Fired heater design and operation to minimize coking: Application in refinery residue services

Carlos Jorge Batista Alcobia

Key information

Authors:

Carlos Jorge Batista Alcobia (Carlos Jorge Batista Alcobia)

Supervisors:

Marie Andrée Senegas (Marie Andrée Senegas); Maria Filipa Gomes Ribeiro (Maria Filipa Gomes Ribeiro); Marie-Andrée Senegas (Marie-Andrée Senegas)

Published in

September 20, 2007

Abstract

The main objective of this work was to specify basic fired heater design and operation criteria that help minimize the formation of coke in vacuum distillation unit fired heaters. Additionally, two heaters with severe coking problems, one from a vacuum distillation unit and another from a visbreaking unit, were analyzed in order to troubleshoot them. This work presents design specifications, operational advice and revamp considerations on vacuum distillation unit fired heaters. Vacuum heater operation data from TOTAL refineries was retrieved and compared to design guidelines found in literature. Fired heater simulation software was used to model several heaters and to study the influence of several parameters on the coke formation rate. The two heaters with coking problems were also modelled to search for possible design or operation problems and latter to analyze possible problem scenarios. The main conclusion is that the most important design parameters in minimizing fired heater coke formation are mass velocity and fluid film temperature in the tubes. The recommended mass velocity for fired heaters in vacuum distillation service is 1500 kg/m2.s at the radiant section inlet. The fluid film temperature should be kept below 460 ºC in all tubes except the heater’s outlet tube. The Donges visbreaker fired heater was found to suffer from high heat flux to the shock tubes and possibly from charge quality variation problems. The Leuna vacuum distillation unit fired heater is probably affected by hotspots caused by high refractory re-radiation from the firebox’s roof.