Steady and Cyclic Purging of Closed-End Side-Branches in Natural Gas Facilities

The problem of purging closed-end side-branches in natural gas facilities is considered in this paper. Experimental results obtained in a scale model are presented, where air and carbon dioxide were used to simulate air and natural gas in the field. The time required to reduce the concentration in the side-branch below the lower explosive limit is determined as a function of purge velocity and side-branch length. Two different purging techniques, steady and intermittent purging, are evaluated in this paper. For steady purging it is shown that, contrary to intuition, more efficient purging occurs at low purge velocities rather than at high purging velocities. It is also shown that when cyclic purging techniques are employed, purge gas savings in excess of 90 percent can be achieved. Application of these methods to operations can provide financial savings and significantly reduce atmospheric pollution.