Komonibo, Ebiundu
(2018)
Liquid-liquid flow in baffled vessels and pipes.
PhD thesis, University of Nottingham.
Abstract
Oil and water separation processes in primary separators and transportation of these fluids through pipelines for further processing, is very vital but has often proved problematic due to changes in composition of the fluids together with build-up of sand or asphaltenes, in many petroleum industries. These separator vessels are large and cost effective to install together with safety implications due to equipment failure. Hence an understanding of the two-phase flow dynamics and motivation to improve upon their design and performance is necessary. Therefore, the main aim of this research programme is to investigate the coalescence efficiencies of droplet size in both stirred tank and horizontal pipe line under turbulence in oil-water two phase systems and also to determine the possibility of using a compact sudden pipe expansion as a phase separator for converting dispersed flow to segregated flow.
For the purpose of experimental investigations, a sudden pipe expansion rig was designed, constructed and commissioned in L3 main laboratory of the department of Chemical and Environmental Engineering, University of Nottingham, UK. The fluids used are tap water ( ; ) and silicone oil 5cp, ( ; ) at operating conditions for mixture velocities between 0.20 ms-1 – 3.50 ms-1 and input oil volume fraction from 20% OVF to 80% OVF at different pipe inclinations (+40, +20, 00, -20,-40). Ring conductance probes were used to obtain phase layer distribution information of the oil-water flow together with the backscatter Lasentec FBRM M500P laser for drop size measurements and Phantom PCC 2.7 high speed camera for imaging.
In both horizontal and upward inclined flows, the input oil volume fraction and mixture velocity strongly influenced the formation of drop sizes downstream of the expansion, due to coalescence mechanism. Coalescence of both oil and water dispersed phase droplets and segregation was found to start at short distance from the inlet section and progresses gradually downstream of the pipe expansion. The water droplets coalesce and settles faster than dispersed oil droplets in water continuous phase flow system and also the bulk oil layer was observed to flow faster at the top than the bottom water layer for the horizontal and upward flow conditions. Therefore the results reveals a strong influence of mixture velocity, input oil volume fraction and pipe angle inclination on drop break up and coalesce mechanisms in oil-water flow systems.
The results obtained satisfactorily agree well with the existing conventional flow patterns and flow pattern maps. The flow patterns identified includes, stratified flow (ST), stratified with mixed interface (ST& MI), oil-water intermittent flow, stratified wavy flow and dispersed flow in all pipe orientations. Additional flow patterns were also observed such as Raleigh Taylor ‘plume shaped’ flow in the horizontal flow and plug wavy flow (Caterpillar like waves) in both upward and downward inclination, which have not been reported in large diameter pipes. There was evidence of stratification for fully developed ST regime at short distance from inlet (10D) at mixture velocities below 0.30ms-1 in both horizontal and upward inclinations.
Therefore, in order to achieve stratified flow in oil-water two-phase flow system, a sudden pipe expansion was used successfully to convert a dispersed flow to segregated flow within a 6m long test pipe distance. The best orientation was that of the horizontal flow position for dispersed flows to separate quickly as both the upward and downward inclined pipe flow conditions tend to hamper the evolution process by increasing the mixed layer region.
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