Air Separation Flow Switching for Turboexpander Turndown
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Solution Overview
Problem
Air separation plants face limitations in cyclically adjusting liquid production rates due to surge issues and restricted pressure ratio variations, leading to limited power savings and turndown capabilities.
Innovation Solution
A branched flow path system that allows selective diversion of compressed refrigerant air streams between a booster compressor branch and a bypass branch, with independent recycle streams to prevent surge and vary production rates, enabling a higher or lower pressure ratio across the turboexpander.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the compressed refrigerant air stream is further compressed by a booster compressor to increase refrigeration and liquid product production, then the productivity and refrigeration capacity are improved, but the device complexity and risk of compressor surge increase
Solution Approach 1:
The system dynamically switches between two operational modes: using the booster compressor for high production rates and bypassing it for low production rates. This dynamic configuration allows the system to adapt to varying production demands while avoiding the complexities and surge risks associated with continuous booster compressor operation.
Solution Approach 2:
The compressed refrigerant air stream is divided into two separate flow paths: one through the booster compressor for high refrigeration needs and another bypassing the booster for lower refrigeration needs. This segmentation allows independent control of each path, enabling flexible adjustment of production rates without subjecting the booster compressor to unstable operating conditions.
2Loss of energy
If the booster compressor is bypassed to decrease refrigeration and liquid product production, then the power consumption is reduced, but the turndown capability and flexibility are limited due to surge issues
Solution Approach 1:
The system employs dynamic flow path switching that allows seamless transition between using and bypassing the booster compressor based on production demands. This dynamic capability significantly expands the turndown range, enabling the plant to operate efficiently across a wide spectrum of production rates from high to low without being constrained by surge limitations.
Solution Approach 2:
The bypass line acts as an intermediary flow path that provides an alternative route for the compressed refrigerant air stream when the booster compressor is not needed. This intermediary path enables smooth transition between high and low production modes, effectively expanding the system's adaptability and turndown capability.
3Power
If the pressure ratio across the turboexpander is increased to enhance refrigeration, then the refrigeration capacity is improved, but the compressor surge risk and operational stability deteriorate
Solution Approach 1:
The system dynamically adjusts the pressure ratio across the turboexpander by switching between two configurations: high pressure ratio when the booster compressor is active for maximum refrigeration, and low pressure ratio when the booster is bypassed for stable low-power operation. This dynamic adjustment prevents the compressor from operating in unstable surge regions while maintaining high refrigeration capacity when needed.
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 allows for a greater range of turndown in liquid production and significant power savings by preventing compressor surge and maintaining constant compressor speeds, thereby enhancing the flexibility and efficiency of air separation plants.
Implementation Method 1
expanding the compressed refrigerant air stream in a turboexpander to produce an exhaust stream
Implementation Method 2
expanding the compressed refrigerant air stream in a turboexpander to produce an exhaust stream that is introduced into the distillation column system
Implementation Method 3
the compressed refrigerant air stream is further compressed by a booster compressor prior to expansion to increase the refrigeration
Implementation Method 4
Air is separated in air separation plants that employ cryogenic rectification to separate the air into products that include nitrogen, oxygen and argon
Implementation Method 5
the air is separated in a higher pressure column into a nitrogen-rich vapor column overhead and a crude liquid oxygen column bottoms
Implementation Method 6
The lower pressure column operates at a lower pressure than the higher pressure column and is thermally linked to the higher pressure column by a heat exchanger known as a condenser reboiler
Implementation Method 7
The condenser reboiler condenses a stream of the of the nitrogen-rich vapor column overhead through indirect heat exchange with the oxygen-rich liquid column bottoms
Implementation Method 8
to create boilup in the lower pressure column by vaporization of part of the oxygen-rich liquid column bottoms
Data Source
AI summary
A method and apparatus for separating air in which production of the liquid products can be selectively varied between high and low production rates by varying the pressure ratio across a turboexpander used in imparting refrigeration with the use of a branched flow path. The branched flow path has a system of valves to selectively and gradually introduce a compressed refrigerant air stream into either a booster compressor branch having a booster compressor to increase the pressure ratio during high modes of liquid production or a bypass branch that bypasses the booster compressor to decrease the pressure ratio during low modes of liquid production. A recycle branch is connected to the booster compressor branch to allow compressed air to be independently recycled from the outlet to the inlet of the booster compressor during turndown from the high to the low liquid mode of liquid production to prevent surge.