Precision Weighing Technology for More Efficient Biogas Plants

Biogas is an environmentally friendly source of energy, which is already making a huge contribution to the energy transition. At the Institute for Agricultural and Urban Ecological Projects of Humboldt University Berlin, scientific teams are researching how biogas plants can become even more sustainable in the future, for example, by increasingly using waste materials. The associated complex long-term tests require precise measurement technology. To perform level measurements in the experimental reactors, scientists rely on an integrated weighing technology measurement chain from HBM—from the PW12C single-point load cell through the PAD digital transducer electronics to the PanelX software.

Biogas is an important pillar of the energy transition. Unlike solar and wind turbine systems, the technology is independent of the weather or the time of day and can thus compensate for fluctuations in the grid in the future, for instance, when not enough energy is being generated from wind and sun. By 2018, electricity from biogas plants in Germany already accounted for around 13% of the electricity produced from renewable sources. However, one point of criticism was: specially grown energy maize has mainly been used in biogas production so far, which is expensive and inefficient.

Problem

In the BioKat project, the scientists at the Institute for Agricultural and Urban Ecological Projects of Humboldt University Berlin are researching how biogas plants can become more efficient, for instance by increasingly using waste materials for biogas production in the future. In the trials with four 25-liter experimental reactors each, the reactor filling level plays a very important role. For a new series of experiments, our scientists are looking for gravimetric level measurement technology that can:

• accurately measure the level over the entire test period,
•  provide reliable data in the demanding process simulation environment, and
• be operated quickly, safely, and in a user-friendly manner.

Four inconspicuous black cylinders form the core of the BioKat research project. "In our four experimental reactors, we are investigating how different enzyme preparations accelerate the fermentation of our test substrate from whole-crop silage," explains Marius Conrady. "For this purpose, we supply our experimental reactors with 176 grams each of whole-crop silage and water every day after a start-up phase.” An agitator stirs the mass continuously, while a temperature-controlled bath ensures a constant 38 degrees Celsius in the reactors to ensure identical conditions throughout the project duration.

The filling level of the reactors, each with a total capacity of 25 liters, plays a special role in the tests. It has a huge impact on the formation of gas and other important factors such as the torque of the agitators that move the mass in the reactors, as well as the volumetric load. "In previous test series, we could only assess the level via the reactors’ inspection windows," says Marius Conrady. "This was a problem because the mass consisting of whole-crop silage and water is very inhomogeneous and has a high dry matter content. Moreover, foam often forms in the reactor.” For a new series of tests, the scientists are therefore looking for a solution that allows additionally determining the filling level using gravimetric measuring technology. HBM's experts advise the IASP, and together with the scientists they are developing a holistic gravimetric weighing concept ranging from sensor technology to software-based electronic evaluation.

“Our PW12C single-point load cell with a capacity of 50 kilograms is at the heart of the weighing concept for the IASP," says Marcel Richter, Head of Product Management Weighing Technology & OEM Sensors at HBM. "With its integrated off-center load compensation, the load cell is ideal for single-point applications with platform sizes up to 800 mm x 800 mm. In the IASP test setup, a single load cell carries the weight of a complete experimental reactor—

offering an overall performance for this design that is unique in the market.”  The PW12C single-point load cell weighs loads ranging from 50 to 750 kilograms precisely in compliance with the C3 Multi-Range accuracy class. In addition, a cable shield connected to the measuring body provides optimum protection against electromagnetic influences, making it ideal for use in laboratory environments. "Its high rigidity and proven strain-gauge technology from HBM make the PW12C ideal for both static and highly dynamic applications; for example, in checkweighers," says Marcel Richter. "At the same time, the load cell is extremely robust.”  The PW12C is also suitable for use in harsh industrial environments due to its IP67 degree of protection and individually adjustable overload protection.

"In our BioKat research project, the PAD digital transducer electronics converts the analog signals of the load cell into digital data at a high resolution," says Marius Conrady. "In this way, we can simply record the measurement results for our test setup using a PC, evaluate them and get a quick overview.” With its load cell, electronics, and complete range of accessories, HBM offers scientists at the IASP everything they need from a single source. "We offer a wide range of accessories to build up an ideal measurement chain for our customers," says Marcel Richter. "And our PAD digital transducer electronics provides users with a simple and user-friendly way to digitize analog, strain gauge based load cells or sensors—at extremely high resolution.”

The PAD can be easily connected to load cells by plug and play and is ready for use within minutes. Owing to integrated measurement signal processing with selectable or automatic filters, the transducer electronics guarantees maximum precision, even with the continuous vibration of the experimental reactor’s agitators in the IASP test setup. Its compact, stainless-steel housing and IP68/IP69K degree of protection also make the transducer electronics ideal for the most demanding environmental conditions.