Yanqiu Long

A review of dioxin-related substances during municipal solid waste incineration

Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) are among the most toxic chemicals and the main restriction on municipal solid waste incineration. To exert more effective control over the formation of dioxin homologues during municipal solid waste incineration, it is significant to investigate dioxin-related compounds. Despite the numerous studies about PCDD/Fs, a unified understanding regarding many problems has yet to be reached because the homologues of PCDD/Fs are excessive, the measurement of PCDD/Fs is difficult, and the formation mechanisms of PCDD/Fs are complicated. Firstly, this paper briefly introduces the different formation mechanisms of PCDD/Fs, including high temperature homogeneous reaction PCDD/Fs formation and low temperature heterogeneous reaction PCDD/Fs formation. Then the sources of PCDD/Fs including precursors (chlorophenols and polycyclic aromatic hydrocarbons) and residual carbon are summarized. In particular, this paper analyzes the substances that influence PCDD/Fs formation and their impact mechanisms, including different categories of chlorine (Cl2, HCl and chloride in fly ash), O2, copper, sulfur, water, and nitrogen compounds (ammonia and urea). Due to the high cost and complexity of PCDD/Fs measurement, PCDD/Fs indicators, especially chlorobenzenes and polycyclic aromatic hydrocarbons, are summarized, to find an effective surrogate for quick, convenient and real-time monitoring of PCDD/Fs. Finally, according to the results of the current study, recommendations for further research and industrial applications prospects are proposed.

A novel method for kinetics analysis of pyrolysis of hemicellulose, cellulose, and lignin in TGA and macro-TGA

The pyrolysis of three biomass components (hemicellulose, cellulose and lignin) was investigated in both a thermogravimetric analyzer (TGA) and self-designed macro-TGA. Slow and fast pyrolysis experiments were carried out in the macro-TGA. A novel peak analysis-least square method (PA-LSM) was developed to analyze the kinetics. The results showed that a complex pyrolysis reaction could be described by a series of parallel reactions, and each reaction could be described by a Gaussian peak. The kinetic parameters could be calculated via the least square method, and the Gaussian peak could be simulated very well. The slow pyrolysis in the TGA and macro-TGA is different, because of the heat transfer process. The pyrolysis and fast pyrolysis in macro-TGA also had considerable differences.

Thermogravimetric characteristics of typical municipal solid waste fractions during co-pyrolysis

The interactions of nine typical municipal solid waste (MSW) fractions during pyrolysis were investigated using the thermogravimetric analyzer (TGA). To compare the mixture results with the calculation results of superposition of single fractions quantitatively, TG overlap ratio was introduced. There were strong interactions between orange peel and rice (overlap ratio 0.9736), and rice and poplar wood (overlap ratio 0.9774). The interactions of mixture experiments postponed the peak and lowered the peak value. Intense interactions between PVC and rice, poplar wood, tissue paper, wool, terylene, and rubber powder during co-pyrolysis were observed, and the pyrolysis at low temperature was usually promoted. The residue yield was increased when PVC was blended with rice, poplar wood, tissue paper, or rubber powder; while the residue yield was decreased when PVC was blended with wool.

Pyrolysis and gasification of typical components in wastes with macro-TGA

The pyrolysis and gasification of typical components of solid waste, cellulose, hemicellulose, lignin, pectin, starch, polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC) and poly(ethylene terephthalate) (PET) were performed and compared in a macro thermogravimetric analyzer (macro-TGA). Three model biomasses, poplar stem, orange peel and Chinese cabbage, were applied to pyrolysis and gasification simulation by their components based on TG curves. Compared to those from TGA, peaks temperature of the differential thermogravimetric (DTG) curves of each samples pyrolysis on macro-TGA delayed 30-55°C due to heat transferring effect. CO2 promoted the thermal decomposition of hemicellulose, lignin, starch, pectin and model biomasses significantly by Boudouard reaction, and enhanced slightly the decomposition of PET. The activation energy (AE) of biomass components pyrolysis on macro-TGA was 167-197 kJ/mol, while that of plastic samples was 185-235 kJ/mol. The activation energy of 351-377 kJ/mol was corresponding to the Boudouard reaction in CO2 gasification. All overlap ratios in pseudo-components simulation were higher than 0.98 to indicate that pseudo-components model could be applied to both pyrolysis and CO2 gasification, and the mass fractions of components derived from pyrolysis and gasification were slightly different but not brought in obvious difference in simulating curves when they were applied across.

Interactions among biomass components during co-pyrolysis in (macro)thermogravimetric analyzers

The interactions of biomass components (hemicellulose, cellulose, and lignin) during co-pyrolysis were investigated in a thermogravimetric analyzer (TGA) as well as a self-designed Macro-TGA with higher heating rate and larger amount of sample. The overlap ratio (OR) was used to evaluate the interaction of biomass components quantitatively. In TGA, the pyrolysis of xylan was not significantly affected by cellulose, whereas the pyrolysis of cellulose was markedly influenced by xylan. The interactions between xylan and lignin were weak with an overlap ratio of 0.9869, whereas co-pyrolysis of cellulose and lignin was strongly inhibited by interactions with the overlap ratio of 0.9737. In Macro-TGA, interactions between components were stronger than that in TGA due to more considerable heat and mass transfer effect.