PTQ Q3 2023 Issue

take these actions quickly and efficiently. Board operators should always be equipped with the necessary knowledge and tools to accomplish the task. Automation of the recommended emergency actions should be considered to ensure that the right actions are taken swiftly and effectively. Conclusions The methods and logic presented in this article can be used to rate the effective quench ability of various emergency actions. The quench rating can identify the most effective actions to prevent a temperature excursion incident from becoming a reactor runaway incident. Every unit should use this methodology to rate the effectiveness of each emergency action and prioritise the actions for that unit. If adequate emergency actions are taken promptly in a hydrocracking unit, a temperature excursion can be stopped before automatic depressuring becomes necessary using the emergency actions recommended in this article. All hydrocrackers should be equipped with the follow - ing emergency features that can be taken from the control room board: • A bility to open a bypass control valve around the feed/ effluent exchangers to reduce heat to the reactor inlet • A bility to cut back the make-up hydrogen flow to less than 25% of normal flow. This could be done with com - pressor unloaders or a control valve (or both) • A bility to double the quench gas flow to two beds at the same time • A bility to chop the reactor feed furnace to minimum fires or pilots • Ability to stop cracked stocks feeding to the unit • Additional actions may be necessary for some units. The methodology discussed should be used to con - sider which emergency actions are available to operators. Modifications to control systems should be undertaken to ensure all the emergency actions listed above are easily available to hydrocracker board operators. Automation of the recommended emergency actions should be considered to increase the probability that the right actions will be taken quickly in the event of a reactor temperature excursion. Hydrocracking units must maintain ADS as the last line of defence to prevent a reactor runaway from overheating the reactor and outlet piping and potentially causing a loss of containment in the unit. This article is based on a presentation derived from Becht’s Hydroprocessing Blog, ‘Under Pressure: Quantitative Method to Select Emergency Actions to Prevent Reactor Runaway’, by Jeff Johns. Jeff Johns has more than 35 years’ experience in the petroleum refining industry. He was honoured as a Chevron Hydroprocessing Fellow for contributions to Chevron and the industry. He has expert knowledge of hydrocracker and hydrotreater design/operation, optimisation, and troubleshooting, and has substantial experience in other key refinery processes. He holds a BS. degree in chemical engineering from the University of Utah and holds six patents in hydroprocessing technology.

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