LM324 comparator IC getting burnt
I think you're using a 24VAC/3A transformer, which will give you a DC voltage of \$ \sqrt 2\ \cdot 24\$ VDC plus whatever regulation the transformer allows under light load, plus maybe some line voltage tolerance. 

That could easily be 40V or 42V, which exceeds the 32V absolute maximum supply voltage of the LM324 quad op-amp by a considerable margin (as Brian Drummond has hinted at).