Cryogenic CO Recovery With Cascade Expansion and Lower Compression Work
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Solution Overview
Problem
Current methods for cryogenic gas separation of hydrogen (H2) and carbon monoxide (CO) are economically inefficient due to high energy requirements and fluctuations in product yields, particularly when dealing with synthesis gas from heavy oil gasification, which affects the purity and availability of CO and H2 products.
Innovation Solution
A cascade expansion process for liquid CO from the separating column, where the CO stream is separated into liquid and gaseous fractions after each partial expansion, with part of the liquid fraction passed to the next cascade stage and the remaining liquid and gaseous fractions fed to a heat exchanger or directly to the CO product stream, optimizing compressor input pressure and minimizing energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If liquid CO is expanded in a single stage to the required pressure, then the compression process is simpler, but the energy requirement of the CO compressor increases significantly
Solution Approach 1:
The expansion of liquid CO is divided into multiple cascade stages, where each stage expands the liquid to an intermediate pressure level. The gas fraction from each stage is separated and fed to the compressor at progressively higher pressure levels, while liquid from subsequent stages is expanded to lower pressure levels. This segmentation of the compression process into multiple stages reduces the total energy requirement compared to single-stage compression.
Solution Approach 2:
The system dynamically adjusts the pressure levels at which gas fractions are fed to different compressor sections based on the cascade expansion stages. The compressor receives gas at varying pressure levels from different cascade stages, optimizing the compression process by matching the dynamic pressure requirements with the expansion characteristics of each stage.
2Temperature
If more liquid CO is used for cooling the feedstock stream, then the cooling capacity increases, but the amount of CO available for compression and product formation decreases
Solution Approach 1:
The system changes the pressure parameter of the CO stream at different stages of the cascade expansion. By expanding liquid CO to progressively lower pressure levels in each cascade stage, the system generates gas fractions at optimized pressure levels for compressor input, thereby maximizing the amount of CO available for compression while maintaining sufficient liquid CO for cooling purposes.
3Loss of energy
If gas fractions are fed to the compressor at lower pressure levels, then the compression work increases, but the system can use more liquid CO for cooling
Solution Approach 1:
The cascade expansion process segments the CO stream into multiple pressure levels, with each cascade stage producing gas at a specific intermediate pressure. This segmentation allows the compressor to receive gas at progressively higher pressure levels from different cascade stages, minimizing the total compression work required while ensuring sufficient liquid CO remains for cooling the feedstock stream.
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 reduces the energy requirement of the CO compressor, increases CO yield, and enhances the purity and efficiency of CO and H2 production by ensuring the gas fractions are fed at the highest possible pressure, while maintaining sufficient liquid CO for cooling, thereby improving overall economic efficiency.
Implementation Method 1
the liquid CO is expanded in a cascade fashion from the bottom of the separating column, with the CO stream being separated into a liquid and a gaseous fraction after each partial expansion
Implementation Method 2
Heat exchangers are vaporized and heated by indirect heat exchange against process streams to be cooled or only heated
Implementation Method 3
single-stage partial condensation with subsequent low-temperature fractionation of the partial condensation of CO-rich, H2-containing condensate formed and separated
Data Source
AI summary
The production of a gaseous carbon monoxide product stream is carried out by decomposition of a feedstock stream (1) composed of hydrogen and carbon monoxide in a cryogenic gas decomposition unit by cooling through indirect heat exchange against a heating process stream. CO-rich and H 2-containing condensate is formed by a single-step partial condensation. H 2-rich and CO-containing gas fraction (flash gas) is separated by a cryogenic fractioning of the condensate in a separating column (T). A liquid CO (11) with product purity is extracted as a sump product in the separating column. The production of a gaseous carbon monoxide product stream is carried out by decomposition of a feedstock stream (1) composed of hydrogen and carbon monoxide in a cryogenic gas decomposition unit by cooling through indirect heat exchange against a heating process stream. CO-rich and H 2-containing condensate is formed by a single-step partial condensation. H 2-rich and CO-containing gas fraction (flash gas) is separated by a cryogenic fractioning of the condensate in a separating column (T). A liquid CO (11) with product purity is extracted as a sump product in the separating column and evaporated, heated and led into a CO compressor (C1) A gaseous CO is compressed by compressor sections at product pressure and the liquid CO is cooled against the heating process stream and split up into partial streams, which are relaxed at a pressure level against a cooling process stream. The liquid CO partial streams are released at the suction face of another compressor section. The liquid CO from the sump of the separating column is strongly under cooled at the lowest pressure level to form a liquid-gas mixture separated in a separator (D1) during the relaxation. The H 2-rich and CO-containing gas phase is heated through indirect heat exchange against cooling process streams. The feedstock stream for the cryogenic gas-separating unit is produced from a synthetic gas by cleaning in a CO 2washing and an adsorbent station (A). The H2-rich and CO-containing gas fraction is used for the recycling of the adsorbents in the adsorbent station after its warming up. The gas fraction is separated into a hydrogen fraction and a CO/H 2mixture in a membrane unit. The hydrogen fraction is used for the recycling of the adsorbents and the CO/H2 mixture is employed for the extraction of carbon monoxide after cooling against heating process streams of the column. An impure gas from adsorbent station used for the recovery of the adsorbent is cleaned in a pressure variable adsorbent station and delivered at a battery limits. A rest gas (37) from the pressure variable adsorption station is led back into the synthesis gas before the CO 2washing. Liquid nitrogen is supplied from beyond the battery limits for cooling process and evaporated in a heat exchanger (E1, E2), which is integrated in the separator and a part of the CO contained in the gas fractioning group is condensed. An independent claim is included for device for production of a gaseous carbon monoxide product stream.