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(2012) Question 24: Given the potential consequences of back flow in high pressure hydroprocessing services, such as furnace tube rupture and pump shutdown, what layers of protection are being employed to reduce risk?

Our layers of protection are very similar here in that we have trip valves activated by SIL-rated instruments and which are only SIL-rated as required. And of course, we have basic process controls and critical alarm systems. In some, but not all, cases, we do have check valves downstream of our furnaces. That is not a standard at all our sites. However, on some sites, we are consistent about having check valves downstream of our furnaces.
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(2012) Question 25: What is your philosophy for mitigating fouling and corrosion in reactor effluent cooler systems in hydrotreater or hydrocracker units during a short-term washwater pump failure scenario? How much time is allowed before initiating a unit shutdown?

Chevron developed a rough set of internal guidelines that determine the allowable time to run without water injection. The guidelines are based upon ammonium bisulfide (NH4HS) concentration. For units that run at what we call low severity, which is zero to 3% NH4HS, we will allow a couple of days of operation without water injection. As the normal NH4HS concentration of the operating unit sour water increases, we allow progressively less time to run without water injection.
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(2012) Question 26: What catalyst and metallurgy design considerations are important when evaluating the co-processing of highly acidic renewable distillates? What can be done to mitigate carbon monoxide formation?

Acidity of renewable distillates can be intrinsic of the material (free acids of the vegetable oil) or generated during its conversion in the hydrotreating unit. Typically, free acids in vegetable oil amount to about 5%. This means that crude vegetable oil has a TAN number around 7, which requires special metallurgy for the pipelines to the feed drum.
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(2012) Question 27: What are the Best Practices around minimizing risk of catalyst or equipment damage during turndown operation of a steam methane reformer hydrogen plant?

Depending on the feedstock and configuration, most units operate with an S/C ratio between 3 and 7. However, during a turndown situation, the operator should target a higher S/C ratio and run at least 75% of the design steam rate. Doing so helps maintain adequate mass flux in the tubes to achieve good distribution, avoid hot tubes, and minimize catalyst damage.
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(2014) Question 82: Units operating with low main fractionator bottoms yield encounter a number of problems including coking and fouling in the slurry system and increased catalyst loading in the circulating slurry. What problems have you encountered and what practices have you done to manage these problems?

Units operating with low main fractionator bottoms yield encounter a number of problems including coking and fouling in the slurry system and increased catalyst loading in the circulating slurry. What problems have you encountered and what practices have you done to manage these problems?
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(2014) Question 83: As the time between FCC unit turnaround events are continuously being extended, what areas have you identified as having a high likelihood of failure due to erosion and what preventive measures can be taken to avoid such failures?

Erosion due to catalyst impact is often a strong function of particle velocity. However overall operating conditions, such as superficial velocity, are often insufficient to predict local erosion characteristics in FCC equipment where the likelihood and severity of erosion is influenced by local catalyst acceleration and impact. The mass, velocity, angle of impact, surface material and other factors all influence this local erosion behavior.
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