Removal of condensed gas from the walls of gas pipelines

摘要

A pipeline pig 21 for removing condensed gas from the wall of a pipeline 23 comprises a cylindrical body 22 which is a sliding fit in the pipeline 23 and has an axial passage 26 extending therethrough and a flow gas ejector inlet tube 37 extending into the passage 26. The passage 26 is formed with a venturi 27 and the tube 37 is formed with a restriction 38, the forward end of the tube 37 terminating upstream of the venturi 27. The pig 21 is propelled through the pipeline 23 by differential gas pressure acting upon it and gas flows through the passage 26 so that condensed gas is entrained into the passage 26 by way of an annular duct 32 and radial ducts 35 into a rear tapering portion 29 of the passage 26 upstream of the venturi 27. The condensed gas is drawn to the forward end of the ejector tube 37 which end is located downstream of the ducts 35 and is subjected to the turbulent flow of the flow gas which has been accelerated by the venturi restriction 38 in the ejector tube 37. The condensed or liquid gas is thus re-vaporized or returned into the dense phase in the case where the pipeline 23 is operated under dense phase conditions or alternatively mist or droplets of the condensed gas are dispersed in the gas flow through the pipeline. The use of the pig 21 thus avoids the necessity of the removal of a large slug of liquid gas from the pipeline as has been necessary with previous methods of removal of condensed gas from the wall of the pipeline 23.