BACK TO TOP

Covers

Floating Covers

The Design Principles
Floating covers must function correctly at all operational water levels, hence their oscillating design. The key to achieving a well balanced, oscillating floating cover is to ensure that the tension of the cover is maintained at all times. Ballast lines bordered by floats must be configured correctly so that as the reservoir fills, the ballast lines the excess material and forms rainwater sumps. Rainwater which collects in these sumps is then pumped away.

Materials
As one of Australia's leading geomembrane lining companies with QA/QC accreditation (ISO9001:2000), Fabtech is committed to ensuring that all materials and workmanship reflect the stringent Quality Control conditions of such accreditation. Fabtech regularly assesses new and existing material suppliers and is able to  recommend the appropriate material for a particular application.

Installation Techniques
The secret to the successful installation and longevity of a floating cover lies in the ratio between thermal welding techniques carried out in-house and those on site. In-house welders differ from on-site welders due to the surface on which geomembrane panels are welded.

  • In a controlled factory situation, the factory floor allows the sheets to be set up with the exact overlap to weld the seam. Factory fabricated seams are 60mm wide, as opposed to on-site seams which are only 40mm wide.
  • On-site seams by necessity have large overlaps on the underside of the cover, resulting in the risk of impregnation of foreign matter and bacteria. Result = increased maintenance costs and risk of water contamination.
  • Quality Control. Destructive testing procedures during factory fabrication result in any possible anomalies being dealt with on a more efficient and immediate basis.
  • It is therefore highly advisable to limit site welding, thereby guaranteeing the integrity of the cover. This is especially applicable with fabricating material for inflation, as any seam failure can be a precursor to major failure. Site welds are much more likely to be contaminated.

 

 

High Rate Anaerobic Lagoon Covers Including Biogas Collection

An effluent anaerobic system requires a covered lagoon with an oxidation and settling pond. An anaerobic system provides many benefits.

  • Land surface area required is approximately half that of an aerobic system.
  • Required retention time is dramatically reduced
  • Because an anaerobic system has the first lagoon encapsulated, most odour problems do not exist.
  • With Fabtech’s design, methane gas is collected and co-generated, providing a tangible pay-back period. You can generate your own power to use and sell, dependent upon your needs.
  • The system ultimately pays for itself and contributes to profitability.

System Description
Anaerobic systems incorporate the use of flexible membrane covers to collect methane gas. This methane gas is collected from around the perimeter via a perforated piping system and then processed in either flaring or co-generation.

Specially designed weights and floats are attached to the cover membrane, which cause the horizontal ‘planes’ or ‘plates’ of the cover to be under tension in two directions. This tension eliminates slack in the cover, providing necessary stability across the surface, as well as clear drainage. Besides providing tension. the weights and floats define the precise location and size of rainwater sumps. At the bottom of the sumps, automatic submersible pumps are placed to discharge rainwater from the cover to wastewater outside the lagoon basin.

Due to its design, Fabtech’s floating cover system has the added benefit of being able to operate and accommodate any fluctuation in the level of the lagoon. The cover is also able to operate as a short term storage facility for any gas produced that can not be immediately processed.

Flotation and gas passages to the piping are manufactured from a closed cell polyethylene foam wrapped in polypropylene and attached to the underside of the cover. The cover is anchored to the top perimeter gas collection pipe.

The gas handling system includes design of the gas and delivery system, pressure control, strainer, fan, control panel, flare stack, flame supervision, instructions, manuals, commissioning and delivery to site, all as a complete package. The flare would be tested completely in the shop, then dismantled and shipped to site. Once installed, Fabtech’s Effluent Anaerobic Lagoon System is simple, environmentally friendly and cost-effective.

Bio-gas flare installed on an anaerobic effluent treatment pond.
An anaerobic digestion pond is covered with a membrane that captures methane produced during the digestion process. This methane and an assortment of other gases are then drawn (via a booster fan) through a gas train system and into an automatically controlled flare.

The flare has an interrupted pilot and flow system that senses the accumulated pressure in the pond and only operates when required. The flare control system also sends signals to the main treatment plant Scada control system to display any malfunctions that may occur.