# Allothermal Gasification of Peat and Lignite by a Focused Light Flow
## 2 Materials and Methods  
A fuel layer can be heated by a light flow in different ways. Using solar light has an obvious economic benefit. However, the main parameters of gasification can be determined using artificial incoherent light sources (different lamps, LEDs, etc.) whose spectrum is quite close to certain solar spectrum segments. The absorption of the fuel is not uniform along the visible light spectrum. This fact is easily proven by the color of the fuel powder (both peat and lignite have perceptible reflection in the orange-red region). However, the wet powder of both peat and lignite becomes closer to black, which means higher unification of the absorption spectrum. The samples of both peat (from the Arkadievskoe peat deposit in the Tomsk region of Russia) and lignite (Class B2 by the Russian standards) were dried at 45\({}^{\circ}\) and milled into a powder with a particle size under 120 \(\upmu\)m. The powder was stored in a sealed container up to the final preparation of the sample before each experiment. This allowed high uniformity of the bulk density and heat conductivity of the composition with different water content. A higher concentration of water increasesthe threshold value of light intensity above which the fuel ignites, turning gasification into trivial combustion. At the same time, the water content determines the chemical composition of syngas due to changes in the operating temperature and the contribution of the steam-carbon reactions. The total moisture content of samples was varied in the range from 10 to 60 wt.% for peat and from 15 to 65 wt.% for lignite with 10 wt.% steps. The natural moisture content of peat and lignite was 9.9 wt.% and 15 wt.%, respectively. The ash content of peat and lignite was about 22 wt.% and 13.5 wt.%, respectively. Peat contained more than 70 wt.% of bound volatiles, whereas lignite had more than 27 wt.%. Due to such differences in the physical and chemical composition of the fuels, the amount of combustibles in them was different. The sample was placed inside a cylindrical chamber with a window on the top side. The volume of the chamber was about 3.5 cm\({}^{3}\), and most of it was free. Therefore, the chamber had some spare air, which was actually enough to gasify a few milligrams of fuel. The chamber was high enough to prevent the window from being polluted by adhering gasification products. The gasification products were permanently pumped out from the chamber by a gas-analyzer pump whose branch pipe was placed below the middle of the chamber height, thus detecting most of the volatile gasification products. The process was done at the normal atmospheric pressure. We used a halogen lamp (total power 490 W and light flow power 12.5 W) with a collimator and focusing optics to heat the fuel. The scheme of the experimental setup and the irradiation spectrum of the lamp are shown in Figure 1. The light was focused on a spot with an average diameter (FWHM) of about 2.5 mm. It allowed the light flow intensity in the focal plane up to 130 W/cm\({}^{2}\). Lower intensities were achieved by limiting the electrical current through the lamp circuit. The changes of the lamp spectrum (in a visible range) with a decrease in the electrical current were not significant. The chemical composition of the fuel conversion products was analyzed using a Bonner Test-1 gas analyzer (Bonner, Novosibirsk, Russian Federation). Syngas was dried, when going through the condensate collector, and filtered by a PTFE-membrane filter (with a pore size of about 0.45 \(\upmu\)m) to remove solid micro-particles and micro-droplets of tar. Such filtering was sufficient to remove tar from syngas due to a small-scale gas production (provided that filters were regularly changed). The analyzer measured the concentrations of the following gases: CO, CO\({}_{2}\), CH\({}_{4}\), H\({}_{2}\), O\({}_{2}\), SO\({}_{2}\), NO using the electro-chemical and optical detectors sensitive to the target gases. It was adjusted to measure small concentrations of the target gases in the air flow.