## 1 Introduction
The results showed that doubling the PVC content of MSW would increase PCDD emissions during combustion by 32% [17]. A study done by [PERSON] and [PERSON], 2003 found that there existed MSW incinerators that emitted more dioxins than the national standard in China [18]. A later study done by [PERSON] et al., 2009 showed that the dioxin emissions from the new-generation MSW incinerators met the national standard [19]. [PERSON] et al., 2007 carried out a case study of air pollutants for an MSW incineration plant in Italy [20]. The results showed that their PCDD/Fs emission levels had a rather small health impact on the surrounding population. However, they also indicated that the source of the waste and the technology used for the incineration would affect the final results. The EPA also has stringent guidelines for PCDD emissions, which require the risk factor to be lower than \(10^{-6}\) (one occurrence per one million people) [21]. Since the source of solid waste is mostly unknown, it is essential to remove the chlorine to reduce the potential PCDD/Fs emission. Chlorine removal from wastes has been studied extensively over the years. [PERSON] et al., 2004 reported a method of hydrothermally treating PVC waste in subcritical and supercritical regions. They were able to decompose the PVC without producing any harmful chlorinated organics. However, the behavior of chlorine removal from mixed waste was still lacking since this study focused on just PVC waste. [PERSON] et al., 2008 carried out a mechano-chemical method of de-chlorination by co-grinding the PVC with various metal oxides using a planetary ball mill. The ground product was dispersed in water to extract the inorganic chlorine compounds, and the release of chlorine was found to increase as the grinding time and additive ration increased. However, the PVC used in this study was in powder form and therefore does not apply to existing PVC waste [22]. [PERSON] et al., 2011 introduced a hydrothermal process to produce chlorine-free solid fuels from MSW. This process used saturated steam at \(\sim\)200 \({}^{\circ}\)C with a pressure of 2 MPa on a one-ton batch feedstock, and they were able to produce chlorine-free solid fuels. However, the product additionally required water washing to remove the inorganic chlorine produced during the hydrothermal treatment. For sufficient chlorine removal, the weight ratio of water used to MSW cleaned was 3:1 [23]. [PERSON] et al., 2018 investigated the method of chlorine removal from solid waste in the previous study [10]; however, it was done at 300 \({}^{\circ}\)C, which required relatively long residence times of torrefaction involved with high-shear mixing with water. In the recent study, [PERSON] et al., 2020 studied the mechanism and kinetics of the de-chlorination of pure PVC [24]. They investigated the products of torrefaction and proposed a comprehensive mechanism of PVC degradation at 300 \({}^{\circ}\)C, which provided insight into the process of PVC de-chlorination. To improve solid waste feedstock quality, this study more closely investigates the issue of chlorine as a contaminant in potential feedstocks. As it is known that waste as a feedstock contains a variety of components that may widely affect the initial chlorine levels, it is essential to study PVC chlorine removal at different chlorine levels in order to apply this method to other types of wastes compositions. The present paper deals with two aspects: (1) determination of appropriate torrefaction process parameters that can maximize the retained energy and minimize the chlorine levels; (2) the effect of different chlorine levels of material on the PVC de-chlorination behavior.