.Reverse Osmosis Membrane Process Design Scheme for Glass Production

1.0 Design Basis and Objectives

• Water Source and Use: Uses municipal tap water or groundwater as the raw water source to produce high-purity water required for various stages of glass manufacturing (e.g., float glass original sheet cleaning, electronic glass substrate cleaning, optical glass batching, coating processes).

• Typical Raw Water Characteristics:

  • Total Hardness (as CaCO₃): 150-300 mg/L

  • Silica (SiO₂): 10-25 mg/L

  • Total Dissolved Solids (TDS): 300-800 mg/L

• Product Water Core Requirements:

  1. Low Hardness: ≤ 0.1 mg/L (to prevent water marks and spots on glass surfaces)

  2. Low Silica and Boron Content: SiO₂ ≤ 0.1 mg/L, Boron (B) ≤ 0.01 mg/L (to prevent deterioration of glass optical properties)

  3. Low Conductivity: ≤ 5 µS/cm (for standard glass cleaning), ≤ 1 µS/cm (for high-end electronic/optical glass)

  4. High Stability: Continuous and stable supply with water quality fluctuation < ±10%

2.0 Core Process Route: Two-Stage Reverse Osmosis + Advanced Polishing

Addressing the special sensitivity of glass production to silica and boron, this scheme adopts the "Enhanced Pretreatment + Two-Stage RO + Selective Post-Treatment" process. The diagram below illustrates the complete treatment process from raw water to ultrapure water:

3.0 Detailed Explanation of Key Process Units

3.1 Enhanced Pretreatment System

• Multi-Media Filtration: Uses dual-layer media (quartz sand + anthracite) to remove particles ≥10µm, ensuring effluent turbidity <0.5 NTU.

• Activated Carbon Filtration: Employs 12-40 mesh coconut shell activated carbon to effectively adsorb residual chlorine (ensuring effluent residual chlorine <0.01 mg/L), protecting RO membranes.

• Antiscalant Dosing: Uses specialized anti-silica scaling inhibitor to control the Langelier Saturation Index (LSI) <1.0, preventing SiO₂ polymerization and deposition on membrane surfaces.

3.2 Primary Reverse Osmosis System

• Membrane Element Selection: Polyamide composite membranes, fouling-resistant type, single element salt rejection ≥99.5%.

• Operating Parameters:

  • Recovery Rate: 70-75%

  • Operating Pressure: 1.0-1.5 MPa

  • Silica Rejection: ≥95%

  • Boron Rejection: ≥85%

• Configuration Features: Uses a 2:1 array configuration, equipped with VFD-controlled high-pressure pumps and an online flushing system.

3.3 Secondary Reverse Osmosis System (Key for Deep Boron/Silica Removal)

• pH Adjustment: Dosing NaOH into the primary permeate to raise pH to 9-9.5.

  • Technical Principle: Under alkaline conditions, boron exists as B(OH)₄⁻, and SiO₂ solubility increases while its surface charge changes, significantly improving RO membrane rejection of boron and silica.

  • Control Precision: pH fluctuation range ±0.2.

• Membrane Element Selection: High boron-rejection membrane elements, achieving boron rejection ≥95% at pH 9.

• Operating Parameters:

  • Recovery Rate: 85-90%

  • Operating Pressure: 1.2-1.8 MPa

  • Permeate Conductivity: ≤10 µS/cm

  • SiO₂ Concentration: ≤0.5 mg/L

  • Boron Concentration: ≤0.1 mg/L

3.4 Terminal Polishing System

• Electrodeionization (EDI) or Mixed Bed:

  • EDI (Continuous Electrodeionization): Reduces conductivity to ≤0.1 µS/cm without acid/base regeneration.

  • Mixed Bed Ion Exchange: Serves as backup or supplemental polishing, producing water with resistivity ≥10 MΩ·cm.

• TOC UV Destruction: 185nm + 254nm dual-wavelength UV lamps reduce TOC to ≤50 ppb.

• Polishing Mixed Bed (Optional): For ultra-high-end requirements like electronic glass, producing water with resistivity ≥18.2 MΩ·cm.

• Nitrogen Blanketing System: High-purity water storage tank uses nitrogen blanketing to prevent CO₂ dissolution and resistivity drop.

4.0 Special Pollutant Control Strategy

5.0 System Intelligent Control and Operation Optimization

5.1 Fully Automatic Control System

• PLC + SCADA Architecture: Siemens S7-1500 series PLC with WinCC SCADA system.

• Key Control Loops:

  1. Precise control of secondary RO feed pH (PID adjustment, accuracy ±0.1).

  2. Automatic adjustment of system recovery rate.

  3. Linkage control of antiscalant dosing with feed water SDI.

5.2 Intelligent Cleaning System

• Fouling Early Warning Model: Based on TMP, normalized flux, and ΔP.

• Cleaning Decision System:

  • Silica Fouling: pH 12 alkaline cleaning + specialized silica scale cleaner.

  • Biofouling: pH 11.5 alkaline cleaning + non-oxidizing biocide.

  • Inorganic Scaling: pH 2-3 acidic cleaning (citric acid or hydrochloric acid).

5.3 Energy Optimization Design

• Energy Recovery Device: Install PX pressure exchanger on primary RO concentrate discharge, saving 25-35% energy.

• Variable Frequency Drive (VFD) Control: All pumps equipped with VFDs for automatic adjustment based on flow demand.

• Heat Recovery System: Utilize waste heat from RO concentrate to preheat pretreatment water (in winter).

6.0 Technical and Economic Indicators

7.0 Installation and Commissioning Key Points

7.1 Special Installation Requirements

• Piping System: 316L stainless steel pipes, internal electropolished (Ra ≤0.6 µm), argon-protected welding.

• Storage Tank Material: SUS316L stainless steel + nitrogen blanketing + vent filter (0.22 µm).

• Installation Environment: Cleanroom (ISO Class 7), temperature 20±2°C, humidity ≤60%.

7.2 Commissioning and Verification Procedure

1. Pretreatment System Verification: SDI₁₅ < 3, residual chlorine < 0.01 mg/L.

2. RO System Performance Test: 72-hour continuous operation, meeting targets for salt rejection, recovery rate, and pressure differential.

3. Boron/Silica Removal Verification: Test removal efficiency under different pH conditions.

4. System Integration Test: 72-hour continuous operation of the entire system with stable and compliant water quality.

7.3 Operation and Maintenance System

• Preventive Maintenance Plan:

  • Daily: Online instrument calibration check.

  • Weekly: Cartridge filter pressure differential check.

  • Monthly: Membrane system performance normalization analysis.

  • Quarterly: Integrity testing, disinfection.

• Critical Spare Parts List: RO membrane elements (2 sets), EDI modules (1 set), UV lamps (10% spare), precision filter cartridges (20% spare).

8.0 Environmental and Safety Design

8.1 Environmental Protection Measures

• Concentrate Reuse: 30-40% of RO concentrate reused for site landscaping and flushing.

• Chemicals: Use environmentally friendly antiscalants and cleaning agents.

• Noise Control: Equipment room noise <75 dB(A).

8.2 Safety Design

• Electrical Protection: Overall IP54 protection, explosion-proof design for Zone 2 areas.

• Chemical Safety: Leak-proof design for acid/alkali storage areas, emergency shower/eyewash stations.

• Structural Safety: Storage tank seismic design (seismic fortification intensity of 7 degrees).

9.0 Scheme Advantages Summary

1. Deep Boron/Silica Removal Technology: Achieves deep control of boron ≤0.01 mg/L and silica ≤0.1 mg/L through high-pH operation and specialized membrane combinations.

2. Intelligent Operation System: Predictive maintenance based on big data reduces unplanned downtime by over 50%.

3. Modular Design: Flexible expansion based on capacity requirements, supporting phased investment.

4. Green and Energy Efficient: Comprehensive energy consumption <2.5 kWh/m³, water recovery rate ≥70%.

5. Full Lifecycle Service: Provides a complete solution from design and installation to digital operation and maintenance.

This scheme, through optimized pretreatment processes, adoption of high boron-rejection RO membranes, precise pH control, and other key technologies, can stably produce ultrapure water meeting the requirements of various glass manufacturing processes. It is particularly suitable for high-end manufacturing fields such as float glass, electronic glass, photovoltaic glass, and optical glass.