Anaerobic digestion is all in the mix

A Nestlé confectionery site in the UK turned to anaerobic digestion, a move which is paying off with converting 200,000 litres a day of feedstock being transformed from waste into power.

The dynamics of the System Mix process resulting in optimum mixing
with minimal settlement.

The Anaerobic Digestion (AD) process is now recognised as an effective and viable method of turning production ‘residues’ into renewable energy and there are a growing number of positive results being achieved at numerous sites which support this.

Renewable energy

The Nestlé plant in Fawdon, UK, is a good example. Previously, production residues from Fawdon were discharged to sewer or fed to pigs in the local area. But following their investment in the AD plant, which was designed and installed by UK renewable energy market leader Clearfleau, all biodegradable residues are being converted into renewable energy on the factory site.

The biogas produced is fuelling a combined heat and power (CHP) engine, which produces 200kW of electricity used in the confectionery process. This represents about 8% of the factory’s power needs, cutting its electricity bill by about £100,000 a year. In addition, the site has registered for the Feed-in Tariff, a UK government incentive for green energy producers, which will pay out another £250,000.

As with any production process the focus is about optimising efficiency and this increasingly applies to the AD process. The reality is that AD operators now have to achieve higher gas yields, reduce foaming and minimise maintenance issues as part of the drive to maximise the sustainability benefits of their AD process plant.

The steps that can be taken to achieve these objectives are often a source of conjecture, although it is widely acknowledged that, regardless of the technologies being used, the efficiency of the mixing process is fundamental to the success of the process. System Mix, together with P&M Pumps, which markets the Rotamix System incorporating the Vaughan chopper pump, is an established supplier of digester mixing systems to Clearfleau and many other private sector food waste AD plants in the UK including Fawdon.

Vaughan Chopper Pump and associated pipework adjoining the mixing tanks.

Durable mixing

The basis of the success of these plants depends on a durable mixing technology supported by reliable Vaughan Chopper Pumps according to System Mix director Andy Parr as he explained the mixing process in more detail.“It is crucial to the AD process that suitable pre-conditioning of solids is carried-out prior to digestion and our system has been proven to be one of the most effective in achieving this. 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,” he said.

“This in turn ensures that digestate is adequately conditioned and actually benefits all post-digestion equipment.” As many AD operators now need to maximise the sustainable credentials of their plant and equipment even further, we are confident the benefits of our mixing systems are becoming even more important as illustrated by the positive results achieved at the Fawdon confectionery plant”.