No, you can't limit the number of security sessions to 1 per user. Simply for the reason that security sessions are maintained locally by each server process. See the attached link for details on security sessions. In case of external authentication, such as SAML, it could be possible to limit the amount of logins per user but you would eventually run into problems with hanging sessions preventing the users to logon...
http://help.sap.com/saphelp_nw73ehp1/helpdata/en/c7/5ee440ba994fa3b187ff2f050cfe7c/frameset.htm