PTQ Q2 2023 Issue

19.3%

Low-sulphur crude oil Medium-sulphur crude oil High-sulphur crude oil

51.4%

High-activity hydrotreating catalyst

29.3%

High-selectivity hydrocracking catalyst

Figure 2 Sulphur content of crude feeds

and, subsequently, isomerisation, diesel desulphurisation, and CCR reformer units. Identifying the issue The 4,500 m 3 /d DHP unit at Kırıkkale is the facility’s most valued asset. Commissioned in 2008, it is operated to max- imise diesel production from variable heavy feeds. Turkey is a net importer of diesel, so the product holds regional value, and a shorter cycle length would have a major economic impact on the refinery. The DHP unit had been running since a turnaround in 2015, following a catalyst change, but retaining the original internals from the initial commissioning. Using the instru - mentation available on the Tüpraş reactor, Shell Catalysts & Technologies was able to track the unit’s long-term per - formance using its proprietary CatCheck * monitoring tool, which is a knowledge management system that enables Shell’s experts to help the unit technologists by building a picture of the unit and the way that it is performing. By studying the information gathered and comparing it with an extensive process database, CatCheck can help with the technologists’ efforts to control the conditions of their unit by continuously optimising performance or quickly troubleshooting any process problems. During this cycle, an issue with gas and liquid distribution was identi - fied. The unit comprised pretreat, cracking, and post-treat

High-selectivity hydrocracking catalyst

High-activity hydrotreating catalyst

Figure 3 The DHP unit cracking reactor containing two cracking catalyst beds

catalyst sections, and the problem involved a high radial temperature differential (DT) measured across the cracking bed. The cracking reactor is shown in Figure 3 . Figure 4 illustrates a comparison of the radial to axial DT ratio in the lower catalyst bed of the cracking reactor. For the run starting in 2015 (plotted in blue), inconsistencies are seen throughout the cycle, compared with the cycle start - ing in 2018 (plotted in red). The high outlying values, as seen in the 2015 cycle, can necessitate unit shutdown due to maximum operating temperature limits being reached. The measured thermal maldistribution suggested subop - timal catalyst utilisation and poor vapour-liquid distribution throughout the cracking bed, which has the important role of shifting the feed’s higher T-95 value into line with the lower T-95 specified for a diesel product. The DHP reactor takes a three-component feed of heavy diesel, light vacuum oil, and light diesel from a crude distillation unit. By cracking more of the heavier components, a bigger cut of the heavier fractions can be economically converted to diesel. In a DHP reactor cracking bed, temperatures naturally increase axially, from the top of the catalyst bed to the bot - tom, due to the exothermicity of the reactions occurring. At the same time, there should be an even radial temperature distribution at any given depth within the bed. The hotspots identified suggested channelling and uneven catalyst wet - ting, causing over-cracking, which, in turn, reduces diesel yield. Poor catalyst utilisation can also mean running at higher temperatures, which drives up energy costs and shortens cycle life. Working on the solution The refinery’s process engineers worked with Shell Catalysts & Technologies to investigate the cause. Analysis

0.0 0.6 0.4 0.2 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.8 2.6 2.4 3.2 3.0

R2B2 bottom radial/axial ratio - SOR April 2015 R2B2 bottom radial/axial ratio - SOR April 2018

200

400

600

800 1000 1200

1400

Days on stream

Figure 4 Ratio of radial to axial DT for the two separate cycles

PTQ Q2 2023