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Uk's Largest Slurry Tank


Simplicity and reliability were among the key requirements for the custom control system developed and supplied by Ralspeed, for use on the UK’s largest slurry tank. The tank which was designed, manufactured and installed by slurry handling specialist Storth, is 40m in diameter almost 6m high and can hold over 7 million litres of slurry.

Slurry which consists of farm animal excrement and water is mixed. It is then stored in the tank at certain times of year as an environmental protection measure. The slurry is then used on farmland at other times of the year, where it acts as a valuable natural fertiliser that is rich in nitrates. Pumps are used to control the flow of slurry into and out of the tank, which is also equipped with motorised agitators to stir the slurry periodically during storage.

To provide the control system for the pump and agitator motors, Storth approached Ralspeed. Ralspeed has been supplying efficient and dependable control systems for several years to Storth

For the new slurry tank, the design of the control system had to consider the limited capacity of the mains supply at the tank installation site. This meant arrangements had to be made to limit the inrush current when starting the pumps and agitators, and to ensure that no more than two agitators could run at the same time. The agitators cannot run when the pumps are running.

Storth also wanted to be sure that the agitators had approximately equal usage, in order to equalise wear and tear, thereby maximizing their operating lives. Further requirements were that the control system should be as simple as possible to facilitate maintenance, and that the user controls should be straightforward and intuitive.

To meet these special requirements, Ralspeed designed and built a fully customised control panel. Ralspeed used 18.5kw three phase soft starters from their own Torq-master range to control the motors.  These units provide excellent control over motor starting current, ensuring that the capacity of the supply is never exceeded, and ensure that the agitators and pumps start and stop smoothly.

No more than two of the motors on the tank could ever be running simultaneously. The Ralspeed engineers realised that substantial cost savings could be achieved by using only two soft starters and connecting them, via main contactors to the appropriate motors needed to meet operational requirements.

Ralspeed provided a single selector switch to configure the operation of the system. This switch allows the user to rotate the duty of the agitators and to select operation of the pumps instead of agitators when necessary. With careful design, it proved possible to implement this straight forward and effective form of control without needing to use a PLC or smart relay, thereby satisfying the end users request for simplicity.

John Hird of Storth said “Throughout the project Ralspeed were helpful and responsive, even when we had a very late change in requirements Ralspeed came to the site and made necessary modifications quickly and efficiently. Now that the control panel is in regular use the end user is very satisfied with performance and reliability”. 

19th February 2019, 11:41
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Page updated 19th Feb 2019, 12:44
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