Particulate functions

Particulate Functions. Table IV sunmarizes the regression results from exploring linear relationships between dust and trash levels in cotton. Exponential and power relationships were considered but the fits were found inferior to the linear case. The unexplained variation ranging from 1% to 9% suggest that a model leading to Equation 7 and 9 may indeed be an appropriate choice. 

The main justification for diesel fuel desulfurization is related to particulate emissions which are subject to very strict rules. Part of the sulfur is transformed first into SO3, then into hydrated sulfuric acid on the filter designed to collect the particulates. Figure 5.21 gives an estimate of the variation of the particulate weights as a function of sulfur content of diesel fuel for heavy vehicles. The effect is greater when the test cycle contains more high temperature operating phases which favor the transformation of SO2 to SO3. This is particularly noticeable in the standard cycle used in Europe (ECE R49). 

Influence of the sulfur content in diesel fuel on particulate emissions as a, function of the catalytic converter inlet temperature. 

If we think in terms of the particulate nature of light (wave-particle duality), the number of particles of light or other electi omagnetic radiation (photons) in a unit of frequency space constitutes a number density. The blackbody radiation curve in Fig. 1-1, a plot of radiation energy density p on the vertical axis as a function of frequency v on the horizontal axis, is essentially a plot of the number densities of light particles in small intervals of frequency space. 

Formation of Airborne Emissions. Airborne emissions are formed from combustion of waste fuels as a function of certain physical and chemical reactions and mechanisms. In grate-fired systems, particulate emissions result from particles being swept through the furnace and boiler in the gaseous combustion products, and from incomplete oxidation of the soHd particles, with consequent char carryover. If pile burning is used, eg, the mass bum units employed for unprocessed MSW, typically only 20—25% of the unbumed soHds and inerts exit the combustion system as flyash. If spreader-stoker technologies are employed, between 75 and 90% of the unbumed soHds and inerts may exit the combustion system in the form of flyash. 

The purity of oxygen from chlorate candles before and after gas filtration is indicated in Table 2. A particulate filter is always used. Filter chemicals are HopcaUte, which oxidizes CO to CO2 molecular sieves (qv), which remove chlorine compounds and basic materials, eg, soda lime, which removes CO2 and chlorine compounds. Other than H2O and N2, impurity levels of <1 ppm can be attained. Moisture can be reduced by using a desiccant (see Desiccants). Gas purity is a function of candle packaging as well as composition. A hotter burning unit, eg, one in which steel wool is the binder, generates more impurities. 

In some cases, a single chemical substance can serve both as a dye and as a pigment. For example, indanthrone [81-77-6] (Pigment Blue 60) functions as a blue pigment or as a dye. As a pigment, indanthrone is a particulate, insoluble soHd dispersed directly into a vehicle, whereas as a dye it is reduced to a base-soluble hydtoquinone derivative and then reoxidized onto a soHd substrate. 

Release agents function by either lessening intermolecular interactions between the two surfaces in contact or preventing such close contact. Thus, they can be low surface-tension materials based on aUphatic hydrocarbon, fluorocarbon groups, or particulate soHds. The principal categories of material used are waxes, fatty acid metal soaps, other long-chain alkyl derivatives, polymers, and fluorinated compounds. 

Aerosol Dynamics. Inclusion of a description of aerosol dynamics within air quaUty models is of primary importance because of the health effects associated with fine particles in the atmosphere, visibiUty deterioration, and the acid deposition problem. Aerosol dynamics differ markedly from gaseous pollutant dynamics in that particles come in a continuous distribution of sizes and can coagulate, evaporate, grow in size by condensation, be formed by nucleation, or be deposited by sedimentation. Furthermore, the species mass concentration alone does not fliUy characterize the aerosol. The particle size distribution, which changes as a function of time, and size-dependent composition determine the fate of particulate air pollutants and their... 

Moments of a distribution often provide information that can be used to characterize particulate matter. Theyth moment of the population density function n is defined as... 

The complete characterization of a particulate material requires development of a functional relationship between crystal size and population or mass. The functional relationship may assume an analytical form (7), but more frequentiy it is necessary to work with data that do not fit such expressions. As such detail may be cumbersome or unavailable for a crystalline product, the material may be more simply (and less completely) described in terms of a single crystal size and a spread of the distribution about that specified dimension. 

Particulate Fluidization Fluid beds of Geldart class A powders that are operated at gas velocities above the minimum fluidizing velocity (L/, y) but belowthe minimum bubbhngvelocity (L/, i) are said to be particulately fluidized. As the gas velocity is increased above L/, y, the bed further expands. Decreasing (p, — Py), d and/or increasing increases the spread between L/, yand U, b until at some point, usually at high pressure, the bed is fully particulately fluidized. Richardson and Zald [Trans. Inst. Chem. Eng., 32, 35 (1954)] showed that U/U = E , where /i is a function of system properties, = void fraction, U = superficial fluid velocity, and Uj = theoretical superficial velocity from the Richardson and Zald plot when = 1. 

There is a gradual transition from particulate setthug into the zone-settling regime, where the particles are constrained to settle as a mass. The principal characteristic of this zone is that the setthug rate of the mass, as observed in batch tests, will be a function of its solids concentration (for any particular condition of flocculation, particle density, etc.). 

FIG. 22-36 Efficiency of an electrofilter as a function of gas flow rate at 5 different voltages. Experimental materials l- im aerosol of dioctyl phthalate glass-fiher filter. Symbols O, no voltage applied A, 2 kV , 3.5 kV , 5 kV , 7 kV. After Fielting et ah, Dielectrophoretic Filtration of Solid and Liquid Aerosol Particulates, Prepr. 75-32.2, 68th ann. meet., AirPollut. Conttol Assoc., Boston, June 1975.)... 

These three functions involve the movement of O2, CO2, and HjO through the epidermal layers of the leaf. The analogy to human inhalation is obvious. With the diffusion of gases into and out of the leaf, pollutant gases have a direct pathway to the cellular system of the leaf structure. Direct deposition of particulate matter also occurs on the outer surfaces of the leaves. 

The major purpose of ambient particulate sampling is to obtain mass concentration and chemical composition data, preferably as a function of particle diameter. This information is valuable for a variety of problems effects on human health, identification of particulate matter sources, understanding of atmospheric haze, and particle removal processes. 

The concentration of indoor pollutants is a function of removal processes such as dilution, filtration, and destruction. Dilution is a function of the air exchange rate and the ambient air quality. Gases and particulate matter may also be removed from indoor air by deposition on surfaces. Filtration systems are part of many ventilahon systems. As air is circulated by the air-conditioning system it passes through a filter which can remove some of the particulate matter. The removal efficiency depends on particle size. In addition, some reactive gases like NOj and SOj are readily adsorbed on interior surfaces of a building or home. 

In other parts of the world, plywood adhesive fillers are obtained from local sources and may be quite different than those used in North America. In Southeast Asia, banana flour is quite important. In Europe, calcium carbonate (chalk) is often used. Nearly any fibrous material or fine particulate material capable of forming a functionally stable suspension can be made to work if the formulator is sufficiently skillful. However, the mix formulator will be very specific about the type and grade of filler to be used in a particular mix. Substitutions may lead to serious gluing problems. 

Wet scrubbers rely on a liquid spray to remove dust particles from a gas stream. They are primarily used to remove gaseous emissions, with particulate control a secondary function. The major types are venturi scrubbers, jet (fume) scrubbers, and spray towers or chambers. Venturi scrubbers consume large quantities of scrubbing liquid (such as water) and electric power and incur high pressure drops. Jet or fume scrubbers rely on the kinetic energy of the liquid stream. The typical removal efficiency of a jet or fume scrubber (for particles 10 g. or less) is lower than that of a venturi scrubber. Spray towers can handle larger gas flows with minimal pressure drop and are therefore often used as precoolers. Because wet scrubbers may contribute to corrosion, removal of water from the effluent gas of the scrubbers may be necessary. 

Health effects attributed to sulfur oxides are likely due to exposure to sulfur dioxide, sulfate aerosols, and sulfur dioxide adsorbed onto particulate matter. Alone, sulfur dioxide will dissolve in the watery fluids of the upper respiratory system and be absorbed into the bloodstream. Sulfur dioxide reacts with other substances in the atmosphere to form sulfate aerosols. Since most sulfate aerosols are part of PMj 5, they may have an important role in the health impacts associated with fine particulates. However, sulfate aerosols can be transported long distances through the atmosphere before deposition actually occurs. Average sulfate aerosol concentrations are about 40% of average fine particulate levels in regions where fuels with high sulfur content are commonly used. Sulfur dioxide adsorbed on particles can be carried deep into the pulmonary system. Therefore, reducing concentrations of particulate matter may also reduce the health impacts of sulfur dioxide. Acid aerosols affect respiratory and sensory functions. 

For filter design and performance prediction it is necessary to predict the rate of filtration (velocity or volumetric flowrate) as a function of pressure drop, and the properties of the fluid and particulate bed. This can be achieved using the modified Darcy equation developed in Chapter 3. 

Since crystallization is a particulate process, the model representing size distribution is written in terms of functions. Evans (1989) and Hounslow and... 

It is important to note tlmt tlic deposition rate is a strong function of particle dimneter tluough the term v, wliich appears twice in tlic deposition flux equation. Equation (9.7.10) must be modified to treat process gas streams discliarging particles of a given size distribution. The suggested procedure is somewhat simihu to tlial for calculating overall collection efficiencies for particulate control equipment (12). For this condition, the overall rale is given by... 

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