Safe furnace switch over cracking ↔ decoking

Our client ExxonMobil approached Alcatraz Interlocks, with the technical possibilities of incorporating Mechanical & Electro-mechanical valve interlocking into their facility. The reasoning was to ensure a higher safety integrity during the switchover procedure, from Cracking to Decoking, and then from Decoking back to Cracking, within their 6x furnaces.

‍

After several in depth technical discussions with the customer, reviewing and defining the various hazards during the switching over process, plus establishing the extra digital parameters required next to the full mechanical scope of supply.

‍

Alcatraz Interlocks created three Technical / Commercial proposals, all with clear Procedures, Sequences & Drawings, giving various solutions from 100% mechanical to a combined mechanical / electrical and digital. There was three main restrictions, which we had to consider before any human interaction, and prior to any Mechanical key interlock sequence could start:

‍

1. When switching over from cracking to decoking, the furnace must have reached a set temperature.
2. When switching over from decoking to cracking, the furnace must have reached a set pressure.
3. There was also a requirement, that all the motor operated valves could be operated locally, plus an intergraded part of the interlocking sequence.

‍

Client together with their E&I partner reviewed our technical proposal and approved our key interlock sequence, which also included our bespoke Atex electronic key cabinet.

‍

Within this scope, Alcatraz delivered our full range of mechanical interlocks for manual valves & line blinds, key exchange boxes and an Atex electrical key cabinet. The electrical cabinet was a bespoke design, tailor made to suit the customer’s process requirements.

‍

• Cabinet material and glands are SS316
• Power & communication with clients DCS, is via the spare terminals within the Rotork IQ3 actuators. Reducing the need for any new cabling, a major cost saving.
• Digital displays of the actual temperature and pressure ratings from the transmitters located on the furnace.
• MOV’s controlled by the means of a push button, and a visual feedback of its position (open/closed) displayed on the Atex cabinet.
• The cabinet is ATEX certified for Ex ic and has a 24 Volt DC power consumption.

‍

‍