Search

Abstract The thermal characteristics and kinetic behavior of various solid wastes, including refuse‐derived fuel (RDF) and municipal solid waste (MSW), were investigated as a potential renewable energy source, in comparison with low‐rank coal. The experimental data were obtained in nonisothermal conditions through TGA analysis at specific heating rates. In addition to thermal characteristics of solid fuels, four isoconversional (model‐free) kinetic methods: a: Kissinger‐Akahira‐Sunose (KAS), b: Flynn‐Wall‐Ozawa (FWO), c: Friedman, and d: Vyazovkin were applied to calculate activation energies. In case of solid wastes, it is possible to say that the trend of activation energies of all isoconversional methods remains almost same in the selected region of conversion (0.1‐0.6 and 0.7‐0.9). Whereas in case of coal, Friedman model exhibits lower and inconsistent values of activation energy than others selected isoconversional methods. The experimental and modeling results revealed that that solid wastes (RDF and MSW) can be promising alternative energy sources to encounter energy crisis and uncontrolled waste disposal issues.

Abstract Due to its high potential for thermal energy storage systems (Huber, Setoodeh Jahromy, Jordan, et al, Energies. 2019;12:17) the decomposition of boric acid is of particular interest in the field of applied research. The complexity of the reaction mechanism, with its multiple partial‐overlapping reaction steps, hitherto prevented a clear identification and analysis of each stoichiometric reaction step. So far, various research teams performed different kinetic analyses of boric acid, which led to various reaction mechanisms and stoichiometric reaction steps with yet inconclusive results for process modeling. Thus, a deeper examination of the process was desirable, to validate whether a proposed reaction is reasonable or not. For this purpose, experimental data were used for a deconvolution of the reaction sequence, using the Fraser‐Suzuki function, which clearly revealed the respective single reactions. The results of the deconvolution were compared with the proposed reaction steps in consideration of the stoichiometric ratio and thereby illustrated that the decomposition of polycrystalline boric acid more likely consists of three reaction steps. In contrary to the two‐step mechanism, the three‐step mechanism showed a very good correlation (r > 99%). Based on these outcomes, kinetic analyses were performed for each reaction step, by means of the nonparametric kinetics 2 (NPK2) method with subsequent determination of kinetic parameters. Additionally, for a deeper insight into the reaction, analyzing techniques like X‐ray diffraction (XRD), scanning electron microscopy (SEM) and simultaneous thermal analysis (STA) were applied.

Abstract Energy crisis and solid waste management have remained challenging issues for authorities in Pakistan. These issues tend to rise with increasing population and economic growth of the society. Therefore, environmentally sustainable waste‐to‐energy program must be part of the waste management system since they may substitute fossil fuels with renewable energy sources by enabling energy recovery instead of landfill of solid wastes. In this work, the combustion characteristics of fossil fuel (coal) and solid wastes such as municipal solid waste (MSW) and refuse‐derived fuel (RDF) were investigated by thermogravimetric analysis (TGA) to compare their thermal decomposition behavior. Furthermore, proximate and ultimate analyses of these samples were carried out along with their heating values. The TGA profiles of samples indicate low reactivity of coal, whereas solid wastes present greater reaction rate reflecting their low ash and high volatile contents. It was found that the heating value of RDF sample was close to that of coal. The obtained thermal data were used to calculate the kinetic parameters using Arrhenius and Coats‐Redfern models with different reaction mechanisms. According to these models, the fuels could be arranged in order of activation energy as coal > RDF > MSW. The percentage difference between activation energy values found from Arrhenius and Coats‐Redfern models was in the range of 4.1%‐26.5%. However, the Coats‐Redfern model exhibited consistency in activation energy values, followed by a high value of R2. These results of the TGA could be very helpful to predict the combustion dynamics and confirm that MSW and RDF may be used as sustainable fuels, to meet the prevailing challenges of the energy crisis and solid waste management.

With rapid increases in population and urbanization, uncontrolled municipal solid waste (MSW) is a threat to public health and environmental safety. In this study, we explore its generation, treatment, and characteristics of physical/chemical composition and assess the potential of MSW as a renewable energy source in Lahore, the second largest city in Pakistan. Based on the average generation rate of MSW (i.e., 0.65 kg/capita/day), the daily production of MSW in this city would reach 7150 tons/day. However, its disposal in a safely engineered way has been restricted due to the lack of: (a) pre-planning, (b) infrastructure, (c) political will, and (d) public awareness. Various samples of MSW considering socio-economic structure were collected. The physical components of MSW in Lahore were found to be in the descending order of biodegradable, nylon plastic bags, textile, diaper, and paper. The inductively coupled plasma optical emission spectroscopy (ICP-OES) technique was used to determine the heavy metal content and leachability of the MSW components to check for the environmental contamination risk. The proximate and ultimate analysis of this MSW was also carried out along with its heating values. The average high heating value of MSW was measured as 14,490 kJ kg−1. Energy recovery potential of 48 MW was assessed further from 2000 tons of MSW/day. The results of this study should be helpful for policy makers to establish a MSW management strategy for the potential renewable energy alternative. Keywords: Incineration, Landfills, Municipal solid waste, Renewable energy, Waste to energy

In connection to present energy demand and waste management crisis in Pakistan, refuse-derived fuel (RDF) is gaining importance as a potential co-fuel for existing coal fired power plants. This research focuses on the co-combustion of low-quality local coal with RDF as a mean to reduce environmental issues in terms of waste management strategy. The combustion characteristics and kinetics of coal, RDF, and their blends were experimentally investigated in a micro-thermal gravimetric analyzer at four heating rates of 10, 20, 30, and 40 °C/min to ramp the temperature from 25 °C to 1000 °C. The mass percentages of RDF in the coal blends were 10%, 20%, 30%, and 40%, respectively. The results show that as the RDF in blends increases, the reactivity of the blends increases, resulting in lower ignition temperatures and a shift in peak and burnout temperatures to a lower temperature zone. This indicates that there was certain interaction during the combustion process of coal and RDF. The activation energies of the samples were calculated using kinetic analysis based on Kissinger–Akahira–Sunnose (KAS) and Flynn–Wall–Ozawa (FWO), isoconversional methods. Both of the methods have produced closer results with average activation energy between 95–121 kJ/mol. With a 30% refuse-derived fuel proportion, the average activation energy of blends hit a minimum value of 95 kJ/mol by KAS method and 103 kJ/mol by FWO method.

As a part of our research in the field of thermochemical energy storage, this study aims to investigate the potential of three fly ash samples derived from the fluidized bed reactors of three different pulp and paper plants in Austria for their use as thermochemical energy (TCES) and CO2 storage materials. The selected samples were analyzed by different physical and chemical analytical techniques such as X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), particle size distribution (PSD), scanning electron microscopy (SEM), inductively coupled plasma atomic emission spectroscopy (ICP-OES), and simultaneous thermal analysis (STA) under different atmospheres (N2, CO2, and H2O/CO2). To evaluate the environmental impact, leaching tests were also performed. The amount of CaO as a promising candidate for TCES was verified by XRF analysis, which was in the range of 25–63% (w/w). XRD results indicate that the CaO lies as free lime (3–32%), calcite (21–29%), and silicate in all fly ash samples. The results of STA show that all fly ash samples could fulfill the requirements for TCES (i.e., charging and discharging). A cycling stability test of three cycles was demonstrated for all samples which indicates a reduction of conversion in the first three reaction cycles. The energy content of the examined samples was up to 504 kJ/kg according to the STA results. More energy (~1090 kJ/kg) in the first discharging step in the CO2/H2O atmosphere could be released through two kinds of fly ash samples due to the already existing free lime (CaO) in those samples. The CO2 storage capacity of these fly ash samples ranged between 18 and 110 kg per ton of fly ash, based on the direct and dry method. The leaching tests showed that all heavy metals were below the limit values of the Austrian landfill ordinance. It is viable to say that the valorization of fly ash from the pulp and paper industries via TCES and CO2 storage is plausible. However, further investigations such as cycling stability improvement, system integration and a life cycle assessment (LCA) still need to be conducted.

This paper aims to describe the capability of the system boric acid–boron oxide for thermochemical energy storage. As part of the systematic research and in-depth analysis of potential solid/gas reaction systems, performed during the last years, this reaction system appears to be highly promising for the future of worldwide sustainable energy supply. The analysis of the reaction heat, by means of thermogravimetric and macroscopic investigations, not only showed a significantly higher energy density of 2.2 GJ/m3, compared to sensible- and latent energy storages, but the reaction kinetic further demonstrated the reactions’ suitability to store energy from renewable energy and waste heat sources. This paper, therefore, shows a new approach regarding the application of the boric acid–boron oxide reaction system and elaborates on the advantages and challenges for its use as energy storage.

Metal oxides are promising potential candidates for thermochemical energy storage in concentrated solar power plants. In particular, the Cu2O/CuO system is suitable because of its high energy density, applied temperature interval, and reduced cost compared to the CoO/Co3O4 system. In heterogenous gas-solid reactions, the pressure affects the kinetics significantly. To quantify this effect for oxidation of Cu2O to CuO, isothermal runs between 800 °C and 930 °C at different oxygen partial pressures (0.1, 0.2, 0.5, and 1.0 bar) were conducted with thermogravimetric analysis (TGA). Defined fractions of CuO samples (1⁻100 µm) were analyzed with X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, and scanning electron microscopy (SEM) analysis. The kinetic analyses were performed with extended non-parametric kinetics (NPK), which is applied for the first time to consider the pressure term in the general kinetic equation in addition to the conversion and the temperature term. The results show how the oxygen partial pressure impacts the kinetics and how reparameterization of the pressure term affects the kinetic analysis of the oxidation reaction of Cu2O to CuO. The best conversion model is a two-dimensional Avrami-Erofeev model with an activation energy of 233 kJ/mol. The kinetic models for conversion, temperature, and pressure presented in this work provide one of the most important requirements for reactor designs.