PTQ Q2 2023 Issue

Comparative analysis of the three different additives

Base chemistry

Magnesium sulphonate with

Magnesium carbonate

Calcium sulphonate

MGO nanoparticles Most effective = 90%

WRI observational results

Effective = 65-70%

Mildly effective = 50-55%

Foulant collected (~23g with no additive)

~1g

~7g

~10g

Pressure drop (psi)

1.1 psi

2.3 psi

2.5 psi

Table 3

different additives utilising both qualitative and quantita- tive approaches has revealed that additive #1 with mag- nesium sulphonate and nanoparticle chemistry is the most effective anti-fouling additive. It significantly reduced fou - lant build-up (see Figures 5 and 6) and, as shown in Table 3, accumulated the least amount of total foulant and mea- sured the lowest pressure drop. One must note that addi- tives #2 and #3 also effectively reduced coke fouling in the testing tower. First-stage testing showed the effectiveness of additive #1 in mitigating polymeric coke formation and accumulation. With improved confidence in the performance of this addi - tive across numerous fouling mechanisms and situations, the main goal of the second-stage testing was to deter- mine the minimum dosage of additive required to suppress fouling and increase the capacity of the delayed coking unit during commercial operations. Second-stage testing: minimum dosage for commercial operations The first test in the second stage determined the impact of additive #1 on an already fouled vessel. The flow loop was operated for 12 hours without additive and then eight hours with 300 ppm of additive injected. Figure 6 shows that additive #1 can significantly reduce the amount of existing foulant in the vessel and prevent new foulant from forming. Also, the amount of foulant collected was reduced to ~6g with additive injection compared to 23g when no additive was injected. Two additional tests with the same duration and

conditions were performed under the scope of stage two to determine the minimum dosage of the additive. The con- centrations investigated were 100 and 150 ppm in addition to the previous testing at 300 ppm. The minimum additive dosage needed to be around 125 ppm to achieve effective fouling mitigation. However, in commercial operations, the dosage is usually half that required in pilot loop testing due to better mixing via turbulent flow. Thus, the nano-additive is recommended to be injected at a concentration of 60-75 ppm to achieve the best performance and most effective fouling mitigation in coker fractionators. Third-stage testing: residence time impact (grid revamp) The final stage of pilot testing determined the impact of modifying the internal tower configuration by installing a grid. Figure 7 shows the effects of residence time on fou- lant generation without additive injection. It is evident that shorter residence times heavily reduce the amount of fou- lant generated: ~2g compared to the trayed tower configu - ration, where 23g of foulant was generated. Neither case involved any additive injection in evaluating the impact on tower performance of revamping a tray to a grid. A grid removes the residence time component, which is encouraging for reducing fouling potential. However, it will further reduce heat transfer, which may impact cut points and the overall performance of the column. Thus, when designing or implementing modifications to tower inter - nals, configuration advantages and limitations need to be considered to optimise tower performance and maximise capacity.

Figure 6 Additive impact on already fouled internals at 300 ppm injection dosage

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PTQ Q2 2023