Innovative and competitive solutions using SS and adhesive bonding in biogas (BiogaSS)

The BiogaSS project explores stainless steel for cost effective design for the fabrication of biodigesters. Although concrete is extensively used, it is not necessarily the most economic choice despite its low purchase cost. To prove stainless steels’ cost-efficiency, three aspects are investigated in detail, namely corrosion resistance, mechanical properties and innovative construction solutions. First, the corrosion resistance was investigated under increasingly realistic conditions, ranging from electrochemical testing in artificial solutions over exposure in lab scale reactors to field exposure in operational biodigesters. The test results delimited alloying content as a function of surface finish. Furthermore, a series of laboratory tests and numerical analyses was carried out to extend the design rules from Eurocode 3: Part 1-4 (EN 1993-1-4). This was done for stainless steel shells under axial or circumferential compression including the post-buckling strength. By taking advantage of the post-critical strength, reduction factors could be significantly increased. Also adhesive bonding was explored as a part of innovative cost-effective design. It was concluded that adhesive bonding was not a suitable method for fabricating stainless steel biodigesters, although more adhesives and more rigorous surface preparation should be studied before definitive recommendations can be made. Combining the project results with cost and maintenance data gathered from the industry, the costs for equivalent in-situ concrete, carbon steel and stainless steel tanks were assessed. Stainless steel was the cheapest option in terms of whole life costs over a 25 and 40 year lifetime. Finally, the project generated design guidance for a range of suitable stainless steel grades for application in biodigesters.