This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
If I have understood your problem well, your session gets timedout because of no activity going on for long time(taking 1.30hr for your task to finish). Solution for this could be, keep sending a request to server after X intervals continuosly till user logout or till your operation is over. You can do this by, sending a request to an image or frame on server.