Cryogenic Air Separation Pressure Control for Oxygen Pipelines
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Solution Overview
Problem
Air separation units (ASUs) face inefficiencies when supplying oxygen to pipelines with varying pressures, as they are designed to operate at constant pressures, leading to power consumption increases when pipeline pressure decreases.
Innovation Solution
The method involves designing ASU equipment and implementing a process control strategy to automatically adjust the production pressure of air gases (nitrogen and oxygen) to match pipeline pressure, using a control loop to adjust the discharge pressure of the booster air compressor and liquid oxygen pump, allowing the gaseous oxygen feed valve to be fully open and controlling the flow with a flow indicator controller.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the ASU is designed to operate at constant pressure, then the production efficiency is improved, but the power consumption increases when pipeline pressure decreases
Solution Approach 1:
The invention applies dynamics by transitioning from constant pressure operation to variable pressure operation. The ASU pressure is dynamically adjusted to follow pipeline pressure variations, allowing the system to adapt its operating conditions in real-time. This resolves the contradiction by enabling the system to maintain production efficiency while reducing power consumption during low pipeline pressure periods through automated pressure tracking.
Solution Approach 2:
The invention changes the pressure parameter from a fixed constant value to a variable that tracks pipeline pressure. By implementing automated control that continuously adjusts ASU output pressure based on pipeline pressure feedback, the system optimizes energy consumption while maintaining operational efficiency across varying demand conditions.
2Reliability
If the ASU pressure is set above the highest pipeline pressure, then the oxygen can be supplied to the pipeline, but power is wasted when pipeline pressure is below design pressure
Solution Approach 1:
The invention implements feedback control where pipeline pressure is continuously monitored and fed back to the ASU control system. This feedback loop enables the ASU to automatically adjust its output pressure to match actual pipeline pressure, ensuring reliable oxygen supply while eliminating energy waste from operating at unnecessarily high pressures when pipeline pressure is lower.
3Adaptability or versatility
If a control valve is used to let down pressure, then the pressure mismatch is resolved, but efficiency is reduced
Solution Approach 1:
The invention applies preliminary action by adjusting the ASU output pressure in advance to match pipeline pressure requirements, rather than using control valves to reduce pressure after production. This proactive pressure matching eliminates the need for throttling and maintains operational efficiency while achieving pressure adaptability.
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 reduces power consumption and maintains process stability by matching the air gas product pressure with the pipeline pressure, resulting in significant power savings without affecting flow rate or operational stability.
Implementation Method 1
compressing atmospheric air in the main air compressor to a pressure suitable for the cryogenic separation of air
Implementation Method 2
cooling the compressed air stream in a heat exchanger by indirect heat exchange against process streams from the cryogenic distillation column
Implementation Method 3
separating the air stream into a nitrogen stream and an oxygen stream in a cryogenic distillation column
Data Source
AI summary
A method for the production of air gases 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; and reducing the difference between the pipeline pressure and the delivery pressure. By operating the method in a dynamic fashion, a power savings can be realized in instances in which the pipeline pressure deviates from its highest value.