CO₂ Absorption Performance From Simulated Biogas And Regeneration Characteristics Of Blended Absorbents

After removing CO₂ and other main impurities to raise the CH₄ content to the natural gas standard,biogas can be upgraded to bio-natural gas.Obviously bio-natural gas is a renewable energy which can achieve near-zero emission of CO₂ during energy utilization.Additionally it can alleviate the contradiction between supply and demand in China if the industrial-scale application of bio-natural gas is possible.The key to produce bio-natural gas is to separate CO₂ from biogas with high efficiently and low consumption.Among many kinds of CO₂ separation technologies from biogas,CO₂ chemical absorption method has the advantages such as high separation efficiency,high CH₄ purity and low CH₄ loss.However the main reason to hinder its large-scale industrial application is huge investment and high operating costs.Screening the suitable absorbents may do a work for overcoming these problems.Therefore the focus of current research is on the study of blended absorbents formed by combining the advantages of single absorbent.Based on these assumptions,from the perspective of blended solutions and concentration screening,CO₂ absorption and regeneration performance from the simulated biogas of blended absorbents were investigated in this study.?1?Firstly,the effects of CO₂ concentration in the simulated biogas,reaction temperature and concentration of monoethanolamine?MEA?,diethanolamine?DEA?,triethanolamine?TEA?,N,N-diethylethanolamine?DEEA?,piperazine?PZ?,potassium argininate?PA?,potassium glycinate?PG?and TEA/MEA,TEA/PZ,TEA/PA,TEA/PG,DEEA/MEA,DEEA/PA,DEEA/PG and DEEA/PZ on CO₂ saturated solubility were evaluated.The results showed that CO₂ saturated solubility can be promoted with the decrease of reaction temperature and concentration of absorbents,and increase of CO₂concentration in the simulated biogas.Besides,DEEA and PZ possess the highest saturated solubility,followed by PA,PG,MEA,DEA and TEA.Comparing to single TEA aqueous solution,CO₂ saturated solubility of TEA-based blended absorbents is higher.CO₂ saturated solubility of 16%TEA+4%PZ is increased by 0.251 mol/mol compared to that of a single TEA?W=20%?.This demonstrated that the addition of active agents such as PZ to the TEA solution can increase its CO₂ absorption capacity.?2?CO₂ absorption and regeneration performance of six typical CO₂ absorbents were investigated based on the overall gas phase volumetric mass transfer coefficient?K_Ga_e?CO₂ removal efficiency???and regeneration degree???respectively.CO₂ comprehensive absorption performance of single absorbents were ranked as:PZ>MEA>PA>PG>DEA>TEA,and regeneration performance were ranked as TEA>PA>DEA>PG>PZ>MEA.Furthermore,the simplified empirical correlations for K_Ga_e as a function of the key operation parameters have been proposed for MEA,DEA,PA,PG and PZ,and most of the calculated K_Ga_e values are in good agreement with the experimental data with an absolute average deviation less than 14%.?3?The optimal concentration ratio of 4 group blended absorbents were screened based on the CO₂ absorption experiments of single absorbents.The results showed that 12%TEA+8%MEA?12%TEA+8%PA?12%TEA+8%PG and 16%TEA+4%PZ possess the best CO₂ absorption and regeneration performance among all blended absorbents,and the rank is 12%TEA+8%PA>12%TEA+8%PG>12%TEA+8%MEA>16%TEA+4%PZ,in which revealed that 12%TEA+8%PA is the optimal hybrid scheme.?4?The regeneration characteristics of absorbents by microwave heating were investigated.The results showed that the regeneration degree of TEA is 89.98%under the condition of T_M?microwave temperature?=100?,??15??the initial CO₂ loading??28??15??13??20?mol/mol,which is nearly close to that obtained by traditional regeneration method with T?heating temperature?=120,?_?15??28??15??13??20?mol/mol?90.89%?.Moreover,under effect of microwave,the regeneration equilibrium of absorbents such as PA,PG and PZ can be reached within 30-40min,which is significantly shorter than traditional thermal regeneration.In conclusion,the absorbents possess higher regeneration rate and lower reaction temperature under microwave heating,which proved the feasibility of microwave regeneration further.CO₂ absorption and regeneration characteristics from simulated biogas of chemical absorbents were verified and revealed based on the experiments.TEA/MEA,TEA/PA,TEA/PG and TEA/PZ possess excellent comprehensive performance,which can replace single absorbents such as TEA,MEA for biogas upgrading.Meanwhile,the regeneration of CO₂ rich absorbents by microwave is feasible.