摘要
随着原油的不断变重变劣,延迟焦化在重油加工的地位愈发重要,但其在液体收率及产物分布等方面仍有不足之处,为了提高加工过程中的馏分油收率,改善产物分布,降低生焦量,延长焦化装置的开工周期,本论文以克拉玛依超稠油(CCY)为原料,进行了减黏-焦化组合工艺研究,提出了焦化馏分油为供氢剂的减黏-焦化组合工艺。
首先对CCY直接焦化的反应规律进行了考察,得到了适宜的焦化反应时间为2.0 h,反应温度为490℃,并在此基础上将焦化液体产物进行实沸点蒸馏切割,将切割的焦化柴油(180℃~350℃)、焦化轻蜡油(350℃~420℃)、焦化重蜡油(>420℃)三段窄馏分分别看作HDA、HDB、HDC进行氢转移能力的考察,结果表明氢转移能力大小为HDB>HDA>HDC,选择氢转移能力最强的HDB进行了在适宜焦化条件下供氢剂的掺炼比考察,结果表明当掺炼比为20%时,液收最高,掺炼比过高或过低都会影响液体收率的提高。将HDA、HDB、HDC在掺炼比20%进行CCY的焦化反应对比考察,研究表明,三种供氢剂中HDB的效果最佳,与直接焦化相比,可降低焦收0.87%,提高液收0.44%,其中轻质油(汽油+柴油)收率可提高1.79%。
其次对CCY减黏-焦化组合工艺和CCY掺炼HDA、HDB、HDC组合工艺分别进行了研究,并将结果进行对比。相同的是,在一定的条件下,减黏温度越高,生焦诱导期越短,裂解产物(气体和汽油)收率和缩合产物(焦)收率越高,减黏油的安定性越差;不同的是,掺炼供氢剂减黏会影响反应体系的安定性,延长生焦诱导期,在三种供氢剂中,以HDB效果为佳,掺炼后减黏与未掺炼相比可使生焦诱导期延迟,相同条件下反应体系的安定性得到加强,有利于裂解反应,提高裂解产物收率。组合工艺研究结果表明,减黏程度过深,减黏油的生焦量会增加,反应体系的安定性变差,不利于焦化工艺的加工,这样会使总液收降低,焦收增加。减黏程度过浅,黏度变化不大,轻质油收率不高,起不到减黏的效果。因此减黏-焦化工艺存在最佳的匹配条件,在三种供氢剂进行的组合工艺的考察中,以HDB的效果最佳,适宜的减黏温度为420℃、反应时间30min、压力为0.4MPa、HDB的掺炼比为10%。与直接焦化相比,焦炭收率可降低1.77%,液体收率提高1.86%,轻质油收率提高5.71%,其中柴油可提高3.57%。
最后将得到的产物的性质进行研究,结果表明CCY减黏-焦化组合工艺与直接焦化工艺相比,对液体产物S、N含量影响不大,焦炭S含量增加,N含量降低。掺炼HDB组合工艺与直接焦化相比,S、N分布变化不大。组合工艺能显著改变成焦形态,可使焦的取向性较好,在三种供氢剂的组合工艺中,掺炼HDB的组合工艺成焦取向性最好。
Delayed coking process plays a more and more important role in upgrading of heavy oil, as the crude oil exploited in the world becomes worse. However, the process still has some practical problems, such as relatively low yield of liquid and the unsatisfied distribution of products. In order to promote the yield of distillates, improve the distribution of products reduce the yield of coke and extend the working period of units, the visbreaking-coking combined process was studied, using Karamay extra-heavy oil(CCY)as the feedstock.
First of all, the coking reaction of CCY was researched under several reaction temperatures and in different time. It was indicated that the suitable reaction temperature was 490℃and the reaction time was 2.0h. After that, the liquid, which was obtained under the suitable condition, was distillated into several parts through true boiling point distillation. The coking diesel(180℃~350℃), LCGO(350℃~420℃) and HCGO(>420℃) were chosen as the HDA, HDB,HDC, respectively. The hydrogen transfer capabilities of the three distillates were studied subsequently. The result showed that the capability of HDB was greater than that of HDA which was greater than HDC. Then, HDB was blended into CCY with different proportion and the mixtures were used as the feedstock for coking reaction under the chosen condition. The result demonstrated that the feed with 20% HDB provided the highest yield of liquid. Under the same blending proportion, HDA, HDC were also blended into CCY and the reactions were carried out. The research indicated that HDB affected the distribution of product most, comparing with the result of reaction using pure CCY as feed. The amount of coke was reduced by 0.87% and the liquid yield was increased by 0.44%, especially the light distillates (gasoline plus diesel) were promoted by 1.79%.
Secondly, the visbeaking-coking combined process with and without hydrogen donor (HDA, HDB, HDC) were studied and the results from the two kinds of combined reactions were compared. The result in common was that the pyrolysis products (gas and gasoline) and condensation products (coke) increased with the increasing of reaction temperature. Meantime, the stability of visbroken residuum fell. Besides, the difference between the two kinds of combined process was that the blending of hydrogen donor would affected the coke-induction period of coking feed and HDB was the most effective donor. That could be beneficial for the crack and the yield of pyrolysis products. In the combined process, the result indicated that the stability of visbroken residuum became worse and the yield of coke increased too when the visbreaking degree exceeded a certain limit. That would increase the total amount of coke in the combined process. However, if the feed had a relatively low level of visbreaking, the viscosity would not change too much and the yield of light distillates was low. So there was a best match between the visbreaking reaction condition and delayed coking reaction condition. In the combined process, HDB affected the result mostly. The proper visbreaking temperature was 420oC. Reaction time was 30min. The pressure was 0.4MPa and the blending proportion (HDB) was 10%. Comparing with the result of reaction using CCY as feed, the coke yield dropped by 1.77%. Liquid, light distillates and diesel increased by 1.86%, 5.71% and 3.57%, respectively.
The properties of products were analyzed at last. Compared with direct coking process, it demonstrated that, the combined process did not affect the amount of S and N in liquid product too much. But the amount of S increased in coke and N did on the opposite way. The combined process with HDB did not affect the distribution of S and N in products very much. Furthermore, the combined process significantly changed the morphology of coke and improved the tropism of coke. The combined process with HDB had a better result comparing the aforementioned combined process.
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