Q&A: Learn About The Tecon Biogas Storage System

The Tecon double-membrane biogas storage system offers a flexible solution that can be tank- or ground-mounted and is quick and cost-effective to install.
Q&A: Learn About The Tecon Biogas Storage System
The biogas storage systems can be slab-mounted on the ground.

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As biogas gains favor as a valued renewable fuel, clean-water plants need effective ways to collect and store it. Using the gas to heat processes and generate electricity saves money and keeps a potent greenhouse gas out of the atmosphere.

A virtue of any biogas storage system is the ability to expand and contract as gas production and usage fluctuate. Metal floating covers have that capability, as do inflatable membrane-based containers. Infilco Degremont (SUEZ ENVIRONNEMENT) offers the Tecon biogas storage system, which uses a double-membrane design.

An outer membrane provides protection and is kept under pressure to withstand wind, snow loads and climate extremes. An inner membrane expands and contracts as biogas is generated and consumed. The membranes can be mounted to a tank or to on-the-ground infrastructure, such as a concrete pad.

Jongmin Kim, biosolids application engineer, and Sudhakar Viswanathan, biosolids product manager, talked about the technology in an interview with Treatment Plant Operator.

TPO: What need was addressed by bringing this technology to the market?

Kim: The Tecon system was invented by an Austrian researcher who was exploring pressurized covers using plastic fabric as an alternative to fixed or floating metal covers. The intent is to use less material while serving the purpose just as well or better.

Viswanathan: In the past, most gas containment systems were single-layer, so the barrier between the biogas and the atmosphere was just one layer of metal or plastic. The concept with the Tecon cover is to have a double layer of protection. The outer membrane withstands the elements, and the inner membrane contains the biogas within the system.

TPO: Is this system only for new installations? Or can it be retrofitted?

Kim: It is suitable for both, and it can be retrofitted to any shape of digester or other gas collection system. A common perception is that this is just a giant spherical balloon, but in reality we can do a square, a triangle or any shape a customer wants.

Viswanathan: These covers are built in a manner similar to the way fabric is used in designing structures like stadiums. You can build it to any shape you want. If a customer has a long, rectangular lagoon or an oval-shaped lagoon, we can build to the existing footprint. The shape is only limited by the imagination.

TPO: What do the two layers of material consist of?

Viswanathan: It is a thick, woven polyester fabric with very high tensile strength. We use fabric of the same thickness for both the outer and inner membranes, both for safety reasons and because our covers are designed to meet very stringent regulations in Germany and Austria. We want to bring the same level of detail and the same level of safety to projects worldwide. In case of damage on the outer membrane, we want the inner fabric to be able to withstand external forces just as if both membranes were intact.

TPO: Are different membrane colors available to fit the appearance of individual facilities?

Viswanathan: The constituents in biogas can discolor a membrane. For that reason, we give the inner membrane a yellow tint, so that if it were to be exposed, it would not give the appearance of being degraded. We can supply the outer membrane in any color the customer wants.  

TPO: How does this double-membrane system function as the containment fills with biogas?

Kim: A blower forces air from outside in between the inner and outer membranes, so that externally it appears that the vessel is always full. A manually weighted check valve regulates the pressure, so that the pressure in the space between the membranes is always constant. As biogas pressure builds up, the inner membrane fills more of the space. The blower operates continuously, so that air containing methane or sulfurous gases is constantly blown out.

Viswanathan: The fluctuation of biogas production in the digester doesn’t affect the operation or the appearance of the system. We don’t use any external instrumentation to control the blower to turn the air on and off. The only instrumentation we have is on large membranes, where we use a level sensor to detect the extent to which the inner membrane is full. That enables the customer to determine how best to use the biogas that is available.

TPO: Is this a cost-competitive gas storage solution?

Viswanathan: The capital cost would generally be significantly lower than for a metal cover. The maintenance cost over a 20-year period would also be less.

TPO: What maintenance does this system require?

Viswanathan: The main moving part is the blower, which requires routine maintenance. The water- and glycol-based check valve also needs to be inspected periodically. Once every 10 to 15 years, the membrane should be inspected to see if it is deteriorating, and if so, it needs to be replaced.

Kim: Minimum membrane life is approximately 15 years in geographic areas with high UV light intensity, and 20 years in low-UV areas.

TPO: What is involved in membrane system installation?

Viswanathan: Typically, we can install a cover in less than a week. It takes a supervisor and a couple of laborers. If the cover is extremely large, we might require a crane. In general, installation is rather easy. We just need to prepare the surface on which to mount the membranes. If a gas holder is ground-mounted on a concrete foundation, a bottom membrane is required to seal the gas storage system to the foundation.

TPO: What is your experience with this technology in actual applications?

Viswanathan: We have more than 2,000 installations of these dual-membrane covers worldwide. It’s a very well accepted technology. Its application is not limited to anaerobic digesters. It can also be used at landfills with biogas recovery, industrial wastewater treatment plants, agricultural biogas recovery facilities and activated sludge treatment systems where the customer needs to limit the amount of oxygen escaping from the process.   



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