A Study on Safety Integrity Improvement of Oxidation Reactor on Propylene Oxide Process by Installed Safety Instrumented System (SIS)

Abstract

Propylene Oxide (PO) process produces PO from propylene produced from Residue Upgrading Complex. PO Process consists of Cumene Oxidation section for producing cumene-hydroperoxide. Epoxidation section of PO, propylene and Cumene-hydroperoxide. Separation section for separating propylene and PO. Hydrogenation section for conversion to alcholiccumene and cumene and PO purification section. Of these, the oxidation section consists of six reactors containing an aqueous alkaline fluid, which oxidizes cumene to air to form cumenehydroperoxide. In this exothermic reaction, the temperature of the reaction is −258.9 kJ/mol, the operation temperature is 104–94°C, the operation pressure is 0.63 Mpa, and there is a risk of runaway reaction if the operation is not controlled properly. Therefore, we analyze the basic process control system (BPCS) and safety protection system through the Layer of Protection Analysis(LOPA) based on the P & ID of the current oxidation section and secure the safety by installing Safety Instrumented System(SIS) as an additional protection system. The TMEL is 1.00E-04 for the incidents caused by the reactor runaway through LOPA, and the current PLs are 1.00E-03. Therefore, the additional protection layer is required, and PFDSIF should be added to 1.00E-01. By adding a depressing system, the SIF of the oxidation section is sufficient to meet SIL conditions. The total PFDavg of SIS, which is the Top event of FTA calculated from the root(basic) events (each SIF element), is 9.61E-04 to verify which the SIF design should be met and satisfied the target SIL3. However, the Logic solver has a HFT of 1, indicating the level of SIL2 according to IEC 61511, and the final level is SIL2. The verification is conducted under each SIF must be performed partial stroke and a proof test periodically according to manufacture manual.