Cryogenic Turboexpander Inlet Control for Variable Liquid Production
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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 potential damage and loss of separation performance.
Innovation Solution
A method and apparatus that manipulate both the turbine expansion ratio and inlet temperature of the turboexpander by controlling the flow rates of two streams within the main heat exchanger, ensuring the exhaust temperature remains at or near saturation temperature, allowing for greater variability in liquid production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the turbine expansion ratio is increased to improve refrigeration capacity and liquid production, then the liquid production rate increases, but the compressed mixture may be liquefied at the turboexpander exhaust causing poor efficiency and potential damage
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the inlet temperature of the turboexpander (a key parameter) to match the desired expansion ratio and liquid production rate. By changing the temperature parameter rather than solely relying on pressure ratio adjustments, the system achieves improved refrigeration capacity while preventing exhaust liquefaction that would damage the turboexpander.
Solution Approach 2:
The patent implements feedback control by continuously monitoring the turboexpander exhaust conditions and adjusting the main heat exchanger operation accordingly. The system uses feedback to ensure the compressed mixture enters the turboexpander at the optimal temperature, preventing harmful liquefaction at the exhaust while maintaining high liquid production rates.
2Reliability
If the turbine inlet temperature is decreased to prevent exhaust liquefaction, then turboexpander reliability improves, but the temperature of the expanded stream increases causing liquids within the column to vaporize and loss of separation performance
Solution Approach 1:
The patent uses parameter changes to precisely control the turboexpander inlet temperature within an optimal range. By making fine adjustments to the temperature parameter through the main heat exchanger, the system prevents both exhaust liquefaction (protecting reliability) and excessive temperature drops that would cause column liquid vaporization (protecting separation performance).
Solution Approach 2:
The patent applies dynamics by making the turboexpander inlet temperature a dynamic, adjustable parameter rather than a fixed value. The system continuously adapts the temperature based on operating conditions, allowing optimal protection of both the turboexpander and separation performance under varying load and environmental conditions.
3Productivity
If liquid production rate is increased by adjusting turbine flow, then more liquid product is produced, but wide swings in air compression requirements occur affecting energy efficiency
Solution Approach 1:
The patent applies parameter changes by adjusting the inlet temperature parameter to control liquid production rate independently of large compression flow changes. This allows the system to modulate output more efficiently, reducing the wide swings in compression energy requirements that occur with traditional flow-adjustment methods.
4Adaptability or versatility
If the flow rates of streams from the main heat exchanger are manipulated to control turboexpander inlet temperature, then liquid production variability increases, but the system complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the compressed mixture stream into multiple separate streams that pass through the main heat exchanger independently. By controlling the flow rates of these segmented streams, the system achieves precise temperature control at the turboexpander inlet, enabling high liquid production variability while managing complexity through modular flow control.
Solution Approach 2:
The patent applies universality by using the main heat exchanger to perform multiple functions: cooling the compressed mixture, controlling the turboexpander inlet temperature, and enabling variable liquid production. This multi-functional approach increases adaptability without proportionally increasing overall system complexity.
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 liquefaction issues, thereby maintaining separation performance and reducing energy costs.
Implementation Method 1
cooling the compressed gaseous mixture by indirect heat exchange with mixture component streams after having been purified
Implementation Method 2
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 3
rectifying the gaseous mixture within a separation unit. The separation unit has at least one distillation column to produce the mixture component streams
Implementation Method 4
Each of the columns has mass transfer elements such as trays or packing, for example, structured packing, which bring liquid and vapor phases of the gaseous mixture into contact with one another and effectuate mass transfer between the vapor and liquid phases
Implementation Method 5
The incoming feed is thereby distilled within the distillation columns or columns to form component streams enriched in the components of the gaseous mixture
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.