| Coal pyrolysis is a solid foundation for deep processing of coal.Through in-depth study on the chemical composition and structural characteristics of coal macerals,the natural macromolecular structure differences of different macerals are used to control the distribution of pyrolysis products,so as to achieve the purpose of high-value utilization of graded macerals.In recent years,coal-based chemical looping combustion(CLC)technology has gradually developed into the most promising carbon capture technology,which can not only realize the efficient utilization of coal to electricity,but also realize the zero emission of CO2 in the combustion process.The high performance of oxygen carrer is one of the important factors for the successful operation of CLC system.The composite oxygen carrier of CuFe2O4 with spinel structure has both the thermal stability of Fe2O3 and the high reactivity of CuO.Ningdong area,as one of the 14 hundred million ton coal bases in China,is of great significance for the efficient and clean utilization of coal resources in the western region of China.In this paper,different macerals of Qinghua coal are taken as the research object.The pyrolysis activity of macerals under different pyrolysis conditions is mainly investigated from the point of view of chemical bond fracture,and the macerals and CuFe2O4 are investigated under the oxygen consumption of ?=1.The combustion characteristics of OC can further reveal the mechanism of pyrolysis and chemical looping combustion from the structure of chars.Firstly,the thermogravimetry coupled with mass spectrometry(TG-MS)was used to study the effect of temperature on the pyrolysis characteristics of macerals at 750?800?850 and 900?.By fitting the DTG curves,the relationship between the pyrolysis behavior of the macerals and the chemical bond fracture was investigated in five pyrolysis stages,including dry dehydration,slow pyrolysis,fast pyrolysis,fast condensation and slow condensation.The results show that the cleavage of Cal-Cal mainly occurs in the fast pyrolysis stage,and the bond energy is 210-320 kJ/mol.The vitrinite shows a higher weight loss rate than the inertinite at this stage because of its more aliphatic side chains.With the increase of the final pyrolysis temperature,the maximum weight loss rate of the macerals increased,and the change of the vitrinite was more obvious.The maximum weight loss rates of vitrinite and inertinite at 900? are 0.1226 and 0.1061%/? respectively,indicating that the pyrolysis activity of vitrinite is higher at the same final temperature.Furthermore,the evolution characteristics of the four gas products,H2?CH4,?H2O and CO2,during the pyrolysis of the macerals were investigated.It was found that there were significant differences in the intensity,temperature and peak value of the evolved gases from the pyrolysis of vitrinite and inertinite.At the same time,combining with Coats-Redfern model,the pyrolysis rules of different macerals are clarified from the dynamics.The results show that in the rapid pyrolysis stage,the average activation energy of macerals is 75 kJ/mol,and the pre-exponential factor of vitrinite is higher.Secondly,the influence of heating rate on the pyrolysis characteristics of the macerals was investigated by thermogravimetry at 15,25 and 35?/min.the pyrolysis characteristic parameters were calculated according to TG/DTG curve.The results showed that the macerals showed the highest weight loss rate at 15?/min and the highest weight loss rate at 35?/min.The pyrolysis characteristic index P of the macerals increased with the increase of the heating rate.The P values of the vitrinite and inertinite at 25?/min were 13.03 and 7.74((10-5·%3)/(min2·?2))respectively.At the same heating rate,the pyrolysis characteristic index P of the vitrinite was higher than that of the inertinite,indicating that it had higher pyrolysis activity.The distribution activation energy of vitrinite and inertinite was calculated by DAEM model.When the pyrolysis conversion was 0.1-0.9,the activation energy ranges of vitrinite and inertinite were 35.09-160.87 and 38.04-185.59 kJ/mol,respectively In the main pyrolysis stage with the conversion of 0.3-0.6,the activation energy of vitrinite is lower than that of inertinite,which may be due to its more fatty carboxyl functional groups and easier decomposition under heat.At the same time,the chars was prepared in vacuum tube furnace at different final pyrolysis temperature,and the influence of final pyrolysis temperature on the structure of chars with different macerals was investigated by various characterization methods.XRD analysis shows that the chars prepared at the high pyrolysis final temperature has a higher degree of aromatic ring polycondensation,and the graphitization degree of inert chars is higher under the same pyrolysis condition.The results of Raman analysis show that the increase of pyrolysis temperature is beneficial to the transformation of small aromatic ring structure to large aromatic ring structure,and to the deepening of aromatic ring polycondensation,thus increasing the aromaticity of chars.XPS analysis showed that with the increase of pyrolysis temperature,the relative content of C-C/C-H increased,while the relative content of oxygen-containing functional groups such as C-O and C=O decreased.Finally,based on the investigation of combustion characteristics of different maceral differentiation chains of Qinghua coal by using CuFe2O4 OC,the mixture of CuFe2O4 and macerals was pyrolyzed by using quartz sand as a parallel blank control under the mass ratio of oxygen consumption ?=1.According to the TG/DTG curve,the combustion characteristic parameters of vitrinite and inertinite are obtained.The results show that the maximum weight loss rate of vitrinite and inertinite is 0.4942 and 0.4533%/min,respectively.Under the same oxygen consumption,inertinite with higher inking degree shows lower combustion activity.Furthermore,the chars of different macerals was obtained by acid treatment under the conditions of pyrolysis and chemical looping combustion.The results show that the chemical looping combustion can significantly reduce the interlayer spacing of the aromatic layers of the macerals,and the interlayer defects of the aromatic rings and the condensation of the aromatic rings can be greatly improved.Under the condition of chemical looping combustion,the relative content of C-C/C-H of chars is significantly reduced,and the content of C-O is significantly increased.The introduction of CuFe2O4 OC is more conducive to promote the conversion of C-C/C-H functional groups in coal to C-O.FSEM-EDS showed that the lattice oxygen and gaseous oxygen released by CuFe2O4 OC ignited at the pore active sites on the surface of chars,resulting in a large amount of volatile matter released,and the char surface was porous honeycomb structure.Vitrinite has high reactivity due to its high degree of side chain branching of alkanes and fatty hydrocarbon bonds,while inertinite has high graphitization degree and silicon mineral content,which limit the further combustion reaction. |
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