# Allothermal Gasification of Peat and Lignite by a Focused Light Flow
## 2 Materials and Methods
The systematic error of the gas concentration measurement was below 5%. Figure 1: Scheme of the experimental setup (**a**) and the normalized emission spectrum of the lamp vs. the standard solar spectrum ASTM G173-03 (**b**). (a) presents a chamber (Ch) with a fuel, a gas analyzer (GA), and a light concentrating mirror (LC). The changes of the sample weight during gasification were controlled in real time by a ViBRA AF 225 DRCE analytical balance (Shinko Denshi Co. Ltd., Tokyo, Japan). The chamber with a fuel was placed onto the platform of the balance, and the light flow was introduced through the hole in the top window of the balance shell. The pipes of the gas analyzer were disconnected in this experiment to keep the precision of the measurements at about \(10^{-5}\) g. The initial weight of the samples was about 300 mg. The typical temperature of the fuel surface during the conversion was measured by a Thermal Imaging System (TIS) Testo-885-2 (Testo SE & Co. KGaA, Lenzkirch, Germany). The glass window of the chamber was removed in this experiment to prevent data distortion. The TIS was calibrated for the fuel gray factor by the co-measurement of the fuel surface temperature using TIS and a fast thermocouple. The determined gray factor was in the range of 0.8-0.83. The average value 0.81 was used for measurements. In general, the measurement procedures in this study were similar to the ones used in [23; 24] for coal processing waste. However, the light flow required for the conversion of peat and lignite is much smaller than that for the conversion of bituminous coals because the heat conductivity of low-grade fuels is 3-5 times as low as that of coals. The overall exposition time was about 6 min (up to the moment when gas productions decayed due to the oxidation of all fuel available in hot area). All the experiments were repeated 5 times to allow for minimum random errors. Applying the localized radiation heating meant that the hottest fuel layers were located near the illuminated fuel surface. The depth \(D\) to which the temperature had significantly changed to the moment \(t\) could be easily calculated with Equation (1) derived from the heat transfer equation. The heat penetration using the heat conduction mechanism (at the beginning of heating when the oxidation heat was negligibly small) generally depends on the thermal conductivity of the fuel. \[D\sim\sqrt{\lambda\cdot t} \tag{1}\]  
where \(t\) is the time of heat transfer and \(\lambda\) is thermal conductivity [25]. The heat penetration depth (HPD) of peat and lignite with natural moisture content was approximately 0.56 mm and 0.27 mm, when heated for one second. The difference between the heat transmission of these fuels and the previously investigated coal processing waste (0.7 mm) was considerable. There were big differences in the chemical composition, as well (see Table 1). These facts suggested that the heating of peat and lignite, using an external source and oxidation reactions, was implemented not in the same way as it was with bituminous coals and the corresponding processing waste. Therefore, the first step of this research was to define the intensity of the light flow required for a successful heating of the fuel up to the temperatures when gasification started.