Solved it by devide the column into smaller parts, with following select statement;
Select NVL(TO_CHAR(DBMS_LOB.SUBSTR(CLOB_COL,3000,1)),'') AS CLOB_COL_Part1,
NVL(TO_CHAR(DBMS_LOB.SUBSTR(CLOB_COL,3000,3001)),'') AS CLOB_COL_Part2,
NVL(TO_CHAR(DBMS_LOB.SUBSTR(CLOB_COL,3000,6001)),'') AS CLOB_COL_Part3,
NVL(TO_CHAR(DBMS_LOB.SUBSTR(CLOB_COL,3000,9001)),'') AS CLOB_COL_Part4,
NVL(TO_CHAR(DBMS_LOB.SUBSTR(CLOB_COL,3000,12001)),'') AS CLOB_COL_Part5,
NVL(TO_CHAR(DBMS_LOB.SUBSTR(CLOB_COL,3000,15001)),'') AS CLOB_COL_Part6,
NVL(TO_CHAR(DBMS_LOB.SUBSTR(CLOB_COL,3000,18001)),'') AS CLOB_COL_Part7,
NVL(TO_CHAR(DBMS_LOB.SUBSTR(CLOB_COL,3000,21001)),'') AS CLOB_COL_Part8,
NVL(TO_CHAR(DBMS_LOB.SUBSTR(CLOB_COL,3000,24001)),'') AS CLOB_COL_Part9,
NVL(TO_CHAR(DBMS_LOB.SUBSTR(CLOB_COL,3000,27001)),'') AS CLOB_COL_Part10
DBMS_LOB.getlength(CLOB_COL) AS CLOB_COL_LENGTH,
from DATABASE_TABLE
I use this to copy the data into an Excel file, and there the data can be concatenated again.