PTQ Q1 2026 Issue

Acid phase ow rate (lbs/h) for Tray 14

Water wt% in acid phase for Tray 14

Operating point

307

306

302 303 304 305 300 301 298 299

2624.9

69.1

1974.0

51.8

1323.1

34.5

672.1

17.3

21.2

0.0

297

Temperature (˚F)

Figure 1 Heat maps for tray 14 at 160 lb/h entrainment with detailed explanation of the left and right panel to follow

around 228°F to dissolve the acid phase, whereas trays 19 and 20 require only 202-210°F. Trays further up the tower (tray 14) require temperatures close to 229°F. These differ- ences reflect the varying composition and pressure at each tray: heavier hydrocarbons and higher pressures lower TT, while lighter hydrocarbons and lower pressures raise TT. w Operating temperatures vs TT: Comparing these tran - sition temperatures to actual tray temperatures indicated that some trays, particularly tray 17 (feed), were operat- ing below TT, allowing a residual acid phase to persist and contribute to corrosion. Raising tray temperatures or reducing entrainment would be required to eliminate the acid phase. Temperature-pressure heat maps While TT gives a single number for each tray, a temper - ature-pressure (T-P) heat map provides a more complete picture of the operating envelope. Figure 1 presents heat maps for tray 14 at 160 lb/h entrainment. The left panel shows acid phase flow rate (lb/h) as a function of tempera - ture and pressure; the right panel shows water weight per cent in the acid phase. The white cross indicates the current operating point. Several observations stand out: • It is important to note that T-P sensitivity studies show how well-defined the acid phase inside the column is, as shown in the TT contour plots. Adding heat to the tower will change the composition, and these TT plots would have to be recreated, as in the original study. The goal of this study is to identify how much heat needs to be added to the column to eliminate an acid phase below tray 17. • In the left panel, the coloured region (red to blue) cor - responds to acid phase flow rates from >2 lb/h down to 0 lb/h. At low temperatures (~200°F) and pressures of around 285 psig, the acid phase flow is >1 lb/h; as the temperature increases at constant pressure, the acid phase rapidly disappears. • The right panel illustrates how water content in the acid phase declines as the temperature increases. At the current

operating point (white cross), water content is around 20 wt%, indicating a highly corrosive composition. • Pressure has a secondary effect: increasing pressure (moving up the plot) slightly shifts the coloured regions to higher temperatures, meaning that raising the column pressure can reduce TT and help dissolve the acid phase. However, pressure adjustments are often constrained by overall column operation. Heat maps for trays 17-20 (not shown here) exhibit sim- ilar patterns, with the coloured region shifting according to composition and pressure. For trays above the flash zone (18-30), the acid phase region occupies lower temperatures, indicating that these trays operate mainly in a full liquid-liq - uid phase regime rather than close to transition zones. Heat duty simulation and operational recommendations Since this plant’s column is integrated with the HF strip - per, the ability to raise tray temperatures via additional reboiler duty is constrained. The simulation showed that increasing duty raised vapour traffic but also increased HF and water in that vapour phase. A simulation of reboiler duty was therefore performed to determine how much additional heat was needed to dissolve the acid phase on each tray. The study concluded that a modest increase in duty (≈4%) combined with adjustments to the reflux ratio and condenser duty could raise tray temperatures enough to eliminate the acid phase on trays below the flash zone. Alternatively, reducing entrainment from 160 lb/h to ~50 lb/h would lower TTs sufficiently (single liquid phase entering the depropaniser) without increasing duty. The refinery was given an operational grid showing safe T-P combinations and was recommended to prioritise reducing entrainment via improved settler operation. Synthesis of lessons learned The case studies highlight several overarching lessons

PTQ Q1 2026