● Scheduled CIP (solvent rinse + ultrasonics) with nitrogen blow-down for residue removal.
● Changeover “solvent displacement” method: rinse with a low-boiling solvent (e.g., ethanol), then condition with the new solvent three times; verify cleanliness by refractive index (deviation < 0.5%).
● Gel suppression: for gel-prone systems (e.g., PSf/DMAc), install ultrasonic oscillators in lines (20 kHz, 50 W) to disrupt nuclei; use low-speed tank agitators (10–20 rpm) to maintain homogeneity.
● Anti-holdup operations: maintain minimum line velocity ≥ 0.3 m/s during long runs; rising pressure/temperature indicates pre-gel—auto trigger cleaning and recirculate with feed for 3 minutes to prevent gelation.
● Zones: tank/line/metering pump/final filter–spinneret as independent control zones.
● Sensors: high-accuracy PT100 in each zone with 2oo3 or main/standby redundancy. Place measurement points on pipe outer wall, in the fluid (where possible), and at jacket medium outlet.
● Control algorithms:
● Cascade PID: master loop on dope temperature setpoint; secondary loop on jacket heat-medium temperature for fast disturbance rejection.
● Feedforward: include ambient temperature and flow changes as feedforward to pre-adjust control valves and suppress gradients.
● Gradient target: zone temperature deviation < ±0.5°C. Optimize insulation, minimize bare flanges, and use equal-length manifolds for balanced branch flows.
● Actuators:
● High-precision control valves or VFD-driven thermal fluid pumps for jacket oil/water flow and temperature. For spinneret proximity, use compact mold-temperature controllers with PID for point control.
● Compensation: when viscosity deviates, the control system finely adjusts fresh solvent addition or temperature setpoints to restore target viscosity. For phase inversion processes (e.g., PVDF hollow fibers), place inline pH and temperature sensors in the coagulation bath; adjust acid/base dosing or cooling flow automatically to stabilize the process.
● Model prediction: build a phase diagram prediction model based on solvent purity to forecast the new phase inversion window (e.g., demixing rate, bath conditions).
● Proactive adjustment: the system suggests or directly adjusts bath temperature/composition or spinning temperature to match the new thermodynamic environment and stabilize membrane morphology.
● Closed-loop calibration: integrate a mass flow meter (MFM) to compare set vs. actual in real time and auto scale for dosing error ≤ 1%.
● Auto-cal routine: every 8 h or at batch switch, run self-check (dry run + flow calibration) and record reports to meet GMP.
● Powder charging/storage: design to ATEX Zone 21; equipment protection level ≥ Ex tD A21 IP65.
● Solvent vapor areas (e.g., viscous liquid charging, solvent recovery): design to ATEX Zone 1; equipment rating ≥ Ex d IIB T4.
● Inerted feeding:
● Combustible powders: nitrogen inerting to O2 ≤ 8% (below MOC); install inline O2 analyzer (±0.1%); auto N2 make-up on exceedance.
● Combustible solvents: use explosion-proof motors, sealed pumps/valves; install flame arrestors; deploy combustible gas alarms + automatic exhaust (face velocity ≥ 0.5 m/s).
● Pressure relief and isolation: dust equipment (dryers, charging stations) with rupture discs (burst pressure 0.15 MPa); solvent lines with check valves to prevent flame propagation.
● Powder charging: fully enclosed charging stations (glovebox type, vacuum loading), enclosure rating ≥ IP65; dust control to ISO 14644-1 Class 6 (shop dust ≤ 10 mg/m³).
● High-viscosity liquid charging: use closed couplings (tri-clamp with PTFE seals) to prevent drips; enclosure rating ≥ IP67; no special dust control (only solvent vapor control).
Negative pressure and LEL:
● Powders (especially combustible powders like PE, PVDF): use negative-pressure charging (−0.02 to −0.05 MPa) to prevent dust dispersion.
● High-viscosity liquids with flammable solvents (e.g., NMP, DMAc): install LEL monitors (≤ 1% LEL accuracy) in charging area; on exceedance, trigger exhaust + alarm.
● Toxic solvents (e.g., DMSO): co-install toxic gas detectors; keep concentrations ≤ OEL.
● Terminal fine filtration: before the spinneret, install high-precision filters (sintered metal or cartridge filters, 10–50 μm or finer).
● Duplex filters in parallel: standard practice. One set runs while the other is standby. When ΔP reaches the setpoint, auto valves switch to the standby set without shutdown.
● Backflushing: configure automatic backwash for sintered elements using clean solvent or compressed gas, regenerating elements and extending life.
Summary:
● Coarse (50–100 μm): basket filter, manual cleaning (upstream).
● Fine (5–20 μm): duplex bag/cartridge filters, switch without stopping.
● Final (0.5–5 μm): high-pressure candle filters or self-cleaning backwash elements (e.g., Pall).
● Alarm and auto switch when filter ΔP > 0.3 MPa.
● Phase 1 (basic automation):
● Investment: replace manual valves with precision metering pumps + VFDs at critical nodes (dope, bore fluid); add sensors for flow, pressure, level.
● Return: enable basic monitoring and remote start/stop; reduce human error; immediately improve product consistency.
● Phase 2 (process automation):
● Investment: build standalone PLCs; implement PID control for key variables (flow, pressure) to automate regulation.
● Return: lower reliance on skilled operators; enhance efficiency and stability.
● Phase 3 (informatization and optimization):
● Investment: introduce MES for batch management/traceability; develop APC (advanced process control), e.g., auto fine-tuning across raw material lots.
● Return: refined production management, reduced raw material loss, higher prime yield.
Principle: prioritize automating tasks that are repetitive, quality-critical, labor-intensive, or hazardous.
● Logic control: configure production recipes in the MES. After feed prep, the system sends a start signal; upon batch completion, the equipment sends a changeover command to the feeding system for fully automatic batch switching.
● Status feedback: install pressure sensors and flow switches in feed lines. On anomalies (low pressure, flow interruption), immediately send a stop signal to prevent dry running or product defects.
● Gelation/crystallization risk: Excessive shear rate or long shear history (dead zones) can over-orient chains, triggering premature crystallization or physical gelation.
● Consequences: Microgels form, accumulating in channels or blocking orifices intermittently or permanently.
● Flow-path optimization: Streamlined, large-orifice, short-land, low-shear design to avoid local high shear.
● Temperature control: Precisely control temperature—key to gelation kinetics.
● Eliminate dead zones: Remove all stagnation regions to minimize shear history.
● Closed-loop control: acquire real-time temperature and viscosity data (via an inline viscometer or IR temperature sensor) and feed back to the pump servo drive to synchronize flow–ΔP–temperature adjustments, reducing flow fluctuation from ±5% to ±0.3%.
● For high-viscosity dope, add a preheating loop (hot water or steam) upstream of the pump to keep the fluid within the set temperature window and reduce feed instability caused by viscosity gradients.
● Gelation/crystallization risk: Excessive shear rate or long shear history (dead zones) can over-orient chains, triggering premature crystallization or physical gelation.
● Consequences: Microgels form, accumulating in channels or blocking orifices intermittently or permanently.
● Flow-path optimization: Streamlined, large-orifice, short-land, low-shear design to avoid local high shear.
● Temperature control: Precisely control temperature—key to gelation kinetics.
● Eliminate dead zones: Remove all stagnation regions to minimize shear history.
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