The amine shell and tube heat exchanger of Fajr Jam refinery, which transfers heat between two rich and light amine fluids, has experienced a decrease in heat capacity over time. Various factors, including the formation of deposits and the blocking of defective pipes, have influenced this decrease in the heat capacity of the exchanger. By using the computational fluid dynamics study on the amine heat exchanger of Fajr Jam refinery, the factors affecting the reduction of the heat capacity of this heat exchanger are investigated. The simulation has been done using Ansys Fluent software and the data required for simulation from the results obtained from the HTRI software and the data received from the employer. After modelling, its validation is done with experimental results obtained from Fajr Jam Refinery. Using this model, parameters such as temperature, speed and heat flux during the heat exchanger have been examined. After obtaining the desired model, by re-designing the heat exchanger for two special cases of blocking 10% of the pipes and increasing the number of baffles by two digits, the thermodynamic parameters have been investigated and compared with the industrial model. The percentage of simulation error with the experimental results for the outlet temperature of the tubes was equal to 0.24% and for the heat transfer rate was equal to 0.73%, which scientifically makes the simulation results acceptable. Therefore, it was determined that in the case of blocking 10% of the number of tubes, the total heat transfer rate is equal to 3.72 megawatts, and in the case of a two-digit increase in the number of baffles, the total heat transfer rate is 3.85 megawatts, which in industrial mode, this total heat transfer rate is equal to 00 It is 4 MW. Also, the temperature of the fluid exiting from the tubes, in the case of blocking 10% of the number of tubes, is equal to 378.89 K, and in the case of increasing the number of baffles by two digits, it is equal to 379.29 K,