Method for preparing ethylene

A method for preparing ethylene comprising:

• feeding a thermally cracked compressed stream to a first distillation apparatus;
• operating the first distillation apparatus as a first deethanizer when the thermally cracked compressed stream has a C1 hydrocarbon compound content of less than 20 mol%, feeding an overhead discharge stream of the first distillation apparatus to a second distillation apparatus, and feeding a bottom discharge stream of the second distillation apparatus to a C2 separator;
• and
• switching the operation of the first distillation apparatus to a first depropanizer when the thermally cracked compressed stream has a C1 hydrocarbon compound content of more than 20 mol%, feeding the overhead discharge stream of the first distillation apparatus to the second distillation apparatus, and feeding the bottom discharge stream of the second distillation apparatus through a third distillation apparatus to the C2 separator.