Advances in concurrent CO2 sequestration and heavy metal mobilization during fly ash carbonation: A review

Photoacoustic response of unburnt carbon in fly ash to infrared radiation

In the present study, the behavior of mercury (Hgp) in solid particles collected from a very cold electrostatic precipitator (VCEP) with the flue gas temperature of 94°C in a large scale pulverized coal power plant in Japan was examined for ten different coal samples. In addition, the investigation of the Hgp content for each particle size in five fly ashes clarified the effect of the particle size of unburned carbons on the Hgp content in fly ash. As a result, the distribution of Hgp into fly ash collected from the VCEP was 13.6-92.3% and increased with the unburned carbon (0.49-2.84%) in fly ash. The decrease of the flue gas temperature heightened the effect of the unburned carbon on the Hgp content in fly ash. The shift of approximately 0.2% in the content of the unburned carbon in fly ash led to the change of 5 - 15% in the distribution of Hgp into fly ash. The increase of the particle size of fly ash heightened the contents of Hgp and the unburned carbon in fly ash. This suggested that the particle size of the unburned carbon in fly ash significantly affected the formation of Hgp.

The catalytic gasification of carbon in incinerator fly ash

A novel method for precise measurement of unburnt carbon in boiler fly ash by ECSA® based on TG-MS

Effect of fly ash composition on the retention of mercury in coal-combustion flue gas

Soil samples from 16 urban sites in Lianyungang, China were collected and analyzed. A pollution index was used to assess the potential ecological risk of heavy metals and a sequential extraction procedure was used to evaluate the relative distribution of Cu, Zn, Pb, Cd, Cr, and As in exchangeable, carbonate, Fe/Mn oxide, organic/sulfide, and residual fractions. The mobility of heavy metals and urease (URE) activity, alkaline phosphatase (ALP) activity, and invertase (INV) activity of soils was determined. The results showed that the average concentrations of Cu, Zn, Pb, Cd, Cr, and As in Lianyungang soils were much higher than those in the coastal city soil background values of Jiangsu and China. Among the five studied regions (utilities, commercial, industrial, tourism, and roadside), the industrial region had the highest metal concentrations demonstrating that land use had a significant impact on the accumulation of heavy metals in Lianyungang soils. Compared to the other metals, Cd showed the highest ecological risk. According to chemical partitioning, Cu was associated with the organic/sulfides and Pb and Zn were mainly in the carbonate and the Fe/Mn oxide phase. The greatest amounts of Cd were found in exchangeable and carbonate fractions, while Cr and As were mainly in the residual fraction. Cd had the highest mobility of all metals, and the order of mobility (highest to lowest) of heavy metals in Lianyungang soils was Cd>Zn>Pb>Cu>As>Cr. Soil urease activity, alkaline phosphatase activity, and invertase activity varied considerably in different pollution degree sites. Soil enzyme activities had the lowest levels in roadside and industrial regions. Across all the soil data in the five regions, the total Cu, Zn, Pb, Cd, Cr, and As level was negatively correlated with urease activity, alkaline phosphatase activity, and invertase activity, but the relationship was not significant. In the industrial region, alkaline phosphatase activity had significant negative correlations with total Cu, Pb, Cr, Zn, Cd, and heavy metal fractions. This showed that alkaline phosphatase activity was sensitive to heavy metals in heavily contaminated regions, whereas urease and invertase were less affected. The combination of the various methods may offer a powerful analytical technique in the study of heavy metal pollution in street soil.

With the recent focus of using coal combustion residue fly ash in mineral carbonation for C capture, an end product, carbonated coal fly ash is generated. The physicochemical changes occur in fly ash during carbonation is hypothesized to improve its soil application potential compared to original fly ash. Therefore, in the present study, we tested carbonated coal fly ash against non‐carbonated (fresh) ash for its effect on soil, plant production, and elemental accumulation in plant parts. Plant pots of sweet corn (Zea mays L.) and snow pea (Pisum sativum L.) added with fresh or carbonated Australian coal fly ash to sandy loam Podosol soil at 5% (w/w) and 10% (w/w) mixing rates were used in the study. Alkalinity of fly ashes attenuated the strong acidity of the soil into weakly acidic to slightly alkaline ranges. Either fresh or carbonated fly ashes added trace elements such as B, Fe, Mn, Zn, Cu, Cd, Mo, Cr, Pb, and Ni into the soil which significantly enhanced the plant growth and yield compared to fly ash absent pots. Accumulation of heavy metals in plant parts were observed in fly ash‐treated pots. Fresh fly ash at 10% (w/w) application rate increased the soil salinity above admissible range and retarded the crop growth and yield. Carbonated fly ash continued to enhance the crop production of sweet corn and snow pea up to 10% (w/w) mixing rate. Carbonation has improved the fly ash from its original state to make it a safer soil amendment at higher dosages such as 10% (w/w).

Responses of heavy metals mobility and resistant bacteria to adding time of activated carbon during chicken manure composting

Unburned carbon in the circulating fluidised bed boiler fly ash The paper describes the results of various actions and industrial tests conducted in order to decrease the content of unburned carbon in the fly ash of a circulating fluidised bed combustor (CFBC). Several attempts to improve the situation were made and the effects of several parameters on the unburned carbon content in the fly ash were investigated (e.g. bed temperature, cyclone separation efficiency, fuel particle size distribution, boiler hydrodynamics, grid design, and fuel data). Unfortunately, no satisfactory solution to these problems was found. Probably, apart from attrition and char fragmentation, additional factors also contributed to the formation of unburned carbon in the CFBC fly ash.

Size distribution of unburned carbon in coal fly ash and its implications

The pollution of heavy metals (HMs) in agricultural soils profoundly threatens national food safety, and the mobility and environmental behaviors of HMs are closely implicated in crop safety. Here, we assessed the pollution level and mobility of ten HMs and explored their environmental behaviors in the soils of three different land uses from a main crop production zone in eastern China. The concentrations of HMs in the soils were higher in the farmland than the woodland and wasteland, and Cd showed a relatively higher pollution and ecological risk levels compared to other metals. Cadmium was dominated by the reducible (41%) and exchangeable (23%) fractions, and the rest of HMs were mainly in the residual fraction (> 60%). The significant correlation between the exchangeable and DGT-labile Cd indicates relatively higher mobility of Cd in the soils. Soil pH, organic matters and mineral elements had significant correlation with the exchangeable and reducible fractions of most of the HMs (e.g., Cd, Co, Mn, Ni, Pb and V; p < 0.05), indicating their good predictors of the HMs mobility. However, this was not the case for the DGT-labile fraction, which suggests a marked difference in the controlling mechanisms of the mobility versus potential bioavailability of HMs in the soils. The results of this study indicate that both the chemically extracted fractions and the bioavailable fractions of HMs need be considered when effectively assessing the safety of agricultural soils.

To achieve significant reductions in NOx emissions and to eliminate strongly asymmetric combustion found in down-fired boilers, a deep-air-staging combustion technology was trialed in a down-fired 600 MWe supercritical utility boiler. By performing industrial-sized measurements taken of gas temperatures and species concentrations in the near wing-wall region, carbon in fly ash and NOx emissions at various settings, effects of overfire air (OFA) and staged-air damper openings on combustion characteristics, and NOx emissions within the furnace were experimentally determined. With increasing the OFA damper opening, both fluctuations in NOx emissions and carbon in fly ash were initially slightly over OFA damper openings of 0-40% but then lengthened dramatically in openings of 40-70% (i.e., NOx emissions reduced sharply accompanied by an apparent increase in carbon in fly ash). Decreasing the staged-air declination angle clearly increased the combustible loss but slightly influenced NOx emissions. In comparison with OFA, the staged-air influence on combustion and NOx emissions was clearly weaker. Only at a high OFA damper opening of 50%, the staged-air effect was relatively clear, i.e., enlarging the staged-air damper opening decreased carbon in fly ash and slightly raised NOx emissions. By sharply opening the OFA damper to deepen the air-staging conditions, although NOx emissions could finally reduce to 503 mg/m(3) at 6% O2 (i.e., an ultralow NOx level for down-fired furnaces), carbon in fly ash jumped sharply to 15.10%. For economical and environment-friendly boiler operations, an optimal damper opening combination (i.e., 60%, 50%, and 50% for secondary air, staged-air, and OFA damper openings, respectively) was recommended for the furnace, at which carbon in fly ash and NOx emissions attained levels of about 10% and 850 mg/m(3) at 6% O2, respectively.

Synthesis of high quality zeolites from coal fly ash: Mobility of hazardous elements and environmental applications

Coal-derived unburned carbons in fly ash: A review

This paper presents an alternate calibration method for measurement of the unburned carbon (UC) in fly ash using laser-induced breakdown spectroscopy (LIBS). Fly ashes studied in this research were produced from pulverized coal in a muffle furnace and the UC was determined by a loss-on-ignition (LOI) test. We apply both univariate calibration and multivariate calibration methods to LIBS data to establish the calibration curve of the UC in measured samples, and the performance of these two approaches was compared. Our analysis shows that traditionally used univariate calibration in LIBS does not qualify quantitative analysis of fly ashes from different kinds of coal due to the presence of matrix effects. Instead, multivariate calibration has a better performance as the matrix effects can be taken into account with the influence of the spectroscopic signals of other components in fly ash. The correlation coefficients R2 of multivariate calibration reach 0.994 (fly ashes from one kind of coal) and 0.981 (fly ashes from different kinds of coal), which is significantly improved compared with univariate calibration.