Properties of middle distillate fractions processed in LNB refinery hydrotreating units
Parameter
SRLGO
SRMGO
SRHGO
LVGO
FCCPT diesel
FCC LCO
H-Oil Diesel
( 180-240°C) (200-300°C) (240-360°C)
Density at 15°C, g/cm 3 ASTM D 86 distillation T 10% , °C
0.801
0.82
0.852
0.877
0.903
0.930
0.872
198 210 232 0.25
228 250 278 0.47
247 262 296 0.85 128
274 306 356 1.17 260 34.5
276 325 360 678 46.5 12.3 0.122
221 245 281 0.26 666 82.2 45.6 12.9
201 269 330
T 50% , °C T 90% , °C
Sulphur, wt% Nitrogen, ppm
0.188
68
Total aromatics, wt%
20
26.6
29
54.7 21.8 37.1 38.5 23.6
Poly-nuclear aromatics, wt% Bromine number, gBr 2 /100g
6
8.5
11.8
15 5.6 45
1.1 43 50
3
3
1.8
Cetane number Cetane index
52
56.1 55.4 38.2
38.6 39.6
53.6
48.4
19.6
Wt% in diesel pool
23.6
3.9
2.6
6.1
5.2
Table 1
Properties and test methods of light and heavy hydrotreated gasoils are presented in Table 2 . SDA is added in such low concentrations that it is extremely difficult to detect by any standard analytical procedure. Therefore, it is controlled by measuring the resultant electrical conductivity of the fuel. The standard field test for electrical conductivity is ASTM D2624/IP 274: Electrical Conductivity of Aviation and Distillate Fuels. Although the method is intended to measure conductivity with the fuel at rest in storage tanks, it can also be used in a laboratory. 5 Results and discussions LNB produces Euro 5 diesel fuel via hydrotreating/HDS sev- eral gasoil fractions, of whose properties are described in Table 1. As can be seen from Table 1, the fractions are both straight run and secondary, i.e., produced from conversion
units like FCC and ebullated bed hydrocracking of vacuum residue (H-Oil). Their properties vary in a wide range. Density of SRLGO is just 0.801 g/cm³, while gasoil frac- tions with secondary origin reveal very high density values – 0.872 g/cm 3 for the H-Oil diesel fraction and up to 0.930 g/cm 3 for FCC LCO. Poly-nuclear aromatics (PNAs) content follows duly density as significantly high values are registered for FCC LCO and H-Oil diesel fractions – 45.6 wt% and 21.8 wt%, respectively. The opposite is distributed sulphur content – higher values are typical for straight-run fractions (SRLGO, SRMGO, SRHGO, and especially LVGO). Also, due to a certain degree of hydrotreatment in the conversion pro- cesses, diesel fractions with secondary origin possess lower sulphur at levels of about 0.2 wt% and less. Gasoil fraction properties should be polished in order for the final diesel fuel to correspond to the requirements of both fuel quality norms 8,9 and specific environmental legislation. 9,10 Figure 1 presents the origin of all diesel fractions in LNB, obtained from different production units, with gasoil divided into light and heavy fractions. The light gasoils are processed in a dedicated HDS unit, HDS-2 or, when the amount of gasoils is limited due to lower refinery through - put, in HDS-3. HDS-5 is designed to process mainly heavier gasoil fractions, as a dearomatisation section is included in this unit. HDS-5 is capable of improving the heavy gasoil fraction as per the following metrics: decreasing density at 15°C from 0.865 g/cm 3 to 0.850 g/cm 3 for the hydrotreated product, lowering feed sulphur content from 0.67% (m/m) down to 8 mg/kg, and polycyclic aromatic content from 12% (m/m) to 4% (m/m). Along with the positive effect of HDS over gasoil frac- tion properties, removing impurities such as hetero-atoms (nitrogen and oxygen-based polar trace compounds) and metal-containing compounds 2 causes some negative effects. With adoption of the HDS process, hydrotreated gasoils lose their inherent lubricity 3 and electrical conduc- tivity. 4 The physico-chemical properties of two types, light hydrotreated gasoils (LHTGO) and heavy hydrotreated gasoils (HHTGO), at LNB are summarised in Table 2.
The physico-chemical properties of light and heavy hydrotreated gasoils produced from LNB HDS units
Parameter
LHTGO (HDS-3)
HHTRGO (HDS-5)
Density at 15°C, g/cm 3
0.809
0.846
Distillation as per ASTM D 86, °C T 10%
184.3 222.5 277.5 291.9 299.9
215
T 50% T 90% T 95%
283.1 333.3 345.6 350.7
EBP
Sulphur, ppm wt.
7
7.9
Mono-aromatic, wt% Di-aromatic, wt% Tri+-aromatic, wt%
25.2
3.2 3.5
Cetane number Cetane index ASTM D 4737 ASTM D 976 Cloud point, °C
49
50.3
50.6 49.5
50.9 51.8
< -51 < -51
-5 -7
CFPP, °C
Electrical conductivity, pS/m
1
2
Table 1
64
PTQ Q2 2023
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