Corion already provided a direct answer. i do think though that it doesn't make much sense to keep alive a browser session for 1/2 hour. after all, the browser environment is all about interactivity...and your program doesn't seem to fit this. you may like to implement something along the lines of...url form to hit submit to start process also shows result of last run, and same url brings up a % complete figure if currently running the computationally intensive task. this or similar way, the display is not tied to the long task...and you don't have to worry about a browser session closing killing the long running task
the hardest line to type correctly is: stty erase ^H