(28h) Spray Section Performance Analysis: an Experimental Approach

This work is related with the setup of a new distillation pilot plant. It was designed in order to get information about operational limits and to get insight on physical phenomena within the range of vapor x liquid flow rates. Main focus is to observe the behavior of liquid sprays and wetness of random packing section under several combinations of liquid and gas flow rates. Analysis was made in a qualitative fashion observing liquid and gas stream patterns. Quantitative information was generated and analyzed by digital processing images taken from the spray cone formed. Spray nozzles are directly responsible for geometric shape of the formed liquid spray. Such devices have spread use to promote liquid-gas contact in process operations. Their performance is related to its ability to form stable homogeneous cones of droplets over a region under counter-current gas flow. Thorough studies of such performance are scarce. We aim to share knowledge acquired with tests we designed to evaluate brand new spray nozzles conjugated with its use in a small column resembling a section of a distillation tower. Experimental design consists of a 1590mm height transparent acrylic cylinder. Air is blown from the bottom through a chimney at flow rates in the range 0-680 m3/h. Water flows from the top through spray nozzles at 40-820 kg/h. Both empty and random packed cylinder tests were performed. Pressure drop through nozzles were measured and compared with manufacturer's predictions. Qualitative analysis regarding three parameters was made: fog formation at the top of the cylinder due to droplets carried by ascending air flow, tendency of flooding along packing and air flow instability at the bottom chimney distributor. It was also made an exploratory study in order to quantify information related to spray features by means of image processing. Photographs from a plane parallel to cylinder's top cross section underwent image processing through customized algorithms in order to quantify spray homogeneity along angular sections. In addition, an index was proposed to identify different levels of fog caused by droplets dispersed by air flow. It was possible to identify regions formed by different combinations of the pair liquid x air volumetric flows associated with progressive appearance of fog, air flow instability and flooding and to compare with packing manufacturer's prediction. One spray nozzle showed marked malfunction expressed by unstable spay cone shape, correlated with divergent pressure drop x liquid flow predictions. Quantitative exploratory study showed some non-uniform patterns of liquid distribution normally not noticed by naked eye observation.


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