Thermochemical and Toxic Element Behavior during Co-Combustion of Coal and Municipal Sludge
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ABSTRACT:
SUBMITTER: Chen Y
PROVIDER: S-EPMC8307717 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Coal gangue has the shortcomings of low calorific value and refractory burnout, while polyvinyl chloride has the advantages of a long combustion process and high calorific value. In order to make up for these shortcomings of coal gangue, the possibility of a treatment method based on co-combustion of coal gangue with polyvinyl chloride, which can be centrally recovered from municipal solid waste, is proposed. In order to analyze the combustion effect of a mixture of these two substances, experimental samples were prepared by mixing these two substances in three different ratios, and they were tested by thermogravimetric analysis. The experimental results were compared, analyzed and evaluated. The effects of the proportion of polyvinyl chloride in the mixture on the temperature parameters, activation energy, and interaction during co-combustion were analyzed. In order to analyze the interaction during co-combustion of the two, a coupling analysis method for mixed combustion is presented, and the effectiveness of this method is verified by comparing with the correlation analysis results of co-combustion. The results show that co-combustion can mitigate the ignition difficulty and burnout of coal gangue. When the proportion of polyvinyl chloride in the mixture was increased from 20% to 80%, the maximum weightlessness rate of the first stage rapidly increased from 4.5%/min to 15.6%/min; however, that of the second stage slowly increased from 3.7%/min to 4.2%/min. A 20% proportion of polyvinyl chloride showed the most significant promotion of co-combustion, with a maximum coupling coefficient of 0.00318, which was 1.11 and 1.35 times greater than that of 50% and 80% proportions, respectively. Co-combustion can reduce the activation energy of coal gangue during the initial and end stages. Therefore, co-combustion is helpful to improve the problems of low calorific value and refractory burnout of coal gangue.
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Project description:Feedstocks such as coal, biomass, plastics, and their blends have the potential to serve as fuels for the thermochemical conversion process owing to their relatively high calorific values. Nevertheless, the relative proportion of these feedstock blends has a pivotal influence over the overall energy conversion efficiency. Consequently, conducting a comprehensive study to optimize the blend proportion becomes crucial in order to obtain an optimal fuel. The study aims to investigate the thermochemical characterization and kinetics of blends composed of lignite coal, southern pine biomass, and municipal waste plastic blend to optimize the blend proportion. This optimization has been achieved through an analysis of 12 distinct blends, considering factors such as combustion reaction kinetics, combustion stability, and comprehensive combustion indices. The reaction kinetics, including activation energy, pre-exponential factor, and reaction order, were estimated using various methods, including Vyazovkin, Kissinger-Akahira-Sunose, Flynn-Wall-Ozawa, Master-plot, and multidistributed activation energy methods. The investigation revealed that increasing the biomass content within the blends enhances both the combustion stability and combustion performance. The multidistributed activation energy model exhibited a good fit with both the experimental thermogravimetric and the derivative thermogravimetric curves, achieving linear regression fitness values of 0.99 and 0.95, respectively. To showcase the viability of these blends as energy generation feedstock, the optimal blend comprised of 60% biomass, 10% coal, and 30% municipal waste plastic blend, possessing the lowest activation energy (110 kJ/mol), was employed as the feedstock for the fluidized bed oxy-steam gasification process. The gasification process resulted in a synthetic gas consisting of 47.79 mol % H2, 27.96 mol % CO, 5.85 mol % CH4, and 18.38 mol % CO2 (nitrogen-free basis) with a cold gas efficiency of 72.88%. The findings of this study can offer valuable insights into global industries engaged in the thermochemical conversion of solid waste materials.
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Project description:This paper reports on the chemical speciation and leaching behavior of a selected group of hazardous trace pollutants in lignite and lignite-petcoke blend co-combustion products from three power stations in China. The evaluation of speciation results showed that, during combustion, oxidizable elements, mainly As and Mo, bound to organic matter and sulfides in coals were mostly transferred to easily water-soluble forms or to slightly acidic states in the ashes. This manner was the most readily bioavailable condition for such an environment. The evaluation of the leaching results shows that the use of petroleum coke as co-fuel has an impact on the ash composition and on the leaching behavior of some inorganic trace pollutants such as Mo and V. The leaching results compared to the European waste acceptance criteria for landfills reveal that the Mo and As' leaching yield brand the coal combustion products as materials that necessitate preventative measures to reduce their potential leaching. Future work will be focused on the application of our novel chemical stabilization method to these coal ashes to reduce the mobility of elements such as Mo and As, and other potentially leachable elements, and on the use of the resulting ash with aggregate products as a substitute for concrete production.
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Project description:This study researched microbial community succession in response to sludge composting efficiency and heavy metal detoxification during municipal sludge co-composting with spent mushroom and spent bleaching. The change law of key physicochemical properties, the heavy metals contents and forms during composting were analyzed, and the passivation of heavy metals after composting was explored. High-throughput sequencing was used to analyze the microbial community structure of treat 2 during composting, and the correlation analysis of microbial community structure with heavy metal contents and forms were carried out. The results showed that the sludge of each treatment reached composting maturity after 26 days of composting. Organic matter content, electrical conductivity, pH and seed germination index of treat 2 were all in line with the standard limit of agricultural sludge. Because of the presence of compost bacteria addition, the passivating heavy metals performance of treat 2 satisfied the standard limit of agricultural sludge after composting, which was superior to that of treat 1 and treat 3. The diversity of microbial communities in treat 2 decreased during composting. Extensive bacteria such as Bacillus, Geobacter, Lactobacillus, and Pseudomonas, which possessed the abilities of heavy metal passivation and organic oxidizing, were dominant in treat 2 during the heating stage. However, as composting proceeded, Tuberibacillus with ability of organic oxidizing gradually became the most dominant species at the thermophilic and cooling stages. Changes in microbial function varied from changes of microbial community in treat 2, subsequently affected the performances of heavy metal passivation and organic oxidizing during composting.
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Project description:Following the nuclear accident at the Fukushima Daiichi Nuclear Power Plant in 2011, even the municipal solid waste (MSW) and sewage sludge (SS) in northeastern Japan became contaminated by radioactive nuclides such as 137Cs and 134Cs. To understand the state of radioactive cesium (r-Cs) in the incineration residues of the municipal wastes, research groups studied the concentration and the chemical form of r-Cs in the residues, as well as its water-leaching behavior. In the present study, we conducted thermodynamic equilibrium calculations to estimate the possible chemical forms of r-Cs in the incineration residues. Thermodynamic data for cesium oxides and aluminosilicates were collected and compiled into a new database to perform equilibrium calculations for systems that include Cs. The calculation results suggested that Cs (radiocesium and stable cesium) in municipal solid waste was transformed into gaseous CsCl or crystalline aluminosilicate at incineration temperatures and, when a molten aluminosilicate phase (i.e., slag phase) was generated, a proportion of the Cs species was dissolved into the slag phase. In the case of sewage sludge, Cs was calculated to be transformed mostly into crystalline aluminosilicate at incineration temperatures, whereas by analogy with the behaviors of Na and K, Ca,Cs-phosphate double salts were also potential incineration products. These results could account for the high leaching rates of r-Cs from the MSW incineration fly ash and the low leaching rates from the MSW incineration bottom ash and SS incineration fly ash reported in earlier studies. In the case of dewatered SS that included a large amount of slaked lime as a flocculant, it was exceptionally difficult for the calculation to represent the fate of Cs, and we needed to include the contribution of silica sand in a fluidized-bed combustor in the equilibrium calculation to represent the low leaching rates of alkali species from the dewatered SS fly ash. From the results of the thermodynamic equilibrium calculations and also from the calculated standard Gibbs energy of cesium aluminosilicate formation/decomposition reactions, the effects of waste composition and incineration temperature on the fate of Cs were examined: High incineration temperature and large amounts of Ca and Cl in the waste composition increased the fraction of gaseous CsCl in the furnace and thus resulted in the high distribution ratios of Cs in the fly ash of MSW and the high leaching rates of Cs from the fly ash.
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Project description:Comprehensive thermochemical treatment (pyrolysis and combustion) is considered to be an efficient method for treatment of oil sludge (OS) or utilization as a heat source. However, combustion of oil sludge char (OSC), the byproduct from OS pyrolysis, is difficult and energy-consuming due to the high ash content and low heating value. In this study, co-combustion of OSC with biomass is proposed, aiming at the efficient thermal treatment with heat recovery. The thermal characteristics, kinetics, and interactive mechanisms of co-combustion of OSC with raw wood (RW) or hydrothermally treated wood (HW) employing thermogravimetric analysis were investigated. The obtained results indicated that RW blending with OSC resulted in negative interactions with decreasing the apparent activation energies (E) of RW, attributed to the inhibited diffusion of volatiles. The developed porous structure in HW effectively promoted volatile matter diffusion. Coupled with the catalytic support by metal oxides in OSC, HW blending yielded positive interactions during co-combustion despite the increased E. The results showed that diffusion models were the most efficient mechanism for OSC/RW combustion. However, chemical reactions were found to be the rate-determining steps for OSC/HW combustion. The catalytic effect of inorganic elements and their physical influence on heat and mass transfer can control the co-combustion performance of OSC and biomass. The findings could offer reference information for understanding OSC co-combustion and provide a basis for implementing and optimizing the co-combustion between biomass and ash-rich waste.
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Project description:The suitability for aided phytoremediation of Cynara cardunculus L. var. altilis and municipal solid waste compost (MSWC) applied at 2% and 4 % rates was evaluated in a multi potentially toxic element (PTE)-contaminated mining soil (Pb ~ 15,383 mg kg-1, Zn ~ 4076 mg kg-1, As ~ 49 mg kg-1, Cd ~ 67 mg kg-1, Cu ~ 181 mg kg-1, and Sb ~ 109 mg kg-1). The growth of C. cardunculus significantly increased with compost amendment and followed the order: MSWC-4% > MSWC-2% > Control. PTE concentrations in the roots of plants grown on amended soils decreased compared with control plants (i.e., less than ~ 82, 94, and 88% for Pb, Zn, and Cd respectively). PTE translocation from roots to shoots depended on both PTE and amendment rate but values were generally low (i.e., < 1). However, PTE mineralomasses were always higher for plants grown on MSWC-amended soils because of their higher biomass production, which favored an overall PTE bioaccumulation in roots and shoots. After plant growth, labile As and Sb increased in amended soils, while labile Pb, Zn, Cu, and Cd significantly decreased. Likewise, dehydrogenase and urease activities increased significantly in planted soils amended with MSWC. Also, the potential metabolic activity and the catabolic versatility of soil microbial communities significantly increased in planted soils amended with MSWC. Overall, our results indicate that C. cardunculus and MSWC can be effective resources for the aided phytoremediation of multi PTE-contaminated soils.
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Project description:Sustainable building material design relies mostly on energy saving processes, decrease of raw materials consumption, and increase of waste and by-products recycling. Natural and lightweight artificial aggregates production implies relevant environmental impact. This paper addresses both the issues of residues recycling and energy optimization. Particularly, three coal combustion wastes (Weathered Fly Ash, WFA; Wastewater Treatment Sludge, WTS; Desulfurization Device Sludge, DDS) supplied by the Italian electric utility company (ENEL) have been employed in the manufacture of cold bonded artificial aggregates. Previously, the residues have been characterized in terms of chemical and mineralogical compositions, water content, particle size distribution, and heavy metal release behavior. These wastes have been used in the mix design of binding systems with the only addition of lime. Finally, the artificial aggregates have been submitted to physical, mechanical, and leaching testing, revealing that they are potentially suitable for many civil engineering applications.
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Project description:Investigating the division of coal spontaneous combustion stages and the selection of indicator gases is significant to the safe production of coal mines. In this study, the characteristic temperature of coal spontaneous combustion, the generation law of indicator gases, the combustion process, and the division of the combustion stages of coal samples taken from Hongqingliang (HQL) and Dayan (DY) mines were investigated using thermogravimetric analysis experiment, indicator gas detection experiment, and coal oxidation spontaneous combustion experiment. The results of the thermogravimetric analysis experiment showed that the pyrolysis temperatures of the HQL and DY coals were 115.76°C and 131.80°C, and the ignition temperatures were 337.74°C and 360.18°C, respectively. The indicator gas detection results showed that the first-appearance temperature of C2H4 was 85°C for the HQL and DY coals, whereas the first-appearance temperature of C2H6 varied: 115°C for the HQL coal and 130°C for the DY coal. The first-appearance temperatures of C2H2 were 180°C and 195°C for the HQL and DY coals, respectively. The experiments on coal oxidation spontaneous combustion showed that the spontaneous combustion period of the HQL and DY coals were 35.45 and 42.3 days, respectively. The heating process during combustion could be divided into four stages: a latent period of spontaneous combustion, a slow spontaneous heating period, an accelerated spontaneous heating period, and a period of combustion. The critical temperature of each stage showed a good correlation with the incipient temperature of the indicator gases, namely C2H2, C2H4, and C2H6, and the appearance of the above gases can be used to characterize the degree of spontaneous combustion of coal.
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