To convert one type of stream into an other (different sets of compounds on each stream are allowed), use the stream converter.
The stream converter has an inlet and one outlet. You can select the flash type that will be used to calculate the equilibrium on the outlet stream.
If compounds are present in the inlet that cannot be present in the outlet, the stream converter cannot succeed to put everything in the outlet. Therefore, the stream converter has a purge port. If you connect a stream to the purge port it must be of the same stream type as the inlet stream (i.e. same number and order of compounds). All compounds that cannot be present in the outlet stream will be put in the purge stream (which will have the same T and P as the inlet).
If there are compounds that cannot be put in the outlet stream and the purge is not connected to a stream, the stream converter will fail to solve.