TWI760003B - Method for predicting temperature rise history of furnace core of graphitizing furnace - Google Patents

Abstract

A method for predicting a temperature rise history of a furnace core of a graphitizing furnace is described. In this method, a furnace resistance model of the graphitizing furnace is built. A heat transfer model of the graphitizing furnace is built. The heat transfer model includes a resistor material heat balance equation, a crucible heat balance equation, a graphite material heat balance equation, a thermal insulation material heat balance equation, and a refractory brick heat balance equation. An iteration calculation operation is performed by using a predetermined power transmission curve, the furnace resistance model, and the heat transfer model to obtain various furnace core temperatures of the graphitizing furnace corresponding to difference power transmission times until an aggregate power transmission time is equal to a predetermined value.

Description

Prediction Method of Heating History of Furnace Core of Graphitization Furnace

The present disclosure relates to a temperature prediction technology of a resistance furnace, and in particular, to a prediction method of the heating history of a furnace core of a graphitization furnace.

The graphitization furnace is a resistance furnace. The function of the graphitization furnace is mainly to perform the graphitization process of heating the mesophase carbon microspheres to above 3000 ℃ to form the mesophase graphitic carbon microspheres. Mesophase graphitic carbon microspheres can be used in the negative electrode material of lithium batteries, suitable for mobile phones, notebook computers, electric vehicles, etc.

Since the capacitance of meso-graphitic carbon microspheres is closely related to the power transmission termination temperature of the graphitization process, the temperature measurement of the furnace core of the graphitization furnace is very important for the graphitization process. At present, a technique is to solve the three-dimensional temperature field of the furnace core of the graphitization furnace by using the three-dimensional heat transfer equation, and to improve the temperature uniformity of the furnace core based on the temperature. This technology can successfully improve the uniformity of the furnace core.

Another technique is to use the two-dimensional heat transfer equation to solve the two-dimensional temperature field of the graphitized furnace core, and to observe the temperature distribution of the center, head and tail of the furnace core under different arrangement of raw materials based on the temperature. This technology can successfully improve the temperature uniformity of the furnace core and effectively improve the product qualification rate.

However, the calculation amount of the three-dimensional heat transfer equation requires huge computing resources and time, and it is impossible to connect the program control to provide the temperature information to the operator in time as the basis for furnace adjustment. In addition, these technologies have no furnace resistance model, and cannot actually combine the electrical end process data to reflect the potential distribution of the furnace core and calculate the correct furnace core temperature. Moreover, these technologies can only calculate the temperature of the furnace core, and cannot calculate the temperature of the crucible, raw materials, raw insulation materials, clinker insulation materials, and insulation bricks.

Therefore, one objective of the present disclosure is to provide a method for predicting the heating history of the core of a graphitization furnace, which combines the furnace resistance model and the one-dimensional heat transfer model, and then uses the on-site process data for model correction. In this way, the actual temperature of the furnace core can be predicted in time. The predicted furnace core temperature can provide on-site operators as a basis for adjusting the furnace, so it can effectively improve the quality of graphitized products and achieve the purpose of saving electricity.

Another object of the present disclosure is to provide a method for predicting the heating history of the furnace core of the graphitization furnace, which can predict the heating history of the furnace core of the graphitization furnace, and can use the furnace core temperature as the basis for the judgment of stopping power transmission. Taking into account the quality and production capacity of graphitized products.

， 其中R _e為爐芯總爐阻，T _e為爐芯溫度，m為爐芯內坩堝橫排數量，n為爐芯內坩堝縱排數量，a為橫排間坩堝間距，d為坩堝直徑，h為坩堝高度，f _ρ為爐阻模型之修正因子，ρ為爐芯內電阻料的電阻率。建立石墨化爐之熱傳模型。熱傳模型包含電阻料熱平衡方程式、坩堝熱平衡方程式、石墨原料熱平衡方程式、保溫料熱平衡方程式、以及耐火磚熱平衡方程式。利用預設送電功率曲線與爐阻模型及熱傳模型進行疊代計算操作，以獲得對應不同送電時間之石墨化爐之數個爐芯溫度，直至送電總時數等於預設值。 According to the above purpose of the present disclosure, a method for predicting the heating history of the core of a graphitization furnace is proposed. In this method, the furnace resistance model of the graphitization furnace is established. The equation for this furnace resistance model is:

, where Re is the total furnace resistance of the furnace core _{, T e is} the furnace core temperature, m is the number of horizontal rows of crucibles in the furnace core, n is the number of vertical rows of crucibles in the furnace core, a is the crucible spacing between the horizontal rows, and d is the diameter of the crucible , h is the height of the crucible, f _ρ is the correction factor of the furnace resistance model, and ρ is the resistivity of the resistance material in the furnace core. Establish the heat transfer model of the graphitization furnace. The heat transfer model includes resistance material heat balance equation, crucible heat balance equation, graphite raw material heat balance equation, insulation material heat balance equation, and refractory brick heat balance equation. The iterative calculation operation is performed using the preset power transmission power curve, the furnace resistance model and the heat transfer model to obtain several furnace core temperatures of the graphitization furnace corresponding to different power transmission times, until the total power transmission time equals the preset value.

， 其中i為流經石墨化爐之爐芯總電流，V _e為爐芯容積，m _e為電阻料質量，C _p,e為電阻料比熱，f _cp為比熱修正因子，k _e、k _i、與k _c分別為電阻料熱傳導係數、保溫料熱傳導係數、與坩堝熱傳導係數，L ₁、L ₂、與L ₃分別為電阻料厚度、保溫料厚度、與坩堝厚度，A _e,i與A _e,c分別為電阻料和保溫料間的熱傳面積與電阻料和坩堝間的熱傳面積，T _i與T _c分別為保溫料溫度與坩堝溫度。 According to an embodiment of the present disclosure, the above-mentioned resistance material heat balance equation is:

, where i is the total current flowing through the furnace core of the graphitization furnace, V _e is the volume of the furnace core, me is the mass of the resistance material, C _{p, e is} the specific heat of the resistance material, f _cp is the specific heat correction factor, _ke , _ki , and k _c are the thermal conductivity of the resistance material, the thermal conductivity of the insulation material, and the thermal conductivity of the crucible, respectively, L ₁ , L ₂ , and L ₃ are the thickness of the resistance material, the thickness of the insulation material, and the thickness of the crucible, A _{e, i} and A _{e, c} are the heat transfer area between the resistance material and the heat preservation material and the heat transfer area between the resistance material and the crucible, respectively, and T _i and T _c are the temperature of the heat preservation material and the crucible temperature, respectively.

， 其中m _c為坩堝質量，C _p,c為坩堝比熱，k _g為石墨原料熱傳導係數，L ₄為石墨原料厚度，A _c,g為坩堝和石墨原料間的熱傳面積，T _g為石墨原料溫度。 According to an embodiment of the present disclosure, the above-mentioned crucible heat balance equation is:

, where m _c is the mass of the crucible, C _p,c is the specific heat of the crucible, k _g is the thermal conductivity coefficient of the graphite raw material, L ₄ is the thickness of the graphite raw material, A _{c, g} is the heat transfer area between the crucible and the graphite raw material, and T _g is the graphite raw material Raw material temperature.

其中m _g為石墨原料質量，C _p,g為石墨原料比熱。 According to an embodiment of the present disclosure, the above-mentioned heat balance equation of graphite raw material is:

Where m _g is the mass of the graphite raw material, and C _p,g is the specific heat of the graphite raw material.

其中m _i為保溫料質量，C _p,i為保溫料比熱，k _w為爐壁熱傳導係數，L ₅為爐壁厚度，A _e,w為爐壁熱傳面積，T _w為爐壁溫度。 According to an embodiment of the present disclosure, the above-mentioned heat balance equation of the heat insulating material is:

Where m _i is the quality of the insulation material, C _p,i is the specific heat of the insulation material, k _w is the heat transfer coefficient of the furnace wall, L ₅ is the thickness of the furnace wall, A _{e,w is} the heat transfer area of the furnace wall, and Tw is the temperature of the furnace wall.

， 其中m _w為爐壁質量，C _p,w為爐壁比熱，h _w為熱對流係數， T _∞為大氣環境溫度。 According to an embodiment of the present disclosure, the above-mentioned heat balance equation of the refractory brick is:

, where m _w is the mass of the furnace wall, C _p,w is the specific heat of the furnace wall, h _w is the thermal convection coefficient, and T _∞ is the atmospheric ambient temperature.

，

， 第二爐溫與電阻率之關係方程式為：

，

。 According to an embodiment of the present disclosure, establishing the furnace resistance model further includes establishing a relationship equation between the first furnace temperature and the resistivity in the first temperature range, and establishing a relationship equation between the second furnace temperature and the resistivity in the second temperature range. The relationship equation between the first furnace temperature and resistivity is:

,

, the relationship between the second furnace temperature and resistivity is:

,

.

According to an embodiment of the present disclosure, an initial power of the above-mentioned preset power transmission power curve is 2100 kW, and after the power is heated up to 7000 kW at 290 kW/hr, power is transmitted at a constant current of 110 kA.

According to an embodiment of the present disclosure, the above-mentioned iterative calculation operation includes: using the furnace resistance model, the first target power and the first operating voltage corresponding to the first power transmission time in the preset power transmission power curve to obtain the first calculation power; determine whether the first absolute value percentage of the error between the first target power and the first calculated power is less than 1%; when the first absolute value percentage of the error is less than 1%, substitute the first calculated power into the heat transfer model; determine the first power transmission Whether the time is equal to the preset value; and when the first power transmission time is equal to the preset value, the prediction of the heating history of the core of the graphitization furnace is completed.

According to an embodiment of the present disclosure, when the first absolute error percentage is not less than 1%, the above method further includes: adjusting the first operating voltage to the second operating voltage, and comparing the first target power with the second operating voltage Substitute into the equation of the furnace resistance model to obtain the second calculated power; determine whether the second absolute error percentage between the first target power and the second calculated power is less than 1%; and when the second absolute error percentage is less than 1%, Substitute the second calculated power into the heat transfer model.

式(1)， 其中R _e為爐芯總爐阻，T _e為爐芯溫度，m為爐芯內坩堝橫排數量，n為爐芯內坩堝縱排數量，a為橫排間坩堝間距，d為坩堝直徑，h為坩堝高度，f _ρ為爐阻模型之修正因子，ρ為爐芯內電阻料的電阻率。在一些示範例子中，爐芯總爐阻之單位為mΩ，爐芯內坩堝橫排數量m為4組，爐芯內坩堝縱排數量n為20組，橫排間坩堝間距a為0.08mm，坩堝直徑d為0.5m，坩堝高度h為1.7m。爐阻模型之修正因子f _ρ可依不同爐溫區間進行修正。電阻料之電阻率ρ會隨著溫度的變化而變化。 Please refer to FIG. 1 , which is a flowchart illustrating a method for predicting a heating history of a core of a graphitization furnace according to an embodiment of the present disclosure. When predicting the heating history of the furnace core of the graphitization furnace, step 100 may be performed first to establish a furnace resistance model of the graphitization furnace. In some examples, the furnace resistance model is established based on the arrangement of crucibles in the furnace core of the actual graphitization furnace, and the furnace resistance model can consider both the crucible size and the number of crucibles. The equation of the furnace resistance model can be expressed as the following formula (1):

Formula (1), where Re is the total furnace resistance of the furnace core _{, T e is} the furnace core temperature, m is the number of horizontal rows of crucibles in the furnace core, n is the number of vertical rows of crucibles in the furnace core, a is the crucible spacing between horizontal rows, d is the diameter of the crucible, h is the height of the crucible, f _ρ is the correction factor of the furnace resistance model, and ρ is the resistivity of the resistance material in the furnace core. In some demonstration examples, the unit of the total furnace resistance of the furnace core is mΩ, the number m of horizontal crucible rows in the furnace core is 4 groups, the number n of vertical crucible rows in the furnace core is 20 groups, and the crucible spacing a between the horizontal rows is 0.08mm, The crucible diameter d is 0.5 m, and the crucible height h is 1.7 m. The correction factor f _ρ of the furnace resistance model can be corrected according to different furnace temperature ranges. The resistivity ρ of the resistive material will change with the change of temperature.

，

式(2)。 第二爐溫與電阻率之關係方程式可表示為下式(3)：

，

式(3)。 The resistivity is related to the resistance, length, and area of the substance, that is, resistivity = resistance * area/length, and it will change with temperature. Therefore, the resistance value can be obtained from the actual process data, and the relationship equation between the furnace temperature and the resistivity in different temperature ranges can be established. The temperature interval can be, for example, two or more. In some exemplary examples, when establishing the furnace resistance model, the prediction method may further include establishing a relationship equation between the first furnace temperature and the resistivity in the first temperature range and the relationship between the second furnace temperature and the resistivity in the second temperature range equation. The first temperature range may be, for example, 30°C to 509°C, and the second temperature range may be, for example, 509°C to 3000°C. The relationship equation between the first furnace temperature and resistivity can be expressed as the following formula (2):

,

Formula (2). The relationship between the second furnace temperature and resistivity can be expressed as the following formula (3):

,

Formula (3).

Next, step 110 may be performed to establish a heat transfer model of the graphitization furnace. In this embodiment, the establishment of the heat transfer model of the graphitization furnace can be performed before the establishment of the furnace resistance model, that is, the sequence of steps 100 and 110 can be intermodulated. Please refer to FIG. 2 , which is a schematic diagram illustrating a heat transfer phenomenon in a graphitization furnace according to an embodiment of the present disclosure. The resistance material 200, that is, the furnace core area, will conduct heat transfer to the crucible 210 and the graphite raw material 220 in the crucible 210 after being subjected to the Joule heat E _{g, e} , and at the same time, the heat E ₁ will also be transferred to the insulating material 230, and the refractory The walls of the bricks 240 are lost. The furnace core temperature can be calculated by one-dimensional transient heat transfer theory. The boundary conditions of the outer wall can be, for example, the natural convection heat transfer type, and the convection coefficient can be corrected by measuring the furnace wall temperature.

式(4)， 其中i為流經石墨化爐之爐芯總電流，單位為kA；V _e為爐芯容積，單位為m ³；m _e為電阻料質量，單位為kg；C _p,e為電阻料比熱，單位為J/kg℃；f _cp為比熱修正因子；k _e、k _i、與k _c分別為電阻料熱傳導係數、保溫料熱傳導係數、與坩堝熱傳導係數，單位為W/m·k；L ₁、L ₂、與L ₃分別為電阻料厚度、保溫料厚度、與坩堝厚度，單位為m；A _e,i與A _e,c分別為電阻料200和保溫料230間的熱傳面積與電阻料200和坩堝210間的熱傳面積，單位為m ²；T _i與T _c分別為保溫料溫度與坩堝溫度，單位為℃。 As shown in FIG. 2 , in some examples, the heat transfer model of the graphitization furnace may include the heat balance equation of resistance material, the heat balance equation of crucible, the heat balance equation of graphite raw material, the heat balance equation of insulating material, and the heat balance equation of refractory brick. The heat balance equation of the resistance material is Joule heat E _g,e = the heat of the resistance material _Est,e + the heat E ₁ transferred to the insulation material 230 , which can be expressed as the following formula (4) after expansion:

Formula (4), where i is the total current of the furnace core flowing through the graphitization furnace, the unit is kA; V _e is the furnace core volume, the unit is m ³ ; m _e is the mass of the resistance material, the unit is kg; C _p,e is the specific heat of the resistance material, the unit is J/kg℃; f _cp is the specific heat correction factor; _ke , _ki , and k _c are the thermal conductivity coefficient of the resistance material, the thermal conductivity coefficient of the insulating material, and the thermal conductivity coefficient of the crucible, the unit is W/m k; L ₁ , L ₂ , and L ₃ are the thickness of the resistance material, the thickness of the insulation material, and the thickness of the crucible, respectively, in m; A _e,i and A _e,c are the distance between the resistance material 200 and the insulation material 230 respectively The heat transfer area and the heat transfer area between the resistance material 200 and the crucible 210 are in m ² ; _Ti and T _c are the temperature of the insulating material and the temperature of the crucible, and the unit is °C.

式(5)， 其中m _c為坩堝質量，C _p,c為坩堝比熱，k _g為石墨原料熱傳導係數，L ₄為石墨原料厚度，A _c,g為坩堝210和石墨原料220間的熱傳面積，T _g為石墨原料溫度。 The crucible heat balance equation is the heat E ₂ transferred from the resistance material 200 to the crucible 210 = the crucible heat E _st,c + the heat E ₃ transferred to the graphite raw material 220 , which can be expressed as the following formula (5) after expansion:

Formula (5), where m _c is the mass of the crucible, C _{p, c} is the specific heat of the crucible, _kg is the thermal conductivity coefficient of the graphite raw material, L ₄ is the thickness of the graphite raw material, and A _{c, g} is the heat transfer between the crucible 210 and the graphite raw material 220. area, T _g is the temperature of graphite raw material.

式(6)

其中m _g為石墨原料質量，C _p,g為石墨原料比熱。 The heat balance equation of the graphite raw material is the heat E ₃ transferred from the crucible 210 to the graphite raw material 220 = the heat of the graphite raw material E _st,g , which can be expressed as the following formula (6) after expansion:

Formula (6)

Where m _g is the mass of the graphite raw material, and C _p,g is the specific heat of the graphite raw material.

式(7)， 其中m _w為爐壁質量，C _p,w為爐壁比熱，h _w為熱對流係數， T _∞為大氣環境溫度。熱對流係數之單位為W/m ²·k。 The heat balance equation of the heat preservation material is the heat E ₁ transmitted to the heat preservation material 230 = the heat heat of the heat preservation material _Est,i + the heat E ₀ of the heat preservation material 230 to the refractory brick 240 , which can be expressed as the following formula (7) after expansion:

Equation (7), where m _w is the mass of the furnace wall, C _p,w is the specific heat of the furnace wall, h _w is the thermal convection coefficient, and T _∞ is the atmospheric ambient temperature. The unit of thermal convection coefficient is W/m ² ·k.

式(8)， 其中m _w為爐壁質量，C _p,w為爐壁比熱，h _w為熱對流係數， T _∞為大氣環境溫度。 The heat balance equation of the refractory brick is the heat E ₀ transferred from the insulating material 230 to the refractory brick 240 = the heat of the refractory brick E _st,w + the heat E _w lost by the wall of the refractory brick, which can be expressed as the following formula (8) after expansion:

Equation (8), where m _w is the mass of the furnace wall, C _p,w is the specific heat of the furnace wall, h _w is the thermal convection coefficient, and T _∞ is the atmospheric ambient temperature.

Referring to FIG. 1 again, after completing the establishment of the furnace resistance model and the heat transfer model, step 120 may be performed to perform an iterative calculation operation using the preset power transmission power curve, the furnace resistance model and the heat transfer model, so as to obtain corresponding different power transmission times. The temperature of the furnace core of the graphitization furnace, until the total number of hours of power transmission is equal to a preset value. In some examples, when performing an iterative calculation operation, a preset power transmission curve can be used as the input condition, and the current and power can be obtained through the furnace resistance model, and the calculated power can be used as the input condition of the heat transfer model. Next, the temperature of the furnace core can be calculated through the heat balance equation of the heat transfer model. After continuous iterative calculation, the heating curve of the furnace core of the graphitization furnace can be obtained.

Please refer to FIG. 3 , which is a flowchart illustrating an iterative computing operation according to an embodiment of the present disclosure. In some examples, as in step 300, the iterative calculation can be started by taking the power transmission time t as 0 and a preset power transmission time interval Δt, such as 1 second, as the first power transmission time. Steps 310 and 320 are performed to find out the first target power corresponding to the first power transmission time from the preset power transmission curve, and obtain the corresponding first operating voltage. Next, step 330 may be performed, taking the first target power and the first operating voltage as input conditions, using the furnace resistance model, and the first target power and the first operating voltage to obtain the corresponding current and the first calculated power.

In some exemplary examples, when step 330 is performed, when the power transmission time t is 0, the initial temperature of the furnace core, such as room temperature, can be obtained. Since the temperature at this time is less than 509°C, equation (2) of the furnace resistance model can be used to obtain the corresponding resistivity from the initial temperature, and equation (1) can be used to obtain the corresponding furnace resistance. The furnace resistance and the obtained operating voltage can be used to obtain the current and the first calculated power.

。 Next, step 340 may be performed to determine whether the first absolute error percentage between the first target power and the first calculated power is less than a predetermined percentage. The preset percentage can be, for example, 1%, as shown in FIG. 3 . When performing step 340, the first absolute error percentage may be calculated first. The formula for the absolute percentage of error is as follows:

.

When the absolute percentage of the first error between the first target power and the first calculated power is less than a predetermined percentage, such as 1%, go to step 350 to substitute the first calculated power into the heat transfer model to obtain the heating through the first power transmission time Then the core temperature of the graphitization furnace. The obtained furnace core temperature can be used as the input furnace core temperature to calculate the resistivity of the next power transmission time.

Next, step 360 may be performed to determine whether the first power transmission time is equal to the preset total power transmission time. When the first power transmission time is equal to the preset total power transmission time, the iterative calculation operation is ended, and the prediction of the heating history of the furnace core of the graphitization furnace is roughly completed. And when the first power transmission time is not equal to the preset total power transmission time, that is, the first power transmission time is less than the preset total power transmission time, return to the start of the iterative calculation operation, and go to step 300 to add the first power transmission time to the The power transmission time interval Δt is preset above, and the steps after step 300 are continued according to the above description. The iterative calculation is continued until the total power transmission hours is equal to the preset total power transmission hours, and then the heating history curve of the furnace core of the graphitization furnace can be obtained.

On the other hand, in step 340, when the first absolute value percentage of the error between the first target power and the first calculated power is not less than a predetermined percentage, such as 1%, go back to step 320, adjust the first operating voltage, and obtain second operating voltage. Then proceed to step 330, taking the first target power and the second operating voltage as input conditions, using the furnace resistance model, and the first target power and the second operating voltage to obtain the corresponding current and the second calculated power.

Next, step 340 is performed to determine whether the second absolute error percentage between the first target power and the second calculated power is less than the predetermined percentage. When the second absolute error percentage between the first target power and the second calculated power is less than the preset percentage, go to step 350 to substitute the second calculated power into the heat transfer model to obtain the graphitization furnace corresponding to the first power transmission time. furnace core temperature. Next, proceed to step 360 as described above to determine whether to end the iterative calculation operation, or to continue the iterative calculation of the next power transmission time.

The furnace resistance at different furnace core temperatures can be calculated from the equation (1) of the above furnace resistance model. The inventor found that the measured data of the actual furnace is different from the calculated result, so the present disclosure adjusts the prediction model by the measurement result, so that the prediction model reflects the actual furnace resistance curve. Table 1 below lists the corresponding correction factors for different core temperature ranges in some exemplary examples. Table 1 correction factor Furnace core resistance material temperature range (℃) f _ρ1 2.31 30~480.3 f _ρ2 2.5 480.3~792.9 f _ρ3 2.23 792.9~1120.3 f _ρ4 2.1 1120.3~1510.8 f _ρ5 2.2 1510.8~1869.9 f _ρ6 2.29 1968.9~2416.7 f _ρ7 2.4 2416.7~2541.4 f _ρ8 2.32 2541.4~3000

After correcting the furnace resistance model with on-site measurement data, the relative error percentage between the simulated and predicted furnace resistance quality and the measured value can be less than 10%.

Using the heat balance equations (4) to (8) of the above heat transfer model, the temperature of the furnace core of the graphitization furnace can be calculated. However, the inventors found that due to the lack of thermal characteristic parameters such as the specific heat and thermal conductivity of each object in the high temperature section, it is also impossible to evaluate the effect of heat dissipation on temperature. Therefore, in some examples, the above equations (4) to (8) are corrected for specific heat terms in different temperature ranges, so that the simulated preset furnace core temperature can match the measured value. Table 2 below lists the corresponding specific heat correction factors for different furnace core temperature ranges in some examples. Among them, the unit of specific heat is J/kgk. Table 2 Furnace core temperature (℃) Specific heat correction factor Resistor material specific heat Crucible specific heat Specific heat of graphite raw material heat preservation specific heat Refractory brick specific heat normal temperature 1 710 400 400 721.4 721.4 30~205 8 5680 3200 3200 5771.2 5771.2 205~612 5.2 3692 2080 2080 3751.3 3751.3 612~850 3.6 2556 1440 1440 2597 2597 850~1225 6 4260 2400 2400 4328.4 4328.4 1225~1800 2.3 1633 920 920 1659.2 1659.2 1800~2134 0.95 674.5 380 380 685.3 685.3 2134~3000 0.9 639 360 360 649.6 649.6

Please refer to FIG. 4 , which is a graph showing prediction and field measurement of furnace resistance and furnace temperature for one heat of a graphitization furnace according to an embodiment of the present disclosure. The comparison error between the predicted furnace resistance and the actual measured value within the furnace core temperature of 3000° C. in this embodiment is all less than 10%. At the same time, it can be observed from Figure 4 that no matter it is the predicted value or the measured value, the furnace resistance will remain unchanged from the 31st hour, and the predicted furnace resistance value and the measured furnace resistance value at this time are 0.433mΩ and 0.438mΩ respectively. Until the 40th hour, the furnace resistance will have a sudden rebound phenomenon. At this time, the predicted furnace resistance value and the measured furnace resistance value are 0.451 mΩ and 0.445 mΩ respectively. This phenomenon of furnace resistance springback can also be used as one of the judgment basis for stopping power transmission.

In addition, it can also be observed from Figure 4 that the comparison error between the predicted furnace core temperature between room temperature and 950 °C and the actual measurement value is less than 10%; while the furnace core temperature between 950 °C and 3000 °C has The comparison error of the actual measurement value is less than 2.6%. The furnace core temperature above 3000°C is not available for comparison, but the furnace core temperature above 3000°C can still be calculated through the prediction model of the embodiment. The total power transmission time of this furnace is 47.1 hours, and the predicted temperature of the furnace core after the power transmission is completed is 3142.8 ℃.

Please refer to FIG. 5A and FIG. 5B , which respectively illustrate a part of a power transmission curve diagram used in a method for predicting the heating history of a core of a graphitization furnace according to an embodiment of the present disclosure, and a part of the power transmission curve used in the prediction method. part of the transmission current curve. In some examples, the initial power of the preset transmission power curve is increased from the original 1500kW to 2100kW, and then the power is increased to 7000kW at 290kW/hr, as shown in FIG. 5A . After the power reaches 7000kW, power transmission is carried out at a constant current of 110kA, and the power transmission stops when the target unit consumption is reached, as shown in Figure 5B.

Please refer to FIG. 6 , which is a graph of furnace temperature prediction and field measurement of one heat of a graphitization furnace according to an embodiment of the present disclosure. In this embodiment, the furnace temperature is predicted based on the target power transmission curve re-established in FIG. 5A and FIG. 5B . In the graphitization process, the temperature of the furnace core completed by the original power transmission mode was 3142.8°C, and the electric capacity of the graphite carbon microspheres was 352.8mAh/g, which was in line with the internal control value. And the temperature of the furnace core after power transmission is completed according to the target power transmission power curve is 3144.7 ℃, and the expected capacitance of the graphitic carbon microspheres can meet the internal control value. The total power transmission time at the power transmission end point 400 in the original power transmission mode is 47.2hr, and the total power transmission time at the power transmission end point 410 in the fast power transmission mode of the present embodiment is 41.4hr. Therefore, the present embodiment can effectively shorten the total power transmission time by 11.3%, which not only saves energy, but also improves production capacity.

Please refer to FIG. 7 , which is a field measurement diagram of one heat of a graphitization furnace according to an embodiment of the present disclosure. The furnace is adjusted based on the furnace core temperature of the predicted result of an embodiment. The total power transmission hours of this furnace is 41hrs, which effectively shortens the total power transmission hours by 11.1% compared with the past average of 46.1hrs, which can increase production capacity. Using the prediction model of this embodiment, it is calculated that the furnace core temperature after power transmission is completed is 3184.7°C, and the expected capacitance of the graphitic carbon microspheres can also meet the internal control value.

As can be seen from the above embodiments, one of the advantages of the present disclosure is that the method for predicting the heating history of the core of the graphitization furnace of the present disclosure combines the furnace resistance model and the one-dimensional heat transfer model, and then uses the on-site process data for model correction. In this way, the actual temperature of the furnace core can be predicted in time. The predicted furnace core temperature can provide on-site operators as a basis for adjusting the furnace, so it can effectively improve the quality of graphitized products and achieve the purpose of saving electricity.

As can be seen from the above-mentioned embodiments, another advantage of the present disclosure is that the method for predicting the heating history of the furnace core of the graphitization furnace of the present disclosure can predict the heating history of the furnace core of the graphitization furnace, and the furnace core temperature can be used as the basis for the prediction. The judgment of stopping power transmission can take into account the quality and production capacity of graphitized products.

Although the present disclosure has been disclosed above with examples, it is not intended to limit the present disclosure. Anyone with ordinary knowledge in this technical field can make various changes and modifications without departing from the spirit and scope of the present disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the appended patent application.

100: Step 110: Step 120: Step 200: Resistive material 210: Crucible 220: Graphite raw material 230: Insulation material 240: Refractory brick 300: Step 310: Step 320: Step 330: Step 340: Step 350: Step 360: Step 400 : End point of power transmission 410: End point of power transmission E ₀ : Heat E ₁ : Heat E ₂ : Heat E ₃ : Heat E _g,e : Joule heat _Est,c : Crucible heat _Est,e : Resistance material heat _Est,g : Graphite raw material heat _Est,i : thermal insulation material heat _Est,w : refractory brick heat E _w : heat t: power transmission time Δt: preset power transmission time interval

In order to make the above and other objects, features, advantages and embodiments of the present disclosure more clearly understood, the accompanying drawings are described as follows: [FIG. 1] is a flowchart illustrating a method for predicting a heating history of a core of a graphitization furnace according to an embodiment of the present disclosure; [ FIG. 2 ] is a schematic diagram illustrating a heat transfer phenomenon in a graphitization furnace according to an embodiment of the present disclosure; [FIG. 3] is a flowchart illustrating an iterative computing operation according to an embodiment of the present disclosure; [ FIG. 4 ] is a graph showing prediction and field measurement of furnace resistance and furnace temperature for one heat of a graphitization furnace according to an embodiment of the present disclosure; [ FIG. 5A ] is a part of a power transmission curve diagram used in a method for predicting the heating history of a core of a graphitization furnace according to an embodiment of the present disclosure; [ FIG. 5B ] is a part of a power transmission current graph used in a method for predicting the heating history of a core of a graphitization furnace according to an embodiment of the present disclosure; [ FIG. 6 ] is a graph showing the furnace temperature prediction and actual field measurement of one heat of a graphitization furnace according to an embodiment of the present disclosure; and [ FIG. 7 ] is a field measurement diagram illustrating one heat of a graphitization furnace according to an embodiment of the present disclosure.

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Claims (5)

A method for predicting the heating history of a furnace core of a graphitization furnace, comprising: establishing a furnace resistance model of a graphitization furnace, wherein one of the equations of the furnace resistance model is:

where Re is the total furnace resistance of the furnace core _{, T e is} the furnace core temperature, m is the number of horizontal rows of crucibles in the furnace core, n is the number of vertical rows of crucibles in the furnace core, a is the crucible spacing between the horizontal rows, d is the diameter of the crucible, h is the height of the crucible, f _ρ is the correction factor of the furnace resistance model, ρ is the resistivity of the resistance material in the furnace core; establish a heat transfer model of the graphitization furnace, wherein the heat transfer model includes a resistance material heat balance equation, A crucible heat balance equation, a graphite raw material heat balance equation, a heat preservation material heat balance equation, and a refractory brick heat balance equation, wherein the resistance material heat balance equation is:

where i is the total current flowing through the furnace core of the graphitization furnace, V _e is the volume of the furnace core, me is the mass of the resistance material, C _{p, e is} the specific heat of the resistance material, f _cp is the specific heat correction factor, _ke , _ki , and k _c are the thermal conductivity of the resistance material, the thermal conductivity of the insulation material, and the thermal conductivity of the crucible, respectively, L ₁ , L ₂ , and L ₃ are the thickness of the resistance material, the thickness of the insulation material, and the thickness of the crucible, A _{e, i} and A _{e, c} are the heat transfer area between the resistance material and the insulating material and the heat transfer area between the resistance material and the crucible, respectively, T _i and T _c are the temperature of the insulating material and the crucible temperature, respectively; the crucible heat balance equation is:

Where m _c is the mass of the crucible, C _p,c is the specific heat of the crucible, _{kg g} is the thermal conductivity coefficient of the graphite raw material, L ₄ is the thickness of the graphite raw material, A _{c, g} is the heat transfer area between the crucible and the graphite raw material, and T _g is the graphite raw material temperature; the heat balance equation of the graphite raw material is:

Where m _g is the quality of graphite raw material, C _{p, g} is the specific heat of graphite raw material; the heat balance equation of the thermal insulation material is:

where m _i is the quality of the heat preservation material, C _p,i is the specific heat of the heat preservation material, k _w is the thermal conductivity coefficient of the furnace wall, L ₅ is the thickness of the furnace wall, A _{e,w is} the heat transfer area of the furnace wall, and Tw is the furnace wall temperature; And the heat balance equation of the refractory brick is:

Where m _w is the quality of the furnace wall, C _p,w is the specific heat of the furnace wall, h _w is the thermal convection coefficient, T _∞ is the atmospheric ambient temperature; and use a preset power transmission curve and the furnace resistance model and the heat transfer model. An iterative calculation operation is performed to obtain a plurality of furnace core temperatures of the graphitization furnace corresponding to different power-on times, until a total power-on time equals a preset value. The method of claim 1, wherein establishing the furnace resistance model further comprises: establishing a relationship equation between a first furnace temperature and resistivity in a first temperature range, wherein the relationship equation between the first furnace temperature and resistivity is: : ρ=8,73×10 ^-3 × T _e ^-4.147 ×( T _e -1)- ^0.298 , 30℃< T _e

509°C; and establishing a relationship equation between a second furnace temperature and resistivity in a second temperature interval, wherein the relationship equation between the second furnace temperature and resistivity is:

The method according to claim 1, wherein an initial power of the preset power transmission power curve is 2100kW, and after the temperature is increased to 7000kW at 290kW/hr, power is transmitted at a constant current of 110kA. The method of claim 1, wherein performing the iterative calculation operation comprises: using the furnace resistance model, and a first target power and a first operating voltage corresponding to a first power transmission time in the preset power transmission power curve , to obtain a first calculation power; determine whether the first absolute value percentage of the first target power and the first absolute value of the first calculation power is less than 1%; when the first absolute value percentage of the error is less than 1%, the Substitute the first calculated power into the heat transfer model; determine whether the first power transmission time is equal to the preset value; and when the first power transmission time is equal to the preset value, complete the heating process of a core of the graphitization furnace predict. The method of claim 4, wherein when the first absolute error percentage is not less than 1%, the method further comprises: adjusting the first operating voltage to a second operating voltage, and using the furnace resistance model, and the first target power and the second operating voltage to obtain a second calculation power; judging whether a second error absolute value percentage between the first target power and the second calculation power is less than 1%; and when the first When the absolute value percentage of the second error is less than 1%, the second calculated power is substituted into the heat transfer model.

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