A New Method for Measuring Hypergol Scrubber Emissions

摘要

Hypergolic propellants are used in spacecraft such as Space Shuttle, Titan, and others launched at Kennedy Space Center (KSC) and Cape Canaveral Air Force Station (CCAFS). Fueling and deservicing spacecraft constitute the bulk of operations in which environmental emissions occur. Monomethylhydrazine (MMH), nitrogen tetroxide (N204), and hydrazine (N2H4) are the main propellants of concern. Federal and State regulations require that KSC and CCAFS measure the amount of hypergols released to the environment. However, existing stack monitoring procedures are not applicable to hypergol operations that are intermittent and forced through the scrubber by inert gases, either nitrogen or helium. NASA and I-NET Space Services developed and validated a method to measure the emissions of toxic vapors under conditions where measurement of the total flow rate through a scrubber is difficult if not impossible to determine. This method is based on: (1) accurate measurements of the scrubber efficiency (EFF) for each type of operation, (2) an estimate of the number of operations and their contributions to the total annual flow through the scrubber, and (3) a measure of the concentration change of toxic vapors trapped by or reacted with reagents in the scrubber liquor. The concentration change of the component of interest in the scrubber liquor before and after an operation can be used to calculate the emissions. A special sample system was constructed at the Toxic Vapor Detection Laboratory (TVDL) of KSC to measure hypergolic fuel or oxidizer in sample gas entering and exiting the test scrubber. The sample system was enclosed in a purged cart, except for tubing and valve electrical service leading to the sample ports and for sample valves positioned at the sample ports. This permitted operation of the sampling system during hazardous operations. This system and the data collected to validate the system are presented.