Study Of Novel Chemical Absorbents And Technologies To Absorb CO₂

Membrane absorption is one of the very prospect technologies to removal CO₂from flue gas. Novel absorbents and low regeneration energy consumptiontechnologies were explored to promote absorption rate and decrease regenerationenergy consumption.First typical single absorbents were studied for their absorption andregeneration performances systematically. It is found that the absorption rate andregeneration energy consumption of various absorbents have the following lawrespectively: PZ＞primary amines＞AMP＞amino acid salt＞secondary amines＞tertiaryamines, primary amines＜PZ＜amino acid salt＜secondary amines＜tertiary amines (PT,AMP). The maximum absorption capacities of PZ, AMP, AAAP and PT are all above0.5molCO₂/mol.Based on the research of single absorbents, in order to meet the requirement of"high absorption rate, low regeneration energy consumption", several researches onthe performances of absorption and regeneration were studied on direct contactbeach-scale experimental bench. In these researches, three typical absorbentmixtures, including the mixture of primary amines and tertiary amines, tertiaryamines and activators, secondary amines and sterically hindered amines, were testedrespectively. It was found that among these absorbents, the mixture of primaryamines with a small amount of tertiary amines worked best on absorption, yet themixture of secondary amines with a small amount of sterically hindered aminesworked best on regeneration energy consumption, followed by blends with mediumactivator addition to tertiary amines, and mixture of primary amines with a smallamount of tertiary amines.The absorption of carbon dioxide was tested in a hollow fiber membranemodule using the chosen absorbents from direct contact experiments. Keyparameters that influence the CO₂ removal performance of the three absorbents wereinvestigated. The blends of MEA with a small amount of MDEA, MDEA withmedium activator addition, DEA with a small amount of AMP were tested in the experiments. It is found that generally, they have advantages on every consideration.The CO₂ removal efficiency of MDEA+PZ/PT increased with increasing of PZ/PTconcentration, and worked best among the three absorbents. Liquid temperature andflow rate have modest effect on CO₂ removal efficiency. The CO₂ removalefficiency of all the absorbents improved with increasing of MDEA concentration.The CO₂ removal efficiency of MEA/MDEA and MDEA/PZ aqueous was70%～90%. It was the highest CO₂ removal efficiency among the three solutions inhollow fiber membrane modules, followed by DEA/AMP and MDEA/PT aqueous(40%～70%), and MDEA has the lowest (10%～40%).Decompression regeneration of the carrier solution was studied on carriersolution regeneration experimental beach. The results shows that the performance ofdecompression regeneration tums better with thinner carrier solution, lower initialCO₂ load, longer regeneration time and lower regeneration pressure. However, thelatter two factors are closely related to regeneration energy consumption. Theregeneration grade of 0.8mm thin carrier solution increased 54.45% compared withthermal-regeneration. And the energy consumption of decompression regeneration islower than thermal-regeneration.CO₂ from 100000Nm³/h flue gas absorption membrane system was designedand its economical efficiency was evaluated. CO₂ was designed to be removed inhollow fiber membrane modules, and regenerated in packed column. Theregeneration energy was supplied from the bottom reboiler. It was estimated that 24tons CO₂ which is more than 98% purity could be obtained within an hour. Thesystem total initial investment is 23.9 million yuan, the operating costs is about19.23 million yuan, and CO₂ recovery cost is 145.7yuan·(t CO₂)^-1. The membranemodules investment which accounts for 38.9% is the main factor of the system totalinitial investment. Steam consumption which accounted for 70.6% of the operatingcosts is the main factor of CO₂ recovery cost.