# Partition of Cu and Pb in a Two-Stage Fluidized-Bed Waste Gasification System
## 2 Materials and Methods  
A two-stage fluidized-bed gasification system at the laboratory scale was used in this study, and a structural diagram of the two-stage fluidized-bed gasification system is shown in Figure 1. Each gasifier body was made of stainless steel (AISI-310) with a thickness of 0.49 cm, a height of 50 cm, an outer diameter of 4.27 cm, and an inner diameter of 3.29 cm. Both the stage 1 and stage 2 gasifier bodies had the same specifications. Both stage 1 and stage 2 gasifiers had a stainless-steel distributor installed in the bed bottom. The heating mode of the gasifiers was electrical heating, while a programmed logical controller (PID) was used to control the temperature inside the gasifiers. The gasifier reactors were coated with fibrous insulation on the outside to reduce heat loss, and the temperature of gasifiers was monitored and recorded by using thermocouples. The bed material used in both stages during the experimental process was silica sand, the bulk density of which was 2.6 g/cm\({}^{3}\). The bed material diameter of stage 1 was 0.775 mm, and bed material diameter of stage 2 was 0.545 mm. During the experimental process, in order to reduce the influence of the waste's composition, artificial simulative waste was mainly used. The simulative waste consisted of polypropylene (PP) plastic granules, wood chips, and a polyethylene (PE) bag. The elemental compositions, principal components, and heating values of the materials used in the simulative waste are derived from [PERSON] and [PERSON] [29]. Cu and Pb were selected as the representative heavy metals in the simulative waste because Cu and Pb usually exist in municipal solid waste. These heavy metals were all added in the form of a nitrate aqueous solution. Simulative waste was mainly composed of wood chips and PP plastic granules wrapped with the PE plastic bag material, and 1 mL aqueous solutions of the nitrate salts of the heavy metals were added to the PE plastic bag for coating. The concentration of the heavy metal was 0.3 wt% of the total weight (2.372 g). A water column manometer was used to determine the minimum fluidization velocity before the experiment; the method was described by [PERSON] et al. [30]. The experimental gas flow rate was 1.3 times that of the minimum fluidization velocity, and the minimum fluidization velocity in this study was 0.1 m/s for the 0.775 mm bed material in stage 1. Experimental parameters that were varied included the operating temperature, S/B, and ER of stage 1. Table 1 lists the operating conditions of the different stages. In the experimental process, artificial simulative waste was first placed into the gasifiers for gasification, and sampling was performed at the sampling ports of the stage 1 and stage 2 gasifiers using an active sampling pump at 3 min intervals after the first 5 min. The syngas first passed through a glass fiber filter so that fly ash was entrapped using GF/A filter paper, and then passed through 100 mL of heavy metal absorption solution (containing H\({}_{2}\)O\({}_{2}\) (33 mL), HNO\({}_{3}\) (7.67 mL), diluted with deionized water to 100 mL) in an impinger placed in a low-temperature water tank so that gaseous heavy metals were absorbed. After the experiment, the bed material was cooled and then removed. The sampling filter papers and bed materials from stage 1 and stage 2 were treated with microwave digestion to completely break down the contained heavy metal substances. \begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Run**} & \multicolumn{2}{c}{**Temperature (\({}^{\circ}\)C)**} & \multirow{2}{*}{**S/B**} & \multirow{2}{*}{**ER**} \\ \cline{2-2} \cline{4-4}  & & **Stage 1** & & **Stage 2** \\ \hline
1–3 & 700 & 900 & 0 & 0.2, 0.3, 0.4 \\
4–6 & 800 & 900 & 0 & 0.2, 0.3, 0.4 \\
7–9 & 900 & 900 & 0 & 0.2, 0.3, 0.4 \\
10–12 & 700, 800, 900 & 900 & 0.25 & 0.3 \\
13–15 & 700, 800, 900 & 900 & 0.5 & 0.3 \\ \hline \end{tabular}
\end{table} 
Table 1: The operating conditions for each experiment. Figure 1: Two-stage fluidized bed gasification system. 1.