API PUBL 4678:1999

It was originally intended that a three-zone emissions model be developed with the ability to estimate VOC emissions from a falling film, water seal, and channel located below a drain. It was impossible to separate (experimentally) the effects of a falling film from volatilization in an underlying channel or water seal. As such, the effects of a falling film were 'lumped' into mass transfer in an underlying channel or water seal. Five volatile tracers were used in determining mass transfer parameters for the two-zone model. These tracers spanned a wide range of Henry's law constants, i.e., 0.0015 m3liq/m3gas to 7.3 m3liq/m3gas at 25 °C. A total of 76 experiments were completed with the use of two separate experimental systems. Twelve of these experiments were completed to study gas-liquid mass transfer in the channel below a process drain. Forty experiments were completed to determine rates of air entrainment in a water seal. Seventeen experiments were completed to study the degree of chemical equilibrium between entrained air bubbles and surrounding liquid in a water seal. Seven experiments were completed to study volatilization across the upstream surface of a water seal. Four additional experiments were completed to ascertain volatilization from a falling film, but were inconclusive and not reported herein. No experiments were completed to determine emissions from a water seal below an inactive drain. No experiments were completed to assess gas-liquid mass transfer in the channel below inactive drains. Several variables can affect mass transfer in a process drain. The primary variables that were studied included process flowrate, hydrodynamic regime (disintegrated or intact liquid flow), and Henry's law constant. The effects of molecular-diffusion coefficients were accounted for in some correlations. The effects of temperature were accounted for through variations in liquid molecular diffusion coefficients, water viscosity and, most importantly, Henry's law constant.