Study On The Calcium Carbonate Decomposition Coupled With Bamboo Charcoal Gasification To Enhance CO₂ In Situ Conversion

The massive emission of greenhouse gases,mainly CO₂,will have a serious impact on climate,ecology,agriculture and other aspects,and carbon emission has become the focus of attention from all walks of life.Carbon Capture Utilization and Storage（CCUS）technology can reduce industrial CO₂ emissions on a large scale.In this thesis,a new idea was proposed to use chemical reactions to enhance the decomposition of Ca CO₃ and realize the conversion and utilization of CO₂.The CO₂produced by the decomposition of Ca CO₃ reacts with the coke at high temperature by coupling the coke gasification and Ca CO₃ decomposition process,which not only promotes the decomposition reaction of Ca CO₃ to the direction of generating CO₂,but also realizes the in-situ conversion of CO₂ to obtain a certain purity of combustible gas CO.Various characterization methods,such as X-ray powder diffraction（XRD）,scanning electron microscopy（SEM）,dynamic flue gas analysis and thermogravimetric analyzer（TG）and so on,were used to analyze the physical composition,microscopic morphology,CO₂ conversion ability and cycle stability of the samples.The main research contents are as follows:Through the establishment of thermodynamic model,thermodynamic analysis and equilibrium constant calculation of related reactions were carried out.The results confirmed that the decomposition process of coke gasification coupled with Ca CO₃was feasible,and the decomposition temperature of Ca CO₃ decreased significantly after coupling.The abundant and low-cost limestone and bamboo charcoal in nature were selected as raw materials for the dynamic heating transformation experiment.The generation of CO was detected by flue gas analyzer.Compared with the control group,the decomposition temperature of limestone with bamboo charcoal was reduced by 35℃,which was consistent with the calculation result.The kinetic calculation results of limestone decomposition process show that the activation energy decreases by more than 12%after adding bamboo charcoal,and the samples after reaction have better microstructure and smaller grain size.In order to solve the problem of low CO yield caused by too fast decomposition rate of limestone and slow gasification process of bamboo charcoal,K₂CO₃ was selected to catalyze the gasification process of bamboo charcoal.By impregnating bamboo charcoal with K₂CO₃,increasing the particle size of limestone and adjusting the doping amount of K₂CO₃,the decomposition process of limestone can match the gasification process of bamboo charcoal as much as possible.The CO yield of L5-C0.5K at 850℃for 15 min was 69.04%.In addition,increasing the partial pressure of CO₂ in the experimental carrier gas can inhibit the decomposition of limestone,which was more conducive to matching the gasification process of bamboo charcoal.When the mixture of 85vol.%N₂ and 15vol.%CO₂ was selected as the carrier gas in the dynamic heating transformation experiment,the CO yield at the highest point of CO concentration in the product gas reached 86.04%.Based on calcium cycle technology,a CO conversion and purification cycle system was proposed:The transformation reaction of Ca CO₃ and biochar at high temperature can produce a mixture of CO and CO₂,and then the Ca O obtained after the transformation can adsorb CO₂ in the mixture to further improve the purity of CO in the product gas.After carbonation,Ca O can obtain Ca CO₃,so as to realize the cycle of calcium and obtain high purity CO gas.In this thesis,limestone and bamboo charcoal were used as raw materials to simulate the CO conversion and purification process of the system.In the constant temperature purification experiment,high purification temperature easily leads to the re-desorption of just fixed CO₂,while the insufficient contact between mixture and Ca O leads to poor purification effect.Finally,in the constant temperature purification experiment conducted in 3 cm reaction tube at600℃and reaction time of 15 min,83.17%CO yield was obtained.Multi cycle experiments,mixed bamboo charcoal CO₂ reduction ability basic K as for the loop is not changed,and Ca O because of CO₂ adsorption performance degradation,on the one hand lead to generate CO"raw material",on the other hand lead to adsorption fixed area for the purification of CO₂ reduction,CO in the product gas yield and production rate along with the cycle of falling fast.In order to reverse this situation,the cyclic stability of the sample was improved by doping dolomite.Due to the support of inert substance Mg O,the sintering resistance of the sample was enhanced.After 10 cycles,the CO yield only decreased by 1/5.There are 33 pictures,7 tables and 107 references in this thesis.