PTQ Q4 2023 Issue

0.50 0.55

0.45

0.40

0.35

0.0 0.15 0.10 0.05 0.20 0.25 0.30

NHCl (Sal ammoniac) - Sol (kg/hr) - Pressure = 3.0 bar NHCl (Sal ammoniac) - Sol (kg/hr) - Pressure = 4.0 bar NHCl (Sal ammoniac) - Sol (kg/hr) - Pressure = 5.0 bar NHCl (Sal ammoniac) - Sol (kg/hr) - Pressure = 6.0 bar NHCl (Sal ammoniac) - Sol (kg/hr) - Pressure = 7.0 bar

Temperature (˚C)

Figure 2 Survey conducted in OLI Studio Stream Analyzer, where the impact of the increasing hydrostatic pressure on the ammonium chloride deposition is examined

column increases, raising the total pressure and dissolving the traces of dispersed gaseous light hydrocarbons into the liquid. At this point, the NH 4Cl salt point is influenced by the activity coefficients of HCl, NH3 , and the water solubility in the hydrocarbon rather than the partial pressures of a non-existent gas phase. The tendency for NH 4 Cl deposition is particularly pro- nounced as the pressure increases along the descending suction line and within the pump impeller. This is illustrated in the Figure 2 survey. As temperature decreases in the initial heat exchangers and without wash water, the propensity for NH 4 Cl depo- sition increases even at minimal chloride concentrations. Further cooling reduces the water solubility in the hydro- carbon, leading to the separation of a highly corrosive aqueous liquid phase. Figure 3 depicts the simulated conditions of the TPA cir- cuit, specifically: • Extraction temperature at 170°C

corrosion rates and the dispersion of solid corrosion prod- ucts. As the condensed acidic water descends the column, it re-evaporates, locally increasing the vapour phase molar concentration of HCl (hydrogen chloride) and NH 3 (ammo- nia) to levels that trigger the NH 4 Cl’s desublimation from the gas phase. These salts are deposited in compromised areas like the structured packing or trays in the TPA extrac- tion zone. • TPA circuit: The increase in HCl, NH 3 , and trace moisture in the TPA extraction zone, due to the overhead temperature reduction, results in a higher concentration of these contam- inants in the extracted TPA. The presence of water, in addi- tion to the physical entrainment of liquid water, is attributed to its good solubility in high-temperature naphtha. This phe- nomenon was quantified using OLI Studio Suites. After the draw-off section of the chimney tray collector, the TPA exhibits a single liquid phase with minimal traces of physically entrained and dispersed gas. As it descends along the suction path, the hydrostatic pressure of the liquid

0.00 0.03 0.02 0.01 0.04 0.05 0.06 0.07 0.08 0.09 0.10 0.12 0.11 0.17 0.14 0.15 0.16 0.13

120 110 100 150 140 130

Water (kg/hr) Ammonuim chloride (Sal ammoniac) - Sol (kg/hr) (Y2)

0 30 20 10 40 50 60 70 80 90

Temperature (˚C)

Figure 3 The profile illustrates the sublimation of NH4 Cl and the formation of the aqueous liquid phase

112

PTQ Q4 2023