how to use export to CSV in asp.net

we are using visual studio 2013 in which we are redirecting the data values in query string in another page. i am using three web pages

Page1 : Default.aspx

Page2 : WebForm1.aspx 

Page3 : WebForm2.aspx

 

My query is when we  will redirect from one page to another , we want to kill the previous page.

In other words i want to kill the session when moving forward.