Method and system for separating carbon dioxide from flue gas
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Solution Overview
Problem
Existing methods for separating carbon dioxide from flue gas risk carbon dioxide liquid evaporation due to temperature differences and heat exchange in buffer drums, leading to inefficiencies and potential losses.
Innovation Solution
The system bypasses buffer drums by directly supplying purified and cooled carbon dioxide liquids from the reboiler to heat exchangers, ensuring they are expanded to the same temperature, thus preventing evaporation and optimizing heat exchange efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If carbon dioxide liquid from cold side and warm side of reboiler are collected in a buffer drum, then carbon dioxide liquid can be accumulated, but evaporation occurs due to temperature differences and heat exchange
Solution Approach 1:
The patent divides the carbon dioxide liquid stream into two separate streams based on temperature origin (cold side and warm side of reboiler) and processes them independently through separate expansion valves and heat exchanger paths, preventing mixing and evaporation that would occur in a buffer drum
Solution Approach 2:
The patent applies preliminary cooling action by expanding the carbon dioxide liquid through expansion valves before it enters the heat exchangers, ensuring it is pre-cooled to the required temperature to prevent evaporation during subsequent heat exchange processes
2Ease of operation
If buffer drum with large heat exchanging surface is used, then carbon dioxide liquid can be collected and temperature equalized, but heat exchange causes evaporation risk
Solution Approach 1:
The patent segments the temperature equalization process into two independent parallel paths (cold side and warm side streams) that are processed separately through their own expansion valves and heat exchangers, eliminating the need for a buffer drum and its associated evaporation risks
Solution Approach 2:
The patent uses expansion valves as intermediary devices to control the temperature and pressure of carbon dioxide liquid streams before they enter the heat exchangers, acting as a mediator to achieve temperature equalization without direct heat exchange between streams of different temperatures
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 approach effectively prevents carbon dioxide liquid evaporation and enhances the separation process by maintaining consistent temperatures, improving the overall efficiency of carbon dioxide recovery without the need for large heat exchanging surfaces.
Implementation Method 1
the flue gas is passed through a sequence of heat exchangers (the so called cold boxes) where the flue gas is separated in carbon dioxide rich streams and carbon dioxide lean streams
Implementation Method 2
where the flue gas is separated in carbon dioxide rich streams and carbon dioxide lean streams, which are supplied into a distillation column
Implementation Method 3
The non-condensable gas, after expansion in an expansion valve, is passed through the heat exchangers (cold boxes) to cool them
Implementation Method 4
the carbon dioxide liquid from the distillation column is passed through a cold side of the reboiler, and already purified carbon dioxide from a high pressure compressor is passed through a warm side of the reboiler
Implementation Method 5
At the buffer drum carbon dioxide evaporation could occur, because of the heat exchange through the surface of the buffer drum and, in addition, because of the different temperatures of the carbon dioxide liquid from the cold side of the reboiler
Data Source
Figure 1
AI summary
The method for separating carbon dioxide from flue gas comprises cooling the compressed flue gas in heat exchangers (3a, 3b) separating a carbon dioxide rich liquid from a carbon dioxide lean gas, supplying the carbon dioxide rich liquid and the carbon dioxide lean gas into a distillation column (8), separating in the distillation column (8) non-condensable gas from carbon dioxide liquid, heating the carbon dioxide liquid (CDL) at a cold side of a reboiler (14) generating a purified carbon dioxide liquid (PCDL), expanding the purified carbon dioxide liquid (PCDL) and supplying the expanded carbon dioxide liquid (ECDL) to the heat exchangers (3a, 3b) for cooling, supplying the expanded carbon dioxide liquid (ECDL) from the heat exchangers (3a, 3b) to a high pressure compressor (25) to generate a compressed carbon dioxide vapor (CCDV), supplying a part of the compressed carbon dioxide vapor (CCDV) from the high pressure compressor (25) to a warm side of the reboiler (14) generating a cooled carbon dioxide liquid (CCDL), expanding the cooled carbon dioxide liquid (CCDL) and passing the cooled carbon dioxide liquid (CCDL) through the heat exchangers (3a, 3b) for cooling. The purified carbon dioxide liquid (PCDL) and the cooled carbon dioxide liquid (CCDL) are directly forwarded to the at least a heat exchanger (3a, 3b).