Steel & Membrane Digester Covers & Gas Storage

Ovivo provides a variety of steel and membrane digester covers to suit the specific needs of our partners.

Steel Covers

Our steel covers are constructed in the shape of a dome, offering maximum strength and structural integrity. They are an affordable and durable option for anaerobic digesters and biogas containment, and are available for tank diameters of various sizes. Each cover is custom engineered to meet the specific requirements of the project.  From the simple and cost-effective Fixed Steel Cover for primary or first stage digesters, to the buoyant Gasholder Steel Cover for digester gas storage, we have a cover to meet the needs of any biosolids facility. Our designs include the following configurations: Fixed, Gasholder, HydroSeal® type and Buoyant steel cover.

Other features and benefits of a steel cover include:

• Simple and rugged construction, designed for a life span of 30+ years
• Radial beams and prefabricated EZ-RECT™ roof system sections for easier and faster field installation
• Easy to insulate using commonly available roofing materials
• No moving parts for simplified maintenance
• Flexible storage capacities
• Compatible with all our available mixing systems to ensure optimal anaerobic digestion
• U.S.-based manufacturing
• Over 1,300 installations worldwide

Membrane Gasholder

Our Ultrastore™ membrane gasholder cover is the only effective and efficient solution for transforming waste into energy. It is simple to set up, operate and monitor, and is custom-designed in both shape and configuration that no other company or technology can approach. The PVC-coated, polyester-fibre fabric membranes are engineered to resist punctures, wind and weather.

Key features and benefits of this system include:

• Cut, welded and tested in the U.S. allows a quick turnaround
• Typically take less than one week to install and put into operation
• Storage availability indicator
• Easy maintenance

Ovivo’s digester steel covers are radial-beam designed to be erected quickly and efficiently on site and offer a rugged structural design. A thrust ring is installed at the periphery of each cover to absorb all loads without transmitting excessive forces to the concrete digester wall. During erection, the cover is supported by radial beams attached to a centre ring and the thrust ring which add strength to the complete unit.

• Fixed Steel Cover (Type F) – the Type F cover is the most economical steel cover. The main application is on digesters with constant water level (primary or first stage digesters). The Fixed covers can be sealed against the tank to combat odours. For this design, the side sheet should be extended below the minimum liquid level.
• Gasholder Steel Cover (Type GV) – the Type GV uses the radial beam design structure with added side sheet and ballast for digester gas storage. Submerged ballast blocks are used to maximise cover stability and maintain adequate gas pressure. The design includes a vertical guide arrangement with guides attached to the tank wall. Guide devices, spanning from the top to the bottom of the cover side sheet, are engaged to stabilise the cover.
• Hydroseal Steel Cover (Type GVL) – the separate launder and liquid seal between the digester tank and the cover eliminates gas and VOC emissions, improves service access and improves the maintenance access. This design allows variable sludge storage capabilities since the side sheet operates independently of sludge storage in clean area. No components come in contact with the sludge.
• Buoyant Steel Cover (Type B) – the Type B uses the radial beam design structure including a peripheral buoyant chamber. The cover floats directly on the digester contents. Precast concrete ballast blocks are placed to maintain a specified gas pressure. A major portion of the buoyant volume which keeps the cover afloat is located at the cover periphery. This feature provides an excellent resistance to tipping. The slide guide system will provide vertical movement without rotation or binding.
• Ultrastore membrane cover – The special stainless steel profiles anchor directly into the concrete base, while the flanges keep the membranes fixed to the ground and under pressure along the external perimeter of the gasholder. They are designed with inner gas and outer air membranes that provide more flexible storage capacities than traditional steel covers. The outer air membrane acts as an air-tight chamber that is kept in constant traction through a system of continuous fans and filters. This continual pressure of air keeps the inner gas membrane at the same working pressure, independent of the biogas quantity being stored. This allows the gas membrane to hold varying volumes of gas, while the outlet flow rate remains constant for steady, stable operations of a waste-to-energy system.

The EZ-RECT cover erection system is a feature that Ovivo offers to reduce the amount of field welding required during installation. Ovivo provides the digester cover with cover plate/radial beam sections pre-assembled and finish welding in the shop to facilitate the erection of the cover. Each assembly consists of two beams and one cover plate. Cover erection is completed in five steps:

1. Side sheet assembly
2. Centre ring and erection beam installation
3. EZ-RECT cover plate assembly installation
4. Remaining cover plate installation
5. Manholes, spools, tubes, etc., installation