Research On Separation Of CO₂ From Flue Gas By Membrane Gas Absorption Method And Regeneration Of CO₂-rich Solutions

The absorption and capture of CO₂ from coal-fired flue gas is an important way to realize the goal of carbon reduction in China.CO₂ absorption and desorption processes based on hollow fiber membrane technology?MGA?are considered to be promising technologies due to their high absorption mass transfer flux and low regenerative energy consumption.However,the current membrane absorption and membrane desorption are mostly studied with a single absorbent,the performance and suitability of the mixed absorbent for membrane absorption and membrane desorption are unclear.In addition,the regeneration of CO₂-rich solutions has the defects of low desorption rate and low cycle absorption capacity.In view of this situation,this paper from the point of absorbent,has made a thorough study in four main aspects mainly,including the CO₂ absorption with MGA,absorbent wetting,regeneration of CO₂-rich solutions by membrane desorption and calcium desorption.In respect of MGA,the membrane absorption properties of the different single/mixed absorbent were compared,the differences of CO₂ absorption performance of mixed absorbent at different concentration/solute ratio were investigated,Combined with the optimization experiment,we concluded that,The results of CO₂ absorption were as follows:MEA>PG>PZ>MDEA and MDEA-MEA>MDEA-PG>MDEA-PZ.The absorption capacity of the mixed absorbent increases with increasing concentration and solute ratio,but too high concentration/ratio was not conducive to its practical application.In the non-regenerative mode,the optimum concentration of the mixed absorbent was 40wt%and the optimum solute ratio was MDEA:MEA/PG/PZ=1:0.8?molar ratio,full text as same?.In respect of membrane wettability with absorbent,the wettability of the membrane under different concentration/ratio was investigated,the effects of the wettability on the membrane wetting speed and CO₂ absorption performance were determined by the membrane wetting rate test and the membrane absorption test.The results showed that the value of membrane wettability were MDEA>MEA>PG and MDEA-PG>MDEA-MEA.When the MGA system was in the long-term running state,CO₂ mass transfer performance of the mixed absorbent with high-solute ratio,which had better CO₂ absorption capability,was less than that of the low-ratio mixed absorbent.Therefore,in the absorption-desorption regeneration mode,the ideal ratio of mixed absorbent was 1:0.4.The relationship between wettability and wetting rate or membrane absorption property was that the greater the wettability,the greater the wetting rate,the lower the CO₂ removal rate/mass transfer rate.In respect of CO₂-rich solutions membrane desorption,using the simulated CO₂-rich solution as the membrane desorption object,the desorption properties of single MDEA-rich and MDEA-MEA mixed solution were investigated under different absorption characteristics?CO₂ loading,solute ratio?and membrane desorption operating conditions?temperature,pressure,liquid flow rate,etc.?,and drew the following conclusions:The desorption rate of single-rich solution increases with the increase of CO₂ loading,and the desorption reaction can be completed in 35min with desorption rate 58.41%.For the mixed solution,the membrane desorption process to be slower?>40min?.The desorption rate was 55.28%at the optimum solute ratio?1:0.6?.Appropriate increase in desorption temperature,liquid flow rate,reduce the desorption pressure on the membrane desorption of liquid desorption effect improved significantly.It was proved that the reasonable temperature range was 45⁶5?the reasonable pressure range was 30¹0kPa,the optimal liquid flow rate was 0.08m/s.For MDEA-MEA mixed absorbent,the reasonable temperature range was 50⁶0?,the ideal pressure range was 40²0kPa,the best liquid flow rate was 0.08m/s.In respect of CO₂-rich solutions calcium regeneration,First,the mechanism of desorption of MEA enrichment by calcium method was explained.Then,the ideal CO₂ treatment loading and Ca?OH?₂ dosing ratio were 0.84mol/L and C:Ca=1:1,respectively,the desorption time was 15min under this condition.Finally,by changing the three operating parameters of solution pH,desorption temperature and stirring rate,the ideal pH value of desorption of MEA rich solution by ideal calcium method was 10,the ideal desorption temperature was20?,and the optimum stirring rate was 800r/min.In the end,the performance of membrane desorption and calcium desorption in three aspects,such as desorption energy consumption/cost,recycled absorption capacity and cycle regeneration rate of regeneration solutions,were analyzed by comparison with pyrolysis desorption.On the premise of obtaining ideal desorption rate,the energy consumption/cost input of calcium desorption was the smallest.Although the cyclic desorption rate of membrane desorption was not high,it had the highest cycle absorption capacity,and its comprehensive performance was better than that of thermal desorption method.