Back-up rings have no intended sealing function. Instead, as their name indicates, they are protective and supporting elements made from extrusion-resistant materials which generally have a rectangular cross-section. They are installed in a groove together with an elastomer sealing element, preferably with a corresponding O-ring in static applications.
Virgin Atlantic’s Flight100 saved 95 tonnes of CO2 in first SAF flight
There are government reports on biomass -includes other costs of preparing (transport and drying are big ones); never mind the lost CO2 sequestration...