Terms Of Number Concentration Research Articles

Formation and emission of fine particles from two coal-fired power plants

The generation and emission of combustion particles from two full-scale coal-fired power plants was studied by field measurements during which particles are sampled for size classification and chemical analysis simultaneously at three positions in the plants: before the electrostatic precipitator, before the desulfurisation plant, and in the stack. The following sampling techniques are used: scanning mobility particle sizer, low pressure cascade impactor, dichotomous PM 2.5 sampler, and total particle filter. The so-called multi-platform method used in this work proves useful for gaining insight into the many particle-affecting processes in a power plant. In the boiler the size of particles extends over four decades, from approximately 20 nm to 200 µm, with the largest mass contained in particles in the size range 10-100 µm. Approximately 99.9% of the particles are removed in the electrostatic precipitator and the desulfurization scrubber. The mass fraction of submicron particles, i.e., PM 1 , increases from ∼0.3% at the exit of the boiler, just before the electrostatic precipitator, to ∼30% in the aerosol emitted via the stack. In the stack aerosol 50-80% of the particles are in the PM 2.5 range. The emitted particles primarily stem from the coal ash with a minor contribution of particles of entrained, dried-out droplets of scrubber slurry. The large emitted particles are compact, almost-spherical single particles originating from the ash mineral inclusions in the coal. The small ones, corresponding in mass approximately to the PM 0.45 fraction--in terms of number concentration by far the dominant fraction--are dendritic clusters, each consisting of several partly fused, even smaller particles. The cluster particles are generated in the burner by volatilization of Si, Al, Ca, and Fe under reducing conditions. Several other ash-contained elements, e.g., P, Ba, Co, Cu, Mn, Ni, Pb, V, and Zn, are partly vaporized in the boiler and enrich the small particles when they condense during cooling of the flue gas. Due to the higher penetration of the small particles through the filter and scrubber, these elements tend to have an enhanced concentration in the emitted particles.

Application of Dispersion Modelling for Analysis of Particle Pollution Sources in a Street Canyon

The dominating source of particles in urban air is road traffic. In terms of number concentration, its main contribution is within the range of ultrafine particles (Dp < 100 nm). The dispersion conditions, i.e. transport and dilution, of the submicrometer particles are expected to be like for gases and therefore the particle concentrations in a street canyon can be calculated using gaseous pollutants dispersion models. Such processes, like coagulation or condensation, are less important due to the short residence time within the street canyon environment.Two extensive measuring campaigns were conducted in the street Jagtvej in Copenhagen, Denmark. The particle size distributions were measured by a Differential Mobility Analyser (DMA) coupled to a particle counter, providing high time resolution data (1/2 hourly) on a continuous basis. Measurements of NOx, CO and meteorological parameters were also available. The measured particle number concentrations, especially below 100 nm, reveal very similar dependence on the meteorological conditions as the NOx concentrations. This underpins the conclusion that dilution properties are similar for particles and NOx. For particle sizes over 100 nm, somewhat different behaviour is observed. This points toward existence of additional particle sources, not related to traffic emissions within the street canyon. A significant contribution is believed here to be attributed to long-range transport. The total particle emission from traffic, including daily variation and size distribution, has been calculated using the OSPM dispersion model. Results are in accordance with a previous analysis based on statistical modelling.

Particulate Formation from the Spray Combustion of Heavy Oil and Biofuel

The Biomass represents an alternative and a relevant solution for using less fossil energy while preserving the environment. Therefore, the performance of the rapeseed oil as a fuel has been investigated in a 100kW pre-pilot plant and the results have been compared with those obtained with light and heavy petroleum fuel oils. In particular, carbonaceous particles and PAH formation along the three spray flame axes have been studied by optical (Laser Light Scattering) and gas-solid sampling techniques. Additional measurements of the local value of the extinction coefficient compared to the scattering information made it possible to distinguish between soot particles and cenospheres. The kinetics of formation and burnout of the particulate matter identified in terms of number concentration of soot particles and cenospheres, have been evaluated. Moreover the results have shown that the rapeseed oil flame is less polluting than fossil oil flames.