Turboexpander Inlet Temperature Control in Cryogenic Air Separation
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Solution Overview
Problem
Existing cryogenic rectification plants face challenges in efficiently controlling liquid production rates and turboexpander efficiency due to variations in energy supply costs and operational conditions, leading to issues such as poor separation performance and potential damage to turbines.
Innovation Solution
A method and apparatus that manipulate the turboexpander inlet temperature and expansion ratio by dividing a compressed gaseous mixture into two streams, controlling their flow rates to maintain the exhaust temperature at saturation, allowing for greater variability in liquid production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the pressure of the compressed mixture is increased to vary the expansion ratio of the turboexpander, then liquid production rate is improved, but the mixture may be liquefied at the exhaust of the turbine causing poor efficiency and potential damage
Solution Approach 1:
The patent changes the temperature parameter of the compressed stream by removing portions at different temperatures from the main heat exchanger. By controlling the flow rates of these temperature-different streams and combining them, the inlet temperature to the turboexpander is adjusted, which allows variation of liquid production rate while maintaining safe expansion conditions without liquefaction at exhaust.
Solution Approach 2:
The compressed stream is divided into two separate streams with different temperatures by removing them at different locations from the main heat exchanger. This segmentation allows independent control of temperature parameters, enabling precise adjustment of the combined stream temperature before turboexpander entry, thus resolving the contradiction between liquid production and turboexpander safety.
2Reliability
If the pressure is decreased to avoid liquefaction in turboexpander exhaust, then turboexpander safety is improved, but the temperature of the expanded stream increases causing liquids within the column to vaporize and loss of separation performance
Solution Approach 1:
By adjusting the temperature parameter of the compressed stream inlet to the turboexpander through controlled removal of streams at different temperatures from the main heat exchanger, the patent achieves optimal expansion conditions. This allows maintaining lower pressures that prevent exhaust liquefaction while controlling the expanded stream temperature to avoid excessive vaporization and maintain separation performance.
Solution Approach 2:
The system uses feedback control by monitoring the temperatures and flow rates of the removed streams, adjusting their proportions in the combined stream to maintain optimal turboexpander inlet temperature. This feedback mechanism ensures that expansion conditions remain within safe and efficient parameters, preventing both exhaust liquefaction and excessive column vaporization.
3Productivity
If flow to the turboexpander is adjusted by recycling air from the bottom of the higher pressure column to a compressor, then liquid product make is adjusted, but wide swings in air compression requirements occur
Solution Approach 1:
The patent extracts (removes) portions of the compressed stream at different temperatures directly from the main heat exchanger, bypassing the need for recycling air through the compressor. This extraction method allows adjustment of liquid product make by controlling the flow rates of removed streams, eliminating the wide swings in compression requirements that would result from recycling approaches.
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 the variability of liquid production, improves turboexpander efficiency, and prevents excessive vaporization in distillation columns, thereby optimizing plant operations and reducing energy costs.
Implementation Method 1
At least part of the combined stream is expanded with the performance of work within a turboexpander to supply refrigeration to the cryogenic plant
Implementation Method 2
cooling the compressed gaseous mixture by indirect heat exchange with mixture component streams after having been purified
Data Source
AI summary
Separation method and apparatus for separating a gaseous mixture, for example, air, in a cryogenic rectification plant in which a compressed stream is divided into subsidiary streams that are extracted from a main heat exchanger of the plant at higher and lower temperatures. The two streams are then combined and expanded in a turboexpander to generate refrigeration for the plant. The flow rates of the two streams are adjusted to control inlet temperature of a turboexpander supplying plant refrigeration and to minimize potential deviation of the turboexpander exhaust from a saturated vapor state. Control of the expansion ratio can advantageously be applied to allow variable liquid production from the rectification plant.