Combination Technology Of Atmospheric Flash And Isopentane Solvent Deasphalting For Tahe Crude Oil

To solve the existing problems in refining Tahe crude oil with high density and high content of sulfur, carbon residue, asphalt and heavy metal, this paper is dedicated to the study of the combination technology of atmospheric flash and isopentane solvent deasphalting for Tahe crude oil.Firstly, the combination technology of atmospheric distillation and delayed coking for Tahe crude oil was investigated. The delayed coking reaction kinetics model of Tahe residue oil was established using the structure oriented lumping method and delayed coking process of Tahe residue was simulated at the molecular level. It demonstrated that the main technical problems of the atmospheric distillation-delayed coking combination technology for Tahe crude oil were serious equipment corrosion, low yield of liquid product and lack competitiveness of inferior coke, whose yield was about 23% of the crude oil. These problems restrict the efficient conversion of oil resources and the long-term operation of the plants.Then Tahe crude oil atmospheric flash experiments were carried out and the true boiling point distillation curve, Engler distillation curve, equilibrium gasification curve and atmospheric flash curve of Tahe crude oil were drawn. Results of atmospheric flash experiments were consistent with equilibrium gasification data. With the increase of flashing distillation temperature, the yield of Tahe light distillate and sulfur content increased, and H/C atomic ratio reduced. When the flash distillation temperature was 260℃, the yield of light distillate oil was 13.6%. Corrosion test showed that when the temperature was below 260℃,the corrosion rate was very slow. The temperature range of 260-270℃ is the main corrosion growing section. To avoid the corrosion on the plants and gain a higher yield of light distillate, the appropriate operating temperature of atmospheric flash distillation was 260℃. At this temperature the C5 fraction of Tahe crude oil was completely separated, and wouldn’t affect the subsequent residue solvent deasphalting process.At the same time, Tahe atmospheric flash residue was separated to six components (saturates+light aromatics, heavy aromatics, light resin, middle resin, heavy resin and asphaltene) using liquid-solid chromatography. The distribution of impurity in the deasphalted oil (DAO) of atmospheric flash residue was predicted. The sulfur contents of heavy aromatics and asphaltene components were as high as 4.47% and 3.13%, respectively. The total nitrogen content of resin and asphaltene was 86.97% and Ni, V in asphaltene were 81.37%,79.42% of total Ni and V, respectively. As components become heaver, hydrogen carbon ratio (H/C) and aromatic ring condensation degree (HAU/CA) of the components decrease gradually and total carbon number(CT), aromatic carbon number(CA), naphthenic carbon number (CN), total ring number(RT), aromatic ring number(RA), naphthenic ring number (RN) and aromatic carbon rate (fA) increase. Saturated carbon number (CS) and alkyl carbon number (CP) were lowest in heavy aromatic component.At the temperatures of 140℃ to 185℃ and solvent ratios of 4.0,5.0 and 6.0, the phase diagrams of Tahe atmospheric flash residue-normal pentane and isopentane systems were investigated using a high temperature and high pressure phase equilibrium experimental apparatus. At a constant temperature, when the pressure decreases, phase transition process of Tahe atmospheric flash residue-solvent system was from uniform liquid (L), to the liquid-liquid phases (L-L), to the liquid-liquid-gas phases (L-L-V) and to the liquid-gas phases (L-V). The phase spliting pressure improved with the increase of the temperature. Liquid-liquid region is a feasible operation range for subcritical solvent deasphalting processof Tahe atmospheric flash desidue. The split phase pressure and bubble point pressure of Tahe atmospheric flash desidue-isopentane system were slightly higher than those of Tahe atmospheric flash desidue-normal pentane system. With the increase of solvent ratio, the phase spliting pressure of Tahe atmospheric flash desidue-isopentane system rose but the bubble point pressure was hardly changed, so the feasible operating pressure range of solvent deasphalting process was enlarged. The phase behavior characteristics of Tahe atmospheric flash distillation residue-pentane system were revealed.The effects of operation conditions including solvent composition, extraction temperature and solvent ratio on solvent deasphalting process were investigated on the continuous solvent deasphalting pilot plant with the Tahe atmospheric flash residue as raw materials. The optimal conditions for Tahe atmospheric flash residue solvent deasphalting process were:solvent of isopentane, extraction temperature of 175℃, pressure of 3.7 MPa and solvent ratio of 5.0. Under this condition, DAO yield was 75.2% and the content of metals (Ni+V) and carbon residue were 24.87μg/g and 4.15%, respectively. The main indexes of DAO met the feed requirements of heavy oil catalytic cracking process. With the reduction of extraction temperature and the increase of solvent ratio, the DAO yield increased but DAO properties became poorer. Using the molecular weight as characteristic property, the continuous thermodynamics model for Tahe atmospheric flash residue-isopentane solvent deasphalting process was established. It can predict the effects of operating conditions of solvent deasphalting process on the molecular weight distribution and yields of DAO and deoiling asphalt (DOA). Compared to the experiemtal results, the absolute errors of the model were less than 4%. The utilization study of DOA shows that the solid residue DOA can be developed into high value-added asphalt modifier and asphalt mixture additive.The results show that total liquid yield of the Tahe crude oil atmospheric flashing-solvent deasphalting combination technology was 78.6%, which was 9.9% higher than that of atmospheric distillation-delayed coking combination technology. DAO met the feed requirements of heavy oil fluid catalytic cracking process. Meanwhile, serious device corrosion problems and the formation of inferior petroleum coke were avoided. The novel combination technology was beneficial to improving the efficient utilization of petroleum resources. These results enrich the theories of solvent deasphalting process.The economy estimates of Tahe crude oil atmospheric flash-isopentane solvent deasphalting combination technology show that the new developed combination process can make the inferior heavy oil processing represented by Tahe crude oil to produce better economic and social benefits.