Sauter mean diameter (d32) particle size, which in this case is 1,912 microns for the SMDmax and 1,213 microns for the traditional nozzle. This large variation in droplet spec - trum suggests a significant decrease in entrainment when using an SMDmax spray nozzle. Theoretical Stokes’ Law- based entrainment calculations based on this droplet data sprayed in a counter-current tower of ~0.4 C factor result in a reduction of entrainment of around 300% in comparison to traditional spray nozzles commonly used in this service. The cumulated volume curves (see Figure 4) illustrate the percentage of volume of liquid sprayed as a function of drop - let size. If one was to suppose that droplets smaller than 975 microns in diameter were to be entrained, the cumulative volume percentage curves illustrate that 6% of the total vol - ume sprayed from a Lechler (4HR.148) nozzle would entrain, whereas 24% of the total volume sprayed from a traditional maximum free passage-style nozzle would be entrained. This 18% difference represents a reduction in the uplift of gasoil and an increase in wash oil rate through the packing. The use of the next-generation spray nozzle allows for more flexibility in operation. The refiner can choose to wash conservatively by ensuring more gasoil makes it to the vac - uum tower bottoms or, conversely, reduce wash oil rates in an effort to maximise yields and improve distillation effi - ciency. This translates to either a reduction in operational costs by avoiding unplanned shutdowns due to premature dry-out-induced coking of the wash bed or reducing the uplift of gasoil, which is a high-value product. The entire product line was spray tested to ensure direc - tional improvement in both droplet sizes and free passage, irrespective of the capacity. Test data at 10 psig differential pressure of the smallest capacity Lechler SMDmax (part no. 4HR.008) compared to an equivalent capacity traditional maximum free passage spray nozzle commonly used in wash zones can be seen in Figures 5 and 6 . The cumulated volume curves in Figure 6 illustrate an even larger offset than that of the larger nozzles in Figure 2. At 10 psig differential pressure, the cumulative volume
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Max f ree p assage - style nozzle Lechler SMDmax equivalent
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Figure 5 Droplet size summary of the Lechler SMDmax (4HR.008) compared to conventional nozzles
The SMDmax spray nozzle produces a significantly higher percentage of larger droplets when compared to a standard maximum free passage nozzle. The purple region in Figure 3 is droplet population that is common to both nozzles. The red region towards the top left of the plot rep - resents droplets unique to the conventional nozzle that are below 500 microns. Conversely, the light blue region represents a population of droplets unique to the SMDmax spray nozzle, which are greater than 500 microns. This region represents 20.6% of total droplets produced by this nozzle. Moreover, since volume is a cubic function of diameter, the higher spectrum of larger droplets shifts the overall volumetric flow fraction towards the non-entrainment region, illustrated in Figures 4 and 6 . This variation in droplet size is also notable in terms of
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Max f ree p assage - style nozzle Lechler SMDmax (4HR.148)
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Max f ree p assage - style nozzle Lechler SMDmax equivalent
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Figure 6 Cumulative volume per cent of Lechler SMDmax (4HR.008) compared to conventional nozzles
Figure 7 Theoretical entrainment per cent vs spray nozzle pressure drop for identical nozzle capacities
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PTQ Q3 2024
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