AD plant increases biogas yields by 43% with Landia system

A food waste-to-energy operation has increased its biogas yields by around 43%, thanks to a new digester mixing system.

After evaluating the performance of the facility’s first digester, built 10 years ago, engineering component specialists Hayley Group were consulted about the availability of an alternative, superior mixing system for its customer’s second digesters. The proposed new mixers, unlike those in the first tank, would eliminate typical biogas process problems such as foam, blocking and crusting, and help to boost levels of methane.

Using the chopper pump invented by Landia in 1950, complete with venturi nozzles, the digester mixing system that is now producing high levels of gas for the second digester has an external knife system to continuously reduce particle sizes and keep solids in suspension.

“We constantly look to help customers improve efficiencies,” said Rob Bentley, Hayley Group’s engineer. “This project is of particular note because with the new, superior mixing system, the increase per cubic metre in gas from the second digester is over 40%. This is extremely encouraging to say the least, especially when you consider that the second digester also has 10% less capacity than the older first tank.

“The first digester, with its compressor mixing set-up, continues to produce a fair bit of gas, but when we carefully evaluated what would be best for the second digester, we recommended a pump/mixing system from Landia.”

With the unpredictability of food waste feedstock, dissolved solids at the facility are typically around 16-18% but can be as high as 22%. This was an area that, with lessons learned from blockages and downtime from the first digester, saw the clear need for a more robust mixing system for the second digester.

“Our customer has not seen the Landia digester mixing system ever struggle to cope,” commented Bentley. “Over time in the first digester, plastics would inevitably float to the top where they would form a blanket and then a crust, which would eventually have to be dug out. This was a rotten job with plenty of unwanted downtime.”

Landia’s chopper pumps did not allow this material build-up to happen. Thanks to the success of the second digester, a third is currently under construction.

On average, digester 1 sees a feedstock intake of 118 tonnes of dry solids per day, producing a gas flow of 27,000 Nm³ per day. In comparison, digester 2 (10% smaller) sees a feedstock intake of 110 tonnes of dry solids per day, producing a gas flow of 36,000 Nm³ per day.

Bentley concluded: “At this food waste-to-energy facility, the big increase in biogas yields shows without doubt just how beneficial a resilient and well-designed digester mixing system can be to the success of an AD/biogas plant.”