Method and device for separating air by cryogenic distillation
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Solution Overview
Problem
The existing cryogenic air separation devices face challenges with high startup temperatures in cold compressors, which can damage heat exchangers and require additional costs for pressure balancing, especially when using turbines connected in parallel.
Innovation Solution
Incorporating a check valve on the duct between the cold compressor and the turbines to divert air from the compressor directly to the turbines without passing through the heat exchanger during startup, reducing the pressure load on the heat exchanger and allowing for efficient operation and reduced costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If air from cold compressor is sent through heat exchanger during startup, then heat exchanger can be cooled effectively, but heat exchanger may be damaged by excessively hot air
Solution Approach 1:
A check valve is introduced as an intermediary device on the bypass duct to automatically control the flow path of compressed air. During startup, the check valve remains closed, forcing air through the bypass duct directly to the turbine, avoiding the heat exchanger. Once the heat exchanger reaches appropriate temperature, the check valve opens to allow air flow through the heat exchanger, thus protecting the heat exchanger from thermal shock while enabling effective cooling.
Solution Approach 2:
The system transitions from a static flow path to a dynamic one using the check valve. The check valve automatically changes the flow configuration based on pressure differential: during startup when compressor pressure exceeds turbine inlet pressure, the valve closes the heat exchanger path; during normal operation, the valve opens to restore the heat exchanger path, enabling adaptive protection and operation.
2Ease of operation
If additional duct is added to send air from cold suppressor to turbine without passing through exchanger, then startup is facilitated, but pressure load on heat exchanger increases requiring additional cost
Solution Approach 1:
The check valve acts as a flow mediator that directs compressed air through the bypass duct during startup, preventing air from entering the heat exchanger. This automatically manages the pressure load on the heat exchanger during startup without requiring manual intervention or additional pressure balancing equipment, thus facilitating startup while controlling pressure stress.
3Reliability
If check valve is disposed to prevent air from entering heat exchanger during startup, then heat exchanger is protected, but pressure computation for installation increases
Solution Approach 1:
The check valve serves as a passive flow control intermediary that automatically isolates the heat exchanger from the compressor outlet during startup based on pressure differential. This simple mechanical device protects the heat exchanger without requiring complex active control systems or sophisticated pressure computation algorithms, thereby maintaining operational simplicity while ensuring protection.
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 facilitates safe startup of cold compressors, reduces the risk of heat exchanger damage, and lowers the computational pressures required for the installation, thereby reducing overall costs and improving operational efficiency.
Implementation Method 1
compressed and purified air is cooled in a heat exchanger, a first part of the air is compressed in a compressor at an intermediate temperature of the heat exchanger and is sent to the heat exchanger, where it cools
Implementation Method 2
at least part of the second fraction is allowed to expand in the second turbine and is sent to the first column
Implementation Method 3
a check valve downstream of the heat exchanger and optionally upstream of the division point, the valve being used to prevent the air from moving in the opposite direction to that of normal operation and from arriving in the exchanger
Implementation Method 4
the double column comprising the first column and a second column, the second column operating at a lower pressure than the first column; oxygen and nitrogen enriched liquids are sent from the first column to the second column
Data Source
AI summary
Method for separating air by cryogenic distillation, wherein air is compressed in a compressor and is subsequently sent to a heat exchanger, with the air cooled in the exchanger being sent to a check valve downstream of the heat exchanger and subsequently to a turbine, the valve being positioned so that air from a short-circuiting duct cannot return to the exchanger from the compressor.