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The thermal cracking of cotton stalks (CS) through pyrolysis was undertaken using a laboratory scale batch pyrolysis reactor. The distribution of pyrolysis products were studied dependent on the final pyrolysis temperature which ranged from 300 to 800 °C by 100K intervals. The maximum biochar yield of 46.5% was obtained at 400 °C. As the pyrolysis process temperature increased, the solid char product yield decreased. The largest higher heating value (25.845 MJ kg−1) was obtained at 600 °C. All biochar samples produced between 500 and 700 °C had an energy densification ratio of 1.41, indicating a higher mass-energy density than the initial feedstock. A larger share of syngas and bio-oil were produced at higher temperatures, as estimated. Preferential selection of a char based on the energy yield would lead to a selection of the 400 °C product, while selection based on the energy densification ratio would be for a product obtained between 500 and 700 °C. An energy simulation was conducted which determined that the process is self-sustaining at and above 400 °C. Furthermore, the global energy potential was determined from CS pyrolysis, which was estimated at 380 PJ yr−1 could contribute to roughly 0.1% of the actual global total primary energy supply of 576 EJ yr−1. • Biochar yields decrease and syngas yields increase with temperature increase from 300 to 800 °C. • The largest higher heating value (25.8 MJ kg−1) of biochar was obtained at 600 °C. • Process simulation showed that the pyrolysis process is energetically self-sustaining at 400 °C and above. • A temperature of 400 °C is optimal for deriving energy from the biochar. • Global energy potential from pyrolysis CS could contribute to 0.1% of the actual global total energy supply. [ABSTRACT FROM AUTHOR]

Three different waste streams from olive oil production from Montenegro are utilized energetically by hydrothermal carbonization (HTC – hydrochar) and pyrolysis (biochar). Pyrolysis experiments of three-phase olive mill solid waste (3POMSW) were conducted for different pyrolysis temperatures of 450, 550, and 700 °C and a residence of 60 min for each experiment. HTC experiments for two-phase olive mill waste (2POMW) and a mixture of olive mill wastewater (3POMWW) and 3POMSW were carried out at 180, 200, and 220 °C, autogenous pressure of (1, 1.6, and 2.3 MPa) for 60 min. Increasing reaction temperature led throughout all experiments to a lower carbon recovery. Furthermore, all hydrochar and biochar samples had energy densification of more than one, indicating a higher mass-energy density than the initial feedstock. The highest energy yields were achieved for the 3POMW, with 46.48 % in hydrochar treated at 180 °C and 44.09 % in biochar treated at 450 °C. Concerning the hydrochar from 2POMW, the highest energy and mass yields of 62.53 % and 49.65 %, respectively obtained at 180 °C. Summarizing, the energy potential of Montenegro's olive mill waste (OMW) was estimated at 43.69 PJ, which roughly could cover the whole energy demand of the olive oil industry in Montenegro. • Biochar and hydrocar energy potential derived from olive mills waste was evaluated. • Hydrocar derived at 200 °C for 60 min are suitable for substituting peat. • Biochar derived at 450 °C and above are suitable for substituting coal. • Pyrolysis and HTC are feasible methods to provide bioenergy olive mill waste. [ABSTRACT FROM AUTHOR]

Abstract Thermal conversion of ligno-cellulosic agricultural waste inside a pyrolysis reactor and soil-storage of pyrolysis char is discussed as a low-tech negative emission technology. Cotton stalks are a typical agricultural residue with little economic value and there is no direct competition to food or feed provision. Currently, the stalks are often burnt on the fields. The investigated rotary kiln pyrolysis process has already been successfully applied at industrial scale before. In the investigated scenario, the pyrolysis char is returned to the soil for long-term carbon storage while the volatile pyrolysis products are used energetically. The steady-state process simulation environment IPSEpro was used to assess a virtual conversion plant. The mass- and energy flows are determined based on earlier measurements at a 500 kg/h test plant. The results show that 52.8% of the carbon contained in the biomass accumulate in the biochar, whereas 38% of the input energy can be exported as heat energy at temperature levels suitable for electricity generation or industrial heat supply. The pyrolysis char shows a low molecular O/C ratio of 0.07 and an H/C ratio of 0.26. The expected half-lives of biochar in soil are in the order of 1000 years for O/C ratios below 0.2. This makes the presented approach an interesting low-tech negative emission option. The predicted net negative emissions through stored carbon amount to 2.42 t CO 2 per hectare and year. The overall CO 2 emission avoidance effect can be increased if fossil fuel is substituted by the energy exported from the pyrolysis process. Highlights • Low-value agricultural waste materials such as cotton stalks can serve as carbon precursor for negative emission solutions. • For slow pyrolysis of dry lingno-cellulosic material, roughly 53% of the carbon are found in the biochar product. • About 40% of the lower heating value-based energy in the feed biomass can be exported as heat. • The direct negative emissions through soil-storage of char from cotton stalks amount to 2.42 t CO 2 per hectare and year. [ABSTRACT FROM AUTHOR]