Cryogenic Simulations

The cryogenic dynamic process simulation consists in reproducing the evolution of temperatures, pressures and massflows in a cryogenic system over the time. To perform this kind of simuation, the process is modelled using an object-oriented approach where each component is first modelled indivividually in a generic way. Then, a set of components can be inter-connected between them to build a particualr cryogenic system.

Objectives of simulations

Dynamic simulation is a great tool to:

Train operators: Safe training with no risk on the process, simulate failure scenarios (e.g turbine or compressor trips), simulate occasional events (e.g. cooldown phases).
Improve control strategies:No disturbance on the real process, fair comparison between strategies, time saving.
Validate future cryogenic design during transients:Fast comparison between several designs, evaluate all process data during transients, anticipate future required control strategies.

How do we simulate cryogenic processes at CERN ?

CERN is using a commercial modelling and simulation software called EcosimPro. Then, a commercial library dedicated to cryogenics called CRYOLIB (originally developed during my phD at CERN) provides the basic cryogenic equipment models with the fluid properties. Note that this library can be then easily modified and enlarged by users for specific models if needed.

The components of the CRYOLIB library in ecosimPro

To simulate the cryogenic system, actuators need to be manipulated by a equivalent control system. Two solutions can be used, depending on the simulation objectives: (1) Stand alone simulation in EcosimPro with simplified control embedded inside the model. (2) Couple the model to a copy of the real control system (PLC and supervision).

Examples of cryogenic process simulation performed at CERN:

LHC Helium main refrigerators (18 kW @ 4.5 K )
LHC 1.8 K refrigeration units (2.4 kW @ 1.8 K )
LHC cryogenic distribution line
LHC Beam Screens
LHC Distribution Feed Boxes
Future HL-LHC cryogenic distribution system
Future String 3 cryogenic system after a quench

References

B. Bradu, P. Gayet, and S.I. Niculescu. A process and control simulator for large scale cryogenic plants. Control Engineering Practice, 17:1388-1397, 2009.
B. Bradu, Modélisation, Simulation et Contrôle des installations cryogéniques du CERN, thèse de doctorat, Université de Paris-Sud XI, 2010.