Model-based Safety

The advantages of PSE's integrated approach

The study enabled us to save $1.5m on the cost of a single vessel.

— Stephen Leng, BP Operational Excellence

The ability to effectively design flare systems and perform blowdown analyses have been very limited to date by the limitations of the available tools.

PSE's aim in creating gPROMS Flare and its associated depressurisation tools has been to provide engineers with a comprehensive capability for the design, analysis and optimisation of blowdown operations and flare networks that addresses all known deficiencies and brings significant new functionality.

Current tools

The set of tools traditionally used for blowdown studies and flare system design has significant limitations:

There are separate modelling tools for flare system network design, upstream process modelling, process vessel blowdown with and without fire, and so on.
Each has different levels of modelling detail, from simple correlations to rigorous 3-D pressure vessel models. There is little consistency between environments; for example, different tools may give significantly different pressure drops across the same flare system components.
There is also limited interoperability between these environments. Flare system design often requires transferring data manually between software, a time consuming process that can introduce errors.
Most current flare design work is based on steady-state analysis. It is well known that the steady-state approach leads to overdesign.
Dynamic simulation is typically not routinely performed outside of specialised vessel blowdown studies, and often involves using simulators not designed to handle rapid transients.
Typically upstream process is not included in flare system design. The dynamic effects of – for example, the blowdown of several vessels in a staggered sequence – cannot easily be calculated.
Most flowsheeting tools or software commonly used for flare design have limited or no capabilities for modelling metal temperature profiles.
Specialised "point solutions" are available for vessel fire analysis, but these tend not to integrate well with more widely-used flare design or flowsheeting tools.
As with all specialised solutions there are questions about long-term tool development, maintenance and support, in addition to the lack of integration with other tools.

gPROMS Flare and depressurisation tools

PSE's approach in developing gPROMS Flare and the associated depressurisation tools has been to address all of the above deficiencies as well as introduce many additional features to help engineers involved in the design, analysis and optimisation of blowdown operations and flare networks.

Some examples are:

An integrated approach. With gPROMS Flare it is possible to incorporate all relevant parts of the system within single model. This:
- enables designers to analyse important interactions
- helps avoid over-conservative assumptions at sub-system boundaries
- eliminates laborious data transfer between models
- reduces the scope for error through data transfer.
The ability to mix-and-match models at different levels of detail in order to focus on aspects of interest while maintaining an overall system perspective. For example, with gPROMS Flare it is possible simply to replace a standard pipe model with a distributed pipe model in order to perform detailed wall temperature analysis while taking into account all relevant upstream and downstream effects.
The ability to perform both steady-state and dynamic simulation of the entire system of relevance.
The ability to perform both steady-state and dynamic optimisation of the entire system of relevance, including:
- steady-state optimisation for system sizing (both continuous and discrete decisions)
- steady-state and/or dynamic optimisation for identifying safe operating envelope and worst-case scenarios.
The ability to perform discrete optimisation means that it is possible to choose the optimal pipe sizes from standard pipe schedules for the required flare system load.
The ability to perform complete depressurisation modelling using rigorous pressure vessel wall temperature calculations (and linked to downstream flare system models).
The ability to include an arbitrary level of upstream process.
Consistent rigorous thermodynamic calculations (optionally, with hydrate prediction) are available throughout.

2-D and 3-D modelling results

Wall temperatures calculated by the 2-D distributed pipe model

Wall temperatures calculated by the 3-D distributed vessel model (for pooling dense-phase CO2)

Pipe and vessel models are available with 2-D and/or 3-D wall temperature modelling, for accurate temperature calculation. These can be used in place of standard pipe and vessel models wherever more detailed analysis is required.
State-of-the-art graphical user environment with:
- full drag-and-drop flowsheeting capability for easy construction of networks
- dialog-based model specification
- full reporting and plotting capabilities
- full audit capability with case archiving and comparison
- many other features.
State-of-the-art numerics for rapid and robust solution for even the largest models, steady-state or dynamic.
Extendibility and customisation. It is possible – when using the full gPROMS ModelBuilder – to customise models in order to more closely reflect reality – for example, when dealing with a particular geometry of water seal. It is also possible to include models from any of PSE's other libraries.
Open software architecture. It is possible to interface to other tools, for example using CAPE-OPEN interfaces to include any physical property package of choice. It is also possible to interface your own physical properties if this is necessary for dealing with special components or mixtures.
Future proofing. gPROMS Flare derives full benefits from the on-going general development of the gPROMS platform. This means that not only is there assured development, but that the cost of this development is spread across several industrial domains.
gPROMS is a general-purpose platform. This means that it is possible for the gPROMS licence to be used by others in the organisation, helping to spread costs.