A double membrane cover is a high-performance, integrated storage solution designed for anaerobic digesters. Engineered to ISO 9001 and international safety standards, these covers utilize a dual-layer system of PVC-coated polyester membranes to provide 100% airtight biogas collection and pressure regulation. Center Enamel engineers these covers with high-frequency (HF) welding and automated air-support systems, offering a 20-year service life and up to 99% methane retention for agricultural, municipal, and industrial biogas projects.
Feature | Technical Specification | Strategic Reliability Value |
Material Substrate | High-Tenacity Polyester (1100-1500 dtex) | Provides the structural "skeleton" for wind and snow loads. |
Coating Type | PVC with PVDF Lacquer | Enhanced UV resistance and self-cleaning properties. |
Methane Permeability | $le 400 cm^3 / (m^2 cdot d cdot bar)$ | Minimizes $CH_4$ loss and prevents localized odors. |
Flame Retardancy | B1 / M2 / DIN 4102-1 | Critical for fire safety in volatile biogas zones. |
Operating Pressure | 0.5 kPa to 5.0 kPa | Stable delivery to CHP units and boilers. |
Seam Technology | High-Frequency (HF) Welding | Molecularly fused seams stronger than the fabric itself. |
The outer membrane is kept permanently inflated by a dedicated low-wattage air blower. This creates a pressurized "buffer zone" that serves as the primary structural defense.
● Environmental Resistance: The dome shape effectively sheds rainwater and resists wind speeds up to 150 km/h.
● Thermal Insulation: The air gap acts as an insulator, helping maintain stable temperatures within the digester, which is vital for consistent microbial metabolic rates.
The inner membrane is the primary gas storage chamber. It inflates and deflates dynamically based on the volume of gas produced.
● Variable Storage: This allows the system to store gas during low-demand periods and release it during peak demand without requiring high-pressure compression.
● Airtight Integrity: Made from specialized gas-tight fabric, it prevents methane from leaking into the inter-membrane space.
Unlike traditional hot-air welding, Center Enamel utilizes High-Frequency (HF) Welding. This process uses electromagnetic energy to agitate the molecules of the PVC coating, creating a fused bond.
● Molecular Fusion: The resulting seam is completely gas-tight and resistant to the chemical degradation caused by Hydrogen Sulfide (H2S).
● Structural Durability: HF-welded seams maintain their tensile strength even under the constant expansion and contraction cycles of a fermentation tank.
● PVRV Safety Valves: Every double membrane cover is equipped with a Pressure Vacuum Relief Valve to prevent over-inflation or vacuum collapse.
● Level Monitoring: Integrated ultrasonic sensors track the height of the inner membrane, providing real-time data on biogas inventory.
● Explosion-Proof Blowers: The air-support system utilizes ATEX-certified blowers to ensure safety in hazardous gas environments.
Q: Can a double membrane cover be installed on a concrete tank?
A: Yes. While optimized for our Glass-Fused-to-Steel (GFS) tanks, they are frequently retrofitted onto concrete ring-walls using stainless steel anchor plates and specialized sealing gaskets.
Q: How does the cover handle extreme snow loads?
A: The air pressure in the inter-membrane space is automatically adjusted by the control system. In heavy snow conditions, the pressure is increased to ensure the dome maintains its structural integrity and sheds snow effectively.
Q: What is the maintenance requirement for a membrane cover?
A: Maintenance is minimal. Annual inspections of the air blowers, safety valves, and a visual check of the membrane skin are sufficient to ensure long-term performance.
