Try this,
<select id="searchfield" name="prid">
<?php
$query = "SELECT project_name, project_id FROM ll_project ORDER BY project_name ASC;";
$result = mysql_query($query) or die(mysql_error());
while($row = mysql_fetch_assoc($result)) {
echo '<option value="'.$row['project_id'].'"'. ((isset($_SESSION['prid']) && !empty($_SESSION['prid']) && ($_SESSION['prid'] == $row['project_id'])) ? 'selected="selected"' : '') .'>'.$row['project_name'].' | '.$row['project_id'].'</option>';
}
?>
</select>
</fieldset>