Ashwani,
Are you running a full DBCC CHECKDB every night? I wasn't sure from the discussion if that was happening or not. DBCC CHECKDB can use up some TempDB space while running. If you are doing this, you can reduce the frequency significantly, as you don't need to do this daily. Try turning off this job, then shrink your TempDB again, and see if the next day it has still grown or not. If not, then you've probably found your culprit. If so, or if you aren't running this daily, then you can use the suggestions from Note 1951819 (How to check which process makes the transaction log get full in SQL Server tempdb) to find the process that is filling it and causing it to autogrow. When you've found the program or job that is the cause, then you can troubleshoot/fine-tune it to use less temporary space.
Basically, for an ECC system, you shouldn't need very much TempDB space, perhaps 10-15 GB is all. BW systems use a lot of TempDB, but not ECC.
Regards,
Matt