Integrated Process Of Heavy Oil Pyrolysis And Coke Gasification

With the depletion of conventional oil resources,the world crude oil supply is developing in the direction of focusing on quality and inferior quality,and the output of inferior heavy oil is increasing.The efficient conversion and utilization of inferior heavy oil is an effective way to improve energy utilization and alleviate energy shortage.At present,the lightening technology of inferior heavy oil mainly includes hydrogenation and decarburization.The hydrogenation process requires a large amount of hydrogen and high temperature and high pressure,which greatly increases the cost of the operating and equipment.In addition,the delayed coking technology as the most widely used technology for treating inferior heavy oil in the decarburization process still exists some problems such as low liquid yield,large amount of high sulfur petroleum coke which is difficult to be used and potential safety hazards caused by pellet coke,which limits its promotion and utilization.In view of the problems existing in the above inferior heavy oil lightweight process,an integrated process of heavy oil pyrolysis and coke gasification was proposed to achieve clean and efficient utilization of heavy oil.The basic feature of this process was to simultaneously realize the pyrolysis of inferior heavy oil in the syngas atmosphere and the gasification of coke in the integrated reactor of heavy oil pyrolysis and coke gasification.At the same time,the coke generated by pyrolysis directly entered the gasification section without cooling to generate high-temperature syngas,providing a hydrogen-containing atmosphere for the pyrolysis section of heavy oil.The process aimed to achieve mass mutual supply and heat complementation between heavy oil pyrolysis and coke gasification to obtain relatively high oil yield and quality and reduce the energy consumption of heavy oil pyrolysis reaction.In this paper,the basic research on the development of the integrated process of heavy oil pyrolysis and coke gasification was carried out,and the following main results were obtained:（1）The pyrolysis behaviors of Dagang slurry oil（DG-SO）,Qingdao vacuum residue（QD-VR）and Canadian oil sand bitumen（CA-OB）were studied by TG-MS.Compared with the Friedman method and the FWO method,the four-component Gaussian DAEM method could describe the whole process of heavy oil conversion rate 0-100%.The calculated weighted average activation energy of DG-SO,QD-VR and CA-OB was148.92,205.92 and 190.37 k J/mol,respectively.By comparing the average activation energy of the virtual four components and the real four components of QD-VR,it was found that the presence of resin and asphaltene increased the average activation energy of saturates and aromatics,while saturates and aromatics decreased the average activation energy of resin and asphaltene.The activation energy obtained by pyrolysis of heavy oil was the result of the interaction of four components.（2）The effect of pyrolysis temperature and initial syngas pressure on product distributions and coke structure evolution during Canadian oil-sands bitumen（CA-OB）pyrolysis was investigated.The complete conversion of residual oil could be achieved under the pyrolysis conditions of 450°C,1 MPa and 60 min.The higher pyrolysis temperature and lower syngas pressure could increase the contents of CH₄,C₂-C₅,and CO₂ in pyrolysis gases and decrease the contents of alkane,olefin,aromatic hydrocarbon,and oxygen/nitrogen/sulfur compounds in pyrolysis oil.Meanwhile,the H/C and O/C ratios,the functional groups,the degree of graphitization of coke and the reactivity of coke decreased with increasing pyrolysis temperature,but increased with increasing initial syngas pressure.The dimensionless index（D_i）was defined to characterize the physical structural parameters,i.e.,H/C and O/C mass ratio,and graphitization degree,which had a strong linear relationship with the oxidation activity index（S）of coke samples,namely S=9.9529×10^-3×D_i+5.4291×10^-7.According to the linear relationship between S and D_i,the reactivity of pyrolysis coke could be accurately predicted for industrial applications.（3）The effects of different atmospheres（N₂,CO,CO/H₂and H₂）on the pyrolysis characteristics of heavy oil were investigated,and the mechanism of syngas atmosphere on the pyrolysis of heavy oil was revealed.Compared with the N₂ atmosphere,the pyrolysis oil yields of DG-SO,QD-VR,and CA-OB increased in turn under CO,CO/H₂,and H₂ atmospheres.On the contrary,their coke and gas yields decreased in turn.Furthermore,the contents of CH₄,C₂-C₅,and CO₂ in pyrolysis gases all decreased in turn,while the contents of their alkane,olefin,aromatic hydrocarbon,and oxygen/nitrogen/sulfur compounds in pyrolysis oil increased in turn.The change of oil and gas composition indicated that compared with N₂,both CO and H₂ could inhibit further decomposition of liquid products.The pyrolysis atmosphere had a certain influence on the elemental composition,functional groups and carbon structure of the pyrolysis coke,and had little effect on the pore structure.Compared with N₂ atmosphere,the content of C element in pyrolysis coke decreased in turn under CO,CO/H₂ and H₂ atmosphere,while the content of H,N,S and O increased in turn.The absorption intensity of surface functional groups of coke increases in turn,and the degree of graphitization decreases in turn.At the same time,compared with N₂ atmosphere,the reactivity of coke produced in CO,CO/H₂ and H₂ atmospheres increased in turn,indicating that compared with N₂,CO and H₂ could reduce the degree of condensation of coke to increase its reactivity,but the effect of CO was not as good as that of H₂.（4）Based on the relationship between the physical and chemical properties and reactivity of the coke,the gasification reaction characteristics of heavy oil pyrolysis coke in steam atmosphere were studied in a micro fluidized bed reactor.With increasing the stream partial pressure,the gasification reactivity of CO/H₂-Coke increased.When the partial pressure of stream reached 40%,further increasing the partial pressure had little effect on the gasification reactivity.Compared with the homogeneous model,the shrinking core model could better fit the gasification experimental values of heavy oil pyrolysis coke,and the gasification activation energies E of N₂-Coke,CO-Coke,CO/H₂-Coke and H₂-Coke were 142.92,132.48,121.96 and 116.92 k J/mol,respectively.When6%oxygen was added to stream partial pressure,the activation energy of CO/H₂-Coke was 52.92 k J/mol,which was 69.04 k J/mol lower than that of pure steam gasification.Adding a small amount of oxygen could greatly reduce the activation energy of heavy oil pyrolysis coke,which provided a strong support for the development of gasification section of the integrated process of heavy oil pyrolysis and coke gasification.