Zongqing Bai

Influences of mineral matter on high temperature gasification of coal char

Abstract X-ray diffraction (XRD) was performed to analyze the mineral matter in coal ash from 1100 to 1500°C, with an interval of 50°C. Relative Intensity Ratio (RIR) method was used to calculate the content of each crystalline in coal ash. The amount of mullite increases with elevated temperature but that of SiO2 decreases. The transformation of mullite and SiO2 accords well with the binary phase diagram of SiO2–Al2O3. At high temperature, the amorphous mineral matters, mainly, aluminosilicates melt above ash softening temperature. During CO2 gasification at high temperature, the carbon conversion is hindered by the aluminosilicates melts, which cover the surface and block the pores of coal particles. Because of the short and ordered sequence of melts, FT-IR analysis was taken for the melts in coal ash after gasification. The structure alteration of aluminosilicates influences the surface tension of melts, which determines the interaction between coal particles and aluminosilicates.

Effect of Na2O on mineral transformation of coal ash under high temperature gasification condition

Abstract In order to reveal the mechanism of Na 2 O influence on ash fusion temperatures (AFTs), effect of Na 2 O on mineral transformation of two coal ashes with different SiO 2 +Al 2 O 3 levels were investigated by XRD and FT-IR under reducing atmosphere at high temperature. Thermodynamic software package FactSage was used to calculate the Δ G of reactions between minerals to reveal the mechanism of Na 2 O influence on mineral transformation. It is found that the effect of Na 2 O on mineral compositions depends on SiO 2 +Al 2 O 3 levels of coal ash. For ash with 82.89% SiO 2 +Al 2 O 3 while Na 2 O content is 5%–20%, albite and nepheline are formed, leading to a decrease of AFTs. However, only nepheline is formed when Na 2 O content is higher than 20%. For ash with 47.85% SiO 2 +Al 2 O 3 , when Na 2 O content is less than 10%, no Na-containing mineral is observed. When Na 2 O content is higher than 10%, Na-containing minerals such as combeite, lazurite and sodium aluminium oxide are formed, resulting in a decrease of AFTs. Furthermore, FactSage results reveal that Na-containing mineral is easily formed at high temperature due to low Δ G of the reactions.

Decomposition kinetics of hydrogen bonds in coal by a new method of in-situ diffuse reflectance FT-IR

Abstract The kinetics of decomposition of hydrogen bonds in a Chinese lignite was studied using a new method of in-situ diffuse reflectance FT-IR (DRIFT) with pulverized coal samples directly. In addition, a new experimental technique in DRIFT measurement to avoid the condensation of volatile matter at high temperatures was introduced and used in this work. Based on two hypotheses, the single reaction model is used to calculate kinetic parameters for decomposition of hydrogen bonds (except OH-π) in coal heated up to 560°C. The results show that the decomposition of carboxylic acid dimers, OH-N and SH-N follows the second order reaction, while the decomposition of OH-OR2, tightly bound hydroxyl tetramers and self-associated hydroxyls follows the first order reaction. The calculated activation energies of some hydrogen bonds agree well with those obtained with other methods in references. Among the six types of hydrogen bonds studied, the decomposition of carboxylic acid dimers, OH-N, SH-N and tightly bound hydroxyl tetramers can be divided into two stages (230-380°C and 380-500°C), while that of OH-OR2 and self-associated hydroxyl groups can be treated as only one stage. Moreover, the mechanism of decomposition of tightly bound hydrogen bond was suggested based on the comparison of decomposition activation energy of self-associated OH with its bond strength in references.

Coal pyrolysis under synthesis gas,hydrogen and nitrogen

Chinese Xundian and Mongolian Shiveeovoo lignites, and Khoot oil shale were pyrolyzed under synthesis gas (SG) at temperature ranging from 400 to 800°C for the lignites and from 300 to 600°C for the oil shale with a heating rate of 10°C/min in a fixed bed reactor. The results were compared with those obtained in pyrolysis under hydrogen and nitrogen. The results show that higher liquid yields with lower yields of char and gas are obtained in pyrolysis of oil shale under SG and H2 than under N2, but the differences are slight. It is found that the pyrite S can be easily removed and partially converted to organic S under various gaseous atmospheres. The total sulfur removal for oil shale is considerably less than lignite, which may be related to its high ash content. The higher total sulfur removal and the less organic S content in the presence of SG in comparison with that under N2 and also under H2 in pyrolysis of Xundian lignite may result from the action of CO in SG. However, CO does not show its function in pyrolysis of Khoot oil shale, which may also be related to the high ash content. The results show the possibility of using synthesis gas instead of pure hydrogen as the reactive gas for coal hydropyrolysis.

Effect of lime addition on slag fluidity of coal ash

Abstract The ash fusibility temperature (AFT) and slag fluidity of three different coal ash samples through addition of CaO with different amounts were studied. Especially the variation of temperature at critical viscosity was examined at different viscosities. The results show that the fusibility temperatures of coal ashes decrease and then increase with increasing addition amount of CaO, which is consistent with the change of liquids temperature with CaO content calculated by FACTsage. Slag viscosity also decreases with increasing amount of CaO addition above the temperature of critical viscosity ( T cv ). The temperature of critical viscosity firstly decreases with increasing addition of CaO, and then reaches a minimum value when the content of CaO is around 15%. FCATsage was employed to calculate the liquid composition at the temperature of critical viscosity. It indicates that high content of FeO of liquid leads to the low temperature of critical viscosity.

Sulfur transformation during pyrolysis of Zunyi coal by atmosphere pressure-temperature programmed reduction-mass spectrum

Abstract The effects of temperatures and atmospheres on sulfur transformation during pyrolysis of Zunyi (ZY) raw coal and its chars were investigated by AP-TPR-MS combined with chemical analysis. The results show that stable organic sulfur is the main sulfur form in ZY coal. Pyrite can be removed under all the atmospheres in the tests, except for nitrogen at 500°C. 1% O 2 -N 2 atmosphere has strong ability to remove the stable organic sulfur in ZY coal, especially at 700°C. Under 1% O 2 -N 2 atmosphere, not only a part of stable organic sulfurs can be decomposed, but also more stable organic sulfur-containing structure can be broken down into less stable one. Syngas and 1% O 2 -N 2 atmospheres have almost the same effect as hydrogen on sulfur transformation at 700°C.

Transformation of minerals in direct coal liquefaction residue under gasification atmosphere at high temperatures

Abstract The transformation behavior of mineral matters in direct coal liquefaction residue from Shenhua Corporation under gasification atmosphere at high temperatures was examined by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Mossbauer spectroscopy was also applied to investigate the iron-bearing minerals and the valence distribution of iron in ash at different temperatures. The results show that the major minerals in coal liquefaction residue are quartz, calcium sulfate, millosevichite, pyrrhotite, kaolinite, and calcite. At high temperatures, they become anorthite, gehlenite, maghemite and magnetite. Due to the formation of anorthite, gehlenite eutectic, ash of coal liquefaction residue exhibits low fusion temperature. The iron-bearing minerals characterized in ash include maghemite, magnetite, fayalite, and the vitreous matter. The content of iron in vitreous matter increases with increasing temperature. Meanwhile, Fe 2+ /Fe 3+ significantly increases from 1.08 to 2.39 as temperature increases from 1100 to 1200°C for the reduction of maghemite, and it is not obviously changed above 1200°C. Furthermore, the liquid phase in ash calculated by FactSage increases with temperature owing to the increase of iron in vitreous phase. In hence, high content of iron in ash from coal liquefaction residue is the major reason for its low ash fusion temperatures.

Production of hydrogen by steam gasification from lignin with Al2O3·Na2O·xH2O/NaOH/Al(OH)3 catalyst

Abstract Some influencing factors on hydrogen production from steam gasification of lignin with Al 2 O 3 ·Na 2 O· x H 2 O/NaOH/Al(OH) 3 catalyst in a fixed bed reactor were examined. The results show that the formation rates of hydrogen increase with increasing ratio of Na 2 O/C and ratio of vapor to lignin as a whole. Higher flow rate of vapor is conducive to inhibit the generation of CO and CO 2 at lower temperature. H 2 O(g) produced by the hydrates contained in the catalyst can bring on more Na + and OH − ions to be formed by dissociation of NaOH within the catalyst. This leads to more remarkable reduction of the C—H bond energies of lignin. The conversion degree of hydrogen of lignin at 473–973 K reaches 134.94%, which shows that the present catalyst has good catalytic activity on hydrogen production from steam gasification of lignin at low temperature.

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.

Influence of coal blending on mineral transformation at high temperatures

Abstract Transformation of mineral matter is important for coal utilization at high temperatures. This is especially true for blended coal. XRD and FTIR were employed together to study the transformation of mineral matter at high temperature in blended coals. It was found that the concentration of catalytic minerals, namely iron oxides, increases with an increasing ratio of Shenfu coal, which could improve coal gasification. The transformation characteristics of the minerals in blended coals are not exactly predictable from the blend ratio. This was proved by comparing the iron oxide content to the blending ratio. The results from FTIR are comparable with those from XRD. FTIR is an effective method for examining variation in mineral matter.