PTQ Q2 2026 Issue

water-to-salt ratio is ≈49.17/50.83, or ≈0.97, meaning around 1 kg of water can be removed using 1 kg of CaCl₂. Use of marine salt Use of marine salt in place of mined rock salt is strongly not recommended. Although some refiners have attempted this substitution to reduce operating expenditure, these attempts have generally proven unsuccessful, resulting in multiple operational issues. Key reasons for avoiding marine salt include: • Marine salt crystals are typically softer, smaller, and mechanically granulated, which easily break down when wetted, causing increased pressure drop, channelling, bridging, salt carryover, and bed plugging. • Insoluble impurities, such as calcium carbonate, com - monly present in marine salt, lead to plugging and opera - tional disruptions in brine drain lines. • Marine salt can harbour sulphur-digesting bacteria, pro - ducing hydrogen sulphide (H₂S) and polysulphides. These contaminants can lead to corrosion issues and negatively impact product quality tests, such as the copper strip test. Commercial-grade mined rock salt is preferred due to: • Higher purity (typically around 99% NaCl), ensuring con - sistent drying performance. • Uniform crystal size, supporting optimal flow distribution and minimising channelling. • Minimal insoluble impurities, significantly reducing oper - ational disruptions and maintenance needs. • Hard macro-crystalline structure, which maintains integ - rity and structure even as it dissolves, preventing bed com - paction and maintaining effective fluid flow. Salt dryer design considerations Key parameters of salt dryer sizing include dryer diameter and height. ULSD superficial velocity is used to determine the salt drier diameter. Design superficial velocities range from 9 to 12 m/hr for rock salt and up to 15 m/hr for CaCl₂. Higher superficial velocity can lead to salt and/or brine car - ryover with the product and could also cause channelling. The salt dryer bed diameter is typically limited to 5.5 m to minimise maldistribution and loss of drying efficiency. As shown in Figure 3 and starting from the bottom, the total dryer height is obtained by summing the vertical allowances for each section: the brine hold-up section (H1), any transition or gap between H1 and the ceramic ball layer, the ceramic ball layer (H2), minimum salt bed height (H3), replacement salt bed (H4), and the top disengage - ment or calming section (H5), with the following detailed considerations for each section: u Brine collection boot [H1] : The boot should be sized to allow removal of brine at least twice per shift, based on separation principles, where dispersed liquid droplets (ULSD) rise in accordance with applicable settling laws, depending on the Reynolds Number (NRe) of the droplets. The boot diameter is sized so that the downward veloc - ity of brine is no more than half the rise velocity of ULSD droplets through brine, allowing adequate time for separa - tion without entrainment. Minimum boot diameter is typi - cally set at 610 mm, in line with API 12J,4 to allow internal

Distributor

Support grid

A - ULSD in B - Dry ULSD out C - Brine out

Figure 3 Typical salt dryer section with labelled heights

access for inspection of painting or cladding. The interface level range is defined by the following constraints: • Hold-up volume (HLL to LLL): The region between High Liquid Level (HLL) and Low Liquid Level (LLL) should pro - vide a minimum total hold-up time of 16 hours (two shifts), with each segment (HLL to NLL and NLL to LLL) contribut - ing at least eight hours. In no case should either sub-sec - tion be less than half the interface float height, which is typically about 180 mm. • Instrumentation clearance: A minimum of 150 mm is maintained above the HLL and below the LLL. v ULSD entrance chamber [H2] ULSD enters just above the support grid through a side-per - forated inlet distributor positioned approximately 50 mm above the grid, with perforations located at the mid-height of the pipe. The ceramic ball layer surrounds the distributor, extending both above and below it. For effective brine con - tact and uniform ULSD distribution, a minimum of 200 mm of ceramic balls is maintained above the mid-height of the distributor. Accordingly, [H2] is calculated as 50 mm + half the inlet pipe diameter + 200 mm. w Minimum salt bed [H3] : A minimum salt bed height of 2 m, corresponding to approximately five minutes of con - tact time, is generally required to achieve effective removal of dissolved water. This criterion is widely adopted in indus - try practice. In operational practice, refiners often sched - ule salt topping up when either 50% or 30% of the bed is consumed. To maintain the required minimum bed depth throughout the cycle, the initial bed height at loading should be twice the minimum required depth if topping-up is done at 50% consumption, or 1.5 times the minimum required depth if topping-up is done at roughly 30% consumption.

PTQ Q2 2026