Impact of radiation models in coupled simulations of steam cracking furnaces and reactors

As large floor-fired furnaces have many applications in refinery and (petro-) chemical units and about 80% of heat transfer in these furnaces is by radiation, the accurate description of radiative heat transfer is of the most importance for accurate design and optimization. However, the impact of using different radiation models in coupled furnace/reactor simulations has never been evaluated before. Therefore, coupled furnace/reactor simulations of an industrial naphtha cracking furnace with a 130 kt/a capacity have been conducted. Computational fluid dynamics simulations were performed for the furnace side, while the one-dimensional reactor model COILSIM1D was used for the reactor simulations. The Adiabatic, P-1, discrete ordinates model (DOM), and discrete transfer radiation model (DTRM) were evaluated for modeling the radiative heat transfer. The results with DOM and DTRM are very similar both on the furnace and the reactor sides. The flue gas temperature using DOM is higher than when using the P-1 radiation model, resulting in higher incident radiation. Comparing the simulated results of all radiation models to the industrial product yields and run lengths shows that DOM and DTRM outperform the others. As DOM has a broader application range than DTRM, and because the current implementation of DTRM in FLUENT/14.0 cannot be run in parallel yet, DOM is the recommended radiation model for run length simulations of steam cracking furnaces