BLAST PIPE AND TUYERE ARRANGEMENT

Abstract: Coal dust and oxygen are supplied to the blast pipes (14) of a blast furnace through lances (22, 23) that comprises two concentric tubes (25, 26) that end adjacent the tuyeres (13) or in the tuyeres. The heat resistant tip of each lance forms an extension of the inner coal dust supply tube, and it also forms an extension of the annular space between the tubes (25, 26) in the form of a number of helical channels (42) through which the oxygen passes. It is advantageous to have more than one lance in each blast pipe and to have the lances extend obliquely into the hot blast channel (24) that is formed by the blast pipe (14) and the tuyere (13).

Description: BLAST PIPE AND TUYERE ARRANGEMENT This invention relates to a blast pipe and tuyere arrangement for a shaft furnace, comprising a blast pipe, a tuyere, and a coal injection lance that ends in the blast pipe or in the tuyere. The lance comprises two concentric tubes, the inner one of which is arranged to supply coal dust and the outer one of which is arranged to supply oxygen. Arrangements of this kind are known from US patents 4921532 and 3758090. It iε an object of the invention to provide an arrangement ' of this kind that provides for a stable combustion for a long period of time, and permits for complete combustion and high addition of coal. To this end, the invention has been given the characteristics stated in the claims. The invention will be described with reference to the accompanying drawings. Fig. 1 shows schematically in a longitudinal section a blast furnace with blast pipe and tuyere arrangements. Fig. 2 shows in a longitudinal secticr. and erlarged a por¬ tion of one of the blast pipe and tuyere arrangements shown in Fig. 1. Fig. 3 is an end view as indicated by the arrows 3-3 in Fig. 2. Fig. h shows in a longitudinal section a coal injection lance that iε schematically indicated in Fig. 2, the tip of the lance being removed in Fig. A. Fig. 5 shows, enlarged, partly in view and partly in a longitudinal section, the front portion of the coal injection lance shown in Fig. 1. Figs. 6 and 7 are transverse sections taken along the lines 6-6 and 7-7, respectively,. in Fig. 5. Fig. 8 shows, partly in view and partly in section, one of the two parts that form 1 the tip of the lance shown in Fig. 5. Fig. 9 shows a modified design of a detail shown in Fig. 2. Figs. 10A and 10B show together a modified design of a lance. iig. 11 is a section taken along lines 11-11 in Fig. 10. Fig. 1 shows schematically in a longitudinal section a blast furnace (shaft furnace). Two blast pipe and tuyere arrangements 10, 11 are shown in the figure. They are all supplied with hot blast from a circular distributing pipe 12. In Fig. 2 are shown a tuyere 13 and a blast pipe 14. In a conventional way, the blast pipe consists of a ceramic-lined steel tube and a water-cooled copper jacket 15 to which the tuyere 13 is affixed. The tuyere 13 is made of copper and it is water-cooled as is conventional. The tuyere 13 seals with a conical surface 16 against a water-cooled copper jacket 17 in the blast furnace wall. The blast pipe 14 and the tuyere 13 form a hot blast channel 24. The tuyere 13 is not symmetrical, but points a few degrees downwardly. It could as well be sym¬ metrical. Two tubes 18, 19 extend as channels obliquely through the wall of the blast pipe 14, and two coal injection lances 22, 23 extend through the tubes 18, 19 into the hot blast channel 24. As shown in Fig. 3, the two tubes 18, 19 are in two planes that pass through the longitudinal axis I of the blast pipe 14, and the axes of the lances 22, 23 intersect the axis I of the blast pipe 14 in a common point. In Fig. 3, the tubes 18, 19 are shown at right angles to each other as seen in a plane transverse to the blast pipe 14. This angle is not the optimum angle, but the optimum angle is probably in the inter¬ val 150-180°. In Fig. 3, only the front end portions of the lances 22, 23 are shown; the rear ends are not shown. A lance without its tip is shown in Fig. 4. It consists of two concentric tubes 25, 26 that are coupled together at their rear ends by means of a resilient compensator 27. The compen¬ sator 27 consists cf two springy steel plates 28, 29 welded to a mantle 30. One of the the steel plates is welded to the inner tube 25 and the other to the outer tube 26. The front end of the inner tube 25 has an outer thread 31, and the front end of the outer tube 26 has a conical surface 32. The inner tube 25 has a fitting 33 for receiving the coal dust suspension (coal dust suspended in air) , and the outer tube 26 has a fitting 34 for receiving oxygen. In Fig. 5, the front end of the lance shown in Fig. 4 is shown with its tip mounted. The tip of the lance consists of a body 40 of heat resistant material screwed onto the inner tube 25 to be affixed thereto. A sleeve 41 iε screwed onto the body 40 before the body 40 is screwed onto the inner tube 25. Then, when the body 40 iε affixed to the inner tube 25, the sleeve 41 is screwed to abut with its conical end surface against the conical end surface 32 of the outer tube 26 so that the com¬ pensator 27 is preεtressed to secure a tight seal between the outer tube 26 and the sleeve 41 also when the longitudinal thermal expansion of the inner tube 25 and the outer tube 26 differs. The tip 40, 41 of the lance can for example be made of heat resistant stainless steel or it can be made of a heat re¬ sistant machinable sinter metal. It can also be ceramic. A longitudinal central channel 45 in the body 40 forms an extension of the inner tube 25. The channel 45 has a mouth 44. The body 40 has a number of helical grooves 25 in its outer cylindrical surface. In the illustrated embodiment there are six grooves 42. The pitch angle of the grooves should prefer¬ ably be 25-55 , it is shown as about 45 . The body 40 with its grooves 42 extends forwardly out of the sleeve 41. The front * edge 43 of the sleeve 41 defines the mouths of the helical channels formed by the grooves 42 and the sleeve 41. The oxygen expands radially when it passes the front edge 43 of the sleeve 41. The body 40 should extend forwardly of the front edge 43 of the sleeve so that the mouth 44 of the coal dust channel 45 iε located a distance forwardly of the mouths of the oxygen chan¬ nels 42. Typically it could be located 5-15 mm forwardly of the mouths of the oxygen channels 42. As much as possible of the pressure drop of the oxygen should take place at the outlet, and the helical channels should therefore not be longer than 1% full turns, preferably they should be 1 full turn or less. They should, however, not be shorter than one third of a full turn in order to ensure proper rotation of the oxygen. Typically, the diameter of the tip body 40 can be 20-30 mm, and the entire length of the lance can be 2 m. With lance tips as shown and illustrated there will be stable lightning, stable rotation and stable combustion. The coal dust will burn completely in the raceway, that iε in 4-6 milliseconds, also at high coal injection levels. The oxygen in the outer tube 26 cools the inner tube 25 so that air can be used as carrier of the coal dust. The oxygen rate of the carr¬ ier air may be reduced by the addition of nitrogen. Figs. 10 and 11 show a modified design of a lance. Fig. 10A shows the rear end of the lance, and Fig. 10B shows the front end. Parts corresponding to parts in the previous figures have been given the same numerals as in these previous figures. The tip body 40 is screwed onto the Inner tube 25 as in the previous embodiment. There iε, however * , no sleeve 41, but the outer tube 26 is extended forwardly, and it has a sliding fit to the tip body 40. The threaded portion 50 of the inner tube 25 extends rearwardly and is in threaded engagement with a nut 51 that has three legs 52 affixed to the outer tube 26 by means of screws 53. At the rear end of the lance there is a sliding connection 54 with an o-ring 55 on the outer tube 26 through which the inner tube 25 extends. Thus, by turning the inner tube 25, one can adjust the axial position of the tip body 40 relative to the front edge 43 of the front portion 41 of the outer tube 26. If the coal suspension is supplied to the inner tube 25 through a swivel coupling, the adjustment can be made also during operation. The difference in thermal expansion be¬ tween the tubes 25, 26 is taken up as a sliding movement in the sliding connection 54 at the rear end of the lance. Thus, the thermal expansion does not change the axial position of the tip body 40 with respect to the front edge 56 of the outer tube. In this respect, there is no difference between this lance and the previously described one. In both embodiments, the two tubes 25, 26 are fixed to each other at their front ends. With this lance of Figs. 10 and 11, however, the axial position of the tip body 40 relative to the edge 56 of the outer tube 26 can be adjusted when the lance is in its operative position. Thus, one can make fine adjustments of the flame by turning the inner tube while the flame is burning, for example if the quality of the coal dust changes. It also permits for adjustment when the lance tip body 40 or the edge 56 of the outer tube 26 has been eroded. In Fig. 10, the front surface of the tip body 40 is shown flush with the front edge 43 of the outer tube 26, but the threaded portion 50 of the inner tube 25 permits for a wide range of axial adjustment. When the tip of the lance is worn out, the damaged front por¬ tion of the outer tube 26 is cut off, a new tip body 40 is screwed onto the inner tube 25 and a new front piece 41 of the outer tube is welded to the outer tube 26. This new front piece of the outer tube 26 corresponds to the sleeve 41 in Fig. 5. The temperature in the annular space between the tubes 25 and 26 is gauged with a thermoelement 56. It is advantageous to have more than one lance in each blast pipe and to have the flames collide, for example to have two lances as illustrated. Then the lance tips should have their grooves helical in opposite directions so that the flames will be counter-rotating in order to further enhance the com¬ bustion. The combustion will be still improved when the lance tips are at an angle to each other and to the centre axis of blast pipe 14, as illustrated, instead of being parallel to each other and to the axis of the blast pipe. The lances will be considerably better supported when they extend obliquely through the wall of the blast pipe 14 instead of extending longitudinally through the entire blast pipe, and the risk of lance tip vibration due to dynamic forces is reduced which is advantageous per se, but is also advantageous to the combus¬ tion. Fig. 9 shows a modified design of the blast pipe 14. The tubes 18, 19 are displaced rearwardly so that the lances 22, 23 end in the blast pipe 14 instead of in the tuyere 13 as in the previous figures. It would also be possible to have the lances extend through the wall of the tuyere 13 instead of through the wall of the blast pipe 14. Then, the lance tips will be dis¬ placed forwardly so that the combustion will not heat the tuyere so much and, consequently, less heat need be conveyed off the tuyere by the cooling water. All the blast pipes 14 can suitably be provided with coal injection lances, but in certain cases it can be desirable to provide only some of the blast pipes with coal injection lances.

Claims: CLAIMS 1 Blast pipe and tuyere arrangement for a shaft furnace, comprising a blast pipe (14) , a tuyere (13) , and a coal In¬ jection lance (23) that ends in the blast pipe or in the tuyere, the lance (23) comprising two concentric tubes (25, 26) , the inner one of which (25) is arranged to supply coal dust and the outer one of which (26) is arranged to supply oxygen, c r a c t e r i z e d in that the lance (23) comprises a heat resistant tip (40, 41) that forms an extension of the annular space between the tubes (25, 26) in the form of a number of helical channels (42) that are separated from and surround a central coal dust supplying channel (45, 44). 2 Arrangement according to claim 1 c h a r a c t e r i z e d in that the mouth (44) of the coal dust supplying channel (45) is located a distance forwardly of the mouths of the helical channels (42) . 3 Arrangement according to claims 1 or 2 c h a r c t e r i z e d in that said helical channels are formed as helical grooves (42) in the outer surface of a tip body (40) in which said central coal dust supplying channel (45) Is formed, the grooves (42) being covered by a sleeve (41). 4 Arrangement according to claim 3 c h a r a c t e r i z e d in that said tip body (40) extends forwardly out of said sleeve (41) so that the front edge (43) of the sleeve defines the mouths of said helical channels (42) . 5 Arrangement according to any one of the preceding claims c h a a c t e r i z e d in that the axial position between the outer tube (26) and the inner tube (25) is fixed adjacent the tip (40, 41) of the lance, and a device (27, 54) iε arranged at the rear end of the tubes to permit relative axial movement between the tubes (25, 26). 6 Arrangement according to claim 5, c h a r a c t e r i z e d in that a nut (51) is fixed to the front portion of the outer tube (26) and is in connection with a threaded portion (50) of the inner tube (25) so that turning of the inner tube (25) will adjust the relative axial positions between the outer and inner tubes (25, 26). 7 Arrangement according to any one of the preceding claims, c h a r a c t e r i z e d in that said helical channels have a pitch angle in the interval 25-55 . 8 Arrangement according to claim 7 c h a r a c t e r i z e d in that the helical channels extend 0.5-1.5 full turns. 9 Arrangement according to any one of the preceding claims c h a r a c t e r i z e d in that there are at least two lances (22, 23) and the lances are directed obliquely to each other, so that their flames collide. 10 Arrangement according to any one of the preceding claims c h a r a c t e r i z e d in that there are two lances (22. 23) , one of which has its helical channels (42) counterrotating relative to the other.

Inventors: LINDFORS NILS OLOV, SKOELD BROR ERIK, WIKSTROEM JAN OLOV, LINDFORS, NILS, OLOV, SKOELD, BROR, ERIK, WIKSTROEM, JAN, OLOV
Applicants: SSAB TUNNPLAAT AB
Application year: 1992
Main classification: C21B7
IPC codes: C21B5, C21B7