 0.5:1 to 5:1. The number-average particle diameter of the inorganic binder particles is 20 to 35 µm and the number of inorganic binder particles is less than 15 in the outermost surface of the molded product. In the disclosed castable, the number of inorganic binder particles in the outermost surface of the molded product is small, less than 15. Disadvantageously, it is difficult to maintain the outside shape of a final product produced by molding a needled blanket having high resilience into a block shape.

In yet another prior art a Japanese Patent Publication 2000-9305A discloses a castable that includes an enclosure made of a heat-resistant material, a molded inorganic fiber blanket compressed in a cavity in the enclosure, and a liner member retained by restoring force of the molded inorganic fiber blanket. The said castable in the liner member, which includes heat resistant long fiber, heat resistant powder, and aluminum phosphate, is thin. Disadvantageously, the heat resistance cannot be maintained for a long term.

OBJECT OF INVENTION

The principle object of the present invention is to provide a castable possessing good fire resistance, heat resistance, erosion resistance, and thermal shock resistance.

Another object of the present invention is to provide a material which is user friendly industrial application & less preheating time.

Another object of the present invention is to provide a material which is a high strength material and have low thermal expansion during use with improved furnace roof and burner life leading higher sinter production.

SUMMARY OF INVENTION

Therefore such as herein described there is provided an improved castable for roofs and curtain flame burners of sinter plant comprising a mullite forming high alumina castable with following composition:-

Chemical % age
Al2O3 % : 58-62
Fe2O3% (Max) 0.9
SiO2% (Max) 35
CaO% (Max). 3
PLC: +/- 1.0
Grain Size: mm 0-5
Water for casting: %, 10-12

Further the castable for curtain flame burners of sinter plant also includes 0.5-1% SS 304 type SS fibre fibres configured for arresting cracks

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Fig.1 is a pictorial representation of the Ignition hearth furnace roof at sinter plant at DSP;

Fig. 2 is a pictorial representation of Burner blocks at DSP;

Fig. 3 is a pictorial representation of Existing roof after 6 months at DSP;

Fig. 4 is a pictorial representation of Existing burner after 4 months at DSP;

Fig. 5 is Modified heating schedule of developed castable in accordance with the present invention;

Fig. 6 is a pictorial representation of Roof with developed mass (after 6 months in operation) in accordance with the present invention;
Fig. 7 is a pictorial representation of the Condition of burner blocks (after 6 months) in accordance with the present invention;

DETAILED DESCRIPTION
Embodiments of the present invention will be described in detail below. The following description sets forth exemplary embodiments of the present invention. The present invention is not limited to the details of these embodiments unless they depart from the spirit and scope of the invention.
An example of a castable according to a present invention will now be described with reference to Figs. 5 to 7. In the present work, a user friendly mullite forming high alumina castable has been developed. The material requires 9-10% water in an ordinary mixer machine during application and achieves better properties due to formation of mullite. It develops higher initial strength as well as better high temperature properties like spalling resistance, very low linear change on repeated permanent linear change (PLCR) at high temperature resulting in formation of stable refractory body during operation. The typical properties of the developed castable are given in table-I below:

An industrial trial was carried out at sinter plant unit of DSP where one full sets of roof structures were fabricated with this developed castable and cured in a remote location. The burner blocks, which are susceptible to higher erosion and thermal spalling, were re-inforced with stainless steel fibre to prevent peeling off refractory from vulnerable burner tips. CO Gas burners were designed and fabricated in-house to dry out the moisture at the remote location itself. The furnace consisting of roof and burner blocks made with developed castable followed by a faster preheating time (by > 30%) to start its production. The heating schedule for the developed castable is given in figure 5:

Therefore the following modifications were done:
? A new type of alumino silicate refractory mass was developed with 0.9% Fe2O3 iron, 0.9% CaO, 58-62% AlO2O3 content mass using Indigenous raw materials.
? The mass has developed high strength at high temperatures.
? The material is having restricted linear change (+1%)
? High spalling resistance
? Required 10-12% water for mixing in a ordinary mixer machine
? 0.5-1% SS 304 type SS fibre was added with the mass as a reinforcing agent
? Faster heating was followed reducing overall shut down time

The typical properties are given in Table-I:

Chemical
Al2O3 % : 58-62
Fe2O3% (Max) 0.9
SiO2% (Max) 35
CaO% (Max). 3
Physical
B.D., kg/cm3: (min at 110 deg.C/24hrs) 2.6
CCS at 110oC/24 hrs.,kg/cm2, (min) 275
at 800oC/3 hrs., kg/cm2, (min) 600
at 1400 oC/3 hrs., kg/cm2, (min) 650
PLC: +/-1.0
Spalling resistance: cycles. (min) 10
(WQ at 1000 deg. C with cube of 50x50x50 cm3 size prefired at 1400 deg. C for 3hrs)
Grain Size: mm 0-5
Water for casting: %, 10-12

The developed material has sustained more than 9 months in operation eliminating intermediate repairs / burner blocks replacement as shown in Fig 6. The condition of the roof & burner blocks made with developed mass was physically inspected after 6 month and depicted in fig. 7.

Inventive step

? Development of low alumina content and in-situ mullite forming castable replacing existing 90% alumina castable.
? A process of manufacturing the material which has been developed in laboratory & first time applied in Sinter Plant Roof & Curtain flame Burners

? A process of application of SS fibre added castable in curtain flame burners for arresting cracks

? Pre-heating schedule has been reduced to 53 hrs in place of more than 80 hrs thereby:
o Reduction in energy consumption
o Increase in furnace availability by reducing intermediate repairs / shut down time

? Overall roof and burner life has been increased to more than 9 months so far and still continuing without any intermediate repairs

? All steel plants can use this material having a lower cost of production than existing 90% Al2O3 castable.

The shop has decided to implement all the roofs and burners with this developed mass. A project has been taken up by RDCIS & DSP to carry out full implementation of one full furnace roof and burner blocks in SP-2.

Although the foregoing description of the present invention has been shown and described with reference to particular embodiments and applications thereof, it has been presented for purposes of illustration by way of examples and description and is not intended to be exhaustive or to limit the invention to the particular embodiments and applications disclosed. It will be apparent to those having ordinary skill in the art that a number of changes, modifications, variations, or alterations to the invention as described herein may be made, none of which depart from the spirit or scope of the present invention. The particular embodiments and applications were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such changes, modifications, variations, and alterations should therefore be seen as being within the scope of the present invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.