What is the reason for settling in another SAP system? Consolidation? Reporting? That is a strange requirement or solution. Will something come back and post in the system from the other system?
Settlement is a reporting of costs within the CO module. Usually summary data is sent to other systems for reporting or consolidation.
It all depends on the requirements from the other system and what it needs to perform the settlement, but I would think that extracting the data through BW is an unnecessary step.