PROJECT SPOTLIGHT

This project spotlight showcases how we managed the replacement of a digester mixing system in a crop fed digester. Read on to find out more about what was involved.

The background

Mixing is such a vital part of maintaining biological stability; a poor mixing design or mechanical failure is guaranteed to lead to biological issues and loss of biogas production.

As part of our role in managing the operations at this crop fed AD facility, we were investigating why their biogas yields were lower than expected. We discovered evidence of poor mixing, and then on further investigation, we uncovered a mechanical failure.

The solution

Following discussion with the client and buy-in/approval of the budget required, we were instructed to project manage a full change of digester mixing system in one of the tanks.

To do so involved careful planning and management of contractors, health and safety, and the volumetric levels of digestate between the tanks. We intended to keep the tank we were working on live; leaving the biology intact and thus saving costs and extended timings of having to reseed its biology. So careful consideration was given over how to empty the open tank enough whilst keeping the digestate onsite to enable refilling once the project was complete.

We dropped the digester levels to gain access to the mechanisms needed, stripped back the covers, removed the gas bag, and used a crane and man cage to lower our team in for access to the mixers. They rectified/improved/replaced all of the mixers. We were assisted by trusted contractors that we had carefully selected and managed throughout.

Whilst the tank was open, we took advantage of the opportunity to get into areas that wouldn’t usually be accessible. We reviewed the tank’s integrity and all safety devices and made various smaller digester modifications to reduce potential downtime in the future.

Once our work was complete, we replaced the gas bag and ensured the tank’s physical and mechanical aspects were stable. Followed by refilling with the digestate we had carefully managed onsite to keep alive.

The result

This was a successful undertaking; we completed the whole project in a few days. We managed the process in a live tank keeping the biology alive & stable, reducing the project costs significantly as there was no need for reseeding and long periods of ramp-up and destabilisation.

We also took advantage of the time and opportunity to complete other modifications reducing possible future downtime and costs.