Cryogenic Air Separation Unit Venting for Warm Startup Heat Control
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Solution Overview
Problem
Starting an air separation unit from a warm condition poses challenges such as inability to remove heat, risk of booster surge, risk of reverse rotation, and risk of main heat exchanger damage due to high gas temperatures, especially when there is no separate heat exchanger for cooling downstream of the booster and upstream of the main heat exchanger.
Innovation Solution
A method involving a venting conduit to release heat from the system, where air is compressed and sent to the booster, and once the turbine reaches a given fraction of its critical speed, the venting conduit opens to release compressed air from the booster outlet to the atmosphere, allowing the main heat exchanger to cool down and reducing the risk of damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If air is compressed in the main air compressor and sent to the booster without a separate heat exchanger for cooling, then device complexity is reduced and compression power is reduced, but the risk of main heat exchanger damage due to high gas temperature increases
Solution Approach 1:
The venting conduit is opened before the turbine reaches its critical speed during startup, allowing compressed air to be vented to the atmosphere before it enters the main heat exchanger. This preliminary action prevents high temperature air from damaging the heat exchanger before the cooling system is fully operational.
Solution Approach 2:
The venting conduit acts as an intermediary pathway that diverts compressed air away from the main heat exchanger during the critical startup phase. This intermediate route allows the system to bypass the heat exchanger when it cannot handle high temperature air, protecting the heat exchanger while maintaining system functionality.
2Temperature
If the venting conduit is opened early during startup, then heat release is improved and heat exchanger damage is prevented, but the risk of booster surge increases
Solution Approach 1:
The system monitors turbine speed and uses this feedback to control the venting conduit operation. The venting conduit is opened only after the turbine reaches a given fraction of its critical speed, ensuring that the booster is operating in a stable regime before venting begins, thus preventing booster surge while enabling heat release.
3Reliability
If the turbine is started before reaching critical speed with the venting conduit closed, then reverse rotation risk is reduced, but heat removal capability is lost
Solution Approach 1:
The venting conduit operation is made dynamic rather than static. It remains closed during turbine acceleration to prevent reverse rotation, then opens automatically when the turbine reaches a given fraction of its critical speed. This dynamic control allows the system to adapt to changing operating conditions, preventing reverse rotation during startup while enabling heat removal during stable operation.
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 method effectively reduces the risks associated with starting an air separation unit from a warm state by managing heat release and preventing damage to the heat exchanger, while ensuring safe operation and efficient startup.
Implementation Method 1
a venting conduit connected downstream of the booster and upstream of the main heat exchanger and in that in order to start up the air separation unit, i) air is compressed in the main air compressor and sent to the booster inlet, ii) air is sent to the turbine inlet and iii) before the turbine is operating at a given fraction of its critical speed, the venting conduit remains closed and once the turbine is operating at said given fraction or above, the venting conduit is opened to send at least part of the air compressed in the booster from the booster outlet to the atmosphere
Data Source
AI summary
In a process for starting up an air separation unit, which is at a temperature of above 0° C., the air separation unit comprising a main air compressor for compressing the feed air, a booster driven by a turbine and a venting conduit connected downstream of the booster and upstream of the main heat exchanger wherein in order to start up the air separation unit, once the turbine is operating at said given speed, the venting conduit is opened to send at least part of the air compressed in the booster from the booster outlet to the atmosphere.