GETTING the best from an anaerobic digestion system includes such parameters as achieving a higher gas yield, reducing foaming and eliminating the potential for maintenance problems. And as operators continue to seek maximisation of the sustainability benefits of AD process plant those elements come in for even closer scrutiny.
Mixing is an important part of the AD process, as Andy Parr is keenly aware. In fact he says it’s crucial to the AD process that suitable pre-conditioning of solids is carried-out prior to digestion.
Parr is director of System Mix which markets the Rotamix System incorporating the Vaughan chopper pump and which has supplied digester mixing systems at installations across the UK. Parr continues: “The Vaughan pump prevents re-accumulation of fibrous and fatty material in the digester and this means that material continues to pass through the nozzles. This in turn ensures that digestate is adequately conditioned and actually benefits all post-digestion equipment.”
And he adds that as many AD operators now look to maximise the sustainable credentials of their plant and equipment even further, mixing systems are becoming even more important.
In recent years System Mix Ltd has been involved with retrofit projects at AD plants where existing mixing systems were contributing to operational and biological issues. For example, high grit deposition was reducing the active volume of digesters and threatening to significantly reduce output outside compliance requirements. Also, compressors were requiring high levels of maintenance and were proving costly to keep running.
Furthermore, as deposition increased, the maintenance issues escalated because not only did the rag mass reweaving within the digester impair their efficiency, it also caused blockage problems in the heat exchangers and further downstream pumps and systems.