Abstract
This study aims to investigate the physical and chemical characterization of six fly ash samples obtained from different municipal solid waste incinerators (MSWIs), namely grate furnaces, rotary kiln, and fluidized bed reactor, to determine their potential for CO2 and thermochemical energy storage (TCES). Representative samples were characterized via simultaneous thermal analysis (STA) in different atmospheres, i.e., N2, air, H2O, CO2, and H2O/CO2, to identify fly ash samples that can meet the minimum requirements, i.e., charging, discharging, and cycling stability, for its consideration as TCES and CO2-storage materials and to determine their energy contents. Furthermore, other techniques, such as inductively coupled plasma optical emission spectroscopy, X-ray fluorescence (XRF) spectrometry, X-ray diffraction (XRD), scanning electron microscopy, leachability tests, specific surface area measurement based on the Brunauer–Emmett–Teller method, and particle-size distribution measurement, were performed. XRF analysis showed that calcium oxide is one of the main components in fly ash, which is a potentially suitable component for TCES systems. XRD results revealed information regarding the crystal structure and phases of various elements, including that of Ca. The STA measurements showed that the samples can store thermal heat with energy contents of 50–394 kJ/kg (charging step). For one fly ash sample obtained from a grate furnace, the release of the stored thermal heat under the selected experimental conditions (discharging step) was demonstrated. The cycling stability tests were conducted thrice, and they were successful for the selected sample. One fly ash sample could store CO2 with a storage capacity of 27 kg CO2/ton based on results obtained under the selected experimental conditions in STA. Samples from rotary kiln and fluidized bed were heated up to 1150 °C in an N2 atmosphere, resulting in complete melting of samples in crucibles; however, other samples obtained from grate furnaces formed compacted powders after undergoing the same thermal treatment in STA. Samples from different grate furnaces showed similarities in their chemical and physical characterization. The leachability test according to the standard (EN 12457-4 (2002)) using water in a ratio of 10 L/S and showed that the leachate of heavy metals is below the maximum permissible values for nonhazardous materials (except for Pb), excluding the fly ash sample obtained using fluidized bed technology. The leachate contents of Cd and Mn in the fly ash samples obtained from the rotary kiln were higher than those in other samples. Characterization performed herein helped in determining the suitable fly ash samples that can be considered as potential CO2-storage and TCES materials.
Highlights
Global population growth, massive urbanization, and economic growth have increased the consumption of natural raw materials and energy, resulting in huge amounts of waste
Fly ash samples A and B have higher BET surface areas owing to the higher unburned carbon contents or activated carbon added to the fly ash sample in the air pollution control system
The lower BET surface areas of fly ash samples correspond to the finest fractions, which contain less unburned carbon and higher inorganic content [45]
Summary
Massive urbanization, and economic growth have increased the consumption of natural raw materials and energy, resulting in huge amounts of waste. Since the resources are limited, sustainable resource management is necessary to secure the physical basis of society and economy in the long run [1]. Waste incineration is a key element in sustainable waste management, which decreases the amount and volume of solid waste and sanitizes the waste during incineration [2]. Waste incinerators produce bottom ash and fly ash. The bottom ash can be deposited in nonhazardous-waste landfills or used as a road construction material. Fly ash is particulate matter carried over from the combustion chamber and removed from the flue–gas stream prior to the addition of any type of sorbent material [3]
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