Inert hydrocarbon-based refrigerants

Abstract

This paper determines the flammability properties of two hydrocarbon blends, natural gas and propane–butane refrigerant, mixed with CF 3I and C 3F 7 H inerting agents. Four flammability envelopes are obtained allowing the determination of the minimum inerting concentrations and the maximum hydrocarbon to suppressant weight ratios for formulating non-flammable hydrocarbon refrigerants. These ratios are calculated from the slopes of lines drawn from the origin and tangent to the lower branches of the flammability envelopes. The flammability measurements are conducted using a tubular flow burner. The apparatus is convenient to operate, yields reproducible results without repetitive testing necessitated by explosion vessels. More importantly, the tubular flow burner applies a clear criterion for extinction avoiding the innate problems of the explosion vessels, which relate to the strength of the ignition source and the vessel size. The results indicate that it is not possible, using CF 3I or C 3F 7 H, to formulate a refrigerant mixture with a substantial hydrocarbon content. Specifically, inertion of the propane–butane blend considered in this study demands 87.7% and 94.2% by weight of CF 3I and C 3F 7 H, respectively. CF 3I displays similar inerting properties to those of CF 3Br. The higher inerting requirement for C 3F 7 H stems from the nature of this agent to decrease the lower flammability limit of the hydrocarbon blends.