Effect of interactions during co-combustion of organic hazardous wastes on thermal characteristics, kinetics, and pollutant emissions

Evaluating combustion kinetics and quantifying fuel-N conversion tendency of shoe manufacturing waste

Combustion is an effective and cost-efficient thermochemical conversion method for solid waste, showing promise for the resource utilization of shoe manufacturing waste (SMW). However, SMW is generally composed of different components, which can lead to unstable combustion and excessive pollutant emissions, especially NOx. To date, combustion characteristics, reaction mechanism and fuel nitrogen (fuel-N) conversion of different SMW components remain unclear. In this work, the combustion behavior of typical SMW components combustion was investigated using Thermogravimetric coupled with Fourier transform infrared spectrum (TG-FTIR). A simplified single-step reaction mechanism was proposed according to the temperature interval to estimate reaction mechanism of SMW. Additionally, the relationship between fuel-N conversion tendency and fuel properties was established. The results indicate that the values for the comprehensive combustion performance index (S) and flammability index (C) range from 1.65 to 0.44 and 3.98 to 1.37, respectively. This demonstrates the significant variability in combustion behavior among different SMW components. Cardboard, leather and sponge have higher values of S and C, suggesting a better ignition characteristic and a stable combustion process. During the combustion of SMW, nitrogen oxides (NO and N2O) are the main nitrogen-containing compounds in the flue gases, with NO being the major contributor, accounting for over 82.97 % of the nitrogen oxides. NO has a negative correlation with nitrogen content, but it is opposite for N2O, HCN and NH3. Furthermore, the conversion of NO, N2O and NH3 is proportional to logarithmic values of O/N, while its conversion to HCN is proportional to logarithmic values of VM/N. These findings facilitate the prediction of the fuel-N conversion of solid waste combustion. This work might shed light on combustion optimization and in-situ pollutant emission control in solid waste combustion.

Insight into the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans in hazardous waste incineration and incinerators: Formation process and reduction strategy

Incineration technology has been widely adopted to safely dispose of hazardous waste (HW). While the incineration process causes the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). Due to its extreme toxicity, many scholars have been committed to determining the PCDD/F formation process and reducing emissions in incinerators. Previous studies ignored the impact of incineration and fluctuation of feeding materials on PCDD/F formation in hazardous waste incinerators (HWIs). In this study, differences in PCDD/F formation between HWIs and municipal solid waste incinerators (MSWIs) were pointed out. The incineration section in HWIs should be carefully considered. Laboratory experiments, conventional analysis and thermogravimetry experiments were conducted. An obvious disparity of PCDD/F formation between 12 kinds of HWs was found. Distillation residue was found with remarkably higher PCDD/F concentrations (11.57 ng/g). Except for the Cl content, aromatic rings and C-O bond organics were also found with high correlation coefficients with PCDD/F concentrations (>0.92). And PCDD/Fs were formed through a chlorination process and structure formation process. All of these are helpful to further understand the PCDD/F formation process during HW incineration, optimize the operation conditions in HWIs and reduce the emission pressure of PCDD/Fs in the future.

Acid gas emission and ash fusion characteristics of multi-component leather solid waste incineration in bubbling fluidized bed

The tanning sludge (TS) and other tanning solid wastes are produced in significant quantities by the leather industry. To evaluate the combustion properties, acid gaseous pollutant conversion, and ash management, co-firing of TS with various wastes was investigated in a bubbling fluidized bed. TG-FTIR test indicated that tanning solid wastes had superior combustion properties and include more gaseous pollutants than TS. The leather mixed solid waste (LMSW) formed by mixing had better fuel characteristics than TS. The conversion rates of SO2 and HCl of LMSW incineration were 67% and 40%, respectively. The co-combustion of TS and solid wastes reduces the conversion rate of acid gas. Increasing the proportion of high-inorganic chlorine raw material could further reduce the conversion rate and increase the ash fusion temperature appropriately. Because ash and slag were primarily composed of Ca and Fe elements, the addition of calcium carbonate (CaCO3) can increase ash melting point while reducing acid gas emissions. When CaCO3 was added at a calcium to sulfur (Ca/S) ratio of 2, the acid gas emission was reduced by more than 80% and the softening temperature was raised by 90 °C. When Ca/S is greater than 2, the economics of adding CaCO3 decreased.

The role of additives in improving the flammability and calorific value of leather shavings and the binding of chromium compounds in ash

Leather processing companies are struggling with the problem of increasing costs of post-production waste disposal. Therefore, the issue of thermal waste disposal at the plant and the use of generated heat in the production process is becoming more and more popular. Leather waste on its own does not allow for autothermal combustion despite the sufficient higher heating value (HHV). Therefore the Authors proposed to improve the flammability of the fuel by adding a small amount of wood sawdust to leather waste and produce premixed pellets. Six such samples were incinerated in a laboratory-scale reactor, which enables the simultaneous measurement of characteristic temperatures, exhaust gas analysis and sample mass loss rate. Research has shown that even a small addition of sawdust enables a stable combustion process and does not cause the formation of sinters. In addition, studies of the ash showed that in the case of chromium-containing waste, a large part of it remained in the ash in the form of Cr₂O₃. Nevertheless, very fine ash causes the small fraction chromium to be carried with the flue gas stream, therefore controlled agglomeration of the ash structure would be advisable in the final installation. Emission analysis showed high and moderately high NO_x and SO₂ emissions, decreasing with the increase in the amount of sawdust addition in the sample. Research has shown that leather waste is not a burden, but can be an attractive and safe source of energy for the company, while improving waste management in a circular economy.

Influence of biomass on coal slime combustion characteristics based on TG-FTIR, principal component analysis, and artificial neural network

The development and utilization of solid waste is an effective way to solve the severe environmental and energy crisis. In this study, Thermogravimetry - Fourier transform infrared spectrometry (TG-FTIR) was used to carry out the co-combustion experiment of coal slime and rice husk under different mixing ratios. With the increase of the mass percentage of rice husk in the sample, the initial ignition temperature and burnout of the sample decreased, and the comprehensive combustion performance improved gradually. The dominant reaction in the co-combustion of coal slime and rice husk was determined by statistical method. When the mass percentage of rice husk in the mixture is between 30 and 90 %, it can inhibit the release of NO_x and SO₂. Taking Kissinger-Akahira-Sunose method as an example, the calculated average activation energies of coal slime and rice husk combustion are 105.66 and 148.93 kJ/mol respectively. With the increase of the mixing ratio of rice husk in the blend, the combustion mechanism of the sample changed. Finally, the mean absolute error, root mean square error and determination coefficient of the artificial neural network model are 0.52697, 0.67866 and 0.99941 respectively.