$re = '/.*\b(PAL)\s?(\d+)\b.*/m';
$str = 'TCNU1573105 HDPE HTA108 155 155 000893520918 PAL990 25.2750 MT 28.9750 MT
TCNU1573105 HDPE HTA108 155 155 000893520918 PAL 990 25.2750 MT 28.9750 MT';
$subst = "$1$2";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php