METHOD FOR FRACTIONATION OF HYDROCARBONS

Abstract

A process for separation of a liquid phase from a gas phase and a process for production of a hydrocarbon product employing such a separation as well as a fractionation section and a hydrocracker section for carrying out such processes. The separation process includes: directing a feed for separation to a feed inlet of a means of separation; directing a stripping medium to a stripping medium inlet of the means of separation; withdrawing a liquid product stream from a means of separation; withdrawing a gaseous fraction comprising the stripping medium from the means of separation; directing the stripping medium fraction or the gaseous fraction as a recycled stripping medium; pressurizing at least an amount of the recycled stripping medium and directing it as the stripping medium, wherein the stripping medium comprises at least 80% vol/vol % of gases from the group comprising N.sub.2, H.sub.2, He, Ar, Ne and CO.sub.2.

Claims

1. A process for separation of a hydrocarbonaceous liquid phase from a gas phase comprising the steps of a. directing a feed for separation to a feed inlet of a means of separation, b. directing a stripping medium to a stripping medium inlet of said means of separation, c. withdrawing a liquid product stream from said means of separation, d. withdrawing a gaseous fraction comprising said stripping medium from said means of separation, e. optionally cooling and separating said gaseous fraction in a light product fraction and a stripping medium fraction, f. directing said stripping medium fraction or said gaseous fraction as a recycled stripping medium, g. pressurizing at least an amount of said recycled stripping medium and directing it as said stripping medium of step b, wherein said stripping medium comprises at least 80% vol/vol % of gases from the group comprising N.sub.2, Hz, He, Ar, Ne and CO.sub.2.

2. The process of claim 1 further comprising the steps of h. directing said liquid product stream to a secondary means of separation, i. directing an amount of said stripping medium as a side stream stripping medium to said secondary means of separation, j. withdrawing a gaseous side stream fraction comprising said side stream stripping medium from said secondary means of separation, k. directing said gaseous side stream fraction to the means of separation and l. withdrawing a liquid product fraction from said secondary means of separation.

3. The process according to claim 1 wherein the operating pressure of said means of separation is from atmospheric pressure to 3 barg and said pressurizing of said recycled stripping medium involves increasing the pressure by 0.1 bar to 2 bar.

4. The process according to claim 1 wherein the operating pressure of said means of separation is from 0 bar absolute to 500 mbar absolute and said pressurizing of said recycled stripping medium involves increasing the pressure by between 5 mbar and 200 mbar.

5. The process according to claim 1 wherein less than 5 wt/wt % of said feed is non-condensable at the boiling point of said stripping medium.

6. The process according to claim 1 wherein at least 95 wt/wt % of said feed is withdrawn from said means of separation in liquid form.

7. The process according to claim 1 wherein the feed has an initial boiling point of at least 100° C.

8. The process according to claim 1 wherein the 95 wt/wt % boiling point of said feed is at least 400° C.

9. The process according to claim 1 wherein the ratio between the amount of stripping medium and the amount of feed directed to the means of separation is from 10 NL/kg to 500 NL/kg.

10. The process according to claim 1 wherein from 1% to 10% of said recycled stripping medium is withdrawn as a purge.

11. A process for production of a low boiling product, said process comprising the steps of x. directing a feed comprising at least 50 wt/wt % hydrocarbons boiling above an upper target boiling point, to contact a material catalytically active in hydrocracking under hydrocracking conditions selected for converting from 30 wt/wt % to 100 wt/wt % of the hydrocarbons boiling above the upper target boiling point to products boiling below the upper target boiling point, providing a hydrocracked product y. directing said hydrocracked product as a feed for separation, optionally after gas/liquid separation in one or more steps, to a process of fractionation employing a recycled stripping medium, z. withdrawing a fraction of hydrocracked product boiling in the low boiling product range.

12. A fractionation section comprising a means of separation having a feed inlet, a means of separation stripping medium inlet, one or more product outlets and a vapor outlet, and a means of pressurization having an inlet and an outlet characterized in said vapor outlet being in fluid communication with the inlet of said means of pressurization, and said outlet of said means of pressurization being in fluid communication with said means of separation stripping medium inlet.

13. The fractionation section according to claim 12 further comprising a side column, having a side column feed inlet, a side column stripping medium inlet, a side column vapor outlet and a side column liquid outlet, wherein said side column stripping medium inlet is in fluid communication with the outlet of said means of pressurization.

14. The fractionation section according to claim 12, further comprising a bottoms stripper having a bottoms stripper stripping medium inlet, a stripper vapor outlet, a bottoms stream inlet and a stripped bottoms outlet, and where said means of separation further has a bottoms outlet, and wherein said bottoms stream inlet is configured for being in fluid communication with said bottoms outlet, optionally via a means of heating, wherein said bottoms stripper stripping medium inlet is configured for being in fluid communication with said outlet of said means of pressurization optionally via a means of heating, and wherein said stripper vapor outlet is in fluid communication with said means of separation stripping medium inlet.

15. A hydrocracker section comprising a hydrocracking reactor having an inlet and an outlet and a fractionation section comprising a means of separation having a feed inlet, a make up stripping medium inlet, one or more product outlets and a vapor outlet, and a means of pressurization having an inlet and an outlet characterized in said hydrocracker section being configured for directing an amount of product from the hydrocracking reactor outlet to the means of separation feed inlet, the vapor outlet being in fluid communication with the inlet of said means of pressurization, and said outlet of said means of pressurization being in fluid communication with said stripping medium inlet.

Description

FIGURES

[0061] FIG. 1 shows a fractionation section according to the present disclosure.

[0062] FIG. 2 shows a fractionation section according to the prior art.

[0063] FIG. 3 shows a hydrocracking section, with a fractionation section according to the present disclosure.

[0064] FIG. 1 shows an aspect of the present disclosure. Two hydrocracked fossil feeds for separation 102 and 104 (or optionally a single combined stream) are directed to a feed inlet of a means of separation 106. An amount of stripping medium 108 is directed to a stripping medium inlet of the means of separation 106. Liquid product fractions 112, 122 are withdrawn from a number of positions of said means of separation 106, and each of these fractions are purified in secondary means of separation such as side column strippers 114, 124, where a further amount of stripping medium is added as side stripper stripping medium 116, 126, stripped liquid fractions 118, 128 are withdrawn and the side stripper gaseous fractions 120, 130 are directed to the means of separation 106. At the top of the means of separation the lightest fraction 142 is withdrawn, and optionally separated in a three phase separator 144, from which the liquid hydrocarbon fraction 145 may be directed to the column as recycle 146 and/or withdrawn as product 148. The gaseous fraction 150 from the three phase separator is directed to a means of pressurization such as a blower or a compressor 152, typically after but optionally before being heated e.g. in heat exchanger 154, and recycled as stripping medium 158, in combination with a limited amount of make-up stripping medium 160. From the bottom of the means of separation a bottoms product 162 is withdrawn.

[0065] In a further aspect a purge of stripping medium may be withdrawn with the objective of avoiding concentrating impurities. The impurities may gaseous product hydrocarbons or oxygen from equipment leaks. The purge stream may be directed to an absorbent or a reactor for removing the impurities. Removal of oxygen may be carried out by catalytic oxidation of hydrocarbons or hydrogen or liquid or solid scavenging and the gaseous products may be collected e.g. in an amine wash. Gaseous hydrocarbons may be directed to other means of separation.

[0066] FIG. 2 shows an aspect of the prior art. Two hydrocracked fossil feeds for separation 202 and 204 are directed to a feed inlet of a means of separation 206. An amount of stripping medium, typically steam 208 is directed to a stripping medium inlet of the means of separation 206. Liquid product fractions 212, 222 are withdrawn from a number of positions of said means of separation 206, and each of these fractions are purified in secondary means of separation such as side column strippers 214, 224, where a further amount of stripping medium is added as side stripper stripping medium 216, 226, stripped liquid fractions 218, 228 are withdrawn and the side stripper gaseous fractions streams 220, 230 are directed to the means of separation 206. At the top of the means of separation the lightest fraction 242 is withdrawn, and after cooling separated in a three phase separator to a gas fraction 264, a liquid hydrocarbon fraction 245 and a water fraction 268 in three phase separator 244. The liquid fraction 266 from the three phase separator 244 may be directed to the column as recycle 246 and/or withdrawn as product 248. From the bottom of the means of separation a bottoms product 262 is withdrawn.

[0067] FIG. 3 shows an aspect of the present disclosure. A feed 372 is directed to a hydrocracking reactor 374 comprising a hydrocracking catalyst. The hydrocracked product 376 is directed to a cascade of separators, 378, 380, 382, 384 from which a cold product stream 386 and a hot product stream 388 are withdrawn and directed to a stripper 390. From the stripper vapor 391 and liquid product stream 392 are withdrawn. The liquid product stream 392 is preheated and separated in flash vessel 394 into a vapor product stream 304 and a liquid product 396. The liquid product is heated in heater 398. The heated liquid product 302 and the vapor product stream 304 are directed to a means of separation 306. An amount of stripping medium 308 is directed to a stripping medium inlet of the means of separation 306. Liquid product fractions 312, 322 are withdrawn from a number of positions of said means of separation 306, and each of these fractions are purified in secondary means of separation such as side column strippers 314, 324, where a further amount of stripping medium is added as side stripper stripping medium 316, 326, stripped liquid fractions 318, 328 is withdrawn and the side stripper vapor gaseous fractions streams 320, 330 are directed to the means of separation 306. At the top of the means of separation the lightest fraction 342 is withdrawn, and optionally separated in a three phase separator 344, from which the liquid hydrocarbon fraction 345 may be directed to the column as recycle 346 and/or withdrawn as product 348. The gaseous fraction 350 from the three phase separator is directed to a means of pressurization such as a blower or a compressor 352 optionally before or after being heated 354, and recycled as stripping medium 358, in combination with a limited amount of make-up stripping medium 360. The make up stripping medium 360 may optionally be supplied as a side stream of the blanket gas used in the storage tanks of products. From the bottom of the means of separation a bottoms product 362 is withdrawn.

EXAMPLES

[0068] The efficiency of separation according to the present disclosure and the prior art has been evaluated by studying the fractionation of the products of a hydrocracking process.

Example 1

[0069] In Example 1 the product of a hydrocracking process is directed to a fractionation according to the present disclosure, as described in FIG. 1, in which the stripping medium is N.sub.2, and the total N.sub.2:HC ratio into the column and side columns is 1.7 mol/kg, and N.sub.2 is recycled to be used as stripping medium. The performance of the fractionation process is shown in Table 1. According to this example, 0.35% of the N.sub.2 must be added as make up gas due to N.sub.2 being dissolved in the products. If a 2% purge of stripping N.sub.2 was included, it would be required to add 2.35% as make up N.sub.2.

[0070] In Table 1 it is seen that all products fulfill the specifications for the respective product types.

Example 2

[0071] In Example 2 the product of a hydrocracking process is directed to a fractionation according to the prior art, as described in FIG. 2, in which the stripping medium is steam and the total H.sub.2O:HC ratio into the column and side columns is 0.7 mol/kg. H.sub.2O is condensed at the outlet of the column, but cannot be recycled to be used as stripping medium, unless it is heated and vaporized in a steam drum.

[0072] The performance of the fractionation process is shown in Table 2, which also show the product fractions. The product qualities are similar to those of Example 1.

[0073] The product yields of Example 1 and Example 2 are compared in Table 3. It is seen that an extra yield of valuable products like kerosene and diesel is obtained and the yield of less valuable products like naphtha and unconverted oil (UCO) is reduced.

[0074] In addition to the increased yield, the use of recycled nitrogen as stripping medium in Example 1 will furthermore have the benefit of having a lower operational expense, compared to the required amount of steam in Example 2.

[0075] The examples thus document that recycled nitrogen provides an improved separation and thus a reduced yield loss while also being a cost effective alternative to steam.

TABLE-US-00001 TABLE 1 Stream 102 104 108 148 128 118 162 Total Mass Rate kg/hr 28,298 296,520 15,785 36,189 115,238 43,912 128,261 Flash Point Temperature ° C. 7 21 1 36 77 173 (Closed Cup) Total RVP psi 2 1 18 0 0 40 (APINAPHTHA) Cetane Index 16 64 12 45 60 59 TBP at 760 mm Hg ° C. IBP 68 87 64 107 138 318  5 wt/wt % 92 115 84 129 247 367 10 wt/wt % 100 131 92 139 278 378 30 wt/wt % 117 238 105 175 320 405 50 wt/wt % 134 337 113 211 337 430 70 wt/wt % 174 406 119 248 353 462 90 wt/wt % 246 476 126 289 375 510 95 wt/wt % 285 505 129 303 383 539 EBP 428 575 137 326 404 583

TABLE-US-00002 TABLE 2 208/216/ Stream 202 204 226 248 228 218 262 Total Mass Rate kg/hr 28,298 296,520 4,250 36,501 113,668 42,325 131,134 Flash Point ° C. 7 21 0.9 36.0 81.2 170.3 Temperature (Closed Cup) Total RVP Psi 2 1 2.2 0.1 0.0 0.9 (APINAPHTHA) Cetane Index 16 64 12 44 60 59 TBP at 760 mm Hg ° C. IBP 68 87 65 107 147 311  5 wt/wt % 92 115 84 129 241 360 10 wt/wt % 100 131 92 139 271 375 30 wt/wt % 117 238 105 174 316 403 50 wt/wt % 134 337 113 210 335 429 70 wt/wt % 174 406 119 246 352 461 90 wt/wt % 246 476 126 288 375 509 95 wt/wt % 285 505 129 302 383 538 EBP 428 575 136 327 405 583

TABLE-US-00003 TABLE 3 Prior art Invention Difference Naphtha (kg/hr)  36,501  36,189 −0.9% Kerosene (kg/hr) 113,668 115,238 1.4% Diesel (kg/hr)  42,325  43,912 3.8% UCO (kg/hr) 131,134 128,261 −2.2%