Cascaded Thermal Processing For Venezuela Deep-Cut Residue

Cascaded Thermal Processing(CTP) is studied for upgrading Venezuelan Deep-Cut Vacuum Residue(DCVR, >500 ℃) which is the representative of extra heavy oil. In CTP technology, mild thermal treatment with hydrogen donor is firstly employed for DCVR prior to deep thermal cracking with cycle oil. In this way, it is expected to realize the high-efficiency utilization of extra heavy oil resources.At first, the spot tests, lab-scale reactor and polarizing optical microscopy are used to characterize the coking behavior of different cut-depth Venezuelan vacuum residue. The results are as follows. Venezuelan atmospheric residue(VNAR, >350 ℃) has good blending compatibility with heavy coker gas oil(HCGO). VNAR tends to form sponge coke after deep thermal cracking. The coke of Venezuelan vacuum residue(VNVR, >420 ℃) after deep thermal cracking belongs to granular mosaic structure like shot coke. The coke of DCVR is in bad quality which is easy to produce shot coke. The role of cycle oil in deep thermal cracking has duality: donating hydrogen chemically and decrease solubility physically. Considering the evaluation parameters of product distribution and economics, using the coker diesel as cycle oil is not a good choice compared to the coker gas oil. The suitable cycle ratio for light coker gas oil(LCGO) is 0.1, while for HCGO is 0.3.Secondly, the effects of CTP are characterized from the points of product distribution and coking tendency. Four refining routes are put forward and compared: Direct Deep Thermal Cracking(Route A), Direct Cascaded Thermal Processing(Route B), CTP with Hydrogen Donor(Route C) and CTP with Hydrogen Donor and Cycle Oil(Route D). The following results could be drawn. CTP technology increases the liquid yield and decreases the coke yield compared with Route A. Relatively speaking, the coke yield of Route C is 0.97% lower than Route B, while the liquid yield is 1.11% higher. Relatively speaking, the diesel yield is always the highest among the four refining routes. The coke induction period of DCVR prolongs 6 min after adding hydrogen donor. Meanwhile, the amounts and diameter of liquid coke decrease due to the addition of hydrogen donor. The coke quality of Route D gets much better with basin structure emerging partly.Finally, The CTP technology is simulated by differential scanning calorimeter(DSC). The thermal behavior of DCVR under CTP is characterized from both the mass and energy alteration. The results show that the appearance initial temperature of DCVR is 353 ℃ and the appearance final temperature is 503 ℃. Therefore, the temperature span is 150 ℃ and the overall caloric effect is endothermic during this period. How to optimize the cracking and condensation reaction happened in this temperature range is the key point to realize the efficient utilization of DCVR. The conversion rate is highest at 468 ℃ and the maximum conversion rate is 1.19%/℃. The thermogravity coke yield is 22.58%. During the mild thermal treatment unit, the hydrogen donor provides an important role in optimizing the hydrogen distribution in the system, but has little effects in deep thermal cracking unit. The programming-increased temperature condition favors to the hydrogen optimization effects of hydrogen donor and thereby raises the conversion ratio. However, under the linear-increased temperature condition, no hydrogen optimization could be found and the conversion ratio decreases instead.