I currently do not have a chat room, but I was wondering, could I block annoying users from my chat room?
To elaborate on what gandalf3 said, no you can not just block a user from your chat room.
Chat room are set up to be public, and in normal rooms there is no mechanism to banish a user from just that room.
The "kick-mute" feature will last (depending on how frequently the user has been kicked) 1, 5, or 30 minutes. So it is not permanent.
Now you can create a restricted room where only people that you let in can talk. That type of room is called a "gallery," only the people you have on the room's access list (and mods) will be able to talk; however anyone can view it.
Those are the only two ways a room owner can control who talks in their room. But there is no way to just block a user from talking.
Yes, as a room owner you'll have the ability to kick/mute users from your room.
For a full list of chat-related abilities and privileges, refer to this answer on meta.