An ammonia synthesis plant at the Nitrogen Works ,,Putawy" started up in the 1960-ties was revamped by changes in the synthesis reactor enabling a replacement of a coarse-grained (6-10 mm) catalyst by a more efficient, fine-grained (1,5-3 mm) one. The gas pressure drop was decreased but a disadvantageously slim pressure vessel of the old TVA reactor has been retained. The new reactor type INS-27 has been working for 2 years, bringing about a substantial energy saving. Moreover, it is particularly resistant to internal crackings. The INS-27 reactor can be an advantageous offer for modernization of other ammonia plants with the reactors adapted to the coarse-grained catalyst started up before 1970.