X. X. Han

TG–DSC analysis of pyrolysis process of two Chinese oil shales

According to the recommendations developed by the Kinetics Committee of the International Confederation for Thermal Analysis and Calorimetry (ICTAC), non-isothermal pyrolysis experiments were carried out to analyze and compare two types of oil shale from the northeast of China using simultaneous differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis at temperatures ranging from 40 to 850xa0°C. The pyrolysis process of oil shale begins with the evaporation of small molecular substances, then continues by the pyrolysis of kerogen, and finally ends mainly with the complete decomposition of carbonates. In this whole process, almost 36xa0% of overall pyrolytic heat was used for the pyrolysis of kerogen. When retorting air-dried basis oil shale below 520xa0°C, a considerable proportion of the heat required will have to be used mainly for the evaporation of small molecular substances below 185xa0°C. Specific heat capacities of two oil shale semicokes were measured below 500xa0°C by DSC method, showing that specific heat capacity of semicoke will increase with the increase of the temperature, and carbonization of kerogen can bring about a further positive effect on it. Coats–Redfern method was used to calculate kinetic parameters in three pyrolysis stages.

Intrinsic Conversion Mechanism on Nitrous Oxide and Nitrogen Oxide During Circulating Fluidized Bed Combustion of Oil Shale

ABSTRACT At a 5-m-high large-scale thermal state circulating fluidized bed (CFB) test rig adopting an automatic discrete control system, an experimental investigation on continuous combustion of oil shale was carried out, analyzing in detail the variation trade of bed temperature distribution and flue gas concentration, including oxygen (O2), moisture (H2O), carbon dioxide (CO2), nitrogen oxide (NO), and nitrous oxide (N2O) at different operational factors consisting of bed temperature and O2 concentration at cyclone outlet. The characteristics of nitrogen (N) conversion during continuous CFB combustion were calculated and analyzed emphatically. The results indicate that N2O and NO emissions decrease gradually when raising bed temperature, and increase considerably when lifting O2 concentration during continuous combustion of oil shale. Adopting a detailed mechanism calculation method, the reaction mechanism during oil shale CFB combustion was studied. The conversion paths about key formation and decomposition mechanism between nitrogen components are that, first NO converting to NO2 and N2O is reversible, then NO2 converts to N2O easily, and finally N2O converts to N2. Promoting N2O formed by NO converted to N2 but not NO is an effective method to decrease N2O and NO emissions. In addition, the high content of CaO in oil shale promotes catalysis on N2O decomposition. It plays an important role on combustion reaction rate of bed temperature and oxidative free radical, which shows that N gross conversion would remain at a lower level at the operational condition with bed temperature reaching to or above 850°C, and low N2O and NO emissions require excess air to be limited. The above finding can provide guidance for the operation and pollution control of oil shale-fired CFB boilers.