Air Separation Plant Pressure Control for Variable Liquid Production
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Solution Overview
Problem
Air separation units (ASUs) face inefficiencies when supplying oxygen to pipelines with variable pressure due to the need to maintain constant production pressure, leading to suboptimal liquid production and increased energy usage.
Innovation Solution
Designing ASU equipment with flexibility to adjust gaseous oxygen production pressure to match pipeline pressure, combined with a process control strategy to automatically adjust product pressure, allowing for increased liquid production without altering the operating conditions of main or booster compressors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the ASU is designed to produce oxygen at a constant pressure above the highest pipeline pressure, then the ASU operates efficiently at steady state conditions, but energy is wasted through pressure let-down across control valves when pipeline pressure is below design pressure
Solution Approach 1:
The invention applies dynamics by making the ASU production pressure variable rather than constant. The system continuously adjusts the gaseous oxygen product pressure to follow the pipeline pressure dynamically, allowing the ASU to adapt to varying pipeline pressure conditions while minimizing energy waste through pressure let-down
Solution Approach 2:
The invention changes the pressure parameter from a fixed design value to a variable parameter that tracks pipeline pressure. By continuously adjusting the production pressure to match pipeline pressure, the system eliminates the need for pressure let-down across control valves and reduces energy losses
2Productivity
If the ASU operates at constant production pressure, then the operating conditions of main and booster compressors remain stable, but liquid oxygen and nitrogen production decreases when pipeline pressure drops
Solution Approach 1:
The system dynamically adjusts production pressure to follow pipeline pressure variations, enabling increased liquid production when pipeline pressure drops while maintaining compressor stability through controlled adjustments
Solution Approach 2:
The invention changes the production pressure parameter to vary with pipeline pressure, allowing the system to maximize liquid production during low pipeline pressure periods while maintaining overall process stability
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 enhances liquid oxygen and nitrogen production by increasing available refrigeration, reducing energy losses, and maintaining process stability, while minimizing power usage and capital expenses.
Implementation Method 1
cooling the gaseous oxygen in the heat exchanger against cold air streams to condense it to liquid oxygen
Implementation Method 2
condense it to liquid oxygen
Implementation Method 3
expanding at least a portion of the cold air in an expansion turbine to provide refrigeration for the system
Implementation Method 4
introducing the cold air into the distillation column for rectification therein
Implementation Method 5
A typical cryogenic air separation process
Data Source
AI summary
A method for the production of air gases with variable liquid production by the cryogenic separation of air can include the steps of sending a purified and compressed air stream to a cold box under conditions effective for cryogenically separating the air stream into an oxygen product and nitrogen using a system of columns, wherein the purified and compressed air stream is at a feed pressure when entering the system of columns; withdrawing the oxygen product at a product pressure; delivering the oxygen product at a delivery pressure to an oxygen pipeline, wherein the oxygen pipeline has a pipeline pressure; wherein during the second mode of operation, the method can include monitoring the pipeline pressure; reducing the difference between the pipeline pressure and the delivery pressure; and adjusting liquid production from the cold box. By operating the method in a dynamic fashion, additional liquid production can be realized in instances in which the pipeline pressure deviates from its highest value.