Variable Expansion Ratio Acid Gas Removal for CO2 Compression
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Solution Overview
Problem
Current acid gas removal systems for synthesis gas, particularly in hydrogen production, face inefficiencies in carbon dioxide compression and sequestration, with high energy consumption and costs due to constant expansion ratios in flash expansions, limiting the effectiveness of carbon dioxide liberation and subsequent compression.
Innovation Solution
Implementing a method with at least three pressure reduction stages in the acid gas removal system, where each subsequent stage has an increasing expansion ratio, allowing more carbon dioxide to be liberated at elevated pressures, thereby reducing the work required for compression and optimizing the liberation process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If constant expansion ratios are used in flash expansion stages, then the acid gas removal system operates with simple control, but compression power consumption increases significantly
Solution Approach 1:
The patent applies dynamics by transitioning from constant expansion ratios to variable expansion ratios that change with each flash expansion stage. The expansion ratio is dynamically adjusted based on the stage number, with later stages having higher expansion ratios than earlier stages. This dynamic approach optimizes the liberation of dissolved acid gases at different pressure levels, reducing the overall compression power required while maintaining manageable system complexity through a systematic progression of expansion stages
Solution Approach 2:
The patent implements parameter changes by systematically varying the expansion ratio parameter across different flash expansion stages. Instead of maintaining a constant expansion ratio, the system changes the expansion ratio parameter incrementally from one stage to the next, with each subsequent stage operating at a higher expansion ratio. This parameter optimization allows more efficient gas liberation at elevated pressures, directly reducing compression power consumption
2Use of energy by moving object
If more flash expansion stages are added to reduce compression power, then energy efficiency improves, but system complexity and capital cost increase
Solution Approach 1:
The patent applies segmentation by dividing the pressure reduction process into multiple discrete flash expansion stages, each operating at a specific expansion ratio. Rather than using a single large expansion stage or a continuous process, the system segments the decompression into sequential steps (first stage, second stage, third stage, etc.), where each stage liberates a portion of the dissolved acid gases. This segmentation allows optimization of gas liberation at different pressure levels while keeping each individual stage relatively simple
Solution Approach 2:
The patent applies dynamics by transitioning from constant expansion ratios to variable expansion ratios that change with each flash expansion stage. The expansion ratio is dynamically adjusted based on the stage number, with later stages having higher expansion ratios than earlier stages. This dynamic approach optimizes the liberation of dissolved acid gases at different pressure levels, reducing the overall compression power required while maintaining manageable system complexity through a systematic progression of expansion stages
3Ease of operation
If carbon dioxide is liberated at lower pressures, then expansion operation is simpler, but compression work increases by more than 50%
Solution Approach 1:
The patent implements parameter changes by systematically varying the expansion ratio parameter across different flash expansion stages. Instead of maintaining a constant expansion ratio, the system changes the expansion ratio parameter incrementally from one stage to the next, with each subsequent stage operating at a higher expansion ratio. This parameter optimization allows more efficient gas liberation at elevated pressures, directly reducing compression power consumption
Solution Approach 2:
The patent applies preliminary action by performing progressive gas liberation in sequential flash expansion stages before the final compression step. Each flash expansion stage pre-liberates a portion of the dissolved acid gases at progressively lower pressures, so that by the time the gas reaches the compressor, a significant amount of compression work has already been performed by the expansion process itself. This preliminary gas liberation reduces the burden on the compression system
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 decreases compression power consumption by up to 4.5% compared to prior art, enhancing the efficiency and reducing operational costs associated with carbon dioxide sequestration and pipeline transport.
Implementation Method 1
Acid gas removal systems which use a physical solvent employ solvents such as dimethyl ethers of polyethylene glycol, methanol, or propylene carbonate, which is brought into contact with the synthesis gas under high pressure (e.g., 1,200 psia) wherein the acid gases are preferentially absorbed by the solvent.
Implementation Method 2
The solvent is then depressurized in a series of 'flash expansions' which liberate the dissolved acid gases from the solvent.
Implementation Method 3
Sequestration of the carbon dioxide requires that substantial compression and pumping facilities be added to the acid gas removal system in view of the high pressures and large gas volumes which sequestration entails. It is calculated that, for pipeline transport and sequestration of the gases, the carbon dioxide will need to be compressed to pressures as great as 200 bar.
Data Source
AI summary
A method and apparatus for removing carbon dioxide from a synthesis gas stream containing hydrogen is disclosed. The method includes absorbing the carbon dioxide using a physical solvent under high pressure and then liberating the carbon dioxide in a series of expansion stages where the pressure on the solvent is reduced. The expansion ratio increases with each expansion stage. The apparatus includes expansion stages having throttling devices and expansion tanks operated at increasing expansion ratios. Carbon dioxide is liberated in this manner so as to minimize the energy required compress for transport via a pipe line for sequestration of the gas. Sequestration of the carbon dioxide is preferred to atmospheric venting to curb the release of greenhouse gases.