Cascade Distillation Liquid Return Bypass for Cryogenic Startup
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Solution Overview
Problem
In cascade distillation processes for isotope enrichment, achieving sufficient liquid head pressure for liquid return to earlier columns is challenging, leading to increased startup time and liquid hold-up, especially in cryogenic conditions where heat leak causes evaporation and reduces liquid storage efficiency.
Innovation Solution
A distillation apparatus with a bypass line connecting the liquid-return line and gas line ensures that evaporated gas is directed back into the gas line, preventing gas accumulation in the liquid-return line and maintaining liquid flow, while vacuum insulation and cooling with a cooling fluid help maintain liquid head pressure, allowing for efficient liquid return without rotary machines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If liquid pumps are used to flow liquid between distillation columns, then liquid can be moved reliably, but liquid hold-up increases and startup time becomes long
Solution Approach 1:
The patent replaces mechanical liquid pumps with a pressure difference-based liquid transfer system. Liquid is moved between distillation columns by creating pressure differences through gas flow control and condensation/evaporation processes, eliminating the need for mechanical pumping equipment and reducing liquid hold-up time.
Solution Approach 2:
The patent uses gas pressure and condensation/evaporation hydraulic principles to drive liquid flow. By controlling gas flow rates and utilizing phase change volume expansion, the system creates the necessary pressure gradients to move liquid through the cascade columns without mechanical pumps.
2Ease of operation
If liquid pumps are used in cryogenic distillation, then liquid can be circulated, but heat inleak increases
Solution Approach 1:
The patent eliminates mechanical liquid pumps from the cryogenic system, replacing them with passive pressure-driven liquid transfer. This removes the mechanical components that would generate heat through friction and motor operation, significantly reducing heat inleak in the cryogenic environment.
Solution Approach 2:
The system uses the inherent properties of the cryogenic fluid itself (phase change volume expansion) to drive liquid circulation. The evaporating liquid naturally expands and creates the pressure needed to push liquid through the system, making the circulation self-powered without external energy input that would cause heat inleak.
3Ease of operation
If pressure is increased toward the last column to enable gas return by pressure difference, then gas can be returned, but separation factor becomes small
Solution Approach 1:
The patent divides the cascade into distinct pressure zones, with each column operating at optimized pressure levels. The first column operates at higher pressure for efficient gas return, while subsequent columns operate at progressively lower pressures to maintain high separation factors, with pressure transitions managed through controlled phase changes.
Solution Approach 2:
The patent changes the operating pressure parameter along the cascade by utilizing phase change volume expansion. The evaporating liquid in each column naturally expands and pushes the gas phase to the next column at a lower pressure, creating a pressure gradient that maintains high separation factors throughout the cascade.
4Loss of time
If inner diameter of liquid-return line is reduced to decrease liquid hold-up, then liquid hold-up decreases, but liquid flow becomes difficult
Solution Approach 1:
The patent uses gas flow pressure and condensation/evaporation hydraulic principles to drive liquid through narrow return lines. By controlling gas flow rates and utilizing phase change volume expansion, the system creates sufficient pressure to overcome the resistance in small-diameter lines, achieving both low liquid hold-up and reliable flow.
Solution Approach 2:
The system preliminarily condenses vapor to liquid in controlled zones before return, ensuring the liquid is in a stable state for flow through narrow lines. The condensation process occurs at optimized pressure and temperature conditions that prepare the liquid for efficient flow through the restricted return geometry.
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 configuration stabilizes the distillation process, reduces startup costs, and enhances productivity by ensuring reliable liquid return and minimizing liquid hold-up, thus improving the efficiency of isotope enrichment without the need for pumps or blowers.
Implementation Method 1
evaporated gas generated in the liquid-return line
Implementation Method 2
a condenser which condenses the gas
Implementation Method 3
a reboiler which evaporates liquid
Implementation Method 4
vacuum insulation and cooling with a cooling fluid
Data Source
AI summary
A distillation apparatus of the present invention includes a distillation column group in which a plurality of distillation columns including a condenser and a reboiler is connected in the form of a cascade; a gas-feeding line which feeds gas from the distillation column to a latter distillation column; a gas line which introduces the gas from the distillation column to the condenser attached to the distillation column; a liquid-line which withdraws a condensed liquid from the condenser; a liquid-reflux line which introduces a part of the condensed liquid from the liquid-line to the distillation column; a liquid-return line which returns the remainder of the condensed liquid from the liquid-line to a former distillation column; a valve provided on the liquid-return line; and a bypass line which connects the liquid-return line and the gas line so as to flow an evaporated gas generated in the liquid-return line to the gas line.