Masami Furuuchi

A Mechanistic Model for Mercury Capture with In Situ–Generated Titania Particles: Role of Water Vapor

Abstract A mechanistic model to predict the capture of gas-phase mercury (Hg) species using in situ-generated titania nanosize particles activated by UV irradiation is developed. The model is an extension of a recently reported model for photochemical reactions by Almquist and Biswas that accounts for the rates of electron-hole pair generation, the adsorption of the compound to be oxidized, and the adsorption of water vapor. The role of water vapor in the removal efficiency of Hg was investigated to evaluate the rates of Hg oxidation at different water vapor concentrations. As the water vapor concentration is increased, more hydroxy radical species are generated on the surface of the titania particle, increasing the number of active sites for the photooxidation and capture of Hg. At very high water vapor concentrations, competitive adsorption is expected to be important and reduce the number of sites available for photooxidation of Hg. The predictions of the developed phenomenological model agreed well with the measured Hg oxidation rates in this study and with the data on oxidation of organic compounds reported in the literature.

Chemical characteristics of size-resolved aerosols in winter in Beijing

Size-resolved aerosols were continuously collected by a Nano Sampler for 13 days at an urban site in Beijing during winter 2012 to measure the chemical composition of ambient aerosol particles. Data collected by the Nano Sampler and an ACSM (Aerodyne Aerosol Chemical Speciation Monitor) were compared. Between the data sets, similar trends and strong correlations were observed, demonstrating the validity of the Nano Sampler. PM₁₀ and PM₂.₅ concentrations during the measurement were 150.5 ± 96.0 μg/m³ (mean ± standard variation) and 106.9 ± 71.6 μg/m³, respectively. The PM₂.₅/PM₁₀ ratio was 0.70 ± 0.10, indicating that PM₂.₅ dominated PM₁₀. The aerosol size distributions showed that three size bins of 0.5-1, 1-2.5 and 2.5-10 μm contributed 21.8%, 23.3% and 26.0% to the total mass concentration (TMC), respectively. OM (organic matter) and SIA (secondary ionic aerosol, mainly SO₄(2-), NO₃(-) and NH₄(+)) were major components of PM₂.₅. Secondary compounds (SIA and secondary organic carbon) accounted for half of TMC (about 49.8%) in PM₂.₅, and suggested that secondary aerosols significantly contributed to the serious particulate matter pollution observed in winter. Coal burning, biomass combustion, vehicle emissions and SIA were found to be the main sources of PM₂.₅. Mass concentrations of water-soluble ions and undetected materials, as well as their fractions in TMC, strikingly increased with deteriorating particle pollution conditions, while OM and EC (elemental carbon) exhibited different variations, with mass concentrations slightly increasing but fractions in TMC decreasing.

Characteristics of nanoparticles emitted from burning of biomass fuels.

The characteristics of the particles of the smoke that is emitted from the burning of biomass fuels were experimentally investigated using a laboratory-scale tube furnace and different types of biomass fuels: rubber wood, whole wood pellets and rice husks. Emitted amounts of particles, particle-bound polycyclic aromatic hydrocarbons (PAHs) and water-soluble organic carbon (WSOC) are discussed relative to the size of the emitted particles, ranging to as small as nano-size (<70nm), and to the rate of heating rate during combustion. differential thermal analysis (DTA) and thermogravimetric analysis (TG) techniques were used to examine the effect of heating rate and biomass type on combustion behaviors relative to the characteristics of particle emissions. In the present study, more than 30% of the smoke particles from the burning of biomass fuel had a mass that fell within a range of <100nm. Particles smaller than 0.43μm contributed greatly to the total levels of toxic PAHs and WSOC. The properties of these particles were influenced by the fuel component, the combustion conditions, and the particle size. Although TG-DTA results indicated that the heating rate in a range of 10-20°C did not show a significant effect on the combustion properties, there was a slight increase in the decomposition temperature as heating rate was increased. The nano-size particles had the smallest fraction of particle mass and particle-bound PAHs, but nonetheless these particles registered the largest fraction of particle-bound WSOC.

Emissions of particulate matter and associated polycyclic aromatic hydrocarbons from agricultural diesel engine fueled with degummed, deacidified mixed crude palm oil blends.

Mixed crude palm oil (MCPO), the mixture of palm fiber oil and palm kernel oil, has become of great interest as a renewable energy source. It can be easily extracted from whole dried palm fruits. In the present work, the degummed, deacidified MCPO was blended in petroleum diesel at portions of 30% and 40% by volume and then tested in agricultural diesel engines for long-term usage. The particulates from the exhaust of the engines were collected every 500 hr using a four-stage cascade air sampler. The 50% cut-off aerodynamic diameters for the first three stages were 10, 2.5 and 1 microm, while the last stage collected all particles smaller than 1 microm. Sixteen particle bounded polycyclic aromatic hydrocarbons (PAHs) were analyzed using a high performance liquid chromatography. The results indicated that the size distribution of particulate matter was in the accumulation mode and the pattern of total PAHs associated with fine-particles (< 1 microm) showed a dominance of larger molecular weight PAHs (4-6 aromatic rings), especially pyrene. The mass median diameter, PM and total PAH concentrations decreased when increasing the palm oil content, but increased when the running hours of the engine were increased. In addition, Commercial petroleum diesel (PB0) gave the highest value of carcinogenic potency equivalent (BaP(eq)) for all particle size ranges. As the palm oil was increased, the BaP(eq) decreased gradually. Therefore the degummed-deacidified MCPO blends are recommended for diesel substitute.

Observation of dust release behavior from ceramic filter elements

The dust-releasing behavior from a ceramic candle filter, which is a key technology of the hot gas cleaning system in advanced coal power generation processes such as pressurized fluidized bed combustion and integrated gasification combined cycle, is discussed based on the observation of the dust-releasing process using a high-speed video camera and the measurement of time change of pressure inside the filter. Time changes of dust-released area and geometrical characteristics and motion of released dust cake fragments were investigated by analyzing photo images from the video camera, compared with the time change and distribution of pressure inside the filter. In order to discuss the influence of porosity of the dust layer, a consolidated dust layer was prepared by clean air filtration at an elevated filtration velocity after the dust filtration. The dust-releasing process was found to be a multi-mode process, i.e. release occurred in a short time after the injection of cleaning air, followed by one or two intermittent releases afterwards. The amount of dust released by the first strike increased with tank pressure. The dust-releasing behavior was sensitive to the cake porosity: the mean size and perimeter of cake fragments increased with porosity and tank pressure for the consolidated dust layer. The initial radial velocity of cake fragment released just after the first strike increased with tank pressure and was almost independent of the filter location.

Evaporation behavior of volatile particles on fibrous filter flushed with particle-free dry air

Abstract Evaporation behavior of volatile particulate nitrates collected on a fibrous filter, challenged with particle-free air, is investigated experimentally and theoretically. Measured evaporation rates are compared with the results of a numerical model, which determines the total evaporation rate by integrating that for a single particle, taking into account the change with time of particle size and vapor saturation distributions inside the filter. The numerical model compares well with experimental results. In particular, it describes better the last period of evaporation than the existing model based on film evaporation. The measured evaporation rates in a region where the evaporation from individual particles becomes predominant decrease as the initial particle loading increases, probably because of an increasing influence of interaction between particles and fibers with increasing particle load.

Simulating the transformation of heavy metals during coal or sewage sludge combustion

A mathematical model (FPM) is presented to predict the transformation of heavy metals in the downstream of combustor or incinerator. The model accounts for the transformation of heavy metals through the combined effect of condensation,_nucleation, coagulation, external force and thermophoresis force. The calculation of heavy metals is embodied in the post-processor appended to Fluent soft. Before the simulation, velocity, temperature, PbCl2 concentration and other initial parameters are obtained by experiment. In addition, the transformation of PbCl2 is also experimentally studied. The comparison of experimental and predicted results indicate that the fine particle model (FPM) is valid for predicting the transformation of heavy metals in the downstream of incinerator or combustor.

Influence of agricultural activities, forest fires and agro-industries on air quality in Thailand

Annual and monthly-based emission inventories in northern, central and north-eastern provinces in Thailand, where agriculture and related agro-industries are very intensive, were estimated to evaluate the contribution of agricultural activity, including crop residue burning, forest fires and related agro-industries on air quality monitored in corresponding provinces. The monthly-based emission inventories of air pollutants, or, particulate matter (PM), NOx and SO2, for various agricultural crops were estimated based on information on the level of production of typical crops: rice, corn, sugarcane, cassava, soybeans and potatoes using emission factors and other parameters related to country-specific values taking into account crop type and the local residue burning period. The estimated monthly emission inventory was compared with air monitoring data obtained at monitoring stations operated by the Pollution Control Department, Thailand (PCD) for validating the estimated emission inventory. The agro-industry that has the greatest impact on the regions being evaluated, is the sugar processing industry, which uses sugarcane as a raw material and its residue as fuel for the boiler. The backward trajectory analysis of the air mass arriving at the PCD station was calculated to confirm this influence. For the provinces being evaluated which are located in the upper northern, lower northern and northeast in Thailand, agricultural activities and forest fires were shown to be closely correlated to the ambient PM concentration while their contribution to the production of gaseous pollutants is much less.

Degradation of bag-filter non-woven fabrics by nitric oxide at high temperatures

Polyphenylene sulfide (PPS) non-woven fabrics are often used at high temperatures for bag filters in incinerating plants. Even though they degrade in the presence of acid gases, there has been not much information on the degradation of mechanical properties of PPS in nitric oxide (NO). At 200°C, which is generally the highest operational temperature of bag filters, PPS fabrics gradually lose their elongation even if the modulus is barely unaffected. On the other hand, at 250°C, which is near its melting temperature of 285°C, the modulus increases while the elongation decreases. Contrary to our first guess, PPS does not soften near its melting temperature and becomes even more rigid. Our hypothesis then becomes that crosslinking and branching dominate around 250°C, leading to the embrittlement of PPS bag-filter materials and severe strength loss. Therefore, it is our recommendation that the operational temperature of PPS bag filters should always be below 200°C and the NO concentration should be far below 1000 p.p.m., at which point chemical degradation occurs severely.

Sediment structure of fine silica spheres in an electrolyte solution

Abstract Monodispersed fine silica spheres were sedimented in KCl solution under an electrophoretic force applied in the gravitational or antigravitational direction. Effects of particle size, particle volume fraction, electrolyte concentration and applied field intensity were experimentally investigated. A Fast Fourier Transform analysis was conducted for the sediment surface and the degree of ordering of particles was evaluated. Two different conditions were found to affect the particle ordering, one related to the kinetic energy of the settling particle and the other related to the agglomeration.