What was found
AT FL290, DURING DESCENT, RECEIVED A NR 2 ENGINE FIRE ALERT, LOOP A, LOOP B MEL FROM PREVIOUS FLIGHT. RAN QRH, NO OPTION BUT TO SHUTDOWN THE NR 2 ENGINE FOR FIRE ALERT. DISCHARGED THE FIRE BOTTLE. RECIEVED A SECOND FIRE ALERT DURING DESCENT MOMENTARLY, THEN EXTINGUISHED. INSPECTED THE NR 2 ENGINE AND NO SIGNS OF FIRE. REMOVED AND REPLACED THE NR 2 ENGINE PYLON FIRE DETECTOR IAW MM 26-11-02-4. OPS CHECKED GOOD.