Charles B. Sedman

Low concentration mercury sorption mechanisms and control by calcium-based sorbents : Application in coal-fired processes

The capture of elemental mercury (Hg0) and mercuric chloride (HgCl2) by three types of calcium (Ca)-based sor-bents was examined in this bench-scale study under conditions prevalent in coal-fired utilities. Ca-based sorbent performances were compared with that of an activated carbon. Hg0 capture of about 40% (nearly half that of the activated carbon) was achieved by two of the Ca-based sorbents. The presence of sulfur dioxide (SO2) in the simulated coal combustion flue gas enhanced the Hg0 capture from about 10 to 40%. Increasing the temperature in the range of 65-100 °C also caused an increase in the Hg0 capture by the two Ca-based sorbents. Mercuric chloride (HgCl2) capture exhibited a totally different pattern. The presence of SO2 inhibited the HgCl2 capture by Ca-based sorbents from about 25 to less than 10%. Increasing the temperature in the studied range also caused a decrease in HgCl2 capture. Upon further pilot-scale confirmations, the results obtained in this bench-scale study can be used to design and manufacture more cost-effective mercury sorbents to replace conventional sorbents already in use in mercury control.

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.

Simultaneous control of Hg0, SO2, and NOx by novel oxidized calcium-based sorbents.

Abstract Efforts to develop multipollutant control strategies have demonstrated that adding certain oxidants to different classes of Ca-based sorbents leads to a significant improvement in elemental Hg vapor (Hg0), SO2, and NOx removal from simulated flue gases. In the study presented here, two classes of Ca-based sorbents (hydrated limes and silicate compounds) were investigated. A number of oxidizing additives at different concentrations were used in the Ca-based sorbent production process. The Hg0, SO2, and NOx capture capacities of these oxidant-enriched sorbents were evaluated and compared to those of a commercially available activated carbon in bench-scale, fixed-bed, and fluid-bed systems. Calcium-based sorbents prepared with two oxidants, designated C and M, exhibited Hg0 sorp-tion capacities (~100 μg/g) comparable to that of the activated carbon; they showed far superior SO2 and NOx sorption capacities. Preliminary cost estimates for the process utilizing these novel sorbents indicate potential for substantial lowering of control costs, as compared with other processes currently used or considered for control of Hg0, SO2, and NOx emissions from coal-fired boilers. The implications of these findings toward development of multipollutant control technologies and planned pilot and field evaluations of more promising multipollutant sorbents are summarily discussed.

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...

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 ...

Stationary combustion NOX control : a summary of the 1991 symposium

The 1991 Symposium on Stationary Combustion NOx Control was held March 25-28,1991 in Washington, DC. The sixth meeting in a biennial series, the Symposium was cosponsored by the Electric Power Research Institute (EPRI) and the U.S. Environmental Protection Agency (EPA). Approximately 500 individuals attended representing 53 domestic and 13 foreign utility companies, federal and state government agencies, research and development organizations, and equipment vendors from the United States and abroad. Sixty-six presentations were made.

Current Status of the ADVACATE Process for Flue Gas Desulfurization

The following report discusses current bench- and pilot-plant advances in preparation of ADVAnced siliCATE (ADVACATE) calcium silicate sorbents for flue gas desulfurization. It also discusses current bench- and pilot-plant advances in sorbent preparation. Fly ash was ground in a laboratory scale grinder prior to slurring in order to decrease the slurring time needed for the sorbent to be reactive with SO2. Reactivity of ADVACATE sorbents with SO2 in the bench-scale reactor correlated with their surface area. ADVACATE sorbents produced with ground fly ash were evaluated in the 50 cfm (85 m3/h) pilot plant providing 2 s duct residence time. ADVACATE sorbent was produced by slurrying ground fly ash (median particle size of 4.3 µm) with Ca(OH)2 at the weight ratio of 3:1 at 90°C (194°F) for 3hto yield solids with 30 weight percent of initial free moisture. When this sorbent was injected into the duct with 1500 ppm SO2 and at 11°C (20°F) approach to saturation, the measured SO2 removal was approximately 60perc...

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.

Preliminary estimates of performance and cost of mercury control technology applications on electric utility boilers.

ABSTRACT Under the Clean Air Act Amendments of 1990, the U.S. Environmental Protection Agency (EPA) determined that regulation of mercury emissions from coal-fired power plants is appropriate and necessary. To aid in this determination, preliminary estimates of the performance and cost of powdered activated carbon (PAC) injection-based mercury control technologies were developed. This paper presents these estimates and develops projections of costs for future applications. Cost estimates were developed using PAC to achieve a minimum of 80% mercury removal at plants using electrostatic precipitators and a minimum of 90% removal at plants using fabric filters. These estimates ranged from 0.305 to 3.783 mills/kWh. However, the higher costs were associated with a minority of plants using hot-side electrostatic precipitators (HESPs). If these costs are excluded, the estimates range from 0.305 to 1.915 mills/kWh. Cost projections developed using a composite lime-PAC sor-bent for mercury removal ranged from 0.183 to 2.270 mills/kWh, with the higher costs being associated with a minority of plants that used HESPs.Under the Clean Air Act Amendments of 1990, the U.S. Environmental Protection Agency (EPA) determined that regulation of mercury emissions from coal-fired power plants is appropriate and necessary. To aid in this determination, preliminary estimates of the performance and cost of powdered activated carbon (PAC) injection-based mercury control technologies were developed. This paper presents these estimates and develops projections of costs for future applications. Cost estimates were developed using PAC to achieve a minimum of 80% mercury removal at plants using electrostatic precipitators and a minimum of 90% removal at plants using fabric filters. These estimates ranged from 0.305 to 3.783 mills/kWh. However, the higher costs were associated with a minority of plants using hot-side electrostatic precipitators (HESPs). If these costs are excluded, the estimates range from 0.305 to 1.915 mills/kWh. Cost projections developed using a composite lime-PAC sorbent for mercury removal ranged from 0.183 to 2.270 mills/kWh, with the higher costs being associated with a minority of plants that used HESPs.

Advances in control of PM2.5 and PM2.5 precursors generated by the combustion of pulverised coal

Particulate matter smaller than 2.5 mm in aerodynamic diametre (PM2.5) from coal-fired boilers is composed of directly emitted (primary) particles and particles formed from precursors (secondary particles). Technologies to reduce emissions of precursors to secondary PM2.5 emitted by coal-fired utility plants include wet and dry flue gas desulphurisation (FGD). Limestone forced oxidation (LSFO) systems are the predominant wet FGD technology in use, and lime spray dryers (LSDs) represent the predominant dry FGD systems. A predictive model indicates that LSD systems have lower annualised costs than LSFO systems for coals with less than 2% sulphur and for plants smaller than 300 MWe. Control technologies for primary PM2.5 include hybrid systems such as the combined hybrid particulate control system and an electrostatically enhanced fabric filter (ESFF) system. The ESFF can provide improved PM2.5 collection and lower fan power requirements compared to a conventional pulse-jet baghouse.