CO2 Purification via Elevated Pressure Oxidation
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Solution Overview
Problem
Current methods for removing sulfur dioxide (SO2) and nitrogen oxides (NOx) from carbon dioxide flue gas in oxyfuel combustion processes are inefficient, particularly at atmospheric pressure and low concentrations, and do not effectively address the need for a method that can handle the specific conditions of oxyfuel combustion processes in pulverized coal-fired power stations.
Innovation Solution
A method involving maintaining the carbon dioxide flue gas at elevated pressures in the presence of oxygen and water at temperatures up to 80°C to convert NOx to nitric acid and SO2 to sulfuric acid, followed by separation to produce SO2-free, NOx-lean carbon dioxide gas, utilizing counter-current gas/liquid contact devices for effective conversion and acid recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional desulphurisation and NOx reduction technologies are used at atmospheric pressure, then the process can be operated under standard conditions, but the removal efficiency of SO2 and NOx is insufficient particularly at low concentrations
Solution Approach 1:
The patent applies parameter changes by operating the scrubbing process at elevated pressures (e.g., 10-100 bar) rather than atmospheric pressure. This pressure increase enhances the absorption efficiency of SO2 and NOx in the liquid scrubbing medium, allowing effective removal even at low contaminant concentrations. The high pressure conditions improve the solubility and reaction kinetics of the acid gases with the scrubbing solution.
2Temperature
If the flue gas is cooled to moderate combustion temperature, then the combustion process becomes practical, but the NOx concentration in flue gas increases
Solution Approach 1:
The patent converts the harmful effect of increased NOx concentration (which is unavoidable at moderate combustion temperatures) into a beneficial outcome by using the NOx as an in-situ oxidizing agent. The NOx in the flue gas oxidizes SO2 to SO3 during the scrubbing process, which then reacts with water to form sulfuric acid that is easily removed. This eliminates the need for external oxidants and utilizes the harmful NOx for the beneficial oxidation of SO2.
3Loss of substance
If the flue gas is cooled to condense water vapour, then the CO2 product can be dried for pipeline delivery, but the combustion temperature becomes too low for practical furnace operation
Solution Approach 1:
The patent segments the temperature control and water removal functions into separate stages. The combustion process operates at high temperatures (practically viable for furnace operation) while the water vapour condensation and acid gas removal occur in a separate downstream scrubbing section where the gas is cooled. This segmentation allows the combustion zone to maintain optimal high temperature while the product gas is subsequently cooled and dried to pipeline specifications.
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 achieves the removal of 90% of NOx and virtually all SOx, producing a high-purity CO2 stream suitable for storage or use in enhanced oil recovery, while also addressing the challenge of low NOx concentrations and kinetic limitations in existing processes.
Implementation Method 1
maintaining said carbon dioxide flue gas at elevated pressure(s) in the presence of molecular oxygen ('O2') and water and NOx, at a temperature of no more than about 80°C for a sufficient time to convert NOx to nitric acid and all of said SO2 to sulfuric acid
Implementation Method 2
utilizing counter-current gas/liquid contact devices for effective conversion and acid recovery
Implementation Method 3
separating said sulfuric acid and nitric acid from said carbon dioxide flue gas to produce SO2-free, NOx-lean carbon dioxide gas
Data Source
AI summary
SO 2 and/or NO x are removed (C101, C102) from gaseous CO 2 (1, 2, 3, 4, 5, 11, 12, 13) at elevated pressure(s) in the presence of molecular oxygen and water and, when SO 2 is to be removed, NO x , to convert SO 2 to sulfuric acid (6) and/or NO x to nitric acid (14). The sulfuric acid (6) and/or nitric acid (14) is/are then removed from the gaseous carbon dioxide to produce SO 2 -free, NO x -lean carbon dioxide gas (20). The invention has particular application in the removal of SO 2 and/or NO x from carbon dioxide flue gas produced in an oxyfuel combustion process, for example, in a pulverized coal fired power station.