Risk Assessment for Increase in Plant Capacity

In a competitive working environment of chemical process industry, it is often required to maximize the production capacity based on the available plant capacity margins or some time going beyond the design capacity by taking into account the cushion available to increase the load as per process conditions without resorting any specific debottlenecking studies. In this exercise the financial gain is a obvious factor but the sustain operation at the elevated plant load (especially beyond design capacity) warrants a structured Risk Assessment for the whole process plant / equipment / machines to assess the hazard and risk to avoid any process safety related incident.

Different Risk Assessment approaches can be used in such scenario like HAZOP, What IF Analysis etc., but typical HAZOP guide words / deviations cannot provide the complete coverage of risk related issues as this is a very special case where all aspects of risk associated right from human factor to catalyst performance needs to take into account. For such cases, one of the approaches adopted is taking into account the layers of protection approach. This structured manner for each selected node with its different layers of protection, will help to check and assess any gaps to bring the overall process at acceptable risk level, while being operated at higher capacity load.

Following layers of protections are taken into account for Risk Assessment study:

BPCS (Basic Process Control System)

• Review of existing Alarm levels
• Control valves (output and response)
• Load margins with pumps/motors/prime movers
• Change in set points for controllers, alarm switch etc.
• Chemical Kinetics at elevated load (runaway reactions)

Equipment (pressure vessels, columns, HEX, pipelines etc.)

• Review of design data sheet.
• Past records of reliability and Turnaround history for equipment
• Erosion issues due to high throughput
• Review of Pressure drop across HEX, columns etc.

ESD / SIS

• Review of existing ESD/SIS data and requirement to change set points due to elevated plant load conditions.

Mechanical Protection system

• PSVs / RD capacity as per the design data sheet and elevated load conditions

Human Factors

• Operators response time in emergency
• Change in operating procedures and trainings
• Upgrade of Emergency Response plan

For a selected node or for any critical piece of equipment like Reactor, all above mentioned factors to be assessed and compared with the design parameters / simulation study and conclude that if the Risk is under acceptable level or not. All relevant process streams to be checked and assessed as per the above mentioned criteria to ensure all hazards and associated risks are taken into account while the plant operated at elevated load capacity.

This approach has been very useful ensuring that hazards and risks associated are taken care with increase in plant load, especially beyond design capacity. This approach can be used with any risk assessment model like What IF analysis or HAZOP while checking each and every parameters (as mentioned above) with available safeguards or recommendations.