Performance of expellers in evacuating gas pipelines—Part II: Effects of plug valve and natural gas as a drive gas

Measurements were conducted on a typical commercial 150 mm expeller mounted on stacks with and without a plug valve and driven with natural gas. Expeller performance in terms of its mass induction ratio, correlated to the system equivalent flow resistance coefficient, was found to be the same whether the expeller is driven with air or natural gas. However, in the case of expellers driven with natural gas, the drive gas flow is reduced by a ratio corresponding to the square root of its molecular weight or specific gravity ratio and not the 60% value provided by the American Gas Association (AGA) guidelines in this regard. The effects of the presence of the plug valve along the stack on the suction flow were found to be 40% of that without a plug valve only in free-access cases. In a pipeline evacuation situation, however, the effect was found to be negligible. Revision to the current AGA guidelines is therefore needed.