Most of the Chinese Crude Oils are quite heavy with poor light distillates and vacuum residue yield up to about 40-50%. The upgrading of residue for meeting the increasing demand of light fuels is an urgent problem for China. Through chemical analysis of the residue, it is clear that the content of saturates and aromatics in the residue is high up to 40-50% with low metal content, high H/C ratio. These components are good feedstock for FCC or Hydrocracking Units. Therefore using the deasphalting process, the asphaltenes and resins (having high metal content and low H/C ratio) which are present in the residue can be removed while the saturates and aromatics are used as FCC feedstock.
A pilot plant of 20 kt/year of supercritical solvent deasphalting (SCSDA) was erected and put into operation over 5000 hrs. Large amount of operating data were obtained with different conditions using three kinds of VR feed.
The SCSDA is a dense gas extraction process using the mixture of C, and C, at 5.0 MPa and the solvent/oil ratio 3: 1 (wt). Since the yield of DAO is a function of the density of the supercritical fluid, different quality and yield of DAO can be obtained by changing the operating conditions of the system. The proper conditions have been found to cover the requirement of the two main products i.e.: DAO and Asphalt.
The most significant advantages of the SCSDA are lower investment, higher net benefit, less energy consumption as compared to the conventional SDA process. SCSDA can be combined with an FCC plant, i.e. the decanted oil from FCC mixed with VR as the feedstock to SCSDA. With this arrangement the yield of DAO can be increased and the quality of paving asphalt is also improved.
Most of the Chinese crude oil are quite heavy with poor light distillates and vacuum residue (VR) yield up to about 40-50% (wt). A large amount of VR (near 50000 kt/year) need to be upgraded in order to obtain lighter products efficiently and economically.
Fan's work' explained the principles of heavy oil upgrading. He used PI (Processibility Index) to identify the processbility of heavy stock using the relationship of H/C and molecular of feed stock and lighter products, thus.
PI = (Rl-R2)(M2-M1) where R1, R2 =HIC of feedstock and gasoline; M1, M2 = molecular of gasoline and feedstock respectively.
The larger the PI the difficulty of heavy oil upgrade, e.g. the larger the molecular weight or the smaller the H/C of the feed, the more difficulty of processing. As well known, asphaltene and resins in heavy oil are the nonideal compositions to upgrade. From the view points of economic and reducing the difficulty of processing, separating asphaltene and resins from VR or allied heavy components is of course accepted.
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