Study Of Coal Direct Liquefaction Residue Pyrolysis Characteristics

Coal direct liquefaction technology is one of the clean and efficient technology of the coal-using, and there are many technologies to separate the solid-liquid product, the most commonly used method is reduced pressure distillation,from which can obtain residue about30%of the raw coal. Coal direct liquefaction residue mainly from the unconverted coal, coal minerals, the product of liquefaction process as well as the reaction catalyst. Coal direct liquefaction industrialization is accelerating at the same time must consider the clean and efficient utilization of liquefaction residue. In this paper, the liquefaction residue of Shenhua coal liquefaction plant is the research object, its physical and chemical characteristics, the behavior of pyrolysis, pyrolysis products and the dynamics and so on have been researched.Residue industrial analysis and elemental analysis showed that the residue is a high carbon, high ash and high sulfur substances; do four-component separation of the Soxhlet extraction residue, its four component heavy oil (HS), asphaltenes (A), before asphaltene (PA) and tetrahydrofuran-insoluble (THFIS) is in the order of (5.46±0.96)%,(30.28±2.88)%,(22.41±1.15)%,(41.00±3.89)%, show that mainly composition of the residue is THFIS and A; the residues and four component FTIR analysis and1H-NMR analysis showed that the whole residue and its respective components mainly are heavy components, the residue of the aromatic carbon ratio is0.815, the degree of condensation of the aromatic ring is0.582; the HS GC-MS analysis showed that the components of the heavy oil mainly containing fused aromatic ring of4to6rings.Investigated using thermal gravimetric analysis to examine the residue pyrolysis behavior in different heating rates, different atmosphere, different granularity, and the results show that the residue in N2,(0.1H2+0.9N2) atmosphere have shown two pyrolytic section that pyrolysis active stage and high temperature decomposition section, but a certain concentration of H2exist, the maximum weight loss rate is relatively higher, the half peak width is minimum and pyrolysis product release characteristic index R is maximum,which have a certain promoting role on the pyrolysis; In CO2atmosphere, cryogenic segment pyrolysis behavior is similar with N2and (0.1H2+0.9N2) atmosphere, but there is a clear downward trend in the above840℃; at pyrolysis heating rate of10/min,30/min,50℃/min,70℃/min, low temperature of30℃/min is conducive sufficient residue pyrolysis, but low10℃/min, the pyrolyzed product escaping contrary less; within the range of40to300mesh, the granularity of the residue have little effect on the pyrolysis behavior.At900℃final temperature while N2atmosphere, weight loss rate is33.9%before demineralizing, while weight loss rate declined slightly to32.8%after demineralizing, corresponding to half peak width increases, the R value also declined slightly, indicating that the pyrolysis characteristics of demineralizing residue is weaker than the raw residue, minerals exist in residue have a certain promoting role on its pyrolysis。For fixed bed pyrolysis experiment, respectively investigated residue pyrolysis behavior at400℃,500℃,600℃,700℃,800℃,900℃final temperature, and maximum is29.2%as600℃final temperature, the value is smaller relative to thermal gravimetric analysis.Pyrolysis tar by GC-MS analysis showed that its composition mainly are the fused ring aromatics and branched chain aliphatic hydrocarbons containing fused ring aromatics, such as fluoranthene, indeno pyrene, phenyl perylene, etc.; pyrolysis tar still include22%residues, which showed the pyrolysis process had the polycondensation phenomenon; SEM found that under the condition of700℃pyrolysis the residue coke the stomatal up, most rough surface; Spectrum analysis showed that the residue coke with the rise of temperature, C content increasing, O content is reduced, and other Fe, S, Ca, Si content change is not big.For residue under N2atmosphere at different heating rates pyrolysis behavior, do the three common kinetic analysis, the results showed that the C-R method best obtained fitting effect at residue lively pyrolysis stage, the activation energy is (63.0-73.1) KJ/mol; F-W-O method and DAEM method fit approximately, the activation energy obtained with the conversion rate a (0.2to0.8) increases monotonously increased change;in the active pyrolysis temperature segment, C-R method is more suitable to describe its pyrolysis kinetics, the pyrolysis behavior is a first order reaction.