Simulationand And Analysis Of Indirectly Heated Carbonate Looping And Exploration Of Gas-solid Flow Patterns In The Carbonator

With the intensification of human activities and development of human science,CO₂ emissions have increased rapidly in this decades,which has had a huge negative effect on the ecological environment and human living.Flue gas is the main source of CO₂ emissions,so the CO₂ capture from flue gas is very important.This thesis pays attention to carbonate looping process which have developed in recent decades.This method is favored by many researchers because it uses natural limestone as an adsorbent,which is widespread in nature.However,domestic scholars have not fully studied the carbonate looping process and the gas-solid flow mechanism in the carbonator,so this thesis will discuss from these two aspects.The thesis analyzes the carbonator and calciner of indirectly heated carbonate looping from the theoretical point of view,and calculates the material balance of the carbonator.The analysis results shows that the carbonation can be divided into two parts,the rapid reaction stage and the slow controlled diffusion stage,and the rapid reaction stage determines the capture efficiency;the system needs to introduce the make-up flow to compensate the inactivated sorbent;when the CO₂capture rate is required to be 85%,the carbonator height is 20m and the solid inventory in the carbonator is 270.25t at least.Based on the power plant,the ASPEN PLUS software is used to establish the indirectly heated carbonate looping process,and the carbonate temperature,calcination temperature,solid flow rate,discharge rate and gas-solid separation efficiency are analyzed.Through the simulation,the change of carbonate and calcination temperature affects the adsorbent activity,meanwhile the solid flow rate,discharge rate and the gas-solid separation efficiency influences the system efficiency by changing the solids inventory.When the carbonate temperature is 625℃,the calcination temperature is1000℃,the flow rate is 1400kmol/h,the discharge rate is 0.05 and the gas-solid separation efficiency is 1.0,the system will achieve the best performance.The ASPEN PLUS software is then used to compare the indirectly heated carbonate looping process and the directly heated process.The 1-D fluidized bed model is used to explore the particle distribution in the riser,the CO₂ absorption rate,and the overall CO₂ capture of the system.Through the analysis,the high energy consumption of the directly heated method is caused by the air separation system,so the thesis choose indirectly heated method.The FLUENT software is used to establish the riser of the carbonator and analyzed the gas-solid flow pattern in the riser.The results show as the flow time increased,the solids in the riser began to accumulate toward the wall area;and with the increase of the solid flow rate,the solid volume fraction decreased and the solid circulation rate increased,which accelerates adsorption reaction rate and decreases the CO₂ and SO₂ concentration at the outlet.At the same time,the CO₂ and SO₂ concentration decreases with the height of riser increasing.