Two-Step Cryogenic Distillation to Prevent Solid CO2 Build-Up
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Solution Overview
Problem
Current cryogenic distillation processes for separating carbon dioxide from methane in acid gas face challenges such as the build-up of solid carbon dioxide inside distillation columns, leading to high costs and inefficiencies, particularly when dealing with high concentrations of acidic components like CO2 and H2S.
Innovation Solution
A two-step cryogenic distillation process at different pressures with an intermediate heating step, where the feed mixture is subjected to a high-pressure distillation followed by a low-pressure distillation, avoiding solid CO2 formation by heating the top product stream above its dew point, allowing for complete separation of methane and recycling the CO2-rich bottom stream.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If cryogenic distillation is used to separate CO2 from methane, then separation efficiency is improved, but solid CO2 builds up inside the distillation column
Solution Approach 1:
The patent applies preliminary action by heating the top product stream from the high-pressure distillation column before it enters the low-pressure distillation column. This heating step raises the temperature above the dew point, preventing CO2 from solidifying in the low-pressure column. By taking this preventive action beforehand, the process avoids solid CO2 build-up that would otherwise occur during cryogenic distillation at low pressures.
2Object-generated harmful factors
If a third component is added to prevent CO2 solidification, then solid CO2 build-up is avoided, but investment costs and operating costs increase
Solution Approach 1:
The patent applies parameter changes by modifying the temperature parameter of the top product stream through heating. Instead of adding a third chemical component to prevent solidification, the process changes the thermal state of the stream by heating it above the dew point before entering the low-pressure column. This parameter change (temperature increase) effectively prevents CO2 solidification without requiring additional chemical additives or complex separation units.
3Productivity
If CO2 and H2S are separated as low pressure vapours, then separation is achieved, but recompression costs increase
Solution Approach 1:
The patent applies equipotentiality by maintaining high pressure throughout the distillation process. Both the high-pressure and low-pressure distillation columns operate in a pressurized environment, and the bottom product from the low-pressure column is recycled back to the high-pressure column. This pressure management strategy allows the separated CO2 and H2S to remain in a high-pressure state suitable for direct reinjection, eliminating the need for additional recompression energy.
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 efficient separation of methane and CO2 without solid CO2 precipitation, reducing costs and operational complexities, and is suitable for high-acidic component mixtures, including biogas, by avoiding the need for additional components to prevent solidification.
Implementation Method 1
subjecting the feed mixture to a first distillation step in a first distillation column or a first section of a distillation column, at a pressure of at least 45 bar
Implementation Method 2
heating said first top product stream or a part of said first top product stream to yield a heated first top product stream
Implementation Method 3
subjecting the heated first top product stream or the heated part of said first top product stream, respectively, to a second distillation step in a second distillation column or a second section of the distillation column, at a pressure lower than 45 bar
Data Source
AI summary
The invention relates to a process for the removal of CO2 from acid gas by cryogenic distillation performed in two steps. The feed mixture is first distilled at high pressure (at least 45 bar) in a first distillation column. The top product or a part thereof is then, after heating, subjected to a second distillation step at a lower pressure (lower than 45 bar). The top product of the second distillation step is methane of high purity (more than 99 mol. %). The bottom product of the second distillation step is recycled back to the first distillation column. The method according to the invention allows complete separation of methane also at higher level of acidic components, is economical and does not result in solid CO2 build-up, which is a common problem in cryogenic distillation.