PTQ Q2 2026 Issue

0.35

Stabili s er reboiler steam Exchanger chiller duty

∆wt% (base feed-operating feed)

0.31

Pressure < 18 kg/cmg >Increased chiller duty >Retrot required to meet product spec

0.27

0.23

Meeting product spec

0.19

-5

0.15

18 16 Pressure (kg/cmg)

-10

iC4

nC4 iC5 nC5 22 DMB

23 DMB

2MP 3MP nH MCP CH C7+

pressure of 20 kg/cm²(g) has been maintained for the oper - ating case. A feed with a higher proportion of low-boiling components requires lower stabiliser column pressure for efficient separation, thereby reducing the reboiler duty required to vaporise the lighter fractions. Thus, based on the feed composition analysis, it was observed that there is significant potential for energy saving by optimising the stabiliser column at a lower pressure. However, operating a column at low pressure increases the overhead vapour load, which can lead to higher duty requirements for downstream equipment, including the air cooler (AC-02), cooling water heat exchanger (E-02), and chiller (E-03). To address this, simulations were performed at reduced pressure and by adjusting the reflux ratio to achieve proper hydrocarbon separation and meet product specifications, while ensuring that the downstream sections‘ heat duty remained within acceptable limits. The key oper - ating parameters captured during the operating case and low-pressure simulation are tabulated in Table 1 . Results and discussion Simulations were carried out with operating case feed over a range of decreasing stabiliser column pressure from 18 kg/cm²(g) to 14 kg/cm²(g) to evaluate the feasibility of operating the column at reduced pressure and to assess its impact on product quality and steam consumption. Based on the simulation results (Table 1), it was observed that operating the stabiliser column at 18 kg/cm²(g) is Figure 3 Relationship between stabiliser pressure reduc- tion on reboiler steam consumption and its effect on prod- uct quality specification

detailed hydrocarbon analysis (DHA) along with relevant operating data, including temperature, pressure, flow rates, and steam consumption. • Thermodynamic framework: The Peng-Robinson equa- tion of state was selected as the fluid package for modelling, as it is highly recommended for predicting the pressure-vol- ume-temperature (PVT) behaviour of liquid and gas phases in petroleum processes. This equation of state provides accu- racy for hydrocarbon systems operating across wide pres- sure and temperature ranges typical of refinery operations. • Stabiliser column convergence criteria were established to meet stream specifications: a) C₅+ content in the FG is ≤0.1 wt%; b) HCl content in the stabiliser bottom stream is ~ 0 ppm (zero tolerance for corrosive species). • LPG stripper convergence was performed to ensure compliance with LPG product specifications: a) C₅+ content in the LPG product is ≤2.0 wt%; b) HCl content in the LPG product is ≤6 ppm. Subsequently, the model predictions were validated against the actual plant conditions (operating case), con- firming the accuracy of DHA lab analysis and the selected thermodynamic fluid package. Further, Figure 2 presents a comparative analysis of the stabiliser feed composition between the base case and the current operating case, with differences expressed as delta wt% (Δ wt%). The analysis indicates that the current stabiliser feed is lighter by approximately 1.5 wt% compared to the base case feed composition. Despite this shift, the stabiliser column Figure 2 Difference of DHA composition from base case stabiliser feed with operating case feed, wt%

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PTQ Q2 2026