Vivergo biorefinery agitates for cost savings
10 Feb 2010
Saltend, UK – Vivergo Fuels has recently selected EKATO Group to design and manufacture the agitators for the fermentation process at its biorefinery, which is currently being built in Saltend, Yorkshire. The mixing units will be used for the continuous suspension of solids and homogenisation of tank contents, and are said to offer significant savings compared to traditional top entry agitator technology.
From 2010 the Vivergo refinery will consume over one million tonnes of wheat per year, producing 420 million litres of biofuel together with 500,000 tonnes of animal feed from the wheat protein and fibre left over from the fermentation process. The biofuels company will use EKATO side entry agitators in all fermentation vessels at the 27-acre site.
“EKATO demonstrated a good understanding of the complex mixing issues surrounding side entry agitators and their experience of supplying a wide range of agitators into the bio-fuels industry combined with an ability to carry out pilot scale trials were key factors in selecting the company’s technology for our plant,” explains Stewart Murray, engineering manager, Vivergo Fuels.
Side entry designs operate by producing fluid flow and therefore tank contents turnover. They can significantly reduces investment costs for biorefineries, as they can be easily installed without the need for heavy duty mobile lifting equipment. Cost per vessel is also reduced, as they eliminate the need for the internal baffles often found in vessels equipped with top entry agitators.
“Top entry agitators would have been prohibitively expensive due to the need to strengthen each vessel to transmit the torque and bending moments,” said Murray of Vivergo Fuels. “EKATO’s side entry agitator design was consistent with our aim to design an installation which had minimal crevices and would be straightforward and economical to implement and maintain.”
In order to design the agitators, EKATO’s design engineers built a pilot model fermenter with scale agitators and vessel internals, including filling and drain points to confirm agitator design to achieve the required degree of particle suspension. The team then simulated flow velocities and solids concentration distribution of the pilot set-up, using computational fluid dynamics (CFD) modelling as the validation method.
Using both pilot modelling and CFD techniques, EKATO defined the optimum agitator quantity, position and shaft angle to the vessel wall to suit the geometry of each vessel. Finally, the mixing requirements for the full scale plant were calculated, using the company’s R&D findings, and with a further CFD study of the plant scale, EKATO can accurately predict and guarantee the results for Vivergo Fuels’ new fermenters.
“Each agitator is designed on the basis of the mixing task in hand: for blending, the viscosity ratio is the determining factor, together with the settling behaviour of the grains, which is influenced by fluid density, grain size, moisture content and settling velocity,” explained John Smith, managing director, EKATO.
