(84h) Deflagration and Pressure Relief of High-Pressure Ethylene and Ethylene-Vinylacetate- Mixtures on a Laboratory Scale

Ömer Delibalta, Markus Busch, TU Darmstadt, Germany,

markus.busch@pre.tu-darmstadt.de

Pressure Relief systems are used to protect pressure vessels and related equipment against situations of excess pressure. In an emergency situation, they should vent sufficient mass to reduce the pressure to a save level, so the development of relief device sizing methods is of extreme importance. To get more insight decomposition and pressure relief phenomena are investigated by fast measurement technique using lab scale autoclaves. Ethylene is taken from cylinders and compressed by means of a membrane compressor into storage vessels and the main autoclave which is designed for pressures up to 500 MPa. To measure the flame front propagation as well as the pressure relief high sensitive piezoelectronic sensors and custom made double typ-S-thermocouples with high response characteristic are implemented in the reactor. For description of time pressure trajectories by venting of vinyl acetate/ethylene mixtures a one phase flow isentropic nozzle model is utilized. The maximal mass flow through the nozzle is calculated with LKP- and PC-SAFT equation of state at supercritical conditions and is applied for determination of the pressure and temperature trajectories by isentropic relief process. The discharge coefficient includes the geometry effects, friction and heat transfer effects in the adiabatic nozzle, so it is the ratio of mass flow in a valve to that in an ideal nozzle. Decomposition of vinylacetate/ethylene mixtures based on defined reaction scheme is calculated by a thermodynamic model including an adiabatic flame temperature. The kinetics of the reaction system is implemented in the laminar burning velocity. A compartmentalization in burned and unburned volume during flame front propagation characterized by response behaviour of the thermocouples allows the calculation of the burned mass per time step, which is appropriate for the time pressure trajectories. The mass balance for the decomposition system is realized by defined gas product composition, which is specified by gas chromatographical analysis. Through combination of the adiabatic nozzle flow model and burning velocity model decomposition relief experiments could described by applying of defined discharge coefficient, experimental adiabatic flame temperature and an enhancement factor.