Method and device for air separation by cryogenic distilling
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Solution Overview
Problem
The existing cryogenic air separation systems face challenges with the cold compressor's high inlet temperature during start-up, which can damage the heat exchanger, and require additional costs for pressure balancing and exchanger design due to the higher pressure imposed by the cold booster's output.
Innovation Solution
Incorporating a check valve on the pipe supplying air to the turbines from an intermediate point of the heat exchanger, preventing hot air from entering the exchanger during start-up and allowing normal operation flow, thus reducing the pressure on the exchanger and facilitating cost-effective design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If a cold compressor is used to compress air at low temperature, then the cooling capacity of the air separation system is improved, but the heat exchanger may be damaged by excessively hot air during start-up
Solution Approach 1:
A check valve is introduced as an intermediary device between the cold compressor and the heat exchanger. This valve automatically prevents hot air from the compressor during start-up from entering the heat exchanger, while allowing normal operation flow to pass through. This resolves the contradiction by protecting the heat exchanger without compromising the cooling capacity of the cold compressor system.
2Reliability
If an additional pipe is added to bypass the heat exchanger for the cold compressor, then the heat exchanger is protected during start-up, but the pressure calculation complexity and installation cost increase
Solution Approach 1:
The harmful function of the additional bypass pipe is extracted and replaced by a check valve integrated into the existing piping. The check valve provides the necessary flow control function without requiring complex additional piping, pressure balancing calculations, or waveform changes. This reduces device complexity while maintaining heat exchanger protection.
3Reliability
If the cold compressor discharge is connected directly to the turbine inlet, then the start-up safety is improved, but the pressure balancing requirements increase the heat exchanger design cost
Solution Approach 1:
The check valve operates automatically based on flow direction, requiring no external control or complex pressure balancing. It self-regulates to prevent backflow into the heat exchanger during start-up while allowing normal operation. This eliminates the need for complex pressure balancing calculations and waveform changes, reducing heat exchanger design cost while maintaining start-up safety.
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 solution enables safe start-up of the cold compressor without overheating the heat exchanger, reduces the exchanger's calculation pressure, and lowers the overall installation costs by allowing for earlier definition of operating pressures without extensive piping volume calculations.
Implementation Method 1
Compressed and purified air is cooled in a heat exchanger
Implementation Method 2
the first part of the air is expanded in a first turbine... the second part of the air... is expanded in a second turbine
Implementation Method 3
separating air by cryogenic distillation... the double column comprising the first column and a second column
Implementation Method 4
the first portion of the air is liquefied and sent to at least one first column
Data Source
Figure 1
AI summary
Cryogenic distillation air separation process in which air is compressed in a compressor (C2) and then sent to a heat exchanger (E), the air cooled in the exchanger being sent to a check valve (CL3) downstream of the heat exchanger and then to a turbine, the valve being positioned so that air from a bypass line (23) cannot flow back into the exchanger from the compressor.