US3308060A - Petroleum distillation - Google Patents

Description

March 7, 1967 J. F. G. ELLIS PETROLEUM DISTILLATION Filed Jan 28, 1965 INVENTOR. JOHN FRANCIS GRIFFITH ELLIS MORGAN, FINNEGAN, DURHAM BI PINE ATTORNEYS United States Patent 3,308,060 PETROLEUM DISTILLATION John Francis Griifith Ellis, Ashford, Middlesex, England, assignor to The British Petroleum Company Limited, 7

This invention relates to the distillation of petroleum and particularly to the maximum separation of gas oil fractions, is. fractions 'boilin-g Within the range 220-400 C. on a TBP curve, from crude oils.

In a conventional crude oil distillation column operating at a pressure of approximately three atmospheres, four side streams are commonly withdrawn, viz. naphtha, kerosine, light gas oil and heavy gas oil. Atmospheric residue is withdrawn from the column base, and a totally condensed overhead distillate from the column head.

The maximum yield of straight-run gas oil of a given pour point obtainable from a conventional crude oil distillation column is limited by the degree of fractionation at the gas oil back end cut point. Thus, improved fractionation would increase the gas oil yield.

The internal reflux in a conventional distillation column has its maximum value at the top of the column and de creases to almost nothing immediately above the flash zone of the column. Both the light and heavy gas oil frac- I tions are drawn from a zone in the column in which the cut point than that demanded by the product require-- ments. A flow of liquid is then provided over the trays i immediately above the flash zone. The amount of additional reflux which can be obtained in this way is, however, limited and insuflicient to effect maximum gas oil separation. 7

According to the present invention, in a crude oil distillati-o-n process conducted in a conventional atmospheric column, the heavy gas oil side stream fraction is combined with at least a portion of the atmospheric residue, the combined fraction being refractionated to give an additional gas oil product. The term heavy gas oil, in this specification, means the distillate fraction which =boi1s above 300 C.

Preferably the heavy gas oil is combined with the front 10-40% weight portion of the atmospheric residue, which is preferably obtained by vacuum flashing the atmospheric residue to give a 1040% weight overhead portion. This portion is subsequently combined with the heavy atmospheric gas oil, and the mixture fractionated under vacuum in a re'boiled column. This method has the advantage that close control can be maintained over the fractionation conditions.

Alternatively the whole of the atmospheric residue may I be combined with the heavy gas oil before vacuum flashing the mixture in a tower containing fractionating trays, under flash conditions arranged to give the required reflux in the fractionation section. This method is not so closely controllable however, but may be suitable where mini 'mum plant alteration is essential.-

The invention is illustrated 'by the following example:

Exam le 1 A crude oil of Middle East origin, when fractionated in a conventional atmospheric distillation unit at the rate of 55,800 -b.p.s.d., resulted in a material balance over the unit as indicated in Table 1. s

TABLE 1 Stream TBP range, Sp. gr. at Percent wt. LbJhr.

C. 60 F. on crude Overhead distillate to 148 0. 700 16. 86 V 117, 066 N aphtha 148-168 0. 775 3. 42 23, 746 Ker0sine 168-223 0. 796 9. 50 64, 962 Light gas oil. 223-308. 5 0 836 15. 84 109, 984 Heavy gas oil 308. 6-347 0 870 6.63 46,035 Atmospheric residue. 347 0. 948 47. 75 331, 549 Crude charge 0. 853 694, 342

The product properties from TABLE 2 Test Crude Overhead Naphtha Kerosine Light gas Heavy gas Atmospheric teed distillate oil oil residue Sp. gr. at 60 F 0.853 0.700 0.775 0.796 0.836 0.870 0.948 ASTM distillation, 0.:

IBP 143 180 223 305 FBP 177 220 319 374 Total distillate, percent vol. 99 99 99 9 Residue 1 1 1 1 Loss TABLE 2 Continued Test Crude Overhead Naphtha Keroslne Light gas Heavy gas Atmospheric teed distillate oil oil residue 1128, percent wt 0.019 Negative Mercaptan sulphur, percent wt 0.0475 0.0187 Total sulphur, percent wt..." 1.38 062 0.104 0.155 0.65 1.34 241/248 Reid vapour pressure, p.s.i Flash point, F Saybolt colour ASTM colour Pour point (upper), F

Carbon residue (Conradson), percent wt Aniline point, C

Diesel index Kin. vise. at 70 F., cs- Kin. vise. at 100 F., cs. Kin. vise. at 122 F., cs-

Kin. visc. at 210 F., cs-

In order to determine the maximum gas oil that could be recovered from the crude oil charge the following experiment was performed in the laboratory.

Heavy atmospheric gas oil was combined with atmospheric residue in the proportions which they were drawn from the crude unit. The resulting composite was put in a 14 plate batch distillation column operating at 2:1 external reflux with a column head pressure of 50 mm. Hg absolute. The distillation was continued until a 20% wt. (on feed) distillate was obtained. Inspection data on the feeds and products are given in Table 3.

The experiment demonstrates that the yield of gas oil boiling above a crude oil TBP cut point of 223 may be increased from 22.47% wt. on crude to 26.72% wt. on crude; the pour point of the total gas oil remains constant at 15 F., While the specific gravity (measured at 60 F.) increases from 0.8462 to 0.8520. At the same time the cloud point decreases from 22 F. to 18 F., while the diesel index decreases from 58 to 55. Thus an improvement in both specific gravity and cloud point is obtained, and although the diesel index decreases slightly the decrease is acceptably small.

Sp. gr. at 00 F.

Cloud point, F--- Pour point, F Aniline point, Diesel index Distillation (ASTM), C.:

2% recovery 271.5 285.5 2945 20 306.5 312.5 318.0 322.0 60 9. 327.0 70%- 330.5 80%- 334.0 90 338.0 FB P 343.0 Total distillate, percent vol 99.0 Residue 1,0 Loss Nil Bad match.

Relevant data on the efiect of (i) incorporating the whole of the distillate product into the gas oil pool (i.e. light gas oil plus vacuum distillate) (ii) incorporating the whole of the heavy atmospheric gas oil into the gas oil pool (i.e. light gas oil plus atmospheric heavy gas oil) are summarised in Table 4.

Example 2 The invention has been further demonstrated on exist ing refinery equipment.

A crude oil of Middle East origin when fractionated in a conventional atmospheric distillation unit, consisting of a primary distillation column and a secondary distillation TABLE 4 Test Atmospheric Atmospheric Vacuum gas Blend of Blend of light gas oil heavy gas oil oil HGO-l-LGO VGO+LGO Percent wt. on crude 15. 84 6. 63 10. 88 22. 47 26. 72 Sp. gr. at F 0.8361 0.8709 0.8776 0. 8462 0.8520 Colour (ASTM) 1 L 1.5 1 C 1.0 1 L 1.0 l L 1.0 Total sulphur, percent wt 0. 32 1. 12 0.86 0. 99 Kinematic viscosity at- F. es 6.19 100 F., cs 2.90 8. 38 6.60 3. 84 3. 92 122 F., cs 2. 31 5. 93 4. 76 2. Cloud point, F 50 40 22 18 Pour point, F 5 45 35 15 15 Aniline point, C. 71.2 79. 0 72. 3 72. 9 71.0 Diesel index 59/60 54 48/49 58 5 1 Bad match.

column, at a rate of 82,000 b.p.s.d., resulted in a material balance over the unit as indicated in Table 5.

A further two experiments were carried out in which the heavy gas oil stream was shut in and the yield of atmospheric residue increased by the amount that the heavy gas oil was decreased. In both these experiments the crude oil was processed at 82,000 b.p.s.d. and the temperature and pressure at the inlet to the secondary column were maintained constant, and at the same values as were observed for the first experiment. During these latter two experiments a portion of the atmospheric residue was passed to an adjacent vacuum distillation unit operating at 21,550 b.s.p.d. and the material balances resulting from the operation of the atmospheric and vacuum distillation units in the above described manner are indicated in Tables 6 and 7.

The product properties resulting from these three experiments are given in Tables 8, 9 and 10.

Relevant data on the efiect of (i) incorporating the whole of the heavy atmospheric gas oil into the gas oil pool (i.e. light gas oil plus heavy gas oil) (ii) incorporat- 6. ing the whole of the vacuum gas oil into the gas oil pool (i.e. light gas oil plus vacuum gas oil) are summarised in Table 11.

The experiments demonstrate that improved fractionation enhances both gas oil yield and gas oil quality, viz:

(9.) Experiment 3 shows that for constant diesel index the yield of gas oil boiling above a crude oil TBP cut point of 235/236 C. is increased from 21.51% wt. on crude (experiment 1) to 23.09% wt. on crude, i.e. an increase of 7.35% wt. on product; at the same time the pour point is reduced from F. to 20 F., whilst the cloud point also shows a significant reduction from 32 F. to 20 F.

(b) Experiment 2 shows that fior substantially constant diesel index and cloud point the yield of gas oil boiling above a crude oil TBP cut point of 235/236 'C. is increased from 21.51% wt. on crude (experiment 1) to 26.38% wt. on crude, i.e. an increase of 22.7% wt. on product; although the pour point is adversely raised from 25 F. to F.

TABLE 5.MATERIAL BALANCE Stream SG 60/60 F. Percent wt. LbJhr. IGPH Percent v01. TBP range on crude, 0.

Crude oil feed 0.8536 100.00 1, 019, 720 119, 461 100.00 Gas and PFD 3.69 37, 628 1 5, 663 4.74 To SRB 0.7285 13.30 135, 623 18, 617 15.58 35-143 Naphtha..- 0.7737 4. 60 46, 907 6, 063 5.08 143-170 Ker0sine 0.8031 11.74 119, 715 14,907 12.48 170-236 Light gas oil 0.8397 14.48 147, 655 17, 584 14.72 236-318 Heavy gas oil 0.8711 7.03 71, 686 8, 229 6.89 318-357.5 Atmospheric residue 0.9515 .16 460, 506 48, 398 40. 51 357.

Total 100.00 1, 019, 720 119, 461 100.00

1 Calculated by difierence.

TABLE 6.-MATERIAL BALANCE Stream SG /60 F. Percent wt. Lb./hr. IGPH Percent vol. TBP range on crude, 0.

Crude oil feed 0.8536 100.00 1, 022,236 119, 826 100.00 Gas and PFD 4.28 43, 752 1 6, 624 5.53 To 46 SRB 0.7288 12.41 126, 859 17, 407 14. 53 46-140 0. 7732 5 .26 53, 770 6, 954 5.80 -170 0.8000 11.28 115, 308 14, 414 12.03 -235 Light gas oil.-- 0.8403 16.28 166, 420 19, 805 16.53 235-3285 Heavy gas oil Nil N' Atmospheric residue 0.9449 50.49 516, 127 54, 622 45.58 328.5 Total 100.00 1, 022, 236 119, 826 100.00

Atmospheric residue feed. 0 9449 100 00 296, 570 31, 386 100. 00 328 5 Vacuum gas oil 0.8831 20.00 59, 314 6, 716 21.40 328.5-3925 Waxy distillate 0.9194 41.30 122, 483 13, 322 42. 45 392 5-543 Vacuum residue 1.0121 38.70 114, 773 11, 340 36 .13 543 Total 100.00 296, 570 31, 378 99.98

1 Calculated by difference.

TABLE 7.-MATERIAL BALANCE Stream SG 60/60 F. Percent wt. LbJhI. IGPH Percent vol. TBP range on crude, C.

Crude oil feed 0.8536 100.00 1, 024, 850 120, 132 100'. 00 Gas and PFD 4.10 42, 019 1 6, 505 5.41 To 42.5 SRB 0.7275 12.56 128, 721 17, 694 14.73 42.5-139 Naphtha 0.7750 4. 81 49, 295 6, 361 5.30 139-167 Kerosine- 0.8037 12.01 123, 084 15, 315 12.75 167-236 Light gas 0 0.8373 14.70 150, 653 17, 993 14.98 236-320 Heavy gas oi Nil Nil Atmospheric residu 0.9439 51.82 531, 078 56, 264 46.83 320 Total 100.00 1, 024, 850 120, 132 100.00

Atmospheric residue feed. 0 .9439 100.00 297, 390 31, 507 100.00 320 Vacuum gas oil 0.8772 16.20 48, 177 5, 492 17.43 320-3725 Waxy distillate 0.9151 45 .70 135, 907 14, 852 47.14 372. 5-543 Vacuum residue 1.0090 38.10 113, 306 11, 230 35.64 543 Total 100.00 297, 390 31, 574 100.21

1 Calculated by difierence.

TABLE 8-INSPECTION DATA ON PRODUCTS Sample Agha J'ari SRB Naphtha Kerosine Light Heavy Atm.

crude oil gas oil gas oil residue Specific gravity /60 0.8536 0.7285 0.7737 0.8031 0.8397 0.8711 1 0.9515 Specific gravity /60. l 0. 9237 Distillation test, 0.:

IBP 72 143 179 219 281 2% vol. recovered 77 146 187. 5 234 222 309 80. 5 147. 5 190. 5 242 285 330. 5 83 149 193 250 307 358. 5 87 5 150.5 195 5 258 5 92 5 152. 5 201 5 154. 5 204. 5 270 5 102 5 156. 5 208 276 108 5 158 212.5 282 5 114 219 289 5 121 163 226 298 129 173 5 228 308 5 146 180. 5 275 325. 5 Recovery, percent- 99. 5 98. 5 98.5 99 Residue, percenr 0. 2 1. 0 1.0 1 Loss, perceni 0. 3 0.5 0.5 Total sulphur, percent wt 1. 31 0.076 0.078 0.198 0.75 Aniline point, C 71.2 Diesel index 59 Cloud point F. 8 Pour point (upper), F 0 Carbon residue (Con), percent wt 3. 93 Kinematic viscosity at- 100 F., cs 122 F., cs 140 F., cs 117. 2 F., cs 54. 74 210 F., cs 24. 29

1 Calculated from value at 140 F.

TABLE 9.INSPECTION DATA ON PRODUCTS Sample Agha Jari SRB N aphtha Kerosine Light Atm. Vacuum Waxy Vacuum crude 011 gas 011 residue gas oil distillate residue Specific gravity 60/60 0. 8536 0. 7288 0. 7732 0.8000 0. 8403 1 0. 9449 Specific gravity 140/60 0 9171 75 140 177 213. 5 297. 5 recovered 78 142 178 233 332 Residue, percent Loss, percent Recovered at 400 0., percent Total sulphur, percent wt. Aniline point, C Diesel index Cloud point, F- Pour point (upper), F Carbon Residue (Con), percent wt Kinematic viscosity at 210 cs Wax content (methylene chloride), percent wt Melting point oi wax, F

1 Calculated from value at 140 F;

TABLE 10.INSPECTION DATA ON PRODUCTS Sample Agha Jan SRB Naphtha Kerosine Light Atm. Vacuum Waxy Vacuum crude oil gas oil residue gas 011 distillate residue Specific gravity 60/60 0. 8536 0. 7275 0.7750 0.8037 0.8373 1 0.9439 Specific gravity 140/60. 0. 9161 Distillation test, C

IB 70 138 174 215 2% vol. recovere 75 141 178 230 a 78 142 180 239. 5 83 143 182 246. 5 7 88 145 186 255. 5 92 146 190 261. 5 96 148 194 267. 5 101 149 199 273 106 151 203 278. 5 111 153 209 285 120 156 216 292. 5 126 1 161 216 302. 5 FBP 153 176 252 316 Recovery, percent. 98.5 98.5 98.5 99 Residue, percent. 0. 5 0. 9 1. 2 1 Loss, percent 1.0 0. 6 0.3 Total sulphur, percent wt 0.097 0.096 0.216 0. 72 Aniline point, C 61. 6 71. 3 Diesel index 64 60 Cloud point, F 2 Pour point (upper), F -5 -65 0 60 Carbon residue (Con), percent wt 3. 9 6. 63 Kinematic viscosity at 100 F cs 5.56 122 F cs F cs F., cs- 210 F., cs--- Wax content (methylene chloride),

percent wt 13.1 Melting point oi wax 116 1 Calculated from value at 140 F.

TABLE 11.-SUMMARIZING TABLE Blend Light gas oil Heavy gas oil Vacuum gas oil of L30 Blend of LGO an HGO and VGO Experiment 1 2 3 1 2 3 2 3 1 2 3 Yield on crude, percent wt 23.09 Front end TBP cut pt., C- 236 Back end TBP cut pt., C- 372. 5 Specific gravity 60/60 0.8513 Total sulphur, percent wt 0. 94 Cloud point, F 20 Pour point, F... 20 Aniline point, C 72. 2 Diesel index. 57 Distillation test, 0.:

1B 224 240 247. 5 256 265 273. 5 281 288 296. 5 306. 5 318 7 335. 5 FBP-. 365 Recovery, percent 98. 5 98. 5 98. 5 Residue, percent 1 1 1 1. 5 1. 5 1. 5 Recovered at 400 0., percent The invention is further illustrated with reference to the accompanying drawing, which is a schematic flow 3 to a vacuum column 4 operating at 96 mm. Hg. A 33.9% weight (based on feed) flash distillate is removed overhead from the vacuum column 4 via line 5 to a collecting vessel 6, vacuum being drawn via line 7. Residue from the vacuum column 4, steam stripped at via line 10 from the collecting vessel 6 and, after heat exchange, is combined, with heavy gas oil drawn from the distillation column 2 Via steam stripper 11 and line 12. The mixture is passed to reboiled distillation coldiagram of a plant suitable for operating the invention, 60 umn 14, which operates at a moderate vacuum so as to the design of which is based on the information obtained reduce cracking to a minimum, via line 13, and a gas oil in the above Example 1. overhead fraction is recovered via line 15. The yield In the drawing, heated crude oil is fed via line 1 into of gas oil product expressed as a percentage of atmosconventional atmospheric distillation column 2. Atmospheric heavy gas oil together with atmospheric residue pheric residue from the base of the column is fed via line 65 is 20% Wt., While on rerun column feed it is equivalent to a 47.6% wt. distillate. Residue from this reboiled column is combined via line 14 with that recovered from the column 4, so as to give a final residue of 80% weight calculated on atmospheric heavy gas oil and atmospheric 70 residue feed to the recovery system.

The gas oil recovery unit will thus produce a good quality gas oil with a pour point of 35 F. (as indicated in Table 3) at a yield on crude of 10.88% wt., so that when blended with the light gas oil drawn from the crude unit (pour point --5 F., yield on crude 15.84%

wt.) the resulting gas oil has a pour point of 15 F. at a yield on crude of 26.72% wt.

Other standard items of equipment, e.g. pumps, heat exchangers and the like, are shown in the drawing.

Equipment of the type described above could be added to an existing crude distillation unit to increase gas oil recovery. If units already exist for vacuum distillation of only a part of the atmospheric residue, the above equipment could be integrated with the existing units. In a new refinery where vacuum distillation of atmospheric residue is required, say to produce feedstock for another process, then the above equipment could be integrated with the vacuum distillation unit with corresponding reduction in capital and operating costs.

I claim:

In a crude oil distillation process, combining the heavy gas oil side stream fraction obtained in an atmospheric References Cited by the Examiner UNITED STATES PATENTS 1,954,839 4/1934 Youker 208364 1,997,675 4/1935 Bahlke et a1. 208365 2,850,436 9/1958 Beuther et a1. 208355 3,234,118 2/1966 Chen 208-364 DELBERT E. GANTZ, Primary Examiner.

H. LEVINE, S. P. JONES, Assistant Examiners.

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