Cryogenic Air Separation Unit Venting for Warm Start-Up Heat Removal
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Solution Overview
Problem
Starting up a cryogenic air separation unit from a warm condition poses risks such as inability to remove heat, booster surge, reverse rotation of the booster, and damage to the main heat exchanger due to high gas temperatures, especially when the unit has been shut down for maintenance or initial start-up.
Innovation Solution
A method involving a venting conduit to release heat from the system, bypass conduits, and controlled valve operations to manage air flow during start-up, ensuring safe and controlled temperature management within the air separation unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If air is compressed in the main air compressor and sent to the main heat exchanger during start-up from a warm condition, then the air separation unit can begin operation, but the main heat exchanger cannot remove heat effectively due to high inlet temperature
Solution Approach 1:
The patent introduces a bypass conduit as an intermediary pathway that allows air to bypass the main heat exchanger during start-up. This mediator enables the air flow to reach the booster without passing through the heat exchanger, thus avoiding the heat removal problem while still enabling system start-up.
Solution Approach 2:
The air flow path is segmented into two separate routes: a normal path through the main heat exchanger for regular operation, and a bypass path for start-up conditions. This segmentation allows the system to optimize performance for different operational states by selecting the appropriate path.
2Device complexity
If air is sent directly to the booster without cooling in a separate heat exchanger, then equipment cost and compression power are reduced, but the risk of booster surge and reverse rotation increases during warm start-up
Solution Approach 1:
The system dynamically adjusts the air flow path based on operational conditions. During start-up from warm condition, the bypass conduit is activated to protect the booster. During normal operation, the air flows through the main heat exchanger. This dynamic adaptation allows the simplified configuration to operate reliably under different conditions.
Solution Approach 2:
The bypass conduit provides a preliminary protective action by allowing air to bypass the heat exchanger during conditions when cooling would be ineffective (warm start-up), preventing the harmful effects of booster surge and reverse rotation before they can occur.
3Temperature
If the venting conduit is kept open during start-up to remove heat, then temperature management is improved, but the system cannot achieve normal operation mode
Solution Approach 1:
The venting conduit operates periodically rather than continuously. It is opened during the start-up phase when heat removal is needed, and then closed when normal operation is achieved and the system can maintain temperatures through regular operation. This periodic action allows temperature management during transition while enabling normal operation thereafter.
Solution Approach 2:
The venting conduit provides preliminary heat removal action during the start-up phase to bring the system to a temperature state where normal operation can commence. Once this preliminary cooling is achieved, the venting function is discontinued and normal operational cooling takes over.
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
Reduces the risks of heat removal failure, booster surge, and main heat exchanger damage by effectively managing temperature and airflow during the start-up process, ensuring safe and efficient operation of the air separation unit.
Implementation Method 1
using a venting conduit to release heat from the system to produce cold
Implementation Method 2
The air from the booster is generally cooled in a separate heat exchanger before being sent to the main heat exchanger in which the products of the air separation unit are warmed
Implementation Method 3
air is compressed in the main air compressor
Data Source
Figure 1
AI summary
In a process for starting up an air separation unit which is at a temperature of above 0℃, the air separation unit comprising a main air compressor (3) for compressing the feed air, a booster (4a) driven by a turbine (5a) and a venting conduit (50) 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.