Hot-season rise of reflux drum temperature in an atmospheric crude distillation unit: Field impacts on overhead corrosion, flare loading, and loss prevention

• Field study quantifies hot-season reflux-drum impacts in an atmospheric CDU. • Hotter drum shrinks condenser margin; header pressure and flare loading rise. • Off-gas shifts heavier (C 1 -C 3 down; C 4 -C 5 + up), diverting gasoline to fuel/flare. • Light naphtha gets heavier; IBP 32-40°C, EP 120-140°C; sulfur slightly higher. • Actionable window for loss prevention: 55-60°C with temp-comp neutralizer. This field study quantifies how reflux drum temperature governs the overhead risk posture of an atmospheric crude distillation unit during hot-season operation, with explicit attention to corrosion, flare loading, and economic loss. During a single summer campaign at Al-Diwaniyah Refinery, the drum temperature was stepped from 50 to 70°C and, at each set point, off gas, light naphtha, and boot water were sampled under steady operation. Hotter drum operation reduced partial condenser driving force and shifted the overhead phase split toward vapor, increasing header pressure from 0.57 to 0.82 barg and standard off gas flows from 320 to 360 and from 35 to 50 Nm 3 /h to the furnace and the flare, respectively. Concomitantly, off gas became heavier: C 1 –C 3 fraction contracted from 56.71 to 41.41 mol%, whereas C 4 rose from 25.53 to 36.72 mol% and C 5+ increased from 5.71 to 15.94 mol%. From a loss prevention perspective, this C4–C5+ enrichment, together with the higher flare rate, indicates increased diversion of gasoline-range material to the gas header and flare (avoidable hydrocarbon loss) and higher propensity for flare smoke if assist is not adjusted. Light naphtha specification drifted unfavorably (IBP from 32 to 40°C; EP from 120 to 140°C) with a modest increase in sulfur (from 300 to 312 ppm), tightening blending margins and risking reprocessing. Overhead corrosion risk increased, as boot water chemistry degraded (pH from 6.4 to 6.0; chloride from 10 to 14 ppm; dissolved iron from 0.15 to 0.44 ppm). These field resolved trends define a practical operating window that favors cooler drum targets (approximately 55–60°C), recovery of condenser effectiveness, and temperature-compensated neutralizer control to stabilize aqueous chemistry while minimizing avoidable flaring. The results provide actionable guidance for balancing product quality, energy use, environmental performance, and corrosion risk in hot-climate refining.