Increasingly, as technology advances in the twenty-first century, people are becoming more concerned about the exhaustion of natural resources and ecological deterioration. Exergy analysis has been considered as a powerful tool for evaluating the efficiency of energy systems and industrial processes, including the oil and gas industries, which can reduce the concerns of this industry. Therefore, the present study was conducted to analyze exergy to identify energy loss points in the process, eliminate inefficient equipment (such as low-efficiency heaters) and replace them with optimal systems, reduce energy consumption and environmental pollutants through heat recovery, and increase production by improving the efficiency of the crude oil processing process in the Cheshme Khosh crude oil pre-refinery, which can have industrial and environmental consequences, including economic savings (reducing operating costs due to energy consumption), environmental sustainability (reducing carbon footprint and other pollutants in accordance with green standards), and generalizability to other oil and gas processing units. In this study, simulation was performed using Aspen Hysys software and based on exergy analysis, 2 heaters were removed and 5 heat exchangers were added to optimize the process, which resulted in a 27.93% reduction in exergy loss in the process. This study shows that combining exergy analysis with heat recovery and equipment upgrades can simultaneously achieve economic, environmental, and technical goals in the oil and gas industries.

Introduction
Crude oil pre-refining processes, which are designed to extract water, gas, sulfur, and salt from crude oil, are among the processes that have significant environmental consequences and high energy demands. For this reason, exergy analysis is performed in the context of industrial environments for more efficient use of energy. Engineers use exergy analysis for optimization Process optimization is an excellent way to achieve production goals. Exergy evaluation is performed in an industrial environment to maximize energy use.
The study area is the Cheshmeh Khosh exploitation unit located 52 km from Dehloran city in Ilam province, which processes the oil produced in the Cheshmeh Khosh, Paydar, Paydar Gharb and Dalpari fields with a nominal capacity of 80 thousand barrels per day and sends it to the Sabzab pumping station, Ahvaz exploitation unit No. 3 and Shahid Chamran pumping station through two 24 and 20 inch pipelines with a length of 53 and 153 km, respectively, in order to supply feed to refineries or export. It should be noted that the length of the pipelines from the wells to the Cheshmeh Khosh exploitation and desalination center is about 1000 km in total. In the exploitation units, the necessary facilities for separating gas from oil in four stages (at four different pressures) have been provided. These stages include the first three stages of separating gas from oil and the fourth stage of the exploitation tank. Depending on the number of flow wells, the four stages of the exploitation unit will be from one to several rows. Therefore, in each stage, the pressure is reduced compared to the previous stage, allowing the gas to be separated from the oil in four stages, and in the final stage (the exploitation tank stage), the gas-free oil (in stabilized conditions) is prepared for transfer to the refinery consumption centers. Each exploitation unit is usually equipped with a pump house and an oil transmission pipeline through which the produced oil is continuously sent to the crude oil distribution network after pressurization and measurement. On all pipelines in the inlets of the exploitation unit, including the well pipelines and wellhead facilities; flow rate, pressure, temperature, safety valves, etc. are installed. These pipelines are directed to different separation sets (non-saline - saline) by means of divided pipelines according to the nature of the incoming oil. Gas-oil separation vessels are horizontal vessels with specific dimensions and suitable operating pressures into which the produced oil enters from one side and, due to the presence of special devices inside it and the force of gravity, the oil is directed to the bottom and the gas to the top, and finally the gas is discharged from the top of the separator and the oil from the bottom. Separators operate based on the reduction of pressure in each separation stage. If the oil entering one or more wells into the exploitation unit is sour (contains hydrogen sulfide gas), it is sent to the desulfurization tower. In this complex, by installing a hydrogen sulfide separation tower, the amount of hydrogen sulfide in the oil is brought to the standard level. Sour oil enters the hydrogen sulfide separation device from above and is directed to this device from below with the appropriate pressure of sweet gas. Finally, due to the presence of suitable contact surfaces in this device, the exchange between oil and gas is carried out and most of the hydrogen sulfide in the oil is transferred to the gas and exits from the top of the device and the relatively sweet oil exits from the bottom. If the produced oil contains salt, upon entering the exploitation unit, the gas-free salt oil is directed through pipelines divided into a separation set dedicated to salt oil, and is directed to desalination facilities that are usually built in the vicinity of the exploitation units for dehydration and desalination. In this unit, wastewater is separated, which, due to its high salt content, is sent to injection wells after treatment.

Materials and Methods
In this study, first, process simulation (based on process maps and mass and heat balance PFD, P&ID, H&MB and diagrams of pipelines and equipment) was performed using the Aspen Hysys software, and using the output data of the software, the amount of exergy and energy consumed throughout all parts of the process and equipment was examined, and then inefficient components were identified, eliminated or modified in order to increase the efficiency of the equipment based on operational parameters, process optimizer, and exergy analysis. Also, using the PipeSim software, the effect of pipeline profiles on the operating pressure of the process was examined.

Results and discussion
In this study, in order to achieve the goals, using Pipe Sim software, the effect of pipeline profile on the operating pressure of the process was investigated and it was determined that it does not have much effect on the operating parameters. Therefore, after simulating the crude oil processing process using Hysys software and exergy analysis, heat exchangers were added to the simulation and the energy of hot streams was used to heat cold streams. Two heaters were removed from the simulation and five heat exchangers were added. With this method, in addition to eliminating inefficient equipment, the heat required for other heaters is also reduced. The results of calculating exergy loss before and after adding heat exchangers and removing heaters indicate a 93.27% reduction in exergy loss in the process, indicating a significant improvement in energy efficiency, reduced fuel consumption and pollutant emissions due to the removal of heaters dependent on external energy sources, increased production efficiency by optimizing the energy balance in the system, which can have industrial and environmental consequences, including economic savings (reducing operating costs due to energy consumption), environmental sustainability (reducing carbon footprint and other pollutants in accordance with green standards), and the ability to generalize to other oil and gas processing units.

Conclusion
This research shows that exergy analysis is not only a theoretical tool, but also that combining exergy analysis with heat recovery and equipment modernization is a practical solution for multidimensional optimization (energy, economy and environment) in the oil and gas industry. The results obtained can be a model for other industrial units to move towards sustainable production with a systematic approach.