Cryogenic Gas Separation Using Segmented Pressure Cooling Circuits
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Solution Overview
Problem
Current methods for cryogenic separation of gas mixtures, such as those involving methane washing, require high pressure cycles to prevent methane solidification, leading to inefficient energy use and the need for reciprocating compressors due to low flow rates, which limits availability and increases maintenance requirements.
Innovation Solution
A method and installation that utilize a centrifugal compressor with a pressure difference between the washing column and separation column, allowing for a lower maximum cycle pressure and enabling the use of centrifugal technology instead of piston compressors, while maintaining the necessary pressure for methane washing, thereby reducing energy consumption and increasing compressor availability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a single low-pressure cycle level (2.6 bar abs) is used to cool the methane washing column, then the pressure level is defined by the temperature of -182°C to avoid solidifying methane, but this requires a high pressure cycle of 28 bar abs to condense CO at the tank reboiler, leading to high energy consumption
Solution Approach 1:
The invention divides the cooling function into two separate circuits: a first circuit operating at 2.6 bar abs to cool the methane washing column and prevent methane solidification, and a second circuit operating at lower pressure (1.6-2.0 bar abs) to cool the distillation column head. This segmentation allows each circuit to operate at its optimal pressure level, reducing the maximum cycle pressure from 28 bar abs to below 28 bar abs and decreasing energy consumption.
Solution Approach 2:
The invention changes the pressure parameter of the cooling circuit by introducing a pressure reduction step (relaxation) between the distillation column head cooling and the compressor inlet. The coolant is relaxed from the distillation column operating pressure to a lower pressure before entering the compressor, enabling the distillation column to operate at lower pressure while maintaining the necessary cooling temperature.
2Productivity
If a piston compressor is used due to low CO compressor flow rate, then the compressor can handle the low flow rate, but the availability is lower and requires installation of two reciprocating compressors to continue operating during maintenance periods
Solution Approach 1:
The invention replaces the piston compressor (reciprocating mechanical system) with a centrifugal compressor. The centrifugal compressor has higher availability and can be operated in parallel more efficiently. The pressure reduction in the system enables the centrifugal compressor to operate at optimal conditions, providing both the required flow rate handling and improved reliability.
3Use of energy by moving object
If the pressure of the coolant is reduced below 2.6 bar abs to lower the maximum cycle pressure, then energy consumption decreases, but the methane circulating in the washing column may solidify
Solution Approach 1:
The invention segments the cooling system into two independent pressure circuits. The first circuit maintains 2.6 bar abs pressure specifically for the methane washing column cooling to prevent methane solidification, while the second circuit operates at lower pressure (1.6-2.0 bar abs) for the distillation column head cooling. This segmentation allows the maximum cycle pressure to be reduced below 28 bar abs while protecting against methane solidification in the washing column.
4Object-affected harmful factors
If the CO/CH4 column operates at 2.6 bar abs minimum pressure to prevent methane solidification in the cooling circuit, then methane solidification is avoided, but the maximum pressure of the CO cycle must be at least 28 bar abs, increasing device complexity
Solution Approach 1:
The invention segments the pressure management into two independent circuits with different pressure levels. The washing column cooling circuit operates at 2.6 bar abs to prevent methane solidification, while the distillation column head cooling circuit operates at lower pressure (1.6-2.0 bar abs) after a relaxation step. This segmentation reduces the maximum cycle pressure requirement from 28 bar abs to below 28 bar abs, simplifying the overall pressure cycle configuration.
Solution Approach 2:
The invention introduces a pressure reduction parameter change (relaxation) in the cooling circuit between the distillation column head and the compressor inlet. This parameter change allows the distillation column to operate at lower pressure while maintaining the necessary cooling temperature, thereby reducing the maximum cycle pressure and simplifying the pressure cycle configuration.
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 required for cryogenic distillation, allows for the use of centrifugal compressors, and decreases maintenance needs by operating at lower pressures, enhancing the efficiency and reliability of the gas separation process.
Implementation Method 1
a gas mixture containing at least hydrogen, carbon monoxide and methane and possibly nitrogen shall be cooled in a heat exchanger
Implementation Method 2
the fluid used to cool at least one fluid withdrawn at an intermediate level of the washing column is sent to an intermediate level of a centrifugal compressor to be compressed
Implementation Method 3
a methane-rich liquid shall be introduced into the washing column as a washing liquid
Implementation Method 4
purification of syngas. We find: a washing unit with a liquid solvent to remove most of the acid gases contained in the synthesis gas
Implementation Method 5
a gas shall be extracted a tank liquid from the washing column and sent to a stripping column, vi) a tank liquid from the strip column is extracted and sent to a carbon monoxide and methane separation column
Implementation Method 6
this temperature level of -182°C is also used to cool the head of the CO/CH4 distillation column. This leads to a high pressure cycle of 28 bar abs to be able to condense the CO at the tank reboiler
Data Source
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AI summary
In a process for the combined production of a) a hydrogen-enriched gas and a carbon monoxide-enriched gas and/or b) a mixture of hydrogen and carbon monoxide by cryogenic distillation and scrubbing, a still liquor (17) is extracted from a scrubbing column and sent to a stripping column (31), a still liquor (35) is extracted from the stripping column and sent to a separating column (37) for carbon monoxide and methane and a cooling fluid is used at a pressure greater than that of the head of the separating column for cooling at least one fluid extracted at an intermediate level from the scrubbing column.