Here is how. First defeat lord nightshade in WC.Then go KT and do all the quests you can get.Then defeat Biti Nirini and Quartermaster.There you go!P.S. please be my friend my name is Cody Spirtrider Lvl.20! :D
Keep in mind that even after you get the quest to go into the Palace of Fire, the bars will still appear over the entry way (at least they did for me). Despite the bars, you can still access the area (provided you have the quest).