Mods don't have that permission, except to ban accounts which is very different than neatly closing an account.
EDIT: It looks like we could also disable your ability to post without banning you. But again that is different than neatly closing up an account and removing all associated content.
As a policy all comments remain on the board. When individuals go through their entire post history and edit posts to things like "I hate everything!" or simply blank the pages, mods and staff will go back through all the posts and revert the formerly-useful posts so that others can learn and grow from the knowledge.
If this is a case of simply having made posts that you want to distance yourself from, the best solution is just time. The Internet never forgets. Even if we blanked out every reference to you on the site, there are many archives on the internet that will remember your posts forever.
: Learned something new.