Automation concept for paddle mixers cuts electricity costs.

The biogas plant operated by AgriGen Limited in Britain supplies around 5000 households with power and heat. Technology from Siemens used to control and automate the plant has enabled a 50 percent reduction in the plant’s electrical energy consumption.

Ingenious twist!

To implement the new plant operated by AgriGen, a consortium comprising large-scale agricultural businesses based in Suffolk (GB), Siemens joined forces with Thöni, an Austrian industrial group specializing in the generation of bioenergy. Designed to generate biogas, the plant uses a special method developed by Thöni. This involves continuously filling fluid and solid matter into a wet fermenter, which is at the heart of natural gas production technology, with the aid of a special feeding technique. The liquid substrate is fed into the fermenter by a pump and renewable resources are added by means of a solids loading device. To enable precise monitoring and simple automation of the plant, Siemens supplied the Simatic S7-300 controller, Simatic ET200S distributed I/O and visualization software WinCC V7.0. The I/O and Sinamics frequency converter are linked via Profibus. Precise height, pressure and temperature measurements are performed using the radar level transmitters Sitrans LR200, Pointek CLS300/500, Sitrans P DSIII and Sitrans T from Siemens.

The plant’s ingenious twist
The unusual feature of this plant are the specially designed paddles used to keep the material moving and well homogenized. This prevents sediment settling on the floor of the fermenter and stops any potential suspended particles forming floating layers, so creating the optimum conditions for biological decomposition of the materials. The paddle mixers are driven by a planetary gear and Sinamics G120 frequency converter. The smaller propeller mixers are also fitted with Sirius 3EW40 soft starters. The optimum automation concept in combination with the patented paddle mixer has reduced the plant’s electricity consumption by 50 percent.

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