PHP - Session problem in codeigniter framework

How do you load the "session" library?
What are the session config settings you are using?

Im Loading Session Library in autoload file.
$autoload['libraries'] = array('database', 'session', 'form_validation');

Session Config Settings:

$config['sess_driver'] = 'files';
$config['sess_cookie_name'] = 'pop_session';
$config['sess_expiration'] = 7200;
$config['sess_save_path'] = NULL;
$config['sess_match_ip'] = FALSE;
$config['sess_time_to_update'] = 300;
$config['sess_regenerate_destroy'] = FALSE;