Experimental Study Of Bio-char Modification And CO₂Absorption

CO₂is the main greenhouse gas. Nowadays, the emissions of CO₂became more andmore, because of the development of the global industry. The coal-fired power plant is oneof the biggest CO₂emitters. How to reduce the CO₂emissions of coal-fired power plant isthe urgent matter. As we all know that China biological gross is abundant, but doesn’t makefull use. We put forward a project that combines the biomass and coal pollution controltogether. We use the biomass as the raw material, and modified it with gaseous ammoniaand CO₂, and then absorb CO₂by its product. In this paper we will study the explore thedifference between modifications,and has a more in-depth analysis of the CO₂absorption。We firstly choose three typical agricultural wastes （rice husk, cotton stalk, rice stems）as raw materials to make modification. Then fixed bed pyrolysis reaction system, FTIR,ASAP2020physical absorption instrument will be used to compare the biomass before andafter modification, and analysis the influence to chemical composition and pore structure bydifferent types of biomass and modifications. The result shows that CO₂modificationmakes the surface area of char increased significantly, the pore of the char became moredeveloped.The surface of NH₃modified char appears lots of nitrogen functional groups.CO₂absorption of cotton stalk is much better than rice stem and rice husk. Because cottonstalk has low ash content,which blocks pore structure formation of biomass char,and hasbad influence on the absorption.Then, we do a modification on cotton stalk, and discuss the influence of differentmodified temperature and atmosphere (NH₃, CO₂,（CO₂+NH₃） to the physical structureand chemmical characteristics, as well as CO₂absorption of the cotton stalk char. Anddiscuss the relationship among temperature, specific surface area, and absorption quantity,as well as the rule of nitrogen functional groups evolution. The results shows that in normaltemperature and pressure, CO₂absorption is proportional to specific surface area, and theexistence of CO₂atmosphere is favors of generating developed pore structure under hightemperature. With the rise of temperature, nitrogen functional groups will decompose partly,and turn to form more stable functional groups. Finally, we study the CO₂absorption characteristics at20℃and120℃by the fixedbed absorption system and gas absorption spectrometer. We introduce the inactivationmodel to fit the breakthrough curve of absorption, and make a analysis from the view ofabsorption dynamics.Then combines absorption capacity of modified char at20℃and120℃, we study therelationship between CO₂absorption and pore structure as well as the nitrogen content. Theresult shows that CO₂absorption is mainly physical absorption at lower temperature, thusthe absorption quantity is proportional to the micropore volume of the char. However, underhigher temperature, molecular thermal motion increases, chemical absorption is dominanted,the absorption is directly proportional to the N contentof the modified char.