Amine Contactor Control Scheme for NGL Processing
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Solution Overview
Problem
In natural gas liquids (NGL) processing, existing control systems for amine strippers struggle to maintain an optimal pickup ratio of acid gases, leading to inefficiencies and potential breakthroughs of hydrogen sulfide, which affects product specifications and equipment integrity.
Innovation Solution
A proactive control scheme that adjusts the pickup ratio based on tray temperature, using a feedforward/cascade control strategy with a PID flow controller, measuring acid gas concentration and solvent flow rate to maintain the pickup ratio within desired limits, and adjusting the solvent flow rate to achieve set points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional control system is used for the amine stripper, then the system operation is simple, but the pickup ratio of acid gases cannot be maintained optimally, leading to potential hydrogen sulfide breakthrough
Solution Approach 1:
The control system proactively adjusts the lean solvent flow rate based on predicted pickup ratio deviations before hydrogen sulfide breakthrough occurs. By using feedforward control based on tray temperature trends and acid gas composition changes, the system prevents problematic states rather than merely reacting to them, thereby maintaining reliable acid gas removal without requiring overly complex real-time control mechanisms.
Solution Approach 2:
The system continuously monitors tray temperature, acid gas composition, and solvent flow rate, using this feedback to dynamically adjust the lean solvent flow rate. The controller compares actual pickup ratio against target ranges and modifies solvent injection accordingly, creating a closed-loop control system that maintains optimal acid gas removal while adapting to changing process conditions.
2Productivity
If the pickup ratio is increased to improve acid gas removal efficiency, then more acid gases are removed, but the temperature variation in the contactor increases, affecting process stability
Solution Approach 1:
The control system dynamically adjusts the lean solvent flow rate based on real-time tray temperature measurements and acid gas composition changes. Rather than operating at a fixed flow rate, the system adapts solvent injection to match varying process conditions, allowing optimal acid gas removal efficiency while automatically compensating for temperature fluctuations to maintain process stability.
Solution Approach 2:
The system changes the lean solvent flow rate parameter in response to measured tray temperature and acid gas composition. By adjusting this key parameter based on actual process conditions rather than operating at a constant setting, the system achieves high acid gas removal efficiency while maintaining temperature stability through adaptive parameter modification.
3Speed
If manual control of solvent flow rate is used, then the control system is simple, but the response to changing acid gas composition is slow, risking product specification violations
Solution Approach 1:
The system replaces manual mechanical control of solvent flow rate with an automated electronic control system that uses acid gas composition measurements to dynamically adjust flow rate. This substitution enables rapid response to composition changes while maintaining relatively simple control logic based on predefined pickup ratio targets and proportional control algorithms.
Solution Approach 2:
The control system automatically monitors acid gas composition and self-adjusts the lean solvent flow rate without requiring manual intervention. The system serves itself by detecting composition changes and independently modifying operating parameters to maintain optimal acid gas removal, enabling fast response while keeping the control system architecture relatively simple.
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 ensures efficient acid gas removal, maintains product specifications, and reduces the risk of hydrogen sulfide breakthrough, thereby enhancing the operational efficiency and integrity of the NGL processing system.
Implementation Method 1
measuring a temperature of a lower tray of the contactor
Implementation Method 2
measuring a flow rate of a sour gas feed stream
Implementation Method 3
an acid gas analyzer on the sour gas feed stream
Implementation Method 4
a proportional-integral-derivative (PID) flow controller on a lean solvent stream to the contactor
Implementation Method 5
a lean solvent is often passed through the gas flow and a countercurrent contactor. As the lean solvent passes through the gas flow, it absorbs contaminants, such as carbon dioxide or hydrogen sulfide
Data Source
AI summary
Systems and methods for controlling an amine contactor are provided. An exemplary method includes determining a pickup ratio for a solvent in the contactor, measuring a temperature of a lower tray of the contactor, adjusting the pickup ratio based, at least in part, on the temperature, and adjusting a flow rate for an injection of lean solvent into the contactor based, at least in part, on the pickup ratio.