Study Of Slug Dissipation In Inlet Pipe Of Gas-liquid Separator

The gas-liquid separator is sensitive to the gas-liquid flow rate fluctuation due to the inner limited space.When the slug flow is formed in the inlet pipe of gas-liquid separator,the narrow separation space of gas-liquid separator can't catch the liquid slug,and the separation performance and structural stability will be greatly reduced.It has also been the main obstacles to expanding the gas-liquid separator industrial application.Therefore,improving the gas-liquid separator separation performance under the harsh conditions is a serious problem.It requires a separate inlet pipe for further improvements to the unfavorable flow patterns to ensure the gas-liquid separator is always in the range of flow patterns which can be handled working.In this paper,the form of the existing gas-liquid separator inlet pipe structure were analyzed and summarized,and the basic inlet pipe structure was presented to ensure the liquid slug can be dissipated.The gas-liquid two-phase flow characteristics and the movement of the liquid slug in the inlet pipe were studied.The influence of bend and expanding pipe on the slug length,slug velocity and slug frequency was analyzed.The impact of slug characteristics and helical pipe structural parameters on the slug dissipation was examined.Considering the transient characteristics of the slug front and tail velocities in downward pipe,the unsteady-state model of slug dissipation was established.Slug dissipation using inlet pipe will not increase the complexity of gas-liquid separator,and extend the range of operating conditions of the separator to maintain its compactness.This is significant for gas-liquid separator application in the offshore oil and gas fields.The main conclusions are as follows:According to the liquid slug actual movement in the combined riser,the liquid slug length calculation method for this experimental system was proposed.The liquid slug length was calculated by two segments at the horizontal inlet and outlet of the combined riser.The liquid slug length was calculated using the average velocity method.Both of the liquid slug length calculation methods were applicable for high-speed slug flow and all the slug flow.When the expanding pipe was add to the combined riser,the liquid slug length at horizontal outlet required to calculate with average velocity method.Compared with the existing reference method of conductivity probe,the dynamic self reference method can eliminate the influence of two parallel conductance probe slightly deformed due to the impact generated by the slug flow on the liquid slug holdup measurements.In the combined riser,the stratified flow characteristic changed along the pipe,but annular flow remained its flow pattern and intermittent flow remained the pulsatility.The film of the intermittent flow became the oscillation film in the vertical pipe.The intermittent flow became stratified flow when the expanding pipe was added to the combined riser.The range of gas and liquid superficial velocity for the evolution of intermittent flow to stratified flow enlarged with the expanding ratio increased,and the liquid slug became high level film at the horizontal outlet.The oscillation film in the vertical pipe was formed with the flooding mechanism.When the liquid slug flow through horizontal-vertical 90°bend,the slug front pushed and absorbed downstream film and liquid slug length increased.When the liquid slug flow through vertical-horizontal 90°bend,the slug tail shed due to gas-liquid stratification and gas impact,causing liquid slug length decreased.The liquid slug length in combined riser followed log-normal distribution.Compared with horizontal inlet pipe,the concentration of liquid slug length in the vertical pipe and horizontal outlet pipe decreased.The slug length increment in horizontal-vertical 90°bend and decrement in vertical-horizontal 90°bend,decreased with slug velocity increased.For both of the bends,the experimental value of the ratio of slug length upstream to downstream was greater than or equal to the equal value.For the horizontal-vertical 90°bend and vertical-horizontal 90°bend,the slug velocities upstream and downstream the bend conform to the relationships of exponential and logarithmic relationship,respectively.When the expanding pipe was added to the combined riser,the relaionships of slug velocities change to the relationships of linear and polynomial respecticely.The ratio of slug momentum upstream and downstream the horizontal-vertical 90°bend significantly after the first slowly reduced and tends to be stable with superficial gas velocity increased.The raito of slug momentum upstream and downstream the vertical-horizontal 90°bend first decreases significantly and tends to the stable with the increase of superficial gas velocity.The slug frequency changed at the vertical-horizontal 90°bend,and the ratio of slug frequency upstream to downstream was mainly affected by gas superficial velocity and expanding ratio.The combined riser enlarges the slug length,slug velocity and slug momentum.The expanding pipe can improve the adverse effects of the combined riser outlet to the separator inlet pipe.The liquid slug dissipation ratio in helical pipe decreased with the slug velocity and slug frequency increased,and increased with the helix angle increased.The relationship between liquid slug dissipation and helix diameter was related with the slug velocity.The results of slug dissipation model were consistent to the experimental data,but the calculated value was less than the experimental value because the effect of slug frequency was not considered in the slug dissipation model.