| C L A I M S
1. The "CART WITH TROLLEY FOR CHANGING TUYERES" (14) operable by two workers only, aims to reduce the time spent on the tuyere and the blast furnace cooling boxes replacements and to increase the work security and hygiene, characterized by consisting of a cart with a superior part that contains a trolley that slides horizontally over the aforesaid table and whose dimensions allow it to get inside the tuyere (8) cooling box (7).
2. The "CART WITH TROLLEY FOR CHANGING TUYERES", according to claim 1 , is characterized by having a superior table (15) and a trolley
(17) that slides on the tracks (18) of such table (15) that can be introduced in the tuyere (8) cooling box (7) and by also having the structure (16) and the wheels (19). |
"CART WITH TROLLEY FOR CHANGING TUYERES" Field of this patent:
Productivity and Work Security in blast furnace maintenance. State of the Art. Blast furnaces constitute the core of the steel industry. It is in them that the iron oxid ores, granulated or pre-processed to make "sinter", are subjected to the hot chemical reduction process, having the carbon as reagent, and they are turned into a metallic alloy composed of more than 97% of the iron element, called "cast iron/pig iron". The metallic iron in liquid state, with a temperature of about 1 ,500 Centigrade degrees and that flows from the blast furnaces in the runs, is taken to the other pieces of equipment of the steel plant, which will process it to turn it into steel, that is, a complex alloy of iron and other elements with the fewest contents of sulfur, phosphorus and other contaminants as possible. We say that the blast furnaces are the core of the steel industry because they supply the raw material to all the subsequent processes. •
The modern blast furnaces are located in the center of a complex of peripheral pieces of equipment that are responsible for their high productions and quality; the regenerators increase their thermal economies allowing the air injection through their tuyeres to be done at about 1 ,200 Centigrade degrees, special lances make the coke or charcoal fines {breeze) be injected through their tuyeres in order to rise their thermal performances, they receive sinter rather than the granulated ore, besides a stoichiometric amount of water steam in such a way, due to their geometry, that they use the hydrogen formed as a reducing element.
Nowadays, supported by the technological advances in the last 50 years and by the recent automation support, the blast furnaces are considered to be near their maximum evolution limit, that is, obtaining improvements in the industrial reduction process for oxidated iron ores is only possible with radical changes of paradigm.
Due to economical matters related to the productivity and to the cost reduction, the blast furnaces must have bigger and bigger production capacities, of about millions of tons/year.
The current operational indices are around 99% of the time and the high productivities reached are also due to the millions of dollars invested in the automation and computerization of the blast furnaces.
However, when the costs of each stopped hour are observed, a huge need of innovating the processes and maintenance equipment of the pieces and of the most wear-to-be equipment is noticed so that the stopped hours can be reduced.
A blast furnace with a production of 2,800,000 tons per year produces 7,670 tons a day or 320 tons an hour.
For the current prices of US$250.00 per ton of cast iron/pig iron, there is a theorical production loss of US$80,000 per stopped hour. Taking the finished products of about US$500.00 per ton into consideration, the production loss per stopped hour is that of US$160,000.00.
One should also take into account that when a blast furnace process is interrupted, it is rather slowly than abruptly, previously decreasing the production for several hours and similar timings are necessary for returning to the status of maximum production process.
This means a loss of basic production - despite other systemic losses - of about US$200,000.00 per stopped hour.
However, despite the great technological advances of the blast furnaces and of the peripheral pieces of equipment that support them, those simplest pieces of equipment, such as the pieces of equipment and tooling for changing tuyeres and many others, have been the same for decades.
Analyses reveal that the maintenance halts, whether programmed or not, of the simplest pieces of equipment which are auxiliaries for the blast furnace work, such as the water hoses, the sealing refractories of the iron notches,
tuyeres and tuyere cooling boxes, etc. , are responsible for great losses of their productivities.
Thus, the equipment productivity and the operational processes improvements, known as "supportive services and equipment to the blast furnace", have been the target of great managing efforts, once their importance is clear in order to reduce the number of stopped hours.
It must be stated that the maintenance services performed in the blast furnaces are carried out in extremely hard conditions, due to the high temperatures near such equipment, due to the restricted conditions of space for movement and correctly anatomic positioning, besides always demanding great physical efforts, as they deal with heavy pieces and tools that are hard to handle; in other words, such tasks take long to be carried out due to the local conditions and to comply with the work security rules.
According to the current State of the Art, the two most difficult and that take the longest time to be removed and replaced are the tuyeres and their cooling boxes, for the following reasons:
1st - They are pieces that respectively weigh an average of 150 and 750 kilos;
2nd - They are very difficult pieces to be handled and they cannot get scratched or suffer any other kind of damage;
3rd - The places where the tasks are carried out are restricted and extremely hot;
4th- The cooling boxes are connected with the tuyeres by pressure in order to generate sealing, by a perfect overlapping; the tuyeres have a straight contact with the hottest area of the blast furnace, that through which the heated air enters at around 1.200 degrees Centigrade, enriched by five percent more of oxygen; it is through them that the coal fines dragged by the nitrogen are injected. As both the tuyeres and part of -their cooling boxes operate under extremely complex and aggressive chemical conditions, both accumulate fused metal and a number of other compounds on their surfaces
that come to weld among themselves and with the places where they are fit in the blast furnaces and, therefore, they are extremely hard to be removed.
5th - The average time for replacing these two pieces is around 17 hours and the operation must be performed when the blast furnace is stopped; taking the aforesaid values into account, one can see the value of hte losses due to the current State of the Art for these two pieces replacement.
The object of this patent "CART WITH TROLLEY FOR CHANGING
TUYERES" constitutes the result of investments and systematic efforts in researches and experiments in the sense of reducing the number of stopped hours for removing and replacing the tuyeres and their cooling boxes.
Advances in the State of the Art of the object of this patent.
The use of the "CART WITH TROLLEY FOR CHANGING TUYERES", object of this paten, comes to replace the tooling and the tuyere replacement process that consists of removing them from the places where they are installed and taking new tuyeres to these places, which, by the current State of the Art it is performed by using pulleys, metallic ramps, winches and it requires human effort besides being a source of risks to the work security.
By using the "CART WITH TROLLEY FOR CHANGING TUYERES", the State of the Art advances as it gets to: A - reduce the average time of the tuyere and cooling boxes replacement operation, decreasing the losses due to production interruption as cited above;
B - minimize the workers' physical efforts and allow them to be made under better postural conditions, complying with the norms of Work Hygiene; C - increase the operation security;
D - minimize the equipment damage risk.
Illustrations, description and operation of the "CART WITH TROLLEY FOR CHANGING TUYERES", object of this patent that consists of a cart with a table on its top that contains a trolley that slides horizontally over such table
and whose dimensions allow it to get inside the tuyere cooling box, both for taking it to the place where it will be installed and to remove it from there when replacing it.
The "CART WITH TROLLEY FOR CHANGING TUYERES" is operable by two workers only under highly safe conditions and it .demands the least human effort as possible.
For the perfect understanding of the advances acquired in the State of the Art by the object of this patent, Figure 1 illustrates the relations of the set "tuyere- cooling box" with the other blast furnace pieces when it is ready in operation; Figure 2 shows the details of the working area where .the tuyere cart will operate after the blast furnace halt and the disassembly of the pieces needed to the tuyere removal operation.
Figure 1 is a schematic frontal cut that omits, for simplicity matters, the representation of the unnecessary pieces for the issue understanding, such as refractories, the display, the fast hitch hoses of cooling water, etc.; in it we see the ring-like tube, the heated air dispenser (1), the straight tube (2), the dilatation joint (3), the several flanges (4) that link these pieces, the pipe bend (11), the conic tube (5), the nozzle (6), the cooling box (7), the tuyere (8), the tuyere (8) seat (9) and the cooling box (7) seat (10), such conformations of these pieces that, respectively, allow the perfect adaptation and sealing between the nozzle (6) of the conic tube (5) and the tuyere (8) and between this and the cooling box.
Figure 1 also shows the blast furnace metallic furnace shell (13) to which the holder (12) is attached, which is seen from a frontal cut in this figure and must be understood as a welded ring, or somehow fa.stened to the blast furnace shell (13) and where the pipe bend (11) and, therefore, the conic tube (5) are tightly held by tie rods, thus keeping the cooling box (7) and the tuyere (8) contained in it, placed in their operational position.
Figure 2 is the same as the Figure 1 illustrating the working area ready for the removal and the placement of the tuyere (8), that is, the conic tube (5) and the pipe bend (11) are removed from it; the cooling box (7), the blast
furnace metallic shell (13) and the holder (12) are also seen in it, besides the A-B and C-D lines that indicate, respectively, the ground level and the maximum height of work area, limited by the flange (4) of the straight tube (2), being the height of such a degree that the workers ' are forced to work inclinedly.
Figure 3 is a schematic view from above of the "CART WITH TROLLEY FOR CHANGING TUYERES", (14) in which the structure (16), the superior table (15) that contains tracks (18) on which the trolley (17) slides horizontally, over rolls, wheels or any other way, can be seen. Figure 4 has a schematic side view of the "CART WITH TROLLEY FOR CHANGING TUYERES", (14) in which the trolley (17), the superior table (15), the structure (16) and the wheels (18) are seen.
Figure 5 illustrates the "CART WITH TROLLEY FOR CHANGING TUYERES" positioned in its work area, that is, introduced in the interior of the cooling box (7) for the tuyere (8) removal operation that was previously separated from the cooling box (7) and the trolley (17) being displaced to as close as possible to the tuyere; the wheels (18), the structure (16), the metallic furnace shell (13) and the holder (12) can also be seen. (14).
Figure 6 is a view of the "CART WITH TROLLEY FOR CHANGING TUYERES" (14) positioned in its work area for the tuyere (8) removal operation already displaced from the cooling box (7) and placed on the trolley
(17), which is shown displaced up to getting over the structure (16) and ready to be removed from the place to give room to another identical piece of equipment, with the new tuyere (8) to be placed by the inverse operation; the metallic furnace shell (13) and the holder (12) can also be seen.
Although the work of the "CART WITH TROLLEY FOR CHANGING TUYERES" is simple and evident, as shown in the Figures, it leads to the expected results of time economy, operational comfort, work security and hygiene.
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