BioG GmbH, headquartered in Upper Austria, manufactures technical components for residual material utilisation in biogas plants. The company’s portfolio includes innovative feeding technology such as the BioFeeder, which is available in various capacities ranging from 12 to 220 m³ (≈ 424 to 7,769 ft³) depending on customer requirements. The associated dosing unit is supplied as a complete solution, including pumps, sensors and actuators from a single source.

The BioFeeder ensures that fresh fermentation substrate is shredded, mixed and homogenised in such a way that the subsequent biogas production process achieves maximum yield with the highest possible biomethane content. In this process, the substrate—comprising organic biomass such as plant residues, livestock manure or energy crops—is blended with liquid fermentation residues (digestate) to form a pumpable slurry. The digestate consists of highly heterogeneous, strongly fibrous liquid residues from the fermenter and may contain not only a high proportion of suspended solids but also fat content. The resulting biogas substrate mixture is then conveyed into the fermenter via progressive cavity pumps, either in batch mode or continuously.

The flow of digestate serves as a key control parameter to ensure that the fresh substrate in the BioFeeder is properly mixed, sufficiently supplied with active microorganisms and pre-heated, thereby maintaining a highly homogeneous medium and stabilising the overall digestion process. If excessive digestate is dosed, the volumetric throughput increases unnecessarily, which in the long term reduces biogas yield. If too little digestate is added, the mixture becomes more difficult to pump, increases energy consumption and raises the risk of pipeline blockages.

BioG GmbH therefore searched for a standard instrumentation for reliable and accurate flow measurement of digestate. The selected flowmeter had to be designed both in terms of measurement principle and construction to withstand the existing process requirements of an abrasive and highly fibre-laden medium.

The company ultimately selected the OPTIFLUX 2300. This electromagnetic flowmeter (MID) is already in successful operation across numerous applications involving fermentation substrate and slurry. It is designed for highly accurate flow measurement of fibre-rich, chemically aggressive liquid digestates, with minimal wear.

Depending on the medium, the customer uses the meter in nominal sizes of DN200 with a robust hard rubber lining or DN150 with a polypropylene lining. As standard, the device is supplied with electrodes made of Alloy 22. These electrodes are highly resistant and therefore already provide an optimal solution for many digestate applications without the need for special materials.

Scratching of the oxide layer on the metallic electrode surface—caused by a high proportion of solid particles and fibres in the medium—can be significantly reduced, thereby also minimising the impact of signal noise on the measurement.

In addition, the electronics of the OPTIFLUX 2300 are specifically designed to reliably process noisy measurement signals, ensuring stable and accurate performance even under demanding process conditions.

The OPTIFLUX 2300 has proven itself as the standard instrumentation for the dosing unit of the BioFeeder. Using this electromagnetic flowmeter (EMF), liquid digestate from the fermenter can be added to the fresh fermentation substrate from the BioFeeder in a controlled and precisely metered manner. In this way, the end user can optimise the substrate mixture to maximise biomethane yield.

The robust design of the flowmeter is ideally suited to liquid digestate with a high solids content. Thanks to a wide range of liner and electrode materials, the OPTIFLUX 2300 outperforms many conventional EMFs. It offers minimal wear due to abrasion and corrosion. Where the abrasiveness and aggressiveness of the medium, or signal noise caused by solids, require it, KROHNE can also supply the flowmeter with alternative liner materials as well as low-noise, tungsten carbide-coated electrodes or electrodes made of conductive rubber.

In addition, the electronics of the OPTIFLUX 2300 are equipped with advanced noise filtering functions. These enable accurate and long-term stable measurement, even in applications with high solids content.

Unlike comparable instruments in its class, the OPTIFLUX 2300 features a fully welded design as standard, providing additional investment protection. The sensor is hermetically sealed, preventing moisture ingress and protecting it from external damage.