Gas Chromatographic Analysis of Incinerator Effluents

Comparative gas cleaning performance of a pilot-scale venturi scrubber with throat dimensions of 6 in. wide × 1 2 in. long × 1 2 in. deep was obtained for the following three methods of water injection: a system of spray nozzles located along each short side of the throat (Figure 2a); a continuous slot located immediately above the nozzles, along each short side of the throat (Figure 2b); and a weir located 2 ft above the spray nozzles along long side of the throat (Figure 2c). For each method of water injection the gas cleaning performance, as a function of the pressure drop, was measured by two tests: absorption of SO₂ and collection efficiency for particles of methylene blue of controlled size.     

Liquid Entrainment from a Mobile Bed Scrubber

Liquid entrainment rate and drop size distribution were measured in the exhaust gas stream from a mobile bed scrubber. The pilot plant scrubber was 46 cm (18 in.) square and was packed with 3.8 cm (1.5 In.) diameter hollow polyethylene spheres to a static depth of 25 cm (10 in.). Entrainment flow rate depends on both gas and liquid rates. At a liquid/gas ratio of 6.7 l/m³ (50 gal/Mcf) and a superficial gas velocity of 2.6 m/sec (8.5 ft/sec) the entrainment flow rate was 0.0064 l/m³ (0.05 gal/Mcf) and at 3.75 m/sec (12.3 ft/sec) it was 0.031 l/m³ (0.23 gal/Mcf). The mass median drop diameter was about 400 nm at a liquid/gas ratio of 6.7 l/m³. The drop size distribution appears to be bimodal. Dye impregnated paper and cascade impactor techniques were used to measure drop size.     

Note On The Collection of Lint Fly by Wet Impingement

A combined water scrubber-impinger was used to control lint cleaner effluent from machine-stripped short staple (11/16-13/16 in.) cotton because of its high efficiency and low pressure drop. The 8 × 4 × 4 ft rectangular scrubber could handle a maximum of 8000 CFM entering air at 80°F, 20% relative humidity and 0.7 g particulates/m³ with a 1-sec residence time at a maximum pressure drop of 0.5 in. of water across the chamber. Water to the chamber’s 6 doublespray and 2 single-spray nozzle taps was supplied from recycle and makeup sources at pressures of 7.5–30 psig with total flows of 21.8–31.1 gpm depending on number of nozzle taps in use. These sprays effectively wetted the particulate- laden air and provided enough water to wash the collected particulate matter down the chamber walls. The four WR-10 nozzles used at the base of the scrubbing chamber provided fine conical spray patterns co-current with the air flow. The two sets of four F-20 nozzles used in the center portion of the chamber provided coarse flat sheet sprays perpendicular to the air flow path. Two large TR-50 nozzles at the top of the chamber provided the necessary coarse conical sprays to wash the collected particulates down the chamber wall to the trash-water separator below. Water flows through the nozzles were determined from pressure readings at each tap. Chamber pressure drop was determined by 15° inclined manometer readings taken across the chamber at the locations where the air inlet and outlet mean square velocities occurred.     

Fine Particle Collection Efficiency Related to Pressure Drop,Scrubbant and Particle Properties,and Contact Mechanism

Collection efficiencies are shown for control of fine particles in venturi scrubbers (1) as a function of pressure drop, and (2) as a function of throat area and liquid to gas ratio. A relationship of pressure drop to throat area, gas density, throat velocity, and liquid to gas ratio is given and is used to provide a method for estimating efficiency knowing only these scrubber design parameters. The effect of charged particles and of surface active agents on collection efficiency are discussed briefly.     

Moving Bed Adsorption System for Control of VOCs from an Aircraft Painting Facility

An activated carbon moving bed system (10 to 100 acf m air flow) was tested for controlling VOC emissions from a commercial aircraft painting facility. The cross-flow moving adsorbent bed showed a VOC collection efficiency in the 77.1 to 99.6 percent range over a superficial gas velocity range of 27 to 185 ft/min (0.14-0.94 m/sec). The collection efficiencies were neither affected by a change in carbon flow rates from 5 to 8 Ib/hr (2.3 to 3.6 kg/hr) nor by a change in the gas superficial velocity from 27 to 185 ft/min. The VOC concentration in the emission stream from the painting hangar was found to vary by at least a factor of 20 (from 0.18 to 15 ppm) both over the five month period (during which the 15 system tests of about three hours each were conducted) and within a single eight hour work shift.     

Dynamics of sulfur dioxide absorption in a raindrop falling at terminal velocity

Sulfur dioxide absorption dynamics in a raindrop are studied numerically by means of a fully numerical simulation method (FNSM) in which a composite orthogonal grid system consisting of both gas- and liquid-phase is adopted. When a raindrop with fixed radius falls in association with terminal velocity, a recirculation bubble always accompanies the gas-phase flow field in the aft region of the drop. With regard to the drop internal flow structure it has a drastic variation with drop size. When the drop radius is small (e.g. r_s=200 μm), only a single vortex motion is seen inside the drop. Under such a situation, sulfur dioxide absorbed from the interface is mainly transported from the area in front of the aft stagnation point. In contrast, as the drop is relatively large, say, r_s=500 μm, it is of interest to find that a double-vortex motion, composed of a primary and a secondary vortexes, is clearly observed. As a result, the onset of SO₂ transport process occurs at the drop’s surface near where the two vortexes meet. By defining a drop mass transport number, it indicates that the mass transported via internal circulation is always much faster than that by mass diffusion and the latter is highly relevant to the drop radius. Accordingly, the SO₂ transport dynamics in a raindrop is essentially determined by drop size.     

A Wind Tunnel Study of Gaseous Pollutants in City Street Canyons

Steady state mean concentrations of tracer gas were measured in a 400:1 scale model of an idealized city with variable geometry placed within a wind tunnel at various orientations to the mean flow for a free stream velocity of 6.8 ft/sec. The tracer gas was released from two parallel line sources to simulate lanes of traffic in an effort to quantify the persistence of pollution as well as the mean values realized at street levels. An aerodynamically rough turbulent boundary layer of neutral thermal stratification was employed to simulate the atmosphere. Values of concentration measured in the model city were converted to prototype concentrations in ppm and compared to National Ambient Air Quality Standards. It was shown that single isolated structures may cause favorable mixing of pollution downwind but very high concentrations exist in the immediate leeward vicinity of the building. Two favorable geometries for city blocks tested were found to reduce pedestrian exposure to pollution both near heavy traffic congestion and downwind. It was concluded that the pollutant dilution was controlled by the mean flow rather than by turbulent diffusion and that the lateral spread of the plume was slight as one proceeded downwind of the line source. The combination of favorable geometry and higher dilution velocities may bring pollution levels down to existing Air Quality Standards. The body of information presented in this paper should interest city planners and air quality monitoring personnel, as well as those researchers attempting to study and model flow in city street canyons. It provides order of magnitude estimates on pedestrian and office worker exposure to pollutants under a wide range of conditions.     

Prediction of pressure drop in an orifice scrubber based on a Lagrangian approach

A mathematical model has been developed to predict pressure drop in an orifice scrubber. This model is based on a Lagrangian approach for droplet movement and a particle-source-in-cell (PSI-CELL) model for calculating droplet concentration distribution. The k-epsilon turbulent model including body force due to the drag force between fluid and droplets was used to evaluate the fluid velocity distribution. The effect of orifice size on pressure drop and the correlations for mean droplet diameter have been studied. The results from the model have been compared with experimental data. This comparison shows excellent agreement between the calculated results and the experimental data.     

Electrofluidized Beds in the Filtration Of a Submicron Aerosol

A plug-flow model is developed showing the way in which efficiency depends on unfluidized bed height, bed particle size, participate mobility, gas flow rate and applied electric field intensity. This model is successfully correlated with tests in which flow rate, bed particle size, and unfluidized bed height are varied. It is shown that efficiencies better than 90% can be achieved in collecting 0.4 µm DOP with a gas residence time less than 50 msec and a pressure drop of about 10 cm of water.     

CFD modelling of electrohydrodynamic gas flow in an electrostatic precipitator

Modelling of the flow velocity fields for electrohydrodynamic flow in a wire-to-plate type electrostatic precipitator was achieved. From calculations for the flow employing different flow models, the Chen-Kim k − ε turbulent model appeared to be the most appropriate choice to obtain a quantitative image of the resulting mean flow field and downstream wake flow of the rear wire, although this was obtained from a qualitative analysis owing to the lack of experimental verification. The flow velocity field pattern showed a strong electrohydrodynamic secondary flow, which was clearly visible in the downstream regions of the corona wire despite the low Reynolds number for the electrode (Re_CW = 12.4). Secondary flow vortices were also caused by the electrohydrodynamic with increases in the discharge current. Pressure drop increased gradually according to the increase of the electrohydrodynamic number.     

Viable Microorganisms in an Urban Atmosphere

The microbial population (types and numbers) of a vertical profile of air in an industrial area of the Twin Cities was determined between May and November 1967. No consistent relationships could be shown to exist between the microbial contamination and the meteorological parameters concurrently measured. The mean viable counts ranged from 58/ft³ at grade level to 22/ft³ at 500 ft. Regardless of altitude, molds constituted approximately 70% of the total airborne microflora, bacteria between 19 and 26%, and yeasts and actinomycetes the remainder. The particle size with which the viable population was associated showed a consistent peak in the 3 – 5 μ range.     

Collection of Aerosol Particles by Electrostatic Droplet Spray Scrubbers

Theoretical calculations and experimental measurements show that the collection of small aerosol particles (0.05 to 5 micron diameter range) by water droplets in spray scrubbers can be substantially increased by electrostatically charging the droplets and particles to opposite polarity. Measurements with a 140 acfm two chamber spray scrubber (7 seconds gas residence time) showed an increase in the overall particle collection efficiency from 68.8% tit uncharged conditions to 93.6% at charged conditions, with a dioctyl phthalate aerosol (1.05 μm particle mass mean diameter and 2.59 geometric standard deviation). The collection efficiency for 0.3 μm particles increased from 35 to 87% when charged. During 1973–1974 a 1000 acfm pilot plant electrostatic scrubber was constructed inside a 40 ft trailer for evaluation on controlling particu-late emissions from pulp mill operations (funded by Northwest Pulp and Paper Association). Field tests performed on the particle emissions exhausting from SO₂ absorption towers treating the gases from a magnesium based sulfite recovery boiler have shown particle collection efficiencies ranging from about 60 to 99% by weight, depending on the electrostatic scrubber operating conditions. Energy requirements for the University of Washington electrostatic scrubber are about 0.5 hp/1000 acfm (350 Watts/1000 acfm) including gas pressure drop, water pressure drop, and electrostatic charging of the water spray droplets and the particles.     

Reducing Pressure Drop in a Baghouse Using Flow Distributors

ABSTRACT

The pressure drop of ladder vanes in a baghouse could be reduced by decreasing the vane number and adjusting the inclined angle of the vane. Two types of flow distributors were utilized to test pressure drop caused by the structure of a baghouse. The pressure drops were measured by an inclined manometer under various filtration velocities. The purpose of this study is to understand the improvement effect of pressure drop saving for the traditional ladder vanes.

Experimental results showed that the pressure drop of the Vane 3-1 configuration (flow distributor with three vanes perpendicular to the inlet flow) was higher than that of the Empty configuration (without flow distributors). The Vane 3-1 configuration could not reduce the pressure drop because of the barrier effect. By reducing the number and adjusting the angle of the vanes, the barrier effect was decreased, and the pressure drop of the Vane 2-1 configuration was much lower than that of the Vane 3-1 configuration. The largest difference in pressure drop between Vane 2-1 and Vane 3-1 was 1.702 cm w.g. at a filtration velocity of 4.17 cm/sec and, in terms of percentage, is 18.52% corresponding to a filtration velocity of 2.25 cm/sec. The improvement effect on the pressure drop saving for Vane 3-1 was significant.     

Atomization and Cloud Behavior In Venturi Scrubbing

The exact collection mechanism of a venturi scrubber has been unknown up to this time. Photographic stop-action techniques and glass venturi scrubbers have made it possible to establish where and how particles are captured and to speculate on possible gas removal possibilities. This report extends the knowledge of pneumatic atomization which is used in gas scrubbing and many other applications by providing further information on cloud-type atomization. Cloud-type atomization which is produced by pneumatic atomization of liquid streams (not drops) results in the formation of liquid droplets which appear to be less than 10 microns in diameter. These droplets coalesce and form clouds which move as single entities. Effective overall cloud diameters are determined to be a function of the velocity of the atomizing gas stream. The effective cloud diameters start at 170 [a and increase as throat gas velocities increase from 150 ft/sec. Throat velocities and liquid inlet nozzle diameters necessary to obtain water clouds of specific effective diameters can be estimated.

These large clouds are efficient impaction targets and stop most of the particulate matter within 0.5 cm from the throat scrubbing liquid inlets. High gas absorption is expected for the clouds of droplets because turbulent gas movement can exist inside and outside the clouds and the 10 μ droplets provide exceptional surface area.     

Reducing pressure drop in a baghouse using flow distributors.

The pressure drop of ladder vanes in a baghouse could be reduced by decreasing the vane number and adjusting the inclined angle of the vane. Two types of flow distributors were utilized to test pressure drop caused by the structure of a baghouse. The pressure drops were measured by an inclined manometer under various filtration velocities. The purpose of this study is to understand the improvement effect of pressure drop saving for the traditional ladder vanes. Experimental results showed that the pressure drop of the Vane 3-1 configuration (flow distributor with three vanes perpendicular to the inlet flow) was higher than that of the Empty configuration (without flow distributors). The Vane 3-1 configuration could not reduce the pressure drop because of the barrier effect. By reducing the number and adjusting the angle of the vanes, the barrier effect was decreased, and the pressure drop of the Vane 2-1 configuration was much lower than that of the Vane 3-1 configuration. The largest difference in pressure drop between Vane 2-1 and Vane 3-1 was 1.702 cm w.g. at a filtration velocity of 4.17 cm/sec and, in terms of percentage, is 18.52% corresponding to a filtration velocity of 2.25 cm/sec. The improvement effect on the pressure drop saving for Vane 3-1 was significant.     

Changes in the pore network structure of Hanford sediment after reaction with caustic tank wastes

At the former nuclear weapon production site in Hanford, WA, caustic radioactive tank waste leaks into subsurface sediments and causes dissolution of quartz and aluminosilicate minerals, and precipitation of sodalite and cancrinite. This work examines changes in pore structure due to these reactions in a previously-conducted column experiment. The column was sectioned and 2D images of the pore space were generated using backscattered electron microscopy and energy dispersive X-ray spectroscopy. A pre-precipitation scenario was created by digitally removing mineral matter identified as secondary precipitates. Porosity, determined by segmenting the images to distinguish pore space from mineral matter, was up to 0.11 less after reaction. Erosion-dilation analysis was used to compute pore and throat size distributions. Images with precipitation had more small and fewer large pores. Precipitation decreased throat sizes and the abundance of large throats. These findings agree with previous findings based on 3D X-ray CMT imaging, observing decreased porosity, clogging of small throats, and little change in large throats. However, 2D imaging found an increase in small pores, mainly in intragranular regions or below the resolution of the 3D images. Also, an increase in large pores observed via 3D imaging was not observed in the 2D analysis. Changes in flow conducting throats that are the key permeability-controlling features were observed in both methods.     

A Theory of Plume Rise Compared with Field Observations

A theory for the rise of a plume in a horizontal wind is proposed in which it is assumed that, for some distance downwind of a high stack, the effects of atmospheric turbulence may be ignored in comparison with the effects of turbulence generated by the plume. The theory, an extension of the local similarity ideas used by Morton, Taylor, and Turner,¹ has two empirical parameters which measure the rate that surrounding fluid is entrained into the plume. Laboratory measurements of buoyant plume motion in laminar unstratified cross flow are used to estimate the empirical parameters. Using this determination of the parameters in the theory, the trajectories of atmospheric plumes may be predicted. To make such a prediction, the observed wind velocity and temperature as functions of altitude, and flow conditions at the stack orifice, are used in numerically integrating the equations. The resulting trajectories are compared with photographs, made by Leavitt, et al.,² of TVA, of plumes from 500 to 600 ft high stacks. Within 10 stack heights downwind of the stack, the root mean square discrepancy between the observed height of the trajectory above ground level and the theoretical value is 14%, which is about the uncertainty in the observed height. The maximum plume rise within the field of observation is within 15% of that predicted by the present theory.     

滤袋数目对翼形上进风袋式除尘器内流场影响的数值模拟研究

针对实际运行过程中,袋式除尘器滤袋使用寿命短,压力损失过大的问题,本文以翼形上进风袋式除尘器为研究对象,采用CFD(computational fluid dynamics)技术模拟分析不同滤袋数(分别为92、88、84、80、76和72)时袋式除尘器内气流分布和压力损失规律。主要考察了流量分配系数、最大流量不均幅值、气流迹线、滤袋表面速度分布与压降等指标。结果表明,滤袋数为76个时,气流分布最为均匀,各滤袋负载均衡;相同过滤速度下,装置的压降随滤袋数目的增加而上升,即压降大小顺序为9288847672;与72个滤袋相比,76个滤袋的可用过滤面积更大。综合考虑,袋式除尘器的最优滤袋数目为76个。模拟结果为袋式除尘器的设计和优化提供了依据。     

Changes in physical properties of a compost biofilter treating hydrogen sulfide

A technique is presented that can be used to estimate the changes in physical structure in a natural biofilter packing medium, such as compost, over time. The technique applies information from tracer studies, grain size distribution, and pressure drop analysis to a model that estimates the number of channels, average channel diameter, number of particles, and specific surface area of the medium. Important operational factors, such as moisture content, pressure drop, and sulfate accumulation also were evaluated both in a conventionally operated biofilter and in one operated with periodic compost mixing. In the conventionally operated laboratory-scale compost biofilter, hydrogen sulfide (H2S) removal efficiency decreased from 100% to approximately 90% over 206 days of operation. In a similar system, operated with compost mixing, the H2S removal efficiency was maintained near 100%. Variations in media moisture conditions and specific surface area can explain the results observed in this study. Under conventional operation, drying near the inlet disintegrated the compost particles, producing a large number of particles and flow channels and increasing the specific surface area. At the top of the column, where moisture was added, particle size increased and specific surface area decreased. In the column with media mixing, moisture content, particle size, and specific surface area remained homogeneous.