Compatibility of Synthetic Paraffinic Liquid Fuels with Plastics in Existing Domestic Heating Systems

In Germany, the energy used in the cold-heat sector is currently dominated by fossil fuels. Studies on energy system transformation predict that climate-friendly liquid fuels will make up a significant share of the energy mix in the near future. Climate-friendly are the "Power to Liquid" (PtL) or E-Fuels, which are synthesised with renewable electricity (EE electricity) from electrolytically produced hydrogen and CO or CO2, as well as hydrogenated vegetable oil (HVO for Hydrogenated Vegetable Oil). HVO and PtL fuel consist almost exclusively of paraffinic hydrocarbons. They have very good combustion properties and a high stability against thermo-oxidative degradation. They are therefore ideal as GHG-reduced admixture components or as a substitute for EL heating oil. Their future use also has the great advantage that the distribution structures and technologies for liquid fuels are already available in Germany and can be used optimally. It is not known what effect a change from the aromatic-rich fuel oil to fuels with a low aromatic hydrocarbon content has on oil heating systems with regard to the function of the elastomer seals, the stability of the tanks, and other plastic components. Negative consequences can be, for example, the wash out of additives added to the plastics, change or destruction of the molecular structure of the polymer, or the initiation of stress cracks in the material due to the migration of the substances absorbed by the plastic during swelling. The aim of the research project is to create the necessary basic knowledge about the behaviour of plastics under such alternating loads. This basic knowledge is a prerequisite for the derivation of measures to ensure the trouble-free use of heating oil EL, low-sulphur with proportions of paraffinic fuels or of pure synthetic mainly paraffinic fuels in oil heating systems. This includes, for example, the adaptation of standards and the granting of approval conditions for new tanks.

In order to obtain statements about the effects of paraffinic fuel substitutes in existing plants, plastics which have been used in oil heating systems for many years and have been in contact with fuel oil are being investigated. Samples of these plastics are stored in the laboratory in a paraffinic fuel with a low aromatic content in order to simulate the effects that occur when switching to synthetic fuels in oil heating systems. Changes in the material properties are determined in the laboratory by means of appropriate tests after the removal from storage. In addition, selected plastics, as new goods, are subjected to a changeover from aromatic to paraffinic fuels. These tests serve to understand the possible damage mechanisms in the plastic.

The project has been completed. The results are documented in DGMK Research Report 838.