Hydrocracker Fractionator Sidedraw Tray Level Control
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Solution Overview
Problem
The hydrocracking process faces challenges in efficiently controlling unexpected increases in fractionator bottoms yield, leading to inefficiencies and economic losses due to over-cracking and energy costs, as existing methods are time-consuming and risk producing off-spec products.
Innovation Solution
A method and system that control the fractionator and hydrocracker reaction loop by monitoring and adjusting the flow rates and liquid levels in the fractionator, specifically using a sidedraw tray to separate and control the flow of hydrocarbons, allowing for precise adjustments to maintain desired boiling ranges and reduce re-cracking inefficiencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the hydrocracker reaction bed temperature is increased to control fractionator bottoms yield, then the conversion efficiency is improved, but energy costs increase and re-cracking into undesired lighter fractions occurs
Solution Approach 1:
The patent implements a feedback control system that continuously monitors fractionator bottoms yield and automatically adjusts the hydrocracker reaction bed temperature to maintain optimal conversion efficiency while preventing excessive temperature increases that would lead to energy waste and re-cracking. The system uses real-time data from bottoms yield monitoring to modulate reactor temperature, creating a closed-loop control mechanism.
Solution Approach 2:
The patent dynamically adjusts operating parameters (temperature, pressure, flow rates) based on real-time process conditions. Specifically, it changes the reaction bed temperature in response to bottoms yield variations, and adjusts sidedraw flow rates to optimize separation efficiency, thereby maintaining high conversion without excessive energy consumption or re-cracking.
2Manufacturing precision
If the sidedraw product flow rate is increased to control fractionator separation, then the separation efficiency is improved, but off-specification product is produced
Solution Approach 1:
The system employs feedback control by continuously monitoring the liquid level on the sidedraw tray and automatically adjusting the sidedraw product flow rate to maintain the desired liquid level. This ensures optimal separation efficiency while preventing excessive draw rates that would compromise product specification. The feedback loop balances separation performance with product quality requirements.
Solution Approach 2:
The patent implements dynamic adjustment of the sidedraw flow rate based on real-time liquid level measurements. Rather than operating at a fixed flow rate, the system dynamically modulates the draw rate to respond to changing process conditions, thereby maintaining both high separation efficiency and consistent product specification across varying operating conditions.
3Measurement precision
If manual examination and adjustment of fractionator operation is performed, then the control accuracy is improved, but the response time is reduced
Solution Approach 1:
The control system performs self-service by automatically monitoring bottoms yield, liquid levels, and flow rates, and autonomously making adjustments to reaction temperature and sidedraw rates without requiring manual operator intervention. This automated self-regulation maintains high control accuracy while significantly reducing the time delay associated with manual detection and adjustment.
Solution Approach 2:
The patent replaces manual mechanical control operations with an automated electronic control system that uses sensors, controllers, and actuators to monitor and adjust process parameters. This substitution of manual operations with automated control systems eliminates human response time limitations while maintaining or improving control accuracy through continuous monitoring and precise actuation.
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 approach provides greater certainty in controlling fractionator bottoms yield, reduces re-cracking inefficiencies, and minimizes the risk of producing off-spec products, leading to more efficient process control and economic benefits.
Implementation Method 1
The fractionator separates the feed stream into different fractions of liquid hydrocarbons each having a desired boiling range. Generally speaking, 'lighter' hydrocarbons (e.g., liquid hydrocarbons having a lower boiling point) are withdrawn from the top and sides of the fractionator as an overhead and sidedraw streams. Heavier fractions (e.g., hydrocarbons having a higher boiling point) collect in the bottom of the fractionator
Implementation Method 2
Hydrocracking is a process in which heavy oil fractions recovered from crude oil are combined with hydrogen gas and subjected to high temperatures and pressures in one or more reactors filled with catalyst. The catalyst helps the longer chain hydrocarbons in the heavy oil fractions break or 'crack' into smaller hydrocarbon molecules
Implementation Method 3
The catalyst helps the longer chain hydrocarbons in the heavy oil fractions break or 'crack' into smaller hydrocarbon molecules that eventually form kerosene, naptha, and gasoil components
Data Source
Figure 1
AI summary
A method and system for controlling a hydrocracker and fractionator reaction loop is disclosed. The method and system utilizes a sidedraw tray within the fractionator distillation zone upon which liquid is collected. This liquid is withdrawn as a sidedraw stream. The withdrawal of the liquid from the sidedraw tray is controlled based on the level of liquid on the sidedraw tray rather than at a set or determined flow rate. The sidedraw stream is separated into a first stream and a product stream. Unlike other processes where the flow rate of the product stream is set and the internal reflux flow rate varies, the method involves fixing the flow rate of the first stream that is returned to the distillation zone of the fractionators with the flow rate of the product stream being set so as to control the liquid level on the sidedraw tray.