In addition of recycle loops always present in the solution of petrochemical plants, XPSIM provides the user the simulation of network systems.
Network simulations can be divided in two general classes:
• gathering systems
• generalized networks
Gathering systems exist when pipelines are connected through a reverse tree structure: e.g. this flowsheet has multiple sources but only one delivery point (sink stream).
An example of a gathering system is shown in the left Figure. Within gathering systems loops and/or crossovers are not allowed.
Generalized networks are formed by links.
A link is a sequence of pipes and other devices, such as valves and pumps, connected through nodes.
Generalized networks may have any number of sources and sinks connected through links and/or crossovers. In this case reverse flow is possible and is taken into account by the program.
For the solution of generalized networks the user should supply a sufficient number of pressure/flowrate specifications in order to completely define the fluid flow and the pressure profile.
This figure shows an example of a generalized network formed by a nitrogen distribution system.
These are solved by computing the pressure drop through pipes in a direct direction and then in a reverse direction.
In the reverse calculation the sink pressure is reset at value nearer to that specified by the user.
The source pressure is adjusted after each reverse iteration.
In these calculations either the feed pressure or flowrates can be varied.
The solution is achieved using a Newton-Raphson type algorithm.