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Title: Capture of toxic metals by vaious sorbents during fluidized bed coal combustion

Abstract

This study investigated the potential of employing suitable sorbents to capture trace metallic substances during fluidized bed coal combustion. The objectives of the study were to demonstrate the capture process, identify effective sorbents, and characterize the capture efficiency. Experiments were carried out in a 25.4 mm (1 ``) quartz fluidized bed coal combustor enclosed in an electric furnace. In an experiment, a coal sample from the DOE Coal Sample Bank or the Illinois Basin Coal Sample Bank was burned in the bed with a sorbent under various combustion conditions and the amount of metal capture by the sorbent was determined. The metals involved in the study were arsenic, cadmium, lead, mercury and selenium, and the sorbents tested included bauxite, zeolite and lime. The combustion conditions examined included bed temperature, particle size, fluidization velocity (percent excess air), and sorbent bed height. In addition to the experimental investigations, potential metal-sorbent reactions were also identified through performing chemical equilibrium analyses based on the minimization of system free energy.

Authors:
; ;
Publication Date:
Research Org.:
Lamar Univ., Beaumont, TX (United States). Dept. of Chemical Engineering
Sponsoring Org.:
USDOE Assistant Secretary for Fossil Energy, Washington, DC (United States)
OSTI Identifier:
434415
Report Number(s):
CONF-951180-4
ON: DE97000633
DOE Contract Number:
FG22-94PC94221
Resource Type:
Conference
Resource Relation:
Conference: Annual meeting of the American Institute of Chemical Engineers, Miami Beach, FL (United States), 12-17 Nov 1995; Other Information: PBD: [1995]
Country of Publication:
United States
Language:
English
Subject:
01 COAL, LIGNITE, AND PEAT; COAL; FLUIDIZED-BED COMBUSTION; BAUXITE; SORPTIVE PROPERTIES; ZEOLITES; CALCIUM OXIDES; ARSENIC; ADSORPTION; CADMIUM; LEAD; MERCURY; SELENIUM; FLUIDIZED-BED COMBUSTORS; CAPTURE; PARTICLE SIZE

Citation Formats

Ho, T.C., Ghebremeskel, A., and Hopper, J.R.. Capture of toxic metals by vaious sorbents during fluidized bed coal combustion. United States: N. p., 1995. Web.
Ho, T.C., Ghebremeskel, A., & Hopper, J.R.. Capture of toxic metals by vaious sorbents during fluidized bed coal combustion. United States.
Ho, T.C., Ghebremeskel, A., and Hopper, J.R.. Sun . "Capture of toxic metals by vaious sorbents during fluidized bed coal combustion". United States. doi:. https://www.osti.gov/servlets/purl/434415.
@article{osti_434415,
title = {Capture of toxic metals by vaious sorbents during fluidized bed coal combustion},
author = {Ho, T.C. and Ghebremeskel, A. and Hopper, J.R.},
abstractNote = {This study investigated the potential of employing suitable sorbents to capture trace metallic substances during fluidized bed coal combustion. The objectives of the study were to demonstrate the capture process, identify effective sorbents, and characterize the capture efficiency. Experiments were carried out in a 25.4 mm (1 ``) quartz fluidized bed coal combustor enclosed in an electric furnace. In an experiment, a coal sample from the DOE Coal Sample Bank or the Illinois Basin Coal Sample Bank was burned in the bed with a sorbent under various combustion conditions and the amount of metal capture by the sorbent was determined. The metals involved in the study were arsenic, cadmium, lead, mercury and selenium, and the sorbents tested included bauxite, zeolite and lime. The combustion conditions examined included bed temperature, particle size, fluidization velocity (percent excess air), and sorbent bed height. In addition to the experimental investigations, potential metal-sorbent reactions were also identified through performing chemical equilibrium analyses based on the minimization of system free energy.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Dec 31 00:00:00 EST 1995},
month = {Sun Dec 31 00:00:00 EST 1995}
}

Conference:
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  • Experiments were conducted in a 1-in. quartz fluidized bed combustor enclosed in an electric furnace. Coal samples were burned in the bed with a sorbent under specific combustion conditions and the amount of metal capture by the sorbent determined. Three different cao samples from the Illinois Basin Coal Sample Bank were tested. Metals involved were Cd, Pb, and Cr; the sorbents included bauxite, zeolite, and lime. Potential metal-sorbent reactions were identified. Results indicated that metal capture by sorbent can be as high as 96%, depending on the metal species and sorbent. All 3 sorbents were capable of capturing Pb, zeolitemore » and lime were able to capture Cr, and bauxite was the only sorbent capable of capturing Cd. Thermodynamic equilibrium calculations suggested the formation of metal-sorbent compounds such as Pb{sub 2}SiO{sub 4}, CdAl{sub 2}O{sub 4}, and CdSiO{sub 3} solids under the combustion conditions.« less
  • This study investigated the potential of employing suitable sorbents to capture toxic trace metallic substances during fluidized bed coal combustion. Metal capture experiments were carried out in a 25.4 mm (1 inch) quartz fluidized bed combustor enclosed in an electric furnace. The metals involved were cadmium, lead, chromium, arsenic and selenium, and the sorbents tested included bauxite, zeolite and lime. In addition to the experimental investigations, potential metal-sorbent reactions were also identified through chemical equilibrium calculations based on the minimization of system free energy. The observed experimental results indicated that metal capture by sorbents can be as high as 88%more » depending on the metal species and sorbent involved. Results from thermodynamic equilibrium simulations suggested the formation of metal-sorbent compounds such as Pb{sub 2}SiO{sub 4}(s), CdAl{sub 2}O{sub 4}(s) and CdSiO{sub 3}(s) under the combustion conditions.« less
  • The primary focus of this research was the removal of alkali from PFBC flue gases to a level specified by turbine manufactures. The target level was less than 24 ppbw. Several of the aluminosilicate minerals have the potential to capture alkalis, especially sodium and potassium, under conditions typical of fluid-bed operation. Other goals of this work were to investigate the potential for simultaneously removing SO{sub 2} and Cl from the PFBC gas stream. The initial work focused primarily on one class of sorbents, sodalites, with the goal of determining whether sodalites can be used as an in-bed sorbent to simultaneouslymore » remove alkali and sulfur. Thermo gravimetric analysis (TGA) was used to study the mechanism of alkali capture using sodalite. Further testing was performed on a 7.6 cm (3-in.)-diameter pressurized fluid-bed reactor (PFBR). Early results indicated that simultaneous removal of alkali and sulfur and/or chlorine was not practical under the conditions for commercial PFBC operations. Therefore, the focus of the latter part of this work was on sorbents that have been shown to capture alkali in other systems. The effectiveness of bauxite and kaolinite to reduce vapor-phase alkali concentrations was determined. In addition to studying the gettering capability of the sorbent, the impact of the getter on operational performance was evaluated. This evaluation included examining potential agglomeration of bed particles, deposition on heat-transfer surfaces, and the bridging and blinding of ceramic candle filters. The focus of this paper is on the work performed on the PFBR.« less
  • Toxic trace metallic elements such as arsenic, beryllium, cadmium, chromium, cobalt, lead, manganese, mercury, nickel, and selenium are usually contained in coal in various forms and trace amounts. These metals will either stay in the ash or be vaporized during high temperature combustion. Portions of the vaporized metals may eventually be emitted from a combustion system in the form of metal fumes or particulates with diameters less than 1 micron, which are potentially hazardous to the environment. Current practice of controlling trace metal emissions during coal combustion employs conventional air pollution control devices (APCDs), such as electrostatic precipitators and baghouses,more » to collect fly ash and metal fumes. The control may not always be effective on metal fumes due to their extremely fine sizes. This study is to explore the opportunities for improved control of toxic trace metal emissions from coal-fired combustion systems. Specifically, the technology proposed is to employ suitable sorbents to reduce the amount of metal volatilization and capture volatilized metal vapors during fluidized bed coal combustion. The objective of the study was to investigate experimentally and theoretically the metal capture process.« less
  • Pressurized fluidized bed combustion has particular advantages compared with conventional firing systems, e.g., in-situ pollutant removal (SO{sub 2}), high thermal efficiencies even in intermediate power ranges. The low combustion temperature of about 1,050--1,200 K results in low NO emissions without any secondary flue gas treatment but on the other hand yields considerable N{sub 2}O emissions. To know in which way the operating pressure influences the gaseous emissions of PFBC, especially SO{sub 2}, NO and N{sub 2}O were studied. Furthermore, examinations were made as to what extent the experiences from AFBC, e.g., influence of temperature, air ratio and additives on pollutantmore » formation, can be transferred to pressurized conditions. At the IVD's PFBC test facility (50 kW thermal power) various experiments were carried out with two different coals (high volatile bituminous coal and subbituminous coal) at defined operating temperatures in the range of 1,073--1,213 K and pressures from 1.5 to 13 bar. Dolomite and calcinated lime were used as additives for in-situ sulfur capture at different molar ratios in each case and its influence on NO and N{sub 2}O emissions were studied. It was found, that NO emissions decreased with increasing pressure and increasing Ca/S molar ratio. At pressures above 4 bar and with more sorbent addition, NO emissions decreased with increasing temperature. N{sub 2}O emissions showed no significant decrease at elevated pressures and were not influenced by dolomite or CaO added, but were found to depend on CO emissions or, rather, carbon conversion. At higher system pressures better carbon conversion rates could be achieved (higher O{sub 2} partial pressure), which results in lower CO concentrations in the fluidized bed and the freeboard, respectively. Therefore, the reduction of NO to N{sub 2}O decreases so that the overall N{sub 2}O emissions in a PFBC are lower compared with atmospheric operation mode.« less