Process Water filtration for raw material pre-treatment, bleaching, wastewater treatment

The pulp and paper industry achieves the following through advanced filtration technologies:

Resource Recovery (reuse rates of fibers, fillers, and chemicals >90%); Water Conservation and Emission Reduction (water consumption per ton of paper produced reduced from 50 m³ to 5–10 m³);

Quality Improvement (reducing coating defects, color inconsistencies, etc.).

Raw Material Pre-treatment and Pulping Stage

1.Bark and Impurity Removal:

· Application: Removal of sand, bark fragments, and other impurities from wood raw materials.

· Filtration Products & Process:

1. Drum Screen: For initial removal of large particles (aperture size 5–20 mm) in combination with high-pressure water rinsing systems, achieving separation efficiency greater than 95%.

2.Black Liquor Filtration and Recovery:

· Challenge: Black liquor after pulping contains lignin, residual alkali, and fibers, requiring the recovery of chemicals and biomass energy extraction.

· Filtration Products & Process:

o Multi-stage Filtration: Pre-filtration followed by ceramic membrane ultrafiltration to remove lignin (retention rate >90%) and improve alkali recovery to 85%.

Bleaching Stage Chemical Purification

1.Bleaching Agent Filtration (ClO₂, H₂O₂):

· Application: Removal of particulate impurities from bleaching agents to prevent nozzle clogging and ensure uniform pulp color.

· Filtration Products & Process:

o Polypropylene Folding Filter Cartridges (1-5 μm): Designed for oxidation resistance and low-pressure drop, with chemical compatibility meeting ASTM E2196 standards.

2.Bleaching Wastewater Treatment:

· Objective: Removal of chlorinated organic compounds (AOX), colorants, and suspended solids from wastewater.

· Filtration Products & Process:

o Activated Carbon Adsorption + Ultrafiltration (UF): UF membranes (molecular weight cutoff at 10 kDa) to reduce AOX by over 80%, ensuring compliance with wastewater discharge standards (GB 3544-2008).

Paper Machine White Water Circulation System

1. Fiber and Filler Recovery:

· Pain Point: White water contains short fibers and calcium carbonate fillers, leading to resource waste if directly discharged.

· Filtration Products & Process:

o Disc Filter: Utilizes vacuum suction to separate fibers, with recovery rates exceeding 98%.

o Microfiltration Membranes (0.1–1 μm): To capture fine fillers like TiO₂, which can be reused in the coating process.

2. Colloids and Soluble Materials Control:

· Solution: Use of dissolved air flotation (DAF) combined with precision filters (10–50 μm) to lower white water COD to <200 mg/L, ensuring closed-loop circulation.

Coating Chemicals and Pigment Filtration

1. Coating Liquid Purification:

· Application: Removal of agglomerated particles (like latex, starch) in coatings to ensure uniform application.

· Filtration Products & Process:

o Bag Filters (5-25 μm): For removing coating contaminants and maintaining consistency.

o Magnetic Filters: To capture ferromagnetic impurities from coating liquids.

o Inline Particle Counter: Real-time monitoring to ensure the quality of coating material.

2. Nano-pigment Dispersion:

· Innovation: Dynamic Shear Filtration technology to break pigment particles down to the nanoscale (<100 nm), enhancing paper gloss and finish.

Wastewater Treatment and Reuse

1. Comprehensive Wastewater Treatment:

· Process Flow:

1. Primary Treatment: Grating and sedimentation tanks to remove large particles.

2. Biological Treatment: Activated sludge method combined with MBBR (Moving Bed Biofilm Reactor) for BOD/COD degradation.

3. Advanced Treatment: Reverse Osmosis (RO) and ozone oxidation for water recovery, achieving desalination rates above 95%.

· Filtration Products & Process:

o RO Membranes: High-efficiency filtration for water reuse in production processes.

2. Sludge Dewatering:

· Technology:

o Belt Filter Press: Reduces sludge moisture from 98% to 75-80%.

o Plate and Frame Filter Press: Further reduces moisture to 60%, cutting down sludge volume by 70%.

Specialty Paper and Functional Additive Processing

1. Functional Coating Filtration:

· Case Study: Waterproof paper production requires filtration of un-emulsified particles in silicone oil emulsions.

· Filtration Products & Process:

o Sintered Stainless Steel Filters (3 μm): To prevent pinhole defects in the coating layers.

2. Nanocellulose Extraction:

· Technology: High-pressure homogenization combined with ceramic membranes (50 nm) to extract nanocellulose from waste paper pulp (diameter <20 nm), suitable for high-strength packaging materials.