Protection Against Backflow in Existing Furnaces - Challenges on Implementing a Homemade Changeover Interlock during Normal Operation

Transfer line protection against backflow deals with the process safety risk scenario under two conditions: transfer line backflow during changeover from the furnace transfer line to the decoking mode and vice versa or during radiant coil rupture events.

The aim of this article is to highlight the various challenges faced by Braskem, in the Chemicals Unit 2 (Triunfo, Brazil), to implement a changeover interlock, since the conception of the logic carried out by the Braskem technical team, to the validation test of the implemented logic. Some aspects to be explored in this present work are: identification of the process safety scenario related to the transfer line backflow scenario during changeover procedures, the strategy to design the changeover logic, feasibility assessment and planning regarding the execution of the installation activities of instruments in the transfer line by hot tapping machine, technical solution to guarantee the availability and reliability of pressure measuring instruments in the transfer line, hardware changes in the motors of the transfer line/decoke valves, modifications in electrical installations in the motors of the transfer line/decoke valves, logic download and logic test challenges during normal operation of the furnace (with no need on shutdown).