# Comparative Analysis of Partially Renewable Composite Fuels Based on Peat, Lignite and Plant Oil
## 3 Results and Discussion  
### Reactivity of the Composite Fuels  
The dependence of the fuel reactivity on the temperature was estimated using the TGA technique. The obtained dependencies for pure peat, pure lignite and rapeseed oil were compared with the curves describing the thermal decomposition of the mixtures: P + RO (35 wt% and 65 wt%) and L + RO (60 wt% and 40 wt%). These particular compositions were chosen following the previous investigations [16] as well as because of the results presented further in Section 3.3. Figure 2 shows the TGA results. With the desired oxygen flow, one can estimate the temperature ranges that correspond to the most effective decomposition of the organic part of the fuel. According to the chemical compositions of our fuel components (Tables 1 and 2), the minimal amount of an air needed for full oxidation of the fuel compositions (for sample weights used for TGA) is about 45-50 mL. In contrast to the pure peat and lignite, which require different amounts of air (29 mL and 45 mL) for full oxidation, the compositions (L + RO and P + RO) require a very close amount of oxidant. Taking into account the effective fuel oxidation range (from Figure 2) and the chosen air feeding regime (2 mL/min), the average coefficient of excess air is less than 1.5 for the L + RO mixture and about 0.9-1 for the P + RO mixture. Thus, the oxidation conditions are suitable for gasification process. The experimental setup shown in Figure 1 provides a similar air excess coefficient for bigger fuel portions. One can see that the weight losses curves (TGA) for the fuel compositions mostly lie between those for single components, similar to [PERSON] et al. [31]. However, the differential thermal analysis (DTA) shows a significant shift in the extensive heat release right along the temperature axis for the composite fuels (relative to the heat release of the fuel components). At the same time, mixing RO with peat makes the TGA curve slope steeper in the temperature range where the most effective decomposition occurs (300-600 \({}^{\circ}\)C). The reactivity peaks of pure components (peat, lignite and RO) occur at 290 \({}^{\circ}\)C, 407 \({}^{\circ}\)C and 393 \({}^{\circ}\)C, respectively. The P + RO and L + RO compositions have maximum weight changes at approx. 390 \({}^{\circ}\)C. Thus, this temperature appears to be the lowest conversion  
Figure 2: TGA results for thermal decomposition of fuels. TGA dependencies (**a**), the DTG dependencies (**b**) and the thermal effect of fuel decomposition (**c**). The shaded area on the plot shows the temperature range where the maximum heat production is recorded for all the fuels. threshold for such compositions (Figure 2b). It is clear that conversion is most effective at higher temperatures. In the considered case of conversion under a focused light flow, the temperature is always close to 700-800 \({}^{\circ}\)C or even higher. At the same time, all the chemical reactions and other processes (such as drying) proceeded separately at lower temperatures, starting at this point, simultaneously, during the rapid heating to high temperatures (within several seconds). The analysis of the heat of reaction (Figure 2c) shows that the heat production peaks during the thermal decomposition of the composite fuels that occurs at higher temperatures than for pure peat, lignite or RO. One can see that the DTA curve maximum for the L + RO mixture occurs at about 600 \({}^{\circ}\)C. The P + RO mixture produces maximal heat at about 550 \({}^{\circ}\)C. The presence of a slight drop in the blue curve near 450 \({}^{\circ}\)C reflects the effect of the evaporation of the volatiles from the RO. The above suggests that the stable self-sustaining ignition of P or L filled with big amount of RO is almost impossible (it requires very intensive external heating). The reason for that is that the fuel self-heating is very weak in the maximum reactivity range.