Seems you are trying to simulate the high pressure section of a urea plant.
Aspen Tech has an example model that can be downloaded from it's support site. It is an example, and not a guaranteed product. They state "consulting may be needed for technology transfer and further model development and validation"
Search there for "urea". In my case was the first result. I've tried it, and it does not replicate what we see in the plant. You cannot modify it since is a compiled dll. So try it and see if it fits your required use.
Most of the publicly available simulations of this system are based on uniquac (available in Aspen, but you need to check all the parameters) or extended uniquac (not available in Aspen).
If you have not done it yet, I would strongly recommend that you study the system first before embarking in simulation. It is a system of only 3 components but is complex (3 salts plus double salts - cuadruple points - supercritical components - ionic species - maximum temperature azeotrope - VLS equilibrium at low temperature).
All of this makes it very difficult to trust your intuition when you are simulating.
One of the best works I've found on this system is a Thesis dissertation by Krishnan RAMASAMY.
http://repository.tu...iss 1616(1).pdf
Hope this helps