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Anaerobic Digester Gas Leak Sealing

Corroless Eastern have been involved in the Anaerobic Digestion Industry since 2014. During this time we have been frequently asked to help clients with sealing gas leaks.

CASE STUDY
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Gas leaks present a significant challenge to Anaerobic Digestion plant operators for the following reasons;

  1. SAFETY – leaking gas can present a significant explosion risk and we have encountered situations where clients have been forced to turn off critical equipment such as pumps and mixers due to gas leaks in close proximity.
  2. ENVIRONMENT – Methane is a green house gas and 80 times for potent than Carbon Dioxide over a 20 year period. Plant operators face regulatory compliance to minimise any potential harm from gas leakage.
  3. LOSS OF PROFITS – the gas leaking is the product from anaerobic digestion and it leaking into atmosphere is equivalent to throwing money down the drain. Any repairs made will normally quicky pay back based upon the gas retained.

Identifying the Leaks

Often leaks from anaerobic digesters and associated vessels are identified by survey using optical gas imaging cameras producing information such as that shown below. Working with clients we use this information to develop a sealing strategy.

Digester Gas Leak 01
Digester Gas Leak 02

Gas leaks are also commonly identified using gas detectors/sniffers, but also as simply as observing bubbling through expansion joints in wet weather or even simpler the recognisable odour of Hydrogen Sulphide.

Gas leaks can sometimes also show as areas of sulphur build up or staining.

Often the point of gas egress from the anaerobic digester is not the source of the gas leak, with the gas emanating from secondary mastic weather sealing, but the leak originating from a hole in the internal lining.

A common cause of gas leaks is where anaerobic digesters have been lined using HDPE cast in type liners. These are not bonded to the concrete in the same way as liquid applied linings, but instead anchored into the concrete with tangs.

This creates an interstitial space in which biogas can move until it finds a point to exit the  anaerobic digester. The challenge with these type of liners is that at joins between sheets they must be thermoplastic welded. A single pin hole in a weld is a potential gas leak.

Digester Gas Leak 03

The Challenge

A particular challenge with sealing digesters externally is that any sealing solution being applied is subjected to a negative/back pressure. If the anaerobic digester is live this also means than any solution that requires on a bond must gain adherence and form a seal before being overwhelmed by this pressure.

Commonly we receive enquiries where operators have attempted to fix leaks using sealants and mastics, but have found that the gas pressure simply pushes the material out or forces gas through.

The works must also be able to be undertaken without use of any ignition sources that could risk an explosion.

Sealing Solutions

We have developed two broad approaches for sealing leaking anaerobic digesters. One which can be undertaken with the anaerobic digester live and the second which requires the anaerobic digester to be shut down.

1. Live Leak Sealing

 This approach makes use of a Hydrophilic polyurethane injection grout that is injected into interstitial spaces and cracks. Upon mixing and reacting with moisture it expands up to 20 times, forming a pressure tight seal that does not rely on adhesion. The stages of this process are shown below. Note all videos were made using an intrinsically safe camera.

Identify and pin point leaks using gas detection equipment.

Where secondary weather sealing exists make a penetration using non sparking tools to create a point where the polyurethane grout can be injected into.

Load, insert and dispense polyurethane grout into the interstitial space via the previously made penetration. The grout is then allowed to react and post cure the area checked for leaks. If necessary the process can be repeated until the gas leaks are sealed or reduced.

2. Non Live Leak Sealing

This approach makes use of a high tensile spray applied polyurea membrane that has been tested to withstand up to 4 Bar of negative pressure.

Due to its spray applied nature this material can be applied seamlessly around penetrations, across expansion joints and around the tank geometry.

The reason this typically has to be applied offline is that the application equipment is not intrinsically safe.

Digester Gas Leak 04
Digester Gas Leak 05

This material has a design life in excess of 20 years, providing a long term anaerobic digester gas leak sealing solution.

Case Study

Sealing Anaerobic Digester Gas Leaks with Polyurea

The HDPE lined Anaerobic Digester was leaking biogas into the surrounding environments, resulting in loss of profits, environmental damage and presenting safety risks on site. This was discovered during an anaerobic digestion gas leak survey and was visible on site from sulphur staining.

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Digester Gas Leak 04