WO2002046499A1

WO2002046499A1 - Method and control unit for operation of aluminum reduction cell

Info

Publication number: WO2002046499A1
Application number: PCT/RU2001/000524
Authority: WO
Inventors: Teimuraz Otarovich Khazaradze; Andrey Pavlovich Revyakin; Sergey Nikolaevich Sinko; Aleksandr Ivanovich Berezin; Sergey Semenovich Goryaev; Igor Vadimovich Katkov; Nicolai Afanasievich Galov
Original assignee: Zakrytoe Aktsionernoe Obshestvo 'toxsoft'
Priority date: 2000-12-05
Filing date: 2001-12-04
Publication date: 2002-06-13
Also published as: RU2189403C2; AU2002217649A1

Abstract

The method comprises the following operations: measurement of the pot voltage and topline current, calculation of the current value of the scaled voltage Usc and its rate of variation in time dUsc/dt, comparison of calculated values with preset ones and making decision on regulation of the inter-pole gap and changing the regime to excess or deficient supply basing on the results of the comparison. The device for pots control comprises units for measuring topline current and voltage linked to the inputs of computational device, outputs of which are linked with the unit for inter-pole gap regulation with actuators, and to the alumina automated feeding system with actuators, the comparison unit, the level controllers, and electric drives. The computational unit comprises the following units interconnected with the internal bus (230): the unit (210) for calculation of the scaled voltage, the unit (211) for calculation of the scaled voltage derivative, the driver (212) of the local area network, the unit (216) for emergency situation analysis, the unit (218) for maintaining the concentration, the unit (220) for maintaining the inter-pole gap, the unit (222) for maintenance operations support, the unit (224) for detection and suppression of magneto-hydrodynamic instability, the unit (226) for pot treatment support, the unit (228) for anode effects support and the serial port (214) linked via the control bus (254) with the display unit (256), keyboard (258) for data input, and external devices and sensors.

Description

METHOD AND CONTROL UNIT FOR OPERATION OF ALUMINUM REDUCTION CELL

FIELD OF THE INVENTION The present invention relates to non-ferrous metallurgy and can be employed for control of the processes of aluminum production through electrolytic method.

BACKGROUND OF THE INVENTION

Efficient control of the electrolysis process is known to require stabilization of power regime (value and density of current), temperature, inter-pole gap, electrolyte composition, level of metal, etc. Inaccuracy of control brings about electric power over- consumption, loss of metal quality and decreasing reduction cell (pot) capacity, and increasing of anode effects number (cf., e.g. V.P.Kadrichev, M.Ya.Mintsis, Measuring and optimizing parameters of aluminum pots. - Chelyabinsk, "Metal", 1995 [1]). Resolution of the above problems is possible provided employing modern computer equipment and respective component base (cf., e.g. G.Pausch, A system for automation of aluminum electrolysis. ALUMAT conception// "Siberia aluminum- '96": Proceedings of the International scientific seminar. - Krasnoyarsk State University. - Krasnoyarsk, 1977 [2]).

Methods of electrolysis process control are essentially different for pots equipped with a system of alumina automated feeding (AAF) and pots without AAF systems, in which alumina feeding is carried out through periodic treatments.

For pots without AAF systems, there exists a known method of control based on varying pot voltage, potline current and determining minimum value of resistance or scaled voltage prior to each sequential treatment. With this, the minimum scaled voltage value is considered the preset value, and in case of difference emerging between the preset value and the current scaled value, the anode is displaced, all displacements between pot treatments being recorded. In case of downward anode displacements being prevalent the alumina concentration is assumed excess, in case of prevailing upward displacement, the alumina concentration is assumed deficient, and provided infrequent displacements immediately after the treatment and prior to the following treatment, the concentration is assumed normal. In case of excess and deficient values of concentration, the mode of alumina feeding is adjusted so that normal concentration regime is attained (RU 2148108 CI, "Soyuztsvetmetavtomatika", C25C 3/20, 04.27.2000) [3]. For pots equipped with AAF system, there exists a known method of control consisting in maintaining of the pot temperature regime through inter-pole gap and alumina concentration regulation within the preset range by means of alternating excess and deficient feed modes. The method comprises the following operations: measurement of the pot voltage and line current, calculation of the current value of the scaled voltage U_se and its rate of variation in time dU_sc/dt, and comparison of calculated values with preset ones. Then, basing on results of the comparison, the decision is made on regulation of the inter-pole gap and changing the regime to excess or deficient supply (SU 1724713 Al, "Soyuztsvetmetavtomatika", C25C 3/20, 04.07.1992 [4]; RU 2113552 CI, Bratsk aluminum works, C25C 3/20, 06.20.1998 [5] - the closest analog of the first object of the group of inventions).

Methods [4] and [5] enable maintaining alumina concentration in the electrolyte in the technologically optimum range 2 to 5%. However, when employing these methods, the criteria for feed regime selection (preset time of excess supply and maximum voltage of deficient supply) do not ensure the required precision of concentration maintaining. Assessments of concentration via regressive model and through the maximum value dU_sc/dt are used in the method [4] as supplementary ones. In the method [5], only the rough assessment (positive/negative) of dU_sc/dt is employed, which is probably due to the lack of sufficient capacity computer equipment for precise online calculations. There is a known control unit for at least one pot comprising anode displacement drive, crust-breaker drive, and feeder drive. The control unit comprises means for measuring of voltage drop and current connected to anode and cathode pot buses and to the signal processing unit equipped with the computer and linked to actuator devices (US 4035251, Shiver et al, 204/67, C25C 3/12, 3/14, 06.10.1975) [6]. The device possesses the capability to avoid consequences of anode effect occurrences through calculation of the current electric resistance, comparing thereof with the preset threshold values and the following regulation of the "anode - cathode" gap with power supply under the skin.

There exists another known pots control unit comprising measuring devices for voltage and current connected to anode and cathode buses linked to computational unit inputs. Inputs of this unit are also connected to the alumina feeding probe (signal of operation of alumina batcher with known treatment amount). Outputs of measuring devices are linked to inputs of computational unit embodying the pot mathematical model. One of the outputs of the computational unit is linked to the unit of determination of the alumina preset value in the melt with respective controllers of limit values. Outputs of the computational unit through the comparison units with respective controllers are linked to regulators and drives for displacement of the anode rack and adjusting of alumina treatments feeding frequency modification (RU 2023058 CI, All-Union Research and Design Institute of Aluminum, Magnesium and Electrode Industry, C 25 C .3/20, 7/06, 15.11.1994) [7]; this is the closest analog of the second object of the group of inventions. The unit embodies the method of controlling pots, the latter including variation of voltage, current, and amount of loaded alumina, measurement of increments of these quantities, determining with the aid of the mathematical model of inter-pole gap, electrolyte temperature and alumina concentration in the melt as a function of deviation of the inter- pole gap from the preset value with temperature adjustment, as well as variation of frequency of feeding alumina treatments as a function of deviation of alumina concentration from the preset value. The latter one is varied depending on the measured concentration value, the coefficient of the mathematical model being adjusted depending on the measured concentration value at anode effects. The invention enables stabilizing power and concentration operation modes, increasing yield in current, reducing frequency of anode effects. However, the complicated computational model described in the method [7] is not adaptable enough to real fluctuations of technological parameters in actual production conditions provided the existing level of computational equipment capacity.

SUMMARY OF THE INVENTION

The claimed invention is intended for increasing quality of controlling pots equipped with automated systems of alumina feeding.

According to the present invention, the method of controlling aluminum-producing pots consists in maintenance of the electrolysis temperature regime through regulation of inter-pole gap and concentration within the specified limits by means of alternating excess and deficient supply modes. This method comprises the following operations: measurement of the pot voltage and potline current, calculation of the current value of the scaled voltage U_sc and its rate of variation in time dU_sc/dt, comparison of calculated values with preset ones and maldng decision on regulation of the inter-pole gap and changing the regime to excess or deficient supply basing on the results of the comparison.

Transfer from deficient supply mode to the excess supply mode is performed provided reaching the rate of change of the scaled voltage in time dU_sc/dt > Gj. Transfer from excess supply mode to the deficient supply mode is performed provided reaching the rate of change of the scaled voltage in time dU_sc/dt < G . Here, G_\ and G% are the threshold values for the rate of change of the scaled voltage determined experimentally (Gj > G₂). With this, the regulation of inter-pole gap is performed at the moment of transition from the deficient supply mode to the excess supply mode .provided that

/u_sc - Uo / > ΔU,

Uo being the rated value of the scaled voltage and AU is the non-sensitivity zone specified by the technological requirements.

The method can be characterized by the fact that in the deficient supply mode provided the rate of variation of the scaled voltage dU_sc/dt < 0, feeding of alumina is not carried out.

The method can be characterized by the fact that at the moment of transition from the deficient supply mode to the excess supply mode additionally introduced is a single feeding of alumina, preferably of 3 to 5 treatments, formed by the alumina automated feeding system.

According to the present invention, the device for pots control comprises units for measuring serial current and voltage linked to the inputs of computational device, outputs of which are linked with the unit for inter-pole gap regulation with actuators, and to the alumina automated feeding system with actuators, the comparison unit, the level controllers, and electric drives. The computational unit 200 comprises the following units interconnected with the internal bus (230): the unit (210) for calculation of the scaled voltage, the unit (211) for calculation of the scaled voltage derivative, the driver (212) of the local area network, the unit (216) for emergency situation analysis, the unit (218) for maintaining the concentration, the unit (220) for maintaining the inter-pole gap, the unit (222) for maintenance operations support, the unit (224) for detection and suppression of magneto-hydrodynamic instability, the unit (226) for pot treatment support, the unit (228) for anode effects support and the serial port (214) linked via the control bus (254) with the display unit (256), keyboard (258) for data input, and external devices and sensors. Also incorporated into the system are the unit (288) of internal power supply and the unit (286) for automatic backup power supply switching, one of the outputs (287) thereof being connected to the internal power supply unit (288) and the other one, to one of the inputs comprises the unit (232) for analog signal normalization, the input thereof being linked to the anode (12) and cathode (14) buses, and in parallel to these, to the inputs (302, 304) of the independent anode effect alarm unit, and the output linked to the input of the analog- to-digital converter unit, the output of which is linked with the unit (234) for calculation of the scaled voltage. The unit (34) for measurement of serial current is linked via the adapter (248) to the local area network driver (212), the limit switches of the anode rack being connected to the input of the emergency situation analysis (216) one of the outputs of which (240) constitutes the terminal for connecting of group contactor circuit breaker. The output of the concentration maintaining unit (218) and one output of each of the following units: maintenance operations support unit (222), magneto-hydrodynamic instability detection and suppression unit (224), pot treatment support unit (226), anode effects support unit (228), are connected the via galvanic decoupler (262) to the actuators of the alumina automated feeding system (18). The output of the unit (220) for inter-pole gap maintenance and another outputs of maintenance operations support unit (222), magneto- hydrodynamic instability detection and suppression unit (224), pot treatment support unit (226), anode effects support unit (228), are connected via the galvanic decoupler (264) to the control input (266) of the reversing-type starter unit (268), the power input of which is linked to the output of the automatic circuit breakers unit (272) connected to the three- phase power mains (via the bus 3), the power outputs (X-15 - XI 8) of the reversing-type starter unit being linked to the electric drives of the anode jacks (26, 28) and housing jacks (30, 32), while the power output of the anode effect support unit is connected to the bus 7 for anode effect group alarm. The signal output (274) of the reversing-type starter unit (268) is connected to the input of the unit 276 for controlling anode (26, 28) and housing (30,32) jacks electric drive motor current control, which is linked with the control bus (254) through the serial port (278); with this, the motor current control unit (276) is linked to the disable input (282) of the automatic circuit breakers (272), linked as well with the other output (284) of the emergency situation analysis unit (216).

The device can be further characterized by the fact that the independent anode effect alarm unit (300) comprises the unit (308) for normalization of the analog signal, inputs (302, 304) thereof being the inputs of the entire unit, which are also linked to the unit (316) for power supply voltage forming for the circuit (318) of the unit internal power supply, while the output of the analog signal normalization unit (308) is linked to one of the inputs of the comparison unit (312) whereas the other input of the latter being linked to the output of the level controller unit (314), with the output of the comparison unit (312) being the output of the entire unit.

Besides, the device can be characterized by the fact that analog-to-digital converter unit (234), limit switches (22, 24) of the anode rack, the output of the emergency situation analysis unit (216) for connecting the group contactor circuit breaker, the power output

(245) of the anode effect support unit (228) are linked with respective units through galvanic decouplers (236, 238, 244, 246).

The device can be also characterized by the fact that the local area network is organized in compliance with the ArcNet standard, the adapter (248) being linked to said network through galvanic decoupling converter (252).

The device can be also characterized by the fact that the control bus (254) is organized in compliance with the interface standard RS-485.

The device can be also characterized by the fact that external devices and sensors are connected to the control bus (254) through galvanically decoupled converter (260) of the data transmission rate of RS-485 interface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 presents structural flowchart of the device controlling two pots;

FIG. 2 is the structural flowchart of connection of an pot to the control unit;

FIG. 3 is the functional scheme of the pot control unit; FIG. 4 is the plot U_SC(C) to explain the regulation principle;

FIG. 5 is plot of U_sc and dU_sc/dt versus time;

FIG. 6 and 7 present the algorithm of the method implementation in the control unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 presents structural flowchart of the device for control or two pots. Two pots

1 are controlled and serviced by the single control unit 2, which is functionally independent and embodied as an integral structural component, a cabinet. Unit 2 is linked: to the power three-phase mains with the bus 3; to the two-phase mains, with the bus 4; to the anode effect independent alarm unit, with the bus 5; to the group contactor circuit breaker, with the bus 7; to the to the anode effect group alarm unit, with the bus 7; to the local area network (LAN), with the bus 8; to external devices and sensors, with the bus 9.

FIG. 2 shows the structural flowchart of connection of pot 1 to the control unit 2.

Each pot 1 possesses anode bus 12 and cathode bus 14, linked to the carbonic anode 16 and cathode 17. Voltage drop on the pot is registered between buses 12 and 14 and is fed to the input terminal block X12, X13 of the unit 2. The pot is also equipped with actuators of the AAF system 18. Control of the AAF system 18 is performed from the output terminal block XI 4 of the unit 2. The anode rack 20 is equipped with limit switches 22, 24 linked to the input terminal block XI 1 of the unit 2 and intended to signal limiting positions of the anode rack in the course of its displacements.

The pot also possesses electric drives 26, 28 of the anode jacks and electric drives 30, 32 of the housing jacks, control of which is exerted from terminal blocks XI 5 - XI 8 of the unit 2. The series of pots is equipped with line current meter 34, output of which through the ArcNet-standard LAN bus 8 is linked to the terminal X6 of the control unit 2. FIG. 3 is the functional scheme of the pot control unit. For the sake of convenience, units and links that are identical for the two pots are not shown.

The basis of the control unit 2 is the computational device 200 comprising the following functional units: unit 210 for calculation of the scaled voltage U_sc; unit 211 for calculation of the scaled voltage time derivative dU_sc/dt; driver 212 of ArcNet-standard LAN; serial port 214 with RS-485 interface; unit 216 for emergency situations analysis. Besides, the computational device 200 comprises concentration support unit 218, inter- pole gap (IPG) maintaining unit 220, maintenance operations support unit 222, magneto- hydrodynamic (MHD) instability detection and suppression unit 224, pot treatment support unit 226, anode effect (AE) support unit 228. All functional units 210 - 228 comprised in the computational device 200 are linked with each other with the internal bus 230.

Analog signal normalization unit 232 inputs are linked to the input terminals XI 2, X13, while output of the unit 232 is connected to the analog-to-digital converter unit 234. The output of the unit 234 through the galvanic decoupler 236 is linked to the unit 210 for calculation of the scaled voltage U_sc. The unit 211 for calculation of the scaled voltage time derivative dU_sc/dt is included in the unit 200 and exchanges data with other units via the internal bus 230. Input 215 of the emergency situation analysis unit 216 is linked to the input terminal block XI 1 of the control unit through the galvanic decoupler 238. Output 240 of the unit 216 is linked through the galvanic decoupler 244 to the output terminal X4 of the control unit 2. Output 245 of the unit 228 is linked through the galvanic decoupler 246 to the output terminal X5 of the control unit 2.

The computational unit 200 through the driver 212 of ArcNet LAN is linked to the adapter 248 of ArcNet LAN connected with the coaxial cable 250 to the optical-fiber communication link converter 252, which is linked to the terminal X6 of the control unit

2. Employing ArcNet LAN enables providing for the guaranteed time of fetching of the current value of pot line current to the computational unit 200.

The computational unit 200 is linked through the serial port 214 to the control bus 254 arranged according to the interface standard RS-485. The control bus is connected with the display unit 256 and data input keyboard 258. Besides, the control bus 254 through the galvanically decoupled converter 260 of the data transmission rate is linked to the port X7 for external devices (sensors of the electrolysis process physico-chemical parameters and other monitoring means). The converter 260 is the memory buffer with two ports. The first port is linked to the control bus 254 at the rate of 115,200 bps. The second port is linked to the external devices and operates at a lower rate. This ensures operation of external devices in conditions of strong electromagnetic interference without reducing the control bus 254 operation rate.

Outputs of units 218, 222 - 228 of the computational device 200 are linked through galvanic decoupler 262 to the output terminal block X14 of the control unit.

Other outputs of units 220 - 228 of the computational unit 200 are linked through the galvanic decoupler 264 to the control input 266 of the reversing-type starter unit 268. The power input 270 of the unit 268 is linked to the output of the automatic circuit breaker unit 272, connected to the power terminal block XI of the control unit. The power outputs of the unit 268 are linked to the output terminals X15 - X18 of the control unit 2.

The signal output 274 of the reversing-type starter unit 268 is linked to the input of motor currents control unit 276, which is linked through the serial port 278 with the bus 254. Besides, the motor currents control unit 276 is linked via the bus 280 to the disable input 278 of the automatic circuit-breakers unit 272. The input 282 is also linked to the output 284 of the emergency situation analysis unit 216. Terminals XI, X2 of the control unit are linked to the automatic backup power supply switching (ABP) unit 286, the output 287 of which is linked to the internal power supply unit 288 of the control unit. The output 290 of the unit 286 is linked through the bus 292 to the input 294 of the unit 216. Output terminals XI 2, XI 3 of the control unit 2 are linked to the inputs 302, 304 of the independent anode effect alarm unit 300, output 306 of which is linked to the output terminal X3 of the control unit 2. Outputs 302, 304 are linked to the input signal normalization unit 308, output of which is linked to the analog-to-digital converter (ADC) unit 310. The output of the ADC unit 310 is linked to one of the inputs of the comparison device unit 312. The other input of the unit 312 is linked to the output of level controller unit 314. The output of the comparison unit 312 is linked to the output 306, which is the output of the unit 300.

Outputs 302, 304 are also linked to the unit 316 for forming of power supply voltage for the circuit 318 of internal power supply of the unit 300. The method is embodied as follows (see FIG. 4 to 7).

Controlling of the pot through the control unit is performed in the working mode of its operation The control program is implemented as independent modules executed asynchronously (p. 700, 701, 702). In the module (p. 700) (see Fig. 6) executed with the frequency 18.2 Hz, measurements of the voltage Uat the pot and of the serial current /are carried out. hi the module (p. 701) executed with the frequency 1 Hz, calculation of the scaled voltage U_sc averaged over 1 s is carried out basing on the data from the module (p. 700). The calculation is carried out according to the known equation (see, e.g., [4])

U_SC = [ (U -E) :I] *I_n X E ,

E being a constant numerically equal to the reverse EMF and practically confined within the limits of 1.55 to 1.70 V; I_n, the nominal value of top lone current set forth by the technological restrictions.

In the module (p. 702) executed with the frequency 1/60 Hz, calculation of the time derivative of the smoothed scaled voltage dU_sc/dt (p. 703) is carried out. Smoothing of voltage means averaging of the scaled voltage U_sc and of its derivative dU_sc/dt each minute over the time interval not less than 10 minutes.

Control of the pot is performed via two channels: through regulation of alumina concentration due to altering the frequency of operation of the AAF system mechanisms (p. 704) and through regulation of the inter-pole gap by anode displacement upwards/downwards (p. 705).

Regulation of alumina concentration (p. 704) is performed depending of the supply mode (p. 7041) (Fig. 7). The principles underlying the control algorithm are explained with the aid of plots (see Fig. 4, 5).

In the deficient feed mode ("scarce" AAF operation mode) the value of the derivative dU_sc/dt increases (fragment "a"). On reaching the upper limiting value dU_sc/dt > Gj (p. 7042), the mode of excess feed is switched on ("frequent" AAF operation mode) (p. 7043) - see fragment "b". The value of dU_sc/dt begins to fall (fragment "c"). On reaching the lower limiting value dU_sc/dt < G_∑ p. 7044), the mode of deficient feed is switched on (p. 7045) - see fragment "d".

At the same moment "d", regulation of the inter-pole gap can be performed if necessary through anode displacement upwards/downwards (p. 705) (Fig. 6). For this purpose comparison of the averaged scaled voltage U_sc with the nominal value Uo is carried out. In case of U_sc > Uo + AU(p. 7051) (Fig. 7), reduction of the IPG is carried out through anode displacement downwards (p. 7052) (fragment "e"). In case of U_sc < Un - AU(p. 7053), increasing of the IPG is carried out through anode displacement upwards (p. 7054) (fragment "f ). The value of AU is the non-sensitivity zone specified by the technological requirements. At high alumina concentrations in the electrolyte (the right-hand branch of the _sc(C) plot (see the plot in Fig. 4) in the deficient supply mode the scaled voltage will fall, i.e. dU_sc dt < 0. With this, it is expedient to suspend alumina feeding to accelerate lowering alumina concentration in the electrolyte.

Following the deficient supply mode, it is necessary to quickly increase the alumina concentration in the electrolyte, as at low concentrations emerging anode effects is likely. For this purpose, it is expedient to perform introduction to the pot of the additional single feeding of alumina constituting several treatments, preferably of 3 to 5 ones, formed by the alumina automated feeding system.

The unit for pots control embodying the claimed control method, operates as follows.

The voltage between the anode bus 12 and the cathode bus 14 (U_w) is fed to the input of unit 232 via input terminals X12, X14. The unit 232 of analog signal normalization is a two-channel divisor-limiter possessing passing channels with different transfer constants. The first chaimel has the transfer constant K = 1 in the range of input voltages 0 to 10 V. In the range of input voltages the input signal in the first channel is limited at the level of 10 V. The second channel has the transfer constant K = 0.1 in the range of input voltages 0 to 100 V.

In case of U_w < 10 V, then this voltage is fed through the first channel to the output of unit 232 without being changed. Should U_w 10 V, it is limited in the first channel at the level of 10 V, while at the output of unit 232 appears the value of 0.1 U_w, and in this case the measurement is performed via the second channel accounting for the transfer constant K = 0.1.

Further, the normalized value of U_w is fed to the input of the two-channel analog- to-digital converter unit 234. The first channel performs measurement in the range of 0 to 10 V, while the second one does it in the range 10 to 100 V. Further the value of the working voltage in the digital form is fed through galvanic decoupler to the unit 210 for calculation of the scaled voltage U_sc-

Unit 210 performs averaging pot working voltage values averaging over 1 second interval (module 700 — see Fig. 6) and calculation of the scaled voltage U_sc (module 701). To implement the module 701, required is the value of the current I for the series measured simultaneously with U_w. The value of the current / is measured in the unit 34 (Fig. 2) and is fed to unit 210 via the input terminal X6, converter 252, adapter 248, driver 212 and via the internal bus 230.

Thus, the averaged over 1 s period value of the scaled voltage U_sc is formed, which is further employed in the calculations in the module 702. The value of U_sc is fed through the serial port 214 and control bus 254 to the display unit 256 for visual monitoring by the. personnel.

Calculation of the smoothed derivative of the scaled voltage dU_sc/dt (module 703) is carried out in unit 211 basing on the data of unit 210 transmitted via the bus 230. The value of dU_sc/dt is fed via the bus 230 to the input of concentration maintenance unit 218 implemented by module 704. Execution of modules 7043 and 7045 result in feeding control signals through the galvanic decoupler 262 and the output terminal block X14 to actuator mechanisms of the AAF system 18 (Fig. 2). Should it prove necessary, the unit 218 accesses via the bus 230 the unit for IGP maintenance 22 implemented by module 705. Execution of modules 7052 and 7054 result in feeding control signals through the galvanic decoupler 264 to the input 266 of reversing-type starter unit 268, which through the output terminal blocks XI 5 - XI 6 switches driving of the anode rack 20 by motors 26, 28 upwards or downwards (Fig. 2). Thus the automatic control of the electrolysis process is performed on the two pots.

Besides, unit 200 controls the process of execution of a number of other operations required by pots maintenance.

The unit 222 for support of maintenance operations on the pot, is intended for such operations as metal discharge, cording of the anode rack, rearrangement of switching the anode rods, leveling of the anode rack or the housing. Start of the maintenance operation is triggered by the operator by depressing the respective key on the keyboard 258. The signal from the keyboard 258 is fed via control bus 254, serial port 214 and internal bus 230 to the unit 222. In compliance with the issued command, unit 222 performs actions in supporting of any of the above operations. For example, it can disable automatic regulation of alumina concentration (p. 704) and automatic regulation of IPG (p. 705).

The unit for detection and suppression of MHD instability 224 receives the value of U_se via the bus 230 from unit 210. The unit 224 performs isolation of oscillations of voltage U_se having the preset frequency, and the amplitude of these oscillations is analyzed over a specified time interval. Should it exceed the minimum preset value, then the algorithm of MHD-instability suppression disables concentration regulation (p. 704) and increments Uo by the preset value δU. This value of δU can be either preset as fixed or be equal to the current value of the MHD-instability amplitude. As IGP regulation (p. 705) is still operative, increasing the preset value UQ causes increasing of IGP, due to which the MHD-instability is cured. After suppression of the above oscillation, the unit 224 switches on alumina concentration regulation and returns the preset value of Uo to the initial value.

In case of performing technological processing operations on the pot (see, e.g. "Handbook of the metallurgist in non-ferrous metals. Production of aluminum". - Moscow, "Metallurgiya" publishing house, 1971, ch. IV, p. 266 - 301) [8], then following the operator's command from the keyboard 258 via bus 254, serial port 214 and bus 230, the signal is fed to the processing maintenance unit 226. Unit 226 disables concentration regulation (p. 704) and increments the value of Uo by the preset value, which causes increasing of IPG on the pot. The latter event promotes temperature increasing, which compensates for electrolyte cooling having occurred due to introduction of the cold alumina in the course of processing. On completion of the processing support, unit 226 reduces the value of Uo to the initial level and restores alumina concentration regulation. The anode effect support unit 228 effects prediction of anode effects emerging basing on values of dU_sc/dt obtained from unit 211 via the bus 230. Besides, unit 228 determines occurrence of AE basing on the value of U_sc received from unit 210 via the bus 230; with this, the signal of AE occurrence through galvanic decoupler 246 and output terminal is fed to the bus 7 of anode effect group alarm. In the mode of AE prediction or in the course of AE occurrence, unit 228 disables operation of units 218 and 220 and itself controls AAF mechanisms through galvanic decoupler 262 and terminal block X14, and controls also motors of electric drives 26, 28 o the anode rack through galvanic decoupler 264 and starter unit 268.

Analog signals corresponding to existence of currents in the phase line of motors are fed from the signal output 274 of starter unit 268 to the motor current control unit 276 input. Unit 276 performs the analysis of magnitude of the current. Through the serial port

278, bus 254 and serial port 214 the values of motor currents are fed to the emergency situation analysis unit 216. Should the values of currents be beyond permissible limits, or should at least one phase be absent, or should there exist current in motors with control signals absent on the input, unit 216 via bus 280 sends the signal to the disable input 282 of the automatic circuit breaker unit. This results in disconnecting the control unit 2 from the bus 3, which rules out the emergency situation, which would be unauthorized operation of electric drives 26, 28, 30, 32 of anode rack or housing jacks. Should unit 2 fail to disconnect from bus 3, the emergency situation analysis unit 216 through the galvanic decoupler 244 and output terminal X4 shall form the signal for the device of group contactor disconnection.

In the course of pot operation emergency situations of various types can occur, which are also processed by the unit 216. Position of the anode rack within the preset limits is verified by signals from limit switches 22, 24. Should the anode rack reach the topmost position, the limit switch 22 closes; if it reaches the limiting lower position, the limit switch 24 closes. The signal of respective limit switch operation is fed through the input terminal block XI 1 and galvanic decoupler 238 to the emergency situation analysis unit 216.

Should the anode rack be located in the topmost position, unit 216 issues inhibition of its displacement upwards, should the anode rack be located in the limiting lower position, displacement downwards is inhibited.

In case of lacking of the power supply voltage in the bus 4, the ABP unit 286 automatically connects two phases from the bus 3 to the internal power supply unit of the control unit 2. With this, the signal of switching to the backup power supply is transmitted via the bus 292 to the unit 216, which forwards the respective message to the operator through bus 230, adapter 212, ArcNet LAN adapter unit 248, optical-fiber communication link converter 252 and output terminal X6.

In case of short circuit (SS) on the power outputs of the reversing-type starter unit

268, the signal of this through the signal output 274 is fed to the motor current control unit

276, which, in its turn, through the bus 280 sends the disable signal to the input 282 of the automatic circuit breaker unit 272, which causes disconnection of the bus 3 linked to the terminal XI of unit 268.

Failure of communication through ArcNet LAN entails absence of values of the potline current I in calculations of the value of U_sc in the unit 210. Communication failure is registered in the unit 216, and the respective message is broadcast through the bus 230 to all units of the computational device 200. In such a case, all operations of the computational device 200 are performed with the measured voltage U_w instead of U_sc.

All operations of the unit 216 are accompanied with voice messages generated by the voice robot, which are intended for personnel notification on occurrence of an emergency situation on the pot. The unit of independent AE alarms 300 (see Fig. 3) operates as follows.

Unit 316 for power supply voltage forming is a limiter stabilizer generating power supply for all components of the unit 300 out of the pot voltage coming to inputs 302, 304. From inputs 32, 34 the pot voltage is fed to the analog signal normalization unit 308 which is embodied as a divisor-limiter and which limits the signal at the ADC unit 310 input at the level of the ADC reference voltage. Unit 310 converts the input signal into the digital form and feeds this signal to the input of the comparison device unit 312. Should this value become greater or equal to that preset in the level controller unit 314, then the unit 312 generates the signal on AE occurrence and feeds the latter to the output 306.

INDUSTRIAL APPLICABILITY

The computational device of the control unit can be embodied on the basis of Intel 386 SX processor employing standard programming tools for IBM PC. ArcNet network adapter can be used as a board with ISA bus; ADC is the 12-digit one in the modular embodiment. The other components of the control unit are commercial automation components. Pot control units are produced commercially under the brand names

TROLL and STELA

Claims

1. The method for aluminum production pots control, consisting in maintaining of the pot temperature regime through regulation of inter-pole gap and of alumina concentration within the preset limits by means of alternating deficient and excess supply regimes, comprising measurement of pot voltage and of potline current, calculation of the current value of the scaled voltage U_sc and its rate of variation in time dU_sc/dt, comparison of calculated values with the preset ones and making the decision on regulation of the inter-pole gap and transfer to regimes of deficient or excess supply basing on results of the comparison, wherein transfer from deficient supply mode to the excess supply mode is performed provided reaching the rate of change of the scaled voltage in time dU_sc/dt > Gi, transfer from excess supply mode to the deficient supply mode is performed provided reaching the rate of change of the scaled voltage in time dU_sc/dt < G₂, G and G₂ being the threshold values for the rate of change of the scaled voltage determined experimentally (G; > G₂), with this, the regulation of inter-pole gap is performed at the moment of transition from the deficient supply mode to the excess supply mode provided that

/u_sc - Uo / > ΔU, Uo being the rated value of the scaled voltage and ΔU is the non-sensitivity zone specified by the technological requirements.

2. The method according to Claim 1, wherein in the deficient supply mode provided the rate of variation of the scaled voltage dU_s dt < 0, feeding of alumina is not carried out.

3. The method according to Claim 1 or Claim 2, wherein at the moment of transition from the deficient supply mode to the excess supply mode additionally introduced is a single feeding of alumina, preferably of 3 to 5 treatmentes, formed by the alumina automated feeding system.

4. The device for pots control, comprising units for measuring potline current and voltage linked to the inputs of computational device, outputs of which are linked with the unit for inter-pole gap regulation with actuators, and to the alumina automated feeding system with actuators, the comparison unit, the level controllers, and electric drives, wherein the computational unit comprises the following units interconnected with the internal bus: the unit for calculation of the scaled voltage, the unit for calculation of the scaled voltage derivative, the driver of the local area network, the unit for emergency situation analysis, the unit for maintaining the concentration, the unit for maintaining the inter-pole gap, the unit for maintenance operations support, the unit for detection and suppression of magneto-hydrodynamic instability, the unit for pot treatment support, the unit for anode effects support and the serial port linked via the control bus with the display unit, keyboard for data input, and external devices and sensors, incorporated into the system are the unit of internal power supply and the unit for automatic backup power supply switching, one of the outputs thereof being connected to the internal power supply unit and the other one, to one of the inputs of the emergency situation analysis unit, the voltage measurement unit comprises the unit for analog signal normalization, the input thereof being linked to the anode and cathode buses, and in parallel to these, to the inputs of the independent anode effect alarm unit, and the output linked to the input of the analog-to-digital converter unit, the output of which is linked with the unit for calculation of the scaled voltage, the unit for measurement of serial current is linked via the adapter to the local area network driver, the limit switches of the anode rack are connected to the input of the emergency situation analysis, one of the outputs of which constitutes the terminal for connecting of group contactor circuit breaker, the output of the concentration maintaining unit and one output of each of the following units: maintenance operations support unit, magneto-hydrodynamic instability detection and suppression unit, pot treatment support unit, anode effects support unit, are connected via the galvanic decoupler to the actuators of the alumina automated feeding system, the output of the unit for inter-pole gap maintenance and another outputs of maintenance operations support unit, magneto-hydrodynamic instability detection and suppression unit, pot treatment support unit, anode effects support unit, are connected via the galvanic decoupler to the control input of the reversing-type starter unit, the power input of which is linked to the output of the automatic circuit breakers unit connected to the three-phase power mains, the power outputs of the reversing-type starter unit being linked to the electric drives of the anode jacks and housing jacks, while the power output of the anode effect support unit is connected to the bus for anode effect group alarm, the signal output of the reversing-type starter unit is connected to the input of the unit for controlling anode and housing jacks electric drive motor current control, which is linked with the control bus through the serial port; with this, the motor current control unit is linked to the disable input of the automatic circuit breakers, linked as well with the other output of the emergency situation analysis unit (216).

5. The device according to Claim 4, wherein the independent anode effect alarm unit comprises the unit for normalization of the . analog signal, inputs thereof being the inputs of the entire unit, which are also linked to the unit for power supply voltage forming for the circuit of the unit internal power supply, while the output of the analog signal normalization unit is linked to one of the inputs of the comparison unit whereas the other input of the latter being linked to the output of the level controller unit, with the output of the comparison unit being the output of the entire unit.

6. The device according to Claim 4 or Claim 5, wherein the analog-to-digital converter unit, limit switches of the anode rack, the output of the emergency situation analysis unit for connecting the group contactor circuit breaker, the power output of the anode effect support unit are linked with respective units through galvanic decouplers.

7. The device according to any of Claims 4 to 6, wherein the local area network is organized in compliance with the ArcNet standard, the adapter being linked to said network through galvanic decoupling converter.

8. The device according to any of Claims 4 to 7, wherein the control bus is organized in compliance with the interface standard RS-485.

9. The device according to any of Claims 4 to 8, wherein external devices and sensors are connected to the control bus through galvanically decoupled converter of the data transmission rate of RS-485 interface.