I'm not sure if i have understood the problem, but isn't it easy as:
protected void ProcessUpload(object sender, AjaxControlToolkit.AsyncFileUploadEventArgs e)
{
string name = System.IO.Path.GetFileName(e.filename);
string dir = Server.MapPath("upload_excel/");
string path = Path.Combine(dir, name);
venfileupld.SaveAs(path);
writetodb(path);
}
SaveAs
will save the file on the server, so you can do what you want with it afterwards.