Critical maintenance and repairs during AD Plant Hibernation

One of our clients paused production for a short period during December, their quietest month. Before the COVID lockdown, the site would have planned to keep the digester running during shutdown periods to maintain digester health which would have led to additional costs and the transportation of feedstock to the site.

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After Alpheus took over the operations and maintenance of the site in 2020 and successfully undertook a first for the site,  by creating and executing a detailed plan to hibernate and their digester in lockdown. Our client is now able to plan breaks in production, without additional expense. The hibernation and restart process now forms part of their crisis plans.

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During the hibernation, alongside regular biomass testing and viability checks, the Alpheus site team have been getting stuck into proactive and preventative maintenance across the AD plant to ensure optimal performance after production commences again in the new year.

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Some of the larger maintenance tasks undertaken included:

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1. Using a freezing method to enable key maintenance to take place safely and effectively

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One of these activities incorporates an innovative approach incorporating the use of freezing to enable the replacement of the main isolation valve, to prevent seizure as a result of struvite build-up. This innovative approach avoided the need to drain the reactor, which would have been high-risk, disruptive and very costly.

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To enable the replacement of the main isolation value, the pipe leading to it was frozen to achieve a temporary plug, thus allowing the work to take place.

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• The hibernation period was the ideal time to schedule this activity as the biomass temperatures are lower than normal and there is no risk of process disruptions as effluent isn’t running through the plant.
  
• The Alpheus team worked alongside specialist contractors to achieve a smooth and successful changeover of the main valve within the scheduled timescale.

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2. Emptying and cleaning the discharge tank to carry out repairs to improve performance.

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3. Installing trace heating and lagging to the scrubber system gas pipework to improve performance by ensuring consistent gas flow and protecting the equipment.