IEC’s Biogas Collection Covers

IEC’s Biogas Collection Covers: Unique Construction Considerations for Agricultural RNG Projects

By Mike Lever, IEC’s Technical Sales & Business Development Manager

Industrial & Environmental Concepts, Inc. (IEC) is a leading supplier and installer of biogas collection covers and flares for tanks and lagoons across Canada and the United States.

IEC recently completed two (2) floating biogas collection covers for manure storage for a large farming operation in southern Saskatchewan.

Separated between two sites of the same operation (roughly 40km apart), each manure storage cover for biogas recovery was unique.

One was a 130-ft diameter (39.6-m) concrete tank-based manure storage, while the other was a 58,000-ft2 footprint (approx 5,400-m2) earthen lagoon manure storage. Each of the two sites had different operational requirements as well, but both with the goal of capturing biogas for the purpose of destroying methane (by flaring) for carbon credits.

The round concrete storage pit (which we will call Site #1) was unique in that some moderate earthworks around the tank had to be performed in order to build a long ramp to “launch” (or pull) the new cover up to the top of the tank wall and float it across the top surface.

Once positioned, the cover was mechanically fastened and sealed to the concrete tank wall and tested for gas tightness.

Due to mechanical mixing equipment restrictions inside the tank, it would be operated at a constant level so the cover would not be damaged should the liquid level drop. This would be operationally challenging for the farm but with some additional level management controls, the owner was able to satisfy the requirements.

The earthen storage lagoon (which we will call Site #2) was unique in that the basin would be operated from full to empty year-round and occasionally mixed using a third-party patented oxygen (O2) injection mixing system.

This is unusual in that oxygen is not recommended to be mixed with biogas under the cover as it can create an unwanted air-to-methane ratio, thus producing a potentially explosive mixture. However, the amount of oxygen was so negligible that it would still be less than 1%. The owner continuously monitors for oxygen under the cover and makes mixing adjustments when necessary to maintain <1% oxygen at all times.

Mixing is required to ensure solids remain in suspension and can be pumped out when needed during the year.

Both floating biogas covers were manufactured using 80mil LLDPE (linear low-density polyethylene) with enhanced UV inhibitors to prolong service life.

For more information, read our Canadian Biogas Magazine.