We have an early am arrival in Brussels and can't access our accommodations until mid-afternoon. I would like a location to stash our luggage for a few hours near or in the Gare Centrale.
The train station has lockers:
We usually arrive at our gateway city in the morning and find that our hotel's staff is very accommodating at holding our bags until we can check in later in the afternoon. Of course that only works if your "accommodation" is staffed.
At Brussel Centraal/Bruxelles Central there are automatic luggage lockers at the concours between track level in the basement and exit/entrance level. Three sizes, €3 (briefcase)/ €3.50 / €4 (big backpack)/24 hours, if I make no mistake. Have some coins with you. There is also a left luggage department but not always open I have seen a few times.
I agree with Edgar, if possible better to store the luggage already at the hotel.