Design of recovery system for the natural gas vented through dry gas seal

Due to its own operation characteristics of dry gas seal (DGS) at the shaft end of centrifugal compressor used in the compressor stations of long-distance natural gas pipelines, some process gas is discharged through the vent pipe, so not only the resource is wasted and the pipeline loss is increased, but also the environment is polluted by the vented greenhouse gas. In order to recover the natural gas vented through DGS, an overall solution to recycle the natural gas vented through DGS of centrifugal compressor set used in long-distance natural gas pipelines was, for the first time, put forward completely in China. In this solution, two-row, four-level reciprocating compressor with the characteristics of frequency conversion control, air cooling and symmetrical balance is used for boosting and the triple safety protection system is designed. And as a result, the safe operation of the original DGS of compressor set is not impacted at all, and the instantaneous flow rate and cumulative flow rate of natural gas recovery can be monitored in real time. It is revealed by the actual operation results that the system is advantageous with simple structure, small maintenance quantity, controllable cost and reliable operation. Besides, the recycled natural gas reaches the expected value, and the payback period is about three years. And thus, the purposes of source tapping & consumption reduction and cost cutting & efficiency increasing are achieved.