Introduced in the literature in 1913 by Bergius, who at the time was studying biomass coalification, Hydrothermal Carbonisation, as many other technologies based on renewables, has been forgotten during the...

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Coal pyrolysis is generally performed in atmospheres without oxygen and at temperatures below 650 °C for producing pyrolysis liquid and gas. To support the development of a new two-stage gasification process integrating a fluidized-bed pyrolyzer and a downdraft fixed-bed gasifier, this paper investigated the coal pyrolysis in atmospheres containing oxygen and steam and at temperatures up to 900 °C to understand the viable pyrolysis conditions in view of process adaptation. The examined pyrolysis characteristics include the product distribution, char gasification reactivity, and tar composition. The pyrolysis gas yield, especially the yields of H2 and CO, increased with elevating the temperature and mass ratio of steam/coal (S/C). Adding O2 to the reaction atmosphere promoted the formation of CO and CO2 but decreased that of H2. The inclusion of O2 and steam in the atmosphere resulted in chars with a larger surface area and more micropores. At 900 °C in N2 atmosphere or at 850 °C with oxygen in the atmosphere (e.g., at an excessive air ratio of 0.22), graphitization was observed in the produced char, which lowered the char gasification reactivity. Analyzing the produced tar via thermogravimetry coupled with Fourier transform infrared (TG−FTIR) spectroscopy clarified that the presence of steam significantly affected the tar composition by leading to more aliphatic hydrocarbons and lowering the contents of single-ring aromatics, phenols, and ketonic species. Thus, the pyrolysis gas product from a steam-containing reaction atmosphere would be easier to crack and be reformed in the downstream char gasifier.

In this paper, the effects of process conditions on catalyst performance and product properties are reported in both batch and continuous set-ups.