REDUCING THE PURGE IN HYDROCARBON VENT STACKS

The purging of hydrocarbon vent stacks is necessary to ensure that large flammable regions are not created within such facilities. In order to minimize the environmental impact of purging, it is vital that purge rates should be set at the lowest level consistent with safe operations. The methods which are currently available for determining these minimum rates are empirical and may be overly conservative; therefore, it is important to develop a more robust basis on which to calculate the required gas flows. To this end, a reduced-scale Rayleigh-scattering investigation of purging flows has yielded two-dimensional concentration maps for a range of purge rates and crosswind velocities. The results indicate that it may be possible to reduce the purge rate significantly without adversely affecting operational safety; full-scale testing must be performed to determine the potential hazards associated with such action.