FIELD OF THE INVENTION
The present invention relates in general to a refractory for use in an inner lining of a blast furnace blow-pipe, and more particularly to improved blow-pipe refractory design having multiple refractory linings.
BACKGROUND OF THE INVENTION
Blast Furnace Blow-pipe 1 plays a vital role in Iron making with its primary function being to deliver hot blast air coming from hot blast stove having temperature in the range of 1100-1250°C to blast furnace. In operation, hot gas generated at hot blast stove first travels through hot blast main pipe, than bustle pipe (pipe encircle blast furnace bosh area structure) and finally into tuyere stock system (tuyere stock system consist of four components: 1. Down-leg 2. Goose neck 3. Blow-pipe 1 4. Copper tuyere) responsible for delivering hot blast air inside the blast furnace. The inner lining of the shell 4 of the blow-pipe 1 is lined with refractory/refractory castable. Further, the life of blow-pipe 1 depends on the factors such as refractory design and quality, pressure & temperature of the hot blast gas etc.
It is conventionally known to have a poured refractory lining of Blow-pipe 1 shell 4 where the inner lining is lined /poured with high alumina based castable. The major reason affecting the blast furnace Blow-pipe 1 availability is untimely or unexpected failures due to localized hot spot formation (as shell 4 temperature rises more than 400ºC) mainly close to tip portion / cracking of working lining refractory castable resulting in leakage of hot blast through refractory castable, thereby leading to failure of blast furnace blow-pipe 1.
Moreover, the conventional technique of blow-pipe 1 lining involves fixing of blow-pipe 1 shell 4 on stand at upright position followed by the insertion of the rubber mould to create the passage for hot blast and a ø30mm dummy lance pipe is inserted to create path for lance guide and then high alumina (60-70% alumina) based castable is filled into the annular space defined in the blow-pipe 1. In detail, the refractory castable paste is prepared with the help of mixer machine (by mixing castable powder with required quantity of

water), then poured and filled the annular space between mould and shell 4 of blow-pipe 1. Further, during operation, in order to ascertain shell 4 temperature, thermal imaging is being regularly done on all the blowpipes 1 in service. It has been experimentally observed that the temperature of blow pipe 1 near the tips ranges between 350 – 475ºC. The blow-pipe 1 is internally lined with refractory to insulate and protect the outer steel shell 4 from the high temperature air inside. The properties of refractory lining materials and decrease of its thickness due to erosion in the above process are the important factors to be considered while designing the refractory for blow-pipe 1 lining application since the blow-pipe 1 has to withstand four bar of hot blast pressure having temperature in the range of 1150-1250°C with refractory design constrain, where refractory thickness along the blow-pipe 1 varies from 135mm to 20mm (near the tip). The major drawbacks associated with the existing refractory design of blow pipe 1 which cause higher shell 4 temperature (hot spot) are described below:
i. Thermal conductivity of refractory castable: The existing lining practice of blowpipe 1 involves casting of 60-70% alumina based castable having thermal conductivity value around 1.6W/mK. This results in more amount of heat to be transfer towards the shell 4, cause high shell 4 temperature.
ii. Thickness of refractory castable inside blowpipe 1: Due to conical shape constraint of blowpipe 1 shell 4, refractory thickness along the length of blow-pipe 1 varies from 135 mm to 20 mm (near the tip). Lower thickness of refractory near tip area causes transfer of relatively higher amount of heat towards the shell 4 of blowpipe 1, resulting in frequent occurrence of hotspot near blow-pipe 1 tip.
For example provide a refractory, to improve thermal conductivity and mechanical strength which also provides a good resistance against dissolution in the molten hot metal and slag, a good corrosion resistance as well as a small penetrability of liquid hot metal and reactive gases. The invention uses

a mixture of coke and graphite in decided proportions, binder and a green block formed from the mixture of coke and graphite. However, in these refractories, even if the material is in principle suitable for the use in an inner lining of a blast furnace, the thermal conductivity, flexural strength and the mechanical strength of the materials chosen are in need of improvement in order to better control the shell 4 temperature.
Thus, in order to overcome the above drawbacks of the existing refractories, there is a need to develop a unique and inventive refractory design equipped to controlling the shell 4 temperature by optimizing parameters such as insulation performance, flexural strength and thermal conductivity.
OBJECTS OF THE INVENTION
An object of the invention is to overcome the aforementioned and other drawbacks existing in prior systems related to refractory designs.
Another object of the present invention is to propose an inventive refractory design according to an embodiment of the invention for Blow-pipe of Blast furnace which includes multiple refractory lining having customized insulation precast pre-fire (PCPF) shape as backup layer against the shell and silicon-carbide sleeve (tube) all along the length of blow-pipe as working/face lining.
Yet another object of the present invention is to enhance performance and longevity of the Blow-pipe life beyond two years.
Still another object of the present invention is to propose a refractory design according to an embodiment of the invention in order to better control the blow-pipe shell temperature.
These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following

detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.
SUMMARY OF THE INVENTION
The present application discloses a new blast furnace blowpipe 1 refractory design. In an embodiment, the proposed refractory comprises a face lining formed by a tube 2 made of high strength and high thermal conductivity material. Further, in an embodiment, the tube 2 being inserted in annular space defined inside the blow-pipe metal shell 4. In another embodiment, the refractory comprises a backup lining formed by a plurality of customized Precast Pre-fired (PCPF) 3 insulation blocks 3 in tight disposition across length of inner lining of an upper portion and a lower portion of the blow-pipe metal shell 4.
In another aspect, the present application discloses a blowpipe 1 refractory for use in an inner lining of a blast furnace blow-pipe 1, which is obtainable by a method comprising the steps of forming a face lining by inserting a silicon-carbide tube 2 in annular space defined inside the blow-pipe metal shell 4 followed by forming a back-up lining by tightly disposing a plurality of customized Precast Pre-fired (PCPF) insulation blocks 3 across length of inner lining of an upper portion and a lower portion of the blow-pipe metal shell 4.
The above and additional advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description when taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The above brief description, as well as further objects, features and advantages, of the present invention can be fully appreciated by reference to the following detailed description. These features of the present invention will become more apparent upon reference to the drawings, wherein:
Fig. 1: Illustrates schematic representation of a blow-pipe shell.

Fig. 2: Illustrates schematically design of silicon carbide tube according to an embodiment of the present invention.
Fig. 3: Illustrates schematically customized insulation PCPF shape.
Fig. 4: Illustrates disposition of the silicon carbide tube inside the blowpipe shell.
Fig. 5: Illustrates of disposition of the PCPF insulation block inside the blowpipe shell.
DETAILED DESCRIPTION OF THE INVENTION
Although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention which may be embodied in other specific structure. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.
It will be apparent, however, to one of ordinary skill in the art that the present invention may be practiced without specific details of the well known components and techniques. Further specific numeric references should not be interpreted as a literal sequential order. Thus, the specific details set forth are merely exemplary. The specific details may be varied from and still be contemplated to be within the scope of the present invention. The features discussed in an embodiment may be implemented in another embodiment.
Moreover, occasional references to the conventional techniques for making a refractory are made in order to better distinguish the present inventive disclosure discussed later in greater detail. Few of the details pertaining to said techniques are well known in the art and therefore, are described herein only in the detail required to fully disclose the present invention while unnecessarily obscuring the present invention.

Improving upon and addressing the problems discussed at length above (background), in the present disclosure an improved refractory as illustrated in the Figs. 1-5 clearly makes the proposed refractory design advantageous over the existing designs of blowpipe 1 refractories as would also become clearer to the knowledgeable in the art with the particulars of the aforesaid unique configuration/disposition being described below in greater detail. The present invention will be described in detail below with reference to embodiments as shown in the drawings.
The innovative refractory design for blow-pipe 1 has multiple layers: the face or working layer, which is exposed to hot blast air. The face or working layer consist silicon carbide tube 2 of thickness 13mm (Figure-2) and the backup layer includes customized insulation PCPF 3 shape against the shell 4 (Figure-3). The arrangement of silicon carbide tube 2 and PCPF insulation block 3 inside blow-pipe 1 is shown Figures: 4 and 5 respectively.
Characteristics of the proposed refractory design are described below:
(i) As working/face lining is made up of silicon carbide tube 2 having very high strength and high thermal conductivity value. This helps to withstand the refractory system against hot blast having high temperature and pressure and also due to its high conductivity provide very good thermal shock resistance property (reduces the chances of cracking).
(ii) The backup PCPF layer 3 made up of high purity Mullite-zirconia based component having good strength (Modulas of rupture=25Kg/cm2) and very low thermal conductivity value (K=0.60 W/mK at 1200°C). Here the good strength of backup layer helps to support the working layer also its lower conductivity provides good insulation property which helps to control the shell 4 temperature below 200°C.

Advantages
(i) The spalling/cracking tendency of refractory castable of existing design is overcome by the use of silicon carbide tube 2.
(ii) The probability of spalling/cracking during operation is very less in case of silicon carbide tube 2 because of its high strength and high thermal conductivity property.
(iii) Use of customised PCPF insulation block 3 as back up lining results into significant reduction of blow-pipe 1 shell 4 temperature.
(iv) The projected shell 4 temperature calculated through thermal modelling with this developed design is around 180°C.
The foregoing is considered as illustrative only of the principles of the invention. Furthermore, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.

We claim:
1. A blast furnace blow-pipe (1) having a metal shell 4 and a refractory having a central axial opening therethrough in communication with a tuyere providing a hot blast flow path through the blow-pipe (1) and the tuyere and into the furnace, said refractory comprising:
a face lining formed by a tube (2) made of high strength and high thermal conductivity material, said tube (2) being inserted in annular space defined inside the blow-pipe metal shell (4);
a backup lining formed by a plurality of customized Precast Pre-fired (PCPF) insulation blocks (3) in tight disposition across length of inner lining of an upper portion and a lower portion of the blow-pipe metal shell (4).
2. The blast furnace blow-pipe (1) as claimed in claim 1, wherein the high strength and the high thermal conductivity material tube (2) is a silicon-carbide tube (2).
3. The blast furnace blow-pipe (1) as claimed in claim 1, wherein the blow-pipe metal shell (4) temperature is in a range of 180ºC to 200ºC.
4. The blast furnace blow-pipe as (1) claimed in claims 1 and 2, wherein the silicon-carbide tube (2) has a thickness of 13mm.
5. The blast furnace blow-pipe (1) as claimed in claim 1, wherein layers of the plurality of customized PCPF insulation blocks (3) are made of material having high flexural strength and very low thermal conductivity.

6. The blast furnace blow-pipe (1) as claimed in claims 1 and 5, wherein the layers of the plurality of customized PCPF insulation blocks (3) are made of high purity mullite-zirconia composites.
7. The blast furnace blow-pipe (1) as claimed in claims 1 and 5, wherein preferred flexural strength is 25Kg/cm2.
8. The blast furnace blow-pipe (1) as claimed in claims 1 and 5, wherein preferred thermal conductivity is 0.60 W/mK at 1200°C.
9. The blast furnace blow-pipe (1) as claimed in claims 1 and 2, wherein the silicon-carbide tube (2) receives hot blast air.
10. A refractory for use in an inner lining of a blast furnace blow-pipe (1),
which is obtainable by a method comprising the following steps:
forming a face lining by inserting a silicon-carbide tube (2) in annular space defined inside the blow-pipe metal shell (4);
forming a back-up lining by tightly disposing a plurality of customized Precast Pre-fired (PCPF) insulation blocks (3) across length of inner lining of an upper portion and a lower portion of the blow-pipe metal shell (4).