Study On Pyrolysis And Combustion Characteristics And Kinetics Of Petrochemical Wastewater Sludge,Coal,And Their Blends

Petrochemical wastewater sludge (PS) is a kind of hazardous wastes that precipitated and separated from organic wastewater after various treatments during the production process of petrochemical enterprises. Without being properly disposed, PS will result in severe ecology environment pollution, and even endanger human health. Furthermore, there is a high content of organic matters in the PS, which can generate certain heating values. Therefore, making a regeneration of PS can recycle some valuable resources and energies. The thermochemical conversion methods, such as pyrolysis and combustion, were popular for hazard-free treatment, volume reduction, stabilization, and energy recovery when compared with traditional disposal technologies. This paper was mainly focus on the thermochemical conversion mechanisms and kinetics of PS by using various thermal analysis methods, thus laying a solid foundation for industrialized application.Firstly, the pyrolysis characteristics of PS, heat effect, evolution of surface chemical functional group for solid products, and release characteristics for gas products were studied by using TG/DSC-FTIR. Furthermore, the multistep independent consecutive reaction model was established for kinetic analysis of PS pyrolysis. The results showed that, with the heating rate increasing, the pyrolysis curves of PS shifted to higher temperatures, all the pyrolysis characteristic parameters except for residual mass had a tendency to increase. Chars FTIR showed that, the absorption of O-H, C-H, C=O, C-O, and C-C decreased as the pyrolysis temperature increased. Gas FTIR showed that there were absorptions of H2O, CH4, CO, and CO2. The pyrolysis kinetic analysis showed that the most potential models for various phases were f(a)=(1-?)2.3, (1-?)2.7, and 4/5(1-?)[-ln(1-?)]-1/4, respectively, which were all deviating from the ideal models. Py-GC results showed that, as the temperatures increased, the yields of H2 and CO increased greatly, while slower growth and even reduction for CH4 and CO2.The combustion characteristics of PS in different oxygen concentrations for O2/N2 and O2/CO2 atmospheres were investigated by using TGA. In addition, the multistep independent consecutive reaction model for different oxygen concentrations was established for kinetic analysis of PS combustion. The results showed that, the combustion pathway of PS was made up of two parts, namely "pyrolytic decomposition with char formation+char combustion". In order to describe the combustion process of PS, some combustion characteristic parameters were introduced. It is found that O2 concentration, diluting gas, heating rate, and initial mass had certain effects on the combustion characteristics of PS. The kinetic analysis results showed that the reaction activation energies of the fourth combustion phase of PS in O2/N2 and the last three combustion phases of PS in O2/CO2 increased with the O2 concentration increasing, while the values of the other combustion phases were not influences by O2.The co-pyrolysis characteristics and kinetics of PS and lignite were investigated by TGA. The results showed that the pyrolysis curves of PS and lignite blends lay between those of the individual materials. With the percentage of PS in the blend increasing, TG curves shifted to lower temperatures, and the mass loss became more. During the co-pyrolysis process, there existed an inhibitive interaction between PS and HL. When the temperature was low, lignite hindered the pyrolysis of PS. With the temperature increasing, the chars generated during the pyrolysis of PS would hinder the thermal degradation of lignite. The kinetic analysis results indicated that volatiles content and particle size could influence the reaction activation energy of the sample during the pyrolysis. Furthermore, the co-pyrolysis tests of PS and lignite were also conducted in a fixed-bed reactor. It is found that the the interactions between PS and HL would be beneficial to produce more gas products. FTIR analysis showed that, the absorption of main chemical functional groups in the pyrolysis products could be influenced by the pyrolysis temperatures and blending ratios. The results of GC analysis for gas products showed that, the yields of H2 and CO clearly increased as the pyrolysis temperature and PS blending ratio increasing, while the changes for CH4 and CO2 yields with the pyrolysis temperature and PS blending ratio were relatively more complex.Finally, the co-combustion behaviors and kinetics of PS and lignite were systematacially investigated by TGA. The results showed that the characteristic combustion temperatures, characteristic combustion rates, and characteristic combustion indexes all increased with the heating rate increasing. With the percentage of PS in the blend increasing, the characteristic combustion temperatures of the blends decreased, while the characteristic combustion rates and characteristic combustion indexes increased. During the co-combustion process, there existed an inhibitive interaction between PS and HL. When the temperature was low, lignite hindered the thermal decomposition of PS. With the temperature increasing, the chars and ashes generated during the thermo-oxidative degradation of PS would hinder the thermal decomposition of lignite. The minerals and microstructure of the combustion residues of the samples were analyzed by using XRD and SEM. It is found that the sintered and fused appearances of the combustion residues became worse as the percentage of PS in the blend increased. The average activation energy of the blends during the co-combustion was in the range of 86.43?201.56 kJ-mol-1 by FWO method and 79.17?202.09 kJ-mol-1 by KAS method. The activation energy of 75HL/25RS was the minimum.