session not closed after close the browser.

session not closed after close the browser. when i reopen the url,the session is active. i am string the sessions.

In config file
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config['sess_driver'] = 'files';
$config['sess_cookie_name'] = 'ci_sessions';

$config['sess_expiration'] = 7200;

$config['sess_match_ip'] = FALSE;
$config['sess_time_to_update'] = 300;
$config['sess_regenerate_destroy'] = TRUE;

$config['sess_expire_on_close'] = TRUE;
$config['sess_encrypt_cookie'] = FALSE;