Common problems with structural membranes in biogas plants

The structural membrane in the biogas plant is a key component, and its performance directly affects the biogas fermentation efficiency and the service life of the equipment. The following are the common problems, causes and solutions of structural films in use:
1. Aging and damage of membrane materials
Problem manifestation
Cracks, hardening and brittleness on the surface of the membrane, or holes causing air leakage.
genesis
Ultraviolet irradiation: Long-term exposure to sunlight will break the polymer chain in the membrane material.
Chemical corrosion: Hydrogen sulfide (H₂S), organic acids and other substances in biogas corrode membranes.
Mechanical wear: Scratched by sharp objects during installation or maintenance, or friction of internal materials.
Workaround
Choose weather-resistant materials: Use PVC, PVDF, or fluoroelastomer membranes with UV-resistant additives.
Take protective measures: the surface of the film is covered with a shading layer, or the equipment is designed as a closed structure.
Regular inspection and maintenance: repair the damage with special patch glue in time, and replace the membrane material when it is serious.
2. Expansion or contraction of the membrane
Problem manifestation
The membrane body is bulging, wrinkled, or shrinking in size due to uneven stress, resulting in seal failure.
genesis
Temperature change: large temperature difference between day and night or high fermentation temperature (such as medium temperature fermentation above 50 °C), thermal expansion and contraction of the membrane material.
Air pressure fluctuations: The amount of biogas produced is unstable, and the air pressure in the membrane fluctuates, resulting in repeated stretching.
Workaround
Optimized design: the membrane structure reserves a certain expansion and contraction margin, or adopts an adjustable tensioning device.
Control of operating parameters: Stabilize the fermentation temperature through the temperature control system, and install a pressure regulator to balance the air pressure.
Choose a highly elastic material: use polyester fiber reinforced film or silicone rubber type elastic film.
3. The membrane seal fails
Problem manifestation
Air leakage at the connection between the membrane and the equipment frame and pipeline, resulting in biogas leakage or air ingress.
genesis
Installation process problems: uneven application of sealant, or insufficient bolt tightening strength.
Material aging: The sealant hardens, cracks, and loses its elasticity.
Thermal expansion and contraction: Temperature changes cause gaps between the seal and the film.
Workaround
Standardized installation process: use special sealant (such as silicone glue), and tighten the bolt evenly diagonally.
Replace seals regularly: Check the sealant every 1-2 years and replace them in time after aging.
Add buffer structure: Design flexible transitions (e.g. rubber flanges) at the joints.
Fourth, the surface of the membrane is fouled and blocked
Problem manifestation
Sludge, microbial colonies or inorganic salt crystals are attached to the surface of the membrane, which affects the gas permeability.
genesis
Fermentation broth splashing: The liquid splashes onto the inside of the membrane during stirring, and dirt forms after drying.
Gas impurity deposition: Dust and sulfide in biogas combine with moisture to form a precipitate.
Workaround
Optimize the structure of the equipment: set up a splash-proof baffle on the inside of the membrane, or adopt an internal circulation spray cleaning system.
Regular cleaning: Rinse the membrane surface with a high-pressure water gun (water temperature ≤ 60°C) or soak with a neutral detergent.
Pre-treatment gas: Install a filter at the biogas outlet to reduce the entry of impurities into the membrane area.
5. The uneven force of the membrane body leads to tearing
Problem manifestation
Membranes are torn at support structures or fixation points, especially in the corners and edges.
genesis
Design defects: Sharp edges in the support frame, or uneven distribution of membrane tension.
Abnormal pressure shock: biogas explosion or sudden overpressure, resulting in excessive local stress of the membrane.
Workaround
Improve the structural design: the edge of the support frame is rounded, and the grid support is used to reduce the stress concentration.
Install safety devices: set up pressure relief valves and explosion-proof membranes to prevent sudden rise in air pressure.
Regular stress detection: Check the stress distribution of the membrane through the thermal imaging camera and adjust the tension in time.
Sixth, the air permeability of the membrane decreases
Problem manifestation
Under the same conditions, the biogas production decreases, or the air pressure difference between the inside and outside of the membrane increases.
genesis
Membrane pore blockage: Fine particles or microbial membranes cover the membrane pores, blocking the passage of gases.
Material deterioration: The membrane material has been eroded by acid and alkali for a long time, and the pore structure is damaged.
Workaround
Choose a hydrophobic membrane, such as PVDF, to reduce moisture and sludge adhesion.
Chemical cleaning: Rinse membrane pores with a solution of dilute acid (e.g., citric acid) or oxidizing agent (e.g., sodium hypochlorite).
Periodic backflushing: high-pressure air is introduced from the outside of the membrane to remove the blockage in reverse.
7. The membrane body is hardened and brittle in winter
Problem manifestation
In a low-temperature environment, the film becomes brittle, and cracks appear when the film is slightly stressed.
genesis
Insufficient low temperature resistance of the material: the elasticity of ordinary PVC film decreases significantly below -10°C.
Workaround
Choose low-temperature resistant films: such as cold-resistant PVC films with plasticizers, or switch to EPDM rubber films (temperature resistant - 40°C~120°C).
Equipment insulation: Wrap insulation cotton on the outside of the membrane, or circulate with hot water.
Control the operating temperature: In winter, the fermentation tank is maintained at a medium temperature (about 35°C) to reduce the temperature difference between the inside and outside of the membrane.