From The Siege of Charleston 1861-1865 by Burton:
When the carriage was repaired, the firing resumed, this time with shells of Greek fire...
That excerpt indicates that Union troops fired on Charleston with Greek fire shells in 1863. Later in the book comes the following:
In early 1865 the bombardment was still in progress. General Foster, who had succeeded General Gillmore as commanding officer of the Department of the South, received a communication from O. S. Halsted, Jr., relative to the use of Greek fire. Halsted assured General Foster that it was of superior quality to the kind first used in the early part of the bombardment and promised him that, if he used it, he could burn Charleston whenever he pleased. Halsted continued, "Nothing would suit the people so entirely just now as to hear that General Foster had burned that hot bed of rebeldom -- Charleston." General Foster answered that he had no such shells on hand but that if Halsted would send some he would "fire them on Charleston with pleasure."
Interesting, especially since the exact composition of Greek Fire has been lost for centuries. Are you sure that the shells weren't filled with tabasco sauce, and thus gave the south a staple for their 20th century cooking?