The first is generally better:
"This is the description of the BankABC project."
And you're right, the noun is being used like an adjective. This is called an "adjectival noun," or a "noun adjunct." See the following for more:
But the second version isn't altogether and completely wrong. As Peter Jennings points out in his comment, project would have to be part of the proper name of the project itself, "Project BankABC." Perhaps a goverment program teaching bankers how to read? Lol. Names like this aren't super common, they're used to sound a little more grand, a little more flamboyant, like something you would see in a James Bond movie, or something a politician would name something grandiose.