WRI has extensive experience developing predictive tools to address fouling and the propensity for coking in refinery operations. Because uncertainty can be expensive and irritating, process control is crucial. WRI has developed methods to minimize fouling, eliminate undesired coking in heat exchangers, maximize distillate yield, and rank residua by predicting relative fouling tendencies for various feedstocks.
The fouling of process equipment due to deposition occurs when heavy oil materials are heated, blended or pyrolyzed in visbreaking or vacuum distillation processes. WRI has developed predictive correlations for nonpyrolytic heat-induced deposition. Our predictive maps correlate residua properties with the amount of coke initially formed with pyrolysis. These predictive maps also allow the ranking of residua according to their initial coke formation tendencies in pyrolytic processes.
Our Coking Indexes determine how near a residuum material is to forming coke, allowing refiners to maximize distillation yield and stop heating before coking occurs.
WRI has enhanced a suspended particle solution model and developed correlations that can be used to predict the susceptibility of heavy oil to heat-induced deposition. Deposition and fouling in upstream and downstream operations occur when polar asphaltene flocs form. Asphaltenes are complex associated species; asphaltene flocs form when a residuum is heated above a temperature at which the intermediate polarity material no longer protects the polar asphaltene cores but below that at which pyrolysis occurs (340 °C). Deposition below pyrolysis temperatures (<340 °C) is caused by the heat induced removal of the intermediate polarity solvating layer around polar asphaltene cores.
The model, which incorporates asphaltene flocculation titration parameters and n-heptane asphaltene content, employs WRI’s Automated Flocculation Titrimeter to collect measurements required for analysis and feedstock control. The WRI predictability model can also be used to rank residua according to their relative tendencies to foul when heated.
WRI offers the Automated Flocculation Titrimeter, and our specialists are available to conduct custom studies of specific residua to provide insight into the effects of additives and treatments to minimize heat-induced deposition.
Using the WRI dispersed particle solution model of petroleum residua structure described above, WRI has developed predictors for how much coke will be formed in the early stages of pyrolytic coke formation. It is well known that the amount of coke formed when pyrolysis is complete is related to the hydrogen-to-carbon atomic ratio, but until now there hasn’t been a model available to predict how much coke will form in the early stages. WRI has created three-dimensional coke make predictability maps at 400 °C and 500 °C. These relate residence time and residuum-free solvent volume to the amount of coke formed at a particular pyrolysis temperature. The results provide a new tool for ranking residua, gauging proximity to coke formation, and predicting initial coke make tendencies.
The predictive maps are generated with WRI’s Automated Flocculation Titrimeter or WRI can perform customized pyrolysis and coking studies.
Distillation Efficiency Improvement using WRI Coking Indexes
WRI’s Coking Indexes can be used to minimize or eliminate downtime disruptions from fouling caused by coking. With the Coking Indexes, coking propensity becomes predictable, and efficiency is improved two ways: Financial losses from unscheduled downtime caused by coking can be minimized, and distillate yield is maximized because refiners can heat residua to the threshold of coke formation instead of quitting too soon because they can’t gauge the onset of coke formation. Reduced energy costs and carbon dioxide emissions are further benefits.