Description of the material

Ground oil shale semicoke was prepared in a laboratory retorting furnace under inert atmosphere. A laboratory combustion cell was then used to operate the combustion of the semicoke added with more or less sand and/or carbonates. This enabled to vary independently the amount of CaCO3 and the amount of fixed carbon in the mix. The temperature of the combustion front propagating in this mix was recorded, together with its velocity. The flue gas was analysed.

Application

Propagating a combustion front through a fixed bed is a way to produce oil and a fuel gas from oil shale or to recover energy from oil shale semicoke in the retort process. When operated with air, this process involves high temperatures - typically larger than 1000C□B0C -resulting in the decarbonation of the carbonate matrix and the emission of additional CO2. The aim of this work was to avoid this decarbonation.

Results, Observations, and Conclusions

It is shown that increasing the amount of CaCO3 in the medium (with constant fixed carbon amount) can decrease the combustion front temperature down to 800C□B0C but not below, which is not sufficient to avoid decarbonation. Decreasing the amount of fixed carbon can decrease the temperature down to 600C□B0C, a temperature at which decarbonation occurs only a bit. At this temperature, not all the oxygen in the fed air is used, which results in a slowing down of the combustion front.

Significance of Subject Matter

To our knowledge, no results have been published yet where the two parameters of carbonate amount and fixed carbon amount were varied independently, and where their impact on the front temperature and decarbonation were determined. Avoiding decarbonation in such processes is a potential very significant way to reduce CO2 emissions.

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