BM-039|HIGH-PERFORMANCE FILTER CLOTH SPECIFICATION FOR SECURITY FILTRATION Engineered Polishing Filtration Media for Alumina Refinery Security Filtration (Bayer Process) Author: Rajendra Kunwar – Alumina Technology Specialist and Bayer Process Expert

 

1. Executive Summary & Application Scope

Application Context: In the Bayer process of alumina refining, green liquor security filtration (polishing filtration) is a critical step occurring immediately prior to precipitation. The primary objective is to lower suspended fine solids (red mud residues) in pregnant liquor to under 10–15 mg/L. Specification BM-039 details the high-performance synthetic filter cloth engineered to endure extreme alkaline conditions, elevated thermal loads, and heavy mechanical stress in Pressure Decanter, Kelly, or Vertical Leaf Filters.

2. Material & Polymer Specifications

Selection of polymer and yarn structures for Specification BM-039 focuses on maintaining structural integrity, resistance to caustic degradation, and dimensional stability over extended thermal cycles.

Property	Specification Standard	Technical Parameter / Benchmark
Base Polymer	100% High-Tenacity Polypropylene (HT-PP) / PTFE Coated Option	Resistant to 100-250 g/L NaOH at elevated temperatures
Maximum Operating Temp	Continuous: 105°C | Peak Spike: 120°C	Zero thermal degradation under standard operating liquor temp (95-105°C)
Yarn Architecture	Multifilament Warp / Monofilament Weft Combination	Combines high particle retention with low cake-sticking and easy discharge
Chemical Resistance	Caustic/Alkaline: Excellent (pH 11–14) Acid Wash: Resistant to 5-10% HCl/Oxalic acid	Tolerates periodic chemical descaling and acid wash cycles without fiber hydrolysis

 

3. Physical & Mechanical Construction Parameters

Technical Metric	Standard Test Method	Target Technical Value
Weave Pattern	ISO 9354	2/2 Satin Weave or Modified Twill (Satin for smooth release)
Fabric Weight	ISO 3801 / ASTM D3776	450 - 550 g/m² (Nominal 500 g/m²)
Air Permeability	ISO 9237 (@ 200 Pa)	15 - 30 L/dm²/min (or 5 - 10 CFM @ 125 Pa)
Tensile Strength (Warp / Weft)	ISO 13934-1	Warp: ≥ 2400 N/5cm | Weft: ≥ 1800 N/5cm
Elongation at Break	ISO 13934-1	Warp: < 15% | Weft: < 12% (Thermoset calendered)
Mean Pore Size (Bubble Point)	ASTM E1294 / Capillary Flow	10 – 18 µm (Optimized for tricalcium aluminate precoat holding)

 

4. Filtration Performance & Operational Criteria

Precoat Compatibility: BM-039 is specifically engineered to form a robust base for filter aid precoat materials (such as Tricalcium Aluminate / TCA or Synthetic Silicates) while maintaining high flow velocity and preventing medium blinding.

Filtrate Clarity & Throughput: Ensures filtrate clarity of < 10 mg/L total suspended solids (TSS) under standard operating liquor flow rates (0.8–1.4 m³/m²/h). High mechanical resistance prevents yarn displacement under hydraulic pressure pulses during filter backwashing.

Cake Release & Anti-Blinding: Thermally calendered surface treatment provides excellent cake release properties during the automatic backwash or mechanical cake discharge phase, minimizing residual mud buildup.

5. Fabrication, Edge Treatment & Quality Assurance

Edge Sealing & Fabrication: Ultrasonic cutting and heat-sealed edges prevent fiber shedding into the clean liquor stream. Reinforcement strips along stitch lines ensure zero tearing under high differential pressure (up to 6.0 bar).

Quality Standards: Each production batch undergoes rigorous quality control testing for mass per unit area, air permeability, break strength, and bubble point pore size distribution, fully compliant with ISO 9001:2015 standards.

 

CETI ENTERPRISES, INDIA

CETI Enterprises supports alumina industry professionals through technical training, process audits, calcination performance assessment, energy optimization, process troubleshooting, equipment design review, debottlenecking and refinery improvement programmes. For further details please visit our website at https://ceti.co.in

About the Author: Rajendra Kunwar is Bayer Process & Alumina Technology Specialist. Through CETI Enterprises, he offers expert technical consultancy in customized online / onsite team training, process for production of specialty grade ATH & Alumina, efficiency enhancement, quality improvement, energy reduction, cost reduction, troubleshooting and plant debottlenecking. To explore how we can support your plant operations or upcoming expansion, please contact us at rajendra@ceti.com.