PTQ Q4 2022 Issue

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Close to 6 million b/d of straight run resid with s ulphur content of less than 0.5% is produced locally

0 1 2 3 4

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 Atmospheric resid supply (million b/d)

Figure 4 Availability of low sulphur atmospheric residue

(Source: McKinsey Energy Insights’ Global Downstream Model )

coal, biomass, or the petroleum coke gasification route. The process starts with syngas generation and, as afore - mentioned, the produced hydrocarbon chain extension is controlled in the Fischer-Tropsch synthesis step through the CO/H₂ ratio in the syngas fed to the FT reactors (beyond temperature and reaction pressure), followed by the pro - duced hydrocarbons being separated and sent to refining steps such as isomerisation, hydrotreating, hydrocracking, and catalytic reforming. According to the produced deriva - tive (gasoline, diesel, lubricant), some side reactions can occur during the hydrocarbon production process, leading to coke deposition on the catalyst, which causes deactiva - tion according to the following chemical reactions:

as gasoline and other liquid fuel products, known as gas- to-liquids technologies (GTL). The liquid hydrocarbons pro - duction can be carried out by direct syngas conversion, in Fischer-Tropsch synthesis reactions or through methanol production as an intermediate product (methanol-to-ole - fins technologies). Fischer-Tropsch is a chemical process that can produce liquid hydrocarbons according to the following chemical reactions:

Paraffin production: n CO + (2n+1)H₂ = CnH₂n+2 + nH₂O

Olefin production: n CO + 2nH₂ = CnH₂n + nH₂O

These reactions are strongly exothermic, and the CO/H₂ ratio in the syngas is a key parameter in defining the hydro - carbon chain extension that will be produced. The reactions normally occur under temperatures ranging from 200 to 350°C and operating pressures in the range of 15 to 30 bar. The catalyst commonly applied to these reac - tions is based on cobalt or iron as active metals deposited upon alumina as a carrier. Figure 5 presents a block diagram for a typical process plant dedicated to producing liquid hydrocarbons from Fischer-Tropsch synthesis. The process is based on the syngas gas generation from steam reforming of natural gas. This is the most common route. However, there are process variations applying syngas production through

2 CO = C + CO₂ (Boudoir Reaction)

CO + H₂ = C + H₂O (CO Reduction)

The type of reactor applied in the FT synthesis step strongly influences yield and the quality of obtained prod - ucts. The run time of the process units also depends on the type of reactor. Fixed-bed reactors are widely employed in FT synthesis. However, they show a reduced campaign time due to low resistance to catalyst deactivation phenomenon. Modern process units apply fluidised bed or slurry phase reactors that present a higher resistance to coke deposi - tion on the catalyst and better heat distribution, leading to higher campaign periods.

Water

Waxes/parans

Steam reforming

Product separation

Heavy ends rening

Fischer-Tropsch synthesis

Natural gas

Olens

Reforming/ energy recovery

Upgrading processes

Unconverted gases

Gasoline, jet fuel, diesel, lubricants, etc.

Heat + CO, H, CO, etc.

Figure 5 Block diagram of a typical Fischer-Tropsch GTL process plant

PTQ Q4 2022