Iranian Journal of Oil and Gas Science and Technology

Abstract The present study deals with the geometry effects of the spherical pressure vessels (SPV) and the crack configuration on the variation of the stress intensity factor (SIF) through the crack line. The vessel is assumed to contain a semi-elliptical crack on the inner surface. The pressurized vessel is subjected to the pressure and thermal gradient (thermomechanical loading). The 3-D analysis of defective thick-walled pressurized spherical vessels is conducted using the numerical finite element method (FEM). This work covers various crack configurations in vessels with different geometries. The effect of the various parameters, such as thermal gradient, R_o/R_i, a/i, and a/t, on the variation of the dominant first mode of SIF through the crack front is studied. The obtained SIFs are compared with the mechanical loading results (without the thermal gradient). The results show that crack parameters (the aspect ratio and the crack depth), the wall thickness of the vessel, and the structural loading can significantly affect the distribution of the values of SIF through the crack front. Keywords: Semi-elliptical Crack, Spherical Pressure Vessel, Stress Intensity Factor, Thermomechanical Loading

Abstract Due to the limitations of existing natural gas fumigation systems, including the bypass and injection systems, there is a need for the design of a new system with fewer restrictions. This paper addresses this issue by conducting a thermodynamic analysis of the performance of a new system, called the ejector gas perfuming system, across a wide range of parameters, including primary gas pressure (Pg = 500-5500 kPa) and secondary gas pressure (Ps = 200-400 kPa). The results demonstrate that the ejector's performance is primarily influenced by two key factors: the pressure at the ejector's exit and the ejector's entrainment ratio. The findings indicate that the ejector performs optimally when Ps > 250 kPa and 1850 kPa ≤ Pg ≤ 5200 kPa. Outside of this range, its performance declines.

Abstract This work pertains to investigate the values of the stress intensity factor (SIF) in a functionally graded spherical pressure vessel with an embedded surface defect (semi elliptical crack) under thermo-mechanical loading. The three dimensional finite element analysis is performed to evaluate the SIFs through the crack front for a wide range of crack profiles and the various layer thickness. It is assumed that the elastic modulus of sphere varies exponentially in the radial direction of the vessel.

The effect of non-uniform coefficient of thermal expansion (CTE) on the fracture parameters is also studied. The obtained results show that the material gradation of spherical pressure vessel can considerably affect the distribution of the SIFs along the crack front. The gradation of material, the wall thickness of spherical pressure vessel and the profile of crack front can affect the critical point through the crack front which is apt to the crack growth.

Abstract Separation of suspended droplets in a fluid flow has been a great concern for scientists and technologists. In the current study, the effect of the surface roughness on flow field and the performance of a gas-oil cyclone is studied numerically. The droplets and the turbulent airflow inside the cyclone are considered to be the discrete and continuous phases respectively. The Reynolds stress model (RSM) is employed to simulate the complex, yet strongly anisotropic, flow inside the cyclone while the Eulerian-Lagrangian approach is selected to track droplet motion. The results are compared to experimental studies; according to the results, the tangential and axial velocities, pressure drop, and Euler number decrease when the surface roughness increases. Moreover, the cyclone efficiency drops when the vortex length decreases as a result of a rise in surface roughness. The differences between the numerical and experimental results become significant at higher flow rates. By calculating the impact energy of droplets and imposing the film-wall condition on the walls, splash does not occur.

Abstract In this paper, an advanced analysis of a novel hybrid compression-absorption refrigeration system (HCARS) for natural gas dew point control unit in a gas refinery is presented. This unit separates the heavy hydrocarbon molecules in the natural gas, which is traditionally carried out by natural gas cooling in a compression refrigeration cycle (CRS). The power input required for the refrigeration cycle compressors is usually provided by gas turbines. The low efficiency of gas turbines and the excessive power required for running the CRS compressors have made it crucial to investigate different means to decrease the energy consumption of this cooling system.
The waste heat of gas turbines flue gas can be recovered and utilized as the heating source for running an absorption refrigeration system (ARS) to provide part of the needed cooling load; hence, a hybrid compression absorption refrigeration system (HCARS) is launched. In this work, the application of HCARS is extended to the Fajr-e-Jam gas refinery currently operating with a CRS, and an advanced exergetic analysis of the proposed ARS is performed to further improve the proposed system. The effect of different variables on the performance of the proposed HCARS is also inspected. The proposed system and these analyses are novel for the gas refinery dew point control unit. Real CRS operational data are utilized in all the investigations, and proper means are presented for the validation of the simulation results.
The proposed system resulted in 63% additional cooling capacity of the HCARS (12550 KW) in comparison to the current CRS (7670 kW) for the equal natural gas consumption, which overall saves about 50000 SCMD of natural gas. Based on the exergy analysis of all the equipment, the exergy efficiency of the proposed ARS is 0.155. In addition, the parametric study of the effects of the gas turbine flue gas exit temperature and flow rate, ambient temperature, partial load operation of CRS, absorption solution flow rate, and concentration on the HCARS performance is carried out. These studies should provide the information needed for operating the proposed system in different situations.