John C. S. Chang

Reactivation of solids from furnace injection of limestone for sulfur dioxide control.

rn Post furnace injection solids and fly ash mixtures were characterized and were tested in a bench-scale reactor for the removal of SO2. Virtually no SOz removal was observed with untreated solids. High SO, capture occurred when the samples were hydrated and dried prior to SOz exposure. The SO2 capture by solids increased with increasing time and temperature of hydration. For the same time/ temperature conditions of hydration, higher SO2 capture was achieved with solids of higher fly ash/sorbent ratio. A possible mechanism of enhanced SO, capture by hydration of the product solids is discussed.

Characterization of emissions of volatile organic compounds from interior alkyd paint

Alkyd paint continues to be used indoors for application to wood trim, cabinet surfaces, and some kitchen and bathroom walls. Alkyd paint may represent a significant source of volatile organic compounds (VOCs) indoors because of the frequency of use and amount of surface painted. The U.S. Environmental Protection Agency (EPA) is conducting research to characterize VOC emissions from paint and to develop source emission models that can be used for exposure assessment and risk management. The technical approach for this research involves both analysis of the liquid paint to identify and quantify the VOC contents and dynamic small chamber emissions tests to characterize the VOC emissions after application. The predominant constituents of the primer and two alkyd paints selected for testing were straight-chain alkanes (C9-C12); C8-C9 aromatics were minor constituents. Branched chain alkanes were the predominant VOCs in a third paint. A series of tests were performed to evaluate factors that may affect emissions following application of the coatings. The type of substrate (glass, wallboard, or pine board) did not have a substantial impact on the emissions with respect to peak concentrations, the emissions profile, or the amount of VOC mass emitted from the paint. Peak concentrations of total volatile organic compounds (TVOCs) as high as 10,000 mg/m3 were measured during small chamber emissions tests at 0.5 air exchanges per hour (ACH). Over 90% of the VOCs were emitted from the primer and paints during the first 10 hr following application. Emissions were similar from paint applied to bare pine board, a primed board, or a board previously painted with the same paint. The impact of other variables, including film thickness, air velocity at the surface, and air-exchange rate (AER) were consistent with theoretical predictions for gas-phase, mass transfer-controlled emissions. In addition to the alkanes and aromatics, aldehydes were detected in the emissions during paint drying. Hexanal, the predominant aldehyde in the emissions, was not detected in the liquid paint and was apparently an oxidation product formed during drying. This paper summarizes the results of the product analyses and a series of small chamber emissions tests. It also describes the use of a mass balance approach to evaluate the impact of test variables and to assess the quality of the emissions data.

Silica-enhanced sorbents for dry injection removal of SO2 from flue gas

Novel silica-enhanced lime sorbents were tested in a bench-scale sand-bed reactor for their potential for SO2 removal from flue gas. Reactor conditions were 64°C (147°F), relative humidity of 60 percent [corresponding to an approach to saturation temperature of 10°C (18°F)], and inlet SO2 concentration of 500 or 1000 ppm. The sorbents were prepared by pressure hydration of CaO or Ca(OH)2 with siliceous materials at 100°C (101 kPa) [212°F (14.7 psi)] to 230°C (2793 kPa) [446°F (405 psi)] for 15 min to 4 h. Pressure hydration fostered the formation of a sorbent reactive with SO2 from fly ash and Ca(OH)2 in a much shorter time than did atmospheric hydration. The conversion of Ca(OH)2 in the sand-bed reactor increased with the increasing weight ratio of fly ash to lime and correlated well with B.E.T. surface area, increasing with increasing surface area. The optimum temperature range for the pressure-hydration of fly ash with Ca(OH)2 was between 110 and 160°C (230 and 320 °F). The pressure hydration of diatom...

Evaluation of sink effects on VOCs from a latex paint.

The sink strength of two common indoor materials, a carpet and a gypsum board, was evaluated by environmental chamber tests with four volatile organic compounds (VOCs): propylene glycol, ethylene glycol, 2-(2-butoxyethoxy)ethanol (BEE), and Texanol. These oxygenated compounds represent the major VOCs emitted from a latex paint. Each chamber test included two phases. Phase 1 was the dosing/sorption period during which sink materials (pieces of carpet and gypsum board samples) were exposed to the four VOCs. The sink strength of each material tested was characterized by the amount of the VOCs adsorbed or absorbed. Phase 2 was the purging/de-sorption period during which the chambers with the dosed sink materials were flushed with purified air. The reemission rates of the adsorbed VOCs from the sinks were reflected by the amount of the VOCs being flushed. Phase 1 results indicated that the sink strength for the four target compounds is more than 1 order of magnitude higher than that for other VOCs previously tested by the U.S. Environmental Protection Agency (EPA). The high sink strength reflected the unusually high sorption capacity of common indoor materials for the four VOCs. Phase 2 results showed that reemission was an extremely slow process. If all the VOCs adsorbed were reemittable, it would take more than a year to completely flush out the VOCs from the sink materials tested. The long reemission process can result in chronic and low-level exposure to the VOCs after painting interior walls and surfaces.

Development and Pilot Plant Evaluation of Silica- Enhanced Lime Sorbents for Dry Flue Gas Desulfurization

EPA’s efforts to develop low cost, retrofitable flue gas cleaning technology include the development of highly reactive sorbents. Recent work addressing lime enhancement and testing at the bench-scale followed by evaluation of the more promising sorbents in a pilot plant are discussed here. The conversion of Ca(OH)2 with SO2 increased several-fold compared with Ca(OH)2 alone when Ca(OH)2 was slurrled with fly ash first and later exposed to SO2 in a laboratory packed bed reactor. Ca(OH)2 enhancement increased with the increased fly ash amount. Dlatomaceous earths were very effective reactivity promoters of lime-based sorbents. Differential scanning calorimetry of the promoted sorbents revealed the formation of a new phase (calcium silicate hydrates) after hydration, which may be the basis for the observed Improved SO2 capture. Fly ash/lime and diatomaceous earth/lime sorbents were tested in a 100 m3/h pilot facility incorporating a gas humidifier, a sorbent duct injection system, and a baghouse. The inlet ...

Evaluation of Para-Dichlorobenzene Emissions from Solid Moth Repellant as a Source of Indoor Air Pollution

The paper reports results of dynamic and static chamber tests to evaluate para-dichlorobenzene emission rates from mothcakes. The data were analyzed by a model that assumes that the emission rate is controlled by gas-phase mass transfer. Results indicate that the para-dichlorobenzene emission from mothcakes is a temperature-sensitive sublimation process. Full-scale house tests were also conducted to measure mass transfer coefficients based on the model developed. The values of the mass transfer coefficient obtained are very comparable to those estimated by theoretical heat transfer studies.

Testing and Commercialization of Byproduct Dibasic cids as Buffer Additives for Limestone Flue Gas esulfurization Systems

Pilot plant (0.1 MW) tests and utility boiler full scale demonstration (194 MW) of byproduct organic dibasic acids (DBA) as buffer additives to limestone scrubbers have shown performance improvements equivalent to those achieved by the addition of pure adipic acid. Both SO2 removal efficiency and limestone utilization increased, and no significant operating problems were observed with three of the four DBA tested. Chemical and biological evaluations of scrubber samples taken during the DBA testing indicated no detectable tOxicity or mutagenicity, and no significant environmental impact is expected as a result of DBA addition. Economic estimates indicate that substitution of DBA for pure adipic acid as a buffer additive will result in additive cost savings of 30 % or greater.

Investigation of contact vacuuming for remediation of fungally contaminated duct materials

Environmental fungi become a potential Indoor Air Quality (IAQ) problem when adequate moisture and nutrients are present in building materials. Because of their potential to rapidly spread contamination throughout a building, ventilation system materials are of particular significance as potential microbial contamination sources. Current recommendations are to discard fibrous glass insulation that appears to be wet or moldy. Unfortunately, this advice is not always followed. Instead, cleaning is sometimes being used in buildings to remediate fibrous glass duct liner that is already contaminated with microbial growth. The objectives of this research program were to: 1) determine, under dynamic test conditions, whether fungal spore levels on heating, ventilating, and air-conditioning (HVAC) duct material surfaces could be substantially reduced by thorough vacuum cleaning, 2) evaluate whether subsequent fungal growth could be limited or contained by mechanical cleaning, and 3) provide data concerning the advisability of cleaning duct materials. The constant high relative humidity (RH) environment to which the test materials were exposed during this study was selected as a favorable growth environment that is frequently found in Southeastern United States HVAC systems. The results showed that, following cleaning, the levels of the two test fungi, A. versicolor and P. chrysogenum, recovered to preclean levels within 6 weeks. Therefore, mechanical cleaning by contact vacuuming alone was able to only temporarily reduce the surface fungal load. The current guidelines to discard contaminated materials should be followed.

Characterization of advanced sorbents for dry SO2 control

New flyash/lime sorbents were developed to remove SO2 from coal-fired flue gas. Flyash-to-lime weight ratios of 11 to 101 and additives for promoting sorbent reactivity were evaluated in a bench-scale reactor simulating conditions in a fabric filter. Of the additives tested, Na2HPO4· 7H2O, (NH4)2HPO4, and H3PO4 significantly enhanced the reactivity of the dry sorbents with SO2. Alternative sources of silica were reacted with lime, and the resultant dry sorbents showed high reactivity with SO2. Of the siliceous materials tested, several diatomaceous earths, montmorillonitic clays, and kaolins were identified as containing reactive silica.

Thiosulfate as an Oxidation Inhibitor in Flue Gas Desulfurization Processes: A Review of R&D Results

Sodium thiosulfate (Na2S2O3) has been tested in a pilot plant as an oxidation inhibitor in flue gas desulfurization by lime and limestone slurry scrubbing with and without MgO and adiplc acid additives. The effectiveness of thiosulfate is proportional to the inhibitor product, defined as the product of thiosulfate concentration (M), calcium concentration (M), and the moles of SO2 absorbed per hour per liter of hold tank volume. Gypsum saturation was less than 100 percent and scaling was eliminated when the inhibitor product exceeded 0.3 × 10−6(gmol/L)3/h. Thiosulfate was relatively more effective in systems with chlorides and less effective in systems promoted by MgO. An inhibitor product greater than 10−6(gmol/L)3/h significantly enhanced dewatering of solids from limestone scrubbing. SO2 removal and/or limestone utilization were increased in systems that started with less than 10 mM dissolved calcium.