Claims:We Claim:

1. Reheating furnace lining of uptake area comprising:

uptake area of said furnace obtained of metallic shell having anchors for lining plurality of light weight and high thermal shock resistant ceramic fibre blanket layers providing for a combination of refractory and insulation characteristics.

2. Reheating furnace lining of uptake area as claimed in claim 1 wherein said metallic shell comprise of strips of 6-8 mm thick, 40-50mm width and 12.5-13.0 meters long mild steel plates providing curved shape of entry wall up-take area for said lining of plurality of ceramic fibre layers.

3. Reheating furnace lining of uptake area as claimed in anyone of claims 1 or 2 wherein said ceramic fibre blankets comprise a combination of ceramic fibre linings of varied bulk density.

4. Reheating furnace lining of uptake area as claimed in anyone of claims 1 to 3 wherein said plurality of ceramic fibre blanket layers comprises blankets with the highest bulk density of 128kg/m3 in the hot face and the blankets with lowest bulk density of 64kg/m3 adjacent to said metal shell which constitutes the cold face.

5. Reheating furnace lining of uptake area as claimed in anyone of claims 1 to 4 comprising providing therebetween said plurality of ceramic fibre blanket layers atleast one intermediate layer of steel sheet layer for minimizing ingress of hot flue gases to the shell and damage of the welding joints therebetween curved shaped shell and anchor studs.

6. Reheating furnace lining of uptake area as claimed in anyone of claims 1 to 5 comprising a layer of sheet steel installed after fourth layer of blanket lining to minimize ingress of hot flue gasses to the metallic shell and welding joints.

7. Reheating furnace lining of uptake area as claimed in claim 6 wherein said sheet steel layer comprise a layer of AISI-304 sheet having 0.15mm thickness.

8. A process for lining of uptake area of reheating furnaces comprising:

i) providing a curved shape of entry side wall up-take area for lining of ceramic fibre layers involving strips of steel plates;
ii) providing anchoring provisions for supporting layers of plurality of light weight and high thermal shock resistant ceramic fibre blanket layers in said shell to minimize ingress of hot and speeding flue gases to said shell; and
iii) involving plurality of ceramic fibre blankets for effectively lining the up-take area.

9. A process as claimed in claim 8 wherein the ceramic fibre blankets are lined in the up-take area keeping the highest bulk density blanket in the hot face and lowest bulk density blankets in adjacent to the metallic shell preferably with a metal sheet blanket therewetween for improved lining.

10. A process as claimed in anyone of claims 8 or 9 comprising providing a layer of AISI-304 sheet having 0.15 mm thickness installed after 4th layer of ceramic blanket lining to minimize ingress of hot flue gases to the shell and damage of the welding joints between curved shaped shell and anchor studs supporting the linings.

Dated this the 5th day of September, 2015
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)
IN/PA-199

, Description:FIELD OF THE INVENTION

The present invention relates to Reheating furnace lining of uptake area for improving their performance and a process thereof. More particularly, the present invention is directed to provide a refractory lining on the curved portion of charging side wall of the up-take area of reheating furnace involving ceramic fibre blankets of suitable quality with proper anchoring and having appropriate bulk density and thickness of lining so that the working life of such lining is enhanced from existing 2-3 months to about one year thus reducing the downtime of furnace and increasing the productivity.

BACKGROUND OF THE INVENTION

Reheating furnaces in steel industry are used for heating of slabs/billets to the working temperature of 1250-1260oC for rolling to different shapes. Mainly there are 3 zones in these furnaces namely pre-heating zone, heating zone and soaking zone after which the hot slabs/billets go out on to the roller table for rolling. In the preheating zone, the charged materials i.e slabs/billets are preheated by the hot flue gases generated in the furnace which move in opposite direction to that of charge materials. At the extreme end i.e in the charging side of the furnaces, there is an area called “up-take area” through which hot flue gases go out of the furnace to recuperators before finally going to the atmosphere through chimneys. In the up-take area of these furnaces, conventional castables of 60% and 90% alumina quality are generally used. The application of castables in this area is difficult because of mechanical structures above it. To maintain the flowability of these castables, more water is used deteriorating the properties of castables. Flue gasses pass through the up-take area at a temperature about 800-1000oC and the thickness of castable lining is about 250mm. Even though the metallic as well as ceramic anchors are used for keeping the castable in position, the castables frequently crack and fall, forcing the furnaces to shut down for repairs in every 2-3 months for about 10 days each.

Main reasons for failure of the castables in the charging side wall curved portion of the up-take area are as follows:

a) The bonding strength attained by castable due to presence of cement in it is lost in the temperature range of 800-1000oC. Therefore, the cold crushing strength of conventional castables in this range of temperature is lowest. The ceramic bonding also does not develop as the temperature is very low for obtaining the same.

b) The lining in this area is most prone to thermal shocks due to escape of abrading hot gases through the up-take and ingress of cold air from the slab charging space of the furnace.

c) Once the cracks are generated in the castable due to thermal shocks, they widen with passage of time and slowly the castable falls.

There has been thus a need in the field of operation of reheating furnaces to develop a refractory lining in the charging side wall curved portion of the up-take area which would be durable and resistant to thermal shock to enhance the operating life of lining. In order to improve the lining life of castables in this area from 2-3 months to about an year, it was decided to go for an alternative lining material and process involving different type of lining material to meet the requirement.
OBJECTS OF THE INVENTION

The basic object of the present invention is directed to provide Reheating furnace lining of uptake area for improving their performance with enhanced life and a process thereof.

A further object of the present invention is directed to provide Reheating furnace lining of uptake area involving Ceramic fibre based materials which have characteristics of low thermal conductivity, light weight, high thermal shock resistance, low heat storage, chemical resistance and thermal efficiency etc. as a remarkable combination of the properties of refractories and traditional insulation materials.

A still further object of the present invention is directed to provide Reheating furnace lining of uptake area involving Ceramic fibre based materials and more specifically suitable quality of ceramic fibre blankets as lining material with proper anchoring.

A still further object of the present invention is directed to provide refractory lining for up-take area of Reheating Furnaces involving ceramic fibre blankets of desired bulk density installed in multiple layers with appropriate anchoring and with intermediate steel sheet of selective thickness to protect from ingress of hot and speeding flue gases to the shell.

A still further object of the present invention is directed to provide refractory lining for up-take area of Reheating Furnaces involving ceramic fibre blankets that avoids damage of the welding joints between anchor studs and shell plate due to flow of hot flue gases.

A still further object of the present invention is directed to provide refractory lining for up-take area of Reheating Furnaces involving ceramic fibre blankets in multi layered disposition on shell wherein highest bulk density (BD) blanket is installed in the hot face and lowest BD blankets in adjacent to shell (cold face).

SUMMARY OF THE INVENTION

The basic aspect of the present invention is thus directed to provide Reheating furnace lining of uptake area comprising:

uptake area of said furnace obtained of metallic shell having anchors for lining plurality of light weight and high thermal shock resistant ceramic fibre blanket layers providing for a combination of refractory and insulation characteristics.

A further aspect of the present invention is directed to said Reheating furnace lining of uptake area wherein said metallic shell comprise of strips of 6-8 mm thick, 40-50mm width and 12.5-13.0 meters long mild steel plates providing curved shape of entry wall up-take area for said lining of plurality of ceramic fibre layers.
A still further aspect of the present invention is directed to said Reheating furnace lining of uptake area wherein said ceramic fibre blankets comprise a combination of ceramic fibre linings of varied bulk density.
Another aspect of the present invention is directed to said Reheating furnace lining of uptake area wherein said plurality of ceramic fibre blanket layers comprises blankets with the highest bulk density of 128kg/m3 in the hot face and the blankets with lowest bulk density of 64kg/m3 adjacent to said metal shell which constitutes the cold face.
Yet another aspect of the present invention is directed to said Reheating furnace lining of uptake area comprising providing there between said plurality of ceramic fibre blanket layers at least one intermediate layer of steel sheet layer for minimizing ingress of hot flue gases to the shell and damage of the welding joints there between curved shaped shell and anchor studs.
A further aspect of the present invention is directed to said Reheating furnace lining of uptake area comprising a layer of sheet steel installed after fourth layer of blanket lining to minimize ingress of hot flue gasses to the metallic shell and welding joints.
A still further aspect of the present invention is directed to said Reheating furnace lining of uptake area wherein said sheet steel layer comprise a layer of AISI-304 sheet having 0.15mm thickness.
A further aspect of the present invention is directed to a process for lining of uptake area of reheating furnaces comprising:

i) providing a curved shape of entry side wall up-take area for lining of ceramic fibre layers involving strips of steel plates;
ii) providing anchoring provisions for supporting layers of plurality of light weight and high thermal shock resistant ceramic fibre blanket layers in said shell to minimize ingress of hot and speeding flue gases to said shell; and
iii) involving plurality of ceramic fibre blankets for effectively lining the up-take area.

A still further aspect of the present invention is directed to said process wherein the ceramic fibre blankets are lined in the up-take area keeping the highest bulk density blanket in the hot face and lowest bulk density blankets in adjacent to the metallic shell preferably with a metal sheet blanket there between for improved lining.

A still further aspect of the present invention is directed to said process comprising providing a layer of AISI-304 sheet having 0.15 mm thickness installed after 4th layer of ceramic blanket lining to minimize ingress of hot flue gases to the shell and damage of the welding joints between curved shaped shell and anchor studs supporting the linings.

The above and other objects and advantages of the present invention are described hereunder in greater details with reference to the following accompanying non limiting illustrative drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Figure 1: shows the longitudinal cross section of the up-take area and charging side wall curved portion of the up-take area where lining gets damaged due to thermal shock by hot abrading flue gas.

Figure 2: shows the image of charging side wall after dismantling of castable.
Figure 3: shows the design of shell plate and ceramic fibre blanket lining according to the present invention.

Figure 4: shows the charging side wall curved portion of the up-take area of reheating furnace after completion of lining with ceramic fibre blankets.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO DRAWINGS

The present invention relates to Reheating furnace lining of uptake area for improving their performance and a process thereof. The lining on the curved portion of charging side wall of the up-take area of reheating furnace is lined with alternative material involving multiple layers of ceramic fibre blankets of suitable quality with proper anchoring and having appropriate bulk density and thickness of lining so that the working life of such lining is enhanced from existing 2-3 months to about one year.

It has already been stated that as the flue gasses pass through the up-take area at a temperature about 800-1000oC where the thickness of conventional castable lining comprising conventional castables of 60% and 90% alumina quality, is about 250mm, with the metallic as well as ceramic anchors used for keeping the castable in position, the castables frequently crack and fall forcing the furnaces to shut down for repairs in every 2-3 months for about 10 days each. The longitudinal cross section of the up-take area is shown in accompanying Figure 1 and after dismantling of castable in curved portion of charging side entry wall is shown in Figure 2.

In order to improve the lining life of castables in this area from 2-3 months to about an year, the present invention attempts to involve an alternative lining process with different type of lining material.

Ceramic fibre based materials which have characteristics of low thermal conductivity, light weight, high thermal shock resistance, low heat storage, chemical resistance and thermal efficiency etc. are a remarkable combination of the properties of refractories and traditional insulation materials. Accordingly, the present invention is directed to incorporate appropriate quality ceramic fibre blankets with proper anchoring for the desired lining in uptake area of reheating furnace to enhance the lining life. One of the pre-requisites for lining with ceramic fibre blankets is a metallic shell, on which the stainless steel anchors are to be welded for supporting the fibre blankets layers, which was not available in up-take area.

Therefore, the following modifications have been undertaken by way of the present invention:

1. A metallic shell(16), in the curved shape, was designed and fabricated to use 6-8mm thick strips of mild steel having width of 40-50 mm and length about 12.50 to 13.0 meters (width of furnace).
2. Lining design with 4 qualities of ceramic fibre blankets was done depending on the bulk density (BD) of the blankets with higher BD blankets in hot face and lower BD blankets in adjacent to shell(16). A total of 10 layers of 25mm each (total 250mm thickness) were installed for lining. The lining pattern is as follows:
a) Installation of 4 layers(Sl. Nos. 8-11 in Figure 3) of 25mm (Total thickness - 100mm) thick 64kg/m3 density blankets over the shell(16).
b) Installation of 0.15mm thick SS-304 sheet (Sl. No. 7 & 14 in Figure 3) for not allowing hot gasses to the shell and fixing it with a SS-310 washer by inserting it through SS anchor studs (Sl. No. 12 in Fig 3)
c) Over the layers specified in (b) above, installation of 2 layers of 25mm(Total thickness – 50mm) thick blankets of 96kg/m3 density (Sl. No. 5-6 in Figure 3)
d) Then over (c), installation of 3 layers of 128kg/m3 density blankets of 25 mm thickness (Total thickness - 75mm) (Sl. Nos. 2-4 in Fig.3).
e) Finally, installation of one layer of 25mm thick moist pak (Sl. No. 1 in Figure 3) and tightening the same with ceramic cuplocks (Sl. No. 15 in Figure 3) and filling the cuplocks with moldable (Sl. No. 13 in Figure 3).
3. A layer of AISI-304 steel sheet having thickness of 0.15mm was introduced after laying 4 layers of blankets to minimize the ingress of hot and speeding flue gases to the shell which otherwise might damage the welding joints between anchor studs and shell plate. The stated configuration of the lining on up take area according to this invention is shown in accompanying Figure 3.

This modifications have eliminated the shutdowns in every 2-3 months of duration and improved the availability of furnace and consequently the production. Lining in the vulnerable charging side wall portion of approximately 13 x 2 meters in up-take area of one of the Reheating Heating Furnace of the applicants was modified from castable lining to ceramic fibre blanket lining. The lining configuration consists of 10 layers of 25mm each thick blankets of 4 qualities using SS-310 anchor studs. The charging side wall curved portion of the up-take area of reheating furnace after completion of lining with ceramic fibre blankets is shown in Figure 4 and the lining condition is found to be satisfactory after completion of 16 months of life against 2-3 months life with conventional castable lining.

Details of shutdown of Reheating Furnace with conventional castable lining versus the modified ceramic fibre blanket based lining of up-take area are as given below in Table I:
Table I:

No. of Trials No. of days of shutdown for repair of up-take area
Trail 1 (conventional castable application) 56/year
Trial 2(conventional castable application) 31/Year
Trial 3(conventional castable application) 22/Year
Trial 4(modified lining with fibre blanket lining in up-take area) No shutdown during the year
Trial 5(modified lining with fibre blanket lining in up-take area) No shutdown during the year

The above comparative result clearly indicate the marked improvement in lining life with ceramic fibre blanket based lining of up-take area over conventional castable lining.

It is thus possible by way of the present invention to provide reheating furnace lining of uptake area wherein ceramic fibre blankets of varied bulk density is selectively involved with suitable anchoring with a shell plate, including a steel sheet incorporated in between the ceramic fiber layers so that the adverse effect of hot and speeding flue gas flowing over the lining could not damage the shell or the weld joints of anchors and thus leading to enhanced lining life of more than one year and consequent improvement in furnace productivity.