In-place HEPA filter testing by the sodium flame method

Abstract

High-efficiency particulate air filter application involves three steps: filter media testing, filter testing, and in-place filter testing. In China, filter media testing and filter testing use the sodium flame method, which involves spraying an aqueous NaCl solution to produce NaCl aerosol. However, in-place filter testing cannot employ this approach because of the low dust production rate. The present study describes a sodium flame method in which a significant amount of NaCl aerosol is generated by burning a special salt bar. In the aerosol-producing experiment, some structural and operational parameters are determined by analyzing the NaCl aerosol production rate and evaporation ratio. These parameters include the spray angle of the burner, salt bar composition and diameter, inflammable gas type and flow rate, as well as the speed of gear device. In the aerosol measurement stage, the measurement range and precision are considered as key factors; the determined parameters include sampling air and hydrogen flow rate. In the final stage, all parameters are identified: a spray angle of 60°; salt bar composition of 78% NaCl, 22% MgCO3 and methylcellulose; a salt bar diameter of 12.5 mm; liquefied petroleum gas (LPG) used as the inflammable gas; speed of gear device at 49 mm/min; as well as LPG, sampling air, and hydrogen flow rates of 3.8 l/min, 2 l/min, and 200 ml/min, respectively. Using one case of in-place testing of the air cleaning system in a waste plant and two applications in a nuclear power plant, we illustrate the applicability, stability, and continuity of the burning type sodium flame method for in-place filter testing.