problem i cant download bigger blob files in php

ini_set("memory_limit","16384M");    
set_time_limit(0); 
require_once("connection_db.php");
$id_file=$_REQUEST['id_doc'];

$qry="Select file_name,size,type,file from file where id='$id_file'";
$res=mysql_query($qry) or die(mysql_error()." qry::$qry");
$obj=mysql_fetch_object($res);

//header
header("Content-Type: application/force-download");
header("Content-Type: application/octet-stream");
header("Content-Type: application/download");
header("Content-type: {$obj->type}");
header('Content-Disposition: attachment; filename="'.$obj->file_name.'"');
header("Content-Transfer-Encoding: binary");
print $obj->file;
		
//close the connection
mysql_close();