Process and apparatus for the separation of a stream containing carbon dioxide, water and at least one light impurity including a separation step at subambient temperature
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Solution Overview
Problem
Current processes for separating carbon dioxide from oxycombustion flue gases at subambient temperatures are inefficient in energy usage and CO2 recovery, particularly in regenerating adsorption units and handling impurities.
Innovation Solution
The process involves recycling the permeate from a membrane unit into the feed gas compressor at an inter-stage, allowing for improved energy efficiency and high CO2 recovery by compressing the stream in multiple stages and using permeation units to regenerate the adsorption unit, with optional configurations including multiple membrane stages and phase separators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the permeate from the membrane unit is vented or sent to the boiler, then the adsorption unit can be regenerated, but the pressure energy of the permeate is wasted and overall energy efficiency is reduced
Solution Approach 1:
The permeate stream serves dual purposes: it regenerates the adsorption unit and its pressure energy is recovered by injecting it into the compressor inter-stage. The system uses its own permeate pressure to drive part of the compression work, eliminating the need for separate energy input for permeate handling and improving overall energy efficiency.
Solution Approach 2:
The permeate stream is utilized for multiple functions: it provides regeneration gas for the adsorption unit and simultaneously serves as a pressure source for compressor inter-stage injection. This multi-functional use of the permeate stream maximizes its value and reduces energy losses.
2Use of energy by moving object
If single-stage compression is used, then the system is simpler, but the energy efficiency and CO2 recovery are reduced
Solution Approach 1:
The compression process is divided into multiple stages with inter-cooling between stages. This segmentation allows for more efficient compression by reducing the work required compared to single-stage compression, as each stage operates at lower pressure ratios and benefits from inter-stage cooling that reduces gas temperature and volume.
3Loss of substance
If the adsorption unit is regenerated with high purity CO2, then CO2 recovery is improved, but the complexity of the regeneration system increases
Solution Approach 1:
The membrane unit acts as an intermediary that separates CO2 from the feed stream to produce a concentrated CO2 stream for adsorption unit regeneration. The compressor inter-stage injection serves as another intermediary that enhances the CO2 concentration in the regeneration gas by injecting high-pressure CO2-rich permeate into the compression stream.
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 enhances energy efficiency and maintains high CO2 recovery by valorizing permeate pressure and optimizing the use of permeate in regenerating the adsorption unit, reducing the need for additional ASU production and improving overall system efficiency.
Implementation Method 1
a feed stream is purified in an adsorption unit to remove water and form a dried stream
Implementation Method 2
the adsorption unit is regenerated using a regeneration gas, the regeneration gas is formed by separating by permeation in a permeation unit the dried compressed stream or a gas derived therefrom
Implementation Method 3
the dried stream or a stream derived therefrom is cooled to a subambient temperature and separated by partial condensation and/or distillation in a separation apparatus
Data Source
AI summary
In a process for the separation of a stream containing carbon dioxide, water and at least one light impurity including a separation step at subambient temperature, the feed stream is compressed in a compressor comprising at least two stages to form a compressed feed stream, the compressed feed stream is purified in an adsorption unit to remove water and form a dried compressed stream, the dried compressed stream or a stream derived therefrom is cooled to a subambient temperature and separated by partial condensation and/or distillation in a separation apparatus, liquid enriched in carbon dioxide is removed from the separation apparatus, the adsorption unit is regenerated using a regeneration gas and the regeneration gas is formed by separating, by permeation in a permeation unit, the dried compressed stream or a gas derived therefrom, the permeate of the permeation unit constituting the regeneration gas.