CN111341389A - 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 and alternating current-direct current hybrid connection, 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 of the static and dynamic models of electrolytic aluminum proposed in the literature mostly describe the external characteristics of the electrolytic aluminum load, and some of them propose the static and dynamic models of electrolytic aluminum load 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, Wangheming and the like, power system automation 2014,38(21):121-126 and 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 characteristics of electrolytic aluminum load. The multi-agent response simulation (YaoMing, Humega, Zhang, etc. China Motor engineering reports 2014,34(25):4219 plus 4226) for providing auxiliary service for the industrial load constructs multi-agent systems of various industrial loads on the basis of analyzing the load controllability of electrolytic aluminum and the like, and explains the target, structure and behavior strategy 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 problems 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: 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.
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:
Al2O3+1.5C＝＝2Al+1.5CO2(1)
2) the side reaction formula of electrolytic aluminum is as follows:
2Al+3CO2＝＝Al2O3+3CO (2)
part of CO2Chemically reacting with C as follows
C+CO2＝＝2CO (3)
3) The overall reaction formula of electrolytic aluminum is as follows:
x(1-y)γ-Al2O3+xyα-Al2O3+(1.5+b)C＝＝2xAl+(3x- 1.5-b)CO2+(3-3x+2b)CO (4)
wherein y is gamma-Al2O3Type fraction, x is percent current efficiency; b is CO2And C.
As a possible implementation manner of this embodiment, the electrolytic aluminum heat dissipation model includes:
1) cell voltage UcellComprises the following steps:
Ucell＝Uemf+Uel+Ubub+Uan+Uca+Uex(5)
in the formula of UemfIs a polarization voltage; u shapeelIs the electrolyte voltage; u shapebubIs the anode bubble voltage in the electrolyte; u shapeanIs the anode voltage; u shapecaIs the cathode voltage; u shapeexIs the external voltage of the electrolytic cell;
2) cell voltage U within heat loss boundariesclComprises the following steps:
Ucl＝Uemf+Uel+Ubub+Uan+Uca(7)
from formulas (5) and (7):
Ucl＝Ucell-Ubus-Ush(8)
in the formula of UbusThe voltage drop of the cathode bus and the anode bus; u shapeshVoltage is evenly shared for the bus; u shapebusAnd UshForm the external voltage U of the electrolytic cellex。
3) Equivalent voltage E of electrolytic aluminumΔH oComprises the following steps:
EΔH o＝-ΔHo(x)/(nF) (9)
the electron transfer n ═ 6(x) can be obtained according to the total reaction formula of electrolytic aluminum;
gamma-Al according to the standard2O3Chemical reaction data, equivalent voltage obtained by multiple regression method, including electrolyte temperature, environment temperature, current efficiency percentage, and gamma-Al2O3Type to volume ratio and CO2As a function of the number of moles in the reaction with C, as shown in equation (10):
EH o＝0.23706+4.6757×10-4Te-2.25×10-7(Te)2+x(1.4024+0.03253y+2.23×10-4Te)+b(0.3086-1.97×10-5Te)+(25-Tr)[0.000145(x-xy)+0.0000138xy+0.000015(b+1.5)](10)
in the formula, TrIs ambient temperature; t iseIs the electrolyte temperature;
4) heat dissipation Q of electrolytic celllossComprises the following steps:
Qloss＝I(Ucl-EH o) (11)
in the formula, I is the current of the electrolytic cell;
as a possible implementation manner of this embodiment, the U isemfThe 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:
Uemf＝Urev+ηsa+ηca+ηcc(6)
Urevto decompose the voltage ηsaη being an overvoltage on the surface of the anodecaIs anodic overvoltage ηccIs 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:
Qloss＝(Tr-Te0)K (12)
wherein K is the heat transfer conductance (W/DEG C); t isrIs ambient temperature; t ise0The temperature of the electrolyte during normal aluminum production;
establishing an electrolyte temperature change model according to a first thermodynamic law:
in the formula CeAs an electrolyteHeat capacity; t ise(t) is the electrolyte temperature; qeHeat 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:
Te(t)≥Tliq(14)
in the formula, TliqThe temperature of primary crystal of electrolyte;
the time constraints of the power failure of the electrolytic aluminum are as follows:
tcut≤τln[(Te0-Tr)/(Tliq-Tr)](15)
in the formula, tcutTime for controlling the cut-off of electrolytic aluminium,. tau. -. Ceand/K is the time constant of the temperature change of the electrolytic bath.
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 diagram of an electrolytic aluminum production train;
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 following detailed description of the present invention is provided with reference to 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, the components and arrangements of specific examples 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 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.
1.1 basic working principle of electrolytic aluminum
1.1.1 electrolytic aluminum working principle
The modern electrolytic aluminum industry mainly adopts cryolite-alumina molten salt electrolytic method. The basic principle of electrolytic aluminum is shown in figure 2, molten cryolite is used as a solvent, aluminum oxide 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 the temperature of 950-970 ℃, electrochemical reaction is carried out on the two electrodes, and CO is generated by the anode2And 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 the direct current electric field and react with anode carbon to generate CO2. Inverting the two polesIt should be synthesized with the following reaction equation:
Al2O3+1.5C＝＝2Al+1.5CO2(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 anode2And (3) oxidizing, wherein the reaction formula is as follows:
2Al+3CO2＝＝Al2O3+3CO (2)
in addition, a part of CO2And C, carrying out chemical reaction:
C+CO2＝＝2CO (3)
3) general reaction of electrolytic aluminum
Alumina has different crystal structure and is generally classified as gamma-Al2O3And α -Al2O3The two have different physical and chemical properties, gamma-Al2O3Conversion to α -Al2O3Then carrying out chemical reaction. The general reaction formula of the electrolytic aluminum is as follows:
x(1-y)γ-Al2O3+xyα-Al2O3+(1.5+b)C＝＝2xAl+(3x-1.5-b)CO2+(3-3x+2b)CO (4)
wherein y is gamma-Al2O3Type fraction, x is percent current efficiency; b is CO2The number of moles in the formula with C can be measured or estimated from the ratio of CO to CO2The 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 Ucell
The cell voltage consists of polarization voltage, electrolyte voltage, anode bubble voltage, pole voltage and cell external voltage:
Ucell＝Uemf+Uel+Ubub+Uan+Uca+Uex(5)
in the formula of UemfIs a polarization voltage; u shapeelIs the electrolyte voltage; u shapebubIs the anode bubble voltage in the electrolyte; u shapeanIs the anode voltage; u shapecaIs the cathode voltage; u shapeexIs the external voltage of the electrolytic cell.
UemfThe 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.
Uemf＝Urev+ηsa+ηca+ηcc(6)
In the formula of UrevTo decompose the voltage ηsaIs an anodeSurface overvoltage ηcaIs anodic overvoltage ηccIs the cathodic overvoltage.
2) Cell voltage U within heat loss boundariescl
The cell voltage within the heat loss boundary consists of the polarization voltage, electrolyte voltage, anode bubble voltage and pole voltage:
Ucl＝Uemf+Uel+Ubub+Uan+Uca(7)
from formulas (5) and (7):
Ucl＝Ucell-Ubus-Ush(8)
in the formula of UbusThe voltage drop of the cathode bus and the anode bus; u shapeshVoltage is evenly shared for the bus; u shapebusAnd UshForm the external voltage U of the electrolytic cellex。
3) Equivalent voltage E of electrolytic aluminumΔH o
The lowest voltage required for the electrolysis of alumina in an aluminium electrolysis cell (carbon anode) is called equivalent voltage EΔH o。
EΔH o＝-ΔHo(x)/(nF) (9)
Since electron transfer n is 6(x) according to the general reaction formula (4) of electrolytic aluminum, Δ H only needs to be obtainedoThus obtaining the voltage equivalent voltage. gamma-Al according to the standard2O3Chemical reaction data, equivalent voltage obtained by multiple regression method, including electrolyte temperature, environment temperature, current efficiency percentage, gamma-Al2O3Type to volume ratio and CO2As a function of the number of moles in the reaction with C, as shown in equation (10):
EΔH o＝0.23706+4.6757×10-4Te-2.25×10-7(Te)2+x(1.4024+0.03253y+2.23×10- 4Te)+b(0.3086-1.97×10-5Te)+(25-Tr)[0.000145(x-xy)+0.0000138xy+0.000015(b+1.5)](10)
in the formula, TrIs ambient temperature; t iseIs the electrolyte temperature.
4) Heat dissipation Q of electrolytic cellloss
The heat Q to be dissipated by the cell in order to maintain the cell at a constant temperaturelossThe following formula:
Qloss＝I(Ucl-EΔH o) (11)
wherein I is the current of the electrolytic cell.
1.2.2 electrolytic aluminum electro-heat exchange model
The heat exchange between the electrolyte and the environment meets the following requirements:
Qloss＝(Tr-Te0)K (12)
wherein K is the heat transfer conductance (W/DEG C); t isrIs ambient temperature; t ise0The temperature of the electrolyte during normal aluminum production.
Establishing an electrolyte temperature change model according to a first thermodynamic law:
in the formula CeThe electrolyte heat capacity can be obtained by identification according to the actually measured temperature change of the electrolyte; t ise(t) is the electrolyte temperature; qeHeat 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 of the electrolytic aluminum production series is cut off by cutting off the total 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-solidification state until the upper part is an aluminum water upturning layer, and the condition of the melt 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 electrolyte primary crystal temperature of the electrolytic aluminum is the temperature at which liquid starts to form solid crystals, and the electrolysis temperature is generally controlled to be 10-20 ℃ above the electrolyte primary crystal temperature in the production process. Thus, the constraints of electrolytic aluminum load control are:
Te(t)≥Tliq(14)
in the formula, TliqThe electrolyte primary crystal temperature.
The time constraint for the outage of the electrolytic aluminium can be obtained according to equations (13) and (14) as:
tcut≤τln[(Te0-Tr)/(Tliq-Tr)](15)
in the formula, tcutTime for controlling the cut-off of electrolytic aluminium,. tau. -. Ceand/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 cutting execution station for collecting basic operation information of the electrolytic aluminum load,
the stability control master station is used for inputting an electrolytic aluminum load electric heating model to obtain the removable 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 electrolyte temperature Change after Power failure of the electrolyzer
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 invention1、τ2And τ3Respectively as follows: 34.91h, 36.03h and 33.29 h.
The operation data of the electrolytic cell is obtained from the heat dissipation capacity and the distribution rule of the aluminum electrolytic cell (Wanmu bath, Wanyifu, Liu military mountain, and the like. light metal 2006,6:31-35.) in the literature, and the heat conductivities of the three electrolytic cells are 438.86W/DEG C, 440.30W/DEG C and 440.30W/DEG C respectively and the heat capacities are 5.52 × 107J/℃、5.71×107J/° C and 5.28 × 107J/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 (8)
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.
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:
Al2O3+1.5C＝＝2Al+1.5CO2(1)
2) the side reaction formula of electrolytic aluminum is as follows:
2Al+3CO2＝＝Al2O3+3CO (2)
part of CO2Chemically reacting with C as follows
C+CO2＝＝2CO (3)
3) The overall reaction formula of electrolytic aluminum is as follows:
x(1-y)γ-Al2O3+xyα-Al2O3+(1.5+b)C＝＝2xAl+(3x-1.5-b)CO2+(3-3x+2b)CO (4)
wherein y is gamma-Al2O3Type fraction, x is percent current efficiency; b is CO2And C.
5. The method of claim 1, wherein the model of electrolytic aluminum heat rejection is selected from the group consisting of:
1) cell voltage UcellComprises the following steps:
Ucell＝Uemf+Uel+Ubub+Uan+Uca+Uex(5)
in the formula of UemfIs a polarization voltage; u shapeelIs the electrolyte voltage; u shapebubIs the anode bubble voltage in the electrolyte; u shapeanIs the anode voltage; u shapecaIs the cathode voltage; u shapeexIs the external voltage of the electrolytic cell;
2) cell voltage U within heat loss boundariesclComprises the following steps:
Ucl＝Uemf+Uel+Ubub+Uan+Uca(7)
from formulas (5) and (7):
Ucl＝Ucell-Ubus-Ush(8)
in the formula of UbusThe voltage drop of the cathode bus and the anode bus; u shapeshVoltage is evenly shared for the bus; u shapebusAnd UshForm the external voltage U of the electrolytic cellex；
3) Equivalent voltage E of electrolytic aluminumΔH oComprises the following steps:
EΔH o＝-ΔHo(x)/(nF) (9)
the electron transfer n ═ 6(x) can be obtained according to the total reaction formula of electrolytic aluminum;
gamma-Al according to the standard2O3Chemical reaction data, equivalent voltage obtained by multiple regression method, including electrolyte temperature, environment temperature, current efficiency percentage, gamma-Al2O3Type to volume ratio and CO2As a function of the number of moles in the reaction with C, as shown in equation (10):
EH o＝0.23706+4.6757×10-4Te-2.25×10-7(Te)2+x(1.4024+0.03253y+2.23×10-4Te)+b(0.3086-1.97×10-5Te)+(25-Tr)[0.000145(x-xy)+0.0000138xy+0.000015(b+1.5)](10)
in the formula, TrIs ambient temperature; t iseIs the electrolyte temperature;
4) heat dissipation Q of electrolytic celllossComprises the following steps:
Qloss＝I(Ucl-EH o) (11)
wherein I is the current of the electrolytic cell.
6. The method as claimed in claim 5, wherein the U is a number of UemfThe 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:
Uemf＝Urev+ηsa+ηca+ηcc(6)
Urevto decompose the voltage ηsaη being an overvoltage on the surface of the anodecaIs anodic overvoltage ηccIs the cathodic overvoltage.
7. The method as claimed in claim 1, wherein the model of load electrothermal property of electrolytic aluminum is an electrothermal exchange model of electrolytic aluminum
The heat exchange between the electrolyte and the environment meets the following requirements:
Qloss＝(Tr-Te0)K (12)
wherein K is the heat transfer conductance (W/DEG C); t isrIs ambient temperature; t ise0The temperature of the electrolyte during normal aluminum production;
establishing an electrolyte temperature change model according to a first thermodynamic law:
in the formula CeIs the electrolyte heat capacity; t ise(t) is the electrolyte temperature; qeHeat is input to the electrolytic cell.
8. The method of modeling electrical thermal characteristics of an electrolytic aluminum load for direct load control as claimed in any one of claims 1 to 7 wherein said electrolytic aluminum load control constraints comprise:
the constraints of electrolytic aluminum load control are:
Te(t)≥Tliq(14)
in the formula, TliqThe temperature of primary crystal of electrolyte;
the time constraints of the power failure of the electrolytic aluminum are as follows:
tcut≤τln[(Te0-Tr)/(Tliq-Tr)](15)
in the formula, tcutTime for controlling the cut-off of electrolytic aluminium,. tau. -. Ceand/K is the time constant of the temperature change of the electrolytic bath.
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