| Coal gasification is the core technology of coal chemical industry,while the mineral elements in coal is one of the important factors that influence the gasification reactivity.It is very important to study the influence of main mineral elements on the gasification activity of coal,which can take significant meaning to the spot utilization of Guizhou anthracite.In this paper the Guizhou anthracite from a certain mine was proposed as research object.First of all,In order to eliminate the influence of raw mineral in coal,the raw material was demineralized,and then some metallic compounds were added to the demineralized coal.CO2 is used as gasify agent,the impact of Si、Al、Fe、Ca on gasification reactivity was investigated in a fixed-bed reactor.The results show that calcium element has better catalytic action on anthracite coal char gasification.In order to further study the effect of calcium on the gasification reactivity of anthracite,four kinds of calcium-based additives(CaCO3、CaO、CaCl2、CaSO4)were chosen to attend to coal samples.Some operational conditions such as the effect of char making process,addition amount of additives and the gasification temperature on char gasification reactivity were investigated.With an emphasis on CaCO3,the gasification reactivity of H2O/Ar、H2O/CO2 and H2O/O2 as gasification agent were compared.By means of FTIR、XRD and SEM,the microstructure、phase transformation and surface morphology were analyzed,the impact mechanism of CaCO3 on anthracite gasification reactivity was investigated.The main conclusions are as follows:(1)The effect of additives on anthracite coal gasification activity was studied.The results show that SiO2 has an inhibitory effect on coal gasification,and Al2O3 has little effect on coal gasification.CaCO3,Fe3O4 and Fe2O3 all have catalytic effect on coal gasification,and CaCO3 was better than others.According to further study and literature analysis,this promoting effect shows that CaCO3 has a certain catalytic function on anthracite coal gasification.(2)The coking method has a certain effect on the gasification activity,CaCO3,CaO,CaCl2 and CaSO4 can increase the activity of anthracite char in some degree obtained by adding additive before pyrolyse or adding the additive to coal char.With the increase of pyrolysis temperature and the prolongation of pyrolysis time,the dispersity of the additive decreased during pyrolysis.For the same additive,the gasification activity of the coal char obtained by adding the additive after pyrolyse is higher than that of the coal char pyrolysed after the catalyst was added.(3)When the addition amount of the additive is constant,the anthracite coal char gasification activity increases with the increase of the gasification reaction temperature in the range of 900 ~ 1100℃.The saturated amount of CaCO3 is about 3.5%.(4)The coal char made by adding CaCO3 to coal before pyrolyse will appear partial agglomeration,leading to poor dispersibility of CaCO3.And CaCO3 will react with sulfur in coal to form CaS during the pyrolysis process,while the catalytic activity of CaS is lower than that of CaCO3.The above two points lead to the activity of the coal char obtained by adding CaCO3 before pyrolyse is lower than that of the coal char which pyrolysed before CaCO3 was added.CaCO3,which added into the coal char,will react with sulfur contained in the coal to form CaS in the process of gasification.Therefore,CaCO3 plays a certain role in sulfur fixation,and the reaction product of metakaolin and CaCO3 can reduce ash melting point.In the process of gasification the coal surface appears spherical particles,with the gasification reaction,spherical particles continue to subsidence into the coal,with the new carbon contact,continue to catalyze coal gasification.Spherical particles will appear on the coal char surface during the gasification process,and the spherical particles continue to subsidence into the coal char,then contacted with the new carbon and catalyze the coal gasification.(5)In the case of H2O/Ar and H2O/CO2 as the gasifying agent,the addition of CaCO3 increased the char conversion rate.However,when H2O/O2 was used as gasifying agent,the conversion rate of coal char was reduced after CaCO3 was added.Scanning electron microscopy analyses of residual chars obtained from diffierent gasification stages show that the main causes of these phenomena are related to the distribution of the active components on the surface of the coal char,whether the catalytic components react with the minerals,whether there is the phenomenon of sintering agglomeration and the pore structure of the coal char. |
