'Unquenchable Fire' in the Bible

Whose fan is in His hand, and He will thoroughly purify His threshing-floor, and gather His wheat into the garner, and will burn up the chaff with unquenchable fire.

Whose fan is in His hand, and He will thoroughly purify His threshing-floor, and gather the wheat into His garner, and will burn up the chaff with unquenchable fire.