*3.2. Fuel*

The raw material processed in the generator were coniferous cuttings—maximum length 10 to 15 cm, maximum width 5 cm, and a maximum thickness of 2 cm. Their typical physiochemical properties are shown in Table 4. The proportion of fine particles and particles with bark in the gasified material was negligible. This fuel was used long-term in this unit. It was available, affordable, and had good quality and properties for gasification. This type of material had a medium agglomeration-slagging propensity [22].


**Table 4.** Properties of used fuel.

r values of original wood sample; d dry sample without moisture.

#### *3.3. Analytical Methods*

Parameters of the fuel from Table 4 (moisture, volatile, and fixed carbon and ash) were measured by thermogravimetric analyzer Netzsch STA 449 F1 Jupiter. The heating rate was 10 ◦C/min in a nitrogen atmosphere up to 900 ◦C. For the amount of ash, there was a change in nitrogen by oxygen and heating continued up to 1200 ◦C. Ultimative analysis of fuel (amount of C, H, O, N and S) was measured by analyzer LECO CHN 628 with added module 628 S. Combustion heat was measured by the calorimeter LECO AC600.

Thermogravimetric analysis (TG) was measured by the analyzer Netzsch STA 449 F1 Jupiter. The heating rate was 10 ◦C/min in nitrogen atmosphere. The differential thermal analysis DTA was measured simultaneously, which measures the temperature difference between the standard sample (aluminium oxide) and the sample during heating.

Composition of the filtration cake inorganic fraction and incrust was measured with apparatus ARL 9400 XP+ equipped with a Rh lamp with a head Be-oxides window.

The distribution of the trapped particle size was performed by a Fritsch Particle Sizer Analysette 22 apparatus, where the light source is an He-Ne-laser with a wavelength of 633 nm and maximum measuring range of 0.1–1250 μm. To ensure the homogeneity of the measured sample and reliable statistics in the illuminated volume, the suspension was permanently mixed in an external mixing device during measurement using ultrasound, which provided for the separation of the agglomerate.

The measuring of organic substances composition trapped by the filtration cake was necessary to solve these substances in the solvent. Mechanically separated cake from the surface of the outer filter layer was inserted into the Soxhlet extractor and washed for four hours by acetone. The obtained solution was injected into the gas chromatograph Hewlett Packard HP 6890 with a mass detector Hewlett Packard MSD 5973 (GC-MS).
