Intensified Heat Transfer Technology – CFD Analysis to Explain How and Why IHT Increases Runlength in Commercial Furnaces

Intensified Heat Transfer Technology (IHT) is the use of radiant coil inserts that have a twisted baffle integrated with their inner surface. The inserts have the same diameter and metallurgy as the radiant coil, and are placed strategically in the coil to create turbulence in the process fluid, thus reducing the boundary layer and increasing runlength by achieving improved heat transfer. Commercial experience in more than 50 heaters – most of them cracking naphtha – has shown that runlength can be extended by a factor of 1.2 to two times the runlength of a bare coil. The main advantage of the inserts, aside from their competitive cost, is that they can be installed into new or existing heater tubes. In this paper, data from units operating with IHT will be presented. We will discuss a computational fluid dynamics (CFD) analysis that was applied to a heater coil to explain the benefit of installing IHT. The velocity and temperature profiles in the coil with and without IHT were studied and the optimum location of the inserts was evaluated. A kinetic scheme was devised to estimate the coke rate formation at the tube surface, which ultimately explains the reduction in tube metal temperature (TMT) when using IHT.