While the biogas industry has benefitted from the technological expertise gained from the digestion of feed crops such as maize and the UK waste water industry the firm says that heavier, fibrous materials create new problems.
Poor mixing directly affects the digester performance by reducing working capacity with settlement or by strangling gas release by blanketing the surface of the digester, according to System Mix.
Failure to suitably condition can mean that concentrated material leaves the digester either via a heat exchanger recirculation system, or onward processing, such as dewatering prior to composting. Premature wear of heat exchanger recirculation pumps caused by grit deposition is also common where poor mixing at low level is prevalent.
Last year the firm replaced submersible and paddle mixers with Rotamix tank mixing systems at a waste-to-energy plant in Bedfordshire. A significant amount of settled solids were removed from the digester tanks, which accounted for over 20% of the available working volume, after only four years of operation. A single externally mounted Vaughan Chopper Pump was installed for each digester and an array of nozzles and pipework were installed.
Since being commissioned, gas production has increased significantly and maintained its high level. The firm says the condition of post-digested sludge is more consistent and more acceptable for use in agriculture.
Contact: System Mix Tel: 01487 830123