<?php
$kucukon = array();
$onyirmi = array();
$yirmiotuz = array();
foreach($_POST['name'] as $key => $name) {
    if (!empty($name)) {
        if ($name<10) {
            $kucukon[] = $name;
        }
        if ($name>=10 && $name<20) {
            $onyirmi[] = $name;
        }
        if ($name>=20 && $name<30) {
            $yirmiotuz[] = $name;
        }
    }
}
print_r($kucukon);
print_r($onyirmi);
print_r($yirmiotuz);
?>
<form action="" method="POST">
    <input name="name[]"><br>
    <input name="name[]"><br>
    <input name="name[]"><br>
    <input name="name[]"><br>
    <button name="submit">Gönder</button>
</form>