Fouling is another very important aspect of the delayed coking process. In the coker preheaters, fouling can cause increases in heating costs, high pressure drops and lost revenue due to having to shut down units to clean out furnaces. Three units are used to study fouling here at The University of Tulsa Refining Technologies Group: the Fouling Serpertine Coil which is a pilot scale furnace, the Hot Liquid Process Simulator (HLPS) which is a bench scale fouling screening unit, and the Turbulent Flow Fouling Device which is a single-pass continuous-flow facility that can simulate fouling process in the transitional to turbulent flow regime. Preliminary fouling correlations were developed for both units as a function of feed properties and operating conditions where applicable.
Significant progress was made in quantitatively identifying the prevailing mechanism at the coking conditions (Asphaltene precipitation versus Coking). This will lay the foundation for a mechanistic fouling model. Studies were conducted using blends of vaccum resid with speciality feeds such as visbroken feed to evaluate the effect on fouling of unconventional coker feeds blended in with vacuum resid. This study opened up a potential new area of research related to the optimization of unconventional blending to minimize fouling. Also, in the pilot unit, gaseous hydrocarbons were found to effectively replace steam velocity without negatively impacting fouling. A unique tube-cutting device was built that allows for the splitting of the serpentine coil tubes so as to allow for in-situ viewing of foulant samples with minimal contamination from the cutting process. EDX and SEM technology was used to analyze foulant samples to identify and or support prevailing fouling mechanisms.
The mechanisms along with the new tools identified in this phase is expected to shed more light on the fundamental understanding of the fouling at coker furnace conditions.