Found this article from Donald Burleson (Burleson Consulting) on his website which gives a very good example of how to identify and kill processes associated with a specific ORACLE_SID.
ps -ef|grep $ORACLE_SID| grep -v grep|awk ‘{print $2}’|xargs -i kill -9 {}
Check out the original article and take a look around his website as there are other useful gems there.