DE1508268A1 - Process for heating a metal batch in an immediate arc furnace and an immediate arc furnace to carry out this process - Google Patents

Description

Dr. Ing.E. BERKENFELD, patent attorney , COLOGNE, Univertitätntraee 31

AnIo ₀ .

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Dr.Expl

Method of heating a metal batch in an immediate arc furnace and an immediate arc furnace for implementation

this procedure. .

The present invention relates to a method and an apparatus for heating a metal charge in an immediate electric arc furnace with carbon electrodes, in which the charge is replaced by an additional Gas combustion unit as well as by the electric arc is heated.

In the manufacture of alloys and castings in the metal industry the direct electric arc furnaces find very widespread use. However, great economic ones arose Problems with the use of electric furnaces for melting metal, because the electric melting of the largest possible batch is quite *, It takes a lot of time and melts a cold Charge a lot of electricity is consumed. At the beginning or during the melting period, electricity and electrodes are consumed in electric furnaces extremely high and is often a multiple of that during the subsequent Prisch period occurring consumption. From the start of melting the batch in an electric furnace to its completion oxidation occurs in the furnace to varying degrees, so that

z. B. in the production of steel the phosphorus, silicon, manganese

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Carbon and other elements present to form slag or gases are oxidized. This oxidation process causes the "cleaning" of the

'' Steel and at the same time leads to an undesirable loss of carbon

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fuel and other alloy elements. Consequently, after the Piling up of the steel and the removal of the Jchl ^ cko frequently Carbon and alloy element additions are added to the furnace to make up for the loss of carbon and desired elements and to the desired chemical composition of the Melt to come. A problem arises, however, as if too much during the melting and fresh odor de-ashing ^ process Carbon and other elements from the furnace charge have been burned out, large carbon and alloy element additions to the Compensation of the losses are necessary, which can lead to an undesirable and premature cooling of the 'Jmmelzbad. E.j is therefore extremely advantageous to keep the oxidation of the carbon as low as possible and to control it, so that the necessary additions are not large enough to control the temperature of the molten batch to change significantly.

The known attempts to solve the problem, namely the high power consumption during metal melting in an electrical Furnaces have resulted in various systems and processes in which the conventional electric furnaces have additional incinerators be used. Typical of these known experiments is the arrangement of complex and ineffective combustion devices, which are arranged in a very special geometric arrangement around the inner cavity of the electric furnace in order to provide support the furnace electrodes add additional heat during the melting process produce.

From the use of the previously known additional heating devices However, a major problem has arisen from the increased oxidation of carbon and other alloy elements because of the

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incomplete combustion of the hydrocarbon fuel and the air in the flame entering the area of the metal contained oxygen, which indirectly intensified the oxidation. These increased oxidation of carbon and other elements to the fact that to compensate for large amounts of expensive additives in the molten metal given v / ground, these amounts being so great that they had a cooling effect on the molten metal bath.

Recent attempts to avoid too high an oxygen content in these additional flames resulted in various expensive and complicated types of burners, the special premix and pre-combustion chambers exhibited. Because of their special flame generating properties, these burners had to be arranged in such a way that the The flame did not hit the charge directly because the charge and the electrodes arranged in its center passed through particularly easily excess oxygen can be damaged. The result was a process in which the flame was the additional heater only acted tangentially or peripherally on the charge, although a compromise at the expense of the efficiency of the flame in addition generated heat was closed and consequently resulted in a fuel consumption that was greater than in the case where the flame can be aimed directly at the center of the batch.

The electric furnace and the additional combustion unit according to of the present invention were designed so that the undesirable oxidation of carbon and other alloying elements of the Metal is as small as possible, while at the same time there is the possibility of the flame acting directly on the middle part of the batch allow. The new arrangement means that the

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Do not melt any more by large and expensive compensatory additions of carbon and alloy elements is cooled and the electrodes of the electric furnace no longer damaged.

The general object of the present invention is to provide one electric furnace and an additional combustion unit to improve the economy in the production of metal and metal alloys.

Furthermore, the invention is intended to provide an immediate electric arc furnace, which has a simple and removable combustion unit, which is mechanically attached to the furnace when the melting capacity of the electric furnace is to be increased.

In particular, the invention is intended to provide an instantaneous arc furnace and to provide an auxiliary gas incineration system in which undesirable oxidation of the metal charge is extremely low and damage of the electrodes is avoided while the flame is directed directly at the metal charge.

The method according to the invention is characterized in that the amount of electrical energy consumed by the arc is carried out by Adjustment of the electrode heat output kept within certain limits and an intense flame from the gas combustion

unit is aimed directly at the batch to a great extent greater heating of the charge than can be achieved with the electric arc.

A direct arc furnace according to the invention is characterized in that the combustion chamber of the combustion unit has an open flame discharge side and that the burner detaches

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bar is attached to a wall side of the furnace, the furnace im Inside has a substantially cylindrical shape and the flame is directed such that it is directly on the metal charge and radially hits the electrodes.

The basis of the present combination is the result of combustion of air and a natural gas such as is commercially available to industrial consumers in an open-front oven, the burner carrying large quantities during combustion Generates nitrogen and at the same time with the flame these carry nitrogen to the charge and leads to the electrodes, so that neither Metal nor the electrodes in the furnace are a lot above normal experience lying oxidation. In fact, the charge and the electrodes are permanently provided with an inert or inert covering, which also strokes through the furnace and withdraws through the ventilation openings, the electrode openings and the tapping opening, during the The burner directs the flame directly onto the batch in order to utilize the maximum amount of thermal units in the fuel. These Results are achieved by the invention without the burner having to have a special geometrical arrangement or the conventional ones electric ovens have to undergo a major modification and without the need for a burner with a special pre-combustion chamber or appropriate fuels would be required.

The invention is explained below using an exemplary embodiment and much more widely described with reference to the accompanying drawings.

Fig. 1 shows a vertical section through a conventional direct Arc furnace to which the transportable combustion unit is attached.

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Pig. 2 shows, on a larger scale, a front view of the transportable Combustion unit according to the invention, with a part of the burner device for better illustration '..'! has broken away.

Pig. j5 shows a plan view of the furnace shown in FIG.

Pig. FIG. 4 shows a vertical cross section through the furnace according to FIG Line 4 - 4 in Pig. yy.

Pig. 5 shows the combination according to the invention in a side view a combustion unit and an electric furnace, wherein both elements are shown separately from one another in solid lines, while the representation in dash-dotted lines Lines depicting the combustion unit attached to the furnace.

Pig. Figure 6 shows a detailed plan view of the combustion unit partly in cross-section to arn the combustion system Furnace attached and to show in operating position.

Pig. Figure 7 shows in a side view that side of the combustion unit which is attached to the furnace.

For example, from Fig. 1 it can be seen that the electric furnace has a substantially cylindrical metal shell 12 with a refractory brick lining 14 which defines an inner, substantially cylindrical cavity 16 which has an either acidic or basic lining or hearth surface Io. J, ± ne loading door 20 provided with a refractory lining is provided on one side of the shell 12 and a tap hole and a discharge channel

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2 ?. Are arranged in a conventional manner offset from the dosing door 20 by 90 in the circumferential direction. In the wall of the shell 12 you can after lie may or expediency (not shown) provide ge suitable ventilation nozzles to facilitate the gas discharge from the furnace 7λχ.

A doniartit? The shaped roof 2h is detachably mounted on the furnace and has three openings 26. In each of the openings 26 is provided an elongate graphite or carbon electrode 2o and also conventional staples ^ O on support arms J> 2 are arranged, the y by an element located next to the furnace mast \ protrude, so that the rush by suitable mechanical means for raising or lowering the electrodes relative to the metal charge on the hearth surface 18 can be raised or lowered. The arms 32 carry power supply cables 36 which connect the electrodes 28 to transformers (not shown) for the controlled supply of electrical energy to the furnace. To remove the roof 24 from the furnace, suitable lifting devices or other mechanical devices can be provided in a known manner, so that the furnace can be loaded from above; If desired, the furnace can also be loaded through door 20. After the furnace has been charged and after the melting and refining process has been completed, the furnace can be tilted forward in the direction of the tapping hole and the channel 22 in order to pull the metal out of the furnace. Suitable mechanical pivoting mechanisms for tilting the oven are known to those skilled in the art and consequently are not shown in the drawings.

For making the oven combination according to the present invention is the loading door 20 with an annular opening 38 provided, through which a portable combustion unit, generally

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at 40 and a substantially cylindrical burner 42 has, at the same time, an intense flame and a stream of inert nitrogen gas directly on the metal charge on the stove top 18 direct. The transportable combustion unit 40 is mechanical attached to the door, the cylindrical burner 42 in the axial direction with an open front 4} and an annular Flange 44, which surrounds the mentioned bore concentrically to opening 38, is in alignment. A ring 45 made of refractory material or from Stainless steel is provided on flange 44 between door 20 and flange 44, around the edge of opening 38 in front of the flame to protect and create a seal to prevent air from entering the furnace near the flame.

A plurality of quick-acting cam release clamps 39 on the door 20 ensure rapid mechanical locking and unlocking of the burner housing 42 with the door 20 by engaging with the annular flange 44. The unit 40 has βΐηφ four-wheeled chassis 47, to be moved on a track 46 in and out of engagement with the Beschiokungstür 20 so that the unit can be gebraoht alternately once in the position in which it causes additional heating, and on the other hand out of this position in order to tilt the oven and to be able to open the door 20 for loading from the side.

In addition to the burner 42, the transportable combustion unit 40 has an electric motor 48 ′ and a low-pressure fan 50 which is driven by the electric motor in order to introduce air into the burner 42 through an air duct arm 52. The burner 42 with its open side 43 encloses a socket-shaped element with an essentially flat bottom, which is a perforated sleeve 54 open on one side

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which is arranged concentrically to the cup-shaped member and is mounted on the bottom 5j5. A plurality of perforations 55 allow air to flow through the sleeve 54 from the air line 52 into the central combustion chamber 56 of the burner 42. Its gas inlet 58 is attached to the flat bottom 55 of the bowl-shaped member 42 coaxially with the sleeve 54, so that gas at regulated line pressure directly into the Chamber 56 can be driven. Under the action of the air pressure generated by the low pressure fan 50 in the line 52 and the channel between the outer sleeve of the burner 42 and the perforated sleeve $ 4, the air flows radially through the perforations 55 inward towards the gas flow from the gas supply line 58 and mixes Simultaneously with this gas flow and burns in the chamber 56. The extreme pressure generated by this combustion together with the force of the air entering the chamber 56 through the openings 55 drives the flame axially out of the open side 4j of the chamber through the opening 58 in the Loading door 20 and directly onto the metal load on the stove surface 18.

* In the wall 53 of the burner 42 is next to the gas supply line 58 Spark plug 60 provided for igniting the burner. The spark plug 60 is connected to a transformer 62 of conventional type which, when switched on, it supplies the voltage required to ignite the spark plug and thus the burner. To ignite is in the Wall 55 also provided an ignition gas line 64, which as a result of her The relatively small diameter provides a limited supply of gas for ignition, thereby preventing an explosion from occurring could if the gas flow of the line 58 were ignited immediately. A suitable> gas shut-off valve 65 is in the ignition gas

■ line 64 provided to the gas flow as required and desired Control ignition.

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One recognizes that the burner just described is somewhat different in this respect works as the air-gas burners that have heretofore been used in connection with electric ovens, as no mixture before Entry of the gas and air into the combustion chamber itself, which is open at its front, occurs. Besides, it's not a conventional one Nozzle provided to prevent the forward flow of the flame and nitrogen to confine and constrict, and as a result the burner throws a comparatively wide flame and a wide nitrogen current directly against the metal charge; in this way there is a relatively uniform and effective heating of the charge, which is located within a protective jacket of inert gas, this gas continuously passing over the surface of the Charge strokes and then through the slectrode openings, the tap hole and the air vents flows out and the static air within the furnace shell is driven in front of it.

The gas supply line 58 is connected at its inlet end to a gas supply hose 66 so that the combustion unit 40 can be moved along the track 46 into and out of engagement with the furnace. In the gas supply line 58 the inlet of the ignition

gas line 64, a gas shut-off valve 67, which is a conventional rotary valve and an air-gas ratio regulating membrane 68 is mounted, which is connected by line 52 to the air supply so that the air-gas ratio can be controlled and kept constant. Conventionally, further valves are provided, about a throttle 69 in the air line 52 for controlling the air supply by hand and a gas valve 71 at the end of the line 58 to finally regulate the gas flow rate.

The gas supply line 70, to which the other end of the gas supply line

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Hose 66 is connected, has a membrane regulator 72, which takes into account seasonal changes in gas pressure from the gas source. In the gas supply line 70 further comprises a safety closure valve 7 ^ is provided which is coupled to a pressure-sensitive switch 75, to provide an automatic verschlug if the hose is damaged 66 or diced ^"! Should be. To read the line pressure appropriate measuring devices can be provided shown schematically at 76.

Various modifications can be made to the control system at will Consider and one can use semi-automatic controls coupled with demand meters that measure the power consumption of the electrodes record of the electric furnace, so that when a certain power consumption is reached, an automatic circuit automatically gives an alarm signal so that the operators switch to additional firing or ignition of the gas burner and the power supply to switch off or decrease the electrodes. This arrangement is very effective when the electricity is on demand for certain periods of time is sold at different tariffs, as is the case with many electricity suppliers in industrial areas;

A suitable way of using the additional combustion unit in connection with a particular heat of the furnace is to use the additional combustion unit until the _; 80% to 90 % of the scrap has melted, after which the additional combustion unit is switched off. If the additional unit is used in this way, the most costly high connected load of the electric furnace is seldom required, since the refining process and the final melting stage consume very little electricity compared to the beginning of the melting process.

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The principle of using a mechanically attached, portable Combustion unit to apply a flame directly to a metal charge in the hearth surface of an electric furnace hitherto considered impracticable because it entails an unsustainable oxidation and burnout of the carbon and other necessary alloys and further damage and premature burning of the electrodes occurs. The special one described here Arrangement in which an open front, the The combustion chamber with the correct air-gas ratio is aimed directly at the metal charge, can only be used if this undesirable oxidation can be avoided or minimized.

In the burner and furnace combination according to the example shown here, natural gas was used, for example, which is supplied by the company OHIO FUEL GAS COMPANY in Toledo, Ohio, this gas having a specific gravity of about 0.6} and about 85.5 % methane, 12.5 % Athens, 0.2 Jg carbon dioxide and 3.8 % nitrogen and contains about 1047 DTU (British Thermal Units) per cubic foot. As a result, according to this example, about 10 cubic feet of air per cubic foot of gas are required for complete combustion of the fuel. Since the burner according to the invention has a membrane ratio regulator 68 which controls the air / gas ratio introduced into the burner, the combustion of the gas mentioned takes place precisely in the theoretical ratio of air to gas of 10: 1. Since the air is primarily a mixture of nitrogen and oxygen in a ratio of about 20 % oxygen to 79 % nitrogen, the following B exemplary equations can be used to illustrate the reaction when a mixture of air and natural gas is burned, ie for example a gas that about $ 86> methane and 1? % Ethane

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holds, set up:

1) 2 of CH ₄ / O 2 ₂ * CO / CO ₂ / 3H _2/2% H.

2) Q ₀ Wf- / 2 O ₀ ** CO / CO ₀ / 2H _O /

In addition to these generated gases, the main gas that is generated is nitrogen. 3o arises z. B. when burning about 1415 irr (50,000 cu.ft.) air with natural gas about II30 irr (40,000 cu.ft.) nitrogen. In fact, this large volume of nitrogen determines the atmosphere in the furnace. The volume and pressure of the inert gas passing through the furnace eliminates or purifies the unwanted oxidizing combustion gases as they break and creates a continuously passing inert envelope around the charge and the electrodes, so that the amount of carbon loss caused by oxidation is increased is reduced to a minimum. The oasis introduced into the furnace during combustion consists primarily of carrying or purifying oases insofar as B. when burning about 0.0283 ti? (1 ou.ft.) of the above-mentioned oasis with 0.283 *? (10 ou.ft) air for about 73% of the total resulting oasis 1st nitrogen, while the rest of the gases consisting primarily of carbon monoxide and carbon dioxide and hydrogen. The volume or the proportions of the gases produced naturally depend on how complete the reaction of the gases with the air is. Incomplete combustion leads to smaller amounts of nitrogen and other gases. Therefore, in order to achieve the maximum efficiency of the system, it is essential that the burner is designed so that it comes as close as possible to the theoretical yield. The burner 42 according to the present invention has been found to be extremely effective in this regard and the generation of Stlokstdff during use of the burner for additional heating of the batch of des

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electric furnace comes the theoretical amount at a given Natural gas close. The composition of natural gas changes naturally to a certain extent, but it is established that by the described use of the combustion products of the burner a sufficient An inert gas envelope is generated provided that the nitrogen generation for any given gas is greater than 50; i ier total amount of gas generated is. Examples of such natural gases are known and these gases occur in many places around the world.

When using a portable combustion unit according to the present invention in combination with an electric furnace, which has a capacity of six tons, it has been shown, for example, that the melting time for a cold charge is reduced to such an extent that in a normal 3 shift of etv / as less than eight hours five itatt previous four 3chmeIzvorgänge performed can ground v /, 1st being given a Oasverbrauch of about 140 or (5 * 000 cu.ft.) per hour »The corresponding · WMrmeerseugunf ImI this - quantity of natural gas is about 5 million BTU per hour, with about the same amount of heat generated by the electrodes of the electric furnace at a medium start-up value , so there is a reduction or avoidance of the operation as far as possible With a high power consumption, a substantial saving is achieved in the 3melting process. This saving is of course only possible because during the combustion in the burner described above, about I.I30 Ώ? (40,000 cu.ft.) nitrogen is generated per hour and. . at the same time the flame is directed directly at the batch

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and the electrodes are working.

Effective protection of the load and electrodes against oxidation in these extreme conditions it is still due to the large cross-section Improved the area of the flame and the 3tick3toffgasstrome3, which is generated by the burner described with an open front, as a substantial part of - if not the entire batch heated essentially uniformly in the case of Verweftbrennung and is protected. The tremendous amounts of nitrogen used during this Process are introduced into the furnace, drive the static air in the furnace through the tap opening, the ventilation openings and the electrode openings so that the furnace is filled with a gas filling almost entirely of nitrogen, particularly in the area of the charge Has.

A noticeable decrease in the rate of consumption of the electrodes results from the fact that these electrodes are surrounded by the rising hot nitrogen as it passes through the electrode openings emanates. It has been found that this inert or inert atmosphere is not detrimental to the composition of the batch and iiii opposite is actually the quality of those produced in the furnace Standardized melting. The reason for this is the fact that nitrogen in the dry state is completely passive to iron is. It is obvious, however, that if the nitrogen content is found to be harmful in any way to the atmosphere special alloying process proves that in the electric furnace with additional high Combustion unit is carried out, the percentage of nitrogen in the furnace by the arrangement of additional vents In the oven and by increasing the proportion of gas in the Combustion mixture can be changed. It turned out to be Jedooh

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indicates -leave lurch -lie continuous sticks toffuimiiantclung which by the method and apparatus according to the present invention does not produce any detrimental effects in normal metal dividing processes Effects occur.

To simplify the description, the principles of the invention have been explained using a single exemplary embodiment. However Jelbstverständlich should neither this from illustrated guide 3 form nor the terminology used in your description to distinguish the invention, are as many variations are possible, of course, within the scope of the inventive concept. The following claims serve exclusively to delimit the concept of the invention.

Claims;

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Claims (1)

Dr. Ing.E. BERKENFELD, patent attorney, COLOGNE, Universitättitraße 31 Appendix "Mt * u" i <J "n for input from March 12th 11) 66 VA + nom. T iS X T R O N INC. PATiHT A IJ 3 P R U C H J, 1. A method for heating a metal charge in an immediate electric arc furnace which has carbon electrodes and in which the charge is heated by an additional gas combustion unit as well as by the arc, characterized in that the amount of the total electric current consumed by the arc is regulated by appropriate regulation the heat output of the electrode is kept within certain limits and an intense flame from the gas combustion unit is aimed directly at the charge in order to introduce an amount of heat into it that is significantly greater than the amount of heat generated by the arc. 2. The method according to claim 1, characterized in that more than 50 % of the flame gases consist of a carrying gas, in particular nitrogen. 5. The method according to claims 1 or 2, characterized in that the burner (42) of the combustion unit (40) has a front side (43) of its combustion chamber (56) for the exit of an open flame, this front side being directed such that it directing the flame radially substantially in the direction of the electrodes (28). 4. The method according to claims 1, 2 or J>, characterized thereby 909845/0262 bathroom ORiGiNAf. _ characterized in that (50) air is blown in He combustion chamber (56) by a fan and at the same time a gaseous coals ;; a: -. jaerstoffmischung in the 7 brennungs chamber (yo) introduced v: ird to produce a mixture in this This mixing ratio ensures essentially complete combustion, so that the pressure generated in the combustion chamber (56) creates an overpressure in the furnace. _s 5. Immediate arc furnace with an additional gas combustion unit for carrying out the method according to An.3pi.uch 1, characterized in that the combustion chamber (5o) of the burner (42) of the combustion unit (.40) has a Voriersjite (4; ·) to the exit of a has an open flame and la.3 ler burner (^ c.) is releasably attached to a side wall (12) of the furnace, v; obei the furnace has a substantially cylindrical interior and is aligned such that the flame is directly on the metal charge and is directed radially in the direction of the electrodes (28). 6. Furnace according to claim 5> characterized by regulators (6d, 69, 71) for the pressure ratio and the flow in the separate air and gas lines (52, 58) to the burner (42). 7. Furnace according to claims 5 or 6, characterized by a movable bearing (47) for the combustion unit (40), the burner of which has a fastening flange (44) for fastening to the furnace. 8. Furnace according to claims 5 »6 or 7, characterized in that the burner (42) has an electrical spark igniter (60) and an ignition gas line (64) for igniting the gas. g ^ -. Q _R jQf _NÄL 909845 / Q2B2 r > ■. U'fen Hi-jii one; n 3er claims 3 bi "- Ό, dad arch ζ - characterizes, let - \ r; v 2i'j: i: iar (4Ii) has a perforated inner sleeve (54), - -, oo -.- iJ; io air rul al do ;;: outside ier llül.sc-i and iie main gas ^ inside ^: \ 3V sleeve lio £ t. 10. .Ju ^ at2-7erbrennun ^ .r .-.? Inhait for oven cu-niäfi einin '1er claims 3 f'i? Due to the fact that it has a burner (4 ^) provided with a flange, it has a central combustion chamber (30) with an open forward side, let a lying gas supply line (υυ) be provided in this burner (42), that a low-pressure fan (30) is provided for the supply of air ± i rien burner (42), that a pressure ratio regulator (6B) for the air and gas lines (i? 2, 5 ^) is also provided, that further regulators ( 69 * 71) are provided in these lines (52, 58) so that a spark igniter (60) and an ignition gas line (64) and a movable support (47) are also provided. BATH 909845/0262 no L e r s e i t e