Baizhong Sun

Research to Trace Element during Huadian Oil Shale Pyrolysis

Oil shale is quite abundant in the world. Today, the industry of oil shale retorting for shale oil production sprang up because of the deficiency in oil. In order to study the migratory behavior of trace elements during oil shale pyrolysis, the experiment was performed at different temperatures from 360 to 560°C on retorter in lab with the oil shale of Hudian China. The trace elements of Ba, Co, Cr, Cu, Mn, Ni, P, Pb, Sr, Ti, V, Y in oil shale and spent shale (semi-coke) were determined by the inductively coupled plasma atomic emission spectroscopy (ICP-AES). Hg and As were determined by atomic fluorescence spectroscopy (AFS). Mass balance and partitioning of trace elements have been studied to determine the fate of trace elements after retorting. By comparing the contents of different trace elements in oil shale and semi-coke, the distribution characteristics of trace elements during pyrolysis were studied. The analyses of trace element, on a whole-coal dry basis, indicate that some elements were enriched in the oil shale samples, including Mn (more than 30 ×), P (more than 6 ×), and Ti (more than 5×). The elements of Ti, Ba, Co, Cr, Cu, Mn, and V were enriched in semi-coke during retorting and could be considered as enriched in semi-coke when compared to Earth’s crust averages. Pb and Hg started to volatilize at 410°C,As and Co were enriched about 60% in semi-coke at 560°C. The release of trace elements was promoted in reducing atmosphere. The effect of heating rate on different elements can be found in these experiments. For most of elements, the characteristics of release from oil shale can be promoted by the high heating rate as well as the nitrogen atmosphere.

Study on The Kinetic Characteristics in Pyrolysis Process of Huadian Oil Shales by Isoconversional Method

Thermal analysis is increasingly used to obtain kinetic datum relating to samples decomposition. The popular model-fitting approach gives excellent fits for nonisothermal data but yields highly uncertain values of Arrhenius parameters. On the other hand, the model-free approach represented by the isoconversional method is recommended as a trustworthy way of obtaining reliable information from nonisothermal. So, in this research the thermal decomposition of Huadian oil shale samples was studied on the thermogravimetric analysis (TG, DTG), at heating rates of 10,20,40,100 °C/min under the nitrogen environment. The apparent activation energy in pyrolysis reactions of two kinds of oil shale samples has been analyzed by the isoconversional method of Friedman. The Sestak’s complex mechanism was used to fit liner for the pyrolysis reaction mechanism of oil shales, and the decomposition mechanism and frequency factor (A) were obtained. The results show that the activation energy is not a constant throughout the reaction process. But in the range of 0.1–0.9 for the conversion rate, the activation energy changes slightly. Oil shale pyrolytic mechanisms are complex and mainly attribute to the nuclear mechanism. The reason was discussed.

Study on Thermal Kinetic Mechanism of Oil Shale

Thermogravimetric experiments were performed on Pyris-1 TGA thermal analyzer, and pyrolysis curves of four oil shale samples at different heating rates were obtained. According to Maleks method, the kinetic mechanism function of sample was determined by using the standard curves and experimental curves of y(Â?)-Â?. The influences of heating rates and species of oil shale samples on the kinetic mechanism function were analyzed. The results showed that, at the different heating rates, the heat transfer rates, temperature gradient and the chemical reactions in the interior of oil shale samples are varied, and then the kinetic mechanism function of sample is changed; The kinetic mechanism functions are not unique at the special heating rate for a single sample, which depend on the conversion rate Â?: When a Â? is less than 0.5, the weight loss during pyrolysis process, has been attributed to the loss of moisture, interlayer water from clay minerals and thermal decomposition of minerals; When Â? equals to 0.5 or so, the weight loss is due to cracking of clay minerals; When Â? is greater than 0.5, the decomposition of carbonate minerals (such as calcite, dolomite, ankerite and other carbonates). When the species of samples are different, chemical structure and the physical characteristics (such as heat transfer coefficient, voidage, specific heat capacity) are various, kinetic mechanism functions are also different, the serial numbers of kinetic mechanism functions are advanced with Â? increasing for a special sample.

Combustion Characteristics studies of oil shale de-ash-like

Oil shale from the 4th layers of Dachengzi mines in Huadian was treated by the acid-type chemical solution process, and the experiment was optimized by the orthogonal method with three factors and three levels. Combustion characteristics of oil shale de-ash-like and the effect of ash content and temperature rising rate on combustion characteristics was investigated by thermogravimetric analysis method. Result and conclusion: the ash content in the treated oil shale is significantly reduced to 4.13%, the volatile content in the treated oil shale is reduced, and the fixed carbon content in the treated oil shale is increased largely from 5.31% to 67.89%. The thermogravimetric analysis shows that with the decrease of ash in oil shale de-ash-like, diffusion resistance of the oxidation medium spreading to combustible ash layer is greatly reduced, which is more conducive to burning, energy consumption of burning is reduced and its effect on ignition and burnout is also reduced to minimum. Under the same final temperature, the burnout degree of oil shale after removing mineral falls with temperature rising rates. Finally, combustion kinetic parameters of oil shale de-ash-like were calculated by the integral method (Coats and Redfern method).

H2S Evolution during Oil Shale Pyrolysis

H2S evolution during different oil shale samples pyrolysis was studied in fixed bed in the nitrogen atmosphere. The results show the H2S evolution is influenced by pyrolysis conditions and properties of oil shale. The yield of H2S released for two samples had a marked change at 300600°C of final temperature and 5-50°C/min of heating rate. Both the H2S yields of two samples increase with grain size increasing. While the H2S yields of Huadian oil shale was far more than that of Wangqing under same pyrolysis conditions, which may be attributed to low sulfur content and high ash content of Wangqing oil shale. It is shown that the curve of H2S escaped for Wangqing has a single wave only below 550°C, while two successive waves for Huadian oil shale occur at 440°C and 590°C respectively. The reasons of such results may be attributed to different distribution of organic and pyrite sulfur between Wangqing oil shale and Huadian oil shale. At 600 , about 10% sulfur is released from Wangqing oil shale, while about 25% sulfur fixed in semi-coke; for Huadian oil shale, about 8% sulfur is distributed in gas while 37% in simi-coke. KeywordsOil shale; pyrolysis; H2S