PTQ Q2 2026 Issue

μ = Dynamic viscosity of ULSD (~3 × 10 ⁻ ³ Pa·s at 40°C). ρ = Density of ULSD (~830 kg/m³). v = Superficial velocity (m/s). L = Bed depth (m). The clean bed pressure drop should be designed to remain below 1.0 bar. However, during the design stage, if the estimated clean pressure drop exceeds 0.7 bar, the addition of a parallel salt dryer should be considered. Dryer operating temperature Operating the salt dryer at a lower temperature reduces both salt consumption and brine generation, as the dis - solved water content in the hydrocarbon phase decreases with temperature. For this reason, a water cooler is typically installed upstream of the coalescer to reduce the hydrocar - bon temperature, enabling the downstream salt dryer to operate at the lowest feasible temperature. As the concentration of dissolved water in hydrocarbons increases with temperature, brine solubility in the ULSD also rises. Consequently, higher operating temperatures promote salt carryover and deposition in downstream piping and stor - age tanks, leading to increased pressure drop and frequent analyser plugging. Field data indicate that, over time, pres - sure losses in ULSD rundown lines can be up to four times greater than clean pipe predictions due to salt accumulation. As per best industry practice, downstream piping should be oversized by at least one nominal diameter to accommodate potential salt deposition and long-term fouling. Part 2: Good operating practices Part 2, scheduled to be published in PTQ Q3 2026, doc - uments the learnings from Part 1 and converts them into clear design and operating guidance. References 1 R. Talukder, P. Mandal, Selection of ULSD dryers: Key technical con - siderations, PTQ Q4 2024 . 2 R. L. Brown, T. H Wines, Improve suspended water removal from fuels, Hydrocarbon Processing , December 1993. 3 American Fuels & Petrochemical Manufacturers (AFPM) Conference Notes. 4 Process Design of Oil and Gas Separators and Scrubbers , API Recommended Practice 12J Ninth Revision. 5 Yaws’ Handbook of Properties for Aqueous System s. 6 Occidental Petroleum, Calcium Chloride Handbook , OxyChem Technical Bulletin, 2019. 7 Huguet, L., et al., Phase diagram of binary mixtures of water (H₂O) and sodium chloride (NaCl), ResearchGate, 2020. Prabhas K Mandal is an Operations Engineer Specialist at Aramco, Saudi Arabia. He has more than 30 years of experience in petroleum refining and supports front-end design development for capital pro - jects. He holds a BTech in chemical engineering and an MTech in petroleum engineering. Email: prabhas.mandal@aramco.com Rajib Talukder is a Process Specialist in the Global Manufacturing Excellence department at Aramco, Saudi Arabia. He has more than 30 years of experience in process engineering and holds a BTech in chemical engineering from NIT Tiruchirappalli, India. Email: rajib.talukder@aramco.com

Regardless of the topping-up strategy, the minimum bed depth [H3] must always be sufficient to ensure the target contact time of at least five minutes, as typically observed in industry designs. To evaluate the required minimum salt bed height, the following parameters are typically calculated: • Superficial velocity (m/h) = ULSD flow rate (m³/h) / dryer cross-sectional area (m²) [the velocity that the fluid would have through an empty vessel]. • Voidage = 1 - (bulk density of salt / true density of salt). • Interstitial velocity (m/h) through void = superficial veloc - ity / voidage. • Contact time (min) ULSD with salt = 60 × [salt bed height (mm) / 1,000] / interstitial velocity (m/h)]. x Replacement salt bed [H4] : This salt bed, above the minimum salt bed, is to maintain the desired salt replace - ment frequency. The volume of replacement salt required depends on: • Water concentration at the salt bed inlet and target water content of product. • Desired cycle time for salt replacement, excluding mini - mum bed height. To estimate the required bed depth: Step 1: Determine the salt consumption rate based on sol - ubility at the operating temperature, inlet water content, and target water content. Step 2: Choose a cycle time (typically three or six months). Step 3: Use salt bulk density to calculate volume. Step 4: From the dryer diameter (based on a superficial velocity of 9-12 m/h), determine the required depth. y Dried ULSD retention section [H5] : A minimum 600 mm height is required between salt bed and vessel top tangent line, or adequate to allow at least five minutes retention of dry ULSD. Operational experience has shown salt deposition at analysers in downstream blending stations, underscoring the importance of conservative design in terms of superficial velocity and retention time. Pressure drop The pressure drop across the salt bed is a key design and operational parameter. Excessive pressure drop can indi - cate salt breakdown, fines accumulation, or the presence of water slugs. For estimating pressure drop through the salt bed, the following form of the Ergun equation for a packed bed is commonly used: ΔP = [150 × (1 - ε )² × μ × v / ( ε ³ × d ₚ ²) + 1.75 × (1 - ε ) × ρ × v² / ( ε ³ × d ₚ )] × L (Eq. 3) Where: ΔP = Pressure drop (Pa). ε = Bed void fraction (typically ~0.40)-[volume fraction not occupied by salt particles]. d ₚ = Equivalent spherical particle diameter (m), repre - senting the hydraulic behaviour of the particle in the bed. For design, 0.005 m is typically used for rock salt crystals (3.5-8 mm angular size), and 0.019 m for CaCl₂ briquettes (30 × 26 × 14 mm nominal).

PTQ Q2 2026