# Partition of Cu and Pb in a Two-Stage Fluidized-Bed Waste Gasification System
## 1 Introduction
[18] also pointed out in their studies that as the S/B increased, H\({}_{2}\) production increased. The main reason that an increase in S/B leads to an increase in H\({}_{2}\) production is that increasing S/B causes more hydrogen to participate in oxidization; thus, more H\({}_{2}\) is produced. However, the S/B needs to be controlled within a certain range; otherwise, excess steam will absorb the heat in the gasifier, causing a drop of temperature, which is unfavorable for gasification to proceed. Regardless of whether wastes are incinerated or gasified, the escape of heavy metals contained in the wastes during heat treatment needs to be discussed. The primary issue is that heavy metal contaminants that escape into the environment not only affect the environment and ecology but also are likely to be harmful to humans [19; 20]. From analyzing the heavy metal distribution contained in wastes, [PERSON] et al. [21] found that the major heavy metal elements included Zn, Cr, Cu, Pb, Ni, Hg, and Cd and that these heavy metal elements might escape into the environment during heat treatment. [PERSON] et al. [22] proposed that less volatile heavy metals do not undergo chemical reactions in the combustion environment, so they do not volatilize and become part of the bottom ash; more volatile heavy metals, however, may react with other substances in incineration systems, producing species with higher boiling points (such as metal oxides), which are left in bottom ash. Furthermore, some heavy metals or compounds will volatilize into vapors under high temperatures, and heavy metals with high boiling points may also react with other species, producing highly volatile species (such as metal chlorides) that will leave the combustion zone with the exhaust gas. [PERSON] [23; 24] pointed out in his study on heavy metal entrapment by the bed material of a fluidized-bed that the distribution of a heavy metal during incineration is associated with the heavy metal's own element properties and boiling point. Metals with higher boiling points (such as Cr) mostly stay in the bottom ash, and heavy metals with higher volatilities (such as Cd) mostly form vapors and leave the combustion zone with the exhaust gas. Hence, the escape of either heavy metals or their compounds is mainly associated with the operating temperature. [PERSON] and [PERSON] [25] and [PERSON] and [PERSON] [26] pointed out in their studies that the combustion temperature will affect the distribution percentages of heavy metals in the bottom ash; an increase in temperature reduces Zn, Pb, and Cd distributions in the bottom ash but increases As, Cd, Hg, Zn, and Pb contents in the exhaust gas. Hence, the transfer behavior of heavy metals during heat treatment may differ depending on the metal's physical and chemical properties, the form of the produced compounds, and the operating conditions. In recent years, gasification-related studies have mostly been focusing on changing the syngas composition or improving gasification efficiency. Two-stage gasification is one of the gasification technologies proposed by researchers. Two-stage gasification consists of two tandem gasification devices. Gasification products generated in the stage 1 gasifier (syngas, tar, or char) enter the stage 2 gasifier, in which they undergo reactions, and the products are gasified or cracked again to increase the syngas yield while reducing the tar or char yield. [PERSON] et al. [27] performed two-stage gasification with two tandem fixed-bed gasifiers, and the results showed that the H\({}_{2}\) yield increased from 7.3% to 22.3%, and the gross syngas yield increased from 30.8% to 54.6%, while the tar yield was reduced (from 18.6% to 14.2%). At present, most two-stage gasifiers are made of two tandem fixed-bed reactors [27; 28]. However, a fluidized-bed reactor has the advantages of high heat transfer and high mass transfer efficiencies. Thus, running two tandem fluidized-bed gasifiers with a two-stage gasification program will help increase the gasification efficiency.