Type-6 fuel oil
Light fuel oil
Refinery fuel gas
LNG
Min Mol. Wt
Max Mol. Wt
(MW=14)
(MW=22)
Lower heating value, Kcal/kg
9680
10,250
12,100
10,960
11,700 NIL H 2 S In Mol%:
Sulphur content Fuel composition
1.0 wt% sulphur 0.5 wt% sulphur 150 ppmv H 2 S
150 ppmv H 2 S
Sp. Gravity- 1.01 Sp. Gravity- 0.83
In Mol%: H 2 : 20.84; C 1 : 74.33 C 2 : 2.31 C 3 : 0.57 C 4 : 0.19 C 5 +: 1.09 C 2 =: 0.07
In Mol%
C/H ratio- 8.20
C/H ratio- 6.5
H 2 : 17.48; C 1 : 32.01 C 2 : 13.57 C 3 : 1.2 C 4 : 0.72 C 5 +: 1.5 C 2 =: 22.2
H 2 : - C 1 : 93
°API- 8.6
°API - 39
C 2 : 4.61 C 3 : 1.08 C 4 : 0.4 C 5 +: 0.15
C 2 =: -
C 3 =: - C 3 =: - Others: Balance Others: Balance Others: Balance C 3 =: 6.50
Table 1 Typical refinery fuel characteristics
Heavy fuel oil
Light fuel oil
Refinery fuel gas
LNG
Min MW
Max MW
Absorbed heat duty, Gcal/hr
46.5 5260
46.5 4950
46.5 4200
46.5 4625
46.5 4340
Fuel fired, kg/hr Flue gas, kg/hr
92,400
91,935
87,625
85,050
88,780
Wt % of CO 2 in flue gas CO 2 emitted, t/d Acid dew point, °C SOx emissions, kg/hr
18.29
16.95
12.58
15.09
13.44
406 137
374 132
264 113 1.74
309 110 1.70
286
60 (water dew point)
52.29
21.42
-
Table 2 Parametric evaluation of various fuels
level for comparison. However, the flue gas exit temperature from APH for RFG may be a bit lower in some instances due to the cleaner nature of the fuel compared to oil. Key performance parameters of the various operating scenarios based on individual fuels are noted in Table 2 . From here, several significant and interesting inferences can be drawn. Considering carbon emissions from HFO as the base value, the carbon footprint merit of other fuels relative to HFO is shown in Figure 1 . For better appreciation of the results, two possible scenarios were envisaged, and the inferences of the tabulated parameters were extended to these two most commonly seen scenarios: Scenario 1: Switching from fuel oil to LNG • Table 2 verifies the assertion that shifting
from fuel oil to LNG is undoubtedly an effective step towards decarbonisation. LFO generates substantially fewer carbon emissions than HFO. More so, a very appreciable cut in carbon emissions of the order of 29% can be realised if the furnace is shifted from HFO to LNG. Fuel oil firing is prevalent in many Asian countries, as well as in many parts of Africa. Shifting to LNG is a very effective and low-cost solution in those refineries in pursuit of carbon reductions. • As the shift is made from fuel oil firing to LNG, the refinery operating team must be vigilant of the key performance parameters. In general, it is experienced that key furnace indications such as Bridgewall temperature and tube metal temperature may increase. This may be due to shifting the heat load from the convection section to the radiant or a variation in flame characteristics observed in the fuel gas flames. A thermal study
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