cannot retrieve data using $wpdb

in my custom_plugin.php im trying to retrieve the pages on my database using this statement below.

but i dont get any results

global $wpdb;

    $posts = $wpdb->wp_posts;
    $result = $wpdb->get_results( " SELECT * FROM  $posts WHERE 'post_type' =  'page' "  );

    foreach ($result as $page) {
            echo $page->ID.'<br/>';

    }