PROCESS FOR THE TREATMENT OF REFINERY PURGE STREAMS

Abstract

The present invention relates to a process for the treatment of refinery purge streams, containing a hydrocarbon component in slurry phase having a boiling point higher than or equal to 140? C., characterized by the presence of quantities of asphaltenes higher than or equal to 5% by weight and characterized by the presence of a solid content higher than or equal to 5% by weight. The process provides that said purge be mixed with a suitable fluxing agent according to appropriate ratios and under certain conditions, forming a suspension with a content higher than or equal to 10% by weight of compounds having a boiling point TbP lower than or equal to 350? C. After mixing, the suspension is sent to a liquid/solid separation step which operates under suitable conditions, separating a solid phase containing a residual organic component and a solid component, called cake, and a liquid phase containing residual solids. The solid phase obtained is cooled to below 60? C., including the upper extreme, forming a granular solid which is stored and maintained at a temperature lower than or equal to 60? C.

Claims

1. A process for the treatment of refinery purge streams, the process comprising: a) withdrawing a refinery purge stream comprising a hydrocarbon component in slurry phase having a boiling point higher than or equal to 140? C., characterized by the presence of quantities of asphaltenes higher than or equal to 5% by weight and characterized by the presence of solid contents greater than or equal to 5% by weight; b) mixing said purge, at a temperature higher than or equal to 100? C., with a mixture of hydrocarbons or fluxing agent, having a total content of aromatic compounds ranging from 50% to 70% by weight, and an initial boiling point equal to or higher than the temperature at which the mixing is carried out, so as to form a suspension with a content higher than or equal to 10% by weight of compounds having a boiling point T.sub.bp lower than or equal to 350? C.; c) sending said suspension to a liquid-solid separation step, which operates at a temperature higher than or equal to 100? C., separating a solid phase comprising a residual organic component and a solid component, or cake, and a liquid phase comprising residual solids; d) cooling the solid phase thus obtained to below 60? C., comprising the upper extreme, and storing it, maintaining it at a temperature lower than or equal to 60? C.; wherein a weight ratio between purge and fluxing agent ranges from 1:0.5 to 1:4; and an average residence time of the mixture during the mixing and before the liquid-solid separation is lower than or equal to 12 hours.

2. The process according to claim 1, wherein the solids contained in the purge stream comprise carbonaceous residues, metallic compounds and catalysts in the form of particles having a D50 lower than or equal to 1 mm.

3. The process according to claim 1, wherein the average residence time of the mixture during the mixing is lower than or equal to 3 hours.

4. The process according to claim 1, wherein the metallic compounds contained in the purge are either Ni sulfides, or V sulfides, or Fe sulfides or mixtures thereof.

5. The process according to claim 1, wherein the mixing temperature ranges from 100? C. to 200? C.

6. The process according to claim 1, wherein the fluxing agents are selected from Vacuum Gas Oil (VGO) with a high content of aromatic compounds, High Vacuum Gas Oil with a reduced content of aromatic compounds (HGVO), gas oils deriving from Fluid Catalytic Cracking (FCC) such as Light Cycle Oil (LCO) and clarified oil (LCLO) and mixtures thereof.

7. The process according to claim 1, wherein the solid-liquid separation takes place at temperatures ranging from 100 to 200? C.

8. The process according to claim 1, wherein the suspension has a content ranging from 15% to 50% of compounds having a boiling point lower than or equal to 350? C.

9. The process according to claim 1, wherein the weight ratio between purge and fluxing agent ranges from 1:1 to 1:2.

10. A solid comprising granules having an average diameter within the range of 0.1 mm to 10 cm, wherein the solid is obtained by the process according to claim 1.

Description

[0056] Further objectives and advantages of the present invention will appear more evident from the following description and enclosed figures, provided for purely illustrative and non-limiting purposes that represent preferred embodiments of the present invention.

[0057] FIG. 1 illustrates a preferred embodiment of the process according to the present invention according to a block scheme.

DETAILED DESCRIPTION

[0058] The present invention is now described in greater detail, which, as already mentioned, is a process for the treatment of refinery purge streams, which, for the purposes of the present invention, is a hydrocarbon stream in slurry phase having a boiling point higher than or equal to 140? C., characterized by the presence of quantities of asphaltenes higher than or equal to 5% by weight and characterized by the presence of solid contents higher than or equal to 5% by weight.

[0059] Said solids preferably contain carbonaceous residues, metallic compounds and catalysts in the form of particles, whose average diameter D50 measured is less than 1 mm. The diameter of the particles is measured with optical methods, such as Focus Beam Reflectance Measurement, dispersing the purge in toluene at 10% w/w and stirring.

[0060] The metallic compounds are dispersed in the purge stream and are typically Ni sulfides, V sulfides, Fe sulfides, Molybdenum sulfides and mixtures thereof.

[0061] A stream in slurry phase, or purge, is mixed with a mixture of hydrocarbons at a temperature higher than 100? C., preferably ranging from 100? C. to 200? C., more preferably from 170? C. to 120? C. The mixture of hydrocarbons, or fluxing agent, has a total content of aromatic compounds ranging from 50% to 70% by weight (defined as aromaticity of the fluxing agent) and an initial boiling point equal to or higher than the temperature at which the mixing is carried out. After mixing, a suspension is formed with a content higher than or equal to 10% by weight of compounds having a boiling point T.sub.bp lower than or equal to 350? C.

[0062] Said suspension is then sent to a liquid-solid separation step, which operates at temperatures higher than or equal to 100? C., preferably at temperatures ranging from 100? C. to 200? C., more preferably ranging from 120? C. to 170? C. separating a solid phase containing a residual organic component and a solid component, in the present text indicated as cake, and a liquid phase containing residual solids.

[0063] The solid phase thus obtained is cooled to below 60? C., extreme included, and stored, keeping it at a temperature lower than or equal to 60? C.

[0064] During the mixing phase, the weight ratio between purge and fluxing agent must range from 1:0.5 to 1:4, preferably from 1:1 to 1:2. The average residence time of the mixture during the mixing and before the liquid-solid separation must be less than or equal to 12 hours, and is preferably less than or equal to 3 hours.

[0065] Preferred fluxing agents are selected from Vacuum Gas Oil (VGO) with a high content of aromatic compounds, High Vacuum Gas Oil with a reduced content of aromatic compounds (HGVO), gas oils deriving from Fluid Catalytic Cracking (FCC) such as Light Cycle Oil (LCO) and clarified oil (LCLO), and mixtures thereof.

[0066] An objective achieved with the present invention is to increase the viscosity of the residual organic component present in the cake separated, which englobes the solid particles initially present in the purge stream. An improvement in the rheology of the cake corresponds to an increase in the viscosity, so that the cake acquires an approximately solid consistency at the storage temperatures, typically lower than 60? C. (David Leinberger, Temperature & Humidity in Ocean Containers Feb. 27, 2006 ISTA). The means whereby the viscosity is increased, consists in an enrichment in asphaltenes of the hydrocarbon fraction, associated with the solids in the cake.

[0067] This phenomenon, for the purposes of the present invention, is defined as mild destabilization of the asphaltenes present in the purge stream. The mild destabilization of the asphaltenes is obtained by mixing the purge stream with an appropriate fluxing agent under suitable conditions. In particular, the fluxing agent must have a suitable content of aromatic compounds and distillation curve, upstream of the device for the solid-liquid separation. Furthermore, the fluxing agent must be added in such a quantity as to satisfy an appropriate weight ratio between purge stream and fluxing agent.

[0068] Operating under the conditions indicated in the process described and claimed, a suspension is obtained, having a content higher than or equal to 10%, of compounds having a boiling point lower than or equal to 350? C., preferably ranging from 15% to 50% by weight, more preferably ranging from 30% to 50% by weight. The content of said compounds always depends on the aromaticity of the fluxing agent.

[0069] The liquid-solid separation is preferably effected by means of filtration or using a centrifugal decanting device (centrifugation) which operates in temperature. The separation is followed by cooling of the cake obtained to below 60? C., upper extreme included.

[0070] It is consequently the nature of the fluxing agent that regulates the mild destabilization of the asphaltene components present in the purge stream, allowing an adequate concentration of the same in the cake phase.

[0071] It is important to observe that, according to the present process, the asphaltenes present in the purge stream do not precipitate completely, as is the case, on the other hand, in the treatment of the refinery purge streams known in the state of the art. In the process according to the present invention, the asphaltenes only precipitate in a sufficient quantity for increasing the viscosity of the cake produced, so as to make it a granular solid that can be stored at a temperature lower than or equal to 60? C.

[0072] After the solid-liquid separation, the separated liquid phase (clarified product) can be recirculated either to the process from which the purge stream derives, possibly after separating the fluxing agent by means of distillation, or it can be sent to another process present for example in a refinery.

[0073] The process of the present invention is aimed at separating a phase containing a granular solid with a solid content higher than or equal to 30% by weight.

[0074] An element that characterizes the invention is the rheology of the solid phase produced, which has the characteristic of being shovelable (semi-solid sludge) according to the definition contained in D.lgs. 152/2006. This type of solid is granular, it is non-sticky and flowing and can therefore be easily transported and/or stored. In order to preserve this feature, the granular solid produced must be maintained at a temperature lower than or equal to 60? C.

[0075] The solid produced is composed of granules whose average diameter varies within the range of 0.1 mm up to a maximum of 10 cm. These dimensions were obtained by means of sieving, using a stack of sieves having various meshes. These granules have much higher dimensions with respect to the granular solids traditionally present in purge streams.

[0076] The cake produced can be used as solid fuel, as charge for coke ovens, as charge for blast furnaces, or it can be destined for processes for the separation of metals (metal reclaiming processes) of possible metals present, such as, for example Vanadium and Nickel. A comparison with a similar purge stream subjected to Thermal drying or Pyrolysis, leads to a preference for using the cake obtained with the process according to the present invention in all applications in which the value of the stream of volatile hydrocarbons generated by the heating of the cake is maximized; whereas a material from Thermal Drying is preferred when the material must not generate volatile products during the heating.

[0077] Mild destabilization also positively influences the recovery degree of the solids, in any case already high when operating in temperature and by dilution of the purge with a solvent.

[0078] The cake produced acquires a granular form, during the various phases of the treatment, with dimensions also influenced by the concentration of solids and asphaltenes; the use of additional equipment is therefore not required for its granulation. Additional treatment such as, for example, sieving and/or briquetting treatment can be added if the final destination requires uniformity in the geometry and dimensions of the end-product. In the latter case, the hydrocarbon matrix present in the cake can exert a useful function as binder during forming, preferably carried out at temperatures higher than or equal to 60? C., more preferably ranging from 60? C. to 110? C.

[0079] A preferred embodiment of the process according to the present invention is described hereunder. With reference to FIG. 1, a purge stream (1) coming from hydroconversion processes in slurry phase, is fed to a mixer (A). A fluxing agent (2) is fed into the same mixer. After mixing, the suspension produced is sent to a solid-liquid separator (B), separating a diluted stream, also called clarified product (4), and a hot stream containing solids, also called cake (3). The hot cake is cooled in a cooling device (C) and subsequently sent for storage maintaining it at a temperature lower than or equal to 60? C. (D).

[0080] Some examples are provided hereunder for a better understanding of the invention and range of application, but in no way representing a limitation of the scope of the present invention.

[0081] Experimental tests were carried out on purge streams obtained during two different running cycles of a hydroconversion unit in slurry phase. Vacuum Gas Oil (VGO) with a high content of aromatic compounds, obtained from the same unit; a High Vacuum Gas Oil (HVGO) with a reduced content of aromatic compounds, obtained from a different Refinery unit (HVGO), and mixtures thereof, were used as fluxing agents, as indicated in Tables 2A and 2B for Examples 2 and 3. The main characteristics of the fluxing agents used are indicated in Table 1.

TABLE-US-00001 TABLE 1 Properties of the fluxing agents used, as resulting from the distillations simulated by means of gaschromatography. VGO VGO VGO VGO VGO HVGO Example Example Example Example Example Examples C1 1 C 2 2 3 2 and 3 Density (kg/m.sup.3) 962 961 987 995 992 888 % weight IBP (? C.) 267 222 221 247 233 143 5% w 290 276 284 301 293 228 10% w 302 304 311 324 318 256 20% w 319 336 342 354 348 288 30% w 332 357 364 375 369 311 40% w 342 375 382 393 387 331 50% w 352 390 397 408 402 348 60% w 362 404 411 422 416 366 70% w 372 416 426 435 429 384 80% w 383 429 441 449 444 405 90% w 398 446 461 467 462 434 95% w 411 460 477 480 477 457 FBP 458 517 524 516 521 514 Saturated (% w) 18.3 53.4 products Aromatics 81.7 46.6

[0082] In Table 1, IBP is the Initial Boiling Point, FBP indicates the Final Boiling Point.

[0083] The mixing device consists of an accumulation tank of the charge, with a conical bottom, equipped with a double-impeller stirrer and traced with Medium Pressure Steam, which receives and mixes the purge and fluxing streams, at a known flow-rate. The fluxed mixture is sent, by means of an eccentric-rotor volumetric pump, to an inertized centrifugal decanting device, with a drum having an internal diameter of 230 mm and capable of operating at a maximum rate of 5,200 rpm, separating the cake from the clarified product.

[0084] The cake thus obtained is cooled on a double-helix cooling cochlea, equipped with an outer jacket and hollow water-cooled shafts. The final product is then collected in drums and stored. The clarified product is collected in a tank which, in turn, is stirred with a single-impeller stirrer. The clarified product can be sent from this tank to other uses in the refinery or recycled to the process from which the purge derives. Samples are collected from the purge and flushing streams, for characterization, in addition to cake samples in the drums and samples of clarified product, sampled immediately downstream of the outlet of the decanting device, before reaching the storage tank. In correspondence with each change in composition and/or operational conditions, the system is left to run for at least 12 hours, in order to stabilize the composition of the treated stream. The residence times indicated hereunder are obtained by dividing the level of liquid in the charge storage tank by the flow-rate fed to the decanting device.

Comparative Example 1 (C1): Fluxing of the Purge without Mild Destabilization

[0085] 450 kg/h of a mixture containing purge and VGO, mixed at a temperature of 155? C. with a weight fluxing ratio between purge and VG0 of 1:1.4, are fed to a centrifugal decanting device. The cake produced, after cooling to room temperature, proves to be pasty. No formation is observed of asphaltene deposits on the bottom of the collection tank of the clarified product. The compositions of the fluxed charge, clarified product and cake produced are indicated in Table 2B.

Example 1: Mild Destabilization Through a Different Distillation Curve

[0086] 472 kg/h of a mixture containing purge and VGO, mixed at a temperature of 155? C., with a weight fluxing ratio between purge and VG0 of 1:1.2, are fed to a centrifugal decanting device. With respect to the comparative example, the fluxed mixture has a different distillation curve with respect to the maltene fraction. The cake produced, after cooling to room temperature, has a solid and fine grain appearance.

[0087] The compositions of the fluxed charge, clarified product and cake produced are indicated in Table 2A.

[0088] An examination of the particle-size distribution of the THF-i in the charge and in the cakes of Examples 1 and 2, Table 3, does not show any significant differences; the different appearance of the cake is not due to a different particle size of the THF-i fed, but an increase in both the THF-i and Asf-05 in the cakes produced can be observed.

Comparative Example 2 (C2): Fluxing of the Purge without Mild Destabilization

[0089] 440 kg/h of a mixture containing purge and VGO, mixed at a temperature of 155? C., with a weight fluxing ratio between purge and VGO of 1:2, are fed to a centrifugal decanting device. The cake produced, after cooling to room temperature, proves to be pasty. No formation is observed of asphaltene deposits on the bottom of the collection tank of clarified product. The compositions of the fluxed charge, clarified product and cake produced are indicated in Table 2B.

Example 2: Decrease in the Aromaticity of the Fluxing Agent (Intermediate Cake)

[0090] 451 kg/h of a purge mixed with a fluxing agent consisting of a mixture containing 22% of HVGO and 78% of VGO, in which a weight fluxing ratio between purge and fluxing agent of 1:2, are fed to a centrifugal decanting device. The mixing takes place at a temperature of 156? C. The cake produced, after cooling to room temperature, proves to be granular but not flowing, with a tendency to re-agglomerate in the storage drum. No formation is observed of deposits in the collection tank of clarified product.

[0091] The compositions of the fluxed charge, clarified product and cake produced are indicated in Table 2A.

Example 3 Further Decrease in the Aromaticity of the Fluxing Agent (Granular Cake)

[0092] 451 kg/h of mixture containing a purge and fluxing agent at a temperature of 155? C. with a weight fluxing ratio between purge and fluxing agent of 1:2, and a fluxing agent consisting of a mixture containing 41% of HVGO and 59% of VGO, are fed to a centrifugal decanting device. The cake produced, after cooling to room temperature, proves to be granular, without the tendency to re-agglomerate in the storage drum. No formation is observed of deposits in the collection tank of clarified product. The compositions of the fluxed charge, clarified product and cake produced are indicated in Table 2A. It should be noted that, also in this example, an increase in the solid content in the cake does not correspond to an improvement in the rheology, as the cakes from comparative Examples 1 and 2, although characterized by a higher solid content, have a pasty consistency.

TABLE-US-00002 TABLE 2A Example 1 2 3 A B B Purge Solids (% w) 9.2 8.4 7.2 Asphaltenes (% w) 28.2 34.9 31.4 Fluxing HVGO (% w) 0% 22% 41% agent VGO (% w) 100% 78% 59% Aromaticity of (% w) 74(*).sup. 67(*).sup. the fluxing agent IBP-350? C. (% w) 26% 26% 33% Compounds with (% w) 73% 73% 66% T.sub.bp 350-500 Compounds with (% w) 1% 1% 1% T.sub.bp 500+ Feeding Flow-rate (kg/h) 472 451 451 to Fluxing (w/w) 2.2 2.1 2.0 decanter agent/purge Average (hour) 2 1 1 residence time in the accumulation tank THF-i (% p) 3% 3% 4% Asf-C5 (% w 6% 18% 16% including THF-i) (% w 7% 18% 16% excluding THF-i) IBP-350? C. (% w) 17% 12% 18% Compounds with (% w) 63% 48% 43% T.sub.bp 350-500 Compounds with (% w) 11% 20% 21% T.sub.bp 500+ Cake Flow-rate (kg/h) 19 18 23 Rheology solid inter- solid mediate THF-i (% w) 70% 51% 55% Asf-C5 (% w 6% 10% 10% THF-i included) (% w 19% 20% 23% excluding THF-i) Enrichment of cake/feed- 2.9 1.1 1.4 asphaltenes ing to the (excluding THF-i) decanter Clarified Flow-rate of the (kg/h) 454 433 428 product clarified product THF-i (% w) 0.4% 1% 1% Asf-C5 (% w) 6% 18% 16% (*)for the VGO component, the same aromaticity as the VGO from Example 3 is considered.

TABLE-US-00003 TABLE 2B Example C1 C2 A B Purge Solids (% w) 8.7 7.4 Asphaltenes (% w) 30.3 36.1 Fluxing HVGO (% w) 0% 0% agent VGO (% w) 100% 100% Aromaticity of (% w) 82 the fluxing agent IBP-350? C. (% w) 47% 19% Compounds with (% w) 53% 79% T.sub.bp 350-500 Compounds with (% w) 0% 3% T.sub.bp 500+ Feeding to Flow-rate (kg/h) 450 440 decanter Fluxing (w/w) 1.4 2.1 agent/purge Average (hours) 2 1 residence time in the accumulation tank THF-i (% w) 3% 3% Asf-C5 (% w 6% 17% including THF-i) (% w 6% 17% excluding THF-i) IBP-350? C. (% w) 28% 7% Compounds with (% w) 51% 51% T.sub.bp 350-500 Compounds with (% w) 12% 22% T.sub.bp 500+ Cake Flow-rate (kg/h) 18 14 Rheology pasty pasty THF-i (% w) 61% 57% Asf-C5 (% w 3% 7% including THF-i) (% w 8% 17% excluding THF-i) Enrichment of cake/feeding 1.2 1 Asphaltenes to the (THF-i) decanter Clarified Flow-rate of the (kg/h) 432 427 product clarified product THF-i (% w) 0.5% 2% Asf-C5 (% w) 7% 17% (*) for the VGO component the same aromaticity as the VGO from Example 3 is considered.

TABLE-US-00004 TABLE 3 Particle size of the solids present in the purge and cake Particle Diameter (microns) Purge Cake Example D(10) D(50) D(90) D(10) D(50) D(90) 1 6 11 21 4 8 17 2 6 12 22 4 8 17 D(90) = diameter below which 90% of the particle population is found D(50) = diameter below which 50% of the particle population is found D(10) = diameter below which 10% of the particle population is found

[0093] As explained in the text of the patent application, the diameter D50 of solids contained in the purge is measured by means of optical methods, such as Focus Beam Reflectance Measurement, by dispersing the purge in 10% w/w of toluene under stirring. The average diameter of the granules produced is measured using a stack of sieves having various meshes.