Dynamic Simulation of Helium Liquefiers using Aspen Hysys®: Problems, Solutions and Prospects

This paper deals with the application of dynamic simulation of helium refrigerators and liquefiers by a general purpose process-simulator Aspen Hysys®. A standardhelium iiquefier for capacities of 100 L/hr and 50 L/hr with and without liquid nitrogen pre-cooling respectively, have been chosen for validation of the code of Aspen Hysys®. To obtain an accurate simulation result we need appropriate equation of state, accurate transport properties of helium and thermal properties of metai, actual equipment specifications and cooi-down sequence with appropriate control, in the present work, the limitations of Aspen Hysys® in simulating helium systems have been identified and techniques to overcome these problems have been discussed. The dynamic simulation has been performed following the above techniques in order to obtain cool-down profiles. The cool-down process has been simulated from 300K to 8 K showing similar trends in the temperature variations at different state points. However, it has not been possible to get below the level of 8 Kand the solution diverges at this temperature. The reasons for this divergence are under investigation and future efforts would be made to achieve a complete cool-down process simulation. To conclude, it may be said that, despite the limitations of Aspen Hysys®. and non-availability of many vital specifications of equipment of plant, we are optimistic about the applicability of Aspen Hysys®. as dynamic simulator for simulation of helium systems down to its liquefaction point.