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The conversion of biogas into electricity provides an opportunity to compensate fluctuations in the supply of wind power and solar power with an adjusted production.
© DBFZ Deutsches Biomasseforschungszentrum gGmbH
Electricity production from biogas
Projektinfo 07/2018

Layout of a stirrer tank digester with integrated pneumatic pre-stressed, double-leaf membrane storage system roof. The available gas volume is located beneath the belt retention system (3) and gas storage system internal membrane (2).
© DBFZ Deutsches Biomasseforschungszentrum gGmbH

Effects of pressure and temperature fluctuations on available gas storage system capacity. At a temperature of 30 °C in the gas storage system (dotted line), 23 % more biogas can be saved than with the 60 °C variant (solid line). This illustrates the importance of predictive gas storage balancing, given the frequency with which biogas plants are improperly operated at 80 to 90 % gas storage fill level.
© DBFZ Deutsches Biomasseforschungszentrum gGmbH
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Adjusting operation of biogas plants to power requirements

Compensating supply fluctuations will prove vital in future power grids utilising high proportions of wind and solar energy. The demand driven generation of electricity from biogas can make a viable contribution in this regard. Researchers are developing new systems and software for biogas plants, integral in facilitating such flexible operational characteristics. This involves the precision monitoring and regulation of biogas production and conversion into electricity. The aim is to optimally harmonise these processes and exploit storage capacities to the full extent possible. One of the many influencing factors to have an impact in this regard is the weather: On a hot, sunny summer’s day, gas expands and storage capacity drops by up to 20 per cent.

The “ManBio” research project involved researchers from the German Biomass Research Centre (Deutsches Biomasseforschungszentrum DBFZ) and project partner Awite Bioenergie working to technically enhance systems designed to facilitate fill level measurement in storage systems. The researchers integrated these in the process control system of the biogas plant. The initial stage involved researchers accumulating extensive data on the technical status of gas storage and fill level measurement systems. The researchers also recorded process data such as gas production rates, gas consumption, temperature and air pressure. The researchers used this data to enhance forecasting with respect to the process chain properties of gas production, gas storage capacities, storage system fill level and consumption rates.

The researchers developed a model of the storage system on this basis and, from this, a forecasting model for the fill level with variable weather conditions.The model can use current weather data and gas storage internal temperatures. For measuring the fill level with yet greater accuracy, the researchers modified a cable control procedure, utilising in parallel two hydrostatic pressure measurement procedures. The researchers tested the innovative configuration on a research biogas plant of the German Biomass Research Centre and a furtherbiogas plant maintained by the practice partner.

Mathias Stur, project manager at the German Biomass Research Centre, was handed the biogas innovation award of the German agricultural industry in 2017 for the research into enhancing gas management in biogas plants.


Minimising gas losses

The researchers looked at how the storage system fill level could be more accurately measured. They were able to put forward proposals around the enhanced utilisation of net gas storage capacity based on their investigative findings. This allowed for the ability to regulate the supply of energy in the connected CHP plant with greater chronological accuracy. A new, model-  upported forecasting approach with respect to the gas storage fill level facilitates a more flexibleproduction process and assists in developing demandoriented feeding and removal strategies.

Plans are in place to adapt the refined systems to as many existing biogas plants as possible with variable gas storage systems and utilise them on these. This should allow for minimising gas losses and consequently greenhouse gas emissions too resulting from operational processes.

Key to the optimal utilisation of produced biogas: Ensuring the storage system does not become excessively full. If the pressure climbs too high, an excess pressure event results; the excess/low pressure safeguard triggers in this eventuality, and methane is directly released into the atmosphere. To prevent this occurring, surplus gas must be burned via a flare stack, which automatically cuts in from a specified gas storage fill level. Maintaining a sufficient buffer capacity in the storage system therefore is essential. Operating the storage system at a fill level of up to 50% is advantageous, given the need to ensure residual capacity remains available including in the event of scheduled or unscheduled downtime of the connected CHP plant.

The impact of weather is considerable in the case of integrated, pneumatically pre-stressed, double-leaf membrane gas storage systems, particularly with a high fill level. In the course of a sunny summer’s day, the gas expands significantly; the net gas storage capacity drops by approx. 20% if the temperature insidethe storage system increases by approx. 30 K. The light-grey outer protective membrane of the gas storage system roof on the biogas research plant reached surface temperatures of up to approx. 68 °C, causing significant temperature and pressure increases inside the storage system.

Projektinfo 07/2018:
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Project management, analysis of gas storage systems and influencing variables

Field testing, gas volume recording and system regulation
AWITE Bioenergie GmbH


Biomass energy use
Website of the funding programm

Website of Fachagentur Nachwachsende Rohstoffe

Website of the research centre of the technical university Ingolstadt

Project profile of the funding programm "biomass energy use"

Project profile of the funding programm "biomass energy use"

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