Intermediate-Pressure Purge Vessel for Cryogenic CO2 Solidification
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Solution Overview
Problem
Cryogenic distillation systems face challenges in preventing unwanted solidification of carbon dioxide outside the freezing section during startup, which can lead to equipment malfunction and production issues due to high CO2 concentrations and transient conditions.
Innovation Solution
Incorporating an intermediate pressure vessel to receive purges from the cryogenic distillation column, maintaining an intermediate pressure to reduce solidification of carbon dioxide, and using a heater to manage any formed solids, allowing for unassisted startup without the need for solidification inhibitors or clean methane reflux.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If purges are discharged directly to low pressure during startup, then CO2 solidification occurs in the purge system, but if purges are held at high pressure, then system complexity increases and startup time is extended
Solution Approach 1:
An intermediate pressure vessel is introduced as a mediator between the high-pressure distillation column and the low-pressure flare system. This vessel allows purges to be temporarily held at an intermediate pressure level, preventing CO2 solidification while maintaining system simplicity during startup operations.
Solution Approach 2:
The intermediate pressure vessel is prepared in advance during startup by establishing intermediate pressure conditions before purges are discharged. This preliminary action ensures that when purges are released, they do not undergo rapid pressure drop that would cause CO2 solidification.
2Reliability
If solidification inhibitors or clean methane reflux are used during startup, then CO2 solidification is prevented, but additional costs and equipment requirements increase
Solution Approach 1:
The system uses its own overhead stream as a purge source during startup, eliminating the need for external clean methane supplies or solidification inhibitors. The intermediate pressure vessel enables the system to handle its own startup purges using readily available process materials.
Solution Approach 2:
Instead of treating CO2-containing purges as harmful waste that must be eliminated, the system converts them into a manageable stream by holding them at intermediate pressure. This allows the CO2-rich purges to be safely discharged to the flare system without causing solidification problems.
3Ease of operation
If purges are discharged to atmospheric pressure during startup, then CO2 solidifies and causes plugging, but if purges are held at operating pressure, then purge system reliability decreases
Solution Approach 1:
The intermediate pressure vessel serves as a mediator that buffers the purge discharge process. It allows purge valves to operate reliably at high pressure while the vessel handles the pressure transition to atmospheric conditions, protecting the valves from solidification issues.
Solution Approach 2:
The pressure reduction process is segmented into two stages: first from high pressure to intermediate pressure (in the vessel), then from intermediate pressure to atmospheric pressure (at the flare system). This segmentation prevents rapid pressure drop that would cause CO2 solidification in the purge valves.
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 effectively reduces solidification and fouling within the distillation system, enabling reliable startup and operation by managing CO2 concentrations and preventing plugging, thus enhancing the efficiency and reliability of natural gas purification.
Implementation Method 1
an intermediate pressure vessel configured to receive a purge and operate at an intermediate pressure to reduce solidification of the purge
Implementation Method 2
using a heater to manage any formed solids
Implementation Method 3
cryogenic distillation system may provide for separating mixtures based on their relative volatility at cryogenic temperatures
Implementation Method 4
the operating temperature, pressure, and component concentrations may lead to solidification of the CO2
Data Source
AI summary
A system and method for an intermediate pressure vessel to receive a purge in a cryogenic distillation column system. The vessel operates at an intermediate pressure to reduce solidification of the purge. The cryogenic distillation column receives a natural gas having methane and acid gas. The column discharges an overhead stream rich in the methane, and a bottoms stream rich in the acid gas. An overhead system receives the overhead stream, and discharges a vapor methane product, and a cooled liquid for reflux to the cryogenic distillation column.