PTQ Q3 2023 Issue

Reactor internals Improved flow distribution technologies continue being developed to improve distribution of the feed and recycle gas. These advanced technologies prevent hot spots from developing and help quench distribution. Certain techniques are also available to ensure distribution trays function optimally. Additionally, thermowell design and reactor loading internal design help maintain sufficient flow distribution. It is also important to design the thermocouple location to best monitor temperature excursions or hot spots. Reactor bed condition To improve catalyst flow distribu - tion and minimise associated delta P (ΔP), it is important to practise proper catalyst loading and monitoring techniques. The reactor top bed catalyst and intergrading materials and design play a vital role in maintaining distribution and miti- gating ΔP. Additionally, the design of dense loading machin - ery continues to improve. Note that the skill of the loading technician is still very important. Filtration It is important to filter and treat the feed to prevent fouling in the bed, which can lead to hot spots. Knowing the fouling type and size helps filter selection. Procedures and training Both standard and emergency operating procedures can be improved to prevent and miti- gate temperature excursions: • Standard procedures should be followed during start-up, which may include adding amine or ammonia to control excursions, especially if feed or recycle flow is low on sulphur or catalyst activity is extremely high • Emergency procedures and feed type, such as loss of recy- cle gas flow, determines whether feed is, or is not, removed in addition to depressurisation • Training operators on how all processes operate and how hot spots can develop • HAZOP/MOC reviews should be conducted when chang- ing catalysts. Some companies conduct exotherm speed potential tests to compare base catalysts against new cata- lysts with higher activity. Control Several control systems can be used to help pre- vent and reduce temperature fluctuations. These controls include: • Thermocouple monitoring can track maximum tempera- ture, rate of temperature change above a certain point, radial temperature distribution, or shell temperatures. Alarms or even emergency depressurisation can be linked to these measurements • Hydrocracking catalyst may have a few separate beds to control heat rise in one bed to mitigate heat rise before the next quench point. Note that in case of an excursion, gas quench is usually inadequate to control the heat rise and, therefore, controlled depressurisation is the better approach • Temperature monitoring instrumentation can also trigger emergency depressurisation. A Fu-Ming Lee, fmlee1227@gmail.com and Maw-Tien Lee, Senior Consultants, Shin-Chuang Technology Corp., Ltd, and Ricky Hsu, Founder, ricky_hsu@msn.com, International Innotech, Inc One of the most common problems with hydrocrack- ing reactor runaway is the sudden reactor pressure rise. Hydrocracking feeds contain different sizes of solid particles

Although very waxy, VGO from waste oil is unlikely to be used for lubes production without new testing. The key cata- lyst issues are discussed as follows: • Some residual metals, notably phosphorus, will be present and must be considered when setting up any special metal trap catalyst at the top of the reactor system • The feed contains oxygenates that will generate COx. At higher temperatures, CO formation will increase, which may impact catalyst activity. Nickel Molybdenum (Ni/Mo) catalyst is less sensitive and should be the preferred catalyst. The pres- ence of a recycle gas amine contactor can help control COx, but it is essential to check its impact on the amine system • Heat rise will increase in the earlier beds, so monitoring the impact on temperature control is important • When VGO service is moving towards an FCC, further treatment consideration may be unnecessary. However, if the feed is going to a diesel product, there might be a need to add a dewaxing zeolite catalyst in a lower bed. For 100% waste oil in diesel/kero service, a second reactor for dewax- ing is typically necessary. Q With global hydrocracking unit capacity and feedstock diversity increasing, what strategies are available to pre- vent reactor runaway and increase overall unit safety? A Jay Parekh, Manager, Technology, Subject Matter Expert, Hydrocracking, ART As refiners look for more opportunities to improve profit - ability and gross margin, feedstocks that are more refractory with higher aromaticity are processed in hydrocracking units to produce high-quality liquid fuels. The more difficult feed - stock adds additional risk to refiners as the temperature exo - therms in normal operation increase and requires additional quench between beds for reactor controllability. Most modern hydrocracking units now have an auto- depressuring system (ADS), which will automatically trigger in the event of a major temperature excursion and bring the unit to a safe condition. The ADS will activate when specific reactor bed or reactor outlet temperatures exceed preset limits or when the recycle compressor fails. Loss of recycle flow is the leading cause of runaway incidents. ADS should also ensure that the reactor feed furnace burners have been tripped and the make-up hydrogen flow is reduced. While the ADS provides a safeguard to avoid a catastrophic event, it is imperative for refiners with hydrocracking units to properly train operators to follow good operating practices and be able to institute emergency procedures quickly. The hydrocracking unit should always be in a posture where reactor heat can be rapidly removed from the unit (cut fur- nace fires) while ensuring adequate compressor capacity to provide additional emergency quench gas capability to cool reactor beds quickly. A Andrew Layton, Principal Consultant, KBC, Andrew. layton@kbc.global, Dave Loubser, Senior Staff Consultant, KBC There are various contributors that can generate a heat rise or even runaway. The following are several mitigations to address potential runaway situations:

PTQ Q3 2023