The main goal of this research is the modeling and optimization of an industrial hydrogen unit in a domestic oil refinery at steady state condition. The considered process consists of steam methane reforming furnace, low and high temperature shift converters, CO2 absorption column and methanation reactor. In the first step, the reactors are heterogeneously modeled based on the mass and energy balance equations considering heat and mass transfer resistances in the gas and catalyst phases. The CO2 absorption column is simulated based on the equilibrium non-ideal approach. In the second step, a single objective optimization problem is formulated to maximize hydrogen production in the plant considering operating and economic constraints. The feed temperature, firebox temperature, and steam flow rate in the reformer, feed temperature in shift converters, lean amine flow rate in the absorption column, and feed temperature in the methanator are selected as decision variables. The calculated effectiveness factors and mass transfer coefficients prove that the methane reforming is inertia-particle mass transfer control, while shift and methanation reactions are surface reaction control. The simulation results show that applying the optimal condition on the system increases hydrogen production capacity from 85.93 to 105.5 mol s(-1). (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.