Capture Carbon From Flue Gas For Coal-fired Power Plants

The combustion of fossil fuels releases plentiful CO₂to the environment, whichhas led to serious green-house effect and global climate anomaly phenomenon. It hasbecome the common concern global problems all over the world. In all kinds ofgreenhouse gas, the contribution rates of CO₂reach to55%for green-house effect.The China energy structure is dominated by coal, CO₂release of production unit heatfrom coal higher than oil and gas about36%and61%, respectively. Therefore, Chinahas faced great pressure in the greenhouse gas emission reduction. The CO₂emissionfrom coal-fired power plants is one of the major stationary sources. Post-combustionhas been recognized as the more effective CO₂separation and capture technology forcoal-fired power plants in the short term. According to the characteristics ofcoal-fired power plants, using original high-temperature flue gas and fly ash from theproduction process separate and capture CO₂from flue gas, which conform to thecurrent idea of Cleaner Production and Recycling Economy.The separation and capture CO₂from flue gas of coal-fired power plants werestudied in this dissertation. The carbonation reaction processes of high temperaturesorbent were investigated at vertical fixed-bed reactor. Considered ordinary calciumbase materials low CO₂adsorption capacity, poor cycle stability and sinter problem,modification and doping means were used to improve and prepare a series of sorbentsfor CO₂separation and capture from simulate flue gas. This dissertation mainlycontents five sections:1. Use of acetic acid calcium, calcium hydroxide, calcium carbonate and calciumoxide, obtained four kinds of Ca-based sorbents by the simple preparation process,and the carbonation characteristics of those sorbents were studied. Reactionconditions for Ca-based sorbents were determined, such as eaction gas velocity,sorbents particle size and carbonation temperature and so on. The constituents,surface morphology information and physical properties of Ca-based sorbents andreaction products were analyzed by XRD, SEM and N2adsorption-desorption. Thedeactivation mode was used to fit experimental breakthrough curves. The CO₂ absorption mechanism of Ca-based sorbents was discussed.2. Doping fly ash to Ca-based sorbents, obtained the Ca-based fly ash sorbents.Taking CaO-CaO/FA sorbent for example, determined the gas velocity0.1L/min,sorbent particle size of0.8mm,25%fly ash doping content and the optimum reactiontemperature and so on. The XRD results shown that a large number of mineralsformed by the preparation process for Ca-based fly ash sorbents. The CO₂experimental breakthrough curves of Ca-based fly ash sorbents can well be fitted withthe deactivation model. Other Ca-based fly ash sorbents, such as CaAc₂-CaO/FA,CaCO3-CaO/FA, Ca（OH）2-CaO/FA and dolomite sorbents, their characteristics ofcarbonation were investigated in detail.3. The cycles performance of sorbents is of critical importance. Results indicatedthat, the optimum calcination temperature of regeneration is850℃, and reducing theCO₂partial pressure of calcining atmosphere can slow down the sorbents activity. Itwas found from multicycles reaction of Ca-based and Ca-based fly ash sorbents that,CaAc₂-CaO and CaAc₂-CaO/FA had the best CO₂absorption performance and cyclestability. And after15thcycles, CaAc₂-CaO/FA shows the better cycle stability thanCaAc₂-CaO sorbent. The characteristics of carbonation of Dolomite-CaO andDolomite-CaO/FA sorbent showed that, they have low CO₂absorption capacity andpoor cycle stability.4. The carbonation performances of rare earth modified Ca-based sorbents wereinvestigated in fix-bed reactor.10%La/CaO and5%Ce/CaO sorbents showedexcellent CO₂absorption performances. The optimum calcination temperature ofLa-/Ce-doping Ca-based sorbents is850℃for the preparation process. La₂O₃in thesorbents is not only as a kind of “skeleton structure” exists, but also an activeingredient can capture CO₂.5%Ce/CaO sorbent contains a series of cerium oxide,could become Ce₄O₂C₂and CeO2C2after carbonation reaction. Multilcycles reactionresults indicated that,10%La/CaO and5%Ce/CaO sorbents have showed bettercycle stability. The SEM morphology showed clearly that5%Ce/CaO sorbent appearserious sintering and collapse phenomenon after20thcycles, and partially sorbentparticles adhesion together.5. The characteristics of carbonation of CaAc₂-CaO and CaAc₂-CaO-FA sorbents were conducted at the fluidized bed reactor. During multicycles fluidizedbed experiments, it was found that CaAc₂-CaO and CaAc₂-CaO-FA sorbents showgood CO₂absorption performance. With the increase of cycles times, thebreakthrough time obviously become short and curves cross and overlap. The XRD ofproducts after cycles found that contains some unreacted CaO. It is mainly becausethe fluidized state of sorbent not good in the reactor. Finally, we have developed akind of fix sulfur in combustion and capture carbon from flue gas technology forcoal-fired power plants in this dissertation.