AD sector 'guilty of poor pump maintenance'
8 Jul 2014
Many of the country’s anaerobic digestion (AD) plants are ignoring maintenance of their mixing systems and “running their pumps into the ground”, according to one industry supplier.
Speaking at last week’s UK AD & Biogas 2014 show in Birmingham, Landia UK & Ireland sales manager Paul Davies said the demands placed on systems by increasing amounts of improperly shredded food waste and contaminants in domestic green bin waste, combined with poor maintenance accessibility, meant there was a high risk of system failures.
“Mass-produced, bog-standard propeller mixers don’t last very long at all in AD environments,” said Davies.
“We now see some operators just running their pumps into the ground because it’s actually cheaper to replace them completely than get at them to carry out maintenance. This can be the case for any type of mixing system that doesn’t allow you to carry out a service from outside the tank.”
Small submersible mixers will often be running flat out, lasting two years or much less
Landia’s Paul Davies
Some submersible mixers, added Davies, only lasted up to two years before needing to be replaced.
“To maintain equipment such as submersible mixers, there’s no option other than to climb up, peel back the lid of the digester and purge the tank, which is extremely costly and time-consuming,” he said.
“Small submersible mixers will often be running flat out, lasting two years or much less - compared to a chopper pump that can last 25 years.”
Davies also pointed to the rising amount of acidic food waste being used as feedstock that corrodes cast iron equipment, and food waste containing plastics from packaging that can cause problems without the right processing or sufficiently strong pumps and mixers to handle it.
“Over-shredding of plastics will make particles too small to be screened out,” he said.
“But under-shredding can create a floating mattress of plastic in the digester, which will see gas production reduce and then eventually have to stop so that someone has to go in manually and remove it all. AD downtime isn’t something you want. Lost revenue can amount to thousands of pounds per day - and a problem with fulfilling your contract to the energy provider.”
