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Good mixing contributes towards sweet success

20 February 2015

The first output results a year after commissioning their AD plant confirm that they are now converting 200,000 litres a day of feedstock into renewable energy.

The AD (Anaerobic Digestion) 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.  A recent example is at Nestle’s confectionery factory at Fawdon the former Rowntree site near Newcastle, home to fruit gums, pastilles and Rolos.  Previously, production residues from Fawdon were discharged to sewer or fed to pigs in the locality.  However, following their investment in 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.

Positive Results
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 their electricity bill by about £100,000 pa. In addition, the site has registered for the Feed-in Tariff and will receive annual payments of around £250,000.

The Challenge to Improve and Optimise Efficiency 
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 comment and opinion, 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.

Why the Mixing Process is Important
Huntingdon based SYSTEM MIX LTD in conjunction with P&M Pumps, who market the Rotamix System incorporating the Vaughan chopper pump are an established supplier of digester mixing systems to Clearfleau and many other private sector food waste AD plants in the UK including Fawdon.  The basis of the success of these plants depends on a durable mixing technology supported by reliable Vaughan Chopper Pumps. Andy Parr, Director of System Mix underlines the reasons for the success of System Mix and explains 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.  This in turn ensures that digestate is adequately conditioned and actually benefits all post-digestion equipment”. He concluded, “As many AD operators now need to maximise the sustainable credentials of their plant and equipment even further, we are confident that the benefits of our mixing systems are becoming even more important as illustrated by the positive results achieved at the Fawdon confectionery plant”. 


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