How to calculate nox in my model of boiler? I am using non-premixed model of combustion and I have several coal injections.

Lots of people have spent the bulk of their career trying to answer this question so it is probably not fair to try and address it in this forum.

Have you looked at the tutorials in the Fluent manual? Using the built-in Fluent postprocessing modules would be a good way to start. If you can get reasonable agreement with field data, this may be okay. Otherwise, you might want to implement some other models. Reaction Engineering seems to have done a lot of good work and has published equations for modeling of NOx from coal combustion.