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Heat capacities of kukersite oil shale in comparison with available data of other oil shales


N. Savest1 and V. Oja1

1Tallinn University of Technology, Estonia

Keywords: thermal properties
property: heat capacity
material: oil shale

Due to large world oil shale reserves, estimated to be equivalent to more than 2.9 trillion barrels of recoverable oil, there is a general expectation that oil shale should become a considerably significant source for high-value oil products and chemicals. Oil shales are complex heterogenous materials with organic part consisting primarily of kerogen that can be described as a highly cross-linked macromolecular structure. Therefore all existing oil shale upgrading technological approaches require heating to take kerogen to temperatures at which thermochemical conversion processes are sufficiently fast. For ex-situ retorting processes, for the primary technology route in industrial practice, the temperature region is at about 500 oC. As oil shales are characterized by high mineral matter content (even for oil shales of industrial interest it is about three to four times higher than the organic content), then the major amount of process heat is consumed with heating oil shale and it can be evaluated approximately based on heat capacity data. The heat of pyrolysis reactions by itself is relatively small. Therefore, the heat capacity of oil shales and its thermo-chemical conversion solid products are desirable engineering information in design of thermochemical conversion processes such as retorting and combustion. However, there are relatively few heat capacity data sets from the past to be found for oil shales in publically available literature. For example, although since 1924 eight different technologies/processes producing oil or/and gas have been applied in Estonian for oil shale thermo-chemical conversion in pilot or commercial scale, our literature review indicated that the research on heat capacity of Estonian Kukersite oil shale were done from 1938 till 1959, mostly from 1955 to 1959. We did not find any newer reports. Later literary sources refer to the data investigated and published in various works of 1955-1959 without indicating the conditions (temperature, the content of the samples) and usage range the equations. Moreover, although the kukersite oil shale heat capacity data sets are consistent in the temperature region below 100 °C (in the measurement region), then when extrapolated up to 350-400 °C the obtained values differed to about twice. This presentation is aimed to evaluate the heat capacity of kukeriste oil shale up to the temperatures of oil shale kerogen thermal degradation. The variation of heat capacity with temperature for other oil shales is to be presented to comparison. Insofar literature indicates a wide variation in heat capacity behavior of specific oil shales from ambient temperature up to about 350- 400 °C, suggesting that the industrial need for accuracy is not so critical.


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