Biogas plant, biomass, corrosion, coating, ETFE

At present, reinforced concrete or steel sheets with glass enamel are used for the construction of bioreactors, fermentation and storage tanks of biogas stations. To a lesser extent, corrosion-resistant steels are used and, in smaller dimensions, also plastics or fiberglass. Against leakage and corrosion due to biomass and biogas, reinforced concrete is mostly protected by bituminous coatings. Steel components are most often protected against corrosion by epoxy resins and cements. On the market there are modern plastic-based coating materials with high chemical and mechanical resistance, which can be applied to biogas stations to certain product dimensions. An initial study on the applicability of low-permeable ETFE ultra+ and PFA ultra+ hydrophobic anti-adhesion coatings of 700-1000 μm for steel components under anaerobic conditions exposed to corrosive effects of biomass and biogas was performed. Laboratory simulated conditions corresponding to the anaerobic bioreactor at 40 °C ± 1 °C included 2 months of incubation of the sample in biomass-based alkaline medium from the 1st fermentation stage of the agricultural biogas plant and then 3 months of incubation in acidic medium based on bio-waste mixture. While a structural steel samples lost a significant portion of their mass in the biomass contact area and also in the biogas contact area, the stainless steel samples exhibited intergranular corrosion under the microscope, and the ETFE and PFA coated samples did not change color or roughness, did not swell and no other change was visible. The tested coatings are found to be suitable for the protection of steel surfaces in contact with fresh acidic biomass entering the bioreactor, in contact with the alkaline slurry or sludge in the bioreactor and in contact with the raw biogas.

At present, reinforced concrete or steel sheets with glass enamel are used for the construction of bioreactors, fermentation and storage tanks of biogas stations. To a lesser extent, corrosion-resistant steels are used and, in smaller dimensions, also plastics or fiberglass. Against leakage and corrosion due to biomass and biogas, reinforced concrete is mostly protected by bituminous coatings. Steel components are most often protected against corrosion by epoxy resins and cements. On the market there are modern plastic-based coating materials with high chemical and mechanical resistance, which can be applied to biogas stations to certain product dimensions. An initial study on the applicability of low-permeable ETFE ultra+ and PFA ultra+ hydrophobic anti-adhesion coatings of 700-1000 μm for steel components under anaerobic conditions exposed to corrosive effects of biomass and biogas was performed. Laboratory simulated conditions corresponding to the anaerobic bioreactor at 40 °C ± 1 °C included 2 months of incubation of the sample in biomass-based alkaline medium from the 1st fermentation stage of the agricultural biogas plant and then 3 months of incubation in acidic medium based on bio-waste mixture. While a structural steel samples lost a significant portion of their mass in the biomass contact area and also in the biogas contact area, the stainless steel samples exhibited intergranular corrosion under the microscope, and the ETFE and PFA coated samples did not change color or roughness, did not swell and no other change was visible. The tested coatings are found to be suitable for the protection of steel surfaces in contact with fresh acidic biomass entering the bioreactor, in contact with the alkaline slurry or sludge in the bioreactor and in contact with the raw biogas.