*3.2. Experimental Setup*

The gasification tests were conducted in a TGA (Netzsch STA 449 F3 Jupiter) at atmospheric pressure, which allows the injection of two dry reaction gases and is fitted with a steam generator. The flow rate of gases is controlled with mass flow controllers (MFCs).

The crucibles used were plate-shaped and had a diameter of 17 mm. On these plates, 10 ± 2 mg of the fuel samples was evenly distributed for ideal gas exchange. The temperature of the sample was monitored with a thermocouple in the sample carrier. The systematic error of the mass measurement was mitigated by a correction run for every gas composition with an empty crucible. The correction measurement was then subtracted from the actual measurement.

In the first step, prior to the actual gasification tests, the samples were heated in the TGA to approximately 1100 ◦C with 20 K/min in a nitrogen atmosphere to ensure a complete drying and devolatilization of the samples. Then, the samples were cooled down to 500 ◦C and stabilized at this temperature for 30 min. During this time period, the reactive purge gases were injected into the oven to ensure enough time for gas mixing and gas distribution with the oven. Then, the experiments were performed under non-isothermal conditions with a heating rate of 20 K/min up to a temperature of 1100 ◦C. Finally, this temperature was held constant for 20 min for a complete reaction of the carbon.

The experiments were conducted for CO2 gasification as well as steam gasification. For both sets of experiments, the gasifying agen<sup>t</sup> was introduced into the oven with 20%, 25%, 33% and 50% of the gas flow. For each gas concentration, a configuration with and without gasifying product, H2 or CO respectively, was tested. In total, 16 different atmospheres were used for the CO2 and steam gasification. Tables 2 and 3 display the matrix of the experiment configurations. For each of the configurations, three separate experiments were performed to test the reproducibility of the results.


**Table 2.** Experiment configurations for CO2 gasification; N2 was added to yield a total gas flow of 100 mL/min.



In order to define the type of function for the mass influence *g*(*<sup>m</sup>*0), an additional set of experiments was performed for a constant gas composition but varying sample masses. The experiments are listed in Table 4.

**Table 4.** Experiment configurations for determination of the sample mass influence; N2 was added to yield a total gas flow of 100 mL/min.


#### *3.3. Data Preparation and Evaluation*

For each measurement, weight and temperature were recorded with a sampling rate of 300 Hz. The char conversion is calculated depending on starting and final mass for every measurement according to Equation (10).

$$X(m) = \frac{m\_0 - m}{m\_0 - m\_{\text{sol}}} \tag{10}$$

The char conversion during the experiment is represented over temperature and time, as well as dX/dt over temperature. To reduce the measurement noise, the signal is smoothed with a first order Savitzky–Golay-Filter [21]. The integration time for the Savitzky–Golay-Filter was obtained based on the method described by Werle et al. [22] through minimizing the Allan variance for each measurement. The standard deviation for the char reaction rate after filtering is in the range of 3.6 × 10−<sup>3</sup> min−<sup>1</sup> and 15.6 × 10−<sup>3</sup> min−<sup>1</sup> with the mean at 8.5 × 10−<sup>3</sup> min−1.

The models investigated in this paper were fitted to the measurement with the nonlinear least-squares method and the parameters of the models were calculated by minimizing the objective function OF, Equation (11).

$$OF = \sum\_{i=1}^{n} \left( \left( \frac{dX}{dt} \right)\_{exp,i} - \left( \frac{dX}{dt} \right)\_{calc,i} \right)^2 \tag{11}$$

#### **4. Results and Discussion**
