Ethylene fractionator pressure relieving system assessment and modification

Abstract

The refinery and petrochemical production facilities process and produce the gaseous and liquid flammable hydrocarbons. Most of the processes are operated under high pressure. In case of any failure, improper design or human mistake there must be autonomous and independent pressure relieving systems activated to release the pressure to the flare systems to protect the equipment against the overpressure, damages and other consequences. The article describes a safety assessment of key process pressure relief valve installation at the Steam Cracker in Litvinov, Czech Republic. The intent of the safety assessments was evaluation the functionality of the process relief valve installation, to ensure the system meets the appropriate recognized and generally acceptable engineering practices and to confirm that the system can be operated safely. The article provides results and recommendations for the Ethylene Fractionator pressure relief valves, pipes, and support modifications as well as results of the relieving scenarios determinations and calculation.acoustic resonance, ethylene fractionator, loss of cooling, pressure relief valves, steam cracker | INTRODUCTIONPressure relief valves (PRVs) are key and irreplaceable devices for safe operation and prevention of extraordinary events. The PRVs are designed to release the excess pressure from the system to protect the pressure vessel or pressure system from overpressure and consequent damages. They are autonomous devices that open and close according to the defined values without the influence of an operator or other systems, such as the control system or the emergency shutdown system. The design of the pressure relieving system is a complex problem and there must be paid a special attention to meet all industrial codes, standards, rules, and best engineering practice. There are many installations worldwide in refining and petrochemical industry built in 70s and 80s of the last century where the original design could not have been donerespecting and reflecting todays level of knowledge, experience as well as the process safety rules and recommendations. As there are technologies designed more than 20 years ago, the pressure relieving systems can be obsolete. It can be observed the original relieving systems design used to be focused mainly on sufficient relieving capacities accepting conservative assumptions without considering other rules to ensure a stability. This article describes specific and critical rules which can strongly impact the proper functionality of the pressure relieving system. 1,2 These are namely the inlet pressure drop limit at a maximum of 3% of the relief valve set pressure, 3,4 the back pressure value 5 at the relief valve outlet, correct setting of the relief valve opening pressure for multiple installations, optimal relief valve relieving capacity and last but not least the resistance of the whole system to any generated vibrations. 6,7

Risks and limitations of steam curtains protection in case of flammable gases leakage

“…The loss of containment was caused by excessive and destructive vibrations triggered by chattering 4 of the pressure relief valve. 5 As part of the comprehensive investigation of this event, in addition to a detailed analysis of the correct design of the safety valves, 6 attention was also paid to the activation of the steam curtains for propylene vapor suppression with regard to their real efficiency and the potential risk of electrostatic charge generation, 7 which could paradoxically be the initiating source. 8 In general, the steam curtains can be used to help disperse small toxic gas leaks but are more often used to divert flammable gases away from identified sources of ignition.…”