CN111341389B - Electrolytic aluminum load electric heating characteristic modeling method for direct load control - Google Patents
Electrolytic aluminum load electric heating characteristic modeling method for direct load control Download PDFInfo
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Abstract
The invention discloses an electrolytic aluminum load electric heating characteristic modeling method for direct load control, which comprises the following steps: building an electrolytic aluminum production series; obtaining electrolytic aluminum load by a cryolite-alumina molten salt electrolysis method; establishing an electrolytic aluminum heat dissipation model; establishing an electrolytic aluminum electric heat exchange model; determining electrolytic aluminum load control constraints.
Description
Technical Field
The invention relates to an electrolytic aluminum load electric heating characteristic modeling method for direct load control, and belongs to the technical field of network source coordination control.
Background
In recent years, domestic power grids present new forms such as high voltage, large capacity, long-distance power transmission, alternating current-direct current hybrid connection and the like, and when large-scale power loss such as direct current blocking occurs, the safe and stable operation of the power grids faces serious challenges. Meanwhile, intermittent renewable energy sources such as wind energy, solar energy and the like are rapidly developed, the power grid faces the situation of lack of capacity regulation resources, and the problem of insufficient peak regulation capacity of the power grid is further highlighted particularly in the peak load period. A large amount of energy storage type loads exist in the power system, the energy storage type loads can play a similar role as energy storage, the flexible adjusting capacity of a power grid can be effectively improved, and the energy storage type load has huge application potential in the aspects of peak regulation, frequency modulation, voltage regulation, emergency response and the like.
Energy storage type loads such as air conditioners, electric automobiles and water heaters are hot spots of current research, most of the energy storage type loads are residential and commercial loads, and have the characteristics of small power, numerous quantities, scattered geographic positions, strong randomness and the like of a single individual, so that the problem of how to aggregate the energy storage type loads and incorporate the loads into a power system dispatching and control framework is a difficult problem. Unlike the small energy storage type loads described above, electrolytic aluminum is a typical high energy consumption large energy storage type industrial load, and the load of a single electrolytic aluminum plant can even reach millions of kilowatts. Electrolytic aluminum utilizes direct current to convert aluminum compounds in a high-temperature molten state into simple aluminum substances, and because an electrolytic cell has good heat preservation and large thermal inertia time constant, the temperature of an electrolyte does not change too much after the electrolytic cell is powered off for a short time, and the electrolytic process is not influenced adversely [13]. Although the capacity of the electrolytic aluminum exceeds the demand in China in recent years, so that the capacity of the electrolytic aluminum is accelerated, the proportion of the electrolytic aluminum in the power consumption of the society is still high. Electrolytic aluminum enterprises are generally provided with self-contained power plants, some self-contained power plants are connected with a power grid, and after the load of electrolytic aluminum is reduced, the self-contained power plants can input a large amount of electric energy to the power grid. Therefore, the method has important significance for fully excavating the adjustment potential of the electrolytic aluminum load, coordinating with the power generation side resource to economically schedule and deal with the direct current blocking fault or peak shaving of the receiving end power grid.
The load model is the basis for researching the participation of the electrolytic aluminum in the scheduling and control of the power system, but the current modeling research on the electricity utilization characteristics of the electrolytic aluminum is relatively less. Some electrolytic aluminum static and dynamic models proposed in the literature mostly describe the external characteristics of the electrolytic aluminum load, and some of them propose electrolytic aluminum load static and dynamic models and parameter identification methods suitable for system analysis and control on the basis of analyzing the internal electrical topology and characteristics of the electrolytic aluminum. However, if the electrothermal characteristics of the electrolytic aluminum are not modeled, it is difficult to quantitatively analyze the negative effects of load control on the electrolytic aluminum. An electrolytic aluminum heavy-load isolated network emergency control optimization method (Wangyu, permission, wang Huaming and the like, power system automation 2014,38 (21): 121-126, 135) provides an electrolytic aluminum heavy-load isolated network emergency control optimization method, and an emergency control scheme with low control cost is obtained according to the operation mode, the model and the parameters of an electrolytic aluminum self-contained power grid and the load characteristics of electrolytic aluminum. The multi-agent response simulation (YaoMing, humega, zhang, etc. China electro-mechanical engineering, 2014,34 (25): 4219-4226) for providing auxiliary service for industrial loads builds multi-agent systems of various industrial loads on the basis of analyzing the controllability of the loads such as electrolytic aluminum and the like, and explains the targets, structures and behavior strategies of various agents. None of the above documents relating to electrolytic aluminum control consider an electric characteristic model of electrolytic aluminum, and therefore, the influence on the electrolytic aluminum production after load control cannot be quantitatively analyzed.
Disclosure of Invention
In order to solve the problems, the invention provides an electrolytic aluminum load electric heating characteristic modeling method for direct load control, and the established electrolytic aluminum load electric heating model can provide a direct control strategy of electrolytic aluminum on the basis of analyzing power consumption constraints.
The technical scheme adopted for solving the technical problem is as follows:
the embodiment of the invention provides an electrolytic aluminum load electric heating characteristic modeling method for direct load control, which comprises the following steps:
building an electrolytic aluminum production series;
obtaining electrolytic aluminum load by a cryolite-alumina molten salt electrolysis method;
establishing an electrolytic aluminum heat dissipation model;
establishing an electrolytic aluminum electric heat exchange model;
determining electrolytic aluminum load control constraints.
As a possible implementation manner of this embodiment, the direct load control includes:
direct control strategy for electrolytic aluminum: carrying out power cut-off of electrolytic aluminum production series through a main drop switch for cutting off electrolytic aluminum;
recovery strategy for electrolytic aluminum: when the power utilization constraint of the electrolytic aluminum load is reached, the power supply of the electrolytic aluminum is recovered, the working voltage of the electrolytic cell is improved, the heat injection of the electrolytic cell is increased, and the heat balance of the electrolytic cell is recovered until the electrolytic cell is shifted to normal.
As a possible implementation manner of this embodiment, the process of building the electrolytic aluminum production series is to connect a plurality of electrolytic cells in series, and supply power by the same dc power supply to form a production series.
As a possible implementation manner of this embodiment, the cryolite-alumina molten salt electrolysis method includes:
1) The two-pole reaction equation for electrolytic aluminum is as follows:
Al 2 O 3 +1.5C＝＝2Al+1.5CO 2 (1)
2) The side reaction formula of electrolytic aluminum is as follows:
2Al+3CO 2 ＝＝Al 2 O 3 +3CO (2)
part of CO 2 Chemically reacting with C as follows
C+CO 2 ＝＝2CO (3)
3) The overall reaction formula of electrolytic aluminum is as follows:
x(1-y)γ-Al 2 O 3 +xyα-Al 2 O 3 +(1.5+b)C＝＝2xAl+(3x- 1.5-b)CO 2 +(3-3x+2b)CO (4)
wherein y is gamma-Al 2 O 3 Type fraction, x is percent current efficiency; b is CO 2 With C.
As a possible implementation manner of this embodiment, the electrolytic aluminum heat dissipation model includes:
1) Cell voltage U cell Comprises the following steps:
U cell ＝U emf +U el +U bub +U an +U ca +U ex (5)
in the formula of U emf Is the polarization voltage; u shape el Is the electrolyte voltage; u shape bub For electrolysis ofThe voltage of the proton anode bubble; u shape an Is the anode voltage; u shape ca Is a cathode voltage; u shape ex Is the external voltage of the electrolytic cell;
2) Cell voltage U within heat loss boundaries cl Comprises the following steps:
U cl ＝U emf +U el +U bub +U an +U ca (7)
from formulas (5) and (7):
U cl ＝U cell -U bus -U sh (8)
in the formula of U bus The voltage drop of the cathode bus and the anode bus; u shape sh Voltage is evenly shared for the bus; u shape bus And U sh Form the external voltage U of the electrolytic cell ex 。
3) Equivalent voltage E of electrolytic aluminum ΔH o Comprises the following steps:
E ΔH o ＝-ΔH o (x)/(nF) (9)
the electron transfer n =6 (x) is obtained according to the total reaction formula of the electrolytic aluminum;
gamma-Al according to the standard 2 O 3 Chemical reaction data, equivalent voltage obtained by multiple regression method, including electrolyte temperature, environment temperature, current efficiency percentage, and gamma-Al 2 O 3 Type to volume ratio and CO 2 As a function of the number of moles in the reaction with C, as shown in equation (10):
E H o ＝0.23706+4.6757×10 -4 T e -2.25×10 -7 (T e ) 2 +x(1.4024+0.03253y+2.23×10 - 4 T e )+b(0.3086-1.97×10 -5 T e )+(25-T r )[0.000145(x-xy)+0.0000138xy+0.000015(b+1.5)] (10)
in the formula, T r Is ambient temperature; t is e Is the electrolyte temperature;
4) Heat dissipation Q of electrolytic cell loss Comprises the following steps:
Q loss ＝I(U cl -E H o ) (11)
in the formula, I is the current of the electrolytic cell;
as a possible implementation manner of this embodiment, the U is emf The minimum voltage which is required to be applied to two poles for electrolyzing and precipitating aluminum for a long time is the sum of the decomposition voltage of the aluminum oxide and the overvoltage of the two poles:
U emf ＝U rev +η sa +η ca +η cc (6)
U rev to a decomposition voltage; eta sa Is anode surface overvoltage; eta ca Is an anodic overvoltage; eta cc Is the cathodic overvoltage.
As a possible implementation manner of this embodiment, the electrolytic aluminum electric heat exchange model electrolyte and the ambient heat exchange satisfy:
Q loss ＝(T r -T e0 )K (12)
wherein K is the heat transfer conductance (W/DEG C); t is r Is ambient temperature; t is e0 The temperature of the electrolyte during normal aluminum production;
establishing an electrolyte temperature change model according to a first thermodynamic law:
in the formula C e Is the electrolyte heat capacity; t is e (t) is the electrolyte temperature; q e Heat is input to the electrolytic cell.
As a possible implementation manner of this embodiment, the electrolytic aluminum load control constraint includes:
the constraints of electrolytic aluminum load control are:
T e (t)≥T liq (14)
in the formula, T liq The temperature of primary crystal of electrolyte;
the time constraints of the power failure of the electrolytic aluminum are as follows:
t cut ≤τln[(T e0 -T r )/(T liq -T r )] (15)
in the formula, t cut For electrolysis ofTime of aluminum power-off direct-cutting control, tau = C e and/K is the time constant of the temperature change of the electrolytic cell.
The technical scheme of the embodiment of the invention has the following beneficial effects:
the technical scheme of the embodiment of the invention provides an electric heating model of electrolytic aluminum load based on the basic working principle of electrolytic aluminum and provides a direct control strategy of electrolytic aluminum on the basis of analyzing electric constraint.
Description of the drawings:
FIG. 1 is a flow chart illustrating a method of modeling electrolytic aluminum load electrothermal characteristics for direct load control in accordance with an exemplary embodiment;
FIG. 2 is a basic schematic diagram of an electrolytic aluminum;
FIG. 3 is a schematic view of an electrolytic aluminum production series;
FIG. 4 is a graph comparing measured and predicted results of electrolyte temperature;
fig. 5 is a schematic diagram of the temperature change of the electrolyte.
Detailed Description
The invention is further illustrated by the following examples in conjunction with the accompanying drawings:
in order to clearly explain the technical features of the present invention, the present invention will be explained in detail by the following embodiments and the accompanying drawings. The following disclosure provides many different embodiments, or examples, for implementing different features of the invention. To simplify the disclosure of the present invention, specific example components and arrangements are described below. Furthermore, the present invention may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. It should be noted that the components illustrated in the figures are not necessarily drawn to scale. Descriptions of well-known components and processing techniques and procedures are omitted so as to not unnecessarily limit the invention.
FIG. 1 is a flow chart illustrating a method of modeling electrolytic aluminum load electrothermal characteristics for direct load control according to an exemplary embodiment. As shown in fig. 1, an embodiment of the present invention provides a method for modeling an electrical thermal characteristic of an electrolytic aluminum load for direct load control, including the following steps:
building an electrolytic aluminum production series;
obtaining electrolytic aluminum load by a cryolite-alumina fused salt electrolysis method;
establishing an electrolytic aluminum heat dissipation model;
establishing an electrolytic aluminum electric heat exchange model;
determining electrolytic aluminum load control constraints.
1.1 basic working principle of electrolytic aluminum
1.1.1 electrolytic aluminum operating principle
The modern electrolytic aluminum industry mainly adopts cryolite-alumina molten salt electrolysis method. The basic principle of electrolytic aluminum is shown in figure 2, molten cryolite is used as a solvent, alumina is used as a solute, a carbon body is used as an anode, aluminum liquid is used as a cathode, direct current is introduced into an electrolytic cell at 950-970 ℃, electrochemical reaction is carried out on the two electrodes, and CO is generated by the anode 2 And CO gas, the cathode producing aluminum.
1) Two-pole reaction of electrolytic aluminium
Under the action of DC electric field, the ions in electrolyte solution are discharged at cathode to separate out simple substance of Al. Oxygen ions move to the anode under the action of a direct current electric field and react with anode carbon to generate CO 2 . The two poles are synthesized by reaction, and the reaction equation is as follows:
Al 2 O 3 +1.5C＝＝2Al+1.5CO 2 (1)
2) Side reactions of electrolytic aluminium
Along with the escape of the anode gas of the electrolytic cell, the electrolyte in the electrolytic cell circulates from bottom to top, so that the aluminum dissolved in the electrolyte is transferred to the vicinity of the anode along with the electrolyte and is CO of the anode 2 And (3) oxidizing, wherein the reaction formula is as follows:
2Al+3CO 2 ＝＝Al 2 O 3 +3CO (2)
in addition, a part of CO 2 And C, carrying out chemical reaction:
C+CO 2 ＝＝2CO (3)
3) General reaction of electrolytic aluminum
Alumina has a different crystal structure, generally classified as gamma-Al 2 O 3 And alpha-Al 2 O 3 The two have different physical and chemical properties, gamma-Al 2 O 3 Conversion to alpha-Al 2 O 3 Then carrying out chemical reaction. The general reaction formula of the electrolytic aluminum is as follows:
x(1-y)γ-Al 2 O 3 +xyα-Al 2 O 3 +(1.5+b)C＝＝2xAl+(3x-1.5-b)CO 2 +(3-3x+2b)CO (4)
wherein y is gamma-Al 2 O 3 Type fraction, x is percent current efficiency; b is CO 2 The number of moles in the formula with C can be measured or estimated from the ratio of CO to CO 2 The ratio of (a) to (b) is obtained.
1.1.2 electrolytic aluminum production series
Electrolytic aluminum production typically involves connecting a number of electrolytic cells in series, powered by the same dc power source, to form a production train, as shown in fig. 3. In an electrolytic aluminum production series, direct current flowing out of a positive electrode of a direct current bus flows to an anode of a #1 electrolytic cell through the bus, sequentially flows through electrolyte, an aluminum liquid layer and a cathode of the #1 electrolytic cell, then flows to a cathode bus of the electrolytic cell and a connecting bus at the bottom of a cell body, then flows to a column bus, a soft bus and an anode bus of a #2 electrolytic cell, and so on, all the electrolytic cells of one production series are connected in series, and current flowing out of a cathode of a final electrolytic cell # N returns to a negative electrode of the direct current bus.
The alternating current bus and the direct current bus respectively play a role in collecting alternating current energy and direct current energy; the rectification system consists of parallel rectification circuits, and each group of rectification circuits comprises an on-load tap changer, a three-winding rectifier transformer, a saturable reactor and a rectifier bridge. The on-load tap changer is used for roughly adjusting the direct current voltage of the electrolytic aluminum load so as to meet the requirement of the electrolytic aluminum load on the voltage adjusting capacity in the starting and production processes. The role of the rectifier transformer is to transform and shift the phase. The saturable reactor is used for finely adjusting the direct current voltage of the electrolytic aluminum load. The rectifier bridge is used for converting alternating current into direct current, and the rectifier elements of large-scale electrolytic aluminum plants are generally uncontrolled element diodes.
1.2 electrolytic aluminum load electric heating model
1.2.1 electrolytic aluminum heat dissipation model
The scholars puts forward a cell voltage calculation formula of the electrolytic cell based on the Gibbs theory, and further establishes a voltage-based electrolytic cell heat dissipation model, and the physical mechanism of the model is clear.
1) Cell voltage U cell
The electrolytic bath voltage consists of polarization voltage, electrolyte voltage, anode bubble voltage, pole voltage and electrolytic bath external voltage:
U cell ＝U emf +U el +U bub +U an +U ca +U ex (5)
in the formula of U emf Is a polarization voltage; u shape el Is the electrolyte voltage; u shape bub Is the anode bubble voltage in the electrolyte; u shape an Is the anode voltage; u shape ca Is a cathode voltage; u shape ex Is the external voltage of the electrolytic cell.
U emf The minimum voltage applied to the two poles is the sum of the decomposition voltage of the aluminum oxide and the overvoltage of the two poles, and is required for electrolyzing and precipitating aluminum for a long time.
U emf ＝U rev +η sa +η ca +η cc (6)
In the formula of U rev To a decomposition voltage; eta sa Overvoltage on the surface layer of the anode; eta ca Is anode overvoltage; eta cc Is the cathodic overvoltage.
2) Cell voltage U within heat loss boundaries cl
The cell voltage within the heat loss boundary consists of the polarization voltage, electrolyte voltage, anode bubble voltage and pole voltage:
U cl ＝U emf +U el +U bub +U an +U ca (7)
from formulas (5) and (7):
U cl ＝U cell -U bus -U sh (8)
in the formula of U bus The voltage drop of the cathode bus and the anode bus; u shape sh Voltage is evenly shared for the bus; u shape bus And U sh Form the external voltage U of the electrolytic cell ex 。
3) Equivalent voltage E of electrolytic aluminum ΔH o
The lowest voltage required for electrolyzing alumina in an aluminum electrolysis cell (carbon anode) is called equivalent voltage E ΔH o 。
E ΔH o ＝-ΔH o (x)/(nF) (9)
Since the electron transfer n =6 (x) according to the total reaction formula (4) of electrolytic aluminum, Δ H only needs to be obtained o The voltage equivalent voltage can be obtained. Gamma-Al according to the standard 2 O 3 Chemical reaction data, equivalent voltage obtained by multiple regression method, including electrolyte temperature, environment temperature, current efficiency percentage, gamma-Al 2 O 3 Type to type ratio and CO 2 As a function of the number of moles in the reaction with C, as shown in equation (10):
E ΔH o ＝0.23706+4.6757×10 -4 T e -2.25×10 -7 (T e ) 2 +x(1.4024+0.03253y+2.23×10 - 4 T e )+b(0.3086-1.97×10 -5 T e )+(25-T r )[0.000145(x-xy)+0.0000138xy+0.000015(b+1.5)] (10)
in the formula, T r Is ambient temperature; t is a unit of e Is the electrolyte temperature.
4) Heat dissipation Q of electrolytic cell loss
The heat Q to be dissipated by the cell in order to maintain the cell at a constant temperature loss The following formula:
Q loss ＝I(U cl -E ΔH o ) (11)
in the formula, I is the current of the electrolytic cell.
1.2.2 electrolytic aluminum electric heat exchange model
The heat exchange between the electrolyte and the environment meets the following requirements:
Q loss ＝(T r -T e0 )K (12)
wherein K is heat exchange thermal conductance (W/DEG C); t is r Is ambient temperature; t is a unit of e0 The temperature of the electrolyte during normal aluminum production.
Establishing an electrolyte temperature change model according to a first thermodynamic law:
in the formula C e The electrolyte heat capacity can be obtained by identification according to the actually measured temperature change of the electrolyte; t is e (t) is the electrolyte temperature; q e Heat is input to the electrolytic cell.
The strategies and constraints of the electrolytic aluminum load control are specifically as follows:
2.1 control strategy for electrolytic aluminum
2.1.1 direct control strategy for electrolytic aluminum
The power cut-off of the electrolytic aluminum production series is realized by cutting off the main drop switch of the electrolytic aluminum. The control strategy realizes discontinuous rapid regulation of the power of the electrolytic aluminum, and the action rate depends on the action rate of the total drop switch.
2.1.2 recovery strategy for electrolytic aluminum
After the electrolytic cell is powered off, the temperature of the electrolytic cell is gradually reduced, the level of the electrolyte is continuously reduced, and the viscosity of the electrolyte is continuously increased. Along with the time, the melt in the tank gradually forms a mixture of aluminum and electrolyte in a semi-solidified state until the upper part of the melt is an aluminum water upturning layer, and the melt condition in the tank is worse as the time goes. When the restriction of the electrolytic process is reached, the power supply of the electrolytic aluminum needs to be recovered, the working voltage of the electrolytic cell is improved, the heat injection of the electrolytic cell is increased, and the heat balance of the electrolytic cell is recovered until the electrolytic cell is switched to normal.
2.2 electrolytic aluminum load control constraints
The primary crystal temperature of the electrolyte of the electrolytic aluminum refers to the temperature at which liquid begins to form solid crystals, and the electrolysis temperature is generally controlled to be 10-20 ℃ above the primary crystal temperature of the electrolyte in the production process. Thus, the constraints of electrolytic aluminum load control are:
T e (t)≥T liq (14)
in the formula, T liq The electrolyte primary crystallization temperature.
The time constraint for the outage of the electrolytic aluminium can be obtained according to equations (13) and (14) as:
t cut ≤τln[(T e0 -T r )/(T liq -T r )] (15)
in the formula, t cut Time for controlling power-off direct cutting of electrolytic aluminum, tau = C e and/K is the time constant of the temperature change of the electrolytic bath.
The embodiment of the invention provides a control system for participating in emergency control of a power grid by electrolytic aluminum load, which comprises:
a load shedding execution station for collecting basic operation information of the electrolytic aluminum load,
the stable control master station is used for inputting the electrolytic aluminum load electric heating model to obtain the cuttable load quantity and the power utilization constraint of the electrolytic aluminum load and issuing a load cutting instruction by adopting an electrolytic aluminum load control method;
and the load shedding master station sends a command of cutting off the main drop switch of the electrolytic aluminum after the direct current blocking fault occurs and closing the main drop switch of the electrolytic aluminum when the power utilization constraint of the electrolytic aluminum load is reached to the load shedding execution station according to the load shedding command.
The invention adopts electrolytic aluminum to participate in the emergency control of the power grid, and concretely comprises the following steps.
The stable control load shedding system is an important means for dealing with the direct current blocking fault, and a control mode for cutting off the whole production series of the electrolytic aluminum can respond to a stable control load shedding signal and ensure the safe and stable operation of a power grid after the direct current blocking fault, as shown in fig. 4.
The load shedding execution station collects basic operation information of the electrolytic aluminum load, obtains the shedding amount and the power utilization constraint of the electrolytic aluminum load, and uploads the shedding amount to the load shedding main station. When the direct current is locked (the loss power reaches a certain value), the stable control main station reaches the load shedding main station under the load shedding instruction, and the load shedding main station comprehensively considers all the load information to formulate and issue load shedding instructions of all the load shedding execution stations. When the electrolytic aluminum receives a load cutting instruction, a main drop switch of the electrolytic aluminum is cut off, and the power cutting of the electrolytic aluminum production series is realized. When the constraint of the electrolytic aluminum load is reached, the power supply of the electrolytic aluminum needs to be recovered, and the recovery strategy of the load after the extra-high voltage direct current fault disposal is not considered herein for the moment.
Simulation of the electrothermal Properties of the electrolytic aluminum of the invention
TABLE 1 variation of electrolyte temperature after cell blackout
As shown in Table 1, the time constants τ of the three electrolytic cells were obtained by identifying the parameters of the model of the thermal characteristics of electrolytic aluminum of the present invention 1 、τ 2 And τ 3 Respectively as follows: 34.91h, 36.03h and 33.29h.
The electrolyzer operating data are taken from electrolyzer operating data taken from literature aluminum electrolyzer heat dissipation capacity and distribution rules (thousands of baths, royal indov, liu military mountains, etc.. Light metals, 2006,6: 438.86W/c, 440.30W/c and 440.30W/c, heat capacities were: 5.52X 10 7 J/℃、5.71×10 7 J/. Degree.C.and 5.28X 10 7 J/DEG C. The identification parameters are input into the model to predict the temperature of the electrolyte after power failure, and a comparison graph of actual measurement and prediction results of the temperature can be obtained, as shown in fig. 4, the actual measurement result and the prediction result are better in coincidence, errors are respectively 2.51%, 2.12% and 1.93%, and the correctness of the electrolytic aluminum heat exchange model and the identified parameters is verified.
Assuming that the primary crystal temperature of the electrolyte is 930 ℃, taking a #1 electrolytic cell as an example to perform power-off cutting control simulation, as shown in fig. 5, the electrolyte temperature drops to the primary crystal temperature 29.87min after the electrolytic cell is powered off, and the electrolyte temperature returns to the original working temperature 29.90min after power supply is resumed. The good controllability of the electrolytic aluminum load was demonstrated.
The invention takes large-capacity industrial load electrolytic aluminum as a research object, analyzes the basic working principle of the electrolytic aluminum, establishes an electrolytic aluminum load electric heating model, quantitatively analyzes the power utilization constraint of the electrolytic aluminum load, and verifies the effectiveness of the electrolytic aluminum load thermal characteristic model through example simulation.
The foregoing is only a preferred embodiment of the present invention, and it will be apparent to those skilled in the art that various modifications and improvements can be made without departing from the principle of the present invention, and these modifications and improvements are also considered to be within the scope of the present invention.
Claims (6)
1. An electrolytic aluminum load electrothermal characteristic modeling method for direct load control is characterized by comprising the following steps:
building an electrolytic aluminum production series;
obtaining electrolytic aluminum load by a cryolite-alumina molten salt electrolysis method;
establishing an electrolytic aluminum heat dissipation model;
establishing an electrolytic aluminum electric heat exchange model;
determining electrolytic aluminum load control constraints;
the electrolytic aluminum electric heat exchange model is as follows:
the heat exchange between the electrolyte and the environment meets the following requirements:
Q loss ＝(T r -T e0 )K (12)
in the formula Q loss The heat dissipation capacity of the electrolytic cell is shown, and K is the heat exchange thermal conductance; t is a unit of r Is ambient temperature; t is e0 The temperature of the electrolyte during normal aluminum production;
establishing an electrolyte temperature change model according to a first thermodynamic law:
in the formula C e Is the electrolyte heat capacity; t is e (t) is the electrolyte temperature; q e Inputting heat to the electrolytic cell;
the electrolytic aluminum load control constraints include:
the constraints of the electrolytic aluminum load control are:
T e (t)≥T liq (14)
in the formula, T liq The electrolyte primary crystal temperature;
the time constraints for the power failure of electrolytic aluminum are:
t cut ≤τln[(T e0 -T r )/(T liq -T r )] (15)
in the formula, t cut Time for controlling power-off direct cutting of electrolytic aluminum, tau = C e and/K is the time constant of the temperature change of the electrolytic bath.
2. The method of modeling electrolytic aluminum load electrothermal characteristics for direct load control according to claim 1, wherein said direct load control comprises:
direct control strategy for electrolytic aluminum: the power of the electrolytic aluminum production series is cut off through a total reduction switch for cutting off the electrolytic aluminum;
recovery strategy for electrolytic aluminum: when the power utilization constraint of the electrolytic aluminum load is reached, the power supply of the electrolytic aluminum is recovered, the working voltage of the electrolytic cell is improved, the heat injection of the electrolytic cell is increased, and the heat balance of the electrolytic cell is recovered until the electrolytic cell is switched to normal.
3. The modeling method for electric heating characteristics of electrolytic aluminum load for direct load control according to claim 1, wherein the process of establishing the electrolytic aluminum production series is to connect a plurality of electrolytic cells in series and supply power by the same direct current power supply to form a production series.
4. The method of claim 1, wherein the cryolite-alumina fused salt electrolysis method comprises:
1) The two-pole reaction equation for electrolytic aluminum is as follows:
Al 2 O 3 +1.5C＝＝2Al+1.5CO 2 (1)
2) The side reaction formula of electrolytic aluminum is as follows:
2Al+3CO 2 ＝＝Al 2 O 3 +3CO (2)
part of CO 2 Chemically reacting with C as follows
C+CO 2 ＝＝2CO (3)
3) The overall reaction formula of electrolytic aluminum is as follows:
x(1-y)γ-Al 2 O 3 +xyα-Al 2 O 3 +(1.5+b)C＝＝2xAl+(3x-1.5-b)CO 2 +(3-3x+2b)CO
(4) Wherein y is gamma-Al 2 O 3 Type fraction, x is percent current efficiency; b is CO 2 And C.
5. The method as claimed in claim 1, wherein the model of the heat dissipation capacity of the electrolytic aluminum comprises:
1) Cell voltage U cell Comprises the following steps:
U cell ＝U emf +U el +U bub +U an +U ca +U ex (5)
in the formula of U emf Is the polarization voltage; u shape el Is the electrolyte voltage; u shape bub Is the anode bubble voltage in the electrolyte; u shape an Is the anode voltage; u shape ca Is a cathode voltage; u shape ex Is the external voltage of the electrolytic cell;
2) Cell voltage U within heat loss boundaries cl Comprises the following steps:
U cl ＝U emf +U el +U bub +U an +U ca (7)
from formulas (5) and (7):
U cl ＝U cell -U bus -U sh (8)
in the formula of U bus The voltage drop of the cathode bus and the anode bus; u shape sh Voltage is evenly shared for the bus; u shape bus And U sh Form the external voltage U of the electrolytic cell ex ；
3) Equivalent voltage E of electrolytic aluminum ΔH o Comprises the following steps:
E ΔH o ＝-ΔH o (x)/(nF) (9)
electron transfer n =6 (x) according to the total reaction formula of electrolytic aluminum;
Gamma-Al according to the standard 2 O 3 Chemical reaction data, equivalent voltage obtained by multiple regression method, including electrolyte temperature, environment temperature, current efficiency percentage, and gamma-Al 2 O 3 Type to volume ratio and CO 2 As a function of the number of moles in the reaction with C, as shown in equation (10):
E ΔH o ＝0.23706+4.6757×10 -4 T e -2.25×10 -7 (T e ) 2 +x(1.4024+0.03253y+2.23×10 -4 T e )+b(0.3086-1.97×10 -5 T e )+(25-T r )[0.000145(x-xy)+0.0000138xy+0.000015(b+1.5)] (10)
in the formula, T r Is ambient temperature; t is e Is the electrolyte temperature; y is gamma-Al 2 O 3 Type to type ratio, x is the percent current efficiency; b is CO 2 With C;
4) Heat dissipation Q of electrolytic cell loss Comprises the following steps:
Q loss ＝I(U cl -E ΔH o ) (11)
in the formula, I is the current of the electrolytic cell.
6. The method as claimed in claim 5, wherein the U is a number of U, and the method is characterized in that emf The minimum voltage which is required to be applied to two poles for electrolyzing and precipitating aluminum for a long time is the sum of the decomposition voltage of the aluminum oxide and the overvoltage of the two poles:
U emf ＝U rev +η sa +η ca +η cc (6)
U rev to a decomposition voltage; eta sa Is anode surface overvoltage; eta ca Is an anodic overvoltage; eta cc Is the cathodic overvoltage.
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