(109b) Multi-Scale Modeling of Fired Process Heaters in Chemical Process Industry

Comprehensive design and analysis of a fired process heater entails the study of the air duct system for combustion air flow regulation, burner and tube placement design on the firebox side to achieve the required heat flux distributions along the tubes, and an adequate description of the process side physics to be able to predict the right conversion rates. Computational Fluid Dynamics (CFD) is a cost effective alternative to time-consuming design of experiments approach to study burner performance, identify potential issues related to tube life, meet emissions standards, and help maintain product quality.

Since the complete systems is made up of several sub-systems each of which could influence the overall performance, a multi-scale modeling approach is employed in this paper where, CFD is used to model each of component parts in a typical fired process heater. First, the air delivery system to the burner is studied and optimized. Next, the burner used on the firebox side is modeled and optimized to meet flame length and emission requirements. The heat from the firebox side is used to heat the process fluid flowing in the tubes. The heat transfer to the process side and the subsequent process side reactions are modeled using a co-simulation approach and the resulting product yield is monitored for a given firing rate and process fluid flow rate. Depending on the application, the tube side physics could involve reactions taking place in a packed bed system as in the case of steam methane reformers. In such a situation, the heat transfer in packed beds depends on particle loading and particle shapes. A methodology to study the pressure drop and evaluate heat transfer in packed bed systems by explicitly modeling the packing in tubes is also presented.