CLIAMS:1. A process for preparing the tap hole mass for plugging the tap hole of blast furnace, the process comprising the steps of:
- crushing the waste refractories into pieces to the desired size followed by removal of the impurities magnetically
- sieving the crushed refractories in a vibrating sieve shaker to avoid clogging of sieves
-mixing the said sieved wastes 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 for obtaining a tap hole mass suitable for smooth operation of tap hole.

2. A process as claimed in claim 1 , wherein the waste refractories consists of SiO2 refractories, Al2O3 refractories, MgO refractories, ZrO2 refractories, and Carbon containing refractories.

3. A process as claimed in claim 1 , wherein the processing of the waste refractories involves crushing the waste refractories into pieces of 200-400mm

4. A process as claimed in claim 1, wherein the composition of sieved waste refractories are 70-75% of Al2O3, 1-5 % of ZrO2 respectively.

5. 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.

6. 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.

7. 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.

8. A process as claimed in claim 1, wherein the Pitch contains 19.21%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

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

10. 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

11. A process as claimed in claim 1 , wherein the wash oil was preheated to 60-70°c in drier.
12. 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
13. 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.

14. 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.

15. 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.

16. 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.

17. A process as claimed in claim 1, wherein the mixture is placed in a sand rammer by pouring the mixture into a mould of 50mm diameter and around 50mm height and applying 20 strokes by the said sand rammer to achieve tap hole mass of 50mm diameter and 50mm height.

18. A process as claimed in claim 1, wherein the mixer used is muller mixer.

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

of the following ingredients:
Materials Percentage (%)
Waste Refractories 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

20. A tap hole mass as claimed in claim 19, wherein pitch and wash oil are used as a binders.

21. A tap hole mass as claimed in claim 19, 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.

22. A tap hole mass as claimed in claim 19, 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.
,TagSPECI:Field of Invention

The invention relates to a process for preparing the tap hole mass for plugging the tap hole of blast furnace from the refractory wastes generated in Steel Plant and the tap hole mass made thereof. 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.

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 production of 1 ton of iron requires approximately 1.4 tons of ore or other iron bearing material; 0.5 to 0.65 tons of coke; 0.25 tons of limestone or dolomite and 1.8 to 2 tons of air. The by-products consist of 0.2 to 0.4 tons of slag and 2.5 to 3.5 tons of blast furnace gas.

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.

Tapping rate (tonnes/min) of iron and slag is determined by tap hole diameter, tap hole length, height 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 during tapping. 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.
Keeping into the view all the above aspects the present invention describes the method for manufacturing the tap hole mass from refractory wastes.

Prior Art
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 refractory which are used to plug the tap hole of Blast Furnace. 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 length that is smooth and permits steady drilling into the cured and hardened tap hole mass, provides a constant and lengthy tapping time with an appropriate tap hole mass durability and has stable filling properties at plugging.

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 tap hole mass should be resistant to erosion & abrasion by the iron and slag stream but must be capable of being drilled.
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 molten iron & slag.
6. Form a stable substrate for the next plug.
7. Provide a stable & controlled tap hole length.
To achieve the above mentioned functions, tap hole mass should have good workability, volume stability under high temperature, fast hardening & sintering behavior and better abrasion & corrosion resistance properties. The relationship between functions & characteristics are shown below:

Tap hole masses are plastic refractories. The essential features are slag resistance, a tendency to swell rather than shrink on firing in-situ and drillability, so that tap hole can readily open when required. These properties are generally achieved by using mixture of medium/high alumina clay and grog with carbonaceous material, such as coke, pitch or even graphite and silicon carbide.

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:
- crushing the waste refractoriesinto pieces to the desired size followed by removal of the impurities magnetically
- sieving the crushed refractories in a vibrating sieve shaker to avoid clogging of sieves
-mixing the said sieved waste refractories 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 and used as tap hole mass
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 (%)
Waste Refractories 30 - 32
Plastic Fire Clay 9.5 - 10.5
Silicon Carbide 14 - 16
Coke 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:
Waste Refractories:
In the iron making and steelmaking processes, different types of refractories are used for lining the furnaces for smelting, refining and transport operations. After a certain period of operation, the refractory lining is broken down and discarded. Previously a part of these waste refractories were recycled in different zones of steel plant and maximum portion were used for road filling. Nowadays, these waste refractories of steel plant are taken back by refractories makers for manufacturing of new refractories, gunning mass, ramming mass etc. In recent years, there has been growing pressure to reduce the specific refractory consumption and for recycling of waste refractories in the iron and steel industries.

In Iron and Steel making process, various types of refractories are used. Maximum refractories are SiO2, Al2O3, MgO, ZrO¬2 and carbon based. The waste refractories are sorted and categorized into SiO2 refractories, Al2O3 refractories, MgO refractories, carbon containing refractories and carbon free refractories etc. Also the waste refractories are associated with large piece of iron, slag and many other impurities. Before using these refractories, it should be free from those foreign particles. Hence, refractories wastes should be processed before using as raw materials for manufacture of tap hole mass. In this process, waste refractories are crushed and impurities are removed (iron, slag and other impurities manually and magnetically). The refractories are roughly crushed into pieces of 200 to 400 mm, so that they can easily be handled in the subsequent crushing/ pulverization steps. Again these crushed pieces are fed into the crusher to get the desired size. Following is the schematic diagram of processing of refractory wastes.
Waste Refractories
Classified Collection
Crushing
Magnetic Separation
Sieving
Sorted by Grain Size
Drying
Addition in the Matrix
The sieve analysis of the crushed refractories and its typical analysis are given below:
Size (mm) +1 mm +0.5 mm +180 microns -180 microns
% of waste refractories 1.5 - 4.5 (%) 0.5 - 5.0 (%) 4 - 8.5 (%) 82 - 94 (%)

Al2O3 (%) 70-75
ZrO2 (%) 1-5
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:
Pitch is used as a binding material, dissolves in wash oil and works as lubricant at high temperature.
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%
Wash Oil:
Wash oil is mainly used as lubricant, improving the fluidity of pitch and bonding in the mass and make the mass fluid enough for good workability. Distillation range of wash oil is chosen between 220-350oC, as the solubility of pitch is maximum in this range.
Properties Amount
Specific Gravity at 30oC 1.080-1.087
Drop point (oC) 200-230
Moisture (%) 2.0 (max)
Naphthalene (%) 2.77- 4.9
Distillation range (oC) 100% between 220-350oC

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. Plastic clay is dried in a rotary dryer 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 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 two roll crusher.

Waste refractories after processing were taken in a Muller mixer along with other dry materials like plastic clay, silicon carbide, coke, pitch and powder resin and mixed homogeneously in dry condition for 10-15 minutes.
The typical size fraction of the dry mix sample collected just before mixing the lubricant 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,wash oil is heated upto 65-70oC in drier. Then hot wash 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.
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)
28-32 1.90-2.03 1.55- 1.65 55-65

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:
- crushing the waste refractories into pieces to the 200mm size followed by removal of the impurities magnetically
- sieving the crushed refractories in a vibrating sieve shaker to avoid clogging of sieves
-mixing the said sieved wastes homogeneously in dry conditions with other dry materials consisting of 9.5% of plastic clay, 14% of silicon carbide, 7.5% of coke, 14% of pitch and 6% of powder resin for 15 minutes
- adding the preheated wash oil at 65°c to the said running mixture and mixing it for 15 minutes
-collecting the discharged mixture from the muller mixer in a container and used as taphole mass.

Example-2
A process for preparing the tap hole mass for plugging the tap hole of blast furnace, the process comprising the steps of:
- crushing the waste refractories into pieces to the 300mm size followed by removal of the impurities magnetically
- sieving the crushed refractories in a vibrating sieve shaker to avoid clogging of sieves
-mixing the said sieved wastes homogeneously in dry conditions with other dry materials consisting of 9.5% of plastic clay, 14% of silicon carbide, 7.5% of coke, 14% of pitch and 6% of powder resin for 15 minutes
- adding the preheated wash oil at 70°c to the said running mixture and mixing it for 10 minutes
-collecting the discharged mixture from the muller mixer in a container and used as taphole mass

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.