Cryogenic CO Separation With Staged Expansion and Reheat
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Solution Overview
Problem
The cryogenic separation of hydrogen and carbon monoxide in syngas production, particularly in coal gasification processes, faces inefficiencies due to insufficient cooling in the cold box, requiring additional liquid nitrogen for refrigeration and resulting in higher energy consumption for CO compressor operation.
Innovation Solution
The method involves subcooling and vaporizing CO-rich flows at different temperature levels before expansion and reheat in the exchange line, optimizing the thermosiphon pot and compressor stages to reduce thermal load and electrical energy consumption, while avoiding two-phase introduction pots and enhancing CO efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If free expansion between synthesis gas and pure CO is used for cooling, then refrigeration is partially achieved, but additional liquid nitrogen is required to complete the refrigeration balance
Solution Approach 1:
The patent changes the pressure parameter of the synthesis gas from high pressure (30-60 bar) to low pressure through expansion, utilizing the Joule-Thomson effect to achieve self-cooling. This parameter change allows the system to reduce its thermal load without requiring additional liquid nitrogen, as the expansion process itself provides the necessary refrigeration.
2Temperature
If liquid nitrogen is supplied to complete refrigeration balance, then cooling is sufficient, but energy consumption increases
Solution Approach 1:
The system uses its own synthesis gas as the refrigerant medium, allowing it to self-cool through controlled expansion. The synthesis gas circulates through heat exchangers and expansion devices, providing its own refrigeration service and eliminating the need for external liquid nitrogen supply, thereby significantly reducing energy consumption.
Solution Approach 2:
The patent utilizes phase transitions of the synthesis gas during expansion, where the gas undergoes cooling upon pressure reduction. This phase change process provides the necessary refrigeration effect internally, replacing the energy-intensive liquid nitrogen cooling system.
3Productivity
If CO compressor operates at high power, then CO production is maintained, but electrical energy consumption increases
Solution Approach 1:
The system performs preliminary cooling of the synthesis gas through expansion and heat exchange before it enters the CO compressor. By pre-cooling the gas and optimizing its thermodynamic state, the compressor operates more efficiently with reduced electrical energy consumption while maintaining the required CO production rate.
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 electrical energy consumption by optimizing the CO compressor's suction pressure and improves the cooling efficiency of the synthesis gas, allowing for more effective separation and reduced investment costs in the main exchange line.
Implementation Method 1
The synthesis gas at a pressure generally between 30 and 60 bar coming from a pretreatment unit (CO2 and MeOH separation) is cooled in the main exchange line and partially condensed
Implementation Method 2
The bottom liquid is sent to a medium-pressure stripping column (around 14 bar) after expansion
Implementation Method 3
The bottom liquid is subcooled in the exchange line to a temperature level less cold than the circuit mentioned above before being expanded, vaporized and reheated
Implementation Method 4
The interest of carrying out the subcooling of the carbon monoxide flows at different temperature levels is to reduce the KS and the thermal load
Implementation Method 5
expanded, sent to a thermosiphon pot then vaporized in the exchange line before being sent to the suction of the CO compressor
Implementation Method 6
sent to a thermosiphon pot then vaporized in the exchange line
Data Source
Figure 1
Figure 2
AI summary
In a method for cryogenically separating a mixture (1) of hydrogen and carbon monoxide optionally including small amounts of methane, argon, and nitrogen for the production of pure CO by partial condensation in one step, the mixture is cooled in an exchange line (3), partially condensed, and at least a portion of the liquid (11) resulting from the partial condensation is sent to the head of a depletion column (15), at least first and second flows (17, 19, 21) rich in carbon monoxide are derived from the depletion column, the first and second flows are cooled at different temperatures, the first flow is sent to a separating pot (27) after expansion, the gas (31) in the separating pot is reheated in the exchange line and sent to the first stage of a carbon monoxide compressor (33, 35, 37) including at least two stages, the second flow is reheated in the exchange line and is sent to a stage of the compressor downstream from the first stage, and the gas in the separating pot and the second flow are reheated in the exchange line at different pressures.