CO2 Distillation Column Reflux for Methane Retention
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Solution Overview
Problem
Existing processes for removing carbon dioxide from gas streams, such as those containing hydrocarbons, are economically unviable due to high capital and operating costs, especially as carbon dioxide concentration increases, and often result in the loss of lighter hydrocarbons during bulk removal.
Innovation Solution
A novel distillation process where the distillation column overhead vapor is compressed and cooled to partially condense, allowing for more efficient carbon dioxide removal, with the condensed liquid used for mid-level refrigeration and reducing power consumption by compressing the residue gas less, thereby increasing efficiency and reducing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If bulk removal of carbon dioxide is performed using semi-permeable membranes, then carbon dioxide removal efficiency is improved, but lighter hydrocarbons are lost in the carbon dioxide stream
Solution Approach 1:
The invention divides the carbon dioxide removal process into two distinct stages: (1) bulk removal through distillation fractionation, and (2) residual removal through solvent treatment. This segmentation allows each stage to be optimized for its specific function, with distillation handling the bulk separation and solvents handling the trace removal, thereby preventing hydrocarbon loss that would occur if solvents were used for bulk removal.
Solution Approach 2:
The distillation column is designed to remove only a portion (bulk) of the carbon dioxide, not all of it. By removing approximately 60-80% of carbon dioxide in the distillation stage and leaving residual amounts for solvent treatment, the process achieves high hydrocarbon recovery while still significantly reducing carbon dioxide content before final polishing.
2Productivity
If solvents or absorbents are used to remove carbon dioxide, then carbon dioxide removal capability is improved, but capital cost and operating cost increase with higher carbon dioxide concentration
Solution Approach 1:
The distillation column performs preliminary bulk removal of carbon dioxide before the gas stream enters the solvent treatment system. This preliminary action reduces the carbon dioxide load on the expensive solvent system, allowing it to operate more efficiently at lower capacity and reducing both capital and operating costs for the overall process.
Solution Approach 2:
The distillation column acts as an intermediary process between the feed gas and the solvent treatment system. It pre-treats the gas by removing bulk carbon dioxide and conditioning the stream, which enables the subsequent solvent system to operate more economically with reduced load and improved efficiency.
3Productivity
If distillation is used to fractionate the gas stream, then carbon dioxide bulk removal is improved, but power consumption increases due to compression requirements
Solution Approach 1:
The invention changes the operating parameters of the distillation column, specifically operating at lower temperatures and pressures compared to conventional designs. By optimizing these parameters and utilizing the specific vapor-liquid equilibrium characteristics of the gas mixture, the process achieves effective carbon dioxide separation with reduced compression requirements and lower power consumption.
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 process achieves over 75% carbon dioxide removal with greater than 99.8% methane retention in the residue gas, reducing power consumption by 8% and lowering operating costs, while improving carbon dioxide purity and reducing downstream processing needs.
Implementation Method 1
The expanded stream, comprising a mixture of liquid and vapor, is fractionated in a distillation column to separate residual methane, nitrogen, and other volatile gases as overhead vapor from the carbon dioxide and the heavier hydrocarbon components as bottom liquid product
Implementation Method 2
Instead of cooling the column overhead vapor to condense reflux for the fractionation column, the overhead vapor is compressed to higher pressure and then cooled to partially condense it
Implementation Method 3
the overhead vapor is compressed to higher pressure and then cooled to partially condense it
Implementation Method 4
The resulting condensate is mostly liquid carbon dioxide, which can be flash expanded to intermediate pressure and used to provide mid-level refrigeration to the process streams
Implementation Method 5
The gas is condensed as it is cooled, and the high-pressure liquid is expanded to an intermediate pressure
Implementation Method 6
The gas is condensed as it is cooled
Data Source
AI summary
A process and an apparatus are disclosed for removing carbon dioxide from a hydrocarbon gas stream. The gas stream is cooled, expanded to intermediate pressure, and supplied to a fractionation tower at a top column feed position. The tower overhead vapor stream is compressed to higher pressure and cooled to partially condense it, forming a condensed stream. The condensed stream is expanded to intermediate pressure, used to subcool a portion of the tower bottom liquid product, then supplied to the tower at a mid-column feed position. The subcooled portion of the tower bottom liquid product is expanded to lower pressure and used to cool the compressed overhead vapor stream. The quantities and temperatures of the feeds to the fractionation tower are effective to maintain the overhead temperature of the fractionation tower at a temperature whereby the major portion of the carbon dioxide is recovered in the tower bottom liquid product.