PTQ Q2 2026 Issue

technically feasible. This leads to a significant 20% reduction in HP steam consumption, decreas - ing from 20 tons per hour (TPH) to 16 TPH, while maintaining the required product specifica - tions. The reflux rate, as well as the column top and bottom temperatures, have been opti - mised accordingly to maintain separation efficiency. Under these conditions, the duties for E-01(7.34 MMkcal/h) and E-03 (0.23 MMkcal/h) remain within the turndown limit. Further, the simulation results

Major parameters captured during simulation

Parameter

Operating case

Low pressure

Case 1

Case 2

Case 3

Stabiliser top pressure, kg/cm2(g)

20.2

18.0

16.0

14.0

Stabiliser top temp, °C Stabiliser bottom temp, °C

201 58.4

189 56.2

181 53.3

173 49.8

Reflux rate, m3/hr

Stabiliser reboiler steam, MT/h

16 (4 i )

14.4 (6 i )

13 (7 i )

Fuel gas flow, Nm3/h E-01 duty, MMkcal/h E-03 duty, MMkcal/h Meeting prod. LPG spec.

2,100

2,230

2,279

2,356

8.82 0.19

7.34 0.23

6.32 0.26

5.89 0.34

O P

Retrofit required

Table 1

was used to assess the hydraulic performance of the stabi - liser and LPG stripper columns by generating vapour-ver - sus-liquid mass flow rate plots, commonly referred to as hydraulic plots. For each tray, an operating point is pre - dicted, and the column is considered stable when this point lies within the hydraulic limits that define the operating zone. Points outside these boundaries, such as in regions of flooding, weeping, or other hydraulic constraints, indicate instability and potential operational issues. Column internals data, such as tray spacing, tray diam - eter, number of passes and trays, and tray type, were entered as inputs to generate hydraulic plots for each tray of the stabiliser and LPG stripper columns, and to evaluate column stability under low-pressure, optimised operating conditions. Figure 4 represents the top tray hydraulic plot of the stabiliser and LPG stripper column under low-pres - sure operation. The hydraulic analysis confirmed that the trays across the column exhibit stable performance, with all operating points falling within the defined stable hydraulic region. Plant demonstration at zero Capex During the demonstration run, the stabiliser feed rate was maintained constant, and the operating pressure was grad - ually reduced from 20 kg/cm²(g) (before demonstration run) to 18 kg/cm²(g) (after demonstration run) in controlled

showed that operating the stabiliser column at pressures below 18 kg/cm²(g) introduces major challenges, including deteriorated product quality, increased LPG carryover into the fuel gas, and limitations in chiller performance. At 16 kg/ cm²(g), the drop in HP steam consumption is ~6 TPH, but product quality and operation become unacceptable. C₅+ and HCl in LPG, at 6 wt% and 36 ppm, respectively, exceed specifications, and the chiller cannot fully condense LPG. Further reducing to 14 kg/cm²(g) offers a marginal energy benefit (reducing steam from 14.4 to 13 TPH), while further degrading product quality and completely overloading the chiller (see Figure 3 ). Overall, the simulations clearly indicate that operating below 18 kg/cm²(g) would necessitate a mandatory retro - fit or replacement of the chiller (E-03) to manage the higher overhead vapour load. Such a modification would require significant Capex, which negates the zero Capex advantage, and a more rigorous cost-benefit analysis. Column hydrodynamics analysis Hydraulic limitations of column internals are defined by the acceptable operating envelope for the column and ensure stable operation under varying process conditions. This is the critical step in evaluating column process performance prior to implementation at the refinery. In this study, the column analysis feature in Aspen HYSYS

100% Jet ood

100% Downcomer backup

Constant V/L

Minimum weir load

Maximum weir load

Minimum weir load

Constant V/L

Operating point

0% Weep

Liquid mass ow

Figure 4 Hydraulic plot for stabiliser column (left) and LPG stripper column (right)

PTQ Q2 2026