Critical Review on the Chemical Reaction Pathways Underpinning the Primary Decomposition Behavior of Chlorine-Bearing Compounds under Simulated Municipal Solid Waste Incineration Conditions

Abstract

Incineration has been proven as one of the most viable and efficient waste-to-energy strategies for the handling of rapidly mounting municipal solid waste (MSW). However, as a generic and key element in MSW, chlorine (Cl) brings about severe corrosion in boilers and the presence of Cl-containing species induces the release of toxic dioxins and furans by acting as chlorine donors. The chlorine release behavior from MSW during incineration has thus drawn plenty of attention. This paper has critically reviewed the origin of different chlorine-bearing species in MSW and their respective thermal decomposition behavior. In general, chlorine in MSW has two primary sources: plastics, mainly polyvinyl chloride (PVC), as the source of organic chlorine and household kitchen and garden waste as the source of inorganic chlorine, mainly chlorides. Distinct chlorine liberation properties have been observed for these two different chlorine groups. Chlorine in PVC converts to HCl gas easily at 300 °C as a result of the thermal decomposition combined with a depolymerization of the polymer chain. In contrast, the release of chlorine from inorganic chloride salts is much lower than that from PVC, mainly attributing to either strong volatilization properties of alkali chlorides (NaCl and KCl) or the high ionic bonding energies between some cations, such as Ca2+/Ni2+ and Cl–. Meanwhile, the decomposition of FeCl2, CoCl2, and MgCl2 is easier with the onset temperature for HCl release being around 180, 300, and 415 °C, respectively. Additionally, the addition of SO2, O2, or acidic solids (such as SiO2 and Al2O3) has been found to promote the chlorine release from chlorides appreciably. However, the exploitation of the underpinning mechanism is far from completion, especially for CaCl2 and CoCl2. This requests extra and intensive studies to elucidate the chlorine liberation mechanism from these inorganic species, even from the molecular level in terms of their ionic bonding propensity and breakage at high temperatures.

Virtual Special Issue of 7th Sino-Australian Symposium on Advanced Coal and Biomass Utilisation Technologies

“…Two reviews are included. Zhou et al (10.1021/acs.energyfuels.9b02958) review the chemical reaction pathways that underpin the primary decomposition behavior of the compounds that contain chlorine (Cl) under simulated municipal solid waste incineration conditions. Fletcher (10.1021/acs.energyfuels.9b02826) reviews the development, improvement, and uses of the chemical percolation devolatilization (CPD) model for coal pyrolysis in the past 30 years, along with extended uses of the CPD model for other solid fuels.…”

“…Two reviews are included. Zhou et al (10.1021/ acs.energyfuels.9b02958) 7 review the chemical reaction pathways that underpin the primary decomposition behavior of the compounds that contain chlorine (Cl) under simulated municipal solid waste incineration conditions. Fletcher (10.1021/acs.energyfuels.9b02826) 8 15 hydrotreat the blends of the lignin-rich fraction of bio-oil and vegetable oil to identify suitable co-processing conditions for the production of liquid transport biofuels.…”

Controlling Role of CaClOH in the Process of Dechlorination for Municipal Solid Incineration Fly Ash Utilization

“…Water-washing dissolution and thermal volatilization are two major ways to remove chlorine from IFA. 7,8 But there was 0.26− 4.11 wt % of chlorine remaining after washing treatment. 8,9 Compared with only IFA heating, cotreatments containing silicon aluminum were beneficial for dechlorination through heat treatment.…”

Formation, Measurement, and Control of Dioxins from the Incineration of Municipal Solid Wastes: Recent Advances and Perspectives

“…The influence of fuel components, the combustion conditions, the phases of the fire (flaming vs smoldering), and other factors are reviewed and discussed in this work. Zhou et al paid attention to the Cl-containing species and chlorine release behavior from MSW . This work reviewed the modes of occurrence of chlorine of both organic and inorganic chlorine-containing species, which is helpful to reveal the role of chlorine in PCDD/F formation.…”

“…Zhou et al paid attention to the Clcontaining species and chlorine release behavior from MSW. 19 This work reviewed the modes of occurrence of chlorine of both organic and inorganic chlorine-containing species, which is helpful to reveal the role of chlorine in PCDD/F formation. Rathna et al reviewed sources of dioxins' pollution and some innovative remediation technologies, such as bioremediation, plasma pyrolysis, and so on.…”