SYSTEM AND PROCESS FOR INCREASING HEAVY OILS CONVERSION CAPACITY

Abstract

System and corresponding process for the hydroconversion of heavy oils essentially comprising a reactor, a liquid-vapor separator and a section for stripping conversion products outside the reactor comprising an inlet conduit for the stripping gases located at a point on the conduit providing a connection between the head of the reactor and the liquid-vapor separator inclined, at least from the point of entry, upwards with a gradient of between 2% and 20%, preferably between 3% and 12%, with respect to a horizontal plane. The inlet conduit for the stripping gases is inclined with respect to the axis of the conduit providing a connection between the reactor head and the liquid-vapor separator through an angle of between 20° and 65°, more preferably between 30° and 60°, even more preferably between 40° and 50°. The stripping gas delivered to the connection conduit between the head of the reactor and the separator flows in a downward direction.

Claims

1. A system for heavy oils hydroconversion comprising: a reactor, a liquid-vapor separator, and a stripping section of conversion products, external to said reactor, comprising a supply conduit of stripping gas in a point of a connection conduit between a reactor head and said liquid-vapor separator, wherein said connection conduit is upwardly inclined, at least from the point of supply of the stripping gas, with a gradient of between 2% and 20% with respect to the horizontal plane.

2. The system according to claim 1, wherein said supply conduit of the stripping gas is inclined to the axis of said connection conduit between said reactor head and said liquid-vapor separator at an angle of between 20° and 65°.

3. The system according to claim 1, wherein the stripping gas flow entering said connection conduit between said reactor head and said liquid-vapor separator is in a downward direction.

4. The system according to claim 1, wherein said supply conduit lies in the vertical plane passing through the axis of said connection conduit.

5. The system according to claim 1 wherein said reactor is a bubble column or ebullated bed reactor.

6. The system according to claim 1, wherein said connection conduit between said reactor head and said liquid-vapor separator, at least from the point of supply of the stripping gas, is inclined upward with a gradient of between 3% and 12%.

7. The system according to claim 1, wherein obstacles of suitable geometry are inserted inside said connection conduit between said reactor head and said liquid-vapor separator, which facilitates intimate mixing of the liquid and vapor phases and makes it possible for liquid/vapor equilibrium to be achieved.

8. A process for heavy oils hydroconversion comprising providing the system according to claim 1, passing the heavy oil to a hydrotreatment stage carried out in a said reactor with a suitable hydrogenation catalyst, to which hydrogen or a mixture of hydrogen and light hydrocarbons are fed, performing a step of stripping with suitable stripping gas on the flow of liquid and vapor phase leaving said reactor, or on the flow obtained merging at least one liquid flow and at least one vapor flow leaving said reactor, passing said flow to liquid-vapor separation in said liquid-vapor separator separating the recycled liquid phase to said reactor, a part from purges, from the vapor phase containing the conversion products obtained only in the vapor phase, wherein said stripping step is carried out by means of feeding stripping gas at a point in said connection conduit between said reactor head and said liquid-vapor separator, characterized in that the said connection conduit is inclined upwards, at least from the point of supply of the stripping gas, with a gradient of between 2% and 20% with respect to a horizontal plane.

9. The process according to claim 8, wherein the hydrotreatment step is carried out insaid reactor with a hydrogenation catalyst in slurry phase.

10. The process according to claim 9, wherein at the exit from said reactor the volumetric ratio: vapor flow rate (Qv)/(vapor flow rate (Q.sub.V)+slurry flow rate (Q.sub.L)) is greater than 0.75, where the slurry comprises the liquid plus solid.

11. The process according to claim 8, wherein the feed conduit for the stripping gas is inclined with respect to the axis of said connection conduit between said reactor head and said liquid-vapor separator at an angle of between 20° and 65°.

12. The process according to claim 8, wherein the section (A) of said connection conduit between said reactor head and said liquid-vapor separator and the length (L) of the section of said connection conduit from the point of entry of the stripping gas to said liquid-vapor separator point of entry satisfy the following relationships (A×L) (Q.sub.V+Q.sub.Vsec+Q.sub.L) >10 s (Q.sub.V+Q.sub.L)/A >0.5 m/s 2>Q.sub.Vsec/Q.sub.V>0.25 where Q.sub.V and Q.sub.L are the volumetric flows of vapor and slurry (liquid+solid) leaving the head of said reactor and the volumetric flow rate of the secondary gas Q.sub.Vsec.

13. The process according to claim 8, wherein the section (A) of said connection conduit between said reactor head and said liquid-vapor separator and the length (L) of the section of said connection conduit from point of entry for the stripping gas to said liquid-vapor separator point of entry satisfy the following relationships (A×L) (Q.sub.V+Q.sub.Vsec+Q.sub.L) >15 s (Q.sub.V+Q.sub.L)/A >1 m/s 1>Q.sub.Vsec/Q.sub.V>0.5.

14. The process according to claim 8, wherein the hydrotreatment step is conducted at a temperature between 400 and 450° C. and at a pressure of between 100 and 200 atm.

15. The process according to claim 8, wherein the hydrogenation catalyst is based on Mo or W sulfide.

Description

EXAMPLES

[0042] As already mentioned previously, a change from the EST system (with conversion products in the liquid phase and the presence of low pressure sections) to an EST-VPO system (in which the products leave only in the gas phase) results in a drastic reduction in the potential capacity of the plant. In order to overcome this the reaction temperature must be increased and secondary gas must be used because in the absence of the latter the potential capacity of the plant, other operating conditions being equal, is in any event reduced by approximately 20% in comparison with the EST reference case.

[0043] The embodiment of conduit (T) connecting the head of the reactor to the liquid-vapor separator and conduit (I) feeding the stripping gases is that already illustrated in FIG. 1, in which: [0044] the section of conduit connecting the point of entry for the secondary gas to point (D) is inclined upwards with a gradient of 6%; [0045] the entry conduit for the stripping gases is inclined with respect to the axis of the conduit connecting the head of the reactor to the liquid-vapor separator by an angle of 45° ; [0046] the flow of stripping gas fed to the connection conduit between the head of the reactor and the separator takes place in a downward direction, in the vertical plane passing through the axis of the connection conduit.

[0047] Bearing in mind that the flow rate of secondary gas (W.sub.sec) varies between 0 and 100, where 0 corresponds to the absence of secondary gas whereas 100 indicates that the flow of secondary gas is capable of ensuring the same potential capacity of a plant using an EST system , (W.sub.sec.sup.EST). although operating at a higher reaction temperature, the increase in plant capacity and percentage terms as the secondary gas is varied is shown in Table 1.

TABLE-US-00001 TABLE 1 Increase in fresh (W.sub.sec/W.sub.sec.sup.EST) × 100 charge  0 — 10  3.4% 20  6.3% 30  8.9% 40 11.1% 50 13.1% 60 14.8% 70 16.3% 80 17.7% 90 18.9% 100  20.1%

[0048] Thus, for example using 50% of the throughput of secondary gas required to achieve the potential capacity of an EST system plant (although operating at higher temperature) there is an increase of 13.1% in fresh charge.

[0049] The effect of secondary gas on the throughput of fresh charge in terms of percentage increase can be displayed by graphically illustrating what is set out in the table (FIG. 3). FIG. 4 also shows the effect of secondary gas on the increase in the capacity of an EST-VPO plant)(W.sub.FF.sup.VPO) operated at higher temperature, in comparison with the potential capacity of an EST (W.sub.FF.sup.EST). In the latter case, using 50% of the flow rate of secondary gas the potential capacity of the plant achieves 94% of the maximum throughput which can be obtained in accordance with the above definition.

[0050] The stripping effect of the secondary gas has the result that products which are “heavier” in comparison with the situation in which it is not used leave the plant, but the benefit achieved in terms of productivity is appreciable. The different quality of the products obtained can be assessed by analysing the percentage increase in Diesel, Naphtha and VGO products as a function of the (W.sub.sec/W.sub.sec.sup.EST) ratio expressed in percentage terms relative to the secondary gas as shown in Table 2.

TABLE-US-00002 TABLE 2 Increase in products as the Secondary Gas varies (W.sub.sec/W.sub.sec.sup.EST) × 100 Diesel Naphtha VGO  0 — — — 10  2.9%  2.9%  6.8% 20  5.4%  5.3% 12.8% 30  7.6%  7.4% 18.1% 40  9.5%  9.1% 22.7% 50 11.2% 10.5% 26.8% 60 12.7% 11.6% 30.4% 70 14.0% 12.7% 33.8% 80 15.2% 13.5% 36.9% 90 16.3% 14.3% 39.8% 100  17.3% 15.0% 42.5%

[0051] Here again, if 50% of the throughput of secondary gas is considered, the effect achieved is increases of 11.2%, 10.5% and 26.8% in Diesel, Naphtha and VGO respectively. The effect of the overall increase on the three products of interest is also shown in FIG. 5 which comprises the change in the throughput of products in relation to the (W.sub.sec/W.sub.sec.sup.EST) X 100 ratio of secondary gas in percentage terms.

[0052] Also, with 50% of secondary gas as defined above, 94%, 96% and 89% of the maximum throughput which can be achieved for Diesel, Naphtha and VGO respectively are achieved (FIG. 6).

[0053] As may be seen, the secondary gas has a greater influence on the VGO leaving the plant in comparison with Diesel and Naphtha, an indication that the stripping effect is effective in displacing even rather heavy compounds towards the gas phase.

[0054] It has already been pointed out that in comparison with an EST-VPO system without the use of secondary gas the liquid recycled to the reactor is heavier than that leaving the reactor itself as a result of the stripping action of the gas. In fact, when the molecular weight of the liquid phase leaving the HP separator recycled to the reactor is monitored in comparison with the molecular weight of the liquid phase leaving the head of the reactor, as the secondary gas increases it is observed that the two flows have an increasingly marked difference in terms of composition and therefore molecular weight. In the absence of secondary gas the molecular weights (MW) of the two liquid phases are identical, but as the throughput of secondary gas is increased the lighter compounds present in the liquid phase pass into the products which then leave the plant in the gas phase, while the liquid phase becomes increasingly heavier. With 50% of secondary gas, according to the definition given above, the molecular weights of the two flows differ by 11%. FIG. 7 shows the change in MW of the two liquid flows as the secondary gas (W.sub.sec/W.sub.sec.sup.EST), both expressed in percentage terms, is varied.