Side-agitator technology offers biorefinery improved efficiency and reliability

Paul Boughton

With plant process managers continually under pressure to identify new means of driving costs down, while improving process efficiency, every element of a plant's equipment is scrutinised to make sure it offers maximum value for money. Investing in effective and affordable equipment is an even greater concern when planning the construction of new plants.

Vivergo Fuels, a company formed in 2007 to help meet the UK's demand for bio-fuel, recently selected EKATO Group to design and manufacture the agitators required for its fermentation process, having been impressed by EKATO's R&D process. The side entry agitators from EKATO, the world's leading developer of mixing technology, will be used for the continuous suspension of solids and homogenisation of tank contents, and offer a highly efficient and reliable mixing solution together with considerable savings compared to traditional top entry agitator technology.

Stewart Murray, Engineering Manager, Vivergo Fuels, explains that: "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."

Vivergo Fuels will use EKATO side entry agitators in all of their Fermentation Vessels in the 27-acre refinery. From 2010 the refinery will consume over one million tons of wheat per year, producing 420 million litres of bio fuel together with 500,000 tonnes of animal feed from the wheat protein and fibre left over from the fermentation process.

EKATO has designed and built innovative side entry agitators for more 25 years for a wide range of applications in different industries, ranging from food processing to flue gas desulphurisation (FGD), where top-entry agitators would be large and costly. The company's ongoing development of side-entry equipment is the result of a continuing market need for efficient mixing designs with lower cost investment. Installing multiple side-entry mixers is more straightforward than installing top entry agitators, and does not require additional equipment such as internal baffles, thereby reducing the cost per vessel.

Side entry agitators operate successfully by producing fluid flow and therefore tank contents turnover. EKATO's impeller technology is designed for fluid displacement, which is fundamental to the process result in applications where side entry agitators are selected.

Although side entry agitator technology is relatively simple in itself, difficulties often arise for manufacturers when assessing the suitability of the equipment for their particular application. EKATO is able to demonstrate how its technology will work in practice by offering a full scale projection using sophisticated R&D methods, and can also reference a large number of applications using its technology that are operating successfully. The agitator can, due to its design, be placed in the exact position and orientation required to achieve suspension or gassing applications.

A side entry agitator system from EKATO significantly reduces investment costs for bio refineries, as it can be easily installed without the need for heavy duty mobile lifting equipment. The cost per vessel is also reduced by using side-agitators, as they eliminate the need for the internal baffles often found in vessels equipped with top entry agitators. As a design option, a 'shut-off' device is also available which allows the mechanical seal to be serviced or removed while the vessel is full of product, reducing maintenance costs as well as servicing time. In addition, side entry agitators enhance process efficiency and allow the user greater control over the mixing process, avoiding deposits of solids in the tank.

"Top entry agitators would have been prohibitively expensive due to the need to strengthen each vessel to transmit the torque and bending moments," explains Stewart Murray, engineering manager, 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 most effective and tailored solution for Vivergo, EKATO's design engineers followed a unique rigorous research and development process, building 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. Following this, the team 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.

"Our R&D process is integral to how we build solutions for our customers," explains John Smith, Managing Director, EKATO. "Our thorough simulation and testing techniques allow us to fine tune the equipment to fit our customers' needs. 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. Our comprehensive approach allows us to provide accurate and efficient equipment with minimal investment."

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