Air Separation Plant Control for Argon Column Nitrogen Balance
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Solution Overview
Problem
Existing air separation plant control systems are conservative and often fail to instantaneously adjust to critical nitrogen concentrations in the argon product, leading to reduced argon production and potential shutdowns of the argon column.
Innovation Solution
A computer program models the air separation plant's columns and condensers, performing dynamic material balances and vapor-liquid equilibrium calculations to optimize flow rates of air, oxygen, and argon feed streams, allowing for precise control of nitrogen and oxygen concentrations without direct measurements, thereby maximizing argon production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the reflux rate to the lower pressure column is reduced to decrease nitrogen content in the crude argon feed stream, then the nitrogen concentration is controlled within targeted ranges, but the flow rate of the crude argon feed stream is reduced with a consequent reduction in argon production
Solution Approach 1:
The control system performs preliminary action by continuously calculating estimated nitrogen concentrations in the crude argon feed stream using dynamic material balances and vapor-liquid equilibrium calculations. This allows the system to predict nitrogen accumulation trends and adjust the crude argon feed flow rate proactively before nitrogen levels become critical, thereby maintaining both concentration control and maximizing argon production without the need to reduce reflux rate.
Solution Approach 2:
The system implements feedback control by continuously monitoring process variables, calculating estimated nitrogen concentrations, and adjusting the crude argon feed flow rate based on these calculations. The control system compares estimated concentrations against targeted ranges and dynamically adjusts the feed rate to the argon column, creating a closed-loop control that simultaneously maintains concentration precision and maximizes productivity.
2Manufacturing precision
If the flow rate of the crude argon feed stream is reduced to control nitrogen content, then the nitrogen concentration in the crude argon feed stream is decreased, but the argon production is reduced
Solution Approach 1:
The control system calculates estimated nitrogen concentrations continuously and performs preliminary adjustments to the crude argon feed flow rate before nitrogen accumulation becomes problematic. This proactive control allows the system to maintain optimal feed rates for maximum production while keeping nitrogen concentrations within targeted ranges through timely adjustments.
Solution Approach 2:
The system uses feedback control to continuously monitor process conditions, calculate estimated nitrogen concentrations, and adjust the crude argon feed flow rate in real-time. This closed-loop control enables the system to maintain both precise nitrogen concentration control and maximum argon production by dynamically optimizing the feed rate based on current process state.
3Reliability
If a conservative control scheme is used to prevent nitrogen accumulation, then the argon column operates stably, but the argon production is not maximized due to reduced feed rates
Solution Approach 1:
The control system performs preliminary calculations of estimated nitrogen concentrations using dynamic material balances and vapor-liquid equilibrium models. This allows the system to maintain stable argon column operation by predicting nitrogen accumulation trends and adjusting feed rates proactively, while simultaneously maximizing production by avoiding excessive conservatism in control decisions.
Solution Approach 2:
The system implements feedback control that continuously monitors process variables, calculates estimated nitrogen concentrations, and adjusts the crude argon feed flow rate to maintain argon column stability. This closed-loop control enables the system to operate reliably at optimal production rates by dynamically adjusting feed rates based on real-time concentration estimates rather than using fixed conservative limits.
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 enables more aggressive control of argon production, reducing nitrogen accumulation and increasing argon yield by dynamically adjusting flow rates based on calculated concentrations, minimizing differences between measured and calculated oxygen concentrations, and ensuring stable operation of the argon column.
Implementation Method 1
current values of controlled variables are calculated in response to manipulated variables by conducting a dynamic material balance
Implementation Method 2
a vapor-liquid equilibrium calculation and an energy balance calculation for the stage models
Implementation Method 3
Argon products are produced by separating the argon from air through the use of cryogenic rectification that is conducted within an air separation plant
Implementation Method 4
The resulting compressed and purified air stream is then cooled to a temperature suitable for its rectification within a distillation column system through indirect heat exchange with waste and product streams
Data Source
AI summary
A method of controlling an air separation plant and a control system to optimize production of an argon product produced by the plant. A computer program is continually executed that has models of each column of the plant, a condenser reboiler and an argon reflux condenser. The models contain stage models of each stage of separation within each of the columns that when assembled are able to calculate current values of controlled variables in response to input variables applied to the models. The controlled variables serve as an input to a controller that controls manipulated variables comprising flow rates of an air feed stream to the air separation plant, a product oxygen stream removed from the lower pressure column and the crude argon feed stream such that the controlled variables are within a targeted range selected to optimize the production of the argon product.