VessFire 2.0: For safer process systems

Petrell launches version 2.0 of VessFire. Version 2.0 makes dynamic calculation possible for all processes involved in depressurisation. In most situations, this means more precise results and thus even better safety for process systems, with better utilisation of the flare system as a result. 

VessFire 2.0 calculates multiphase flow in pipe networks and treats different vessel types. A new and improved interface provides a better description of the process systems. It also allows data stored in Excel to be pasted into the user interface. It is easy and it is fast.

New thermodynamic library
Certain constraints in version 1.0 have been eliminated and new features added. For example: there is no limit to the number of vessels, blowdown valves and pressure relief valves in the process segment. Petrell has also developed a new thermodynamic library (ThermoProp), implemented in version 2.0. ThermoProp handles water/oil mixtures and CO2.

Major improvements
Version 2.0 is more stable and precise. Users familiar with version 1.0 will find major improvements to the user interface in terms of modelling and result presentation.

Faster simulations
During the development of the 2.0 version, Petrell identified calculations that took the most time. Improved algorithms, the new thermodynamic library and smarter implementation have resulted in an increased calculation speed.

Dynamic analysis of flare system
Design of process systems for oil and gas has traditionally been based on a stationary approach. This applies to flare system design as well. When gas is discharged into the flare header, the pressure rises and then gradually decreases as the segments are emptied. In flare analyses, a fixed backpressure is traditionally used, because the dynamic pressure profile is not known. VessFire 2.0 calculates backpressure dynamically based on the properties and condition of the gas released into the flare system from various segments. A process system should be dimensioned for actual conditions and what is dynamic should be dealt with dynamically. That’s what VessFire 2.0 is designed to do.

Pipes and vessels
Previous versions of VessFire is based on the condition that the vessel is the dominating object in the segment. If the segment contained more than one vessel, the additional vessels were modelled as pipes. In version 2.0, all vessels are recognised as vessels and pipes as pipes. All components constitute a network interconnected by the flow between the components. Segments without vessels (or pipes) are of course permitted. As in version 1.0, users can select steel quality and materials for passive fire protection, and if the material is not listed, new types can be added.

Figure 1 Screen shot showing how pipes and vessels etc. are defined. The list can be export as an Excel file or the list can be prepared in excel and inserted in VessFire using copy/paste.

Figure 2 Screen shot showing a graphical representation of a process segment. Heat load and low temperatures

Heat load and low temperatures
There is no limitation on defining heat loads – peak and background loads can vary over time as before, and if required, a fire load can be allocated for each vessel or pipe.
Version 2.0 provides better support for analysis of low temperatures in connection with e.g. cold depressurisation, through a much broader spectrum of reporting options. For example: temperature fluctuations during a given period for a given pipe section can be extracted.

Licenses available 1Q 2017
Licenses will be made available to existing and new customers in 1Q2017. Until then is VessFire 2.0 available through consultancy services from Petrell.

Fact box on process systems and depressurisation:
The blowdown and flare system is the most important process safety system as their purpose during an accidental event or emergency situation is to reduce the pressure in process segments in order to reduce the risk of rupture and subsequent release of flammable substances that cause fire and explosion. Once overpressure occurs in a process system, getting the pressure down as quickly as possible is important, by diverting the contents to the flare header. Blowdown is a challenging process, even more so in a situation where parts or all of the system are exposed to fire. The blowdown and flare system must handle both scenarios.

Fact box, VessFire:
VessFire is a multi-physics simulation system for blowdown analysis, treating the thermo-mechanical processes interacting with each other. VessFire meets the requirements for advanced depressurisation analysis as outlined in the 2014 edition of API 521 (ISO 23251). Blowdown analysis in VessFire takes into account external heat sources, heat transfer from the outside and through vessel and pipe walls, and through the fluid and gas phases. Evaporation and condensation take place inside vessels and pipes causing the composition of phases to change over time. When a blowdown valve (and/or pressure release valve) opens, mass is removed from the segment, reducing pressure. If the pressure is reduced too slowly in a fire case, rupture can result. VessFire calculates time to rupture. Parameters such as wall thickness, flow orifice diameter, material quality etc. can be varied to see the effect on time to rupture.