Mixing Matters for Eco’s Sustainable Solution

Comprehensive mixing of biogas digesters is playing a crucial role at one of the most dynamic and well-run food-waste-to-energy facilities in Europe.

Typically operating at more than 90% efficiency, Eco Sustainable Solutions’ plant near Dorchester in southwest England, produces biogas at an average of 140m3 per tonne of food waste, which is sourced from 60,000 domestic kerbside collections in Dorset.

Processing 42,000 tonnes of food waste per annum (posting its best performance results since opening in 2014), Eco’s two 2600m3 digesters are each fitted with Landia’s externally-mounted mixing system, comprising 18.5kW chopper pumps (invented by Landia in 1950) and venturi nozzles.

Running for just 20 minutes per hour, the mixing system’s chopper pumps benefit from a unique knife design that prevents solids from entering the casing.

The initial upswing in biogas came in 2014, when Landia was chosen for a new, second digester. As well as greatly reducing the health and safety risks, the boost in producing more biogas with consistent concentration of methane circa 58-62% saw Eco move to upgrade the equipment on its first, existing digester. Here, a rotary submerged system had been in operation, but the considerable downside of downtime became very apparent when an internal mixer broke, meaning that the digester had to be drained down to retrieve it. During days of lost production, this type of scenario can cost a biogas plant a loss of in the region of £250,000. As with all biogas digesters – even when very well managed – draining down to remove accumulated grit every two to three years is a very costly exercise in going offline.

Compared to mixers that have to run 24/7, the Landia units make energy savings, and at only 20 minutes per hour operation, means far less wear and tear, greater longevity and less requirement for spare parts. Landia has also worked with Eco on modifying the inlet flange into the pumps so that the food waste feedstock goes straight to the macerating blades of the chopper pumps at the lower half of the digesters; improving the infeed with specially adapted pipework to enhance the process.

In what has become a real science at innovative Eco, half of the clean, renewable energy (12,000 MW per annum) is utilised by the neighbouring Dorchester Feed Mill; (owned by the Mole Valley famers co-operative) the first feed mill in the UK to be powered completely by renewable power. The other 50% from the 2.5 acres site is sold to the National Grid. From its nutrient-rich digestate, Eco also produces and supplies a diverse range of sustainable landscaping products that return goodness back into soils.

As such a successful operation that has already recycled over 4,000,000 tonnes of organic material, it is no surprise that family-run Eco Sustainable Solutions is looking to expand with a new biogas facility to add to its plant near Dorchester.  As part of its firm ethos in providing a safer, happier and healthier working environment, mixing will continue to play an important part in the company’s firm commitment to making its processes more carbon efficient.

Courtesy of Eco.

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Sara Mathov is a feature editor contributing to Valve World Americas, Stainless steel World Americas and other related print & online media.