Fly Ash Desulfurization Research Articles

Flue gas desulfurization (FGD) fly ash as a sustainable, safe alternative for cement-based materials

The reduction in fly ash production in coal-fired power plants has created an opportunity to explore alternative types of fly ashes previously deemed unfit for use in concrete. In plants using flue gas desulfurization (FGD) processes, fly ash could contain high amounts of sulfur oxides, making its use in concrete inadvisable. However, the type of sulfur compound present in a fly ash strongly impacts its performance in concrete. In this study, two types of fly ash were used to evaluate the effect of sulfur oxides on mortar mixtures incorporating fly ash as supplementary cementitious material (SCM); one from an FGD unit, with high sulfur oxide content (in the form of hannebachite), and the other generated in a system without FGD, with negligible sulfur oxide. Calorimetry results show that hannebachite can effectively control C3A hydration similar to gypsum; however, its presence in FGD fly ash does not induce deleterious expansion associated with internal sulfate attack in mortars. TGA and XRD analyses suggest that hannebachite has lower reactivity than sulfate. Hannebachite not only maintains the pozzolanic reactivity of the fly ash, but its fineness may promote OPC hydration, increasing compressive strength. The results of this study indicate that FGD fly ash can be used as an SCM, allowing more sustainable concrete production.

Durability and microstructure analysis of the road base material prepared from red mud and flue gas desulfurization fly ash

The present study aimed to investigate the durability and microstructure evolution of road base materials (RBM) prepared from red mud and flue gas desulfurization fly ash. The durability testing showed that the strength of RBM with the blast furnace slag addition of 1wt%, 3wt% and 5wt% reached 3.81, 4.87, and 5.84 MPa after 5 freezing–thawing (F–T) cycles and reached 5.21, 5.75, and 6.98 MPa after 20 weting–drying (W–D) cycles, respectively. The results also indicated that hydration products were continuously formed even during W–D and F–T exposures, resulting in an increase of the strength and durability of RBM. The observed increase of macropores (>1 μm) after F–T and W–D exposures suggested that the mechanism of RBM deterioration is pore enlargement due to cracks that develop inside their matrix. Moreover, the F–T exposure showed a greater negative effect on the durability of RBM compared to the W–D exposure. The leaching tests showed that sodium and heavy metals were solidified below the minimum requirement, which indicates that these wastes are suitable for use as a natural material replacement in road base construction.

Preparation and characterization of a red mud-based road base material: Strength formation mechanism and leaching characteristics

The present study was designed to prepare and characterize an eco-friendly road base material using mainly red mud in terms of mechanical properties, hydration and leaching characteristics. The microstructure was characterized by using scanning electron microscopy, X-ray diffractometer, Fourier transform infrared spectroscopy, electron probe microanalysis, Magnetic angle spinning Nuclear magnetic resonance and mercury intrusion porosimetry while inductively coupled plasma emission spectrometer was adopted to characterize the leaching behavior of hazardous compounds. The results showed that the strength of the optimum proportion reached 5.92 MPa and 6.66 MPa after curing for 7 and 28 days respectively and meet the highest strength requirement (class I) of 5–7 MPa for road base in Chinese standards. The results also showed that the strength increased with long term soaking which implies a good durability of RBM against water. The microstructure analysis indicated that predominant hydration products are C-S-H, C-A-S-H, N-A-S-H gels, ettringite and are responsible for strength development in the road base. The leaching results showed that all parameters in specimens cured for 7d and 28d are lower than drinking water GB 5749-2006 standard limits. Therefore, based on strength and environmental performance, red mud-flue gas desulfurization fly ash mix can be used as a road base material. This process is believed to reduce environmental pollution related to red mud and flue gas desulfurization fly ash, lower the road base cost and also save huge disposal fees that is used for safe disposal of these wastes.

The experimental study of fly ash recirculation combustion characteristics on a circulating fluidized bed combustor

Fly ash recirculation combustion (FARC) technology is an effective way to improve the combustion performance due to the improvement of carbon burnout as well as the utilization of calcium oxide. In order to study the effect of FARC on operation and emission characteristics of CFB boilers, a series of experiments were carried out on a lab-scale CFB combustor by using two types of fly ash (desulfurization and non-desulfurization fly ashes). Results show that with FARC, the temperature distribution in the furnace becomes uniform. The difference between the two different types of fly ash is mainly reflected in the emissions of SO2 and NOX. Desulfurization fly ash would increase the NOX emission while decrease the SO2 emission, and the optimum desulfurization temperature is 880°C. On the contrary, non-desulfurization fly ash would increase SO2 emission while decrease NOX emission. FARC could effectively improve the combustion performance, as the recirculation rate increases from 0 to 0.3, the combustion efficiency increases by 2% for both two fly ashes and the CO emission decreases, but the particulate matter emission increases. For desulfurization fly ash, Ca/S molar ratio should be appropriately reduced for inhibiting the NOX emission when limestone was used for in situ desulfurization.

Preparation of FGD Gypsum-Fly Ash Plaster Material

FGD gypsum-fly ash plaster material was prepared by desulfurization gypsum plaster and fly ash as main materials, compound retarder A (composed of citric acid, sodium metaphosphate and borax), methylcellulose (MC) as super absorbent polymers (SAP) and water reducing agent of lignosulfonate. Mix proportion was determined through studying effects of the experimental factors, including fly ash mixing amount, retarders of citric acid, bone glue and compound retarder A, and SAP of MC and dextrin, on plaster material properties. Final mix proportion was followed as: FGD gypsum to fly ash mass ratio of 4.0, compound retarder of 0.2%, methylcellulose of 0.2% and lignosulfonate of 0.1%.

Experimental Study on Desulfurization of Fly Ash Slurry

This paper designs a bubbling type of desulfurization reactor, which simulates flue gas nitrogen and sulfur dioxide according to a certain flow ratio, equipped with absorber through into the bubbling type desulfurization absorb and reactor by iodine volume method, measures import and export of SO2 concentration and pH value of absorber. The desulfurization rate of fly ash slurry is measured in the small drum bubble desulfurization reactor device. Results show that increasing the concentration of fly ash and entrance SO2 concentration, and decreasing particle size of fly ash will increase the desulfurization rate of fly ash slurry. The main mechanisms of fly ash desulfurization are physical adsorption and chemical adsorption.

Fly Ash-Desulfurization Gypsum Mortar and Concrete Part I: Mix Proportions and Hydration

Fly ash (FA) and flue gas desulphurization gypsum (FGD) were blended in proportion into a new composite binder added with cement, lime and some modifiers. In the paper, the mix proportions of composite binder with low-quality FA and FGD were studied. FA-FGD more than 80% with FA:FGD 3:2 was suggested for mortar, plastering and slurry while FA:FGD 2:1 and FA-FGD 30~40% was recommended for middle-strength concrete. Hydration process of typical mixtures of FA-FGD paste was investigated through SEM and XRD tests. The conclusion could be made that FA showed much improved pozzolana activity especially at early ages due to the existence of FGD as an ideal sulfate activator, which also crystallized later to strengthen the hardened paste. The microstructure of hydrated FA-FGD paste was more excellent than that of neat cement stone or one blended with the same percentage of pure FA.

Preparing and Characterization of the Geopolymer Based on Desulfurization Ash and Fly Ash

The desulfurization ash, fly ash and metakaolin were uesd to prepare the geopolymer. Compressive strength test demonstrated that the optimum mass ratio of desulfurization ash, fly ash and metakaolin was 30:55:10 and the max strength reached 17.3 MPa. The XRD and SEM show that there is not new crystalline phase. The main crystalline phase of the matrix is non-reacted mullite in the fly ash. It was suggested that the emission of CO2 and SO2 were rehabited from geopolymer by analysis of those compositions volatilizing using TG/MS.

95/04710 Possible utilization of flue-gas desulfurization gypsum and fly ash for citrus production evaluation of crop growth response

95/04710 Possible utilization of flue-gas desulfurization gypsum and fly ash for citrus production evaluation of crop growth response