Spray Charging and Trapping Scrubber for Fugitive Particle Emission Control

The control of fugitive process emissions (FPE) with Spray Charging and Trapping (SCAT) scrubber was evaluated both theoretically and experimentally. The SCAT uses air curtain and/or jets to contain, convey, and divert the FPE into a charged spray scrubber.

Experiments were performed on an 8000 cfm bench-scale spray scrubber to verify the theory and feasibility of collecting fugitive particles with charged water spray. The effects of charge levels on drops and particles, nozzle type, drop size, gas velocity, and liquid/gas ratio on collection efficiency were determined experimentally. The results of the experiments and the comparison between theory and data are presented.

An air curtain was developed for conveying the FPE to the spray scrubber, deflecting the crosswind, and containing hot buoyant plume. The design and air flow field for the air curtain are presented.     

Charged Droplet Scrubbing for Fine Particle Control

Some basic mechanisms of interaction of highly charged scrubbing droplets with fine particulate are studied. In the fine particulate size range (1.0-0.1 micron), the most effective mechanisms are electrically augmented impact scrubbing and charge exchange without impact. A charged droplet scrubber using electrohydrodynamically sprayed droplets and an applied field to achieve electrical impact scrubbing is described. It is shown that such scrubbers are capable of high densities of droplets in the 100 jum size range, and charged to near their upper stability limit. Collection efficiencies of 30 to 50% per stage are demonstrated in the submicron particulate size range.     

Specifying Venturi Scrubber Throat Length for Effective Particle Capture at Minimum Pressure Loss Penalty

A simplified equation for specifying the optimum minimum length for commercial venturi scrubber throats is presented in this paper. This theoretical correlation is derived using an optimum velocity ratio (velocity of collector droplet at end of venturi throat to velocity of gas in throat) and is a function of throat gas velocity and liquid to gas ratio. This velocity ratio establishes the minimum throat length and is based on available literature data. Predicted venturi scrubber particle collection for throats specified by this procedure compare favorably with reported commercial venturi collection efficiencies and with modeled venturi efficiencies over the practical range of venturi scrubber operation.     

Fine Paniculate Removal and S02 Absorption with a Two Stage Wet Scrubber

This paper includes results from pilot plant studies and early field demonstration units and a discussion of the application of the limestone wet scrubbing process to a low sulfur syb-butuminous coal. This latter application required the development of a hybrid two stage scrubber to enable collection of the fine particulate matter as well as removal of a significant amount of the sulfur dioxide.     

Engineering Design of Fine Particle Scrubbers

A concise, quantitative picture of the state of the art of particle scrubbing is presented in the form of performance prediction methods. A new relationship between the particle diameter collected at 50% efficiency and scrubber pressure drop for several of the most common scrubber types is a design tool of great utility. Scrubber capability for the collection of submicron particles by diffusion is described in a graph for several scrubber types.     

Fine Particle Control Using Sulfur Oxide Scrubbers

Compliance with sulfur oxides standards will in many cases result in the installation of scrubbing devices. If these devices operate on an effluent gas stream containing particulate as well as sulfur oxides, simultaneous removal would be expected. Since effective simultaneous removal of particulate matter and sulfur oxides is economically desirable, it is of considerable import to characterize scrubber designs being considered as sulfur oxide absorbers as particulate control devices; especially, for fine particulate control.

Data on the fine particle collection efficiency of sulfur oxides scrubbers at two power generating stations is presented. At the first, a venturi and a turbulent contacting absorber (TCA) both with capacities of 30,000 cfm were tested. At the second, a venturi with 600,000 scfm capacity was tested. Fine particle collection efficiency was determined at three pressure drops for the TCA using a cascade impactor. Results for the TCA show high removal efficiencies. It collected more than 90% of submicron particles when the pressure drop was nearly 10 in. H₂0. The overall particulate removal in the TCA scrubber as determined by modified method 5 or by Brink impactor was greater than 99% when the pressure drop was greater than 6 in. H₂0. For both the venturi scrubber at the Shawnee Steam Plant and that at the Mystic Power Station, the collection efficiency decreased rapidly with decreasing particle size in the fine particle region.     

PM Fine Standards and Implied Modeling/Analysis Needs

ABSTRACT

New National Ambient Air Quality Standards (NAAQS) were promulgated for fine particulate matter (FPM) in July 1997. This paper summarizes likely timing for implementing programs to meet these standards, which have a bearing on future modeling/analysis needs. The paper notes technical requirements implied by the nature of the NAAQS, as well as feedback the agency has received concerning modeling/analysis through Federal Advisory Committee Act (FACA) subcommittee work groups. Conclusions and recommendations drawn from recently completed U.S. Environmental Protection Agency (EPA)- sponsored workshops on modeling and other source attribution techniques are also described. Efforts to respond to needs implied by the NAAQS and feedback are noted by outlining major topics and issues that future guidance on use of modeling and other analyses used for attainment demonstrations will need to address. The paper concludes by highlighting several as yet unmet modeling/analysis needs to support a well-founded strategy for meeting air quality goals for FPM. These are suggested as potential areas for policy-relevant research.     

Observations and Interpretations from the Canadian Fine Particle Monitoring Program

ABSTRACT

Canadian particle monitoring programs examining PM10, PM2.5, and particle composition have been in operation for over 10 years. Until recently, the measurements were manual/filter-based with 24-hr sample collection varying in frequency from daily to every sixth day, using GrasebyAnderson dichotomous samplers. In the past few years, these monitoring activities have been expanded to include hourly measurements using tapered element oscillating microbalances (TEOMs). This continuous monitoring program started operation focusing on PM_10, but now emphasizes PM_2.5 through the addition of more TEOMs and switching of the inlets of some of the existing units. The data from all of these measurement activities show that there are broad geographical differences and also local- to regional-scale spatial differences in mass and composition of PM2.5. Due to variations in sources, significantly different PM2.5 concentrations are not uncommon within the same city. Comparison of nearby urban and rural sites indicates that 30 and 40% of the PM_2.5 is from local urban sources in Montreal and Toronto, respectively. Hourly PM_2.5 measurements in Toronto suggest that vehicular emissions are an important contributor to urban PM_2.5. There has been a decreasing trend in urban PM_2.5, with annual average concentrations between the 1987–1990 and 1993–1995 periods decreasing by 11 to 39%, depending upon the site. The largest declines were in Montreal and Halifax, and the smallest decline was in Toronto. Comparison of 24-hr TEOM and manual dichotomous sampler PM_2.5 measurements from a site in Toronto indicates that the TEOM results in lower concentrations. The magnitude of this difference is relatively small in the warmer months, averaging about 12%. During the colder months the difference averages about 23%, but can be as large as 50%.     

Application of High Gradient Magnetic Separation to Fine Particle Control

The char produced in the thermolysis of granulated scrap tyres has few market outlets, reducing the economic viability of the thermolytic process. This paper reports the potential of this char as a low-cost precursor of porous carbons. The tyre-derived char was demineralized in either alkaline or acidic media to reduce its ash, zinc, sulfur, and silica contents. The lowest impurity content was achieved with an HNO₃/H₂O treatment. The resulting demineralized char was then subjected to activation by KOH or CO₂. The Brunauer-Emmett-Teller (BET)-specific surface area of the activated carbon produced by the KOH treatment was 242 m²/g, whereas that of the CO₂-activated carbon was 720 m²/g. The textural properties of the latter product were similar to those of some commercial activated carbons. The use of tyre-derived char as a precursor of porous carbons could render the thermolytic treatment of scrap tyres more economically attractive.

Implications: Char produced in thermolysis of granulated scrap tyres has a few market outlets; in this paper an alternative for its use is presented. The char was converted into activated carbon with textural properties similar to those of some commercial activated carbons. This process could render the thermolytic treatment of scrap tyres more economically attractive.     

Fine Particle Receptor Modeling in the Atmosphere of Mexico City

Abstract

Source apportionment analyses were carried out by means of receptor modeling techniques to determine the contribution of major fine particulate matter (PM_2.5) sources found at six sites in Mexico City. Thirty-six source profiles were determined within Mexico City to establish the fingerprints of particulate matter sources. Additionally, the profiles under the same source category were averaged using cluster analysis and the fingerprints of 10 sources were included. Before application of the chemical mass balance (CMB), several tests were carried out to determine the best combination of source profiles and species used for the fitting. CMB results showed significant spatial variations in source contributions among the six sites that are influenced by local soil types and land use. On average, 24-hr PM_2.5 concentrations were dominated by mobile source emissions (45%), followed by secondary inorganic aerosols (16%) and geological material (17%). Industrial emissions representing oil combustion and incineration contributed less than 5%, and their contribution was higher at the industrial areas of Tlalnepantla (11%) and Xalostoc (8%). Other sources such as cooking, biomass burning, and oil fuel combustion were identified at lower levels. A second receptor model (principal component analysis, [PCA]) was subsequently applied to three of the monitoring sites for comparison purposes. Although differences were obtained between source contributions, results evidence the advantages of the combined use of different receptor modeling techniques for source apportionment, given the complementary nature of their results. Further research is needed in this direction to reach a better agreement between the estimated source contributions to the particulate matter mass.     

Mobile Air Quality Monitoring Systems: Present Problems and Future Needs

This overview represents much of the discussion and summarizes many of the concerns emerging from the recent APCA Specialty Conference, “In-Situ Air Quality Monitoring from Moving Platforms.”

Users of mobile air quality monitoring systems have been hampered in their attempts to generate dependable data because of a lack of suitable instrumentation. Most equipment used in mobile systems was designed for laboratory or stationary monitoring applications and cannot cope well with the harsh environment encountered in aircraft or other mobile platforms. Only through innovative modifications have investigators been able to utilize off-the-shelf equipment. The technology exists, however, for manufacturers to build a much higher quality product if only a market incentive could be created.

This paper outlines problem areas which need to be addressed in the production of reliable “mobile quality” instrumentation, and suggests some market incentives.     

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.     

Regional Transport and Urban Contributions to Fine Particle Concentrations in Southeastern Canada

Abstract

The impact of various atmospheric transport directions on ambient fine particle (PM_2.5) concentrations at several sites in southeastern Canada was estimated (for May-September) using back-trajectory analysis. Three-day back trajectories (four per day) were paired with 6-hr average PM_2.5 mass concentrations measured using tapered element oscillating microbalances (TEOM). PM_2.5 concentrations at rural locations in the region were affected by nonlocal sources originating in both Canada and the United States. Comparison of sites revealed that, on average, the local contribution to total PM_2.5 in the greater Toronto area (GTA) is approximately 30–35%. At each location, average PM_2.5 concentrations under south/southwesterly flow conditions were 2–4 times higher than under the corresponding northerly flow conditions. The chemical composition of both urban and rural PM_2.5 was determined during two separate 2-week spring/summer measurement campaigns. Components identified included SO₄ ^2?, NO₃ ^?, NH₄+, black carbon and organic carbon (OC), and trace elements. Higher particle mass at the urban Toronto site was composed of a higher proportion of all components. However, black carbon, NO₃ ^?, NaCl, and trace elements were found to be the most enriched over the rural/regional background levels.     

Fine Particle Removal Performance of a Two-Stage Wet Electrostatic Precipitator Using a Nonmetallic Pre-Charger

ABSTRACT

A novel two-stage wet electrostatic precipitator (ESP) has been developed using a carbon brush pre-charger and collection plates with a thin water film. The electrical and particle collection performance was evaluated for submicrometer particles smaller than 0.01～0.5 μm in diameter by varying the voltages applied to the pre-charger and collection plates as well as the polarity of the voltage. The collection efficiency was compared with that calculated by the theoretical models. The long-term performances of the ESP with and without water films were also compared in tests using Japanese Industrial Standards dust. The experimental results show that the carbon brush pre-charger of the two-stage wet ESP had approximately 10% particle capture, while producing ozone concentrations of less than 30 ppb. The produced amounts of ozone are significantly lower than the current limits set by international agencies. The ESP also achieved a high collection rate performance, averaging 90% for ultrafine particles, as based on the particle number concentration at an average velocity of 1 m/sec corresponding to a residence time of 0.17 sec. Higher particle collection efficiency for the ESP can be achieved by increasing the voltages applied to the pre-charger and the collection plates. The decreased collection efficiency that occurred during dust loading without water films was completely avoided by forming a thin water film on the collection plates at a water flow rate of 6.5 L/min/m2 Zukeran, A., Ikeda, Y., Ehara, Y., Matsuyama, M., Ito, T., Takahashi, T., Kawakami, H. and Takamatsu, T. 1999. Two-Stage-Type Electrostatic Precipitator Re-entrainment Phenomena under Diesel Flue Gases. IEEE. Trans. Ind. Appl, 35: 346–351. [Crossref], [Web of Science ®] , [Google Scholar].

IMPLICATIONS Current two-stage electrostatic precipitators (ESPs) have several technical problems such as a drop in collection efficiencies by small-particle re-entrainment during rapping and corrosion of metallic electrodes of the ESPs by corrosive gases. This paper evaluates a novel two-stage ESP that uses a nonmetallic pre-charger and water film collection plates to avoid the above mentioned problems of other ESPs. This ESP can be used not only for industrial applications but also for residential purposes because it has a high removal performance for fine particles with low ozone generation and maintains its efficiency due to the continuous cleaning of the collection plates with water film.     

Laboratory Evaluation of an Aldehyde Scrubber System Specifically for the Detection of Acrolein

Abstract

We demonstrate the use of an aldehyde scrubber system to resolve isobaric aldehyde/alkene interferences in a proton transfer reaction mass spectrometer (PTR-MS) by selectively removing the aldehydes from the gas mixture without loss of quantitative information for the alkene components. The aldehyde scrubber system uses a bisulfite solution, which scrubs carbonyl compounds from the gas stream by forming water-soluble carbonyl bisulfite addition products, and has been evaluated using a synthetic mixture of acrolein and isoprene. Trapping efficiencies of acrolein exceeded 97%, whereas the transmission efficiency of isoprene was better than 92%. Quantification of the PTR-MS response to acrolein was validated through an intercomparison study that included two derivatization methods, dinitrophenylhydrazine (DNPH) and O-(4-cyano-2-ethoxybenzyl)hydroxylamine (CNET), and a spectroscopic method using a quantum cascade laser infrared absorption spectroscopy (QCL) instrument. Finally, using cigarette smoke as a complex matrix, the acrolein content was assessed using the scrubber and compared with direct QCL-based detection.     

Total Human Exposure: Basic Concepts,EPA Field Studies,and Future Research Needs

Historically, environmental regulatory programs designed to protect public health have monitored pollutants only in geophysical carrier media (for example, outdoor air, streams, soil). Field studies have identified a gap between the levels observed in geophysical carrier media and the concentrations with which people actually come into contact: their daily exposures. A new approach—Total Human Exposure (THE)—has evolved to fill this gap and provide the critical data needed for accurately assessing public health risk. The THE approach considers a three-dimensional "bubble" around each person and measures the concentrations of all pollutants contacting that bubble, either through the air, food, water, or skin. Two basic THE approaches have emerged: (1) the direct approach using probability samples of populations and measuring pollutant concentrations in the food eaten, air breathed, water drunk, and skin contacted; and (2) the indirect approach using human activity pattern-exposure models to predict population exposure distributions. Using the direct approach, EPA has conducted over 20 field studies for pollutants representing four groups—volatile organic compounds, carbon monoxide, pesticides, and particles—in 15 cities in 12 states. The indirect modeling approach has been applied to several of these pollutants. Additional research is needed in a great variety of areas. Even from the few projects completed thus far, the THE approach has yielded a rich new data base for risk assessments and has provided many surprises about the relative contribution of various pollutant sources to public health risk.