Plant-simulation optimization of an atmospheric distillation
unit: kerosene side-draw tuning to increase gasoil while meeting
specifications
Ahmed Qasim1 · Hayder A. Alhameedi2 · Shahd Ammar Hatem3 · Hameed Hussein Alwan4 · Paul C. Ani5

Abstract
Diesel (straight-run gasoil, SRGO) is pivotal to global energy systems, and any increase in throughput must preserve
specification compliance. This plant–model case study at the Diwaniyah Refinery evaluates a no-CAPEX lever: reducing
the atmospheric kerosene side-draw while holding other product draws at plant averages. In controlled plant trials,
the side-draw was reduced from 5 to 1 m3/h; SRGO increased by approximately 44 percent, from 9 to 13 m3/h. Quality
outcomes were as follows: sulfur decreased from 15,100 to 10,000 ppm, with the ≤ 10,000 ppm limit met only at 1 m3/h;
flash point decreased from 85 to 70 °C yet remained at or above 60 °C across all tests; cetane number remained at or
above 50 (minimum 50.2); diesel index improved from 48.23 to 56.16–56.98, meeting the ≥ 55 threshold at 2–1 m3/h;
and kinematic viscosity decreased from 1.8 to 1.4 cSt, always within the ≤ 5.6 cSt limit. Aspen Hysys simulation program
was used to evaluate scenarios for increasing SRGO and maintaining its specifications. Following laboratory validation,
the simulation model showed good agreement with plant data, reproducing the observed operational trends. In addition,
Minitab program was used to develop simple empirical models over the 1–5 m3/h range to quantify the effect of kerosene
side-draw on SRGO yield and other specifications, and to select an operating point (1 m3/h) that maximizes SRGO while
maintaining specification compliance. The results provide actionable guidance for refineries seeking higher diesel output
while respecting quality specification