Hydrothermal carbonization of typical components of municipal solid waste for deriving hydrochars and their combustion behavior
Introduction
Due to their simplicity to perform (Prawisudha et al., 2012), the elimination of an energy-extensive drying process (Danso-Boateng et al., 2015, Zhao et al., 2014b), high energy yield (Kim et al., 2014, Lin et al., 2015) and fewer pollutant gases (Berge et al., 2011, Parshetti and Balasubramanian, 2014), hydrothermal carbonization (HTC) process has been considered as one of the most effective and promising thermochemical upgrading technology for municipal solid waste (MSW) (Zhao et al., 2014a). The energy density of HTC-derived hydrochars are upgraded compared to raw MSW (Kim et al., 2015, Lu et al., 2011). And its nature properties are more easily for dewatering, grinding, handling, transport and storage (Zhao et al., 2014a). Subsequently, energy can be recovered by combusting or co-combusting MSW hydrochar with coal (Kim et al., 2015, Lu et al., 2011, Muthuraman et al., 2010). Preliminary investigations clearly showed that HTC process exerted significant effects on the thermal behavior (Lin et al., 2017, Lin et al., 2016b). Under suitable HTC conditions, hydrochars could achieve relatively excellent thermal conversion performance (Lin et al., 2016b). Therefore, these studies had proved that HTC can be performed as both environment-friendly MSW management and efficient energy recovery technology. Moreover, some HTC pilot-scale applications had some successful cooperation cases (Chinnathan Areeprasert et al., 2016, Hitzl et al., 2015, Lu et al., 2014), suggesting its huge application prospects.
Unfortunately, because of complicated components in MSW and undetectable of intermediate process, more-detailed and clear reaction mechanisms are largely unknown. Previous studies had tried to model only a single representative or specific fraction of MSW from its basic constituents, such as paper (Weiner et al., 2014), waste wood (Gao et al., 2016, Zheng et al., 2016), waste food (Deb-Choudhury et al., 2014, Li et al., 2013), waste rubber (Zhang et al., 2016), waste plastic (Poerschmann et al., 2015), lignocellulosic component (Hoekman et al., 2011) and protein (Teri et al., 2014). However, the variation of these studies from researchers to researchers, some results were only meaningful and reproducible for specific fractions of MSW. The comprehensive and systematic integrated research about specific formation pathways of MSW hydrochars is still very difficult and scarce. From this perspective, it seems unfeasible to model complicated MSW directly during HTC. As mentioned in the previous paper (Lin et al., 2016a), HTC mechanism of each representative pseudo-component will be investigated separately. Finally, envisaging integrated and systematic reaction mechanisms during the HTC of complicated MSW or mixtures will be speculated based on the HTC mechanisms of each representative pseudo-component. In the previous paper (Lin et al., 2016a), a possible conversion pathway of HTC of waste textile had been proposed. Follow this representative pseudo-component simulation research system, the remaining typical components in MSW (waste paper, waste wood, waste food, waste rubber and waste plastic) will be studied in this paper. This paper firstly focused on the fuel characteristics and combustion behavior of HTC hydrochars since it was the product fraction of primary interest. And parts of product distribution characteristics and infrared functional group analysis of hydrochars would be referred to support some inferences.
Section snippets
Materials
In this work, the remaining five pseudo-components were systematically researched. The waste paper was office printing waste paper and was carefully cut into small shape by a scissor. The waste food was collected from campus canteen. The waste wood was collected campus garbage station. The waste rubber was collected from waste tire. The plastic were polypropylene (PP), polyethylene (PE) and polyvinyl chloride (PVC), which were provided by Huazhong Plastic Co., Ltd. The waste wood, rubber and
Ultimate and proximate analyses
Table 1 displayed the chemical properties of five typical components and their hydrochars. As expected, the carbon contents of all hydrochars were higher than their parent feedstock. But the increments of representative components were much different. The carbon content of P-250-120 grew only 9.2% compared to waste paper. While 52.0% and 44.3% increase were observed in F-250-30 and W-250-60, respectively. The composition of the representative component and its source were the essential cause of
Conclusions
Follow the representative pseudo-components HTC simulation system proposed before, the remaining typical components in MSW (waste paper, waste wood, waste food, waste rubber and waste plastic) were studied in this paper. Based on the different components contained in feedstock and preliminary exploration experiment, different HTC conditions were employed. The results clearly demonstrated the upgrades of energy grade were observed for all HTC-derived hydrochars. However, the different
Acknowledgements
The authors are grateful to the support given by the National Natural Science Foundation of China (51406058, 51476060, 51606071); Guangdong Key Laboratory of Efficient and Clean Energy Utilization (2013A061401005); the Fundamental Research Funds for the Central Universities (2015ZZ015); Guangdong Natural Science Foundation (2015A030311037, 2015A030313227, 2016A030310424); China Postdoctoral Science Foundation (2015M582382).
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