The process of slow pyrolysis of seven nut shell samples, in a nitrogen-purged atmosphere, has been studied, as well as characteristics of biochar obtained. The heat carrier with a temperature of 400–600 °C (with a step of 100 °C) was supplied indirectly using a double-walled reactor. The heating rate was 60 °C/min. At increased temperature of the heating medium, a decrease in the amount of the resulting carbon residue averaged 6.2 wt%. The release of non-condensable combustible gas-phase compounds CO, CH₄, and H₂, with maximum concentrations of 12.7, 14.0, and 0.7 vol%, respectively, was registered. The features of the obtained biochar sample conversions were studied using thermal analysis in inert (nitrogen) and oxidative (air) mediums at 10 °C/min heating rate. Kinetic analysis was performed using Coats–Redfern method. Thermal analysis showed that the main weight loss (Δm = 32.8–43.0 wt%) occurs at temperatures ranging between 290 °C and 400 °C, which is due to cellulose decomposition. The maximum carbon content and, hence, heat value were obtained for biochars made from macadamia nut and walnut shells. An increased degree of coalification of the biochar samples affected their reactivity and, in particular, caused an increase in the initial temperature of intense oxidation (on average, by 73 °C). While technical and elemental composition of nut shell samples studied were quite similar, the morphology of obtained biochar was different. The morphology of particles was also observed to change as the heating medium temperature increased, which was expressed in the increased inhomogeneity of particle surface. The activation energy values, for biochar conversion in an inert medium, were found to vary in the range of 10–35 kJ/mol and, in an oxidative medium—50–80 kJ/mol. According to literature data, these values were characteristic for lignin fibers decomposition and oxidation, respectively.

MATEC Web of Conferences, open access proceedings in Materials science, Engineering and Chemistry

The oxidation of lignite and bituminous coal samples modified by 5 wt% (in terms of dry salt) addition of copper salts Cu(NO₃)₂, CuSO₄, and Cu(CH₃COO)₂ was studied. The samples’ reactivity was studied by thermogravimetry within a temperature range of 45–600 °C at a heating rate of 2.5 °C/min in an oxidizing environment. The introduction of activating additives has resulted in a significant decrease in the temperature of intense oxidation onset (ΔT_i = 20/94 °C), in a reduction in the sample residence time in the volatile matter release region (Δt_e = 2/22 min) and the total duration of the coal combustible mass oxidation (Δt_f = 8/14 min). The Friedman method was used to calculate the activation energy values for the oxidation process of the modified samples. The maximum change in activation energy values was observed for the bituminous coal sample. The possible mechanism behind the action of the copper-salt additives, which activate the oxidation of lignite and bituminous coal, is discussed. According to the data of mass spectrometric analysis, the concentration of NO_x in the reaction products decreases as the temperature of the activated oxidation process is shifted towards the low-temperature region.

The process of anthracite and its semi-coke combustion in the presence of 5 wt.% (in terms of dry salt) additives of copper salts Cu(NO₃)₂ and Cu(CH₃COO)₂ was studied. The activating additives were introduced by an incipient wetness procedure. The ignition and combustion parameters for coal samples were examined in the combustion chamber at the heating medium temperatures (T_g) of 600–800 °C. The composition of the gaseous combustion products was controlled using an on-line gas analyzer. The fuel modification with copper salts was found to reduce the ignition delay time on average, along with a drop in the minimum ignition temperature T_min by 138–277 °C. With an increase in T_g temperature, a significant reduction in the ignition delay time for the anthracite and semi-coke samples (by a factor of 6.7) was observed. The maximum difference in the ignition delay time between the original and modified samples of anthracite (ΔT_i = 5.5 s) and semi-coke (ΔT_i = 5.4 s) was recorded at a T_g temperature of 600 °C in the case of Cu(CH₃COO)₂. The emergence of micro-explosions was detected at an early stage of combustion via high-speed video imaging for samples modified by copper acetate. According to the on-line gas analysis data, the addition of copper salts permits one to reduce the volume of CO formed by 40% on average, providing complete oxidation of the fuel to CO₂. It was shown that the introduction of additives promoted the reduction in the NO_x emissions during the combustion of the anthracite and semi-coke samples.

The oxidation and pyrolysis of brown coal containing 5 wt % CuSO4as an initiating additive was studied. The experiment was performed by thermogravimetry at a heating rate of 2.5 K/min in an...