DE2459253C2 - PROCESS AND SYSTEM FOR FEEDING SOLID RAW MATERIALS THROUGH A HOLLOW ELECTRODE - Google Patents

Description

The present invention relates to a method for feeding solid raw materials with the aid of an operating gas through a hollow electrode into a closed electrothermal reduction furnace, the material supply to the hollow electrode being automatically interrupted as soon as the gas pressure inside the furnace below the hollow electrode reaches a predetermined percentage of the operating gas pressure while the operating gas supply is maintained as well as an installation for its implementation.
From DT-PS 17 58 759 a method for feeding solid raw materials through a hollow electrode into a closed electrothermal reduction furnace is known, in which the supply of solid raw materials is interrupted when the gas pressure inside the furnace below the hollow electrode a predetermined percentage of the Operating gas pressure reached while the supply of the operating gas is maintained. After the gas pressure inside the furnace has fallen below the specified percentage of the operating gas pressure, solid raw materials are fed back through the hollow electrode. Up to 15 ⁰ O of the raw materials to be fed to the reduction furnace can be introduced in finely divided form via the hollow electrode.

This process made it possible to use self-burning electrodes for the first time to operate electrothermal reduction furnaces with more than 50 MW electrical power per furnace unit and in doing so, for example in carbide furnaces, to produce about 80% calcium carbide without danger to run that, as a result of excessive electrode wear, the electrodes are not sufficiently solidified be moved later, causing electrode breaks or that not deep enough into the Möller immersed electrodes are the cause of high exhaust gas temperatures, whereby z. B. from carbide furnaces Calcium-containing gases with a temperature of more than 2000 ° C are emitted from the carbide decomposition can.

3 4

Even if initially with increasing solidity, a system for carrying out the entry of the invention due to the hollow electrodes advantages for moderate processes, soft from a furnace vessel the furnace operation (reduction of the electrode removal with hollow electrodes, from feed units, Fire per unit of time, deep in the Möller bunkers, operating gas supply lines, conveyor divers Electrodes) result from a 5 screws, pressure regulating devices, pressure measuring conscience Point at a further increase in this solid as well as consisting of amperes and voltmeters is Substance input to a radical deterioration of the characterized in that the measurement data of the furnace state, wherein voltmeters are generally not assigned to a hollow electrode lets see at which time unit through the and ammeter one for the formation of a quo hollow electrode Solids charged into the furnace are fed to suitable computing elements; that quantity changes the tendency in oven behavior. The results of the respective arithmetic link are sent to one seems to give ofeu states which at times differentiate according to time, which are not suitable for computation only an increased solids feed can be fed through member; that a first rule cabinet allow the hollow electrodes, but is even provided for in which fixed, by Konblick Quantity control ranges that can be selected for optimum oven behavior demand, while with other furnace states one depending on the signals of the arithmetic logic unit in contrast, reduced solids feed by being switched on and off; and that another the hollow electrodes may still be too big. Hence the control cabinet, which has a series of contact manoeuvers the entry of solids through the hollow electrode contains meters for pressure area formation, provided continuously adapted to the furnace behavior. A 20 is, the other control cabinet signals from the jezur Achieving optimal oven behavior, the pressure gauges deviate from this with regard to their graded adjustment of the height assigned to a certain pressure range by the hollow electrodes and The amount of solid matter to be fed in is matched by the corresponding signals for pressure / volume control DT-PS 17 58 759 is not within the process described in the first control cabinet possible. 25 range from which adjustment

It is therefore the object of the present invention and / or running commands to be given to an actuating drive

a method for feeding solid raw materials through, which is with the respective screw conveyor

Hollow electrodes is connected in a closed electrical force-locking manner.

Reduction furnace, for example in a carbide furnace, with the method according to the invention it is possible

to create, in which the per unit of time in the 30 Hch, on average about 25% of that in the reduction

Oven to be introduced through the hollow electrodes, raw materials to be fed in in finely divided

To introduce solid quantities according to the requirements of the respective shape via the hollow electrodes.

Oven state are adapted and which continues in the method of the invention as

the introduction of an average high fixed control variable of the hollow electrode inner

amount of substance, based on the total pressure that can be measured in the pipe 35 below the electrode (because of

The quantity of raw materials to be imported into the induction furnace is permitted. its strong temporal fluctuations its mean

This is achieved according to the invention by the fact that value) and the stove resistance (in the form of its

the amount of line per unit of time through the hollow electrode according to the time) used,

raw materials to be fed in depending on the state of the art

Pressure under the electrode is changed as long as 40 hollow electrode tube measured furnace pressure

the hearth resistance increases over time or is not used, the material feed to the hollow electrode

changes remains. Achievement of a specified percentage of the

The method according to the invention can thereby automatically interrupt and drive gas pressure

designed or trained to prevent the feed pipe from being permanently

45 clogged, serves in the present invention

a, the fed raw material quantity) so higher, the pressure of the hollow electrode P, _{i £} to the ever niedrigei the pressure and so as to lower the instantaneously possible and necessary Materialzuhöher the pressure under the hollow electrode went to determine per unit time and to ensure.

b) the supplied amount of raw material when changing For this purpose, at a low pressure the pressure of the hollow electrode 50 gradually increased Pur the material feed per time m _H s is changed on, high pressure m _he lowered. But that's only true

c) the step-by-step change in the length of the fed-in, such as the tendency of the stove resistance k determined from phase current and raw material quantity within a pressure range of phase voltage, takes place, the position of which is determined by the furnace current, i.e. the change in stove resistance Λ, 55 of the time, positive or zero , as long as one of the

d) in the event of a decrease in the amount of pressure in the hearth resistance-like change over time, the amount of raw material fed in increases to the low level R or remains the same.

The most rigorous value of the range is reduced How the controlled variables Phe and k reciprocally and that when the stove resistance increases again from the furnace events and the pressure line of the quantity ^{intervene again in the furnace frame} , so that the hollow electrodes pick up. if necessary, an optimal oven cycle can be achieved with a l:; delivery, time delay. will now be explained in more detail:

e) for the step-by-step change in the amount of the control pressure P _l1f . is built up by the Strömaßgebende Dun km certain time interval flow resistance, to ring, medium or high pressure control range of the electrode tip to the process gas stream at the retrieved and duieh assignment to a nied- ⁶ 5 finds passage through the Möllcrabdeckung. A deep in the Möller would cause an increase, no change or decrease in the electrode and / or a relatively gas-impermeable decrease in the amount. Möller cause a high pressure P _HE , a high

standing electrode and / or a well gas-permeable Möller a low pressure P _11n .

As long as the fine-grained material introduced by the hollow electrode is converted immediately, there is no additional burden on the gas permeability of the Möllers. However, the gas permeability is reduced by excess hollow electrode material when it clogs the cavities. For example, an increasing pressure P _nE would sensibly lead to a throttling of the material supply via a quantity control, and a lower pressure P _HT to an increased material supply.

As a result, the material supply per line M would be adapted to the actual need. The electrode level , which _{influences the control pressure P, u} , also seems to have an operationally appropriate effect on the pressure / volume control:

When material is fed in through the hollow electrode tube, the impedance-regulated electrode stand initially changes in such a way that the electrode dips deeper into the Möller. This should result in a higher pressure P ₁₁₁ - which leads to a throttling of the material supply. The throttling of the material supply, in turn, initially causes the electrode to emerge.

Now, however, the impedance-controlled immersion of the hollow electrode is only up to a certain point approximately proportional to the quantity supplied per time M _H r . This emergence is then accompanied by phenomena such as outbreaks of overheated gases from the reaction vessel and increased electrode burn-off, which can bring the furnace to a standstill. If the furnace is kept in operation anyway, the current and material yield decrease, since the material is only reduced incompletely.

Through a consistent sole pressure volume control in the sense described, based on a maximiening the amount of material charged through the hollow electrode runs out, would therefore affect the behavior of the furnace adversely affected.

The optimization of the furnace process aimed at with the regulation with regard to gas temperature, electrode burn-up, energy and material yield requires the addition of the oven resistance R or its change over time R.

The stove resistance R of a hollow electrode is referred to below as the total electrical resistance in the current path, which is the quotient of phase voltage and phase current.

In electrothermal furnaces, the gases leaving the reaction vessel are only permitted at temperatures at which neither the furnace equipment, for example the water-cooled parts of the electrode holder that can be felt through the furnace hood, are destroyed, nor are downstream devices, e.g. electrostatic precipitators in phosphor furnaces, functional. The gases leaving the reaction vessel are cooled to such permissible temperatures when the electrode tip is covered with a larger layer of dirt. So if the electrode is deep in the bed. This is the case with an impedance-controlled electrical system when the hearth resistance in R is high.

The prerequisite for a low reaction temperature is thus a low brand, a large energy yield and an extensive reduction of the raw material lies in the smooth Course of the endothermic chemical reaction. For this it is necessary that the Strom-S heat is only available where there is a willingness to react, the mixture at the reaction temperature is available in an appropriate amount. Included must be the amount of mixture that is enforced per unit of time by a certain volume

ίο correspond to the existing electrical power, the electrical and scenic routes must coincide. This prerequisite is given if the entire furnace current flows as far as possible from the electrode tip directly to the furnace bottom or vice versa, since the largest part of the mixture sinks through this area between the electrode and the furnace bottom as reaction melt or as coke that has reacted. A larger part of the furnace stream flows directly to the furnace floor if the distance between the tip of the electrode and the floor is small compared to the distance from electrode to electrode. But this is the case with a large hearth resistance R.

The optimum for the oven aisle is therefore present.

if under the given circumstances the stove resistance is at its maximum. In order to avoid exceeding the optimum, the tendency to increase the hearth resistance R or its change over time must be R ^ O.

The immersion of the impedance-controlled hollow electrode R> 0) with increasing material supply per unit time Xf _HE at not too large values of M _HE as well as the tendency revolution (A <C 0) by a certain value fÜTM _HB from related to the influence of the introduced through the hollow electrode material on the stove resistance R together. Material introduced through the hollow electrode cools the electrode tip so that the ohmic resistance is greatly increased here. The current transfer to the Möller is shifted further from the tip of the electrode towards its upper cylindrical surface.

In accordance with Kirchhoff's law, the current on the way to the furnace floor initially deviates from the cooled area directly below the electrode, but then follows the highly conductive melt below from the finely divided mixture downwards. As a result of the longer current path around the cooled electrode tip to the furnace floor, the furnace resistance R increases. It can be seen

The desired effect with subcritical values for the material supply m _he , if the impedance-regulated hollow electrode is moved deeper into the furnace vessel with increasing material loading Mhe. With further increases in supply _he m, this effect is amplified until the evasive currents of two electrodes are sufficiently close to that so-called side line occurs. In doing so, larger amounts of current pass directly from electrode to electrode. The oven resistance R then decreases, and the electrodes are moved out of the furnace vessel by further increases in M " _f due to the impedance control. When the side line starts, the current flowing directly around the furnace floor is reduced more and more. This is the principle outlined for

leave the optimal furnace condition, according to which the material and current paths should coincide.

Accordingly, those are hinaiisl.-iiifcndc Pressure volume control, with the cm

low pressure P ₁₁₁ -. a larger feed of material per time Μηέ. and vice versa, to be supplemented by monitoring the oven resistance R , which is changing in the process. The change of the positive effect of the hollow electrode into a negative one is recognized in good time from the change in the hearth resistance over time. For as long as a specific, fed through the hollow electrode per unit time in the furnace material quantity m _height of the oven resistance R increases or remains the same, under the pressure-flow control meters _he be strengthened, however, is taken from the oven resistance R, so Mijir must be reduced. Accordingly, the following applies:

Mm: > 0 if R ^ O
M _11,. <0 if R <0

Here, k ^ 0 indicates that the set pressure / volume control can be retained. For k <0, however, M _HE must be reduced until k > 0. If necessary, normal operating mode can then only be resumed after a line delay.

The pressure volume control of the material feed through the hollow electrode takes place in pressure areas.

For this purpose, three pressure ranges _{0 PyP 1} - ■ P ₁ and P, - P ₃ are advantageously used:

At P ₁₁ , in the range 0 - P ₁ , m _{he is} increased; with P _HV in the area P ₁ P ₂ , M _HE remains unchanged; at Pm in the range P., P ₃ , M _{Ht is} reduced and at Ρ, ιι above P ₃ , the feed of solids through the hollow electrode is switched off.

The control of m _he via P _n takes place in fixed areas, which are adapted to the respective furnace output, in which Mhi can be regulated continuously or in steps.

This regulation takes into account the capacity of the furnace for the finely divided solids fed in through the hollow electrode. However, so that an optimum is always achieved, the increase in the solids input through the hollow electrode has a limit in the described reversal of the tendency of the hearth resistance R: The pressure signal to increase M _1n is only followed as long as k ^? 0 is. If k <C 0, M _{11 is} regulated down, for example, to the lowest value of the pressure range and remains in this setting until there is a renewed trend reversal of the stove resistance. Only then, gcgebenen ^f alls after a certain! After a delay, the pressure / volume control is resumed.

In the drawing, a system for carrying out the method according to the invention is shown schematically, which is a section through a three-phase furnace with two electrodes are visible.

Hollow electrodes 2 are height-adjustable and electrically insulated through the cover of a furnace vessel 10 passed through. The hollow electrodes 2 are surrounded by power supply jaws 1. Two hollow each A feed transformer 11 is assigned to electrodes 2, each of which has half of a Stromzufühningsbackc 17 four electrodes electrically powered. Above each Hohlclcktrode 2 a screw conveyor 6 is arranged, which flows through a feed pipe 8 with the inner pipe of the hollow electrode 2. The screw conveyor 6, which can be charged with finely divided solids from a bunker 7, is controllably driven by a sliding drive 9.

An operating gas feed line 12 opens into the upper part of the screw conveyor 6, in which there is an inlet valve 3. Flow in front of the inlet valve 3 is in the operating gas supply line 12 a pressure regulating device 4 is arranged while downstream of the inlet valve 3 a pressure gauge 5 is located. The values measured with the pressure meter 5 are shown in a further Control cabinet 13 entered.

In the circuit of the supply transformer Il and the associated hollow electrode 2 is an ammeter / switched while a voltmeter (/ to the power supply pad 1 of the hollow electrode 2 and the bottom of the furnace body 10 are electrically conductively connected. The measured values of both instruments are an arithmetic unit R for forming the quotient supplied and determine the stove resistance, while the result of the arithmetic device R another Rechcng'ied k for differentiation with respect to time is entered. the result of the arithmetic device, k is input to a first control cabinet 14 together with the signals of the contact ammeter 15 which signals from the other Receives control cabinet 13. The further control cabinet 13 contains contact manometers and processes the measured values of the pressure gauge 5 for the first control cabinet 14, which sends adjustment and running commands to the actuating drive 9.

The fixed areas for the amount of solids fed in m _hi . within which at pressures below the hollow electrode between 0 to P ₁ is regulated upwards, between P ₁ to P "no change takes place and between P" to P _s is regulated down, are im

first control cabinet 14 and are selected with the help of the contact perimeter 15. Included three areas are provided, which are assigned according to the level of the corresponding phase current are and are switched on; namely applies to the phase current range

. I _x /, d.?r amount range ¹ Mi ₁ F ² M / ,, / _2/3 of the Volume Area ² M _{H /} - ³ M _{// (/ 3/4} of the range of amount ³ M _{/ F} ⁴ M ,, ,

_{The pressure ranges C to P 1} set up in the further storage cabinet 13 with the aid of contact manometers. P ₁ to P ₂ and P ₂ to P ₃ . to which the pending value of the pressure gauge 5 is assigned, a signal to the first control cabinet 14 causes an actuating impulse for the actuating drive 9 of the metering screw 6 to generate an amplified, constant! or a reduced amount of solid material introduced via the hollow electrode 2.

The method according to the invention will now be explained by means of an example.

The speed of the screw conveyor 6 is ei Time relay, which monitors the actuating time of the actuating drive, stepped up and down. this However, regulation is only possible within a certain period of time, since the structure is in one upper and lower end position switched off win this speed determined by limit switch bcrcuhc are about the Konlaktamperemclcr dci Furnace current corresponding power ranges d (furnace assigned, so that always with a certain Drelvahlbcrcieh an associated Rcpe'bmic fiit d

The amount of solids to be fed in via the hollow electrode, based on the total raw material input, is given. The pressure determined there is queried by the pressure gauge 5 via a time relay at intervals of about 60 seconds, by means of which a new quantity level M, _1E ± Am, _{1e may be} established for the following 60 seconds.

10

The pressure ranges required for regulation are given by three pressure conacts. To correct a volume-dependent pressure depression, which is caused by the solids falling in the hollow electrode inner tube, three special pressure contacts P ₁ , P ₂ and P _{3 are} set up for each quantity range.

Contact ammeter Furnace output Control range Λί _{/ ί £} Control range P _HE pi Pz (Λ) (MW) (t'h) (mm WS) 400 to 500 500 to 800 (primary) 300 to 400 400 to 800 Circuit at Circuit at Pl 200 to 300 300 to 800 2200 30th 0.6 to 1.2 0 to 400 2800 38 0.9 to 1.8 0 to 300 > 3400 > 46 1.3 to 2.6 0 to 200

The control ranges for Mhe each correspond to a solid content of 16 to 32%.

When the stove resistance decreases over time, the control is intervened in such a way that at Average amount of solids introduced via the hollow electrode:

26.2%.

Elevation of the electrode by the impedance control 25 Electrode burn-off:

the actuator 9 the gear of the screw conveyor 6 m brings the lowest position of the speed range. The pressure control is only released again when when the upward movement of the electrode has stopped and the lowering of the electrode begins.

This operating result was achieved with a control made according to the example:

9.5 kg of Ot norm carbide.

Stroin yield:

3.15 MWh / t standard carbide.

C content in the carbide:
0.2%.

Carbide housing:
81%.

1 sheet of drawings

Claims (7)

Patent claims: 1. Method for feeding solid raw materials with the aid of an operating gas through a hollow electrode in a closed electrothermal reduction furnace, with the material supply to the electrode is automatically interrupted as soon as the gas pressure inside the furnace • reaches a specified percentage of the operating gas pressure below the hollow electrode while the operating gas flow is maintained, characterized in that the amount of per unit of time through the hollow electrode raw materials to be fed in is changed depending on the pressure under the electrode, as long as the hearth resistance increases over time or remains unchanged. 2. The method according to claim 1, characterized in that the amount of raw material fed the higher, the lower the pressure and the lower, the higher the pressure under the hollow electrode is. 3. The method according to claim 1 or 2, characterized in that the amount of raw material fed is changed gradually when the pressure under the hollow electrode changes. 4. The method according to any one of claims 1 to 3, characterized in that the stepwise Change in the amount of raw material fed in takes place within a pressure range, whose position is determined by the furnace current. 5. The method according to any one of claims 1 to 4, characterized in that at a time Decrease in stove resistance, the amount of raw material fed in to the lowest value of the area is reduced and that when the hearth resistance increases again the Pressure control of the amount is resumed, possibly with a time delay. 6. The method according to any one of claims 1 to 5, characterized in that the for the incremental change in the amount of decisive pressure queried and at a certain time interval an increase due to assignment to a low, medium or high pressure regulation range, no change or decrease in the amount is effected. 7. Plant for performing the method according to one of claims 1 to 6, consisting of a furnace vessel in which hollow electrodes are electrically insulated and surrounded by power supply jaws reach in; from supply transformers, which are electrically conductively connected to the power supply jaws; from bunkers, which via screw conveyors and feed (tubes are connected to the inner tubes of the hollow electrodes; from operating gas supply lines which open into the screw conveyor and each have a pressure control device and a pressure gauge; from an ammeter arranged in each circuit between the supply transformer and the hollow electrode and from one in the connecting line between voltmeter each of a hollow electrode and the furnace bottom, characterized in that the measurement data of the voltmeter (U) and ammeter (/) assigned to a hollow electrode are fed to a calculator (R) suitable for forming a quotient; that the results of the respective calculator (R ) to a computing element (k) suitable for differentiation according to time; that a first control cabinet (14) is provided, in which fixed, by contact ammeter (15) selectable quantity control ranges depending on the signals of the computing element (R) are switched on and off who the; and that a further control cabinet (13) containing a number of contact manometers for forming the pressure range is provided, the further control cabinet (13) receiving signals from the respective pressure gauge (5), assigning these to a specific pressure range with regard to their height and corresponding signals for pressure -Quantity control transmitted within the quantity range in the first control cabinet (14), from which adjustment and / or running commands are given to an actuating drive (9) which is positively connected to the respective screw conveyor (6).