| Efficient and low energy consumption capture of low partial pressure CO2 in flue gas of coal-fired power plants is of great significance to promote the technological progress of CCUS in China and to achieve the goal of carbon peak in 2030 as scheduled.Organic amine absorption is one of the most mature and most suitable methods for CO2 capture in flue gas.However,the commercial water-based absorption technology(e.g.,MEA absorption technology)has not been satisfactory in the demonstration of low partial pressure CO2 capture in domestic coal-fired power plants.Solvent water consumes a lot of useless work in the process of rich solution regeneration and lean solution cooling,resulting in very high overall energy consumption,which seriously restricts the promotion and application of this technology.Compared with the water-based absorption process,the water-free absorption process replaces water with organic solvents with high boiling point and low heat capacity,which can effectively reduce the sensible heat of warming and latent heat of evaporation,thus reducing the overall energy consumption in the regeneration process.In this thesis,we have constructed a water-free system which can keep homogeneous phase before and after absorbing CO2,using 2-ethylhexylamine(EHA)as the main absorption reagent and diglyme,triglyme and tetraglyme as organic solvents.We combined the advantages of water-free system to save regeneration energy and homogeneous system to facilitate operation,and achieved the capture of low partial pressure CO2 in flue gas with high efficiency and low energy consumption.The viscosity and time-dependent absorption amount of EHA+glyme water-free absorbent were measured,and the effects of glyme type,absorbent composition and temperature on the absorption amount,apparent absorption rate and activation energy were clarified by using Weiland equation,Lagergren model,modified Avrami model and Arrhenius equation.The competitive effects of EHA concentration and solution viscosity on the absorption performance were also clarified.Then the reaction mechanism of EHA and CO2 in organic solvent atmosphere was deduced.We selected diglyme as organic solvent and optimized the composition of EHA+diglyme absorbent.Considering the high water vapor content in coal-fired flue gas and the resulting water-lean absorption conditions,we measured the whole process characteristics of absorption-desorption of EHA+diglyme for low partial pressure CO2 under a series of water-lean conditions,and clarified the influence of water content and desorption temperature on desorption capacity and efficiency.The cycle stability of the absorbent was verified and the mechanism of CO2 absorption and desorption in the homogeneous water-lean system was revealed by 13C NMR characterization to determine the evolution of system composition.In addition,based on the two ways of electric energy consumption and average isobaric heat capacity,we established the estimation method for regeneration energy consumption and analyzed its influencing factors.A pilot packed tower was set up and the Dg16 type polypropylene step ring was taken as packing to test the capture efficiency and mass transfer performance of EHA+diglyme water-lean system for low partial pressure CO2 in simulated flue gas,and then the effects of operating conditions,such as gas-liquid ratio,CO2 partial pressure and packing height,on the capture performance were clarified.It provides basic data for the design of CO2 capture process based on water-lean absorption in packed tower.In summary,a homogeneous EHA+diglyme water-free(water-lean)system with high efficiency and low energy consumption was constructed,and its capture efficiency for low partial pressure CO2 in flue gas was verified.The whole process of absorption-desorption and the CO2 capture performance in the packed tower showed that the performance of the water-lean system is better than that of the water-based MEA absorption process which has been in commercial operation,not only in terms of the absorption capacity and absorption rate,but also in terms of the desorption capacity,desorption rate,desorption efficiency and regeneration energy consumption.Therefore,the homogeneous water-free(water-lean)system constructed in this thesis is of great significance for the efficient and low energy consumption capture of low partial pressure CO2 in coal-fired power plant flue gas,and has a good application prospect. |
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