STARTUP/SHUTDOWN PHILOSOPHY FOR OIL AND GAS INSTALLATIONS

Start-up and Shutdown are two terminologies that would be familiar to every person working in the Oil and Gas installation, or for that matter any production facility.

Good Engineering design should incorporate all possible Start-up and Shutdown scenarios and work towards building Oil and Gas installations that are safe to operate and produce.

In a Typical Oil and Gas installation, Integrated Control and Safety System(ICSS) works to safely Start-up and Shutdown the facilities in case of any eventualities.

ICSS is an Integrated system comprises of

• Human Machine Interface: The means by which information is communicated between human operator(s) and the Process Control and Safety system (for example, monitors, indicating lights, push-buttons, horns, alarms). The HMI is also known as the operator interface.
• Process Control system: a system that responds to input signals from equipment under control and/or from an operator and generates output signals, causing the equipment under control to operate in the desired manner, i.e. within its operating envelope.
• Process Safety system: The System that executes hazard prevention functions: such as production shutdowns (PSD) or unit shutdowns (USD). It responds to excursions of process conditions outside the prescribed limits by initiating shutdowns to prevent equipment damage or further development of process hazards to the personnel.

( PSHH,PSLL, LSHH,LSLL etc)

• Fire and Gas system: The Fire and Gas system encompasses the fire and gas detection equipment, signal processing, monitoring, alarming, and voting. Its function is to generate confirmed fire initiators for ESD functions and to execute firefighting functions such as firewater/foam/fire suppressant deployment.
• Emergency Shutdown systems: The ESD System affects the process, production, and non-essential utility shutdown in response to a detected hazard, typically from the FGS system or a manual initiation. As such the ESD system is a hazard mitigation system that executes ESD and PESD levels of shutdowns.

The ICSS provides a means to monitor, control, and operate the Production Unit from a Central Control Room and it shall incorporate Control and Automation, Hazard Prevention, and Hazard Mitigation systems.

SAFEGUARDING/SHUTDOWN SYSTEM: In a typical Oil and Gas installation the safeguarding system or shutdown system is designed based on Levels of Hierarchy. This is to ensure there is safety as well interdependence in case of demand. For example, if there is a high-pressure excursion (PSHH) in the separator system we shut down the separator system and not the entire plant.

The Hierarchy for safeguarding system are

• Level 4 - Abandon platform PESD( post Emergency shutdown): This is the highest level of shutdown Hierarchy. This is initiated by using manual call points or push buttons located at strategic points all along the installation. This shutdown is initiated when the Commanding authority (OIM) decides to abandon the platform to save lives when the fire or gas scenario cannot be bought under control. When initiated this shut's down the few remaining systems onboard ( emergency generator, HVAC Essential generator, power systems etc).
• Level 3 - Emergency shutdown (ESD): The Emergency Shutdown System is there to minimize the consequences of emergency situations due to the escape of hydrocarbons or the outbreak of fire. The ESD system initiates shutdowns of process systems and equipment, eliminates possible hydrocarbon ignition sources through electrical isolations, and initiates emergency depressurization of the process plant to remove hydrocarbon inventory and process system pressure. The ESD system is connected to field sensors (like field push buttons, limit switches, and status switches) and final elements (like blowdown valves, electrical switchgear, and trips outputs to Package Control Systems). The ESD system is interfaced with the FGS system. The ESD portion executes production and non-essential utility shutdowns, including electrical isolations. The ESD activation enables manual or automatic initiation of emergency depressurization.
• Level 2 - Process Shutdown (PSD): This is a full field shut down when there is pressure or level excursions that might pose a danger to the safety of personnel or equipment but does not threaten the integrity of the platform as a whole. An example of this type of shutdown is LSHH on the Flare knock-out drum. During PSD the entire installation is shutdown except that there shall be no blowdown. Restart from this scenario is fast once the cause of the excursion is addressed.
• Level 1 or Level 0 - Unit shutdown(USD): This is the lowest level of Hierarchy where a particular unit like Oil system or Gas system is selectively shut down due to some excursion in pressure or level. In this type of shutdown, the rest of the plant continues to function normally, while the cause of the shutdown is addressed in the other units.

STARTUP SYSTEM: unlike in a shutdown system there is no particular hierarchy in a startup system. but we have to address few different scenarios for start-up depending upon the systems which shall be available for the same.

• Initial startup: This is when the plant has to be started for the very first time after Pre-commissioning/commissioning has been finished. This is when hydrocarbon or Oil and Gas are introduced into the system.
• Black start: This is a scenario almost similar to the initial start but can occur at any time during plant life. This is called black start since during this scenario all systems including power generation, instrument air would have failed and the plant has to be started using diesel as fuel to start one unit of power generation and subsequently starting up the entire facility in a sequential manner.
• Unit or Process startup: This type of start-up is when you have to start up one particular system like Oil system or the Gas system after USD.

To conclude during engineering the team has to understand the shutdown/start-up and operating philosophy of individual systems as well as the entire system as a whole to design a facility that can start up from any scenario and safely shut down during an emergency.