DE2742109A1 - Wind heater for blast furnaces - has internal sheath made of high alloy steel preventing stress corrosion at high temps. - Google Patents

Abstract

The heater, i.e. a Cowper stove, has a casing formed by welding several sections together, and inside the casing is a thermal insulating lining sepd. from the casing by an elastically deformable sheath extending from the dome of the stove to below the burner, the bottom end of the sheath being open and welded to the inner wall of the casing. Sheath deforms under the thermal and mechanical stresses arising in the stove. The sheath is pref. assembled from segments made of alloy steel contg. by wt. 0.03% max. C, 1% max, Si, 2% max. Mn, 0.03% max. P, 0.02% max. S, 21-23% Cr, 2.5-3.5% Mo, 4.5-6.5% Ni, 0.08-0.2% N2, remainder Fe, and the segments are welded together via U-sections permitting expansion and contraction. Provides cowper stoves operating above 1500 degrees C. on modern blast furnaces, where the sheath prevents stress corrosion cracking of the casing.

Description

Wind heater with one welded from jacket shots

Jacket The invention relates to a blast heater with one of jacket shots welded jacket, on the inner wall of which there is masonry for lowering the heat dissipation is arranged.

As is well known, wind heaters are used to heat the wind, i.e. more atmospheric Air under pressure, the oxygen of which is necessary for burning the coke in the blast furnace is.

By heating the wind for the blast furnace are opposite to the cold wind supply significant fuel savings achieved (an increase in wind temperature around 1000C each time brings a saving of about 4% coke).

In addition, the heating of the wind has a better influence on the Combustion processes in the blast furnace and the production of difficult-to-melt ones in the first place Pig iron types possible.

In principle, a distinction is made between two different methods of heating the wind. The periodically working regenerative process requires several wind heaters, whose working periods overlap, so that the blast furnace is constantly with a hot blast is supplied. During the working period, the heaters concerned are through Burning of furnace gas or mixed gas consisting of furnace gas and high-strength gas heated and in the subsequent period (wind time) of Wind through them passed through, heated and fed to the blast furnace. The cooled down stove are then heated up again, etc.

The second method, recuperative wind heating, only requires a stove. As with every recuperator (heat exchanger) takes place in a pipe system a heat exchange takes place between the burning furnace gas and the blast furnace wind.

The invention relates in principle to wind heaters for heating the wind both by one method and the other.

With modern hot air heaters for high temperatures, the dome temperatures are 0 reached up to 1600 C. It turned out that at such high hot wind temperatures and at the same time high wind pressures stress corrosion cracking occurs.

Nitrogen oxides are formed during the combustion of the furnace gas and the like as well as sulfur and chlorine oxides. There are also considerable amounts of hydrogen released from the hydrocarbons to be burned, which also oxidizes and is converted into the vapor phase. This steam hits the colder one Areas of the heater (below the dew point) and then reacts with the nitrogen oxides and the other acid-forming compounds with the formation of acids. Here, CO and C02 also lead to stress corrosion cracking.

Furthermore, considerable amounts of sulfur dioxide are also emitted released the fuels that condensed with the in these colder areas Water vapor under Formation of sulphurous acids react. Farther chlorides can also be formed, if appropriate for gas scrubbing Depending on the local conditions, water containing chlorine must be used.

Furthermore, for wind heaters according to the building regulations low-alloy structural steels are always used, which are always subject to mechanical tensile stresses and thermal stresses as well as residual welding stresses occur.

All of these factors, namely the mixtures of acids, the low Alloyed structural steel and tensile stresses cause stress corrosion cracking.

Various measures have already been taken to remedy this. To a To avoid condensation of the acid mixtures from the outset, wind heaters were already used Provided with an external insulation, which prevented falling below the dew point. The disadvantage is that the jacket of such an insulated heater is no longer readily accessible to an inspection. In addition there is that This isolation is difficult, especially in the area of the flanges and closures must be attached and local temperature increases cannot be safely avoided. This has the consequence that the heater cracks or explodes at these points can.

Attempts were also made to prevent stress corrosion cracking To prevent interior painting. Because these paints are always a plastic component exhibit, they decompose at the critical points, namely at those whose temperatures are above 1500C.

There were also already on the inside wall of the heater Aluminum- or stainless steel foil sheets attached, the material against stress corrosion cracking is insensitive.

However, these film webs have the disadvantage that they because of their very thin walls cannot be welded together in a gastight manner. A Gluing also did not lead to the desired success, since the adhesive material decomposes at higher temperatures.

The invention is based on the object of designing the heater in such a way that that they are under the current operating conditions, especially under the high Operating temperatures, at 15000 C and also below those expected in the future even higher operating temperatures can be operated without stress corrosion cracking occurs.

This object is achieved in that between the Mantle and the mantle masonry a from the dome to a level below the Burner for the furnace gas or fuel gas reaching, more open at the bottom under the thermal and mechanical stresses arranged elastically deformable protective sheath and the edge of the protective jacket is welded to the inner wall of the jacket is. According to the invention, completely new, Taken completely different paths from the state of the art.

The measures according to the invention ensure that the jacket The inside of the heater is to a certain extent shielded by a protective skin becomes, in which due to its elasticity under the thermal and mechanical stresses no tensions are built up, so that provided that if at residual stresses and welding stresses were avoided in their production, Stress corrosion cracking cannot occur even after long periods of operation. For these reasons the protective sheath consists of the low-alloy structural steels previously used, it can also for the same reason likewise as before aluminum, bronze and Like. Be used without the previous disadvantages occurring. As a result of his Elasticity, this protective jacket can easily follow changing operating pressures and, under extremely high pressures, can become attached to the inner wall of the jacket of the heater snugly, which consequently only has to apply the reaction forces.

In a further embodiment of the invention, the protective jacket consists of high-alloy stainless steel. These measures ensure that the protective jacket is resistant to stress corrosion cracking, even if during assembly or installation minor stresses have been applied. Surprisingly, it turned out that high-alloy steels of the following composition for the purpose according to the invention The following are particularly suitable: C maximum 0.030 percent by weight Si maximum 1,000 Mn maximum 2.000 P maximum 0.030 II S maximum 0.020 Cr 21,000 - 23,000 Mo 2,500 - 3,500 Ni 4,500 - 6,500 N 0.08 - 0.20 remainder iron The jacket of the heater is here welded together in the usual way from sheath sections made of low-alloy steels.

According to a first embodiment principle, there is the elastic protective jacket from jacket weft sections that are spaced apart from one another arranged are, the opposite edge zones of two jacket weft sections are welded to the legs of a U-profile. These measures achieve that even at different temperatures in the individual areas of a jacket shot the sheath weft sections expand or expand as a result of their spaced arrangement can move relative to each other and these movements and stretches from the Legs of the U-profiles are included. The can also in the radial direction Shell weft sections perform different movements, since U-profiles in this Direction perpendicular to the lateral surface also have spring properties. This distant arrangement on the one hand and the connection of the U-profiles On the other hand, it is possible to keep the protective sheath free from internal stresses as well as from Welding stresses together and at the same time avoiding that while longer operating times due to the different thermal and mechanical Loads in individual areas, internal stresses in the jacket sections or jacket section sections build up, which, as already mentioned above, could lead to stress corrosion cracking.

The jacket weft sections are advantageously in the direction of the dome of the successive jacket shots arranged offset to one another, with an two U-profiles each at the joints of three shell section sections Form T-shaped element. On the one hand, this staggered arrangement accordingly the usual conditions and regulations of welding technology are done and on the other hand through the use of these T-shaped elements an efficient production of the invention Protective sheath possible.

The U-profiles or the T-shaped elements are advantageous Arranged on the side of the protective jacket facing the jacket masonry, so that In the event of extremely high operating pressures, the protective jacket easily attaches itself to the inner wall of the jacket can snuggle up, which then acts as an abutment and to apply serves the reaction forces.

According to a second embodiment of the elastic protective jacket this consists of jacket shots, the jacket shots each with their upper, to the dome facing edge with the inner wall of the jacket and with its lower Edge the upper edge of the mantle section adjacent to the dome in the opposite direction overlap in a zone and are welded to it. Through these measures is created a protective jacket which is designed in the manner of a bellows and for this reason follow the thermal and mechanical loads without further ado can. Here, the jacket weft sections of the individual jacket wefts are continuous welded together, i.e. they are not like according to the first design principle arranged at a distance from one another.

A combination of the first and second embodiment is also possible possible.

In a further advantageous embodiment of the invention, both in the case of the protective jacket according to the first as well as according to the second embodiment principle the jacket weft sections provided with beads so that the jacket weft sections with changing thermal and mechanical loads in the area of these beads can deform, so take care of this through these additional safety measures It is borne in mind that internal stresses build up under all operating conditions is avoided.

Advantages and features of the invention are based on exemplary embodiments explained in more detail in the drawing. There are shown: FIG. 1 a section through a wind heater with external firing shaft in a simplified representation; Fig. 2 in a perspective illustration of two sheaths of the protective sheath according to FIG first embodiment; 3 shows a detail from FIG. 2 and the connection of two adjacent jacket weft sections by means of a U-shaped profile; Fig. 4 also shows a detail from FIG. 2 with a T-shaped element; Fig. 5 in perspective view of a section of the inner wall of the jacket, with the protective sheath also shown in the section according to the second embodiment and FIG. 6 shows a jacket weft section with beads.

In Fig. 1 is a blast heater with an external combustion shaft in the Section shown schematically. It consists of the burning shaft 1, the stocking shaft 2 and the dome connecting the two shafts 3. The burning shaft and the stocking shaft are each arranged on a foundation 4 and 5, respectively.

Burning shaft, stocking shaft and dome are known per se Way from jacket weft sections welded together. As can be seen from Fig. 1, is a walled masonry for thermal insulation and reduction of heat radiation to the outside 6 arranged in a manner known per se in the area of the inner wall of the jacket 12.

The firing shaft has a nozzle 7 and a nozzle 8 for the Supply of the furnace gas or another fuel gas and a nozzle 9 for the hot wind. The furnace gas or fuel gas is supplied with the Air burns in the schematically illustrated burner 10, with temperatures up to 17000C can be reached. In the stocking shaft there is a latticework (not shown) Arranged from refractory bricks, through whose channels the hot combustion gases are passed through and through the outlet 11 during a chimney, not shown the so-called heating time. As soon as the trimming stones have a predetermined Reached temperature, the heating time is activated by pressing the slider the wind time switched and the wind to be heated via the nozzle 11 through the Trimming stones passed, which is then fed to the blast furnace via the outlet nozzle 9 will.

Between the jacket 12 of the boiler and the jacket masonry 6, which is only shown schematically in part for the stocking shaft, is that according to the invention under the thermal and mechanical stresses elastic protective jacket 13, the is open at the bottom, arranged. It is at its lower end through the weld 14 in the combustion shaft and in the filling shaft through the weld 15 with the inner wall of the jacket 12 welded. These two weld seams 14 and 15 are in one Area in which such operating temperatures always prevail, so that stress corrosion cracking cannot occur.

In Fig. 1, the two weld seams 14 land15 run in one Height below the burner, so that it is ensured from the outset that the for the occurrence of stress corrosion cracking is not reached will.

According to the first embodiment principle, the protective jacket consists of one another distantly arranged jacket weft sections, the opposite edge zones from two coat weft sections each with the legs of one U-profile are welded.

Fig. 2 shows a perspective view of two sheaths of one such protective jacket. The successive jacket shots are 16 resp. 17 denotes, with a jacket weft 16 and this is followed by a nantel shot 17. These sheath shots consist of the sheath weft sections 16 ', 16 ", 16"' or 17, 17 ', 17 ", ...

In the present case, the jacket wefts 16 ', 16 ", etc.

and the jacket weft sections 17 ', 17 ", etc. have the same dimensions. The jacket wefts 16 and 17 differ only in that their jacket weft sections are arranged offset to one another.

As can be seen from Fig. 2, the opposite edge zones are connected by two shell sections with the legs of a U-profile 18.

Fig. 3 shows such a connection in perspective in the cutout. The edges 21 and 22 of the jacket weft sections 17 'and 17 ", respectively, are located at such a mutual distance that with all stretches this two jacket weft sections in their plane, both edges do not touch. Here the web 18 'of the U-profile is much wider than the mutual distance between them two edges 21 and 22, so that the two legs 20 and 19 of this U-profile in welded to these jacket weft sections at a predetermined distance from these edges are. When the two jacket weft sections 17 'and 17 "are stretched in their plane can the two legs 19 and 20 these movements, as indicated by the double arrows 23 is shown to follow elastically, while on the other hand for example upon movement of the jacket weft section 17 "in the direction of arrow 24 of the Web 18 'and the leg 19 in the manner of a spring element of this movement as well can follow elastically and reversibly. By this connection according to the invention of the sheath weft sections with the U-profiles arranged at a distance from one another the result is a very elastic connection, through which the build-up of tensions is safely avoided even during longer operating times.

Fig. 4 shows a perspective view of the joint of three Jacket weft sections, the jacket weft sections 16 "and 16" 'to the one Jacket weft 16 and the jacket weft section 17 'belongs to a jacket weft 17. At this joint is to connect the two jacket weft sections 16 "and 16 '' 'with each other and their connection with the jacket weft section 17 from two U-profiles existing T-shaped element 25 is provided, the webs 26 and 27 are wider than the mutual spacing of the jacket weft sections 16 " and 16 "'or the jacket weft sections 16' and 17 'or

16 '' 'and 17', so that a connection according to FIG. 3 through this T-shaped element is created. Also the staggered arrangement of these T-shaped ones Elements, the protective skin can follow the movements of the jacket without being in it Tensions can be built up.

Fig. 5 shows a perspective view of a detail of the Protective jacket according to the second embodiment principle. This is denoted by 30 and consists of the successive channel sections 31 and 32. Each channel section 31 or 32 consists of channel section sections 31 ', 31 ", ..., as well as 32', 32", 32 "', each over Weld seams 33 and 34 to form conical annular surfaces are welded together. These coat shots are each with their upper, to Dome-facing edge 35 or 36 welded to the inner wall of the jacket, protrude with their lower edge 37 or 38 over the weld 35 or 36 of the in the opposite direction to the dome adjacent jacket section 31 and 32 and are with this by a Weld 37 and 38 connected. In this way, the protective jacket has the elastic ones Properties of a bellows and can be subjected to mechanical or thermal loads easily follow, as well as at very high working pressures on the wall of the Cling to the coat. The welds 33 and 34 and 37 and 38 can be T-shaped Profiles 25 or U-shaped profiles 18 are bridged. This will increase the elasticity of the protective jacket enlarged. Tensions cannot arise.

Fig. 6 shows a jacket weft section 17 ″, the additional beads having. The shell section deforms under extremely high pressure loads in the area of these beads, so that the build-up of tension also through these beads are avoided.

The measures according to the invention result in a state of the art Completely new way of blasting heaters, whereby by the invention Measures from the outset the occurrence of stress corrosion cracking at the present prevailing and future working conditions, such as pressure and temperature, is sure to be avoided.

By using high-alloy stainless steel of the composition: C maximum 0.030 percent by weight Si maximum 1.000 Mn maximum 2.000 P maximum 0.030 S maximum 0.020 Cr 21.000 - 23.000 Mo 2.500 - 3.500 Ni 4.500 - 6.500 N 0.08 - 0.20 Remaining iron results in the highest level of safety, even when welding together of the protective jacket according to the invention should have developed tensions.

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Claims (8)

Claims 1. Wind heater with a welded from jacket shots Coat, on the inner wall of which there is a coat of masonry to reduce heat dissipation is arranged, characterized in that between the jacket (12) and the jacket masonry (6) one extending from the dome to a height below the burner, according to More open at the bottom under the thermal and mechanical stresses, more elastically deformable Protective jacket (13) is arranged and the edge of the protective jacket with the inner wall of the jacket is welded. 2. Wind heater according to claim 1, characterized in that the protective jacket consists of high-alloy stainless steel. 3. Wind heater according to claim 2, characterized in that the high-alloyed Stainless steel has the following composition: C maximum 0.030 percent by weight Si maximum 1,000 Mn maximum 2,000 P maximum 0.030 s maximum 0.020 Cr 21,000 - 23,000 Mo 2,500 - 3,500 Ni 4,500 - 6,500 N 0.08 - 0.20 balance iron 4. Wind heater according to claim 1, 2 or 3, characterized in that the protective jacket consists of jacket weft sections (16 ', 16 ", ..., 17 ', 17", ...), the jacket weft sections are spaced apart from one another are arranged and the opposite edge zones of two jacket weft sections are welded to the legs of a U-profile (18). 5. Wind heater according to claim 4, characterized in that in the direction to the dome, the jacket weft sections of the successive jacket wefts to one another are arranged offset and at the joints of three jacket weft sections two U-profiles each form a T-shaped element (25). 6. Wind heater according to claim 4 or 5, characterized in that the U-profiles are arranged on the side of the protective jacket facing the jacket masonry are. 7. Wind heater according to one or more of claims 1 to 6, characterized characterized in that the protective jacket consists of jacket shots (31,32), the jacket shots (31 ', 31 ", ..., 32', 32" ...) each with its upper edge facing the dome are welded to the inner wall of the jacket and with their lower edge the upper edge of the mantle section adjacent in the opposite direction to the dome in the edge zone overlap and are welded to it. 8. Wind heater according to one or more of claims 1 to 7, characterized characterized in that the shell weft sections have beads.