Boiler flue gas carbon capture technology

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CCUS (carbon capture, utilization and storage) refers to the capture, utilization, and storage of carbon, and it is considered an essential technology by the International Energy Agency in the context of the Paris Agreement. In terms of carbon capture, it is primarily used in the treatment of flue gases, process exhaust gases, stripping gases, and shift gases, as well as in the decarbonization of natural gas extracted from underground. It is applied to coal-fired boilers, oil-fired boilers, natural gas-fired boilers, petroleum coke-fired boilers, and water-coal slurry boilers in power plants; to sintering machines, pelletizing units, and blast furnaces in the metallurgy industry; to MTO reactors in the coal chemical industry; to coking furnaces; and to the exhaust gases from atmospheric and vacuum distillation units, catalytic cracking units, ethylene cracking furnaces, propane hydrogenation units, and other similar facilities in petrochemical plants. The CO2 concentration in these exhaust gases ranges from 2%v to 50%v, and decarburization treatment is required for all of them. Post-combustion capture technologies: adsorption method (long process, many units required, high investment), low-temperature distillation method (high energy consumption), membrane separation method (high consumption of materials, high costs), physical absorption method, and chemical absorption method, etc. Among them, chemical absorption is the main technical approach currently used for capturing CO2 from large stationary emission sources such as coal-fired and gas-fired power plants, with organic amine solutions being the commonly used absorbents. This technology utilizes the dual acidity of CO2 and employs a weak alkaline absorbent to capture CO2 from exhaust gases, thereby allowing purified flue gas to be discharged. The absorbent bound to CO2 is desorbed in a desorption tower to obtain CO2 product. Since CO2 absorption and desorption utilize temperature variation, it is crucial to reduce energy consumption during desorption. MSTN-CO2C carbon dioxide capture technology developed by Beijing Meiston Company has undergone extensive research, development, optimization, and improvement in terms of reagents and processes; it uses a special two-phase absorbent to reduce the load associated with solvent recovery, thereby significantly lowering energy consumption. The system mainly includes a CO2 absorption tower, a CO2 regeneration tower, an amine liquid purification unit (APU), an amine liquid filtration unit (AFU), and a phase separation system. 1. Introduction to the technical principle: The flue gas first enters the bottom of the absorption tower, while the absorbent is sprayed from the top of the tower. Inside the tower, the flue gas comes into countercurrent contact with the absorbent. During this mass transfer process from the gas phase to the liquid phase, CO2 is efficiently absorbed, resulting in the formation of carbamate. The purified flue gas is discharged from the top of the absorption tower. The reaction principle equations are given as (1) to (3). CO2 + H2O → H+ + HCO3-- (reversible) (1)
HCO3-- → H+ + CO32- (reversible) (2)
R1R2R3N + H+ ⇌ R1R2R3NH+ (3)
The absorbent forms an ammonium salt with H+, thereby driving the above reactions to the right. The absorbent that has absorbed CO2 is discharged from the bottom of the absorption tower and enters the desorption tower. There, the carbamate or bicarbonate is heated to decompose and release CO2. The regenerated absorbent is then discharged from the bottom of the desorption tower and sent back to the absorption tower for reuse. The CO2 desorbed gas is discharged from the top of the desorption tower, yielding CO2 with a purity of up to 95-99%, which then enters subsequent treatment units. For special application requirements, distillation can be used to achieve a CO2 purity of 99.9% to 99.999%. The \"combination process of purification through washing, adsorption drying, and low-temperature distillation\" is employed, which includes steps such as pressurization, washing, adsorption, drying, liquefaction, and distillation in order to produce high-purity food-grade and electronic-grade carbon dioxide. II. Technical features: Chemical absorption is used for decarbonization, requiring the absorbent to have a high selective absorption capacity for CO2. An alkaline mixed amine absorbent is used, with an amine concentration of 50% to 75%. While ensuring the efficiency of CO2 absorption, the absorbent can be desorbed and regenerated with low energy consumption. The principle by which this process reduces energy consumption in regeneration is to lower the reboiler load of the desorption tower by reducing the amount of rich liquid flow entering it. Furthermore, by heat exchange between the lean and rich solutions, the temperature of the lean solution is reduced, thereby decreasing the amount of circulating water required in the lean solution cooler. (1) The CO2 absorption efficiency can reach over 99.999% ； (2) The product gas CO2 has a high purity, with low moisture content