internal geometries of the spray nozzle. Since entrainment reduction was the key driver for this new product, the new spray nozzle design had to feature internal geometries that promoted the creation of coarse droplets while reducing the percentage of fine droplets. To achieve this, energy from dif - ferential pressure had to be dissipated within the spray noz- zle to reduce the spray nozzle’s propensity to over-atomise. Since clog resistance was a secondary design driver, experience with a vaneless swirl chamber design was lev- eraged to ensure the product featured both entrainment reduction and large maximum free passage characteristics. Traditional axial full cone nozzles rely on the constriction of an open cross-sectional area, known as a swirl vane or swirl insert, to increase liquid velocities and turbulence within the spray nozzle chamber. This turbulence promotes small droplet formation. The internals of the proprietary SMDmax spray nozzle feature unique large-diameter channels to aid in the dis- sipation of energy from the liquid stream being sprayed. These channels feed an engineered swirl chamber to develop a spray plume without excessive turbulence and the penalty of a constricted cross-sectional area. This dis - tinctive design of the internals of the spray nozzle allows for the production of very coarse droplets for spray nozzles that have relatively low flow rates. In the process of making the droplet size bigger, the vane- less design also offered a much larger free cross-section area compared to the traditional free passage design. For similar nozzle capacities operating at the same differential pressure, a vaneless full cone design offers approximately a 90% larger free cross-section area. Additionally, the coarse droplets inherently have higher mass than finer droplets. Since momentum is directly proportional to a droplet’s mass, the droplet’s chances of reaching packing are greater when compared to a similar velocity but smaller diameter droplet. Extensive spray testing was conducted to evaluate the performance of both the new SMDmax spray nozzles and conventional nozzles widely used in this application. The spray lab used to facilitate this testing was established in 2019 and features state-of-the-art measurement technol- ogy in a controlled environment, as seen in Figures 1 and 2 . The experiments focused on gathering droplet size and droplet velocity data of spray nozzles traditionally used in the wash section of vacuum towers and the new nozzle design on the same Phase Doppler Analysis (PDA) equip - ment in order to draw conclusions on a comparable basis. Traverse spray plume analysis (across the entire spray plume) was carried out at various operating points (3, 5, 7, 10 psi differential pressure) in an effort to holistically under - stand the spray plume’s characteristics across the typical operating range of a wash bed spray nozzle. It is important to note that testing was conducted using water, spraying in a downward direction in atmospheric conditions. Test conditions differ from the actual operating conditions of a wash-bed spray header. However, the intention of the spray testing was to illus- trate directional improvements in performance against widely used traditional nozzles in this service. Trends in
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Max f ree p assage - style nozzle Lechler SMDmax equivalent
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Figure 3 Droplet size summary of the Lechler SMDmax (4HR.148) compared to conventional nozzles
both droplet sizes and velocities would still hold true when comparing spray characteristics of liquids of different den- sities and surface tension. The PDA equipment used to gather spray droplet infor - mation measures the droplet sizes of the entire spray plume in real time to populate droplets based on their diameter. A typical droplet size report illustrates the number of droplets of a certain diameter in addition to the cumulative volume percentage of liquid based on these measured droplet size values. Figure 3 is an overlay comparison of droplet data between both a traditional maximum free passage-style nozzle and a comparable capacity Lechler nozzle (Part No. 4HR.148). Both nozzles have the same equivalent flow rate at differential pressure, and the data shown are for both nozzles at a differential pressure of 10 psig.
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Max f ree p assage - style nozzle Lechler SMDmax equivalent
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Figure 4 Cumulative volume per cent of Lechler SMDmax (4HR.148) compared to conventional nozzles
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PTQ Q3 2024
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