Use of Tracer Gas Techniques for Industrial Exhaust Hood Efficiency Evaluation — Application of Sulfur Hexafluoride for Hood Controlling Particulate Emissions

Abstract

One of the most commonly used controls of harmful industrial contaminants is a local exhaust hood. The efficiency of this system is defined as the ratio of air contaminant quantity captured by the system per unit time to the total contaminant quantity produced by the process per unit time. A tracer gas technique, using sulfur hexafluoride (SF6), has been developed for the efficiency estimation of hoods controlling gaseous or vaporous contaminants. To extend the applicability of this method to hoods controlling particulate contaminants, a relationship between the hood particle capture efficiency and the hood efficiency determined by the tracer gas technique was studied. A particulate tracer was used for the hood efficiency and the data were compared with those obtained by the SF6 technique. Both tracers were discharged under the same conditions. Based on a statistical data analysis, described in detail in this paper, a mathematical relationship between the efficiency obtained by both particulate and SF6 was obtained for different velocity ratios (discharge velocity to capture velocity). For a hood controlling particles' of 3 µm in diameter, no correction of the hood efficiency data estimated by the SF6 technique is required. For larger particles, a corrective factor should be used for modification of the efficiency results obtained by the SF6 technique.