"I will be writing although I am working."
Translation:Εγώ θα γράφω αν και δουλεύω.
θα γράψω should also be correct. The other form is only correct if there is a repetition or habbit.
Θα γράψω shows short-duration future action and translates as "I will write" and never "I will be writing". It is the Future Simple (μέλλοντας) and not the future continuous ( εξακολουθητικός μέλλοντας) form of the verb γράφω.