VON PLOETZ, Klaus (1 Maja 15, Pezinik, Pezinik, SK-90201, SK)
ί. A tiltable electric arc furnace comprising:
(i) a tilt platform (5),
(ii) a shell (3) containing bath (4) of molten metal and provided with a peripheral opening,
c h a r a c te ri z e d by th e fa c t t h a t said bath (4) of molten metal is fed with scrap through an angled shaft (9) having a first lower end airtight connected with said opening of shell (3) and a second upper end with a charging box (12), flow of the scrap being controlled by movable fingers (10) placed at said first end and pushers (11) placed at angle of said shaft (9) which communicates with a duct (15) rotationally connected with a grounded duct (16), said ducts (15, 16) collecting process off gas preheating scrap being fed.
2. The tiltable electric arc furnace according to claim 1 , wherein said shaft (9) is supported on extension base (5b) of said tilt platform (5).
3. The tiltable electric arc furnace according to claim 1, wherein said shaft (9) communicated with duct ( 5) at a position approximatively below said charging box (12).
4. The tiltable electric arc furnace according to claim 1 , wherein said charging box (12) can be closed to the atmosphere by a pair of opposite cantilevered fingers.
5. The tiltable electric arc furnace according to preceding claim, wherein said charging box (12) is coupled with bucket (13) having a pair of opposite cantilevered fingers at lower end thereof.
The present invention relates to a scrap feeding system and, more particularly to a scrap feeding system able to be used to a conventional tiltable electric arc furnace.
The present invention also provides for controlling scrap feeding through an angled shaft into electric arc furnace; such angled shaft is connected to the electric arc furnace shell and supported through the platform allowing tilt movement thereof.
The conventional charging of an electric arc furnace is generally achieved by using a huge scrap bucket that involves some important problems for the electric arc furnace process such as generation of huge quantities of hot and dirty fumes and generation of flicker in the electrical network.
The trial to improve the situation through a better design of furnace plant in order to reduce the electrical flicker disturbance in the electrical network and the trial to use some of the energy associated with the off gas leaving the electric arc furnace shell for scrap preheating has a long history. In the beginning— around 1980— preheating of scrap in special scrap buckets became a popular option. However the smell that often accompanied this process created a big problem and stopped further improvements on this basis.
Florid Steel in Charlotte USA together with Valomy created the first complete Consteel ® Furnace. Tenova SpA took over this development years later and improved the performance, especially related to the maintenance issue. A continuous scrap feeding into electric arc furnace shell according to such process is generated through a big round opening in the off gas side of the shell. Through a horizontal conveyor system the scrap reaches the round opening and drops the scrap into the liquid bath. The whole electric arc furnace turns around the round shell opening thus allowing electric arc furnace tilting. The process is based on a big hot metal sump by which the scrap is molten. The electrical power is mainly used for heating up the liquid bath of metal sump and in such manner the flicker problem could be mostly solved. The process claims also gains in scrap preheating, but the final result is poor, since the required post treatment of the off gas consumes extra energy. Today Tenova SpA is offering the Consteel ® process and has contributed through improving the maintenance issues of this development. But the conveyor system requires a very special scrap handling arrangement and an effective sealing of the system against the outside atmosphere is difficult. Moreover the conveyor system and the tilting system are expensive and require intensive maintenance efforts. Also an effective sealing of the system against the outside atmosphere is difficult. Parallel to the Consteel process development several shaft solutions have been introduced, especially from the Fuchs company. Said solutions concentrated originally in the scrap preheating. Only recently the Continuous Optimized Shaft System (COSS) process tries also to reduce the flicker problem. However these shaft arrangements are all based on a separate foundation: for the electric arc furnace tilting function the connection between the electric arc furnace shell and the shaft needs to be opened, which results as a considerable disadvantage for the process control. The equipment that is needed for this process is still big and maintenance intensive and the required processing of the off gases can become expensive, depending on the scrap quality and the control options for the process. In addition due to the vertical shaft arrangement the preheated scrap has to change its flow direction drastically before it can enter the electric arc furnace shell.
The ECOARC ® furnace, designed by NKK Corporation, integrates the vertical shaft as a fixed part of the electric arc furnace design. It allows a continuous feeding, the liquid metal is melting the scrap and therefore the flicker problem is reduced like in Consteel ® process. However this approach requires the electric arc furnace design to be dramatically changed. Different space arrangements are required and at the bottom of the shaft it is still required to change considerably the flow direction of the scrap for which reason a strong and sophisticated pusher system is needed; moreover it definitively adds friction wear to the shell refractory.
All working solutions have still special weak points as mentioned in their brief description above thus leaving options for improvements. Either the required space for the integrated shaft unit is large, or the design requires too sophisticated pusher and sealing arrangements or a sophisticated treatment of the final off gas consumes too much of the original energy savings.
The scrap feeding system for a conventional electric arc furnace according to the present invention proposes a design capable to solve most of these weakness through a combination of special design features that will be clear from a detailed description of a preferred embodiment taken with reference to the annexed drawings in which:
fig. 1 is a perspective view of a conventional electric arc furnace provided with a scrap feeding system according to the present invention,
fig. 2 is a top view of the embodiment in fig. 1,
fig. 3 is a cross sectional view of the embodiment in fig. 1, and
figs. 4A and 4B show embodiment in its tilted end positions. Referring now to the figures, there is shown a conventional electric arc furnace 1 comprising a shell 3 and a roof 2 above it. Said electric arc furnace 1 is supported by a tilt platform 5 constituted by a gantry side 5a and an extension 5b on the off gas side which forms the base of a scrap feeding system, in turn, comprising an angled shaft 9 and a scrap preheating system 8 connected therewith. Tilt platform 5 is supported and driven by a set of foundations 6 and rockers 6a.
The embodiment therefore enlarges design of the electric arc furnace 1 with integrated scrap preheating system 8 that is based on the common tilt platform 5. This is the best option in order to always guaranty an airtight connection between the shell system 3 and the shaft 9. Moreover the use of the scrap preheating system 8 that is based on an angled shaft solution 9 allows for avoiding any mayor change in direction for the flow of the scrap into the shell section 3. Another option in order to improve the scrap preheating efficiency for the shaft section is to base the cooling system for this section on hot water or steam. Especially the common tilt platform supports such a solution. A controlled flow of the scrap into a liquid pool 4 of molten steel within shell 3 is important in order to reduce electrical flicker during the process of scrap melting.
The entrance of the shaft 9 into the shell 3 is controlled through a special combination of near vertical fingers 10 and near horizontal pushers 11 for pushing the scrap in a controlled manner into the liquid bath 4. An optional rotary pusher system 17 can help to improve the control of the scrap movement through the shaft 9. The fingers 10 are located in the top side of the shaft 9 controlling the top part of the opening between the section of shell 3 and section of the shaft 9. The system of near horizontal pusher 11 is located behind the bottom part of the shaft entrance into the section of shell 3. These devices control the flow of the scrap into the liquid metal bath 4.
The shaft 9 is designed as part of a duct system 7 for collecting the hot off gases generated by the electric arc furnace process. This allows to use part of the energy of these hot gases for preheating the scrap fed through the shaft 9. On the top entrance to this shaft 9, a special box system 12 allows to charge the shaft 9 without opening the shaft 9 and off gas duct system 7 to the surrounding atmosphere: a special scrap bucket 13 is designed to become part of the system 12 in order to achieve the fast and air tight recharging practice. Optionally said scrap bucket 13 can be used only during charging step thus not being fixed part of system 12. The main off gas quantity will leave the shaft 9 in an elevation considerable below the top charging box 12 at an off take point will which ensures that off gas temperature is high enough in order to avoid the creation of dioxin and furan. The off gas are then collected in a near vertical duct section 15. The transition point between the section of duct 15 based over tilt platform 5 and the section of grounded duct 16 is just below the tilt platform 5. The top elevation of the rockers [6a?] is the point where the transition from the movable duct section 15 and the stationary off gas section of grounded duct 16 becomes a minimum. A permanent sealing of this transition is best possible in this location.
An optional separate duct system 14 around the angled shaft 9 allows some of the off gases to bypass the bottom section of the scrap feeding shaft 9 and enter, through an air intake 14a, direct into the charging box 12. These gas will preheat the scrap that was charged last.
There is also an option to blow or allow the entrance of fresh air into the charging box 12 if this is required in order to support the final post combustion of the process off gas.
It is clear from the above detailed description that the present invention overcomes the drawbacks of the prior art and provides a scrap feeding system which does not require a specially designed shell incorporating the same. Those skilled in the art will also envision modifications and changes which can be applied to the disclosed preferred embodiment relating, for example, the scrap bucket or pusher system thus nevertheless falling within the scope of the present invention as claimed in the following.