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Advanced Model Library for Pressure Relief Systems

Integrated modelling of blowdown and flare systems

AML:PRS - library palette

Some of the AML:PRS library models

The Advanced Model Library for Pressure Relief Systems (AML:PRS) provides a comprehensive capability for the design, analysis and optimisation of blowdown operations and flare networks.

Adhering to the API-520 and API-521 standards, the AML:PRS has unparalleled scope and functionality. It is specifically designed to address all depressurisation and flare requirements in a way that has never been possible before.

Power and flexibility

The AML:PRS takes advantage of gPROMS's power to enable you to:

  • Incorporate all relevant parts of the system within a single model to analyse important interactions and help avoid over-conservative assumptions at sub-system boundaries. It also eliminates laborious data transfer between models and reduces the scope for error.
  • "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, you can simply 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.
  • Perform both steady-state and dynamic analysis of the entire system of relevance, including steady-state optimisation for system sizing (both continuous and discrete decisions) and steady-state and/or dynamic optimisation for identifying safe operating envelope and worst-case scenarios.

The AML:PRS is used from within the gPROMS ModelBuilder, taking advantage of its advanced user interface, including drag-and-drop flowsheeting designed to handle very large flowsheets, user-friendly dialogs for problem specification, in-flowsheet results display, animation, and many more.

AML:PRS models executing within gPROMS ModelBuilder for dynamic study of a flare network.

The flare relieves pressure from an upstream separator (bottom left) that is overpressured because of a blocked outlet pipe. Pressure relief valve hysteresis leads to multiple pulses of relief flow.

Colour coding (animation) indicates instantaneous pressures in various parts of the network.

AML:PRS - flare system design with standard pipe

Component models

The library contains models for the following components:

Sources Sinks
Control valves
Relief valves		 Flare tips
Pipes & pipe fittings Vessels
Junctions
Enlargers/contractors
Orifice plates
Nozzles		 Drum
Separators

Multi-level models:
Mix-and-match

AML:PRS - flare system design with standard pipe

In-place model refinement for single pipe in flare network – from Level 0 model (above) to Level 1 model (below).

AML:PRS - flare system design with distributed pipe

None of the other units in the system is affected by this refinement.

All models in the AML:PRS:

  • are based on API/ISO standards
  • are capable of both steady-state and dynamic operation, the latter supporting flow reversal where this is required
  • perform rigorous multicomponent calculations based on the true composition of the fluids in them
  • can access the full range of rigorous thermodynamics within gPROMS for physical property calculation.

Multi-level modelling

The library is organised on several levels corresponding to different levels of modelling detail and fidelity:

Level 0: Basic models

This comprises models at the typical level of fidelity of commercial steady-state systems for flare network analysis currently available on the market, but with the added capabilities of dynamic (transient) operation and optimisation, plus the ability to link flare system and upstream process.

Level 1: Spatially distributed models

These are primarily models of pipe segments which take account of 1-dimensional spatial variation of pressure, velocity, temperature and composition within them.

They are typically used for detailed modelling of wall temperatures in areas where brittle fracture is a design consideration. Accurate modelling can provide quantification in support of decisions to use lower-cost metals, or can help minimise the cost of pipework where high-cost alloys are required.

Spatially-distributed pipe model

2-D pipe wall temperatures

Wall temperatures calculated by the
2-D distributed pipe model

Level 2: High-fidelity pressure vessels

AML:PRS Level-2 models deliver high-fidelity, predictive modelling of pressure vessels under blowdown conditions. They model vertical or horizontal vessels containing gas and liquid (including separate organic and water phases).

See here for more detail on multi-level modelling.

Custom models

Using the advanced modelling facilities of gPROMS ModelBuilder, it is always possible to add custom models to whatever level of modelling fidelity you require.

It is also possible to incorporate models from the gPROMS Process Model Library (PML) in any execution.

This means that virtually any scenario can be described to any level of detail and fidelity.