A very compact Selective Catalytic Reduction (SCR) system with a very low footprint comprising an SCR reactor, an inlet flow system, and a vaporizer module is described. The SCR reactor comprises at least one SCR catalyst which is in communication with the inlet flow system and the vaporizer module. The inlet flow system is configured to provide an approximately uniform flow of the exhaust gas through the catalyst and to provide heat to the vaporizer module. The vaporizer module is configured to allow for the conversion of urea to ammonia and to contact the ammonia with the exhaust gases in the SCR reactor upstream of the SCR catalyst.
