PTQ Q4 2024 Issue

y Four ULSD systems use a two-stage VD. z One ULSD system uses a single-stage VD after a flash vessel. The operability and reliability of single-stage VDs are comparable to those of two-stage VDs, indicating that the simpler configuration does not compromise performance. Facilities with only a coalescer for ULSD drying do not aim to meet a total water content below 100 wppm. The number of facilities employing single-stage VDs is the highest, reflect - ing a broader industry preference. Newly commissioned ULSD facilities show a preference for single-stage VDs, sug - gesting a shift towards simpler, possibly more cost-effective configurations. To assess the impact of feed temperature and water con - tent on the performance of VDs, a case study was conducted using Hysys simulation for a single-stage VD. The study var - ied feed temperatures from 60°C to 165°C and analysed two scenarios with total water content in the feed at 200 wppm and 5,000 wppm, respectively. In both scenarios, the VD’s pressure was adjusted to achieve a target water content of 50 wppm in the VD bottom. The outcomes of this study are depicted in Figure 3 . Additionally, the steam consumption of the ejector was estimated for these varying feed water contents to maintain 50 wppm water in the VD bottom ( Figure 4 ). Key takeways include: • Deep vacuum requirements: For feed temperatures below 120°C, a very deep vacuum is necessary for effective water removal, regardless of whether the feed water content is 200 wppm or 5,000 wppm

200 wppm 5000 wppm

-0.73

-0.78

-0.83

-0.88

-0.93

-0.98

70 80 90 100

110

120 130

140

150

160

Vacuum dryer feed inlet temp (˚C)

• Reduced vacuum for higher temperatures: At feed tem - peratures above 120°C, the vacuum requirement in the VD is comparatively lower, especially when the feed water content is 200 wppm as opposed to 5,000 wppm. • Steam consumption variances: Below 120°C, steam con - sumption for the ejector is considerably higher when the feed water content is 5,000 wppm compared to 200 wppm. However, above 120°C, steam consumption levels off and becomes similar for both levels of water content • Operational optimisation: Operating the VD at higher temperatures, preferably above 120°C, is beneficial after maximum energy recovery for uses such as DHT feed pre - heating, BFW preheating, or LP steam generation • Contradictions with coalescer use: The integration of Figure 3 Effect of water in VD feed for VD operating pres - sure and temperature

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PTQ Q4 2024