Model-Based Safety – an overview

Advanced Process Modelling for risk decision support

Gas flare

It is essential that models have a high degree of predictive accuracy

High-Integrity Pressure Protection System (HIPPS) flowsheet

BP Texas City Refinery accident report – see Appendix 15 [16MB download]

Model-based safety design and analysis uses high-fidelity models of processes and process equipment to provide high-quality information for decision support in design and risk assessment of safety systems.

This helps companies to manage risk based on reliable and auditable quantification, as well as to investigate many different failure scenarios within a relatively short timeframe.

Typical applications

Typical Model-Based Safety applications include:

Depressurisation studies to determine peak pressure and flowrate transients, flare system loads and vessel and pipe wall temperatures during blowdown
Optimal flare system design
Pressure relief system (for example, HIPPS) analysis
Optimal design of exothermic reactors to avoid runaway
Detailed analysis of accident scenarios, such as the BP Texas City Refinery accident analysis

gPROMS provides comprehensive and industry-leading facilities fo all of the above, primarily through the Advanced Model Libary for Pressure Relief Systems (AML:PRS).

The importance of rigorous modelling

Until now much safety design and analysis has been done using steady-state or "pseudo-dynamic" trial-and-error modelling, looking at units in isolation, using off-the-shelf models that did not capture process complexity, or attempting to "bend" flowsheeting packages into doing something they were not designed for.

It goes without saying that the models used for safety design and analysis need to be of the highest quality:

It is essential that models have a high degree of predictive accuracy. This requires first-principles models with rigorous physical properties.
Frequently it is necessary to use spatially-distributed 2-D or 3-D models within a process flowsheeting framework – for example to accurately model wall temperatures in depressurisation studies.
As most safety work deals with transient conditions, it is essential to use full dynamic models with proper modelling of pressure-flow behaviour.
In particular it is essential to be able to predict peak pressures and flows accurately.
Control design needs to determine optimal control parameter settings taking into account all anticipated disturbances.
Dynamic models need to accurately model reverse flow through pipes and vessels during pressure transients, and irreversible events such as bursting disk or pipe rupture correctly.
A custom modelling capability is essential in order to deal with non-standard equipment (for example, water seals in flare headers) or abnormal situations (for example, complete flooding of distillation column trays).
As many accidents occur from a combination of conditions, the ability to use stoichastic optimisation techniques is an advantage.

PSE provides

PSE provides industry-leading tools and services that more than cover all of the above:

The gPROMS Advanced Process Modelling environment, which is the only tool on the market that can provide all of the above within a fast and robust solution environment.

The gPROMS Advanced Model Library for Pressure Relief Systems (AML:PRS), the industry-leading tool for the design, analysis and optimisation of blowdown operations and flare networks.

PSE's expert ModelCare modelling, project and consulting services, for rapid execution of projects.

Specialised assistance to companies to build and maintain their own customised corporate safety libraries.