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The low quality municipal solid wastes (MSW) derived char has a potential to be used as a methanation catalyst to achieve low-cost methanation of the syngas derived from MSW, and its performance with varying reaction parameters should be explored for better application. In this study, a MSW char supported Ni-based catalyst (Ni-MSWC) was prepared by impregnation; the influences of CO 2 and CH 4 impurities in the raw syngas on methanation and the feasibility of conducting methanation in a low-pressure condition were investigated, then the catalyst's response to the changing parameters was identified. The results showed that the presence of low concentration CO 2 in the H 2 -rich syngas is favorable to the gasification of the char carrier and activates Ni-MSWC catalyst. However, it also promotes F–T synthesis reaction and leads to a decrease in the methane yield (Y CH4). The decrease in reaction pressure causes a decrease in Y CH4 and results in coke formation; but inhibits F–T synthesis reaction and increases methane selectivity (S CH4). A higher reaction pressure increases system complexity and accelerates char carrier consumption. Moreover, presence of methane by 2.8% (vol.) promotes the methanation of CO 2 through the methane dry reforming reaction, but it inevitably causes coke formation and affects the catalyst's stability. Based on Y CH4 and Ni-MSWC's responses, CO:CO 2 ≥ 3:2 and reaction pressure of 1 MPa (gauge pressure) are recommended, which help to inhibit the side reactions and maintain a high Y CH4 (>95%). [Display omitted] • Methanation performance of the syngas explored using the Ni-MSWC catalyst. • The ratio of CO/CO 2 in the syngas recommended to be not less than 3/2. • Lower CO 2 concentration in the syngas helps to activate the MSWC carrier. • 80% or more CH 4 yield from CO x obtained at atmospheric pressure. • The feeding CH 4 promotes the CO 2 conversion but causes carbon deposition. [ABSTRACT FROM AUTHOR]

The lack of standardized products is a key hindrance to the widespread commercialization of municipal solid wastes (MSW) pyrolysis technology. In this paper, a cost-effective roadmap employing pyro-gasification and methanation processes is developed, with CH 4 -rich gas as the target product. In this roadmap, a two-stage catalytic conversion of "MSW → syngas → CH 4 -rich gas" was realized using MSW char, a by-product of the pyrolysis process as the catalyst/catalyst carrier. The results showed that, in the pyro-gasification stage, a syngas yield of 1.3 L/g MSW could be obtained at 800 °C and a steam-to-MSW mass ratio of 0.4, with a H 2 fraction reaching 56.6 vol%. The effective conversion of MSW to syngas was attributed to the superior catalytic activity of the MSW char. By comparing the catalytic activity and structural characteristics of the chars produced from various waste components, it could be determined that the high catalytic activity of the char required both active minerals derived from contaminated plastics and residue, and an appropriate proportion of carbon matrix from the biomass components in MSW. The gasified MSW char (G-MSWC), co-produced with the syngas, served as a carrier for the subsequent methanation catalyst. Due to the activation effect of steam during the syngas production stage, the pore structure of G-MSWC was improved and its defect density also increased. Consequently, G-MSWC demonstrated enhanced Ni–C interaction, facilitating the methanation activity. The final product from the methanation stage achieved a CH 4 concentration of 52.9 vol%, and a CH 4 yield of 11.25 mol/kg MSW. The above findings demonstrate the feasibility of the complete roadmap from MSW to CH 4 and provide valuable guidance for decentralized MSW management based on pyrolysis technology. [Display omitted] • A novel complete roadmap was developed to convert MSW into methane-rich gaseous fuel. • Wastes pyrolysis char as a catalyst for both syngas production and subsequent methanation. • Mixed MSW pyrolysis produced a more active char catalyst compared to any independent component. • Fuel gas with methane of up to 53 vol% was obtained from dry MSW at atmospheric pressure. [ABSTRACT FROM AUTHOR]

[Display omitted] • Promotion effect of the char combustion on its ash melting investigated. • The carbon contained in the MSWC resulted in an earlier melting of the ash in it. • Kinetic parameters of the char combustion and the ash melting were obtained. • Simulation models for combustion and melting established and validated. • O 2 content in the combustion air is more important than carbon content in MSWC. The municipal solid wastes pyrolysis char (MSWC) is a mixture of carbon and ash. Its direct melting contributes to the harmless and most weight-reducing disposal of the municipal solid wastes (MSW). To investigate the impact of the MSWC's combustion on its ash melting, in this research direct MSWC melting was investigated, the apparent activation energies and pre-exponential factors of the char combustion and ash melting reactions were obtained experimentally; reaction models of the MSWC's combustion and its ash melting were established for MSWC in a crucible and for a single particle to investigate the important factors affecting the ash melting. Thermodynamic analysis results showed that the presence of carbon can reduce the ash melting temperature by approximately 40 °C. The apparent activation energies of combustion and ash melting were 148.06 kJ/mol and 878.79 kJ/mol, respectively; but the MSWC combustion rate was much faster than that of ash melting. The combustion heat promoted its ash melting in a crucible inside furnace. The simulation results for a single MSWC particle showed that both the combustion and ash melting processes can be promoted by increasing the surrounding temperature and O 2 concentration in combustion air; while the higher carbon content in the MSWC only slightly improved ash melting when supplying air for combustion. Moreover, a reduction in the MSWC's particle size can make the carbon combustion faster but does not contribute to higher ash melting ratio due to the increase in specific heat dissipation; and particle radius larger than 1.5 mm would result in incomplete combustion of MSWC. These findings can provide guidance for the application of the MSW pyrolysis and char melting technology. [ABSTRACT FROM AUTHOR]

Behavior of ignition and combustion of coal particle cluster under a quiescent condition was numerically simulated by solving balance equations of mass and enthalpy with combustion kinetic models of volatiles and char. Two-flame structure, one flame penetrating into the cluster and the other moving out of the cluster, was predicted during the combustion of coal particle cluster. Effects of radiative heat transfer, group number, ambient temperature, coal particle size, and oxygen concentration on ignition and combustion of coal particle clusters were also analyzed. Simulations indicated that the gas volume fraction of coal particle cluster increases with time after devolatilization. Gas velocity passing through the cluster surface varied significantly at volatile liberation. The ignition time delay was reduced with the increase of ambient temperature. The cluster devolatilization rate and char burning rate increased while the ignition time delay decreased with the increase of ambient oxygen concentration. [Copyright &y& Elsevier]