Geothermal paper drying

Industrial process steam is the most important source of energy in the paper industry alongside electricity. Within the framework of the "Kabel ZERO" initiative, an innovative steam generation based on deep geothermal energy is being sought to replace fossil fuels. The funded R&D project "Geothermal Paper Drying" is the first step in this direction. Geological investigations - including a seismic survey and an exploratory borehole – will be carried out at the Kabel Premium Pulp & Paper GmbH site in Hagen, and process routes for process steam generation based on renewable heat from the ground will be developed and analyzed.

The paper industry is one of the five most energy-intensive industries in Germany. Large quantities of process steam in the temperature range of 100 to 200 °C are required especially for drying moist paper webs. Usually this process steam is provided by the combustion of fossil fuels (natural gas, coal, fuel oil). Since optimizing the energy efficiency of the paper manufacturing process is increasingly reaching its physical and economic limits, innovative approaches such as renewable heat are needed to further reduce CO₂ emissions. This problem can also be found in other branches of industry – for example in the chemical industry.

The dilemma of the heat transition in German industry lies in the lack of usability of many renewable energies for the production of renewable heat at the required temperature level. In principle, biogas or biomass combustion systems, renewable gases (hydrogen or EE-methane), solar thermal systems, geothermal energy or power-to-heat (heat pumps or electric heating systems) would be suitable. However, none of these technologies has yet achieved widespread use – whether for cost reasons, lack of supply or lack of consistency. Although heat accounts for 70 to 75 % of the final energy consumption of German industry, renewable heat contributes only 4.3 % of final energy consumption.

Geothermal energy in particular has the potential to cover a larger share of the heat demand due to its base load capacity. The focus of the project is particularly on the temperature range up to 200 °C, which accounts for around 30 % of industrial process heat requirements. However, geological sites with sufficiently high temperatures for direct process steam generation of sufficient quality for industrial processes are rare in Germany. Therefore, processes are necessary to upgrade the thermal water or the generated steam. In the course of the UMSICHT sub-project, possible process routes are being developed and analyzed for this purpose and evaluated for the pilot site Kabel Premium Pulp & Paper (KPPP) in Hagen.

The "Geothermal paper drying" research project successfully investigated how geothermal heat can be integrated into the paper drying process at the Kabel paper mill site in a technically and economically viable way and how it can replace imported fossil fuels such as natural gas. The project partners provided relevant findings as a basis for the further development of the industrial use of renewable, deep geothermal heat.

Within the sub-project Integration into the processes of the paper industry, Kabel Premium Pulp & Paper defined framework conditions and requirements from the user and industry perspective. The focus: the continuous synchronization of the framework conditions with regard to energy and production processes as well as the consideration of the spatial conditions on the mill site.

Within the Geothermal exploration and development concept sub-project, the Fraunhofer IEG investigated the geological formation of Devonian mass limestone and its use as a hydrothermal reservoir. The results of the 2D seismic measurements carried out indicate that the mass limestone in the area of the paper mill site lies at depths of 2.6 to 3.6 km, which are suitable for geothermal process heat utilization. Both an initial shallow exploratory borehole in the nearby Steltenberg quarry and laboratory tests on mass limestone samples provided important data on the reservoir properties. In particular, a strong (hydrothermal) dolomitization due to the location in the area of the Großholthausener Sprung and the Ennepe overthrust could be proven. Based on the reservoir parameters determined, analytical and numerical thermo-hydraulic-mechanical modeling was carried out with regard to the possible thermal extraction rates and the geomechanical behavior. For further underground exploration at the site, a preliminary geological profile was created on the basis of the structural data obtained in the above-mentioned investigations and a drilling concept for a first deep exploratory well was developed.

Within the process development sub-project for process steam generation, Fraunhofer UMSICHT was able to demonstrate that deep geothermal energy is highly suitable for providing industrial process heat and process steam as a base-load-capable, renewable energy. A wide range of possible process routes could be developed and identified for the upgrading of deep geothermal heat to industrially usable process steam. The basic technical feasibility of utilization in the entire paper industry (process steam at 100-240 °C) was demonstrated for the range of reservoir temperatures that can be expected in Germany (90-180 °C). The large number of possible process routes requires an individual evaluation and selection for each application. For this purpose, a characteristic number-based evaluation methodology was developed as part of the project and integrated into the simulation models used.

The results and findings of the project can be transferred to other sites in the paper industry and adapted to other industries and heat sources by further developing the models and methods. With the close proximity of outcropping mass limestone accessible for geoscientific investigations in the Steltenberg quarry in Hagen and the site of the KPPP paper mill, which is only approx. 9 km north of the outcrop, there is currently a unique constellation in the Hagen region for low-risk exploration of the reservoir formation of the mass limestone in NRW. Following successful exploration in the Hagen area, the concept for utilizing the characteristic spring tectonics and its fault systems in the Devonian mass limestone can be applied, transferred and further explored in the Rhine-Ruhr area. The (further) development and optimization of promising process routes and their technological subcomponents and systems for upgrading deep geothermal heat to industrially usable process heat addresses a broad field of application and should therefore be further advanced.

• Fraunhofer-Einrichtung für Energieinfrastrukturen und Geothermie IEG
• Kabel Premium Pulp & Paper