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In this work, the PM 2.5 emission characteristics, the comparison of the morphological characteristics, and the sizeclassified elemental composition of PM 2.5 are determined experimentally before and after the fabric filter at an industrial circulating fluidized-bed boiler. Measurement in situ was taken with an electrical low-pressure impactor equipped with a two-stage dilution sampling system. The morphological characteristics and size-classified elemental composition were performed by scanning electron microscopy and energy-dispersive X-ray analysis. The size distribution was measured in the range from 0.029 to 2.38 μm. Before and after the fabric filter, the number size distribution displays a bimodal distribution. The fabric filter total removal efficiency of PM 2.5 without pulse back blowing cleaning is 99.449%, and that with pulse back blowing cleaning can reach 99.029%. The minimum size-classified removal efficiencies appear in the particle size range from 0.1 to 1 μm. In this size range, the fabric filter size-classified removal efficiencies are 99.15−99.59%, and the pulse back blowing cleaning can result in the lowest value of 98.46%. The morphological characteristics before and after the fabric filter are nearly the same, except channels 3−5. Sodium, potassium, and zinc show enrichment with decreasing particle size; calcium and titanium show clear enrichment with increasing particle size; however, silicon, aluminum, magnesium, iron, and manganese show no enrichment with particle size variation.

Ash deposition on heat-exchanger surfaces in boiler systems can cause numerous problems, including slagging, fouling, and corrosion. These deleterious processes can be compounded if the boiler combustion process is changed from air to oxy-fuel. In this paper, fly ash deposition characteristics under both air and oxy-fuel combustion conditions were investigated using a bench-scale fluidized-bed combustor (FBC) based on measurements of ash deposition rates via a temperature-controlled probe. Three different combustion atmospheres were studied, and results demonstrated that, under similar combustion temperature profiles and equivalent fluidization velocities, the deposition rate increased when transitioning from combustion atmospheres consisting of 21% O 2 /79% CO 2 to air to 30% O 2 /70% CO 2 . To determine the primary factors associated with the observed variations in deposition rates, the chemical compositions and micromorphologies of ash and fly ash deposits were analyzed by inductively coupled plasma−atomic emission spectrometry (ICP−AES) and scanning electron microscopy (SEM). Particulate matter with aerodynamic diameters less than 10 μm (PM 10 ) was measured by an electrical low-pressure impactor (ELPI), and the particle size distributions (PSDs) and carbon contents of the collected filter ash were also ascertained. The results indicate that the higher deposition propensity associated with a 30% O 2 /70% CO 2 atmosphere can be largely attributed to a wider PSD rather than any changes in the chemical compositions of the fly ash or deposited ash, in which there are no obvious differences between air and oxy-fuel combustion. In addition, the slightly higher concentration of fine particles produced under this atmosphere also promotes the deposition of fly ash.

NO emission is a significant source of pollutant from coal combustion. With the establishment of industry flue gas emission standards, removal of NO has been attracting attention and research globally. In this paper, the denitration process through the use of a FeII complex solvent has been studied based on the approach of the wet desulfurization method. The kinetic parameters of the chemical reaction for NO absorption by FeII complex have also been deduced to provide theoretical consideration for the feasibility of this process. It is demonstrated that FeIIEDTA adsorbs NO efficiently under the conditions investigated, achieving the maximum NO reduction efficiency at a neutral pH value at 50 °C. The inlet O2 content in flue gas is a crucial factor affecting the performance of FeII complex, the increment in which leads to the oxidation of FeII into FeIII and hence reduces the absorption capability of the sorbent. The coexistence of SO2 and NO in flue gas decreases the NO removal efficiency by being preferentially adsorbed by the sorbent. However, with the increasing content of SO2 in flue gas, the solvent’s capability in absorbing NO is recovered to its original level.

A fixed reactor was employed to investigate the influence of SO2 absorption process on NO2 removal by Ca(OH)2 under low-temperature and humid circumstance. The step experiments and pretreatment experiments were carried out to investigate the effect of the desulfurization product CaSO3 on NO2 removal. The roles of gas components (O2, H2O) and reaction temperature in SO2 enhancing NO2 removal were discussed by comparing their influences on NO2 removal in and without the presence of SO2. It is interesting to observe that NO x removal first increases and then decreases with the increase of SO2 concentration. The presence of SO2 in the flue gas was found to restrain NO release and enhance NO2 removal. SO2 removal product CaSO3 did provide an additional reaction path for NO2 removal, but the reaction rate of NO2 and CaSO3 was lower than that of Ca(OH)2 due to the lower solubility of CaSO3. The enhancement effect of SO2 on NO2 removal can be explained by the presence of SO3 2− and HSO3 − ions derived from the hydrolysis of SO2 in the water layer. HSO3 − and SO3 2− reacted with NO2 to form sulfate, which was detected in the spent absorbent by X-ray diffraction. The higher relative humidity can accelerate the hydrolysis of SO2 and the dissolution of Ca(OH)2, which are in favor of NO2 removal. However, the oxidization of SO3 2− to SO4 2− by O2 lowers NO2 removal. Reaction temperature has negligible influence on the enhancement of NO x removal by the presence of SO2.

In this research, the emission characteristics, morphological characteristics and size-classified elemental compositions of PM 2.5 are determined experimentally before and after a fabric filter (FF) at an industrial pulverized coal boiler. Sampling and measurement of PM 2.5 in situ were taken with an ELPI with a two-stage dilution sampling system. The morphological characteristics were analyzed by scanning electron microscopy. The size-classified elemental compositions were analyzed by energy-dispersive X-ray analysis and inductively coupled plasma−atomic emission spectrometry. The number size distribution of PM 2.5 before the FF displays a unimodal distribution. The mass distribution of PM 2.5 before the FF displays a unimodal distribution with the peak near 0.1 μm, but the mass distribution of PM 2.5 after the FF shows no peak. The pulse back blowing of the FF exerts significant influence on PM 2.5 number and mass concentrations after the FF, especially on the number and mass concentrations of PM 0.007−0.029 . There appears a penetration window in nearly 0.1−1 μm; however, the removal efficiency of PM 0.007−0.029 is lowest. The pulse back blowing of the FF can reduce the removal efficiency of PM 0.007−0.029 from 99.37% to 97.80%. The microstructures of super-micrometer and sub-micrometer particles are different before and after the FF; however, the ultrafine particles in 0.007−0.029 μm are nearly the same before and after the FF. The fractional mass distributions of silicon, aluminum, iron, calcium, and magnesium vary little with variation of the particle size. Cadmium, arsenic, and selenium are enriched with the particle size decreasing.

The efficiency increases of black carbon and fly ash upon the addition of an electric field to a wet scrubber were expatiated.