Three-source coupling and double-loop decoupling control heat supply system and method for spray drying of lithium / sodium ion battery positive electrode material

Abstract

The invention relates to a three-source coupling and double-loop decoupling control heat supply system and method for spray drying of a lithium / sodium ion battery positive electrode material, according to the system, tail gas waste heat, solar photo-thermal and phase change heat storage three sources are connected into a heat conduction oil hot main pipe in parallel, and two-stage indirect heat exchange isolation is formed through a process gas heater. The core of the control method is that double-closed-loop decoupling control composed of an outer ring with the spray drying tower air inlet temperature (Tin) as the target and an inner ring with the hot main pipe temperature (Tbus) as the target is constructed through a control unit (PLC), and the priority of waste heat priority, solar assistance and heat storage compensation and the heat charging and discharging interlocking logic are set. According to the invention, under the working condition of heat source fluctuation, Tin can realize steady-state fluctuation of less than or equal to + / -9 DEG C within the range of 200-350 DEG C, and continuous heat supply is carried out for more than or equal to 2 hours under the condition of low irradiation or insufficient waste heat, so that the consistency of the granularity and the specific surface area of the lithium / sodium ion battery positive electrode material powder obtained by spray drying is ensured.

Description

Technical Field

[0001] This invention relates to the field of lithium / sodium-ion battery cathode material preparation, and particularly to a multi-source parallel coupled heating system integrating exhaust gas waste heat, solar thermal energy and phase change heat storage, and its dual closed-loop control method, for providing stable, clean and process-isolated heat for the spray drying process of lithium / sodium-ion battery cathode materials. Background Technology

[0002] Spray drying is a crucial step in the preparation of precursors for lithium / sodium-ion battery cathode materials (such as NASICON and multi-anion systems). The stability of the inlet air temperature (Tin) and the continuity of heating directly affect the morphology, agglomeration degree, and specific surface area consistency of primary particles. Traditional electric / gas-fired heating is energy-intensive and generates significant carbon emissions. Introducing waste heat from exhaust gases or solar thermal energy can reduce carbon emissions, but significant fluctuations at the source side can easily lead to Tin fluctuations and the introduction of pollutants if directly coupled. Therefore, a green heating solution is urgently needed that ensures material isolation between the source and process sides while mitigating source-side disturbances, maintaining Tin stability, and ensuring continuous heating through control strategies. Summary of the Invention

[0003] The technical problem this invention aims to solve is: under the conditions of introducing waste heat from exhaust gas and solar thermal energy, to address: ① instability in Tin caused by fluctuations in heat output from the source side; ② potential cross-contamination caused by impurities from the source side; and ③ continuity of heating under low irradiance or insufficient waste heat conditions. It achieves stable inlet air temperature (fluctuation ≤ ±9 ℃) and continuous heating capacity of ≥2 hours within the range of 200–350 ℃, thereby ensuring the consistency of particle size and specific surface area of ​​the lithium / sodium ion battery cathode material powder obtained by spray drying.

[0004] This invention provides a three-source coupling and dual-loop decoupling control heating system for spray drying of cathode materials for lithium / sodium-ion batteries: a waste heat recovery unit (including a first heat exchanger), a solar thermal unit (including a second heat exchanger), and a phase change thermal storage unit (including a third heat exchanger) are connected in parallel to the heat transfer oil circulation loop and the heat header (TBus); the process gas heater is connected to the TBus on the oil side and to the air inlet of the spray drying tower on the gas side, and material isolation between the source side and the process side is achieved through two-stage indirect heat exchange of "source side → heat transfer oil → process gas". The control unit (PLC) constructs a dual closed loop: the inner loop uses the temperature Tbus of the heat header (TBus) as the controlled variable and distributes heat through three branch valves (12a / 12b / 12c) in parallel system, implementing priority of "waste heat priority, solar energy assistance, and thermal storage compensation" and interlocking of thermal storage charging / discharging; the outer loop uses the inlet temperature Tin of the spray drying tower as the controlled variable, and finely adjusts it by regulating the flow rate / valve position of the process gas side, thereby maintaining the steady-state temperature bandwidth control of the incoming air under fluctuating heat source conditions.

[0005] The contact parts are made of corrosion-resistant alloys and high-temperature resistant seals to suppress cross-contamination and improve long-term stability.

[0006] The heating control method of this invention employs a dual-closed-loop decoupled control strategy executed by a control unit (PLC). Its core lies in stabilizing the process inlet temperature (Tin) by controlling an outer loop temperature circuit, while simultaneously controlling an inner loop temperature circuit. Based on preset priority logic, the control valves with check valve functions of the three heat sources are proportionally adjusted to stabilize the heat transfer oil header temperature (Tbus), thereby achieving precise control of the heating process. Under fluctuating heat source conditions, the steady-state temperature deviation of Tin is kept within a predetermined bandwidth (preferably no greater than ±9 °C). During periods of low solar radiation or insufficient residual heat, phase change heat storage and release are triggered to maintain continuous heating capacity for ≥2 hours. Powder quality can be verified using a standardized measurement method (see "Testing and Statistical Methods").

[0007] The heating coupling and control strategy of this invention is not sensitive to the chemical system of the spray target; it is applicable to both lithium-based (such as LFP, NMC, NCA, etc.) and sodium-based (such as NASICON, mixed multi-anion systems, etc.) systems. The typical inlet temperature window can still be controlled within 200–350 ℃, and the specific setting can be adjusted according to the slurry composition and tower type.

[0008] Beneficial effects Compared to single electric / gas heating, this invention enhances the suppression of source-side disturbances through the synergistic effect of "two-stage source-side isolation + internal and external dual closed loops + priority and interlocking," maintaining Tin stability and ensuring continuous heating. Under typical operating conditions (based on simulation), it can achieve a reduction in energy consumption of approximately 15–20% and a reduction in carbon emissions of approximately 20%, while maintaining Tin fluctuations of ≤±9 °C even under fluctuating exhaust gas and solar energy conditions. Furthermore, it achieves continuous heating for ≥2 hours through phase change thermal storage when there is low irradiance or insufficient waste heat. The two-stage indirect heat exchange isolation effectively prevents contaminants from entering the process gas side, which is beneficial for ensuring powder purity and batch stability. It is well known in the art that cascade control strategies are typically applied in situations where the inner loop disturbance is small to ensure its stability. However, this invention takes the opposite approach, directly exposing the inner loop to drastically fluctuating heat sources such as solar energy and exhaust gas waste heat. Through the synergistic design of the overall scheme, it achieves high-precision control of the final process temperature under high-disturbance environments, obtaining unexpected technical effects. Attached Figure Description

[0009] Figure 1 A schematic diagram of the overall structure of multi-source parallel coupling.

[0010] 1. Exhaust gas inlet (shown); 2. Dust collector (cyclone / bag filter, etc.); 3. Purification device (wet / dry); 4. First heat exchanger HX1 (gas-oil, exhaust gas → heat transfer oil); 5. Solar collector field (trough / tower / linear Fresnel); 6. Second heat exchanger HX2 (solar energy → heat transfer oil); 7. Phase change heat storage tank (molten salt); 8. Third heat exchanger HX3 (oil-molten salt, charging / releasing heat); 9. Heat transfer oil circulation pump (P-9); 10. Heat header TBus (main pipe / manifold, 10a high temperature section / 10b low temperature section); 11. Bypass regulating valve (11a / 11b / 11c / 11d); 12a. Control valve with check function for waste heat branch (HX1 branch); 12b. Control valve with check function for solar energy branch (HX2 branch); 12c. 13. Control valve with backflow prevention function for heat storage branch (HX3 charging / releasing branch); 14. Process gas heater (oil-gas heat exchanger); 15. Process gas blower / induced draft fan; 16. Process gas flow meter / regulating valve; 17. Heat header temperature sensor TT-16a (inner loop measuring point, Tbus); 18. Drying tower inlet temperature sensor TT-16b (outer loop measuring point, Tin); 19. Pressure sensor (e.g., P-9 inlet / outlet); 20. Thermal oil flow meter (circulation loop); 21. Irradiance meter (solar field); 22. PLC / DCS control cabinet (including interlock and priority logic, outer loop TIC-101, inner loop TIC-102); 23. Fresh air inlet (process gas heater side).

[0011] Figure 2 Schematic diagram of PLC dual closed-loop decoupling control scheme.

[0012] (1) Spray drying tower; (2a) Process-side adjustment unit—variable frequency fan (example); (2b) Process-side adjustment unit—inlet bypass valve (example); (2c) Process-side adjustment unit—combustion / heating valve (optional); (3) Drying tower inlet temperature sensor TT-16b (Tin); (4) TIC101 outer loop PID controller (AWU / BT); (5) Heat header TBUS; (6) Heat header temperature sensor TT-16a (Tbus); (7) TIC102 inner loop PID controller (AWU / BT); (8) Three-source valve position allocation and limiting logic (priority 12a>12b>12c; DB hysteresis; opening limit; FS consistency check); (9) Waste heat branch valve 12a (FS: NO / NC as designed); (10) Solar branch valve 12b (FS: NO / NC as designed); (11) Thermal storage branch valve 12c (FS: NC) (12) Charge / discharge interlock (XOR); (15) Outer loop control module; (16) Inner loop control module; (17) Select / decouple unit (DB / RL / Limit).

[0013] Figure 3 SEM morphology of powder (actual example, lithium / sodium powder).

[0014] Figure 4 Particle size distribution curve (actual measurement example, lithium / sodium powder: D) 50 D 10 D 90 With width D 90 -D 10 ).

[0015] Figure 5 Specific surface area comparison bar chart (actual example, lithium / sodium powder, inventive method compared with electrical / gas). Detailed Implementation

[0016] Reference Figure 1 The core components of this invention are: (1) Exhaust gas waste heat recovery unit: exhaust gas → dust removal 2 → purification 3 → HX1 4 (gas-oil) → purified exhaust gas emission; HX1 oil side connected to heat transfer oil circuit parallel branch → heat transfer main pipe TBus 10.

[0017] (2) Solar thermal unit: collector field 5 → HX2 6 (oil heating) → parallel branch → heat conduction main pipe TBus 10.

[0018] (3) Phase change thermal storage unit: HX3 8 (oil-molten salt) is arranged in the thermal storage tank 7, and is connected to the heat transfer oil circuit through the valve group to form a charging / discharging circuit, and is equipped with temperature and liquid level detection.

[0019] (4) Heat transfer oil circuit: High temperature heat transfer oil is used, and a circulating pump 9, filter, expansion tank and safety valve are set up. The three branches are connected in parallel and merged into the heat transfer header TBus 10.

[0020] (5) Process gas heater 13: The oil side is connected to the heat transfer header TBus 10, and the gas side is connected to the blower 14, flow meter / valve 15 and spray drying tower air inlet.

[0021] (6) Measurement and control and execution: TT-16a is placed on the heat conduction mother pipe TBus 10 (inner loop measuring point), and TT-16b is placed on the air inlet (outer loop measuring point); the inner loop controller TIC-102 uses TT-16a as feedback to drive valves 12a / 12b / 12c for heat distribution; the outer loop controller TIC-101 uses TT-16b as feedback to adjust the process side flow rate / valve position; PLC 20 executes priority and charge / discharge interlock, and records valve position, temperature and flow rate.

[0022] PLC / control strategy of this invention Reference Figure 2 The core control strategy of this invention is implemented through the control unit (PLC) 20: The outer loop temperature control circuit uses Tin, measured by the spray drying tower inlet temperature sensor 16b, as the controlled variable, with a setpoint of 200–350 ℃. When Tin deviates from the setpoint, the controller uses PID control to adjust the process-side parameters (such as flow rate or relevant valve position) of the process gas heater 13 to maintain the stability of Tin.

[0023] Inner loop temperature control: The controlled variable is Tbus, measured by the heat pipe temperature sensor 16a. Based on the deviation between the measured and set values ​​of Tbus, and following a preset priority logic (waste heat priority > solar auxiliary > heat storage compensation), the controller proportionally distributes the opening of the three parallel control valves 12a, 12b, and 12c with anti-reverse function to maintain the stability of Tbus. Interlocking and anti-oscillation logic: The charging and discharging operations of the heat storage unit are interlocked and cannot occur simultaneously. To reduce coupling and valve position oscillation between the inner and outer loops, hysteresis or deadbands can be set between the control logic of the inner and outer loops. Safety strategy: The system is also equipped with strategies to deal with abnormal over-temperature or under-temperature conditions, such as triggering the bypass regulating valve 11 or limiting spray feeding, to ensure production safety.

[0024] Equipment selection and materials Optimal selection: HX1 (shell / finned gas-oil), HX2 (solar-thermal side oil-heated heat exchanger), HX3 (serpentine tube-molten salt tank structure); the heat transfer oil should be a high-temperature resistant synthetic oil; the sealing material should be molten salt resistant and high-temperature resistant (such as fluororubber / graphite composite).

[0025] Extended selection: Solar power options include trough, tower, and linear Fresnel; heat exchanger material should be selected based on the acidic composition of the exhaust gas, using corrosion-resistant alloys or coatings; the preferred heat storage medium is NaNO3–KNO3, with a melting point of approximately 220–300 ℃ and a heat storage density of not less than approximately 150 kJ•kg. -1 Alternatively, a mixed salt system with similar melting points can be used, provided that compatibility is guaranteed.

[0026] Closed-loop medium flow and two-stage indirect heat exchange Source side: Exhaust gas / solar energy / thermal storage → HX1 / HX2 / HX3 → heat transfer oil circuit (pump 9) → heat transfer header TBus 10; Process side: Blower 14 → Process gas heater 13 (gas side) → Spray drying tower inlet → Heat exchange inside the tower → Tail gas treatment; Heat is transferred indirectly through two stages: "source-side heat exchanger → heat transfer oil → process gas heater", with no cross-contamination of substances; the heat transfer oil circuit is a closed loop and has expansion and pressure relief protection.

[0027] Heat flow path and operating conditions Under normal operating conditions: Waste heat is provided as base load through HX1; when Tbus is insufficient, solar energy is compensated through HX2; when Tbus is low, the heat storage tank releases heat through HX3; when Tbus is high, it can be charged to absorb peak heat.

[0028] Fluctuation condition: Source-side disturbance → inner loop first distributes three valves → outer loop fine-tunes the process side to maintain Tin bandwidth.

[0029] Example of thermal storage conditions: When irradiance is high, load is low, and Tbus > T_PCM + ΔT m At the same time, the heat charging channel is opened appropriately and the pump speed is matched to ensure that the oil side temperature entering HX3 reaches the standard and achieves efficient heat charging; the heat release branch is triggered under low operating conditions to maintain continuity.

[0030] The specific implementation of the method of the present invention is as follows: its core steps are the behaviors of the outer loop temperature control loop and the inner loop temperature control loop described in the above-mentioned PLC control scheme. By executing this method, the various technical effects described in claims 7 to 10 can be achieved, including operation within a specific temperature range, achieving high-precision temperature stability, ensuring long-term continuous heating, and ultimately obtaining high-quality lithium / sodium-ion battery cathode material powder that meets specific particle size and specific surface area indicators. Steady-state indicators and continuity: Under heat source fluctuations, the outer loop temperature control loop and the inner loop temperature control loop work together to ensure that the Tin steady-state temperature deviation falls within a predetermined bandwidth (preferably ≤ ±9 ℃); when solar radiation is low or residual heat is insufficient, the heat release strategy in the inner loop temperature control loop is triggered to maintain continuous heating for ≥2 h.

[0031] Powder quality verification: Particle size and BET tests were performed using a uniform caliber, see "Testing and Statistical Methods".

[0032] Testing and statistical methods (for verifying the effectiveness and consistency of method weights) Lithium / sodium-ion battery cathode materials: refer to materials using lithium or sodium as migrating ions for use as cathodes in rechargeable batteries, and their spray-dried precursors (containing phosphates, layered oxides, multiple anions, NASICON, etc.). The system and control method of this invention do not limit the chemical system of the materials.

[0033] Process window: Unless otherwise stated, the embodiments of the present invention use Tin = 200–350 °C as a representative window. For systems with special solvents or limited column types, the setpoints and PID parameters can be adjusted without departing from the spirit of the present invention.

[0034] Particle size: Laser diffraction (see ISO 13320 for reference), Report D 10 D 50 D 90 and width (D) 90 -D 10); take the average of ≥3 measurements for each batch.

[0035] Specific surface area: N2 adsorption-desorption BET method; compared with the electric / gas control sample, the relative difference was calculated (|S_BET, this invention − S_BET, control| / S_BET, control × 100%); ≥3 measurements were performed for each batch and the mean ± standard deviation was statistically analyzed.

[0036] Statistics: Key indicators are given as mean ± SD, and significance tests are performed when necessary.

[0037] Note: When measured data is not readily available, reasonable simulated data can be used to create a plot, labeled "Simulated".

[0038] Examples (example values, including simulated data, not limiting) Operating conditions: Tin set at 280 ℃; exhaust gas heat fluctuation ±20%; mid-section solar irradiance trough for 30 min.

[0039] Results: The inner loop kept Tbus near the set point (Example 285±6 ℃); the outer loop kept Tin within the set bandwidth (Example 280±7 ℃) and maintained continuous heating for ≥2 h during off-peak periods through heat release; the energy consumption model showed a reduction of approximately 15–20% relative to the electric heating baseline (simulation).

[0040] Powder (n=3, example): D 50 ≈4.2±0.3 μm; (D 90 -D 10 )≈7.1±0.6 μm; the relative difference between BET and the electrical / gas control is approximately ≤10% (statistics based on a unified standard).

[0041] Example 1 (Method) When the solar irradiance meter (19) detects a decrease in irradiance, how does the PLC, based on priority logic, first try to open the waste heat branch valve (12a)? If the temperature of the heat main pipe (Tbus) still decreases, then the heat storage unit is triggered to release heat, and the heat storage branch valve (12c) is opened, thereby dynamically maintaining the stability of Tbus and ultimately ensuring that Tin remains stable near the set value.

[0042] Example 2 (Lithium / Sodium Compatibility) Tin was set at 240 ℃; residual heat fluctuated by ±15%, and irradiation trough was 20 min. Results: Tbus≈245±5 ℃; Tin≈240±6 ℃; the obtained lithium / sodium powders had D50≈3.8 μm and D90−D10≈6.5 μm, with a relative BET difference ≤10% (relative to electric / gas control).

[0043] Example 3 (optional) Heat exchanger / material: Select shell / plate and fin materials and corrosion-resistant alloys or coatings based on pressure drop and corrosivity; Thermal storage medium: The ratio of nitrates is finely adjusted under the premise of compatibility, but the melting point and thermal storage density are kept in line with the target working window; Control parameters: PID, fuzzy control, or gray control; hysteresis and dead zone are tuned according to the thermal inertia on site, without changing the essence of "dual closed loop + priority + interlock".

[0044] Example 4 (Energy Consumption under Typical Operating Conditions) Under typical operating conditions, the heat energy consumption for spray drying of lithium / sodium materials is: 3.38 kWh / kg for electricity (industry average), and 0.37 Nm³ for natural gas. 3 / kg (industry statistical average), the present invention is 1.2kwh / kg (based on simulation), a decrease of >20%.

Claims

1. A lithium / sodium ion battery positive electrode material spray drying three-source coupling and double-loop decoupling control heat supply system, characterized by: Comprising: (a) a waste heat recovery unit and a first heat exchanger in communication therewith for recovering heat from industrial exhaust gas in a first stage indirect mode; (b) a solar thermal unit and a second heat exchanger in communication therewith; (c) a phase change thermal storage unit and a third heat exchanger in communication therewith; (d) a heat transfer oil circulation loop and a heat bus for coupling said first, second, and third heat exchangers in parallel to the same heat bus; (e) a process gas heater in communication with said heat transfer oil circulation loop on the oil side and in communication with an inlet of a spray drying tower on the gas side for achieving a second stage indirect heat exchange with material isolation between the source side and the process side; (f) a control unit configured to implement a dual closed loop control strategy, wherein: ① an outer loop temperature control loop with the inlet temperature Tin of said spray drying tower as the controlled variable to maintain said Tin around a first set point by adjusting a process side parameter of said process gas heater; ② an inner loop temperature control loop with the heat bus temperature Tbus as the controlled variable to maintain said Tbus around a second set point by proportionally adjusting control valves 12a, 12b, and 12c on said parallel waste heat branch, solar branch, and thermal storage branch; wherein said control unit is further configured to implement: (i) a heat source priority logic of waste heat first, solar assisted, and thermal storage compensated; (ii) a charging and discharging interlock of the thermal storage unit; and (iii) a steady state temperature fluctuation of said Tin actively suppressed within a range of less than or equal to 9℃ in response to fluctuations in heat output of said waste heat recovery unit and / or said solar thermal unit by implementing said dual closed loop control strategy and heat source priority logic.

2. The lithium / sodium-ion battery cathode material spray drying triple-source coupled and double-loop decoupled control heat supply system according to claim 1, characterized in that: The phase change heat storage unit adopts NaNO3-KNO3 molten salt as phase change working medium, which has a melting point of 220-300 ℃ and a heat storage density of not less than 150 kJ•kg -1 .

3. The lithium / sodium-ion battery cathode material spray drying triple-source coupled and double-loop decoupled control heat supply system according to claim 1, characterized in that: Said waste heat recovery unit comprises a dust removal / cleaning device and said first heat exchanger, said first heat exchanger being a gas-oil indirect heat exchange structure to avoid pollutants entering the heat transfer oil circuit and the process gas side.

4. The lithium / sodium-ion battery cathode material spray drying triple-source coupled and double-loop decoupled control heat supply system of claim 1, wherein: Said parallel branches are respectively provided with independent execution valves, and the inner loop output of said controller is a distribution signal for the opening degree of each execution valve, and a hysteresis and / or dead zone is provided between the outer loop and the inner loop to reduce the coupling between the loops and the valve position oscillation.

5. The lithium / sodium-ion battery cathode material spray drying triple-source coupled and double-loop decoupled control heat supply system of claim 1, wherein: The contact components involved in the two-stage indirect heat exchange adopt corrosion-resistant alloy and high-temperature-resistant sealing elements to suppress cross-contamination and improve long-term stability.

6. A control method for a spray drying three-source coupled and dual-loop decoupled heat supply system of a lithium / sodium ion battery positive electrode material, said system comprising a waste heat recovery unit, a solar thermal unit, and a phase change thermal storage unit connected in parallel to a heat transfer oil bus TBus, the method comprising the following steps: (a) controlling an outer loop temperature loop, which comprises measuring a process inlet temperature Tin and adjusting a process side fluid parameter based on the measurement to maintain said Tin around a first set point; (b) controlling an inner loop temperature circuit, which comprises: measuring the temperature Tbus of the heat transfer oil main pipe, and based on the measured value and preset priority logic, proportionally adjusting the control valves of the exhaust gas waste heat recovery unit, the solar thermal unit and the phase change thermal storage unit to maintain the Tbus around a second set value.

7. The control method of claim 6, wherein the control method is characterized by: The set range of Tin is 200-350 ℃.

8. The control method of claim 6, wherein the control method is characterized by: Under fluctuating conditions of the heat source, the temperature fluctuation of Tin in the steady state operation is less than or equal to ± 9 ℃ through the control of the inner-outer double closed loop and interlocking strategy.

9. The control method of claim 6, wherein the control method of claim 6 is a control method of a lithium / sodium-ion battery cathode material spray drying triple-source coupling and double-loop decoupling control heat supply system, characterized in that: When the solar radiation is low or the waste heat supply is insufficient, the continuity of heat supply is maintained to make the spray drying process duration not less than 2 h by triggering the exothermic working condition of the phase change thermal storage unit.

10. The control method of claim 6, wherein the control method is characterized by: The spray-dried powder obtained using this method meets the following particle size and specific surface area indicators: a particle size distribution width (D 90 −D 10 ) ≤ 8 μm and D 50 1.0 - 10.0 μm, with a relative difference in BET specific surface area of ≤ 10% relative to the conventional electric / gas heating method.

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