Michael Strand

Characteristics of aerosol particles formed during grate combustion of moist forest residue

The characteristics of aerosol particles formed during combustion of moist forest residue were studied as a function of load in a I MW moving grate boiler and at almost full load in a similar larger 6 MW boiler. The coarse (1 mum 12) were K, S and Cl in the fine mode and Ca, K and S in the coarse mode. The dominant ions in the fine mode were K+, SO42- and CO32-. The fine mode particles had hygroscopic growth factors of around 1.65 at RH=90%, with a deliquescence point at a relative humidity between 30% and 60%. It was assessed that K2CO3 is responsible for the low deliquescence point. Fine mode particles of a given dry diameter had similar chemical composition

Hygroscopic Behavior of Aerosol Particles Emitted from Biomass Fired Grate Boilers

This study focuses on the hygroscopic properties of submicrometer aerosol particles emitted from two small-scale district heating combustion plants (1 and 1.5 MW) burning two types of biomass fuels (moist forest residue and pellets). The hygroscopic particle diameter growth factor (Gf) was measured when taken from a dehydrated to a humidified state for particle diameters between 30–350 nm (dry size) using a Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA). Particles of a certain dry size all showed similar diameter growth and the Gf at RH = 90% for 110/100 nm particles was 1.68 in the 1 MW boiler, and 1.5 in the 1.5 MW boiler. These growth factors are considerably higher in comparison to other combustion aerosol particles such as diesel exhaust, and are the result of the efficient combustion and the high concentration of alkali species in the fuel. The observed water uptake could be explained using the Zdanovski-Stokes-Robinson (ZSR) mixing rule and a chemical composition of potassium salts only, taken from ion chromatography analysis of filter and impactor samples (KCl, K2SO4, and K2CO3). Agglomerated particles collapsed and became more spherical when initially exposed to a moderately high relative humidity. When diluted with hot particle-free air, the fractal-like structures remained intact until humidified in the H-TDMA. A method to estimate the fractal dimension of the agglomerated combustion aerosol and to convert the measured mobility diameter hygroscopic growth to the more useful property volume diameter growth is presented. The fractal dimension was estimated to be ∼ 2.5.

Laboratory and field test of a sampling method for characterization of combustion aerosols at high temperatures

The objective of this study was to design and experimentally examine a sampling method for high-temperature aerosols from biomass combustion, in which nucleation and condensation from fly ash forming vapors is controlled. The sampling method includes a high-temperature probe in which the hot gas is diluted and then cooled. Laboratory results from sampling a model aerosol with known concentrations of SiO2 particles and KCl vapor showed that when using a high dilution ratio, the KCl vapor was effectively separated from the aerosol by deposition onto the probe walls. When a lower dilution ratio was used, the KCl vapor generated a distinct nucleation mode when cooled in the probe. The sampling method was also used for sampling flue gas from a circulating fluidized bed boiler fired with forest residues. The results suggest that the major fractions of Ca, K, S, and Zn were present as particles at 780°C, whereas most of the Cl and Pb were present as gases. The field results are consistent with results previously reported and indicate that the method can be used for efficient and precise characterization of high-temperature combustion aerosols containing inorganic vapors.

Particle Emissions from Biomass Fired Grate Boilers

Abstract Possible mechanisms of formation of aerosols in the air by chemical reactions in the gas phase are described. In the basic reactions, formation of HCl, H 2 SO 4 and HNO 3 molecules from chlorine, sulphur dioxide and oxides of nitrogen, in the presence of water vapour, have been considered along with the role of solar radiations, ionizing radiations, electric discharges and ozone in the formation of these acids. Formation of nuclei by the hydration of acid molecules and their reaction with other organic and inorganic trace gases have also been discussed. The reactions important in the formation of Aitken nuclei and aerosols are suggested to be, mainly, oxidation, hydration, acid-base reactions and addition and recombination reactions. In these reactions, the combined role of solar and ionizing radiations has been considered. The formation of embryos and growth of particles in the humid air have been discussed on the basis of Raoults law. The important role of chemically formed particles in the atmospheric processes and the possible impact of nuclear power production on the nuclei content of the atmosphere are suggested.

Metal Oxide Nanoparticles as Novel Gate Materials for Field-Effect Gas Sensors

ABSTRACT Oxide nanoparticle layers have shown interesting behavior as gate materials for high temperature (typically at 300–400°C) metal-insulator-silicon carbide (MISiC) capacitive sensors. Distinct shifts in the depletion region of the C-V (capacitance-voltage) characteristics could be observed while switching between different oxidizing and reducing gas ambients (air, O2, H2, NH3, CO, NO x , C3H6). Shifts were also noticed in the accumulation region of the C-V curves, which can be attributed to the change in resistivity of the gate material. Sensor response patterns have been found to depend on operating temperature.

Alkali salt vapour deposition and in-line ion exchange on flat glass surfaces

This study suggests a different route for the modification of flat/float glass surfaces; i.e. exchange of ionic species originatingfrom in-line vapour deposition of salt as compared to the conventional route of immersing the glass in a molten saltbath. The aim of this work is to develop a more flexible and, eventually, more rapid process for improving the mechanicalstrength of flat glass by introducing external material into the surface. We discuss how chemical strengthening can beperformed through the application of potassium chloride on the glass surface by vapour deposition, and in-line thermallyactivated ion exchange. The method presented here has the potential to be up-scaled and to be used in in-line productionin the future, which would make it possible to produce large quantities of chemically strengthened flat glass at aconsiderably lower cost.

Reactor modelling assessment for urea-SNCR applications

Purpose – The work investigates the effects of neglecting, modeling or partly resolving turbulent fluctuations of velocity, temperature and concentrations on the predicted turbulence-chemistry interaction in urea-SNCR systems. Design/methodology/approach – Numerical predictions of the NO conversion efficiency in an industrial urea-SNCR system are compared to experimental data. Reactor models of varying complexity are assessed, ranging from one-dimensional ideal reactor models to state-of-the-art CFD simulations based on the DES approach. The models employ the same reaction mechanism, but differ in the degree to which they resolve the turbulent fluctuations of the gas phase. A methodology for handling of unknown experimental data with regard to providing adequate boundary conditions is also proposed. Findings – One-dimensional reactor models may be useful for a first quick assessment of urea-SNCR system performance. It is critical to account for heat losses, if present, due to the significant sensitivity of the overall process to temperature. The most comprehensive DES setup evaluated is associated with approximately two orders of magnitude higher computational cost than the conventional RANS-based simulations. For studies that require a large number of simulations (e.g. optimizations or handling of incomplete experimental data), the less costly approaches may be favored with a tolerable loss of accuracy. Originality/value – Novel numerical and experimental results are presented to elucidate the role of turbulent fluctuations on the performance of a complex, turbulent, reacting multiphase flow.

Characterization of Particulate Matter in Biomass Gasification

The purpose of this work is to examine the potential of monitoring heavy tar compounds contained in the product gas of a biomass gasifier. The hot product gas from atmospheric indirect bubbling flu ...

Particle characterization at high temperature in a 5 MW moving grate biomass boiler

The particles and inorganic gaseous compounds from a 5 MW moving grate biomass boiler were characterized at two sampling positions at 1100 °C and 800 °C respectivly. Samples were extracted with hig ...