Wojciech Jozewicz

Sorption of elemental mercury by activated carbons.

The mechanisms and rate of elemental mercury (Hg 0 ) capture by activated carbons have been studied using a bench-scale apparatus. Three types of activated carbons, two of which are thermally activated (PC-100 and FGD) and one with elemental sulfur (S) impregnated in it (HGR), were chosen to study the effects of surface area (approximately 550-1000 m 2 /g), sorption temperature (23-140 o C), and Hg 0 concentration (30 and 60 ppb of Hg 0 in nitrogen). Investigations revealed that sorption occurs in active sites in PC-100 and FGD which are either depleted or deactivated upon heat treatment at 140 o C. For HGR, sorption at 23 o C occurred in non-S sites residing in the external surface, and sorption of 140 o C primarily occurred through the reaction of Hg 0 and S.

Flue Gas Desulfurization: The State of the Art

ABSTRACT Coal-fired electricity-generating plants may use SO2 scrubbers to meet the requirements of Phase II of the Acid Rain SO2 Reduction Program. Additionally, the use of scrubbers can result in reduction of Hg and other emissions from combustion sources. It is timely, therefore, to examine the current status of SO2 scrubbing technologies. This paper presents a comprehensive review of the state of the art in flue gas desulfurization (FGD) technologies for coal-fired boilers. Data on worldwide FGD applications reveal that wet FGD technologies, and specifically wet limestone FGD, have been predominantly selected over other FGD technologies. However, lime spray drying (LSD) is being used at the majority of the plants employing dry FGD technologies. Additional review of the U.S. FGD technology applications that began operation in 1991 through 1995 reveals that FGD processes of choice recently in the United States have been wet limestone FGD, magnesium-enhanced lime (MEL), and LSD. Further, of the wet limestone processes, limestone forced oxidation (LSFO) has been used most often in recent applications. The SO2 removal performance of scrubbers has been reviewed. Data reflect that most wet limestone and LSD installations appear to be capable of ~90% SO2 removal. Advanced, state-of-the-art wet scrubbers can provide SO2 removal in excess of 95%. Costs associated with state-of-the-art applications of LSFO, MEL, and LSD technologies have been analyzed with appropriate cost models. Analyses indicate that the capital cost of an LSD system is lower than those of same capacity LSFO and MEL systems, reflective of the relatively less complex hardware used in LSD. Analyses also reflect that, based on total annualized cost and SO2 removal requirements: (1) plants up to ~250 MWe in size and firing low- to medium-sulfur coals (i.e., coals with a sulfur content of 2% or lower) may use LSD; and (2) plants larger than 250 MWe and firing medium- to high-sulfur coals (i.e., coals with a sulfur content of 2% or higher) may use either LSFO or MEL.

An Assessment of Costs and Benefits Associated with Mercury Emission Reductions from Major Anthropogenic Sources

Abstract Several measures are available for reducing mercury emissions; however, these measures differ with regard to emission control efficiency, cost, and environmental benefits obtained through their implementation. Measures that include the application of technology, such as technology to remove mercury from flue gases in electric power plants, waste incinerators, and smelters, are rather expensive compared with nontechnological measures. In general, dedicated mercury removal is considerably more expensive than a co-benefit strategy, using air pollution control equipment originally designed to limit emissions of criterion pollutants, such as particulate matter, sulfur dioxide, or oxides of nitrogen. Substantial benefits can be achieved globally by introducing mercury emission reduction measures because they reduce human and wildlife exposure to methyl mercury. Although the reduction potential is greatest with the technological measures, technological and nontechnological solutions for mercury emissions and exposure reductions can be carried out in parallel.

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.

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 ...

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.

Commercial Development Of The Advacate Process For Flue Gas Desulfurization

Commercialization of the ADVACATE process for flue gas SO/sub 2/ removal follows several years of bench-scale sorbent development pilot plant process optimization and field pilot evaluation. Results are presented showing the importance of silica dissolution in preparation of calcium silicates. Pilot and field optimization and evaluation shows excellent potential for over 90 percent SO/sub 2/ control at half the cost of conventional wet flue gas desulfurinzation (FGD) processes. Projected costs and commercialization plans are presented.

Advantage of Illinois Coal for FGD Removal of Mercury

An investigation was conducted to characterize and modify mercury speciation in Illinois coal combustion flue gas so that a mercury control strategy can be implemented in conventional flue gas desulfurization (FGD) units. Mercury is readily volatilized during coal combustion and leaves the high-temperature zone as gas-phase elemental mercury (Hg0). As the flue gas is cooled, a portion of the Hg0 is converted, primarily to mercuric chloride (HgCl2), in the presence of catalytically active surfaces. Unlike Hg0, HgCl2 is highly soluble in water and has a high affinity for alkaline sorbents; it can, therefore, be easily removed in wet scrubbers and spray dryers (FGD units). This study specifically examined the effect of injection of Illinois coal combustion residues (ICCRs) on the conversion of Hg0 to HgCl2 in coal combustion flue gases. Tests were conducted in two tasks. Task I studied Hg0 oxidation using a fixed-bed, bench-scale reactor in a simulated Illinois coal combustion environment. Various types of I...