Design and operation of salt dryer for ULSD: Part 1
Practical guidance on salt selection, vessel configuration, process control, and reliability for effective application in ULSD service
Prabhas K Mandal and Rajib Talukder Aramco
T he presence of water, both dissolved and free, in ultra-low sulphur diesel (ULSD) can result in haze, corrosion, and microbial growth, necessitating strin- gent control to meet product quality specifications. Various methods exist for water removal in refinery products. However, this article focuses exclusively on the design and operation of salt dryers for ULSD service. Related aspects, including the relationship between water content and haze, haze testing methodologies, alternative drying technolo- gies, and vacuum dryer systems, have been comprehen- sively addressed in prior work.¹ Salt dryers have been used in petroleum refining since the 1950s, predating the widespread adoption of vacuum dry- ers and other advanced dehydration technologies. Despite their long-standing application, published literature on the detailed design, operation, and troubleshooting of salt dry- ers for ULSD remains limited. Salt dryers are used to remove free water and part of the dissolved water from ULSD. The objective is to reduce total water content to below 80 wppm at operating conditions,
It also acts as a medium where brine flowing downward dissolves the free water entering with the incoming ULSD. ULSD enters the vessel from the bottom through an inlet distributor located just above the support grid. The distrib - utor ensures uniform flow distribution across the salt bed. As ULSD flows upward through the bed, water is absorbed into the salt, forming brine, which settles by gravity and accumulates in a boot for periodic draining. The dry ULSD product exits from the top. In some installations, the vessel is filled with salt without a support grid. In such configurations, the inlet distributor is placed at the bottom and wrapped with a stainless-steel screen to prevent salt ingress. The brine drain collector is also a custom screen designed to resist plugging. While this simpli - fies construction, it is prone to screen fouling, outlet corrosion, and requires periodic salt dissolution/mechanical cleaning. An external drain pot may be added to allow continuous brine withdrawal, minimise corrosion, and reduce screen blockage. Against this backdrop, this discussion focuses on the stand- ard configuration where salt is supported on ceramic balls.
ensuring the product remains bright and clear when tested at 22°C. These units are typi - cally located downstream of a coalescer, which reduces free water content, often to as low as 15 vppm,² minimising salt consumption and improving drying efficiency. Process description Salt dryers are vertical vessels packed with a salt bed sup- ported on a ceramic ball layer resting on a support grid. In earlier designs, gravel was used instead of ceramic balls. Since the openings in the sup- port grid are larger than some of the smaller salt pieces, the ceramic ball layer is used to prevent salt migration and provide mechanical support.
Steam + CaCl H O
200
178 175
150
Steam + brine
100
CaCl H O + Ca Cl
Brine + sinjarite
50 45.1 30.1
Brine
0
Brine + antarcticite
Ice + brine
-49.8
Ice + CaCl 6H O
-75
0
20
40
60
80
100
30.2
50 56.6
75
H O
Weight per cent CaCl
CaCl
Figure 1 CaClâ‚‚-water phase diagram6
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PTQ Q2 2026
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