CO₂ Absorption Performance And Agricultural Utilization Potential Of A Renewable Solvent System Derived From Biomass Ash And Biogas Slurry

At present,the CO₂ chemical absorption process is one of the most mature carbon capture technologies,but the high regeneration energy consumption of the absorbent results in the high cost of CO₂ separation.In theory,the energy consumption can be reduced by rejecting the heat regeneration process with CO₂-rich absorbent or only retaining the absorption process.In this process,the cost of CO₂ separation would be mainly controlled by the cost of absorbent.A large amount of weakly alkaline biogas slurry was produced by the wet anaerobic fermentation biogas project,with a individual capacity of CO₂ absorption.The CO₂-rich biogas slurry can be directly used for agricultural irrigation,which can store CO₂ in plants and soil,and effectively solve the problem of CO₂ separation and outlet.However,due to the low reaction rate and minor capacity,the CO₂ absorption of biogas slurry must be enhanced.The alkaline components（mainly Ca O）in biomass ash can react with CO₂ to form carbonate precipitates used for CO₂ absorption.Thus,this paper combined biomass ash with biogas slurry to form a renewable absorbent system for CO₂absorption and utilization.Firstly,the CO₂ absorption capacity,reaction mechanism and biogas upgrading performance of mixture absorbent were investigated in this study.Additionally,the feasibility of agricultural application of biomass ash and biogas slurry after the reaction was focused on.Finally,analysis of economic analysis and environmental benefit was carried out.The main conclusions are as follows:（1）Under normal temperature and pressure,the CO₂ absorption capacity and mechanism of biomass ash and biogas slurry mixture absorbent were investigated.The results showed that the CO₂ absorption capacity of the mixture absorbents decreased with the increase of the liquid-solid ratio,while the carbonation efficiency of biomass ash showed the opposite trend.When the mass ratio of liquid to solid was 4:1,the CO₂absorption capacity of this mixture absorbent reached up to 19.89 g-CO₂/（kg-slurry）,which was about 160%higher than that of the biomass ash and water mixture.（2）The CO₂ absorption capacity of this mixture absorbent increased with CO₂ pressure.Under 25°C and a liquid-solid ratio of 9:1,the maximum CO₂ absorption capacity was about 22.32 g-CO₂/（kg-slurry）when the initial CO₂ pressure was 1400 k Pa.In the simulated biogas atmosphere,when CO₂ partial pressure was 500 k Pa,the CO₂ absorption capacity of the mixture absorbent could reach 13.96 g-CO₂/（kg-slurry）.When the reaction temperature and pressure were constant,the CO₂ absorption capacity decreased with the liquid-solid ratio,but the carbonation efficiency of the biomass ash showed the opposite trend.At room temperature,when CO₂ partial pressure was 400 k Pa and the liquid-solid ratio was 4:1,the CO₂ absorption capacity of the mixture absorbent was 23.72 g-CO₂/（kg-slurry）,which was about 13 times at the 99:1 liquid-solid ratio at.At this time,the CO₂removal rate of simulated biogas could reach 66.38%.The effect of temperature on CO₂absorption capacity by this mixture absorbent is complicated.When the liquid-solid ratio reached 9:1 or less,H₂S could be removed entirely.（3）A novel system for simultaneous biogas upgrading,biogas slurry decrement and agricultural utilization was established by adding biomass ash into biogas slurry to form a renewable CO₂ mixture absorbent.The physiological toxicity of the mixture absorbent was weakened after CO₂ absorption.When used for seed germination,the germination index of CO₂-rich mixture absorbent was higher than 0.8 when the ash content in the culture soil was less than 10%,which could promote the seed germination.The CO₂-rich mixture absorbent was feasible for agricultural utilization when the ash content was less than 20%.In this study,the CH₄ content of the treated biogas could reach 95 vol.%,when the CO₂partial pressure was 400 k Pa（total pressure is 1000 k Pa）and the ratio of solid-liquid-gas in the reactor was 13:52:235（kg/kg/L）.The CO₂ emission in biogas upgrading was mainly related to the biomass ash transport distance and the electric energy sources consumed by the system.The biomass ash transportation distance significantly affected the cost of biogas upgrading.When the transportation distance was less than 46 km,the biogas upgrading cost could be lower than the global average level（about 0.7 RMB/Nm³-biogas）.The results showed that the novel concept using the mixture renewable absorbent is beneficial to reduce the cost of CO₂ capture from biogas.In addition,the valuable results can also be beneficial to the treatment of biomass ash and biogas slurry,as well as the development of carbon negative emission technology.