Fired-heater efficiency (excess-air control, air preheat) and steam-system losses incl. insulation — single-digit % of site fuel with paybacks under 2 years, before any capital project.
From our guide: Decarbonizing Oil refining — full context, charts and sources there.
Boilers, kilns, heat exchangers, valves and steam lines lose energy continuously. Inzonex makes patented (UK GB2508992.1) removable modular insulation — snap-fastened covers engineered per temperature tier, not generic off-the-shelf jackets: