Structural Features And Combustion Reactivity Of Fine Slag From Entrained-flow Gasification

Modern coal chemical industry is one of the effective ways to deal with the challenges of energy security in China today and in the future.As the leading technology of modern advanced coal chemical industry,entrained bed gasification has vigorously promoted the clean and efficient conversion and utilization of coal,but it also produces a lot of solid wastes.In particular,a large amount of coal gasification slag accumulation has an important impact on the ecological environment,so it is urgent to seek efficient,high-value and large-scale utilization of fine slag.The content and type of carbon in slag is one of the key problems to limit the utilization of fine slag and the understanding of this problem is very limited.In addition,the mixing of fine slag is expected to provide a choice for the large-scale utilization of fine slag.Therefore,this study focuses on the analysis of the structural feature and the evaluation of combustion characteristics of fine slag,in order to provide theoretical support for the resource utilization of fine slag.In this study,fine slag produced by typical GE,OMB and GSP gasification processes in Ningxia Ningdong Energy and Chemical Industry was selected as the research object,which were labeled as FSGE,FSOMB and FSGSP respectively.Meanwhile,raw coal corresponding to these three gasification processes was selected.Respectively for Yangchangwan Zaoquan blending(YZP),Yangchangwan blending(YP)and Shuangma Zaoquan Meihuajing blending(SZMP)as a reference object,The residual carbon of fine slag was obtained by acid washing for ash removal,which was used to analyze the structure and type of carbon,with physical adsorption,scanning electron microscope,laser Raman spectroscopy and thermogravimetric analyzer analysis characterization methods,The structural characteristics and combustion characteristics of fine slag were systematically studied.The specific results are as follows:(1)It is found that the original fine slag exists in the form of spherical particles,porous irregular particles and single spherical particles with a large size.Differently,the slag washed by acid is in the existence of loose particles and porous irregular blocks.Additionally,The pore size of residual carbon in fine slag is mainly distributed in the mesopore range of 4-8nm,the specific surface area and active sites of that decrease orderly as follows:FSGE>FSOMB>FSGSP.The order degree of residual carbon structure in FSGE is the lowest,amorphous carbon structure is the most,and the combustion rate is the fastest.The comprehensive combustion index is 5.26×10-7%2·min-2·?-3.(2)According to the peaking fitting of the CO2 release peak of the TPO curve of FSGE,it can be found that there are mainly three types of residual carbon,which are defined as easily reactive carbon(520?),moderately reactive carbon(570?)and unreactive carbon(605?).This shows that there is not only one type of residual carbon in the fine slag,but there are three types of residual carbon with different structure.By GC-MS can detect fine slag extract contains a certain content of polycyclic aromatic hydrocarbons,and most of the ternary ring,quaternary ring and other polycyclic aromatic hydrocarbons.There are high-value organic compounds in the residual carbon of fine slag.In the future,the comprehensive utilization of fine slag should be considered step by step and quality by quality,and the environmental protection and safety of downstream products produced from fine slag should be fully considered.(3)Based on a thermogravimetric analyzer,FSGE,FSOMB and FSGSP were mixed with YZP,YP and SZMP in the proportions of 25%,50%,75%and 80%respectively to study their co-combustion characteristics and combustion reaction kinetics,so as to help design and optimize the co-combustion system of fine slag and coal.The results show that with the increase of the addition ratio of fine slag,the initial combustion loss temperature of the mixed samples is pushed back,the combustion characteristic index is reduced,and the overall combustion performance is deteriorated.The Ti and Th of FSOMB combustion are higher than that of YP,and the order of composite combustion characteristics is YP>FSOMB.Therefore,YP burns at the fastest rate,while FSOMB burns at the lowest rate.Among all the samples,the composite combustion index and activation energy of YP were the highest,which were 97.67 × 10-8%2·min-2·?-3 and 35.16 kJ/mol,respectively,while those of FSOMB were the lowest,which were 0.51 X 10-8%2·min-2·?-3 and 90.53 kJ/mol,respectively.