CodeIgniter is not a component based framework.
A component based framework is also called a pull based framework, CodeIgniter is a push based framework.
Think of component based as one way to organize car parts in a garage.
In a component based garage you would have all your tires in one area, and all the suspension parts in another area, and the transmission parts elsewhere etc.
But then a different garage that was an object oriented type garage structure would have different sections in your garage for each type of car. So all your chrysler parts would be in one section; you could get tires there and the suspension parts and transmission parts specific to that model all in one location. Then the different section in that same oo garage would have all your mercedes parts; the tires, suspension, and tranny. This garage is based on the fact that all the cars have the same parts, and kept organized according to each specific object (a.k.a manufacturer).
http://en.wikipedia.org/wiki/Web_application_framework