Activated Carbon CO2 Purification for SOx and NOx Removal
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Solution Overview
Problem
Flue gases from combustion processes, such as coal-fired boilers, contain high levels of CO2, but are contaminated with SOx and NOx, which must be removed to produce pure CO2 for enhanced oil recovery or sequestration, posing a challenge due to the complexity of existing removal methods.
Innovation Solution
A process involving activated carbon beds that adsorb and oxidize SO2 and NOx, followed by water washing to form sulfuric and nitric acids, which are then recycled, and a subambient-temperature recovery process using refrigeration to produce a CO2-rich stream, with subsequent separation and recycling of CO2.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If activated carbon beds are used to adsorb and oxidize SO2 and NOx, then impurity removal efficiency is improved, but process complexity increases due to multiple beds and washing steps
Solution Approach 1:
The process divides impurity removal into separate functional stages: first bed for SO2 adsorption and oxidation, second bed for NOx adsorption and oxidation, followed by sequential washing steps. This segmentation allows each component to be optimized independently while achieving high overall purity.
Solution Approach 2:
The activated carbon beds perform preliminary oxidation of SO2 to SO3 and NO to NO2 before the washing step, converting less soluble gases into more water-soluble forms that can be efficiently removed in subsequent washing operations.
2Quantity of substance
If water washing is used to desorb SO3 and NO2 from activated carbon, then acid production is improved, but water consumption increases
Solution Approach 1:
The process recovers the water used in washing steps by condensing and recycling it back into the system, transforming what would be waste water into a useful resource that reduces overall water consumption while maintaining acid production efficiency.
Solution Approach 2:
The washed activated carbon from one bed is reused to treat the other bed's effluent, creating a feedback loop where treatment capacity is maximized and water consumption is minimized through multiple passes of the same media.
3Manufacturing precision
If subambient-temperature recovery process is used to produce CO2-rich stream, then CO2 purity is improved, but energy consumption increases due to refrigeration requirements
Solution Approach 1:
The process utilizes phase transitions of CO2 (gas to liquid and back) during compression and expansion cycles to achieve separation and purification at subambient temperatures, leveraging the natural thermodynamic properties of CO2 rather than requiring continuous external refrigeration.
Solution Approach 2:
The system uses its own product stream (CO2) to provide refrigeration through expansion, where the phase change of CO2 from liquid to gas absorbs heat and cools the system, eliminating the need for separate refrigeration equipment and reducing energy consumption.
4Reliability
If multiple activated carbon beds are used in series, then impurity removal completeness is improved, but equipment investment increases
Solution Approach 1:
The activated carbon beds serve multiple functions: adsorption of impurities, catalytic oxidation of SO2 and NO, and subsequent washing to produce acids. This multi-functionality reduces the need for separate equipment for each function, lowering overall equipment investment while maintaining removal completeness.
Solution Approach 2:
The washed activated carbon from one bed is recovered and reused in another bed, maximizing the utilization of the carbon material and reducing the total quantity of activated carbon required, thereby lowering equipment and material investment costs.
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 method effectively removes SOx and NOx from CO2 streams, producing a high-purity CO2 product that can be recycled, enhancing the efficiency and cost-effectiveness of CO2 capture and utilization.
Implementation Method 1
adsorbing SO2 and NOx from said feed stream onto a regenerated first bed of activated carbon
Implementation Method 2
to convert said adsorbed sulfur dioxide to sulfur trioxide and to convert said adsorbed NO to nitrogen dioxide, thereby forming SOx-depleted NOx-depleted carbon dioxide
Implementation Method 3
washing said loaded first bed with water to desorb sulfur trioxide and nitrogen dioxide therefrom into said water to form an aqueous solution containing sulfuric acid and nitric acid
Implementation Method 4
subjecting the SO2-depleted NOx-depleted carbon dioxide to a subambient-temperature recovery process, employing refrigeration provided by expansion of at least one liquid carbon dioxide product stream
Data Source
AI summary
Carbon dioxide-containing feed stream such as flue gas is treated to produce a high-purity carbon dioxide stream by a series of steps including removing SOx and NOx with activated carbon, carrying out subambient-temperature processing to produce a product stream and a vent stream, and treating the vent stream by pressure swing adsorption or by physical or chemical absorption to produce a product stream which is recycled to the feed stream.