There are two ways to close inactive sessions, preventing orphan sessions.
The first is the Server to Client Heartbeat under the Users -> Handheld page. This will send a signal to the client after the configured period of time, then disconnect the session, if the server does not receive a response from the client.
The other is the Idle Session Timeout under the User General Settings page. This will shut the session down after a fixed period of inactivity.