Resettable PSV Overpressure Protection in Hydrocracking Reactors
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Solution Overview
Problem
In hydrocracking processes, existing pressure relief systems face issues with fluid fouling and coking, leading to potential blockages and extended downtime due to the use of rupture discs that do not reset automatically, causing unnecessary flaring and increased emissions, and requiring excessive Vacuum Gas Oil (VGO) for cooling, which prolongs reactor cooling and increases reprocessing needs.
Innovation Solution
Implementing a pressure relief system using conventional or balanced bellows PSVs, where the PSV inlet line is purged with hydrogen-rich gas or hot VGO, allowing relief fluid to be routed to downstream process equipment, minimizing flaring and emissions, and enabling quick reactor restart by automatically resetting the PSV once the overpressure event is resolved, thus reducing VGO usage and cooling time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a rupture disc is used for pressure relief, then overpressure protection is provided, but the system does not reset automatically causing extended downtime and unnecessary flaring
Solution Approach 1:
The patent applies the discarding and recovering principle by replacing the non-resettable rupture disc with a resettable pressure safety valve (PSV) system. The PSV automatically recovers and resets after relieving overpressure, eliminating the need to discard the relief device. This allows the system to automatically return to normal operation without extended downtime, while still providing reliable overpressure protection through the PSV's automatic closing mechanism after pressure normalization.
Solution Approach 2:
The patent implements self-service through the automatic operation of the PSV system. The PSV automatically opens when overpressure occurs, relieves the pressure, and then automatically closes and resets when pressure returns to normal levels. This self-service capability eliminates the need for manual intervention or replacement of the relief device, thereby reducing downtime and allowing rapid restart of the hydrocracking process.
2Reliability
If relief fluid is routed to flare, then overpressure is relieved, but valuable hydrocarbons are lost and emissions increase
Solution Approach 1:
The patent applies the intermediary principle by introducing a purge gas stream (hydrogen-rich gas from compressor discharge or hot VGO) as a mediator between the relief fluid and the flare system. This purge gas continuously flows through the PSV inlet line and mixes with the relief fluid, preventing fouling and coking while allowing the relief fluid to be routed to downstream process equipment rather than flared. This intermediary approach preserves valuable hydrocarbons and reduces emissions while maintaining effective pressure relief.
Solution Approach 2:
The patent implements local quality by applying different properties to different parts of the relief system. The PSV inlet line receives continuous purge gas flow to prevent fouling, while the relief fluid routing is designed to discharge to downstream process equipment rather than flare. This localized application of protective measures (purge gas in inlet line) and alternative routing (to process equipment) allows effective pressure relief without hydrocarbon loss or increased emissions.
3Temperature
If excessive VGO is used for cooling, then reactor cooling is achieved, but reprocessing needs increase and cooling time is prolonged
Solution Approach 1:
The patent applies continuity of useful action by maintaining continuous purge gas flow through the PSV inlet line during both normal operation and overpressure events. This continuous purge prevents fouling and coking in the relief system, eliminating the need for excessive VGO to be used for cooling and reprocessing. The continuous useful action of the purge gas protects the system throughout operation, reducing both cooling time and reprocessing requirements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively manages pressure relief in hydrocracking processes by minimizing flaring, reducing downtime, and lowering the risk of fouling, while allowing for rapid cooling and efficient restart of reactors, thereby improving operational efficiency and reducing capital and operating expenditures.
Implementation Method 1
the pressure difference between the ISS and Hot HP Separator is small and hence conventional or balanced bellows PSV cannot be used
Implementation Method 2
conventional or balanced bellows PSV
Implementation Method 3
The fluid that is relieved from the ISS has a tendency to coke and build-up fouling in stagnant areas
Data Source
AI summary
The invention relates to an improved system and method for relief of hot, high pressure, fouling fluid from the 1st Stage Reactor and the ISS in case of an unintended overpressure situation while allowing the quick establishing of normal fluid flow path once the overpressure situation has been corrected. This allows for rapid cooling of all subsequent reactor stages while minimizing VGO slop generation that needs reprocessing.