Replacement mixer yields productivity benefits
28 Sep 2022
With Landia input, a state of the art energy-from-food waste operation has upped its yields by nearly half.
A leading food waste-to-energy operation has increased its biogas yields by an average of more than 43 percent, thanks to a new digester mixing system.
After evaluating the performance of the facility’s first digester, built a decade ago, British engineering component specialists Hayley Group were consulted by the food waste-to-energy client about the availability of an alternative, superior mixing system for its second digester.
The object was to improve on biogas yields attained by the first digester, built ten years earlier.It had struggled to eliminate typical biogas process problems such as foam, blocking and crusting.
Furthermore, with the unpredictability of food waste feedstock, dissolved solids (DS) at the food waste-to-energy facility are typically around 16-18 percent, but can be as high as 22 percent.
Hayley Group’s engineer Rob Bentley, said: “Over time in the first digester, plastics would inevitably float to the top where they’d 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.
“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.”
Utilising the Landia chopper pump with venturi nozzles, the new digester mixing system has an external knife system to continuously reduce particle sizes and keep solids in suspension.
“The success of the second digester, which has also seen reduced maintenance times and lower parasitic load means that for a third digester currently under construction, our customer has ordered a second Landia pump/mixing system.”
The existing digester had a feedstock intake of 118 tonnes of dry solids per day, which produced a daily gas flow of 27,000 Nm3 (normal metres cubed per hour). In contrast, the new digester is 10 percent smaller but boasted a feedstock intake of 110 tonnes of dry solids per day, to produce a gas flow of 36,000 Nm3.
Said Bentley: “This is extremely encouraging to say the least, especially when you consider that the second digester also has 10 percent less capacity than the older first tank.
“Assessing the change to a more resilient digester mixing system, our customer anticipated a decent increase in gas yields – but as high as 43 percent is phenomenal.”
As part of the support process, Hayley Group has also assisted its customer in replacing an ineffective and troublesome pump unit in its hydrolysis tank with a new three-pump Landia system.
There are now 11 Landia pumps in active use, with three more ready to go into service for the new, third digester. Energy-savings are also very apparent, because unlike other mixers that have to run 24/7, the Landia digester mixing system usually only requires 20 minutes on and then 20 minutes off, stated Bentley.
