CAPE-OPEN

I have a small flowsheet containing an equilibrium reactor, a fixed conversion reactor and a heat exchanger.
It crashes everytime I try to solve it.
Can't find the reason...

The crash is resolved (CUP), and resulted from 0 reactions taking place in the Gibbs reactor on the first pass. I am not sure whether your reactor is properly solved. Please check carefully.

As an aside, you can in your inner flowsheet refer to the thermodynamics of the outer flowsheet.

How to refer to the Thermodynamics of the outer sheet?

Just by selecting the right reaction package and material stream types?

For an embedded flowsheet, if you add a property package, an additional option appears. See "Internal thermodynamic systems" in https://www.cocosimulator.org/index_hel ... heetuo.htm