PTQ Q4 2025 Issue

Feed quality issues

Contamination from tankage feed

Imported feed quality issues

Crude contaminents

Frequency of imports (2)

Heavier feed has high N (1)

No checks or mitigations for contaminents

Solids

Chloride

Oxygen

Water

HDS2 feed high nitrogen

HDS2 feed high chloride

HDS2 feed high sulphur

Feed blanketing

N 2 blanketing is not regularly checked and lack of sampling

No oxygen scavenger injection or stripping

No check for oxygen content of feed

Signicant contributor Unlikely

Very likely

To be conrmed

Possible Probable

Figure 1 Feed contaminant source fault tree – top level

(WABT) requirement. When moving to a 10 ppm sul- phur operation in diesel units, the better units switch from ASTM D86 to gas chromatography (GC) distillation to track fractionation. Contaminants control: Contaminants can come from sev- eral sources. Slop processing on the crude unit is another unpredicted source of contaminants, such as chemicals, cracked stock, and oxygenates. Crudes can contain arsenic, organic chlorides, and other chemicals. Crudes from shale oils and fracking are notorious for having varying levels of contamination. The key is that with a new feed, the correct feed analy- ses are done. There have been several cases of unexpected naphtha hydrotreater deactivation due to arsenic, as staff members rarely check naphtha for metals. Deactivation due to normal feed coking is usually zero, and contamina- tion/fouling are causes of poor performance for these low severity-units, even at very low H₂ pp. Stable, clean feed to the catalyst is the foundation for predictable and efficient operation, as well as optimum cycle length. Emergency and restart procedures A good reaction to emergencies will preserve catalyst per- formance. One common mistake is trying to keep the unit online for too long. Procedures should be well understood and easy to access. They should include actions that, in severe situations such as fire, require certain instrumenta - tion to be in place to remove the feed, fire source, isolation cooling, and pressure reduction. Cooling should not rely on gas quench alone for control of

exotherms. The heat source needs to be removed, and the system frequently cooled, even if it is by feed. In the case of fire, hydrocarbon sources should be isolated. The key, then, is cooling and depressurisation. Controlled depressurisation, even before any emergency trip, is key to reducing the exotherm rate of change, main- taining equipment integrity, and creating inbuilt cooling in mixed-phase systems as the liquid vapourises. Controlled depressurisation, which can be slowed or halted, should be a primary tool for reactor protection. Restart procedures are also important. Sometimes the intention is to restart as quickly as possible. However, this can cause more damage due to thermal stresses and create new shutdown situations. The frequency of shutdowns and thermal cycling should be built into equipment inspection frequency or even the need for hot bolting, as bolts relax. Corrosion control Corrosion is a particular concern in areas where water or salts can be present, such as reactor effluent air coolers (REAC). Report API 932B 2019 provides great guidance on REAC issues, which can significantly impact the unit and, thus, catalyst utilisation. REAC systems are suscepti- ble to ammonium bisulphide corrosion. The API report rec- ommends alloy selection, expected corrosion rates, water wash equipment requirements, and corrosion monitoring programmes to mitigate failures. More difficult are chloride-related issues. Under-deposit corrosion from chloride salts, which is more difficult to detect and predict, is best addressed by much better mixing,

REAC corrosion

Material inspection issues

Instrumentation issues

Feed quality

Design issues

Operational issues

Monitoring gaps

Contamination issues

Maintenence

Figure 2 REAC corrosion top-level fault tree

PTQ Q4 2025