Intrinsic Characteristics Of Coal Gasification Slag And Its Fundamental Research For Applications

Coal gasification slag is a by-product from coalgasification process in Integrated Gasification Combined Cycle(IGCC)system.In the gasifier,molten ash originated from the mineral component in coal flows down into a water quenching system,which leading to the formation of glassy CGS.With the rapid development of coal chemical industry,the discharge of CGS is increasing year by year.Massive stockpiling not only occupies valuable land resources,but also,importantly,degrades the ecological environment and threatens human health.In the literature,there are many researches on coal gasification technology and downstream extension of polygeneration technology,but few researches on CGS,especially on comprehensive utilization of CGS.Based on the above,this thesis,firstly,the intrinsic characteristics of CGSs were studied by means of wet chemical analysis,X-ray fluorescence analysis,X-ray diffraction analysis,petrographic analysis,microstructural analysis,analysis of the ash melting point and high temperature melt viscosity and melting temperature(range)analysis,and nuclear magnetic resonance(NMR)analysis methods,which provide the foundation for the further comprehensive of the slags;Secondly,by compared experiments,the formation of phase composition and micro structure in the process of carbothermal reduction nitridation(CRN)of CGSs,glass and minerals,reveals the mechanism of CRN of CGS.Thirdly,SiAlON phosphors were prepared by CRN process with adding appropriate rare earth elements.Finally,in order to pursue higher utilization rate,CGS was used to prepare foam ceramic lightweight wall material.The main conclusions are as follows:(1)The main chemical components of the six kinds of CGSs were Al2O3,SiO2,CaO,Fe2O3 and residual carbon.An internal atom binding state is the frame structure of SiO4 tetrahedron and AlO4 tetrahedron.And the first five kinds of slags all contained more spherical vitreous and residual carbon particles.However,the content of the residual carbon of QP slag was very small,and the melting temperature of itwas higher.Based on the intrinsic characteristics,it could be inferred that the first five kinds of slag could be directly carbothermal reduction and nitriding,while QP slag wasirrealizable.(2)By comparing carbothermal reduction nitridation(CRN)processofthe glass,gasification slag and mineral,the CRN mechanism of CGS was indicated:the CRN process was dominated by nitridation of the Ca-Si-Al-O glass component in slag.With the increase of processing temperature,spherical Ca-Si-Al-O particles were firstlynitrided into porous Ca-Si-Al-O-N spheres,plate-like O-SiAlON grains,and then nitrogen-rich SiAlONs(?-SiAlON,15R polytypoid and ?-SiAlON).At the end of CRN,Ca-?-SiAlON was found to be the only SiAlON phase presenting elongated prismatic morphology.In addition,it was found that the formation of high temperature liquid and formation of gas phases could promote the formation of bar morphology of Ca-?-SiAlONduring the process of CRN.(3)Ca-?-SiAlON powder with high purity can be obtained after removal of impurities by adding CeO2 or Eu2O3 rare earth oxides.The process of removing carbon and iron greatly improves the luminescence performance of phosphors.With the increase of nitridation temperature,the morphology of Ca-?-SiAlON powder aggregates became more and more clear,and developed into acicular aggregate Ce(Si,Al)3(O,N)5 and fine strip aggregate Eu2(Si,Al)5(N,O)8.Ca-?-SiAlON:Ce emitted green light under the excitation of 383 nm ultraviolet light,and Ca-?-SiAlON:Eu emitted yellow light under the excitation of 420 nm ultraviolet light.(4)It was feasible to use SiC as the foaming agent and CGS as the main raw material to prepare foaming ceramics.And it can be indicated that:the optimum particle size rang was 0.25?1mm,at the sintering temperature was 1160?,the foam ceramic wall material with 77%CGS presented relatively volume density of 0.21g/cm3,heat conductivity coefficient of 0.05W/(m-k),and the corresponding compress strength of 1.18MPa.Moreover,the total amount of CGS is up to 77%,which greatly reduces the cost of raw materials and has played a very beneficial role in environmental protection.Finally,it will have great potential in the application in the field of new building materials.