methods. The only unintended (and undesirable) refinery reaction to reduce the Ni/V content is through hydrocracking (when Ni and V deposit on the nickel-molybdenum fixed-bed catalyst reducing activity) • The formation of coke on the CC catalyst causes significant deactiva- tion and is an undesirable reaction. However, it does serve to initiate poly- condensation of thermally reactive species (asphaltenes and unstable hydrocarbons) forming coke on the catalyst. It thus leaves a thermally sta- ble residual (FCCDO), which is highly desirable during the coking reaction, resulting in greater microstructural order • The prevalence of sulphur hetero- cycles may form three- dimensional structures providing steric hindrance (also known as ONS obstruction), dis- rupting the formation of an ordered microstructure • The thermal stability of sulphur heterocycles results in their incorpo- ration in the coke matrix, even surviv- ing calcination (1350°C). However, within the electrode graphitisation cycle (between 1500°C and 1800°C), sulphur dissociates (CS₂), causing irreversible volumetric expansion and potentially causing electrode cracks due to the puffing reaction. The mar- ket dominance of petroleum-based needle cokes has meant that the study of sulphur puffing inhibitors (such as borates, iron oxides, and sodium carbonates) has received greater attention • A potential concern with FCCDO is the incorporation of the catalyst (alumina-silicates) in the DCU feed. As with other metal complexes, they can disrupt the crystalline structure by way of obstruction-to-microstructural order, resulting in an increased CTE. Petroleum-based needle coke is typ- ically associated with lighter, sweeter crude oil. Refineries are increasingly having to process cheaper, heavier, and higher sulphur crudes. This sub- stantially increases the concentration of thermally stable sulphur hetero- cycles presenting both in the FCCDO and ultimately in the coke (eventually contributing to increased electrode puffing). However, perhaps more of an
immediate impact is the competition for low sulphur crude oil derivatives from the bunker fuel market. Since 1 January 2020, the International Maritime Organization (IMO) has required ships to reduce their SOx emissions. Thus, in accordance, the sulphur content of marine fuels has been reduced from a 3.5% max to 0.5% max. This will result in sub- stantial refinery reforms away from heavy fuel oil (HFO) towards lower sulphur lighter fuels (such as marine gas oil [MGO] or very low sulphur fuel oil [LSFO]), at least over the medium term. This will lead to increased competition for downstream refin- ery products associated with lighter sweeter crude oils, increasing the value of these residuals. Future quality assurance measures will very much relate to the nature of the crude oil and development of the FCC process to further ensure consis- tent precursor characteristics. Due to the necessity to comply with IMO 2020, refiners with low bottom- of-the-barrel conversion capacity are looking for middle API crude oils with low sulphur content, capable of producing the new marine fuel oil (bunker) through simple blending of bottom-of-the-barrel streams with dilutants like hydrotreated diesel (see Figure 4 ), limiting the availability of this kind of crude. The shortage of low sulphur crudes that can comply with IMO 2020 tends to create competition by refiners focused on producing needle coke and refiners looking to comply with IMO 2020 in a way that is cheaper than deep bottom-of-the-barrel conver- sion units. This competition relies on the price gap between high sulphur fuel oil (HSFO) and LSFO, as well as the price differential between needle coke and LSFO. In this business envi- ronment, it can be expected to raise prices of low sulphur crudes and provide a competitive advantage to refiners with high complexity refining hardware. Alternative options: The GTL route One of the most promising and well- developed technologies currently is the conversion of syngas (CO + H₂) into longer-chain hydrocarbons such
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