234:
visbreakers therefore require frequent de-coking. This is quite labour-intensive, but can be developed into a routine where tubes are de-coked sequentially without the need to shut down the visbreaking operation. Soaker drums require far less frequent attention but their being taken out of service normally requires a complete halt to the operation. Which is the more disruptive activity will vary from refinery to refinery.
846:
423:
addition of a diluent to manufacture a finished fuel oil can cause the colloid to break down, precipitating asphaltenes as a sludge. It has been observed that a paraffinic diluent is more likely to cause precipitation than an aromatic one. Stability of fuel oil is assessed using a number of proprietary tests (for example "P" value and SHF tests).
169:
In soaker visbreaking, the bulk of the cracking reaction occurs not in the furnace but in a drum located after the furnace called the soaker. Here the oil is held at an elevated temperature for a pre-determined period of time to allow cracking to occur before being quenched. The oil then passes to a
555:
As middle distillates have a far higher value in the market place than fuel oils, it can be seen that the use of a visbreaker will considerably improve the economics of fuel oil manufacture. For example, if the cutter stock is taken to have a value of $ 300 per tonne and fuel oil $ 150 per ton (oil
160:
to halt the cracking reactions: frequently this is achieved by heat exchange with the virgin material being fed to the furnace, which in turn is a good energy efficiency step, but sometimes a stream of cold oil (usually gas oil) is used to the same effect. The gas oil is recovered and re-used. The
129:
Increase the proportion of middle distillates in the refinery output: Middle distillate is used as a diluent with residual oils to bring their viscosity down to a marketable level. By reducing the viscosity of the residual stream in a visbreaker, a fuel oil can be made using less diluent and the
233:
as a byproduct. In coil visbreaking, this deposits in the tubes of the furnace and will eventually lead to fouling or blocking of the tubes. The same will occur in the drum of a soaker visbreaker, though the lower temperatures used in the soaker drum lead to fouling at a much slower rate. Coil
422:
compounds which have relatively low sulphur contents, low density and high viscosity and the effect of their removal can be clearly seen in the change in quality between feed and product. A too severe cracking in a visbreaker will lead to the asphaltene colloid becoming metastable. Subsequent
524:
A marketable fuel oil, such as for fueling a power station, might be required to have a viscosity of 40 centistokes at 100 °C. It might be prepared using either the virgin or visbroken residue described above combined with a distillate diluent ("cutter stock"). Such a cutter stock could
359:
The yields of the various hydrocarbon products will depend on the "severity" of the cracking operation as determined by the temperature the oil is heated to in the visbreaker furnace. At the low end of the scale, a furnace heating to 425 °C would crack only mildly, while operations at
240:: The lower temperatures used in the soaker approach mean that these units use less fuel. In cases where a refinery buys fuel to support process operations, any savings in fuel consumption could be extremely valuable. In such cases, soaker visbreaking may be advantageous.
161:
extent of the cracking reaction is controlled by regulation of the speed of flow of the oil through the furnace tubes. The quenched oil then passes to a fractionator where the products of the cracking (gas, LPG, gasoline, gas oil and tar) are separated and recovered.
117:
Reduce the amount of residual fuel oil produced by a refinery: Residual fuel oil is generally regarded as a low value product. Demand for residual fuel continues to decrease as it is replaced in its traditional markets, such as fuel needed to generate steam in
436:
The viscosity blending of two or more liquids having different viscosities is a three-step procedure. The first step is to calculate the
Viscosity Blending Index (VBI) of each component of the blend using the following equation (known as a Refutas equation):
371:
Stability in this case is taken to mean the tendency of a fuel oil to produce sediments when stored. These sediments are undesirable as they can quickly foul the filters of pumps used to move the oil necessitating time-consuming maintenance.
254:
The quality of the feed going into a visbreaker will vary considerably with the type of crude oil that the refinery is processing. The following is a typical quality for the vacuum distillation residue of
Arabian light (a crude oil from
306:
Once this material has been run through a visbreaker (and, again, there will be considerable variation from visbreaker to visbreaker as no two will operate under exactly the same conditions) the reduction in viscosity is dramatic:
145:
556:
prices naturally change quickly, but these prices, and more importantly the differences between them, are not unrealistic), it is a simple matter to calculate the value of the different residues in this example as being:
360:
500 °C would be considered as very severe. Arabian light crude residue when visbroken at 450 °C would yield around 76% (by weight) of tar, 15% middle distillates, 6% gasolines and 3% gas and LPG.
489:
Once the viscosity blending number of a blend has been calculated using equation (2), the final step is to determine the viscosity of the blend by using the invert of equation (1):
222:
From the standpoint of yield, there is little or nothing to choose between the two approaches. However, each offers significant advantages in particular situations:
676:
708:
174:. In soaker visbreaking, lower temperatures are used than in coil visbreaking. The comparatively long duration of the cracking reaction is used instead.
538:
Using the viscosities quoted in the tables above for the residues from Arab Light crude oil and calculating VBNs according to equation (1) gives:
368:
The severity of visbreaker operation is normally limited by the need to produce a visbreaker tar that can be blended to make a stable fuel oil.
529:. Rearranging equation (2) above for a simple two component blend shows that the percentage of cutterstock required in the blend is found by:
762:
156:) visbreaking is applied to units where the cracking process occurs in the furnace tubes (or "coils"). Material exiting the furnace is
641:
616:
588:
850:
871:
701:
694:
802:
681:
876:
71:
733:
464:). It is important that the viscosity of each component of the blend be obtained at the same temperature.
792:
881:
797:
787:
509:
812:
171:
56:
777:
767:
183:
99:
78:). The process name of "visbreaker" refers to the fact that the process reduces (i.e., breaks) the
202:) is then routed to fuel oil blending. In a few refinery locations, visbreaker tar is routed to a
827:
772:
717:
187:
153:
67:
207:
637:
612:
584:
513:
457:
195:
782:
130:
middle distillate saved can be diverted to higher value diesel or heating oil manufacture.
545:
residue (i.e., the unconverted feed to the visbreaker): 27.5% cutter stock in the blend
230:
375:
Vacuum residue fed to a visbreaker can be considered to be composed of the following:
865:
807:
203:
199:
191:
119:
103:
661:
452:
is the viscosity in square millimeters per second (mm²/s) or centistokes (cSt) and
256:
44:
36:
32:
817:
526:
211:
123:
70:
to reduce its viscosity and to produce small quantities of light hydrocarbons. (
60:
52:
48:
822:
382:: large polycyclic molecules that are suspended in the oil in a coloidal form
728:
486:
is the weight fraction (i.e., % ÷ 100) of each component of the blend.
419:
326:
320:
278:
272:
111:
98:
Reduce the viscosity of the feed stream: Typically this is the residue from
83:
79:
63:
40:
17:
757:
467:
The next step is to calculate the VBN of the blend, using this equation:
157:
75:
198:
units on the refinery. The vacuum-flashed tar (sometimes referred to as
35:
whose purpose is to reduce the quantity of residual oil produced in the
412:
403:
399:
395:
332:
313:
284:
265:
144:
107:
186:. Here additional heavy gas oil may be recovered and routed either to
686:
388:: also polycyclic but of a lower molecular weight than asphaltenes
143:
746:
690:
182:
Visbreaker tar can be further refined by feeding it to a
206:
for the production of certain specialist cokes such as
504:is the viscosity blending number of the blend and
525:typically have a viscosity at 100 °C of 1.3
122:, by cleaner burning alternative fuels such as
102:of crude oil but can also be the residue from
702:
114:, and even certain high viscosity crude oils.
8:
579:James H. Gary and Glenn E. Handwerk (1984).
581:Petroleum Refining Technology and Economics
520:Example economics for a two-component blend
43:and to increase the yield of more valuable
743:
709:
695:
687:
552:residue: 13.3% cutter stock in the blend.
218:Soaker visbreaking versus coil visbreaking
634:The Chemistry and Technology of Petroleum
602:
600:
309:
261:
148:A schematic diagram of a Visbreaker unit
82:of the residual oil. The process is non-
571:
259:and widely refined around the world):
562:Visbroken residue: $ 127.0 per tonne
7:
845:
609:Petroleum Refinery Process Economics
583:(2nd ed.). Marcel Dekker, Inc.
658:Guide to Petroleum Product Blending
94:The objectives of visbreaking are:
418:Visbreaking preferentially cracks
25:
559:Virgin residue: $ 93.1 per tonne
844:
611:(2nd ed.). Pennwell Books.
250:Feed quality and product quality
55:) by the refinery. A visbreaker
229:: The cracking reaction forms
1:
110:from seeps in the ground or
636:(4th ed.). CRC Press.
66:in the oil by heating in a
31:is a processing unit in an
898:
682:Fuel Oil Stability Testing
443:VBN = 14.534 × ln + 10.975
840:
753:
742:
724:
632:James G. Speight (2006).
607:Robert E. Maples (2000).
763:Atmospheric distillation
677:Shell Thermal Conversion
660:, HPI Consultants, Inc.
512:2.71828, also known as
734:List of oil refineries
409:Parafinic hydrocarbons
149:
798:Hydrodesulphurisation
510:transcendental number
392:Aromatic hydrocarbons
147:
813:Solvent deasphalting
106:operations, natural
778:Catalytic reforming
768:Vacuum distillation
656:C.T. Baird (1989),
534:%cutter stock = ÷
184:vacuum fractionator
100:vacuum distillation
872:Chemical processes
828:Amine gas treating
773:Catalytic cracking
718:Petroleum refining
432:Viscosity blending
364:Fuel oil stability
245:Quality and yields
188:catalytic cracking
165:Soaker visbreaking
152:The term coil (or
150:
90:Process objectives
45:middle distillates
859:
858:
836:
835:
458:natural logarithm
394:: derivatives of
352:
351:
304:
303:
16:(Redirected from
889:
848:
847:
744:
711:
704:
697:
688:
664:
654:
648:
647:
629:
623:
622:
604:
595:
594:
576:
310:
262:
196:thermal cracking
140:Coil visbreaking
57:thermally cracks
21:
897:
896:
892:
891:
890:
888:
887:
886:
862:
861:
860:
855:
832:
749:
738:
720:
715:
673:
668:
667:
655:
651:
644:
631:
630:
626:
619:
606:
605:
598:
591:
578:
577:
573:
568:
522:
476:
463:
434:
429:
366:
357:
336:
324:
316:
288:
276:
268:
252:
247:
220:
180:
178:Process options
167:
142:
137:
92:
23:
22:
15:
12:
11:
5:
895:
893:
885:
884:
879:
877:Oil refineries
874:
864:
863:
857:
856:
854:
853:
841:
838:
837:
834:
833:
831:
830:
825:
820:
815:
810:
805:
800:
795:
793:Polymerisation
790:
785:
780:
775:
770:
765:
760:
754:
751:
750:
747:
740:
739:
737:
736:
731:
725:
722:
721:
716:
714:
713:
706:
699:
691:
685:
684:
679:
672:
671:External links
669:
666:
665:
649:
642:
624:
617:
596:
589:
570:
569:
567:
564:
521:
518:
514:Euler's number
498:
497:
480:
479:
477:= + + ... +
474:
461:
446:
445:
433:
430:
428:
425:
416:
415:
406:
389:
383:
365:
362:
356:
353:
350:
349:
346:
343:
339:
338:
330:
323:at 100 °C
318:
302:
301:
298:
295:
291:
290:
282:
275:at 100 °C
270:
251:
248:
246:
243:
242:
241:
235:
231:petroleum coke
219:
216:
179:
176:
166:
163:
141:
138:
136:
133:
132:
131:
127:
120:power stations
115:
91:
88:
24:
14:
13:
10:
9:
6:
4:
3:
2:
894:
883:
880:
878:
875:
873:
870:
869:
867:
852:
843:
842:
839:
829:
826:
824:
821:
819:
816:
814:
811:
809:
808:Hydrocracking
806:
804:
801:
799:
796:
794:
791:
789:
788:Isomerisation
786:
784:
781:
779:
776:
774:
771:
769:
766:
764:
761:
759:
756:
755:
752:
745:
741:
735:
732:
730:
727:
726:
723:
719:
712:
707:
705:
700:
698:
693:
692:
689:
683:
680:
678:
675:
674:
670:
663:
659:
653:
650:
645:
643:0-8493-9067-2
639:
635:
628:
625:
620:
618:0-87814-779-9
614:
610:
603:
601:
597:
592:
590:0-8247-7150-8
586:
582:
575:
572:
565:
563:
560:
557:
553:
551:
546:
544:
539:
536:
535:
530:
528:
519:
517:
515:
511:
507:
503:
496:
492:
491:
490:
487:
485:
478:
470:
469:
468:
465:
459:
455:
451:
444:
440:
439:
438:
431:
426:
424:
421:
414:
410:
407:
405:
401:
397:
393:
390:
387:
384:
381:
378:
377:
376:
373:
369:
363:
361:
354:
347:
344:
341:
340:
334:
331:
328:
322:
319:
315:
312:
311:
308:
299:
296:
293:
292:
286:
283:
280:
274:
271:
267:
264:
263:
260:
258:
249:
244:
239:
236:
232:
228:
225:
224:
223:
217:
215:
213:
209:
205:
204:delayed coker
201:
197:
193:
192:hydrocracking
189:
185:
177:
175:
173:
164:
162:
159:
155:
146:
139:
134:
128:
125:
121:
116:
113:
109:
105:
104:hydroskimming
101:
97:
96:
95:
89:
87:
85:
81:
77:
73:
69:
65:
62:
58:
54:
50:
46:
42:
38:
34:
30:
19:
882:Distillation
657:
652:
633:
627:
608:
580:
574:
561:
558:
554:
549:
547:
542:
540:
537:
533:
531:
523:
505:
501:
499:
495:v = e − 0.8
494:
488:
483:
481:
472:
466:
453:
449:
447:
442:
435:
417:
408:
391:
385:
379:
374:
370:
367:
358:
305:
257:Saudi Arabia
253:
238:Fuel Economy
237:
226:
221:
181:
172:fractionator
168:
151:
93:
37:distillation
33:oil refinery
28:
26:
818:Visbreaking
662:HPI website
532:(4)
527:centistokes
493:(3)
471:(2)
441:(1)
380:Asphaltenes
327:centistokes
279:centistokes
212:needle coke
124:natural gas
61:hydrocarbon
49:heating oil
18:Visbreaking
866:Categories
803:Sweetening
783:Alkylation
566:References
208:anode coke
135:Technology
29:visbreaker
758:Desalting
748:Processes
729:Petroleum
550:visbroken
427:Economics
420:aliphatic
321:Viscosity
273:Viscosity
227:De-coking
112:tar sands
84:catalytic
80:viscosity
64:molecules
41:crude oil
158:quenched
76:gasoline
851:Commons
508:is the
456:is the
413:alkanes
404:xylenes
400:toluene
396:benzene
335:Content
333:Sulphur
317:(kg/L)
314:Density
287:Content
285:Sulphur
269:(kg/L)
266:Density
154:furnace
108:bitumen
68:furnace
849:
823:Coking
640:
615:
587:
543:virgin
500:where
482:where
448:where
386:Resins
355:Yields
342:1.048
337:(wt%)
294:1.020
289:(wt%)
59:large
53:diesel
475:Blend
200:pitch
74:and
638:ISBN
613:ISBN
585:ISBN
548:For
541:For
460:(log
402:and
348:4.7
345:115
300:4.0
297:930
51:and
502:VBN
473:VBN
210:or
194:or
72:LPG
39:of
868::
599:^
516:.
454:ln
411::
398:,
329:)
281:)
214:.
190:,
86:.
27:A
710:e
703:t
696:v
646:.
621:.
593:.
506:e
484:w
462:e
450:v
325:(
277:(
126:.
47:(
20:)
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
