Jiantao Zhao

Effect of CO2 on pyrolysis behaviors of lignite

Abstract The pyrolysis of Huolinhe lignite under CO2 atmosphere was carried out in a thermobalance and a fast heating-up fixed bed reactor. The distribution of gases, char yield and its property such as element, surface structure, FT-IR spectra were analyzed. By this, the effect of CO2 on the pyrolysis behaviors was studied. The results show that CO2 gasification of the nascent char, which destroys the hydrogen-containing char structure, not only promotes cracking of benzene ring and fracture of hydroxyl, methyl and methylene groups etc., but also weakens the interaction between H and char matrix and increases the H fluidity, leading to the increase in the generation of H radicals. These H radicals can combine with other free radical fragments generated from fracture of the coal macromolecules to produce more volatiles. This will produce the char with a high specific surface and high pore volume and porosity. The introduction of CO2 promotes the coal pyrolysis and generation of volatile, resulting in decrease in char yield and increase in the evolution amount of H2, CO, CH4 and other small molecules hydrocarbons.

Regeneration characteristics of sulfided zinc titanate sorbent for hot gas cleaning

Abstract The regenerated zinc titanate sorbent is one of the leading candidates for hot coal-derived gas desulfurization. The effects of the regeneration temperature, O 2 concentration, and sorbent granular size on the regeneration performance of the Zn 2 TiO 4 sorbent were investigated using the thermogravimetric analyzer. Zinc sulfate formed through side reactions was inferred from TGA curves and confirmed by XRD analysis when the sorbent was regenerated at higher concentration of O 2 and lower temperature ( 2 with regenerated ZnO in the presence of O 2 may be the main reason for the formation of ZnSO 4 . The reasonable regeneration conditions must avoid the sulfate formation. Regeneration kinetic studies were also performed at regeneration temperatures ranging from 725 to 800°C. Higher regeneration temperature and O 2 concentration, and smaller granular size can increase the regeneration rate. The reaction order with respect to O 2 can reasonably be assumed to be 1. Kinetic model tests show that the regeneration process can be well fitted by the shrinking core model. The kinetic controlling steps change with the sorbent regenerating. The chemical reaction rate is the controlling step at the early regenerating stage (x 75%). The reaction rate constants and the effective diffusivities were calculated according to the model. The apparent activation energy of chemical reaction and the corresponding frequency factor are 19.11 kJ/mol and 8.01×10 −2 m/s, respectively, and the diffusion activation energy and the corresponding frequency factor are 48.84 kJ/mol and 3.12×10 −4 m 2 /s, respectively.

Coal to Liquid Fuels by Gasification and the Associated Hot Gas Cleanup Challenges

Abstract Coal is the most important energy source in China. The utilization of coal should consider not only the efficiency but also the reduction of pollutants and CO2 emission. Compared with coal utilization by conventional combustion, the route to different products via coal gasification is recognized as the most advanced technological concept for clean coal use. The products from coal gasification cover the whole product spectra currently obtained from oil. This paper summarizes recent progress made in the Institute of Coal Chemistry, Chinese Academy of Sciences in the field of coal gasification, mainly in the gasification using an ash agglomerating fluidized bed gasifier together with the gas cleanup challenges, Fischer-Tropsch synthesis with an iron-based catalyst and a slurry bed reactor, higher alcohol synthesis, and the one-step dimethyl ether synthesis from coal-based syngas.

Catalytic deoxygenating characteristics of oxygen-bearing coal mine methane in the fluidized bed reactor

Abstract The catalytic deoxygenating experiment of oxygen-bearing coal mine methane (CMM) was carried out in a bench-scale fluidized bed reactor with the spherical Cu-based catalyst. The effects of the bed temperature, the particle size and the space velocity were investigated on the oxygen removal efficiency and CO2 selectivity. The rise of bed temperature could promote the oxygen conversion due to the high activity of the catalyst. The O2 conversion could reach more than 95% when the temperature was above 450°C. The smaller particle size was beneficial to the CO2 selectivity of the catalyst because of the decrease in inner diffusion resistance. The lower space velocity also could improve the oxygen removal efficiency when the bed temperature was below 450°C although the improvement almost disappears above 450°C due to the increase catalytic combustion rate. Additionally, by adjusting the CH4/Air ratio, the catalytic deoxygenation adaptability of the fluidized bed reactor and the catalyst were evaluated for the variable oxygen content in CMM. The results indicate that the process has a perfect oxygen removal performance with the O2 concentration less than 0.2% and the CO2 selectivity more than 98% for the O2 content from 5% to 15% in the simulated CMM.

Investigation on the fates of vanadium and nickel during co-gasification of petroleum coke with biomass.

This study investigates the volatilization behaviors and mineral transformation of vanadium and nickel during co-gasification of petroleum coke with biomass. Moreover, the evolution of occurrence modes of vanadium and nickel was also determined by the method of sequential chemical extraction. The results show that the volatilities of vanadium and nickel in petroleum coke have a certain level of growth with an increase in the temperature. With the addition of biomass, their volatilities both show an obvious decrease. Organic matter and stable forms are the dominant chemical forms of vanadium and nickel. After gasification, organic-bound vanadium and nickel decompose completely and convert into other chemical forms. The crystalline phases of vanadium trioxide, coulsonite, nickel sulfide, and elemental nickel are clearly present in petroleum coke and biomass gasification ashes. When the addition of biomass reaches 60 wt%, the diffraction peaks of orthovanadate are found while that of vanadium trioxide disappear.

Ash fusion characteristics during co-gasification of biomass and petroleum coke

In this study, the effect of biomass ash on petroleum coke ash fusibility was investigated at a reducing atmosphere. Some analytical methods, such as ash fusion temperatures (AFTs) analysis, X-ray diffraction (XRD), FactSage and scanning electron microscopy (SEM), were applied to determine the characteristics of ash fusion and transformation of mineral matters. The results indicated that AFTs were closely associated with ash mineral compositions. It was found that the formations of high melting point calcium silicate, vanadium trioxide and coulsonite resulted in the high AFTs of Yanqing petroleum coke (YQ). When blending with certain proportional pine sawdust (PS), corn stalk (CS), the AFTs of mixture could be decreased significantly. For PS addition, the formations of low-melting point calcium vanadium oxide should be responsible for the reduction of AFTs, whereas for CS addition the reason was ascribed to the formation of low-melting point leucite and the disappearance of high-melting V2O3.