• Energy Research

Recently, a widely used method for recycling fly ash waste of coal collected from the electrostatic precipitators has been the synthesis of zeolites from this waste material [...]

The present study is aimed to the preparation of synthetic zeolites of a defined Na-X type (Faujasite) from the fly ash (FA) generated by the incineration of Bulgarian lignite coals. FA zeolitization was carried out by three different methods: classical alkaline conversion, two-stage fusion-hydrothermal synthesis, and atmospheric aging, all with sodium hydroxide (NaOH) as an alkaline activator. The nature, morphology and chemistry of the zeolites were studied by X-ray diffraction, scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analyses. The results from the classical alkaline conversion show the formation of an aluminosilicate hydrogel on the surface of the FA particles but a crystallization of any zeolitic phase does not take place. Zeolites with a dominant Na-X phase were obtained under by a two-stage synthesis under the following conditions: fusion at 550 °C, hydrothermal treatment at 90 °C for 2 h of duration, and NaOH/FA ratios of 2.0–2.4. Zeolite Na-X is also obtained by atmospheric aging for 1 year at a NaOH/FA ratio of 1.

The combustion of coal in Thermal Power Plants generates fine dust particles (coal fly ash, CFA), which are collected from the flue gas streams and deposited as solid wastes. One of the technologically reliable solutions for utilization of CFA is its alkaline conversion into zeolites. The present study focuses on the influence of calcium content in CFA on the chemical and phase composition, morphology and surface properties of coal fly ash zeolites. Comparative studies of the capacity of zeolites of Na-X and Na-Ca-X types from coal fly ash to capture carbon emissions under static and dynamic conditions have been performed. The present study answers a key question from a practical point of view, how does moisture in flue gases affect the adsorption of carbon dioxide on zeolites. The development of efficient adsorbents from CFA with varying composition will contribute to a number of environmental benefits and to the development of efficient CO2 capture technologies in the context of the circular economy.

At present, mitigating carbon emissions from energy production and industrial processes is more relevant than ever to limit climate change. The widespread implementation of carbon capture technologies requires the development of cost-effective and selective adsorbents with high CO2 capture capacity and low thermal recovery. Coal fly ash has been extensively studied as a raw material for the synthesis of low-cost zeolite-like adsorbents for CO2 capture. Laboratory tests for CO2 adsorption onto coal fly ash zeolites (CFAZ) reveal promising results, but detailed computational studies are required to clarify the applicability of these materials as CO2 adsorbents on a pilot and industrial scale. The present study provides results for the validation of a simulation model for the design of adsorption columns for CO2 capture on CFAZ based on the experimental equilibrium and dynamic adsorption on a laboratory scale. The simulations were performed using ProSim DAC dynamic adsorption software to study mass transfer and energy balance in the thermal swing adsorption mode and in the most widely operated adsorption unit configuration.