Other Components of Thermal Efficiency
In this section, we will discuss how different components of olefins furnace design have
contributed to increasing thermal efficiency over the years. Again, the olefins furnace is
an extreme example of process furnace design, and most improvements in olefins furnace
technology can be applied to boilers and other process furnaces.
Insulation and Sealing. The firebox is the heart of a furnace. In olefins furnaces,
this is where the cracking reaction takes place to thermally break down hydrocarbon
feeds into valuable products. The cracking process is highly endothermic, and large
amounts of heat must be input to the process fluids to crack the hydrocarbons to lighter
components. The reaction takes place inside the radiant coil, where radiant heat is
provided by combusting fuel in burners.
In the 1970s and 1980s, tube alloy materials were less resilient and their corresponding
maximum firebox temperatures were lower than those for modern furnaces.
Olefins furnace fireboxes were once operated at 2000 °F or less. The furnaces typically
had a refractory thickness of 9 in. to maintain the outer skin temperatures under the API
recommended 180 °F. Insulation bricks were designed for 2300 °F.