Haokan Chen

The variation of structural characteristics of macerals during pyrolysis

Abstract Vitrinite and inertinite were separated by DGC from Chinese Shenmu bituminous coal and the structural characteristics of the macerals, before and after pyrolysis, were analyzed by ultimate analysis, FTIR and 13 C NMR. The results showed that vitrinite chars always had higher H and lower C content than inertinite char at the same pyrolysis temperature. The FTIR and 13 C NMR indicated that vitrinite had more aliphatic C–H, hydrogen bonding and lower aromaticity. With increasing temperature, the aliphatic C–H decreased, aromatic C–H, aromaticity and H ar /H al ratio increased. At the same temperature, inertinite always had higher H ar /H al ratio than vitrinite, which is consistent with that inertinite had higher aromaticity than vitrinite. And the H ar /H al ratio was also related to the remainder volatile matter. With increasing H ar /H al ratio, the remainder volatile matter in vitrinite and inertinite decreased. The higher aromaticity and H ar /H al ratio and lower H content of the inertinite in all temperature range were correlated with its higher thermal stability and lower volatile yield than vitrinite.

Occurrence and volatilization behavior of Pb, Cd, Cr in Yima coal during fluidized-bed pyrolysis

The volatilization behavior of Pb, Cd, Cr and the influence of coexisting mineral matters were investigated during pyrolysis of Yima coal in a fluidized-bed reactor at temperatures ranging from 500 to 900 °C. The modes of occurrence of Pb, Cd, Cr in Yima raw coal and two char samples were determined using density fractionation, demineralization and sequential chemical extraction methods. Lead in Yima coal is mostly associated with mineral matter in various forms, mainly pyrite, sulfates and monosulfides. Large part of cadmium is associated with pyrite. Chromium in Yima coal is mainly associated with organic matter. Different trends are observed for various forms of trace metals during pyrolysis. Lead associated with pyrite, sulfates and carbonates, lead in water soluble and ion exchangeable forms, and cadmium associated with pyrite are all unstable under pyrolysis conditions. During Yima coal pyrolysis, the volatilities of lead and cadmium vary greatly with pyrolysis temperature, while chromium volatility in Yima raw coal only has slight changes over the temperature range (500–900 °C) studied. The volatility of Pb, Cd, Cr in demineralized Yima coal (YimaD) is much higher than that of Yima coal during pyrolysis. New thermally stable forms of Pb, Cd and Cr are formed during pyrolysis of Yima, whereas the sources of them are different. The interactions between chromium and its coexisting mineral matters in Yima coal retard its vaporization during pyrolysis.

Effects of Coal Characteristics on the Properties of Coal Water Slurry

ABSTRACT The effects of coal characteristics on the properties of coal water slurry (CWS) were systemically studied using sixteen Chinese coals of different ranks from lignite to anthracite. The correlation between coal properties and CWS characteristics were investigated by multivariate progressive regression analysis. CWS properties examined in this study included slurryability (concentration of slurry that gives an apparent viscosity at 1200 mPa · s at a shear rate of 28.38 s−1), rheological behavior (represented by a flow index), and static stability (days for formation of soft sediment). Coal properties examined in the study included coal rank, air equilibrium moisture (Mad), maximum moisture holding capacity (MHC), ash content, surface properties, petrographic macerals, pore structure, and adsorption characteristics of dispersants.

Devolatilization Characteristics of Shenmu Coal Macerals and Kinetic Analysis

The pyrolysis of Shenmu coal macerals was performed in TG151 thermobalance. The volatile matter evolved in primary and secondary devolatilization and devolatilization kinetics were studied. The volatile matter evolved during primary devolatilization is the major part of the total volatile matter, especially for vitrinite. The percentage of volatile matter evolved during primary and secondary devolatilization suggested that inertinite have higher thermal stability. Though the heating rate can affect the percentage of volatile matter evolved during primary and secondary devolatilization, the order of volatile matter in all the temperature range is the same: vitrinite > parent coal > inertinite. The kinetic analysis of devolatilization using distributed activation energy model (DAEM) shows that the activation energy existed relatively large error at the conversion of initial 10% and final 10%. And the conversion of 10% to 90% was used to describe the variation of activation energy during pyrolysis. The activation energy of vitrinite appeared a minimum of about 50% conversion, but that of inertinite always increased as pyrolysis went on, indicating the different structure and chemical composition between them. Inertinite has higher activation energy and lower pyrolysis rate than vitrinite.

Suppressing cross-linking reactions during pyrolysis of lignite pretreated by pyridine

Abstract A Chinese lignite Yitai (YT) was pretreated by pyridine vapor and pyridine solvent. The effects of the treatments on the pyrolysis behavior of the pretreated coals were studied by thermogravimetric mass spectrometry (TG-MS). The results showed that both treatments could suppress the cross-linking reactions (CLRs) during pyrolysis of the treated coal, but the suppressing temperature range and mechanism were different. Some inherent hydrogen bonds (HBs) in the coal were broken by pyridine vapor treatment and new stronger N—OH HBs were formed. Thus, low temperature CLRs (below 400°C) that were related to the hydrogen-bonded COOH—COOH and COOH—OH were suppressed. However, pyridine solvent pretreatment influenced the pyrolysis behavior by reducing the association interactions between the low molecular weight compounds and macromolecular network, thus, relaxing the three-dimensional network of coal and enhancing the transmission efficiency of hydrogen in coal.

Thermogravimetric-Mass Spectrometric Study of the Pyrolysis Behavior of Shenmu Macerals Under Hydrogen and Argon

The pyrolysis characteristics of macerals separated from Chinese Shenmu coal were systematically investigated using TG-151 pressurized thermobalance coupling with mass spectrometer under 0.1 MPa of Ar and H2, heating rate of 10°C/min and final temperature of 900°C. The TG/DTG results showed that vitrinite always had a higher volatile matter yield, larger maximum rate of weight loss, lower temperature of the maximum rate of weight loss than inertinite. Inertinite showed high response to the external hydrogen, especially at a higher temperature. The gases evolved during thermogravimetric analysis of macerals were analyzed on-line by mass spectrometer for the relative intensity of H2O, C1–C4, and C6H6. An obvious difference in evolution curves could be observed. The content of all gases evolved from vitrinite was higher than those from inertinite in both atmospheres. The amount of H2O and light hydrocarbons was higher in H2 than that in Ar, indicating the hydrogenation of oxygen-containing functional groups and free radicals formed during pyrolysis. The evolution curves of H2O and CH4 had different peak distributions and evolution temperatures under H2 and Ar, suggesting the different reaction mechanism during pyrolysis in different atmosphere. The evolution curves also revealed the different structural characteristics among vitrinite, inertinite and the parent coal.