PTQ Q4 2025 Issue

workshop for all stakeholders, well before the shutdown, should be called to discuss all the required actions to identify and apply the best ideas. This strategy has been successful at several sites, resulting not only in good catalyst perfor- mance but also much shorter shutdown times. KBC has seen this type of workshop process, with full stakeholder attendance, reduce catalyst changeout time by 30-50%. Good integration of processes with mechanical, inspection, and contractors are vital. A set of key checklists for each phase of the shutdown is a good tool for benchmarking and identifying new oppor- tunities, without omitting anything. Detailed checklists can be developed for all key steps in implementing the catalyst change and assigning a weighting to the various param- eters. Some checklists contain up to 500 items. This also helps prioritise improvement areas and real roadblocks. Such a checklist can be broken down to include planning (the most important), safety and reliability procedures, cat - alyst handling, mechanical procedures around the reactor system, equipment design features, modifications and reac - tor design. Benchmarking Typically, benchmarking may compare total or individual time taken for different units. However, there are various other parameters to look at when performing a more real- istic benchmarking, including catalyst volume, recycle gas rate capability, number of reactors, access, MPT restrictions, and even furnace capability, where start-up is often limited by furnace duty (when there is no heat rise in the reactor). Some of these factors, such as catalyst amount and recycle gas ratio, can be normalised to standard numbers to pro- vide a more realistic benchmarking target for each step of the changeout. Feed quality control Feed quality is often the main factor that determines running length. Maximise direct feed wherever possible. Oxygen promotes free radical formation and polymer deposits, espe- cially with cracked stocks. Mixing the feed with hydrogen early helps suppress polymer formation. Tankage feed is a source of scale, sediment, and oxygen. For example, some units processing part coker naphtha and tankage feed have fouling issues. Others, which have no intermediate tankage, have no fouling and must only worry about the silica. A fault tree-type approach to looking at feed quality issues is good. Figure 1 shows a first-level fault tree for reviewing feed quality issues. Lower-level trees can exist for developing the more likely problem areas. Filtration: Focus filtration on streams that have particulates resistance to upstream separation, such as coker streams. Measurement of solids in the streams will determine the need for filtering other streams. Limiting the feeds using the filters improves their effectiveness. Fractionation: Control fractionation in the upstream frac - tionators to manage the feed endpoint, and for the heavier feed units, the level of metal contamination. The feed tail contains all the hard sulphur, so poor fractionation can sig- nificantly impact the weighted average bed temperature

the scope of this article, unloading options can involve dry dumping under nitrogen; wet dumping; passivation and air dumping; vacuum unloading with high and very low losses; use of high pressure jetting for catalyst balls and some fixed bed residue units; and occasionally use of small explosive charges. Start-up procedures Several factors can affect catalyst performance during pre- start-up and start-up. Care at this stage protects catalyst activity and prevents early-life damage. Avoid using tankage feed unless it is well filtered. Storage tanks often introduce scale, sediment, and oxygen. Oxygen in cracked stocks can significantly increase polymer forma - tion, leading to fouling and blocked flow paths. After any required hydrotesting, clean the preheat system thoroughly and remove all water. A water slug can vapour - ise and wash debris into the reactor or quench zones, dam- aging trays. Control heat-up rates to avoid thermal shock. Uneven heating can crack internals, damage catalyst structure, and cause maldistribution. This step may be limited by minimum pressurisation temperature constraints (MPT) if the reactor was specified to be too high. Designers do not always fully account for operations away from steady-state conditions. Ensure catalyst passivation is adequate for hydrocrack- ing catalyst, which is highly active at start-up. Temperature excursion has been seen when using liquid recycle to mini - mise slop, where organic nitrogen, which is a natural activ- ity suppressor, is slowly removed through recycling in the reactor. Fully pre-activated catalysts eliminate the need for the sulphiding step and can cut start-up time. Even so, they still require controlled heating to protect the catalyst, reac- tor internals, and other mechanical equipment. The quality of the procedures also impacts a successful start-up. It must have an adequate explanation and direc - tion. If the intent and reason behind various steps are not understood, it will become difficult to manage any resulting unplanned events. There should be adequate checks and balances at the beginning and end of key steps, clearly outlining the state of the equipment. Any interactions with supply and product units should also be referenced within the procedure to make sure everything works in the correct sequences. Added reliability is achieved with bar charts of the var- ious steps so that key equipment conditions are known. There are marked-up flowsheets/sketches, so any different start-up routings are more easily understood than written instructions alone. For example, a procedure rarely relates all the equipment status on a block as the procedure pro- gresses. This is very important to optimise time, avoid unexpected events, and better plan mechanical work. To maximise catalyst utilisation, catalyst changeout time should be minimised. This requires the development of a good catalyst handling plan and create a good relationship with the catalyst handling and catalyst loading contractors. Planning Planning before shutdown is the most important task. A

PTQ Q4 2025