CN112210795B - Aluminum electrolysis energy balance adjusting method and system based on superheat degree and aluminum electrolysis cell - Google Patents
Aluminum electrolysis energy balance adjusting method and system based on superheat degree and aluminum electrolysis cell Download PDFInfo
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- CN112210795B CN112210795B CN202010575557.3A CN202010575557A CN112210795B CN 112210795 B CN112210795 B CN 112210795B CN 202010575557 A CN202010575557 A CN 202010575557A CN 112210795 B CN112210795 B CN 112210795B
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
- C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
- C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
- C25C3/20—Automatic control or regulation of cells
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
- C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
- C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
- C25C3/08—Cell construction, e.g. bottoms, walls, cathodes
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
- F28D20/00—Heat storage plants or apparatus in general; Regenerative heat-exchange apparatus not covered by groups F28D17/00 or F28D19/00
- F28D20/0034—Heat storage plants or apparatus in general; Regenerative heat-exchange apparatus not covered by groups F28D17/00 or F28D19/00 using liquid heat storage material
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/14—Thermal energy storage
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E70/00—Other energy conversion or management systems reducing GHG emissions
- Y02E70/30—Systems combining energy storage with energy generation of non-fossil origin
Abstract
The invention relates to an aluminum electrolysis energy balance adjusting method, system and aluminum electrolysis cell based on superheat degree, wherein the method comprises the following steps: 1) presetting a standard superheat interval, and collecting a superheat measured value of an electrolyte; 2) comparing the measured value of the superheat degree with a standard superheat degree interval, and if the measured value of the superheat degree is higher than the upper limit of the standard superheat degree interval, increasing the heat exchange quantity of the tank wall; if the measured value of the superheat degree is lower than the lower limit of the standard superheat degree interval, reducing the heat exchange quantity of the tank wall; if the measured superheat value is within the range of the standard superheat interval, no adjustment is made. The invention reversely adjusts the heat balance of the electrolytic cell from the heat dissipation side (namely the heat output end) of the electrolytic cell, is independent of the energy balance and material balance adjusting parameters of the input end, realizes the decoupling control of the superheat degree of the electrolytic cell and other process parameters, can realize the performance optimization of electrolytic aluminum and the stable operation when the energy input fluctuates, and obtains better energy-saving effect.
Description
Technical Field
The invention relates to an aluminum electrolysis energy balance adjusting method and system based on superheat degree and an aluminum electrolysis cell, belonging to the technical field of energy saving of aluminum electrolysis cells.
Background
The aluminum electrolysis industrial production adopts a cryolite-alumina molten salt electrolysis method. So-called cryolite-alumina fused saltThe electrolyte system is a multiphase electrolyte system which is composed of fluoride salt mainly comprising cryolite as a flux and alumina as a flux. Taking a carbon body as an anode and aluminum liquid as a cathode, introducing strong direct current, and then carrying out electrochemical reaction on the two electrodes in the electrolytic cell at 920-970 ℃. The chemical reaction proceeds mainly through the following equation: 2Al2O3+3C＝4Al+3CO2. The anode product is mainly carbon dioxide and carbon monoxide gas, and the cathode product is aluminum liquid.
The schematic diagram of the aluminum electrolysis cell shown in fig. 1 comprises a cathode 1, an anode conducting rod 2, an anode bus 3, a crust breaking and blanking mechanism 4, a gas collecting hood 5, anode carbon blocks 6, a ledge crust 7, a side wall lining 8, a cathode rod 9, a cell shell 10, an impermeable and heat-insulating material 11, an electrolyte 12, molten aluminum 13 and a flue opening 14. After electrification, current passes through the anode carbon blocks 6, the electrolyte 12, the aluminum water 13, the cathode 1 and the cathode bar 9 in sequence, and the aluminum water generated by electrolysis is formed on the cathode 1. The temperature at which the crystallization of the electrolyte 12 starts is the primary crystal point or the primary crystal temperature, and the difference between the temperature of the electrolyte 12 and the primary crystal point is the degree of superheat. The distance from the anode carbon block 6 to the surface of the molten aluminum 13 is a polar distance. During the electrolysis process, the electrolyte radiates heat through the side wall of the bath, the electrolyte close to the side wall of the bath is solidified to form the ledge crust 7, the shape of the ledge crust 7 is determined by the temperature of the electrolyte, a part of the ledge crust is melted when the temperature is high, and the ledge crust 7 becomes thicker when the temperature is low.
In 2017, the electricity consumption of the aluminum electrolysis in China is up to 5000 hundred million kWh, the electricity consumption of the whole aluminum electrolysis industry accounts for more than 9% of the total electricity consumption of the whole country, and the energy utilization rate of the aluminum electrolysis is less than 50%, so that the high energy consumption and low energy efficiency of the aluminum electrolysis production are serious problems.
The direct current consumption per ton of aluminium is equal to 2980 x average voltage/current efficiency. The low temperature and low voltage process is two major ways to realize energy saving of electrolytic aluminum. Research shows that the current efficiency is improved by about 1 percent when the electrolysis temperature is reduced by 10 ℃, and electricity is saved by 140 degrees per ton of aluminum. However, the conductivity of the electrolyte, the solubility of alumina, the types of additives and the addition method all affect the electrolysis process in a low-temperature state, and an appropriate low-temperature electrolyte system is not found, so that the industrial application of low-temperature electrolysis in large-scale aluminum electrolysis cells is restricted.
And each time the average voltage is reduced by 0.1V, the electricity is saved by 320 degrees for each ton of aluminum, so that the reduction of the cell voltage of the aluminum electrolysis cell and the improvement of the current efficiency are realized, and the realization of energy conservation is the main way for realizing energy conservation in the current aluminum electrolysis industry.
However, in the aluminum electrolysis production process, the cell voltage is one of a plurality of coupled variables in the energy balance of the electrolytic cell, the existing balance of the electrolytic cell is broken due to the change of any variable in the energy balance of the electrolytic cell, if other variables cannot be controlled to enable the electrolytic cell to reach the new energy balance, the aluminum electrolysis reaction in the electrolytic cell is influenced, the operation of the electrolytic cell also becomes unstable, and even the electrolytic cell is damaged. For example, a reduction in the pole pitch reduces the cell voltage, resulting in a reduction in the energy input to the cell, which has the direct effect of lowering the temperature and superheat of the electrolyte, leading to a higher crust and thicker legs, changing the shape of the ledge, affecting the current distribution in the cell and the electromagnetic stability of the cell. The energy balance is broken and changed to influence the material balance (the stability of alumina and aluminum fluoride components) in the cell, for example, the melting or thickening of the ledge crust and the extending legs can influence the electrolyte level, the alumina concentration is changed, and the solubility of the alumina is influenced by the change of the electrolyte temperature; eventually, the molecular ratio and the primary crystal point of the electrolyte are changed, and the change of the primary crystal temperature can adversely affect the degree of superheat, which can cause a series of parameter and variable changes. That is to say, the energy balance and the material balance of the electrolytic cell are not independent, but the coupling relationship exists between each variable of each parameter in the energy balance and the material balance, and the coupling relationship and the mutual influence are related, so in the prior art, the energy balance and the material balance of the electrolytic cell are controlled well at the same time, so that the good technical and economic indexes can be obtained, and the stable operation of the electrolytic cell can be ensured.
For controlling the energy balance and the material balance of the electrolytic cell, in the current aluminum electrolysis production process, as shown in fig. 2, the current aluminum electrolysis process and the critical stability control system judge the cell condition by collecting cell state parameters, and then adjust the energy balance of the electrolytic cell by adjusting the pole distance, the voltage, the current and the aluminum level; and continuously adjusting the material balance of the electrolytic cell by a reasonable feeding system of aluminum oxide and fluoride salt based on the prediction of the cell condition. Under the coordination of two balances in the electrolytic bath, the basic conditions of the electrochemical reaction of the electrolytic bath are ensured, the stability of the electrolytic bath and the electrolytic reaction is maintained, and the current efficiency is improved as much as possible to realize energy conservation. Namely, the input end is used for adjusting, so that the stability of the electrolytic aluminum and the energy-saving control are realized.
However, because the real-time data collected by the electrolytic cell for the control system is very little, and the energy balance and the material balance are mutually influenced, it is difficult to simultaneously realize the stability of the electrolytic reaction and the improvement of the current efficiency to realize the maximum energy saving, and the current efficiency is usually sacrificed to improve the energy consumption in order to ensure the basic conditions of the electrochemical reaction and the safety and stability of the electrolytic cell and the electrolytic reaction. The most basic process condition of the electrolysis process, namely energy balance, cannot be independently adjusted in real time, so that the electrolysis process is difficult to ensure in an optimized state; it is difficult to achieve the stability of the aluminum electrolysis process and the optimization under the energy-saving balance.
Disclosure of Invention
The invention aims to provide an aluminum electrolysis energy balance adjusting method capable of realizing the stability of an aluminum electrolysis cell and further reducing the energy consumption, the aluminum electrolysis cell for realizing the method and a waste heat recovery system.
In order to achieve the above object, the scheme of the invention comprises:
the invention provides an aluminum electrolysis energy balance adjusting method, which comprises the following steps:
1) presetting a standard superheat interval, and collecting a superheat measured value of electrolyte in an aluminum electrolytic cell;
2) comparing the measured value of the degree of superheat with the standard degree of superheat interval, and if the measured value of the degree of superheat is higher than the upper limit of the standard degree of superheat interval, controlling the groove wall heat exchange device to increase the heat exchange quantity of the groove wall; if the measured value of the superheat degree is lower than the lower limit of the standard superheat degree interval, controlling the groove wall heat exchange device to reduce the heat exchange quantity of the groove wall; if the measured value of the superheat degree is within the range of the standard superheat degree interval, no adjustment is made; the groove wall heat exchange device is a heat exchange device for adjusting the heat exchange amount of the groove wall.
The invention also provides an aluminum electrolytic cell, which comprises an electrolytic cell controller and a cell wall heat exchange device for adjusting the heat dissipation capacity of the cell wall, wherein the cell wall heat exchange device is at least arranged on one side wall of the electrolytic cell; the electrolytic cell controller controls the cell wall heat exchange device, and the electrolytic cell controller also executes instructions for implementing the energy balance adjustment method for the aluminum electrolytic cell.
The invention also provides an aluminum electrolytic cell waste heat recovery system, which comprises a waste heat recovery system controller and a cell wall heat exchange device for adjusting the heat dissipation capacity of the cell wall, wherein the cell wall heat exchange device is at least arranged on one side wall of the electrolytic cell; the waste heat recovery system controller controls the cell wall heat exchange device, and the waste heat recovery system controller also executes instructions for implementing the energy balance adjustment method for the aluminum electrolysis cell.
The invention has the technical effects that:
1) 50% of the energy consumption of the electrolytic aluminum is dissipated to the environment in a thermal mode, so that the thermal balance is an important link in the electrolytic reaction energy balance of the electrolytic cell.
The scheme of the invention collects the thermal parameters of the electrolyte of the electrolytic cell (the superheat degree is obtained through the temperature and the primary crystal point), and carries out independent optimization adjustment aiming at the superheat degree of the electrolytic cell, and on the basis of the energy control and the material control of the existing electrolytic cell, namely the input end control balance, the superheat degree is independently controlled through the heat dissipation or the heat preservation output end control of the electrolytic cell on the basis of not interfering the input end adjustment and not destroying the existing balance, so that the independent adjustment of the thermal balance and the decoupling of the superheat degree, which are important process parameters, are realized, and the further optimization of the safety, the stability and the energy conservation of the electrolytic aluminum can be realized.
2) The heat dissipated by the electrolytic tank is mainly dissipated through the tank wall, and the temperature of the electrolyte in the electrolytic tank can be influenced to the greatest extent through the heat exchange device arranged on the tank wall, so that the superheat degree is controlled, the period for adjusting the temperature of the electrolyte through the tank wall is short, and the adjustment of the temperature of the electrolyte and the superheat degree is most suitable for being realized.
3) The method can realize reverse adjustment of the heat balance of the electrolytic cell from the heat dissipation side (namely the heat output end) of the electrolytic cell, and does not interfere with the control of the energy and material balance of the input end, and when the method is implemented, the control of the polar distance and the control of the molecular ratio do not need to be considered, so that the decoupling control of the superheat degree of the electrolytic cell and other process parameters is realized, and the further balance optimization of the safety, stability and energy conservation of electrolytic aluminum can be realized.
4) Taking a 400kA aluminum electrolytic cell as an example, the heat which can be obtained by a single aluminum electrolytic cell is about 155kW, and the total heat which can be recovered by heat exchange by adopting the method for recovering the waste heat is 32000kW according to the calculation of an aluminum production line which produces 25 ten thousand tons every year.
If the recovered heat is sent to a thermal power plant, the electric power of the steam turbine generator unit can be increased by about 6000kW through heat balance analysis, and the coal consumption of the unit is reduced by 4.9 g/kWh. If the recovered heat is used for urban heating, 330000GJ can be supplied, and the benefit is about 1000 ten thousand yuan.
As a further improvement on the method, the aluminum electrolysis cell and the aluminum electrolysis cell waste heat recovery system, the heat exchange amount is increased by increasing the flow of the heat exchange medium in the cell wall heat exchange device; and the heat exchange amount is reduced by reducing the flow of the heat exchange medium in the tank wall heat exchange device.
The groove wall heat exchange device takes away the temperature of the groove wall through the heat dissipation medium, accelerates the flow velocity of the heat dissipation medium to realize accelerated groove wall heat dissipation, reduces the temperature of the groove wall so as to reduce the temperature of the electrolyte, and finally realizes the reduction of superheat degree; the flow speed of the heat dissipation medium is reduced, even the flow of the heat dissipation medium is stopped, so that the heat dissipation of the groove wall is reduced or kept, the temperature of the groove wall is increased, and the temperature and the superheat degree of the electrolyte are increased.
The flow of the heat exchange medium in the groove wall heat exchange device is increased or reduced, the flow can be adjusted by adjusting the flow speed, particularly the variable frequency speed regulation of the pump, the flow speed is easy to adjust accurately, the heat dissipation capacity is easy to control and calculate, the control is simple, reliable and easy to realize, and the quantitative control can be accurate.
As further improvement of the method, the aluminum electrolytic cell and the aluminum electrolytic cell waste heat recovery system, the method for acquiring the superheat degree measured value comprises the steps of measuring and obtaining the real-time temperature of the electrolyte in the aluminum electrolytic cell and the crystallization temperature of the electrolyte at the time of starting crystallization by natural cooling on line, and taking the crystallization temperature as the primary crystal temperature; and subtracting the primary crystal temperature from the real-time temperature to obtain the superheat degree measured value.
The temperature of the electrolyte in the cell and the crystallization temperature (namely a primary crystal point) of the electrolyte can be rapidly measured on site through the probe and the temperature sensor, the superheat degree can be obtained by subtracting, the method is rapid and reliable, the result can be obtained on site in a short time, and the result can be automatically obtained by a system.
As further improvement of the method, the aluminum electrolytic cell and the aluminum electrolytic cell waste heat recovery system, the method for acquiring the superheat degree measured value comprises the steps of obtaining a sample of electrolyte in the aluminum electrolytic cell and the real-time temperature of the electrolyte, obtaining the molecular ratio of the electrolyte in the aluminum electrolytic cell by detecting the sample, obtaining the corresponding primary crystal temperature by looking up a table, and subtracting the primary crystal temperature from the real-time temperature of the electrolyte to obtain the superheat degree measured value.
The method has the advantages that the components (molecular ratio) are measured by collecting samples and utilizing a laboratory test mode, the primary crystal point is obtained according to the components, the difference between the real-time temperature and the primary crystal point is the superheat degree, the test method is accurate and feasible, and the superheat degree can be accurately obtained.
As a further improvement on the method, the aluminum electrolysis cell and the aluminum electrolysis cell waste heat recovery system, the standard superheat degree interval is 5-15 ℃, 6-8 ℃, 8-10 ℃ or 10-12 ℃.
As a further improvement on the aluminum electrolysis cell and the aluminum electrolysis cell waste heat recovery system, the cell wall heat exchange device comprises a heat pipe.
The heat pipe combines the heat conduction and the fluid phase change principle to realize high-efficiency heat conduction, the heat conduction capability of the heat pipe exceeds that of copper, and the transfer control of the temperature of the groove wall can be effectively realized.
Drawings
FIG. 1 is a schematic view of a prior art aluminum electrolysis cell configuration;
FIG. 2 is a schematic diagram of a prior art aluminum electrolysis process and critical stability control system;
FIG. 3 is a flow chart of a method of the present invention to enable independent energy balance adjustment;
FIG. 4 is a schematic view of an aluminum electrolysis cell system of the present invention.
The figure includes: the device comprises a cathode 1, an anode conducting rod 2, an anode bus 3, a crust breaking and blanking mechanism 4, a gas collecting hood 5, an anode carbon block 6, a ledge crust 7, a side wall lining 8, a cathode rod 9, a cell shell 10, an impermeable and heat-insulating material 11, an electrolyte 12, molten aluminum 13 and a flue opening 14; the tank body 100, the tank wall heat exchange device 31, the flow regulating station 34, the heat output device 35 and the pipeline 36.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
The embodiment of the aluminum electrolytic cell comprises:
hardware part:
the aluminum electrolysis cell system of the present invention as shown in fig. 4 comprises: the aluminum electrolysis cell comprises a cell body 100 and a heat exchange system, wherein the structure of the cell body 100 is the same as that of the aluminum electrolysis cell body in the prior art.
The heat exchange system is used for controlling the heat dissipation of the wall of the electrolytic cell and can further realize the secondary utilization of the waste heat of the electrolytic cell. The heat exchange system comprises a groove wall heat exchange device 31, a flue gas heat exchange device (not shown in the figure), a flow regulating station 34, a heat output device 35 and a pipeline 36. The cell wall heat exchange device 31 is arranged on the cell wall of the aluminum electrolysis cell or is arranged integrally with the aluminum electrolysis cell, is used for assisting the heat dissipation of the side wall (cell wall) of the aluminum electrolysis cell, and can absorb the heat of the cell wall of the aluminum electrolysis cell and take away and transfer the heat through a heat exchange medium. The top of the aluminum electrolysis cell is provided with a flue (not shown in the figure), and the flue is connected with a flue opening of the aluminum electrolysis cell and is used for discharging high-temperature flue gas generated by electrochemical reaction in the aluminum electrolysis cell. The flue 32 is provided with a flue gas heat exchange device, the flue gas heat exchange device can also be connected in series into the heat exchange system shown in fig. 4 through a pipeline 36, high-temperature flue gas can be cooled after passing through the flue gas heat exchange device, and meanwhile, heat is transferred to a heat exchange medium in the flue gas heat exchange device. The flow regulating station 34 regulates the flow velocity of the heat exchange medium in the heat exchange system, and finally regulates the flow rate of the heat exchange medium in the cell wall heat exchange device 31 in unit time, the flow regulating station 34 may specifically be a pump driven by a speed-adjustable motor, and the speed-adjustable motor (i.e., the rotation speed of the pump) is controlled by the aluminum electrolysis cell control system, and is used for driving the heat exchange medium to circulate among the cell wall heat exchange device 31, the flue gas heat exchange device (not shown in the figure) and the heat output device 35 through a pipeline 36. The heat output device 35 is used for cooling the heat exchange medium, transferring heat carried by the heat exchange medium, and recycling the heat. The heat output device 35 may be a heat exchange station, and the heated heat exchange medium carries heat to heat water in the heat exchange station, and the heated water may be used for heating or power generation.
The heat exchange medium adopts heat conducting oil, and other media such as cooling liquid, water or gas can also be adopted. The heat exchange medium is not limited in the present invention.
The groove wall heat exchange device 31 includes a heat collecting plate integrated with a heat pipe, heat conducting oil is introduced into the heat collecting plate, one end of the heat pipe is in contact with the groove wall, the other end of the heat pipe is inserted into the heat collecting plate and is in full contact with the heat conducting oil, the groove wall heat exchange device 31 utilizes the heat pipe to transfer heat of the groove wall to the heat conducting oil in the heat collecting plate, the heat conducting oil is heated, and high-temperature heat conducting oil carrying energy flows to take away the heat of the groove wall, so that the temperature of the groove wall is adjusted.
As another embodiment, the slot wall heat exchange device 31 may not employ a heat pipe, but other types of heat exchange devices may be directly disposed on the slot wall.
The heat transfer oil is driven by the flow regulating station 34 and flows into the heat output device 35. The heat output device 35 may be a heat exchange water station, the heat conduction oil pipe may be fully contacted with water in the heat exchange water station by bending or connecting the heat radiation fins, the heat exchange water station cools the heat conduction oil in the heat conduction oil pipe by using water, and the water may be further boiled after being heated for power generation or heating. The medium used for cooling the heat conduction oil in the heat output device 35 may also be other mediums such as gas, cooling liquid, etc., and the cooling method may be a method of spraying, soaking or accelerating air flow by using a cooling fan on the heat conduction oil pipe, and the purpose is mainly to cool the heat conduction oil, so that the cooled heat conduction oil enters the next cooling cycle, and whether the heat of the heat conduction oil is reused or how to use the heat is not limited in the present invention.
In this embodiment, in order to effectively utilize the heat that the conduction oil brought out, the conduction oil still utilizes the high temperature flue gas to preheat after the cooling, the conduction oil is advanced into flue gas heat transfer device before getting into cell wall heat transfer device 31 promptly, flue gas heat transfer device sets up on the flue, the high temperature flue gas fully contacts with heat conduction oil pipe in flue gas heat transfer device, the heat make full use of that the flue gas carried, preheat for the conduction oil, the conduction oil rethread cell wall heat transfer device 31 after preheating, the heat that the improvement conduction oil carried that can further be step forward, the high temperature conduction oil of being convenient for exports energy in heat output device 35 in order to improve waste heat utilization. As another embodiment, a flue gas heat exchange device may not be disposed on the flue, and the heat transfer oil is not preheated, so that the cooled heat transfer oil directly enters the groove wall heat exchange device 31, thereby improving the cooling efficiency of the groove wall heat exchange device 31 on the groove wall.
A software part:
the aluminum electrolysis cell control system adopts the strategy of the existing aluminum electrolysis process and the critical stability control system as shown in figure 2 to control the energy balance and the material balance of the electrolysis cell, namely realizing the polar distance control and the molecular ratio control; meanwhile, the method also comprises the control of the heat exchange system, namely a method for controlling the groove wall heat exchange device 31, the flow regulating station 34 and even the heat output device 35 according to the heat dissipation degree. Specific control strategies are described in method embodiments.
In the present example, the control of the heat exchange system is the same as the control of the pole pitch and the control of the molecular ratio, and belongs to the control of the electrolytic cell. That is, the software formed by the control method of the heat exchange system is loaded and run in the control device of the electrolytic cell (for example, the control cabinet of the electrolytic cell).
Waste heat recovery system embodiment:
the waste heat recovery system comprises the heat exchange system (no longer described in this embodiment) and the waste heat recovery controller in the aluminum electrolysis cell embodiment, the waste heat recovery controller controls the heat exchange system to execute control for implementing the energy balance adjustment method for the aluminum electrolysis cell, and a specific control strategy is described in the method embodiment.
Note that, in the present embodiment, software formed by the control method of the heat exchange system is loaded and run in the heat recovery control device (for example, a motor controller or a heat recovery system control cabinet as a pump of the flow rate regulation station 34). In this embodiment, the heat dissipation control of the waste heat recovery system and the current aluminum electrolysis control strategy (such as the control method shown in fig. 2) of the aluminum electrolysis cell itself operate independently and may not interfere with each other.
The method comprises the following steps:
the method for realizing independent energy balance adjustment as shown in fig. 3 comprises the following steps: 1) the control system collects the superheat degree of electrolyte in the electrolytic cell; 2) and comparing the collected superheat degree with a preset standard superheat degree. If the collected superheat degree is larger than the standard superheat degree, the control system controls the heat exchange system to accelerate the heat dissipation speed of the wall of the electrolytic cell, so that the temperature of the wall of the electrolytic cell is reduced, the temperature of electrolyte in the electrolytic cell is further reduced, and finally the superheat degree of the electrolyte is reduced, so that the superheat degree of the electrolyte is close to the standard superheat degree; if the collected superheat degree is smaller than the standard superheat degree, the control system controls the heat exchange system to slow down the heat dissipation speed of the wall of the electrolytic cell, so that the temperature of the wall of the electrolytic cell is increased, the temperature of electrolyte in the electrolytic cell is increased, and finally the superheat degree of the electrolyte is increased, so that the superheat degree of the electrolyte is close to the standard superheat degree; and if the collected superheat degree is equal to the standard superheat degree, the control system controls the heat exchange system to maintain the heat dissipation speed of the wall of the current electrolytic cell, namely, the current superheat degree close to the standard superheat degree is maintained.
The control system can be a control system of the aluminum electrolysis cell, and can also be an independent control system of the waste heat recovery system.
The reasonable superheat range of the electrolyte is 5-15 ℃, the set standard superheat is a certain temperature range, and the set superheat range can be an ideal narrow range (for example, 6-8 ℃) or a wider range (for example, 6-10 ℃ or 8-12 ℃) or a temperature range close to the ideal superheat. When the measured value of the superheat degree exceeds the standard superheat degree, the regulation is carried out, for example, a standard superheat degree interval is set to be 8-10 ℃, the regulation is carried out when the superheat degree is lower than 8 ℃ and reaches 7 ℃ or higher than 10 ℃ and reaches 11 ℃, and the regulation is stopped until a target value in the standard superheat degree interval is reached, so that frequent oscillation and repeated regulation caused by difficulty in stabilizing the system are prevented.
The collected superheat degree is larger than a standard superheat degree interval or larger than the standard superheat degree interval and exceeds a set value, and the collected superheat degree can be determined to be larger than the standard superheat degree; the collected superheat degree is smaller than the standard superheat degree interval or smaller than the standard superheat degree interval and exceeds a set value, and the collected superheat degree is considered to be smaller than the standard superheat degree. The desired degree of superheat or the range of the desired degree of superheat may be set by a skilled person based on experience, or the degree of superheat of an electrolytic cell having a high current efficiency and good operation in the related art may be selected as the desired degree of superheat of an electrolytic cell having a similar cell condition.
The method for accelerating the heat dissipation speed of the wall of the electrolytic cell comprises the step that the aluminum electrolytic cell control system accelerates the flow rate of heat conducting oil in the heat exchange system in the cell wall heat exchange device 31 by controlling the rotating speed of a pump serving as a flow regulating station 34 in the heat exchange system, so that the heat taken away from the cell wall by the cell wall heat exchange device 31 in unit time is added, and the heat dissipation speed of the cell wall of the electrolytic cell is accelerated finally. The method for reducing the heat dissipation speed of the wall of the electrolytic cell is opposite to the method for increasing the heat dissipation speed of the wall of the electrolytic cell, namely, the aluminum electrolytic cell control system reduces the rotating speed of the pump 34 in the heat exchange system, and finally the heat dissipation speed of the wall of the electrolytic cell is reduced.
As other examples, the heat dissipation speed of the wall of the electrolytic cell can be accelerated or slowed by other methods. For example, the initial temperature of the heat transfer oil entering the tank wall heat exchange device 31 is controlled, and under the condition that the rotating speed of the pump 34 is unchanged and the flow rate of the heat transfer oil is constant, the initial temperature of the heat transfer oil entering the tank wall heat exchange device 31 is reduced by increasing the cooling rate of the heat output device 35 on the heat transfer oil, so that the heat dissipation speed of the tank wall of the electrolytic tank can be increased; on the contrary, the initial temperature of the heat-conducting oil entering the tank wall heat exchange device 31 is increased by reducing the cooling rate of the heat output device 35 to the heat-conducting oil, so that the heat dissipation speed of the tank wall of the electrolytic tank can be reduced. On the premise of ensuring a certain flow rate, the flow rate of the heat-conducting oil entering the groove wall heat exchange device 31 in unit time can be controlled by adjusting the opening degree of the valve, but if quantitative accurate control needs to be realized in the method, the flow rate of the heat-conducting oil in the cooling system (namely the rotating speed of the pump) and the opening degree of the valve entering the heat exchange system need to be controlled jointly, so that the flow rate is ensured to be constant, and the control method is complex.
Meanwhile, the heat output device 35 can be controlled, and the cooling rate of the heat output device 35 to the heat conduction oil is adjusted to adapt to the flow rate control of the heat conduction oil. For example, when the rotation speed of the pump serving as the flow rate adjusting station 34 is increased, that is, the flow rate of the heat transfer oil is increased, the cooling rate of the heat output device 35 is controlled to be increased to adapt to the flow rate of the heat transfer oil, specifically, the length of the heat transfer oil pipe soaked by water is increased, the spraying amount of the cooling liquid is increased, or the rotation speed of the cooling fan is increased. Meanwhile, the aluminum cell control system can also acquire the temperature of a heat-conducting oil inlet and outlet of the cell wall heat exchange device 31, the flow velocity of the heat-conducting oil and other parameters, namely, the flow velocity of the heat-conducting oil and the initial temperature of the heat-conducting oil entering the cell wall heat exchange device 31 are accurately controlled by acquiring related parameters, so that the accurate calculation of the heat dissipation capacity of the cell wall is realized, and the accurate adjustment of the heat dissipation capacity of the cell wall is realized.
The method for collecting the superheat degree of electrolyte in the electrolytic cell by the aluminum electrolytic cell control system is based on the following principle: when the electrolyte melt crystallizes, latent heat of solidification is released, so that an inflection point appears on an electrolyte cooling temperature curve, and the inflection point temperature is the primary crystal temperature of the electrolyte. The primary crystal temperature is subtracted from the working temperature of the electrolyte to obtain the degree of superheat. The method specifically comprises the steps of digging a part of electrolyte samples of the electrolytic cell, continuously measuring the temperature of the electrolyte samples through a temperature probe, obtaining the temperature of the electrolyte when the electrolyte starts to crystallize according to the characteristic that the temperature change curve of the electrolyte when the electrolyte starts to crystallize is different from the temperature change of other conditions, taking the temperature as the primary crystal temperature, and subtracting the primary crystal temperature from the initial temperature of the electrolyte samples to obtain the superheat degree of the electrolyte, wherein the superheat degree can be obtained by an aluminum electrolytic cell control system in a manual input or online real-time detection mode. On-line measurement of electrolyte superheat degree can be carried out by using STARProbeTMAnd (4) realizing a superheat degree measuring instrument.
The method for acquiring the superheat degree of the electrolyte in the electrolytic cell by the aluminum electrolytic cell control system can also be characterized in that an electrolytic cell electrolyte sample is obtained, the molecular ratio of the electrolyte in the sample is determined by adopting a laboratory test method, the primary crystal temperature of the corresponding electrolyte is obtained by a table look-up method, the primary crystal temperature is subtracted from the initial temperature of the electrolyte sample to obtain the superheat degree of the electrolyte, and the superheat degree can be obtained by the aluminum electrolytic cell control system in a manual input mode.
According to the invention, the temperature of the electrolyte in the cell is adjusted by adjusting the temperature and the heat dissipation capacity of the cell wall, and finally, the adjustment and control of the heat dissipation of the output end on the superheat degree of the electrolyte are realized; the flow rate of the heat exchange medium passing through the cell wall heat exchange device 31 is controlled by the flow rate regulation station 34 to regulate the cell wall temperature, for example, the regulation of the electrolyte superheat degree can be realized for the precise control of the heat dissipation capacity of the cell wall based on the control of the rotation speed of the pump, and specifically, the PID closed-loop control with the electrolyte superheat degree as the control target and the heat exchange system (including the pump) as the execution regulation mechanism can be realized.
Specifically, for example, in the set period (t)04h) the measured superheat value (delta T) of the electrolyte in the aluminum cell is collectedSide 1The measured superheat is Δ T in fig. 3 at 6 ℃b) The control system measures the superheat1Comparing the temperature of 6 ℃ with a preset standard superheat range (8-10 ℃) to obtain a superheat measured value (delta T)Side 1The temperature is 6 ℃ lower than the lower limit value (lower limit value delta T) of the preset standard superheat range (8-10 ℃)b18 ℃ upper limit Δ T b210 deg.C), and a deviation value of the degree of superheat Δ T is calculated as Δ Tb1-ΔTSide 1When the superheat deviation value is regular, the heat dissipation needs to be decelerated to increase the superheat degree, wherein the superheat deviation value is 8-6 ═ 2 ℃, and whether the heat dissipation needs to be accelerated or decelerated is judged according to the positive and negative of the superheat deviation value (delta T ═ 2 ℃). The specific control and adjustment method can be as follows: calculating the percentage of superheat deviation xi ═ delta Tb1Measurement of-Delta T1)/ΔT b12/8 ≈ 33.33%, that is, the electrolytic cell needs to reduce the amount of heat radiation. Firstly, adjusting and reducing the heat dissipation by 10%; after adjustment, measuring the superheat degree again, wherein the measured value is still lower than the lower limit of the standard superheat degree, and adjusting again to reduce the heat dissipation by 20%; each adjustment cycle is sequentially incremented until the measured value returns to within the standard superheat interval.
The invention aims to adjust the superheat degree by a method without changing other process parameters so as to maintain the superheat degree of an electrolytic cell under different cell conditions within an ideal range, and simultaneously, the method can coexist with the aluminum electrolysis process and a critical stability control method in the prior art, namely, an aluminum electrolysis cell control system adjusts the input end of other process parameters of the aluminum electrolysis cell according to the existing control method shown in figure 4 to control the energy balance and the material balance of the electrolytic cell, and simultaneously, the aluminum electrolysis cell control system adjusts the heat balance of the electrolytic cell from the output end by the method of the invention so as to realize the decoupling control of the superheat degree of the electrolytic cell, and finally, the safety and the stability of the aluminum electrolysis process of the electrolytic cell can be maintained and energy conservation can be realized as far as possible.
Computer storage medium embodiments:
according to the above method, a computer program is programmed, stored in a storage medium, called and executed by a processor(s), so that the energy balance adjustment method for the aluminum reduction cell can be implemented. As can be seen from the description of the embodiment of the electrolytic cell and the embodiment of the waste heat utilization, the computer program may be run in the electrolytic cell control device or in the waste heat recovery controller.
The media described above are programmable data processing apparatus that store computer program instructions. For example, the controller may be a controller integrated with a memory, such as a single chip microcomputer or an industrial personal computer, and/or other independent memories and internal memories. The media described above may also be one or more computer-readable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) having computer-usable program code embodied therein.
Claims (9)
1. An aluminum electrolysis energy balance adjusting method is characterized by comprising the following steps:
1) presetting a standard superheat interval, and collecting a superheat measured value of electrolyte in an aluminum electrolytic cell;
2) comparing the measured value of the degree of superheat with the standard degree of superheat interval, and if the measured value of the degree of superheat is higher than the upper limit of the standard degree of superheat interval, controlling the groove wall heat exchange device to increase the heat exchange quantity of the groove wall; if the measured value of the superheat degree is lower than the lower limit of the standard superheat degree interval, controlling the groove wall heat exchange device to reduce the heat exchange quantity of the groove wall; if the measured value of the superheat degree is within the range of the standard superheat degree interval, no adjustment is made; the groove wall heat exchange device is a heat exchange device for adjusting the heat dissipation capacity of the groove wall.
2. The aluminum electrolysis energy balance adjustment method according to claim 1, wherein the heat exchange amount is increased by increasing the flow rate of the heat exchange medium in the cell wall heat exchange device; and the heat exchange amount is reduced by reducing the flow of the heat exchange medium in the tank wall heat exchange device.
3. The aluminum electrolysis energy balance adjustment method according to claim 1 or 2, wherein the acquisition method of the superheat measurement value comprises the steps of measuring and obtaining the real-time temperature of the electrolyte in the aluminum electrolysis cell and the crystallization temperature when the electrolyte starts to crystallize after natural cooling, and taking the crystallization temperature as the primary crystallization temperature; and subtracting the primary crystal temperature from the real-time temperature to obtain the superheat degree measured value.
4. The aluminum electrolysis energy balance adjustment method according to claim 1 or 2, wherein the acquisition method of the superheat measurement value comprises obtaining a sample of the electrolyte in the aluminum electrolysis cell and a real-time temperature of the electrolyte, obtaining a molecular ratio of the electrolyte in the aluminum electrolysis cell by detecting the sample, obtaining a corresponding primary crystal temperature by looking up a table, and subtracting the primary crystal temperature from the real-time temperature of the electrolyte to obtain the superheat measurement value.
5. The aluminum electrolysis energy balance adjustment method according to claim 1 or 2, wherein the standard superheat range is 5 to 15 ℃, 6 to 8 ℃, 8 to 10 ℃ or 10 to 12 ℃.
6. An aluminum electrolysis cell is characterized by comprising an electrolysis cell controller and a cell wall heat exchange device for adjusting the heat dissipation capacity of a cell wall, wherein the cell wall heat exchange device is at least arranged on one side wall of the electrolysis cell; the electrolytic cell controller controls the cell wall heat exchange device, and the electrolytic cell controller also executes instructions for implementing the aluminum electrolysis energy balance adjusting method according to any one of claims 1 to 5.
7. The aluminum reduction cell according to claim 6, wherein the cell wall heat exchange means comprises heat pipes.
8. The aluminum electrolysis cell waste heat recovery system is characterized by comprising a waste heat recovery system controller and a cell wall heat exchange device for adjusting the heat dissipation capacity of a cell wall, wherein the cell wall heat exchange device is at least arranged on one side wall of an electrolysis cell; the waste heat recovery system controller controls the cell wall heat exchange device, and the waste heat recovery system controller further executes instructions for implementing the aluminum electrolysis energy balance adjustment method according to any one of claims 1 to 5.
9. The aluminum reduction cell residual heat recovery system of claim 8, wherein the cell wall heat exchange device comprises a heat pipe.
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