**4. Conclusions**

A rapid integrated numerical model for industrial steam natural gas reformer within ammonia production based on m. files in an open source code software was developed. The developed model was tested, and calculated data was reconciled against real process data for the top-fired SMR designed by Kellogg Inc. within ammonia production. Applications of a series of differential equations were used for very close description of the reaction kinetics, molar flow, temperature, and pressure changes along the reformer tubes based on the previous literature models. Reaction rates follow the theoretical model from previous work very closely. Methane molar outlet concentration and temperature approach to equilibrium as two main process parameters for monitoring of the reformer operation has demonstrated satisfactory alignment with performance of the real plant. Pressure drop and temperature profile were taken, and the diffusional resistance of the catalyst bed at any point inside of the reformer tube and the real process conditions were reliably replicated. The computational speed is rapid enough for application in real conditions by the industrial users. The coupling between the discrete model and any DCS was achieved by compiling the model algorithm with standard system-function in an appropriately designed memory block. The model can be reliably used for evaluation of the performance of the vast majority commercially available SMR catalysts. The proposed model can be potentially used in application of an APC of any steam natural gas reformer in hydrogen production and for continuous on-line performance evaluation procedure of all relevant process parameters and catalyst performance through a predictive simulation model to clarify the cost and risk associated with making operational improvements of the plant, as well as support upskilling of the workforce. In the case of application of the developed model, energy savings up to 3% can be achieved and at the same time it can serve as the base for digital transformation of any syngas plant.

**Author Contributions:** N.Z. is responsible for writing the article and simulation calculations of the model. N.B. is responsible for the guidance of article writing, and for the language and format of the article. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.
