Vacuum residue
Pyrolysis oil
50
High
39
31
40
35
27
30
23
19
20
15
11
10
7
Low
0
0
10
20
30
40
50
60
70
80
90
10
20
30
40
50
60
70
80
90
Carbon number
Carbon number
Figure 2 Double bond equivalent vs carbon number for residue and fuel oil
device that separates a heart cut with carbon number vary- ing between 20 and 35, depending on the TC2C variant. The heart cut is sent for fixed bed hydroprocessing to remove nitrogen and sulphur, hydrogenation of aromatics, ring open- ing and hydrocracking. The catalyst systems are carefully selected to optimise the molecular profile for subsequent processing. The heaviest fraction of the crude with a carbon number exceeding 35 is routed to a liquid circulation (LC) reactor with either extrudate or slurry catalyst. These reactors have small online catalyst addition and withdrawal capabilities and can run continuously for more than five years. LC reactor infor - mation can be found elsewhere. 2 The liquid circulation reac - tors convert the asphaltene and recycle pyrolysis oil from the ethylene plant to lighter components that are hydrotreated/ hydrocracked to suitable steam cracker feed. This system ensures no heavy polynuclear aromatics (HPNA) reach the steam cracker. Some known structures that impede the full conversion of residue hydrocracked VGO are shown in Figure 1 . Through extensive analysis of commercial data from residue hydrocracking and tailored pilot plant tests, residue hydrocracking has an increased concentration of double bond equivalent (DBE) value of 15+ compounds. For pure hydrocarbons, DBE=C+1-H/2, where C is the number of carbon atoms, and H is the number of hydrogen atoms. It represents the level of unsaturation or hydrogen deficiency.
The measured DBE of a typical ethylene plant pyrolysis fuel oil and a residue are shown in Figure 2 . Typical pyrol- ysis fuel oil characteristics are shown in Table 1 . Within the integrated hydrocracking system, the catalysts system and operating conditions are carefully controlled such that DBE is restricted to 15 or lower in the effluent. Slurry hydrocracking utilising a very special catalyst can increase the conversion of residue to more than 97%. The addition of pyrolysis fuel oil to the residue feed increased the residue conversion signifi - cantly. The remaining unconverted oil is filtered and sent over a fixed bed reactor system to meet IMO-compliant very low sulphur fuel oil (VLSFO) specifications (<0.5 wt% sulphur). Thus, TC2C ensures that no part of the converted crude is wasted while maximising the yield of chemicals. Changes in DBE before and after an LC technology are shown in Figure 3 . High DBE value species are almost reduced to zero. When a crude is primarily used to produce chemicals only, it is important to know whether it is worthwhile to upgrade it or not. Upgrading typically requires either carbon rejection or hydrogen addition. Upgrading naphtha may not improve the olefin yields sig - nificantly, and it produces only a small quantity of fuel oil.
9 8 10
3 2 1 4 5 6 7
Before
After
Typical pyrolysis oil properties
API
10.3 1.01 592 8.65 4.47
5 wt%
200 267 606 735
Sulphur, wt% Nitrogen, wppm Hydrogen, wt%
50 wt% 95 wt% 99 wt%
24 13 14 15 16 17 18 19 21 22 23 20 10 11 12 4 5 6 7 8 9 DBE 0
MCRT, wt% Simdist,ºC 0.5 wt%
Recovery, wt%
98 44
Metals by ICP, wppm
164
Figure 3 Changes in DBE before (blue) and after (red) hydrocracking
Table 1
52
PTQ Q1 2024
www.digitalrefining.com
Powered by FlippingBook