This paper summarizes and discusses our recent work on modelling of several steelmaking processes. The work started by developing a detailed sub-model for a single gas bubble reacting in liquid steel. The key feature in this model was an approach based on LOMA, Law of Mass Action, which was employed for defining the chemical rate of a reaction in a robust way. The bubble reaction model was then coupled with a new simulator concept for the AOD process, Argon-Oxygen Decarburization. After a successful validation, the same approach was used to model chemical reactions and chemical heating of liquid steel in the CAS-OB process, Composition Adjustment by Sealed Argon Bubbling Oxygen Blowing,using a supersonic lance. Finally, a new model was developed and implemented into the existing AOD process model for slag reduction with slag droplets. The purpose of this paper is to present a generalised framework for applying and validating the LOMA approach into modelling of metallurgical unit operations. In addition, the use of Computational Fluid Dynamics (CFD) in the validation and verification work is discussed.