Abstract
In order to contribute to the decarbonization of the economy, efficient alternatives to coal and coke should be found not only in the power sector but also in the industrial sectors (like steel, silicon and manganese production) in which coal and coke are used as a reductant and for steel production also as a fuel. To this aim many research works have been focused on the development of a coke substitute based on woody biomass and known as “biocarbon”. There are still barriers to overcome, among them: the biocarbon low density, poor mechanical strength and high reactivity. In this paper a new biocarbon production methodology is proposed, based on: pyrolysis at 600 °C, densification (using pyrolysis oil as binder), reheating of the obtained pellet. Response surface methodology with a Box-Behnken experimental design was utilized to evaluate the effects of the process conditions on the pellet’s quality. Responses showed that densification was mainly affected by oil content and pelleting temperature, while pelleting pressure had a minor influence. The pelleting process has been finally optimized using Derringer’s desired function methodology. Optimal pelletizing conditions are: temperature equal to 60 °C, pressure equal to 116.7 MPa, oil content concentration of 33.9 wt%. These results are relevant for metal production industries at a global level. The identified optimal parameters of the new biocarbon production process can contribute to replace coke with sustainable fuels and probably reduce great part of the related greenhouse gases emissions.
Highlights
Vegetal biomass can be used as a valid substitute for fossil fuels, reducing Greenhouse Gases (GHG) emissions and energy imports [1]
It was previously demonstrated that the mechanical properties of biocarbon pellets blended with pyrolysis oil improved significantly when the pellets were thermally treated at high temperatures, due to a further carbonization of the biocarbonoil structure [26]
This work was carried out to analyze the coupling between pyrolysis of wood and pelletization of the obtained biocarbon, using recovered pyrolysis oil as binder
Summary
Vegetal biomass can be used as a valid substitute for fossil fuels, reducing Greenhouse Gases (GHG) emissions and energy imports [1]. Biocarbon is a product similar to coke and coal and is obtained by thermally treating of the biomass in absence of oxygen [4] This treatment (pyrolysis) is usually performed at ambient pressure at temperatures between 300 and 600 °C [5]. Bio-oil, which is a by-product of pyrolysis, may be used as binder in order to both improve the energy recovery of the process and to improve the characteristics of the biocarbon pellets. In [22], the introduction of bio-oil as binder improved the mechanical properties and the energy density of biocarbon pellets. It was previously demonstrated that the mechanical properties of biocarbon pellets blended with pyrolysis oil improved significantly when the pellets were thermally treated at high temperatures, due to a further carbonization (and polymerization) of the biocarbonoil structure [26]. Biocarbon and raw wood differ in chemical and physical composition and the available results should not be lightheartedly used for pyrolyzed biomass
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