Abstract: In order to promote the emptying efficiency of mobile pipeline, a dynamic model of emptying is established, which is solved by the method of characteristics (MOC), and the velocity of spherical pig and the variation of pressure drop are obtained. The model was verified by experiments. The emptying rate is related to the critical length of pipeline, the gas flow rate and max pressure of compressor. If the length of pipeline is longer than its critical length, the gas flow rate plays a dominant role in the emptying rate, and a high-flow-rate compressor should be used. On the contrary, if the length of pipeline is shorter than its critical length, the gas pressure plays a dominant role, and a high-pressure compressor should be used. The critical length increases with the development of pipe length, while the critical length decreases with the development of gas flow rate and pressure. Hence, in order to promote the emptying efficiency, the critical length should be determined in the design, and then an appropriate compressor is chosen in terms of the overall length and critical length of pipeline or the length of emptying segment is partitioned according the compressor performance. Key

Key words: petrochemistryengineering, mobilepipeline, emptying, pressure, flowrate, criticallength