Claims:1. A process for preparing the tap hole mass for plugging the tap hole of blast furnace, the process comprising the steps of:
- mixing the bauxite homogeneously in dry conditions with other dry materials consisting of plastic clay, silicon carbide, coke, pitch and powder resin for 10-20 minutes.
- adding the preheated wash oil to the said running mixture and mixing it for 10-20 minutes.
-collecting the discharged mixture from the mixer in a container

2. A process as claimed in claim 1, wherein the bauxite contains 85-88%w/w of Al2O3, 2%w/w of Fe2O3, 4% w/w of TiO2, 0.7%w/w of Alkali, 0.5% of Moisture.

3. A process as claimed in claim 1, wherein the size of sieved plastic fire
clay is -1mm, Silicon carbide is -100microns, pitch is -1mm, coke breeze is -1mm and powder resin is 200mesh size.

4. A process as claimed in claim 1, wherein the plastic fire clay contains 35-40%w/w of Al2O3, 45-50% w/w of SiO2, 1.0-1.5%w/w of Fe2O3, 2-3%w/w of moisture.

5. A process as claimed in claim 1, wherein the Silicon carbide contains 85-88%w/w of SiC, 2-3%w/w of SiO2, 0.80-1.0%w/w of free Carbon, 2.75-3.0%w/w of Fe2O3, 0.80-0.95%w/w of free Silica, 0.2-2.5%w/w of moisture, 3.5-4.0%w/w of others.

6. A process as claimed in claim 1, wherein the Pitch contains 19.21-25.64%w/w of Quinoline insoluble, 54.34-59.25%w/w of toluene insoluble, 63.43-65.74%w/w of coking value, 0.15-0.20%w/w of ash content, 30.45-35.94%w/w of Beta resin

7. A process as claimed in claim 1, wherein powder resin contains 8.20-10%w/w of hexamine content, 10-25%w/w of ash content

8. A process as claimed in claim 1 , wherein the wash oil contains 2.77-4.9%w/w of naphthalene,1.5-2.0% of moisture

9. A process as claimed in claim 1 , wherein the wash oil was preheated to 60-70°c in drier.
10. A process as claimed in claim 1, wherein the coke breeze contains 82-84%w/w of carbon, 15-18%w/w of ash, 0.5-0.8% w/w of volatile material
11. A process as claimed in claim 1, wherein the solubility of pitch with wash oil is due to high softening point of Pitch in the range of 170-176°c.

12. A process as claimed in claim 1, wherein the quality in tap hole mass can be improved by restricting the ash content in the resin.

13. A process as claimed in claim 1, wherein the curing or setting time of tap hole mass depends on the gel time of resin at 150c which is in the range of 75-90°c.

14. A process as claimed in claim 1, wherein the distillation range of wash oil used is 220-350°c to achieve the maximum solubility of pitch and increasing the fluidity of the pitch.

15. A tap hole mass for plugging the tap hole of blast furnace comprising

of the following ingredients:
Materials Percentage (%)
Bauxite 30 - 32
Plastic Fire Clay 9.5 - 10.5
Silicon Carbide 14 - 16
Coke Breeze 7.5 -8.5
Pitch 14 - 15.5
Powder Resin 6 - 7
Wash Oil 11 - 12

16. A tap hole mass as claimed in claim 15, wherein the bauxite provides high melting point, high refractoriness and cold crushing strength in the tap hole mass and it also acts as a filter material to the mixture.

17. A tap hole mass as claimed in claim 15, wherein pitch and wash oil are used as a binders.

18. A tap hole mass as claimed in claim 15, wherein the coke is used to increase the porosity which allows inside gas of blast furnace to escape through the mass thereby heating up the mass and hardening it within a short period.

19. A tap hole mass as claimed in claim 15, wherein the silicon carbide used has a high melting and high thermal conductivity which makes it suitable for using as an ingredients in the tap hole mass.

t

, Description:Field of Invention

The invention relates to a process for preparing the tap hole mass for plugging the tap hole of blast furnace for better working, manufacturing and operating environment of blast furnace in Steel Plant and the tap hole mass made thereof. Plugging mass compositions for blast furnace tap holes comprising bauxite, plastic fire clay, silicon carbide, coke breeze, Pitch, powder resin and wash oil and are characterized by enhanced compressive strength at elevated temperatures, increased plasticity and expansion characteristics at high temperatures.

Background

Iron is produced in blast furnaces by the reduction of iron bearing materials with a hot gas. The large, refractory lined furnace is charged through its top with iron as ore, pellets, and/or sinter, limestone, dolomite and coke. Iron oxides, coke and fluxes react with the blast of air to form molten reduced iron, carbon monoxide (CO), and slag. The molten iron and slag collect in the hearth at the base of the furnace. The by-product gas is collected through the collector located at the top of the furnace and is recovered for use as fuel.

The molten iron and slag are removed, or casted, from the furnace
periodically. The casting process begins with drilling a hole, called the tap hole, filled with tap hole mass, and drilled with drilling machine.

During casting, molten iron flows into runners that lead to transport ladles. Slag also flows into the tap hole mass filled iron notch at the base of the hearth and is directed through separate runners to a slag granulation plant adjacent to the cast house, or into slag pots for transport to a remote slag pit. At the conclusion of the cast, the tap hole is re-plugged with tap hole mass using a Mudgun machine. The area around the base of the furnace, including all iron and slag runners is enclosed by a cast house.

Tap hole mass plays important roles in blast furnace cast house operation. Tap hole masses are unshaped refractories which are used to plug the tap hole of a Blast Furnace. Tap hole mass is a combination of different refractory materials, suitable binders and lubricants. The major functions of the tap hole mass are sealing the tap hole after metal & slag tapping, smooth removal of hot metal & slag after opening the tap hole and protection of hearth refractories. To achieve the above mentioned functions, tap hole mass should have good extrusion pressure, workability, fast hardening, sintering and volume stability at high temperature, easy drilling, high corrosion and abrasion resistance properties. A high solid content in the tap hole mass results in improved abrasion and chemical resistance and reduces curing shrinkage but makes injection to the tap hole more difficult. Again a pitch bonded tap hole mass softens at moderate temperature and requires the gun machine to be held in the position for longer times than resin bonded tap hole mass. In this sense, a great efforts has been made to manufacture a good quality tap hole mass. Hence, selection of the raw materials is very important to manufacture good & strong tap hole mass with appropriate physical and chemical properties.
In this development process, tap hole mass is manufactured by using mixture of high alumina clay and grog with carbonaceous material, such as coke, pitch, powder resin, silicon carbide and lubricant. The current invention relates to use of suitable lubricant without affecting the quality of tap hole mass. The lubricant was tested and found suitable for application in tap hole mass. Unlike normal tap hole mass the lubricant can keep the tap hole mass workable at room temperature. The lubricant has higher flash point and high viscosity. The following are the advantages of developed lubricant in use of tap hole mass.
1. The tap hole mass will have better workability at room temperature
2. The heating of clay gun or mud gun can be avoided during use of tap hole mass.
3. The tap hole opening will be smooth with less flames
4. Lubricant is environment friendly compared to the normally used one.
5. Lubricant is easy to handle.
6. Developed Lubricant can give a better working and manufacturing environment.

The importance of having a good quality tap hole mass is more and more obvious as the volume of the blast furnace is going larger & larger and the complexity of casting operation is increasing accordingly.

Keeping into the view all the above aspects the present invention describes the method for manufacturing the tap hole mass for better working, manufacturing and operating environment of blast furnace.

Prior Art
IN 3513/CHE/2014 teaches about the process for preparing the tap hole mass for plugging the tap hole of blast furnace from the refractory wastes generated in the steel Plant. The plugging mass compositions for blast furnace tap holes comprising waste refractories, plastic fire clay, silicon carbide, coke breeze, Pitch, powder resin and wash oil and are characterized by enhanced compressive strength at elevated temperatures, increased plasticity and expansion characteristics at high temperatures.

WO 1997041264 A1 teaches about the process and device are disclosed
for closing a tap hole. A plugging mass is pressed by a tap hole plugging machine into the tap hole to be closed and thermally set therein. The plugging mass is tempered in the tap hole plugging machine in such a way that its temperature is set at a processing temperature at which the plugging mass is very ductile. For this purpose, the tap hole plugging machine has a device for tempering the plugging mass in the plugging chamber (4) which preferably includes a device for heating the plugging mass before it is pressed into the tap hole and a device for cooling the plugging mass in the tap hole plugging machine while and/or after it is pressed therein.

US Patent No. US4, 399,982 teaches about a blast furnace tap hole plugging composition comprising a coal tar binder, refractory filler and a very heavy aromatic petroleum oil which fails to polymerize at the high heating rates experienced during normal application of the tap hole mix to the tap hole. Preferred aromatic petroleum oils useful in the present invention have a minimum boiling temperature of 700° F. and above and a boiling range between 700° F. and 1000” F. Methods of making and using such plasticized tar bonded blast furnace tap hole mixes are also disclosed.

WIPO Patent Application WO 2012011880 A2 teaches about an invention relates to a composition of plastic refractory material intended for stopping-in tap holes of blast furnaces intended for molten iron production. The nature of the invention lies in an appropriate composition of material made by grogs of refractory shales and silica sand, additives enhancing resistance to molten metals, plasticizers of clay and resins. An appropriate proportion of refractory grogs, clays, carbon additives is mixed with an appropriate proportion of Novolak and Phenolic - resol resin in a mixer and by shaping homogenous mass to loaves under vacuum, when loaf bulk density of about 2,100 kg.m'3 is reached. Mixing time is controlled in dependence on temperature of mass mixed and must not exceed 40 °C. According to the invention, mass compaction occurs, e.g. at pressure 8 MPa per loaf surface of e.g. 250 x 120 mm. When designing mass composition for a final customer, it is possible to select an appropriate proportion, combination of synthetic resins of the Novolak and resol type, in order to obtain technological effect required for its application.

Detailed Description

Tap hole masses are unshaped and plastic refractories which are used to plug the tap hole of Blast Furnace. The essential features are reasonable refractoriness and slag resistance, a tendency to swell on firing in-situ and drillability, so that tap hole can readily open when required. To achieve the above mentioned functions, tap hole mass should have good workability, volume stability under high temperature, fast hardening & sintering behaviour and better abrasion & corrosion resistance properties. These properties are generally achieved by using mixture of medium/high alumina clay and grog with carbonaceous material, such as coke, pitch and silicon carbide.
Blast furnace operation is featured by a series of tapping operations in which tap hole opening-tapping-plugging is carried out repeatedly. The tap hole mass has an important role to play in attaining a good tap hole that is smooth and permits steady drilling into the cured and hardened tap hole mass. It should also provide a constant and lengthy tapping time with an appropriate tap hole mass durability.
Tap hole mass are plugged into tap hole of blast furnace where hot metal temperature would be around 1400oC -1500oC. The plasticity of the tap hole mass decreases due to decrease of tar viscosity and deterioration of texture due to rapid volatilization of tar. The plugging softness is an important factor which influences the durability of the tap hole mass. The solidification behaviour of the tap hole mass reflects the formation of texture at high temperature and determines the durability.
To form good tap hole, it is necessary to investigate the flow and deformation behaviours of the tap hole mass with the change of temperature. A good quality tap hole mass should be able to perform the following functions,
1. Easy flow when pushed by the gun, to plug the tap hole.
2. Cure within the tap hole & ensure a tight seal.
3. To be drilled within a certain period of time.
4. Allow a stable, controlled melt stream.
5. Without erosion & corrosion by iron & slag.
6. Form a stable substrate for the next plug.
7. Provide a stable & controlled tap hole length.
Tapping rate (tonnes/min) of iron and slag is determined by tap hole diameter, tap hole length, thickness of the molten iron and slag layer as well as gas pressure of furnace and other factors. Out of these factors, the influence of the hole diameter is significant as tap hole mass is washed away by the molten iron and slag. To obtain longer tapping time, it is very much important to avoid rapid increase of tapping rate and have a good abrasion resistant tap hole mass.
The importance of having a good quality tap hole mass is more and more obvious as the volume of the blast furnace is going larger & larger and the complexity of casting operation is increasing accordingly. The location of tap hole mass with its mushroom structure in a Blast Furnace is shown in Fig. 1.

Fig.1: The tap hole mass with mushroom structure
Good tap hole practice results in improvement in many aspects of furnace operation. Inconsistency in the quality of tap hole mass will affect tap hole operations and results in loss of production of hot metal. Control of tap hole length minimizes hearth refractory wear and contributes to long campaigns. The following table depicts the various functions and properties for tap hole mass.
Function Properties
Closing tap hole Easy plugging & drilling • Plasticity of fire clay

• Good gas permeability

• Proper sintering
Hearth protection Constant length • Resistance to hot metal & slag

• High stickiness to furnace wall
Constant delivery Erosion resistance • Expansive nature

• Resistance to hot metal & slag

According to an embodiment of the invention, a process for preparing the tap hole mass for plugging the tap hole of blast furnace, the process comprising:
- mixing the bauxite homogeneously in dry conditions with other dry materials consisting of plastic clay, silicon carbide, coke, pitch and powder resin for 10-20 minutes.
- adding the preheated wash oil to the said running mixture and mixing it for 10-20 minutes.
-collecting the discharged mixture from the mixer in a container.

According to an embodiment of the invention, the percentage of different materials used for manufacture of the tap hole mass is as follows:
Materials Percentage (%)
Bauxite 30 - 32
Plastic Fire Clay 9.5 - 10.5
Silicon Carbide 14 - 16
Coke Breeze 7.5 -8.5
Pitch 14 - 15.5
Powder Resin 6 - 7
Wash Oil 11 - 12

The different ingredients used for the manufacture of tap hole mass are described below:
Bauxite:
Bauxite is the main aggregate material, containing high percentage of Al2O3, has a high melting point. It provides high refractoriness and cold crushing strength in the tap hole mass. It also acts as filler material to the mixture.
Properties Value
Al2O3 (%) 85-88
Fe2O3 (%) (max) 2
TiO2 (%) (max) 4
Alkali (%) (max) 0.7
Moisture (%) (max) 0.5
Density (ton/m3) 3.2
The sieve analysis of the Bauxite material is given below:
+1 mm +0.5 mm +180 microns -180 microns
1.5 - 4.5 (%) 0.5 - 5.0 (%) 4 - 8.5 (%) 82 - 94 (%)

Plastic Fire Clay:
Plastic fire clay is used to give plasticity in tap hole mass, gives extruding properties which is very much required to plug the tap hole. It also provides the expansion characteristics to the tap hole mass.
Properties Amount
Al2O3 (%) 35-40
SiO2 (%) 45-50
Fe2O3 (%) 1.0-1.5
Moisture (%) 2-3
Loss on ignition (LOI) (%) 10-12
Refractoriness 1700oC
Size -1mm (80%min)

Silicon Carbide (SiC):
Silicon carbide (SiC) is having high melting point (2700oC), high volume stability, high abrasion resistance and high thermal conductivity makes it suitable for using as an ingredient in the tap hole mass.

Properties Amount
SiC (%) 85-88
SiO2 (%) 2.95
Free Carbon (%) 0.85-1.0
Total Fe2O3 (%) 2.75-3.0
Free Silica (%) 0.80-0.95
Others (%) 3.5-4.0
Moisture (%) 0.50
Size -100 microns

Pitch:
Plastic fire clay is used to give plasticity in tap hole mass, gives extruding properties which is very much required to plug the tap hole. It also provides the expansion characteristics to the tap hole mass.

Properties Amount
Softening Point (oC) 170 (min) - 176 (max)
Quinoline insoluble (%) 19.21 (min) - 25.64 (max)
Toluene insoluble (%) 54.34 (min) - 59.25 (max)
Coking Value (%) 63.43 (min) - 65.74 (max)
Ash content (%) 0.15 (min) - 0.20 (max)
Beta resin 30.45 (min) - 35.94 (max)
Size -1mm (60% min)

Powder Resin:
Resin is used to increase the speed of setting of mass in tap hole (curing time) which will reduce the holding time of mass in tap hole, gives more time to make it ready for next tapping. Quality of the tap hole mass can be improved by restricting the ash content in the resin.
Properties Amount
Gel time (Second) at 150oC 75-90
Hexamine content (%) 8.20-10
Melting point (oC) 100
Ash content (%) 10-25
Size 200 mesh more than 90%

Oil:
Oil is mainly used for lubrication, improving the fluidity of pitch and bonding in the mass and makes the mass fluid enough for good workability.

Properties Value
Viscosity at 40oC <320 Centistoke
Moisture <0.5
Specific Gravity 0.9-1.0
Sediment (% Volume) <0.3

Coke Breeze:
Coke is used to increase porosity, increase volume of mass and decrease density. The porosity allows inside gas of Blast Furnace to escape through the mass, so that mass will heat up readily and harden within a very short period.
Carbon (%) 82-84
Ash (%) 16-18
Volatile Matter (%) 0.5-0.8
Size -1 mm

According to further embodiment of the invention, all the ingredients used for manufacture of the tap hole mass are processed before mixing in Muller Mixer (Fig.2).Muller Mixer is also knows as a Sand Muller, Sand Mixer, Edge Runner etc. Muller Mixer is used in Foundry, Ayurvedic & Herbal Products, Pharmaceutical, Minerals (Mica powder Grinding), Lime Mortar Grinding, Fly Ash Mixing, Rice Ash Husk Mixing , Carbon Black Mixing etc. Roller is casted. Roller fitted in such a way that maximum bottom area is covered. Both rollers are overlapping each other, so that no material is left on-ground. The rollers are running on ball bearing with sealing arrangement to prevent the powder going in to rollers are driven by oil filled specially design heavy duty 2 stage gear box and electric motor with starter & control panel. The main drive from motor to gearbox is attached by V-Belt pulley.

Plastic clay is dried in a rotary dryer (it is a type of industrial dryer used to reduce or minimize the liquid moisture content of the material by bringing it into direct contact with a heated gas. The dryer is made up of rotating cylindrical tube. The dryer slopes slightly so that the discharge end is lower than the material feed end in order to convey the material through the dryer under gravity) and then crushed.

The sieve analysis was carried out with a wide range of sieve sizes 1-3 mm (coarse fraction or CF), 0-1mm (middle fraction or MF) and -200 mesh or =75µm (small fraction or SF) and sieved in a vibrating sieve shaker (It is electrically fitted and provide three dimensional sieving motion with excellent separation efficiency within short sieving time) to avoid the clogging of sieves as well as to ensure efficient sieving. Coke is dried after screening it for (-) 1 mm size.

Pitch is crushed using Toothed Double Roll Crusher. Toothed Double Roll Crushers are used as primary as well as secondary crushing of the friable and brittle materials like Coal, Coke, Sinter (hot and cold), Clay, Earth, Slag, Chalk, Soft Limestone etc.

Due to cutting action of the teeth, crushing of material takes place mostly due to shear and not by pressing. Crushing takes place due to two rolls running in to each other and crushing the material caught in the valley of the rolls. One roll is fixed, while other one is adjustable.

Main aggregate bauxite along with other dry materials like plastic clay, silicon carbide, coke, pitch and powder resin were taken in a Muller mixer and mixed homogeneously in dry condition for 10-15 minutes.
The typical size fraction of the dry mix sample collected just before mixing the oil was noted as given below.

Size (mm) +1mm +0.5mm +180 mesh -180 mesh
% of mixed sample 17.5 - 19.5 (%) 12 - 13.5 (%) 20 - 23 (%) 44 - 50.5 (%)

According to further embodiment of the invention, Oil is heated up to 65-70oC in drier. Then hot oil was slowly added to the running Muller mixer and mixing/blending was continued for another 10-15 minutes. The entire process takes about 20-30 minutes. The lumpy mass discharged from the mixer was collected in a container and cut manually to pieces around 250 grams and kept in the boxes.
To characterise the prepared tap hole mass suitable for smooth operation of tap hole, different tests have been carried out both for green and fired samples. To shape the tap hole mass for different testing, a mould of size 50 mm diameter and around 80 mm height ware used. The tap hole mass was tightly poured into the mould and placed in sand rammer. Applying 20 strokes, samples with 50 mm diameter and 50 mm height were made. Samples were de-moulded and first dried in the drying oven at 100-120oC for 30 minutes and then fired in a gas fired furnace at 10000C for 8 hrs at reducing atmosphere.
The typical characteristics of tap hole mass manufactured above are given below:
Apparent Porosity (%) Bulk Density (gm/cc)
(Green Sample) Bulk Density (gm/cc)
(Fired Sample) Cold Crushing Strength (kg/cm2)
27-31 1.90-2.03 1.55- 1.65 53.5-63

The invention will be described with reference to following example without restricting the scope of the invention.

Example -1:
A process for preparing the tap hole mass for plugging the tap hole of blast furnace, the process comprising the steps of:
- mixing the bauxite homogeneously in dry conditions with other dry materials consisting of plastic clay, silicon carbide, coke, pitch and powder resin for 10-15 minutes.
- adding the preheated wash oil to the said running mixture and mixing it for 10-15 minutes.
-collecting the discharged mixture from the mixer in a container
-compressing the discharged mixture in a sand rammer by pouring the mixture into a mould and applying fixed strokes to achieve tap hole mass of desired shape.
-drying the tap hole mass produced after compression at 100-120°C for 30 minutes in a drying oven
-heating the dried tap hole mass at 1000°C temperature in a gas fired furnace for 7-9 hr at reducing atmosphere for obtaining a tap hole mass suitable for smooth operation of tap hole.

Example-2
A process for preparing the tap hole mass for plugging the tap hole of blast furnace, the process comprising the steps of:
- mixing the bauxite homogeneously in dry conditions with other dry materials consisting of plastic clay, silicon carbide, coke, pitch and powder resin for 10-20 minutes.
- adding the preheated wash oil to the said running mixture and mixing it for 10-20 minutes.
-collecting the discharged mixture from the mixer in a container
-compressing the discharged mixture in a sand rammer by pouring the mixture into a mould and applying fixed strokes to achieve tap hole mass of desired shape.
-drying the tap hole mass produced after compression at 100-110°C for 25 minutes in a drying oven
-heating the dried tap hole mass at 1000°C temperature in a gas fired furnace for 8 hr at reducing atmosphere for obtaining a tap hole mass suitable for smooth operation of tap hole.

While the invention has been described in detail with the help of a
preferred embodiment, the invention is not limited to the disclosed examples. Other variations can be deducted by those skilled in the art without leaving the scope of protection of the claimed invention.