I'm working on projects that processing a large amount of data, a lot of accouting operations and data reporting, that are shown in grids and pivots.
Currently I use devexpress web controls and everything works fine.
and my question is, will it be Justified if I move to silverlight, can this technology be used for this kind of solutions?
When you write
processing a large amount of data
I assume you mean client side processing, correct? In that case you would see an great boost in processing speed over javascript. You can see an example of that here: Silverlight C# vs Javascript. That should make your application much more responsive, and with silverlight you could also easily use multithreading to push process heavy operation to the background.
If you're talking about server side processing, then it properly wouldn't be justified to make the move if you already got a working application. Unless you are planning on adding more "flashy" features in Silverlight.
With that being said I'm a big fan of Silverlight, and for a new application I would go with Silverlight. I use it all the time for big B2B web-based applications. Being able to code the frontend in C# over javascript just makes your life a little more enjoyable.