Abstract
Pressure relief systems for high-pressure applications such as the high-pressure polymerization process are calculated mostly via API 520[1]. Here and in other empirical methods like the DuPont method, the mass relief is calculated via the density of ethene for the given process conditions. The valve body characteristic is further considered. Different physical properties of an unburned and burned phase in the case of a ventilated deflagration are generally not considered. The objective of the presented work is to generate an in-depth understanding and increase the reliability of venting process gases exemplary from the high-pressure polymerization process regarding real scenarios like considering polymer content and pyrolysis products from ethene decomposition. A transient pressure relief model and method is employed with the help of an isentropic nozzle model and a real gas equation of state. Polymerization mixtures are relieved from pressure up to 2000 bar, throughout a defined nozzle diameter. Thermodynamic behavior of gas mixtures is calculated with a real gas equation of state. The ventilation of ethene with a polymer component up to 20 wt.% content does reduce the discharge coefficient in comparison to sole ethen. Still, the resulting depressurization rates are mostly faster due to the higher density of the mixture. When pyrolysis gas from ethene decomposition is ventilated, the increased temperatures from decomposition heat and the resulting products do affect the relief process in a systematic manner. Hereby the depressurization takes longer in comparison to the unburned phase. Calculated discharge coefficients are significantly reduced compared to polymerization mixtures.
